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Restorations of (A) the hypothetical proavian, and (B) the toothed bird Archeopteryx. 
After Heilmann. 


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The Evolution of the Earth 


AND ITS INHABITANTS 


cA series of Lectures Delivered before the 
Yale (hapter of the Sigma Xi during the 
eAcademic Year 1916-1917 
“Foseph Barrell 
Charles Schuchert 
Lorande Loss Woodruff 


‘Richard Swann Lull 
Ellsworth Huntington 


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NEW HAVEN 
YALE UNIVERSITY PRESS 
London : Humphrey NGlford : Oxford University Press 
MDCCCCXXIII 


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COPYRIGHT, 1918, BY 
YALE UNIVERSITY PRESS 


First published, 1918. 
Second printing, 1919. 
Third printing, 1920. 
Fourth printing, 1922. 
Fifth printing, 1923. 


PREFACE 


DuRincG the collegiate year 1916-1917, the conduct of the 
Yale Chapter of the honorary scientific society of the Sigma Xi 
was entrusted to my guidance, and in order to render the meet- _ 
ings of the chapter as profitable as possible, a symposium was 
proposed on the geological and biological evidences for the 
_ evolution of our planet and the earth-borne life. I therefore 
asked such of my colleagues as were authorities on the several 
subjects involved to prepare addresses to be delivered before 
_ the chapter and later to be published in the form of the pres- 
ent book. The course of lectures was as follows: 


THE EVOLUTION OF THE EARTH AND ITS INHABITANTS 


Lecture I. The Origin of the Earth, November 23, 1916, 
Professor Joseph Barrell. 

Lecture I]. The Earth’s Changing Surface and Climate, 
December 13, 1916, Professor Charles Schuchert. 

‘Lecture III. The Origin of Life, January 24, 1917, Pro- 
fessor Lorande Loss Woodruff. 

Lecture IV. The Pulse of Life, February 15, 1917, Professor 
Richard Swann Lull. | 

Lecture V. Climate and Civilization, April 20, 1917, Dector 
Ellsworth Huntington. 


The scope of the combined essays is of necessity very broad, 
ranging as it does from a conception of the universe to the 
trend of modern civilization. ‘Thus the first chapter deals not 
alone with the genesis of the earth but of the parent solar 
system, and, the earth having been established, its history ts 
traced until the time of its becoming a fit environment for the 
abode of life. The second lecture deals with the changing lines 


vi | PREFACE 

of demarcation between land and sea, the rise and growth of 
continents, the formation and severance of land-bridges, and 
the climatic changes which are recorded for geologic time. 
The physical environment once established, Professor Wood- 
ruff tells what we know and do not know of the origin of life. 
This is largely an academic discussion of the several theories 
which have been advanced to account for the evolution of life- 
less into living matter, for from the nature of the problem 
evidences of direct observation are not available. ‘The lecture 
on the pulse of life attempts to link up cause and effect; to find 
those forces which are responsible for the more or less 
rhythmic accelerations of evolution shown by the fossil record. | 
The main cause is found to be climatic change, which in turn — 
has as a chief controlling factor earth shrinkage and the con- ~ 
sequent warping of the crust discussed in the second lecture. 
The pulse of life applies not alone to the evolution of animals 
and plants, but also to mankind. How climatic changes have 
influenced the growth of civilization and the formation of 
racial characteristics of mentality is set forth in the last lecture, — 
that by Doctor Huntington. In so far as possible, these essays 
are the fruits of the original research of their several authors, 
which in certain instances are set forth here for the first time. 
The treatment of the entire subject and the marshaling of the 
facts thus assembled are entirely new. 

I am deeply grateful to my, colleagues, not only for their 
having accepted the tasks thus laid upon them, which in several 
instances implied new and extensive research, but also for the 
success with which the lectures were presented, as attested by 
_ the society. 

RICHARD SWANN LULL, 
President, Yale Chapter, Sigma XI. 
1916-1917. 
Yale University, 
December 1, 1917. 


Preface . . 


Chapter 
Chapter 


Chapter 
Chapter 
Chapter 


Index 


CONTENTS 


ee ne enigee ak RICHARD SWANN LULL 
The Origin of the Earth . . JOSEPH BARRELL 
The Earth’s Changing Surface and 
Climate. . . . #. + CHARLES SCHUCHERT 
The Origin of Life . LORANDE LOSS WOODRUFF 
The Pulse of Life . RICHARD SWANN LULL 
Climate and the Evolution of Civilization 
ELLSWORTH HUNTINGTON 


ILLUSTRATIONS 


Restorations of: A. the hypothetical proavian, B. the 


toothed bird Archaeopteryx . . . . Frontispiece 


A. Nebulosity in the Pleiades. B. Spiral nebula in 
Ursa Major . . . . facing page 
Diagram to illustrate tidal ices ‘ 
Origin of a spiral nebula according to Ciaihentin 
and Moulton . : 
The western and eastern jeateaeres Wocize dave 
Diagram showing the times and probable extent of the 
more or less marked climatic changes in the geologic 
history of North America, and of its elevation into 
chains of mountains j ane ty 
Glacially striated diabase, ‘cide in pees. Penal 
time. South Africa . . . . . facing page 
Lower Cambrian quartzite, striated in early Permian 
time. South Australia . . . . facing page 
Glacial bowlder beds beneath thick formations of 
dolomite on the upper Yangtse River, China. Age 
of till, late Proterozoic . . . . facing page 
Eroded exposure of the oldest known glacial deposits 
(Lower Huronian), near Cobalt, Ontario 

facing page 
Striated bowlder taken from the oldest known glacial 
deposits Sits Bilger g th te itor RI ae 
Generalized map oe North America in Paleozoic time 
The marine inundation in Pennsylvanian time . 
Earlier and maximal phases of the Silurian flood 


. Great Middle Cretaceous sees of the oceans 


over the lands . 

Diagram showing time aba extent ‘at ‘te men 
floods that have inundated North America since the 
close of the Proterozoic era 


62 


77 


79 


x 


Figure 14. 
Figure 15. 
Figure 16. 
Figure 17. 


Figure 18. 
Figure 19. 
Plate III. 
Figure 20. 


Figure 21. 
Figure 22. 


Figure 23. 
Figure 24. 
Figure 25. 
Plate IV. 
Figure 26. 


Figure 27. 


Figure 28. 
Figure 29. 
Figure 30. 


Figure 31. 
Figure 32. 
Figure 33. 


ILLUSTRATIONS 

Diagram of the pulse of life . 
Squid, Loligo sp., 4a yagi a fish } 
Fish forms . facing pt 
Laurentian peneplain as seen from the south end of 
Lake Michikamau, Labrador . facing page 
Lung-fish, Neoceratodus, breathing . 
African fringe-finned ganoid, Polypterus delhexi 
Cast of the oldest known fossil footprint, Thinopus 
antiquus, from the Upper Devonian of Pennsylvania 

facing page 
Development of the hind foot of a salamander, 
Triton teniatus : AA aie 
Foot of a reptile, Ranodon penne ‘ : 
Restoration of the Permian stegocephalian, Cases 
aspidephorus ~iadile 
Diagram showing the elation ei the extta-equliry ae 
membranes: A. bird or reptile, B. mammal 

facing page 
Skull of cynodont reptile, Nythosaurus larvatus . 


Tooth of a carnivorous dinosaur, Allosaurus, and jaw 


of a contemporary mammal, Diplocynodon 

facing page 
Restoration of archaic mammals: A. Phenacodus pri- 
maevus, B. Coryphodon, C. Dinoceras facing page 
Restoration of the creodont, Dromocyon . 
Map showing the geographical distribution af the 
primates, living and extinct, and their indicated dis- 
persal from Holarctica Ut 
Gorilla, Gorilla gorilla facing page 
Gibbon, Hylobates lar facing page 
Photograph of a submarine, twenty feet below the 
surface, taken from the aeroplane whose shadow is 
shown in the picture facing page 
Climograph of the eth cice tn United States . 
Climograph of France and Italy . 
Climograph of Southern California 


124 
124 


Figure 34. 


Figure 35. 
Figure 36. 


Figure 37. 
Figure 38. 


ILLUSTRATIONS 


Climograph of deaths among colored people in the 
eastern United States, 1912-1915. sae hesiattay 


_ diseases 


Climograph of dias sa white sbonie in the eastern 
United States, 1912-1915. Non-contagious diseases 
The distribution of human energy on the basis of 
climate Be ig 

The distribution of Ecilization 

Changes of climate in the abniienl « zone darling 
historic times, on the basis of the growth of trees in 
NE a 


rigs 
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CHAPTER I 
THE ORIGIN OF THE EARTH? 


JOSEPH BARRELL 
PROFESSOR OF STRUCTURAL GEOLOGY IN YALE UNIVERSITY 


INTRODUCTION 


THE logic of all branches of science points to the existence 
of some system of evolution of the universe, its complete 
nature hidden in the vastnesses of time and space, but never- 
theless developed in accordance with Nature’s laws. The 
earth is one of the celestial host, its beginnings are bound up 
with that of other bodies. In the history written in the struc- 
ture of the earth and in the relations of the earth to the planets, 
stars, and nebulz lies concealed the story of its genesis. “Two 
chief methods of approach, the geologic and astronomic, lead 
toward the solution of this fundamental problem. 

The history of the earth is read in the rocks which have 
been thrust up by internal forces and beveled across by erosion. 
The nearer events are clearly recorded in the sequence and 
nature of the sedimentary rocks and their fossils. But the 
oldest formations have been folded, mashed, and crystallized 
out of all resemblance to their original nature, and intruded 
by molten masses now solidified into granite and other 


_ 1 Also presented before the Geological Society of Boston, January 19, 1917. 

Some pages of the following article have been drawn from one by the writer 
entitled “Origin of the Solar System Under the Planetesimal Hypothesis,” pub- 
lished as Chapter XXV in Pirsson and Schuchert’s “Text-book of Geology,” 
1915. For permission to use this material grateful acknowledgment is made to 
the authors and publishers of that work. 


2 EVOLUTION OF THE EARTH 

igneous rocks. Fossils, the time markers of geology, if once 
existent, have been destroyed, and, as in the dawn of human 
history, vast periods of time are dimly sensed through the 
disordered and illegible record. This crystallized and intri- 
cately distorted series of the oldest terrestrial rocks tells of an 
earth surface on which air and water played their parts, much 
as now. But it was a surface repeatedly overwhelmed by out- 
pourings of basaltic lava on a vaster scale than those of later 
ages, and the crust was recurrently broken up and engulfed in 
the floods of rising granitic magmas. Here the geologic 
record begins, but the nature of its beginning points clearly to 
the existence of a prehistoric eon. At the farther bounds of 
this unrecorded time, forever hidden from direct observation, 
lies the origin of the earth. 

But the mind of man will not be baffled. Since he may not 
see directly he will see by inference. Convergent lines of 
evidence derived from various fields of knowledge may be 
followed part way toward this goal, like those rays perceived 
through the telescope on the. full moon near the margin of its 
visible hemisphere, which converge toward craters on the side 
of the moon that no eye shall ever see. 

Leaving the geologic field of evidence, the problem of the 
origin of the earth may be approached from the astronomic 
side. The relationships of the earth to the stars and the 
planets are displayed in the depths of the heavens, and vestiges 
must there exist of the cosmic conditions which gave birth to 
our world and the other planets of our system. ‘The forces 
of nature are found to obey the same laws as far as the tele- 
scope can penetrate. ‘The spectroscope detects the familiar 
chemical elements in distant stars. These instruments give 
assurance of the unity of the cosmos, but the diversity of 
objects indicates various stages and various types of evolution. 
Which approaches nearest to that of our solar system? We 
must be content to study very much larger and therefore unlike 


AIND ITS INHABITANTS 3 
systems, since from the distances of even the nearer stars the 
earth and her sister planets would be hopelessly invisible in the 
most powerful telescope. We cannot, then, follow into the 
planetary stage the evolution of other systems comparable to 
our own. Yet in nebula, in stars, and in the inherited motions 
and configurations of our planetary system are clues which 
pieced together lead up toward the origin of the earth. 

The problem of the origin of the earth is within the domain 
of scientific investigation, but as yet the pictures which may 
be drawn are varied. The vague outlines shift and change 
but become clearer with the growth of knowledge. Where 
the solution of a problem is not yet definitive and certain, the 
method of multiple working hypotheses should be used. All 
facts and theories should be matched to these several hypoth- 
eses to determine which one of them shall be selected and 
modified, and which shall meet the fate of the unfit. At the 
present stage of investigation any one view should not be 
regarded as established beyond question, even though the 
assembled evidence seems strongly to support it. In a single 
presentation, however, all hypotheses cannot be equally treated 
and each investigator, while recognizing the existence of other 
hypotheses, may properly emphasize that one which seems 
to him most in accordance with the various categories of facts 
and more firmly established inferences. 

The hypotheses of earth origin begin more especially in 
the astronomic field in the search for initial causes; they end 
in the geologic field where they dovetail into the known rela- 
‘tions. The surviving hypothesis must give a sound explana- 
‘tion of those broader terrestrial conditions of atmosphere, 
_hydrosphere, and lithosphere, of ocean basins and continental 
platforms, which had become established by the beginning of 
the geologic record. But, although much has been learned, it 
is still unsettled among geologists as to how far those funda- 
“mental conditions in early geologic times were different from 


4 EVOLUTION OF THE EARTH 

those of the present. On the whole, the problem of the genesis 
of the earth appears to lie somewhat more in the field of the 
geologist than in that of the astronomer. 


THE PLACE OF THE EARTH IN THE UNIVERSE 


The earth, a member of the solar system-, The earth is 
but one among the planets which together with the sun con- 
stitute the solar system. It is neither the largest nor the 
smallest, neither nearest to nor most remote from the sun. 

The sun is a star and is but one among the millions of stars, 
and, though apparently so great as seen from the earth, is 
mediocre among them in size and brightness. The origin of 
the earth is obviously bound up with the origin of the other 
planets and all in the history of the sun. A presentation of 
the significant facts of magnitudes, motions, and distribution 
of these bodies, familiar though they are to most readers, 
should therefore precede the consideration of the genesis of 
the earth. | 

The planets visible to the unassisted eye are, besides the 
earth, five in number, distinguished by the ancients from the 
stars by their steady light and by their wanderings through 
the zodiacal path in the sky, wanderings produced as a result 
of the combined effect of their motions and that of the earth in 
nearly circular paths about the sun, their common center. The 
telescope has added to the number of planets two large ones, 
Uranus and Neptune, invisible to the naked eye because of 
their distance from sun and earth, and, in one zone of inter- 
mediate distance, a swarm of smaller bodies, the asteroids, 
better called planetoids. In size the planets sink to vanishing 
insignificance in comparison with the sun or any other star. 
Their distances from the sun and from each other are also 
almost infinitesimal in comparison with the distances which 
separate the stars. ‘They shine by light reflected from the 


AND ITS INHABITANTS — 5 
sun, and as all the planets and planetoids are attendant upon 
the sun, they form a common system, the solar system. The 
facts regarding their size, their distance from the sun, and the 
inclination and position of the planes of their orbits with 
respect to the orbit of the earth are tabulated as follows: 


PRINCIPAL ELEMENTS OF THE SOLAR SYSTEM 


Mean distance | Inclination 

ee Diameter, Density, in millions of of plane of 
miles water=1 miles from orbit to 

the sun earth’s orbit 

UME gidccc ioe a" alw'sre 866,400 1.39 Be a 7° 359 
[ Mercury......... 3,030 ? 36 7 00 
Mi OUR as die's cbse a's 7,700 4.85 67 3 24 
fs Oe ee 7,918 5.58 93 0 00 
oe | Moon...... ER 2,162 3.40 - 0.2392 5 09 
DOES oii Oiein cic oes 4,230 4.01 141 $2 S52 

0 to 

Planetoids........ 0 to 485 ? 200 to 400 34 42 
ie EE 86,500 1.33 483 £89 
Major } Saturn........... 73,000 0.72 886 2 30 
planets | Uranus........... 31,900 1.22 1,782 0 46 
Neptune......... 34,800 2.11 2,792 1 47 


1 Inclination of sun’s equator to earth’s orbit. 
2 Mean distance of moon from earth. 


Notable Planetary Relations. That the orderly nature of 
this system implies some mode of evolution was seen by the 


framers of the nebular hypothesis. The more notable of 


these relations, following the summary by Young, are: 


1. The orbits are all nearly circular. 
2. hey are nearly in one plane (excepting the cases of 


. 


some of the little planetoids). : 


3. The revolution of all is in the same direction. 
_ 4. There is a curiously regular progression of distances 
from the sun (expressed by Bode’s law, which, however, breaks 
down at Neptune). See foregoing table. 


6 EVOLUTION OF THE EARTH 


5. There is a rough progression of density, increasing both: 
ways from Saturn, the least dense of all the planets in the 
system. | 

As regards the planets themselves, we have: | 

6. The plane of the planets’ rotation, the plane of their 
equators, roughly coinciding with those of the orbits (probably 
excepting Uranus). 

7.. The direction of the rotation of the planets about thei 
polar axes the same as that of their revolution in their orbits 
(excepting probably Uranus and Neptune). 

8. The plane of orbital revolution of the satellites of eac 
planet coinciding nearly with that of the planet’s rotation, its 
equatorial plane. - 

9. The direction of the satellites’ revolution in their orbits 
also coinciding with that of the planet’s rotation about its axis, 
with exceptions in the case of the ninth satellite of Saturn and 
probably the seventh of Jupiter. : . 

10. The largest planets rotating most swiftly. : 

The sun, a member of the stellar system. The sun, as has 
been stated, is but a star and a member of the stellar syste 
What are the orders of magnitude in number, in size, in dis- 
tance, in speed, in duration among these countless orbs, and 
how do these relations enter into the problem of the origin o 
the earth as one of that retinue of planets which attend upon 
the sun? : 

The luminous stars of our system are estimated to be more 
than a hundred million in number. The number of the dark 
stars is unknown. Giving no ray of light to reveal their exist- 
ence, they may for all we know be as numerous or more 
numerous than those in the radiant stages of their existence. 
The few stars whose sizes are known range in diameter from 
somewhat below a million to upward of ten million miles and 
more. { 

Many of the stars are in reality double or multiple stars, 
consisting of companions so close that the two or more appear 
as one star to the naked eye, or even under the highest power 


AND ITS INHABITANTS 7 
of the telescope, the evidence of their composite nature being 
revealed only through the analysis of their light by the spectro- 
scope. Jhese double stars revolve swiftly about each other, 
but such internal motions must be sharply distinguished in 
thought from the streaming or drifting of the stars as parts of © 
the great stellar system. Relatively to the sun they are found 
to move through space with speeds averaging between 10 and 
30 miles per second, but ranging from less than 10 to more 
than 200 miles per second. They do not move, however, 
singly and in closed orbits, but rather in broadly scattered 
groups whose paths are almost straight lines. ‘These courses 
of the stars must slowly curve under the aggregate attraction 
of the millions of stars, but can never return into themselves. 
The paths of groups of stars intersect other groups and are 
to some extent interwoven among themselves. These groups 
have been found to be integrated into two greater groups inter- 
meshed among each other and forming two great star streams 
whose average motions are in opposite directions. With the 
passage of millions of years, the stars thus continually enter 
into new relations and build new configurations in the skies: 
a myriad host of stellar fireflies, the living and the dead, 
streaming through space hundreds of millions of miles per 
year. | 
Although the stars are so great in number, their distances 
from each other average tens of millions of millions of miles, 
those in our part of the stellar system averaging between sixty 
and eighty trillions. ‘The star nearest to the sun, a Centauri, 
happens, however, to be at a lesser distance of about twenty- 
six trillions of miles. 

To bring down the dimensions of the universe to finite 
comprehension, we must divide the scale of nature by a 
thousand million. Then the earth would be represented by a 
pebble half an inch in diameter, circling once a year about a 
sun 4.5 feet in diameter, at a distance of 500 feet. The nearest 


8 EVOLUTION OF THE EARTH 
star, a Centauri, would on this same scale be seen as two 
spheres revolving about each other at a distance apart equal 
to 2 miles, and each comparable in size to the sun. This 
double star would be situated at a distance of about 25,000 
miles from our planetary system with its sun, but the other 
stars in this part of the stellar system would be separated 
from each other on the average by more than twice this dis- 
tance. The Galaxy, or Milky Way, is the cloud-like zone of 
faint stars which extends as a belt around the sky. The stars 
in it appear faint and close together because of their remote- 
ness. They seem to constitute the outer zone of our stellar 
system, and its dimensions are only vaguely known. On this 
diminutive scale the Milky Way might be found to be encom- 
passed by a circle of a hundred million miles diameter, or it 
might be more or less. | 
The nebule. All hypotheses of earth origin derive the 
planets and the sun from an antecedent nebulous or meteoritic 
state. The cloudy patches of light known as nebula, which 
are revealed especially by stellar photography, are, however, 
of several very different natures and it is a vital question as 
to which, if. any, of these types, could have given birth to our 
planetary system. | 
First are the irregular nebule, diffuse clouds of luminol 
matter, pervading whole groups of stars as in Orion and the 
Pleiades, shown in Plate I, A, denser about certain stars, but 
nevertheless enormously attenuated. This kind of nebulosity 
is associated with certain regions of the Milky Way. From 
the characteristics of their spectra, the stars in such nebule 
are regarded as young stars and the nebulous matter may 
represent the remains of an antecedent stage. 
The planetary nebule are a distinct type, comparatively 
few in number, and also found associated with the Milky Way. 
They show in the telescope faint, greenish, circular discs from 
which they derive their name rather than from any known 


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AND ITS INHABITANTS 9 
relationships to planetary systems. [hey seem to be related 
in their origin to New Stars and these in turn are thought to 
be produced by stars sweeping through clouds of meteoric or 
gaseous matter and attaining temporarily, from the swift 
impacts, an enormous brilliancy. The impact is so super- 


ficial, however, that the extreme brilliance is usually lost 


in a few days or weeks, and the star subsides through a 
stage like a planetary nebula into a peculiar type of star 
known as the Wolf-Rayet stars. The origin of the true plane- 
tary nebule has not, however, been observed, as they appear 


_ to possess a longer life than those which have originated in 
the past few centuries from new stars. 


The ring nebule are few and special, having the form of a 
vortex ring. 

The stellar nebule form another small group which look 
in the telescope like hazy stars. 

By far the greatest number of the nebulz are classified as 
spiral nebula, more than 120,000 of which have been made 
Sowa by photography in connection with the greater tele- 
scopes. Their actual number must of course be far greater. 
These objects, unlike the other forms of nebule, avoid the 
Milky Way, and are scattered over regions where the stars 
are more widely spaced. They are very remote and may be 
entirely beyond the stellar system. This implies enormous 
magnitude. It seems probable that in general they possess 
high internal velocities, which implies in turn enormous 
masses to generate such velocities. “These nebule possess 
spectra similar to those of stars rather than, like the other 


_ types of nebule, spectra of diffuse clouds of gas. Some 
_ astronomers look upon them, therefore, as possibly systems 
_ of stars rather than true nebule; systems so remote as to give 
the appearance of faint cloud-like spirals, even when viewed 


under the highest powers of the telescope. A typical spiral 


nebula is shown in Plate I, B. 


Bh : 
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10 EVOLUTION OF THE EARTH 
HyporTuHEsis OF PLANETS DERIVED FROM A PRIMAL NEBULA 

The original hypothesis of Kant and Laplace. In 1754 
and 1755 Immanuel Kant, the philosopher, published the most 
remarkable papers which had appeared up to that time upon 
the evolution of the solar system. He concéived matter to 
have been originally diffused and cold. From a position of 


rest it began to converge under the influence of gravitation 


and gave rise to the sun. In some manner he held that the 
matter in converging acquired a movement of rotation. 
Certain nuclei grew up independently from the center and 
gave rise to the planets and satellites. In 1785 he developed 


the idea that the contraction of the sun’s mass would develop ~ 
its heat, a view elaborated by Helmholtz in 1854 and generally © 


held by astronomers at the present time. Thus Kant sought, 
and with a large measure of success, to evolve the present state 
of the universe from the simplest condition by means of 
mechanical laws alone. 


In 1796 Laplace, one of the most eminent of French 


astronomers, published a general work on astronomy, and im 
a short note at the end of the appendix proposed a theory of 
the origin of the solar system which shortly became widely 
known as the nebular hypothesis. He was evidently unaware 
of Kant’s work published forty-one years previously. Laplace 


is most noted for his mathematical work on celestial mechanics, — 
yet he did not develop his hypothesis along such lines and 
apparently did not attach much importance to it. Neverithe-— 


less, it became the dominant idea in cosmic evolution through- 
out the next century. 


Laplace postulated an original nebula as a very hot, gaseous 


mass extending beyond the orbit of the farthest planet and 
possessing a uniform rotation throughout, as if it were a solid 
body. Its size was the result of a balance between expansion 
from its heat and contraction from its gravitation. As it lost 


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AND ITS INHABITANTS II 


heat it contracted and, with the same energy of rotation that 


it possessed before, necessarily revolved on its axis in a shorter 
time. At last a stage was reached where, in the equatorial 
belt, centrifugal force balanced gravitation and the matter 
subjected to this balance of forces could sink in no further. 
It is thought to have existed as a ring, left behind by the 
condensing mass. ‘he ring, however, was unstable; it broke 
up and gathered into one body. During the further shrinking 
of the main mass other rings were in turn abandoned. Each 
gathered into a subordinate nebula, passed through an inde- 
pendent evolution, and the whole gave rise to the system of 
planets and their satellites. 

_ Modifications of the nebular hypothesis. During the first 
half of the nineteenth century the nebular hypothesis was 
accepted by astronomers almost without question, but during 
the second half many serious dynamical objections were de- 
veloped and a process of modification began, until now not 
much remains of the original conception of Laplace. A 
_ rather full statement of the hypothesis and the objections to 
it has been given recently by Campbell.” A briefer summary 
and a citation of but a few of the modifications in the general 
concept must here suffice. 

George Darwin, Lockyer, Faye, Fouché, Poincaré, and 
others have taken part in this work, and in the opinion of these 
mathematicians and astronomers the framework of the result- 
_ ing structure is still sound, though subject of course to further 
modification as knowledge increases. It was shown that the 
original nebula need not have been hot, but, as perceived by 
Kant, would develop heat from its self-condensation. A loose 
swarm of cold meteorites would suffice as well as an original 
gas for the initial state. The mass could never have revolved 
asa unit body, as if it were a solid. On the contrary, the inner 


2 Campbell, W. W., “The Evolution of the Stars and the Formation of the 
Earth.” Scientific Monthly, vol. 1, 1915, pp. 189-194. 


12 EVOLUTION OF THE EARTH 
parts would be condensed and revolve fast while the outer 
parts were still diffuse and revolved slowly. The mode sug- 
gested by Laplace for the separation of the rings is also’ 
dynamically very unsatisfactory. Moulton has shown that the 
growth of the planets and the development of rotation in the 
same direction as their orbital motion could be much better 
attained from an initial state in which the component particles 
revolved in the same plane but independently and in highly 
elliptic orbits about the central nucleus. This is a wide de- 
parture from the idea of a circular ring revolving as a unit 
body. | . 
Still more fundamental objections, emphasized by Cham- 
berlin and Moulton, are found in certain of the existing 
dynamical relations of the solar system. It would be expected 
that in condensation the central mass would continually aban- 
don matter from its equatorial zone, the inner planets would 
presumably have possessed the greater masses, and the final 
sun would now show a high speed of rotation, giving an equa- 
torial diameter far greater than the polar. Such expectations 
are contrary to the facts. The sun revolves so slowly on its 
axis, once in twenty-five days, that it has no measurable equa- 
torial bulge. In other words, centrifugal force is negligible 
in the sun. Furthermore, the equatorial plane of the sun, 
instead of lying precisely in the mean plane of the planets’ 
orbits, is inclined seven degrees to such a mean plane. : 
A hypothesis to gain scientific credence must emerge success- 
ful from the test of observed facts and mathematical theory. 
The nebular hypothesis has not done so. It is on the defensive 
and has lost standing during the past generation. Neverthe- 
less, it would be premature to abandon it entirely. It has the 
advantage of simplicity in that satellites, planets, and sun are 
explained as the products of a single process, convergence in a 
rotating nebula. But nature is often found to be complex in 
her operations, so that this advantage is of doubtful weight. 


AND ITS INHABITANTS 13 


HYypoTuHeEsis oF PLANETS DERIVED FROM A SMALL 
SECONDARY NEBULA 


Distinctive features of the planetesimal hypothesis. The 
planetesimal or spiral nebula hypothesis of Chamberlin and 
Moulton postulates the sun already in existence from the in- 
gathering of a primal nebula. It was at some later stage dis- 
rupted through the tidal forces produced by the close approach 
and passage of another star. The result was a secondary 
nebula, but one essentially unlike the primary. The secondary 
nebula was developed in a plane and initially possessed a 
spiral form with the sun at its center. All of its parts moved 
with freedom and independence in elliptic orbits, a point of 
difference from the Laplacian hypothesis. The nebula con- 
tained only a minute fraction of the solar matter, but was 
endowed by the passing star with a great rotational energy, 
so that, although so insignificant in mass, the planetary matter 
dominates enormously over the sun in the moment of momen- 
tum of the whole system. Thus the planetesimal hypothesis 
is a bold and frank abandonment of the terms of the original 
or nebular theory. It is too early as yet to predict what will 
be the ultimate fate of this hypothesis of a secondary, and, in a 
measure, an accidental origin of the planets, but, as expounded 
by its originators, it must be regarded as dynamically more 
satisfactory than the present form of the hypothesis of primary 
origin. ‘The essential features will, therefore, be presented as 
the more probable preliminary steps in the genesis of the earth. 

Forces of tidal disruption. The power of stars to disrupt 
each other without coming into actual contact, merely through 
relatively close approach, must be understood, as it is the basis 
of the planetesimal hypothesis. 

The sun and moon raise terrestrial tides by virtue of the 
pull of gravity and thus medify that spheroidal form of the 
earth which is given by its own gravity and the centrifugal 


14 EVOLUTION OF THE EARTH 
force of its revolution. Suppose, in other examples of © 
heavenly bodies, the tidal pull to be many times stronger, the — 
self-gravitative cohesion to be many times weaker. A limit 
will be reached at which the body may be pulled to pieces. This — 
phenomenon, which has been actually observed in the case of — 
comets passing close to the sun, has been called tidal dis- 
ruption. 


= 


Fic. 1.—Diagram to illustrate tidal forces. 


Let M and N in Figure 1 bé two-bodies passing each other 
in space, and consider the action of the larger on the smaller. — 
According to Newton’s law, the bodies attract each other 
directly as their masses and inversely as the square of their 
distances, causing them to swing toward each other while 
passing by, but soon losing influence as they separate in their — 
journeys through space. Consider three particles, a, b, c, on — 
the line of attraction, taking them as separate parts of the 
smaller body. But a is nearer to M than is b, and b is nearer 
than c. Therefore if we represent the relative attractions by © 
lines, these lines will correspond to the distances which the — 
particles would move in a given time if free to obey the attrac- 


AND ITS INHABITANTS 15 
tion of the other body. The line at a is longer than that at b 
and the latter is longer than that atc. If N was not bound 
together by its own gravity or rigidity, a, b, and c would 
therefore drift apart and fan out while passing M. Consider 
that rigidity is negligible, as in a fluid globe; then, if a minus 
b, or b minus c are quantities which become greater than the 
self-gravitative force of N holding together a and c, the unity 
of the body becomes destroyed. ‘The problem, however, is 
not quite so simple, since the influence of all other points in 
N must also be considered. 

As the nearer part of the body is pulled from the center, 
and as the center is pulled from the farther side, there will, 
further, be two simultaneous tides of approximately equal 
height, but on opposite sides of the distorted body. They 
tend to be always on the line joining the two bodies. Thus, on 
the earth there are two tides on opposite sides, but the revolu- 
tion of the earth on its axis, like a car wheel under two oppo- 
site brake-shoes, gives an apparent effect, to one on the 
surface of the earth, of a revolution of the tidal wave. As 
a result of the equal tides at opposite ends of a diameter there 
are, on any part of the ocean, two high tides in twenty-four 
hours. 

Mode of tidal disruption in stars. A star is characterized 
by its enormous size and mass and by the possession of a 
gaseous constitution. The diameter and density are dependent 
upon the balance at every point between the tremendous ex- 
pansive forces of internal heat and the equally great compres- 
sive forces due to its own gravity. If it contracts, then its 
surface and each component shell below comes nearer to the 
center, the effect of,gravity upon any shell accordingly increases 
inversely as the square of the new radius, and a higher internal 
temperature becomes necessary to balance the higher gravita- 
tive force. From this there results the paradox known as 
Lane’s law,—that so long as a body maintains a gaseous 


16 EVOLUTION OF THE EARTH 

constitution its temperature must rise as it contracts, even 
though at the same time it is radiating heat. The temperature 
of the interior must furthermore be higher than the tempera- 
ture of the surface, because of the greater compression with 
depth, as is illustrated in the different strata of the terrestrial 
atmosphere. In those convective or slow boiling movements 
which are necessary in the sun and other stars in order that 
they should be able to maintain their surface radiation, there 


is then a constant liberation of energy from the depths and» 


a system of balanced motion which if disturbed could lead in 
any star to an explosive blowing out of material from it on an 
enormous scale. | 


VX eee eee 


The tide-generating force varies directly with the mass of — 


the disturbing body and also with the radius of the body dis- 


turbed. It varies approximately inversely with the cube of 
the distance between the centers. The deforming force is, 
furthermore, greatest in the interior because the tidal forces 


acting on the zone at right angles to the line of attraction — 
have a component which tends to squeeze in the points d, d’ 


’ 
: 
f 
i 
‘ 


f 


of Figure 1 toward the center. The gravitative control is 


accordingly weakened along the line a, b, c, and is strengthened 


in the directions at right angles. Now apply this’ principle 


to the gaseous balanced nature of a star, and it is seen that the — 


expansion in the line a, b, c is no longer exactly balanced by © 


the gravitative compression, and the unbalancing is greatest 
in the center, where also is the region of highest compression 
and highest temperature. The effect is as if one squeezed a 
syringe bulb with orifices for exit at both ends, a bulb, however, 
like an air rifle, filled with gas compressed to an explosive 
degree. 


Tidal disruption of the ancestral sun. The sun is occa-— 
sionally observed to shoot out streams of gas, known as solar — 
prominences, to heights of nearly 300,000 miles, and at — 
velocities ranging up to 300 miles per second. Such phe- 


AND ITS INHABITANTS 17 
nomena indicate the enormous elastic and explosive energy 
resident in the sun’s interior, an expansive potency held in 
_ restraint by the equally prodigious power of the sun’s gravity. 

Supposing then that the ancestral sun was subjected to tidal 
disruption by the approach of another and possibly much more 
massive star, it remains to be seen how the nebula resulting 
from tidal disruption can become the embryo of an orderly 
planetary system. If the matter were shot out from great 
depths in the sun by its normal expansive forces plus the tidal 
forces, the velocity of departure might rise high above the 
observed velocities of 300 miles per second. If 400 miles or 
more, it would be above the “‘critical velocity” of the sun. The 
gravitative attraction of the latter could then never reclaim 
that matter, because the decrease in the outward velocity due 
to the solar attraction would never bring the velocity down to 

zero, and could therefore never reverse the motion of the 
_ escaping matter and bring it back to the sun. 

It is doubtful if the sun could have drawn back to itself 
material expelled with a velocity of even 300 miles per second, 
for the passing star, by lowering the gravitative power of the 
sun on the line passing through the two, would temporarily 
decrease on that line the critical velocity. In other words, it 
would help to drag matter away from the sun, even though 
that matter could not catch up to the passing star, but would 
be left wandering in interstellar space, forming possibly come- 
tary_and meteoric material for other systems. But some, 
or possibly all, of the matter of the exploded sun may have 
had lesser velocities of escape and would consequently remain 
within its gravitative control. In so far as it was not deflected 
sideways by some extraneous force, it would fall back on the 
surface of the sun as the water of a geyser falls back into its 
pool. But the gravitative pull of the passing star would serve 
‘as such an extraneous force, analogous to the wind which 
blows part of the geyser water, as it rises and falls, to one 


18 EVOLUTION OF THE EARTH 
side of the basin. The matter shot out toward the passing star 
would be attracted sideways after it as the star receded into 
space. On falling back toward the sun it would consequently 
_ pass to one side and elliptical orbits of the separate particles 
would become established. The material shot out in the 
reverse direction, from the opposite side of the sun, would 
meet much the same conditions except that the sidewise pull © 
of the passing star would be less on it than on the sun. It is” 
seen that the lateral or deflecting force acting on both arms of ! 
the nebula would be due to the difference between the pull of 
the passing star on each arm and on the central body. The 
initial spiral arms do not then represent the path along which 
the material was shot out, but mark the rotation around the 
central body or sun, both of the axis of expulsion during the 
passing of the star and of the matter after it is expelled, as | 
shown in Figure 2. . 


Fic. 2.—Origin of a spiral nebula according to Chamberlin and Moulton. 


The spiral nebula would be developed in a plane. That 
plane is established by the hyperbolic orbit of the passing star 
with the sun at the focus of the orbit. The new system would” 
thus show in its nature features imposed by both its parents. 

From such a nebulous fiery birth Moulton especially has _ 
shown how, in accordance with the laws of celestial mechanics, 
a planetary system could result. . 

The matter which has converged into the planets would be 
that residue of the solar tidal disruption which did not pass 
beyond gravitative control and did not fall back into the body 


AND ITS INHABITANTS 19 
ée the sun. ‘This residue is only a very small fraction of the 
sun’ smass. It would appear probable, however, that the solar 
disruption was very great in order to give an axial revolution 
to the reaggregated matter forming the present sun, so that 
lits equator should be, as observed, only seven degrees from 
\the mean plane of all of the planetary orbits. The present 
revolution of the sun is probably due then to the whirl pro- 
duced during tidal disruption and not to an axial rotation 
belonging to the sun before the event took place. 

This brings us to the final stage in the evolution of the 
planets according to the planetesimal hypothesis. In the arms 
of the spiral nebula were knots or nuclei of matter constituting 
the cores of the planets. Four small knots, the earth-moon 
knot being a double one, represented the beginnings of the 
four small inner planets (see table, page 5). In the zone of 
the planetoids there was, however, no dominating nucleus, and 
they have therefore remained to this day largely in the plan- 
etesimal state. Four greater nuclei beyond were the begin- 
nings of the major planets. Smaller nuclei associated with 
the larger marked the presence of satellites. 

The orbits of the planetary nuclei and of the scattered 
\planetesimal swarm were highly eccentric, having the form 
of a tangle of ellipses of all forms and sizes but lying in nearly 
a common plane and with a common direction of revolution 
about the central body. Collisions would inevitably occur at 
the crossing of the paths in the course of numberless revolu- 
jtions and the nuclei would have sufficient mass and conse- 
quent gravitative power to retain the matter colliding with 
\them. In this way, each planet would in the course of time 
‘clear up an orbital zone, and these zones, because of the eccen- 
|tricities of the orbits of the component particles, overlapped 
each other with the exception of a region between Mars 
and Jupiter. But Moulton has shown that in such planetary 
growth by accretion, an axial revolution would arise in the 


Pe 


20 EVOLUTION OF THE EARTH 
same direction as the orbital revolution, and that the incor- 
poration of all the planetesimals would cause the eccentrici- 
ties to cancel out, giving to the whole mass a nearly circular 
instead of a highly elliptical orbit. This would lead us to 
believe that the original nucleus was but a small part of the 
completed planet, so that its original ellipticity of orbit was 
submerged beneath the average influence of the added masses. 
Outstanding difficulties of the planetesimal hypothesis. The 
disruption or spiral nebula hypothesis explains the features 
of the solar system more successfully than the older nebular 
hypothesis has thus far been able to do, but there are difficul- 
ties still remaining, though these may perhaps be the result of 
special conditions. 
The most striking departure of the real system from that 
expectation deduced from the hypothesis is found in the rota- 
tion of the sun. The passing of a star able to drag matter 
from the sun to the distance of the planet Neptune would be 
expected to lead to an enormous tidal distortion of the sun 
mass. This great tidal wave would involve a lifting on 
revolution about the sun, tending to give it a certain energy’ 
of rotation. A very little stronger action and the sun would) 
in fact have been literally pulled to pieces and its matter 
scattered beyond its gravitative control. It is possible that! 
it may in this way have lost a part of its mass. Considerable 
quantities of the expelled matter should have fallen back. 
obliquely in the sun and tended further to increase its velocity: 
of rotation. ‘The path of the approaching star could hav " 
had no relation to the previous equatorial plane of the sun. 
The probabilities would consequently be that the final rotation 
would be a resultant between the older and newer forces and 
lie in an intermediate plane at a considerable angle to the 
plane of the planets’ orbits. Now, as a matter of fact, the 
sun, as has been previously noted, revolves but once in twenty- 
five days and its equator is inclined but seven degrees to “te 


———i 


ae ee 


AND ITS INHABITANTS 21 
mean plane of the planets’ orbits.. I'o explain this, Chamber- 
3 supposes that the sun had originally a rotation in a plane 
not greatly different from that in which the passing star ap- 

roached, but rotated in the opposite direction. The whirl 


ave been a little greater than its initial rotation, but, being — 


ire to the solar mass by the tidal disruption is assumed to | 


n the opposite direction, the resultant was at a slow speed 
and yet 1 et nearly in the plane of the planetary orbits.? Campbell 
points out that the chances are highly against such a special 
‘arrangement. If ina number of solar systems such an arrange- 
‘ment prevailed, it would constitute a conclusive proof against 
‘the hypothesis, but in the one example the exceptional com- 
bination may have occurred and it cannot be urged as a 
disproof.* 
_ Turning to another aspect of the hypothesis, the innumer- 
able spiral nebule of the heavens, although good illustrations 
of the initial hypothetical form of the solar planetary system, 
do not appear to be stages in a similar evolution in the way 
} that Chamberlin and Moulton have conceived them to be. 
They are, as previously stated, of a much vaster order of 
magnitude, they avoid the region where the stars are clustered, 
are at remote stellar distances, and by their very number show 
a notable duration of their form. On the other hand, the 
postulated originally spiral form of the solar nebula would 
have been evanescent. Within a century from the time of 
origin all except the outer nuclei would have completed many 
‘revolutions about the sun. But the different periodic times of 
‘the nuclei would in a few revolutions have caused the initial 
‘spiral form to disappear. It would become wound up and 
Marther blended together owing to the high ellipticities of the 
“constituent orbits. 


8 8 Chamberlin, T. C., “The Origin of the Earth,” 1916, pp. 130-132. 

| #Campbell, W. W., “The Evolution of the Stars and the Formation of the 
| Earth.” Scientific Monthly, vol. 1, 1915, p. 241. 

i) 


— 


22 EVOLUTION OF THE EARTH 

The temporary dispersal of the solar mass would lead te 
an enormous increase in its radiant energy. The planetesimal 
matter would as a consequence of its dispersion and increased 
radiating surface cool with great rapidity, except in the nuclei 
of masses, and cease to be self-luminous, the smaller particles 
almost immediately becoming cold except as they were heatec 
by the larger and profoundly disturbed solar mass. 

The new stars which have been observed are not regarded” 
as of this nature since they are not expanded into a spiral. In 
fact, as previously mentioned, no examples are known which 
serve as illustrations, in the terms of this hypothesis, of the 
birth stage of planetary systems. This lack of examples may 
be connected with the small scale as well as the temporary 
character of such a nebula. The whole solar system, extend- 
ing to the orbit of Neptune, would subtend slightly less than 
half a minute of arc as seen from the nearest star. Tne” 
average star is hundreds of times farther away and at the 
greater distances a nebula of this order would not betray its” 
existence by its form but only by the temporary great increase 
in radiance at the time of its birth. | 

Chances of close approach. Whether the chance is great 
or small of a planetary system being generated from any 
particular star by tidal disruption cannot be used as an argu-" 
ment for or against this hypothesis unless it were known what 
proportion of the stars possessed planetary systems. But tha 
knowledge is hopelessly concealed from us in the depths of 
space, since such a system as ours after its temporary initial) 
brilliance would, as shown, be invisible in the most powerful 
telescopes even if it existed about the nearest star. 

It is not known how near an approach would be necessary 
to generate such a solar system; but the chances of close” 
approach must be very small for any particular star. The 
motion at any instant of any individual star is the result of it: 


motion inherited from the past plus the attractions of all the 
is, 


Ne OE aii oe 


AND ITS INHABITANTS 23 
fmatter in the universe pulling upon it in the present. If two 
dies without previous motion were to be attracted toward 
‘each other, and were able to ignore the gravitative pull of 
all other bodies, they would move in a straight line toward 
‘each other’s centers with ever increasing velocity until colli- 
: would result. But the least inherited motion in any 
other direction, or the least deflecting pull upon one of them 
more than upon the other by other bodies would prevent to 
that degree a central collision, or in almost all cases any 
collision whatever. Now the velocities of the stars through 
‘space at great distances from each other are so great that 


‘individual stars can have almost no attractive influence upon 
‘each other. They must move in nearly straight lines past 


each other unless they happen to pass within a thousandth 
‘part of their average distance. It is seen then that the 


‘chances of close approach depend primarily upon the acci- 


‘dental crossing of their paths and only secondarily upon their 


‘mutually attracting each other. For this reason the chance 
of actual collisions may be regarded as negligible, even con- 
‘sidering the vast number of stars. Approach sufficiently 


near to generate strong tidal forces would, however, have 
occurred during their long lifetimes as radiant bodies to a 
considerable number out of the hundred million or more of 
‘stars which are known to exist in the stellar system, but for 
‘any one individual star, where the spacing is of the magni- 


| tude existing in our part of the stellar system, the chance of 
| such approach even in a billion’: years would be very small. 


In fact, it has been estimated as only one chance in 1,800 in 


‘that time. It is possible, however, that this happened once 


to our star, that is, to our sun of that time, in the distant 


“past and from that disruptive tidal force was born our 
“$system of planets. If such an event was in fact a necessary 


antecedent condition, fortunate indeed has been our planetary 
fate, for not only did this happen so early in the sun’s career 


24 EVOLUTION OF THE EARTH 
that its radiant energy has been able to endure through all 
the ages needed for organic evolution, but the spacing of 
the stars is so wide and the chance of approach so rare that 
no other of them has since advanced sufficiently near to 
throw this system into disorder, or to disrupt and sweep 
away the earth and its sister planets as a wasted effort, and 9 
start the re-creation of a new heaven and a new earth. 


HypoTHEsis OF EARTH-GROWTH BY SLOW ACCRETION 
OF PLANETESIMALS | 


Under the terms of either nebular or planetesimal hypoth- 7 
esis a scattered state of the planetary material is implied 
as a stage antecedent to the origin of the planets. Was this 
growth of the planets geologically slow or rapid? Did it 
take tens or hundreds of millions of years, or was it on the 
contrary largely accomplished in tens or hundreds of thou- 
sands of years? Was the material largely in dust-like or 7 
molecular form, or was it to a large extent in nuclei of con- 
siderable size? From these different postulates very diver- 
gent consequences may be traced in the formative stages of © 
the earth; and finally the present nature of the earth itself 7 
may speak in favor of one or the other of these views. 

Chamberlin, who has been the chief writer on this sub- 
ject, adopts the hypothesis that the stages of earth-growth 
were very prolonged, even geologically speaking, and that 7 
the accretion was dominantly of dust-like or molecular par- 7 
ticles. According to him the building up of the planets fol- 7 
lowed three stages: first, the direct condensation of the 7) 
nuclear knots of the spirals into liquid or solid cores; second, © 
the less direct collection of the outer, or orbital and satelli- 
tesimal matter; third, the still slower gathering up of the — 
planetesimal material scattered over the zone between © 
adjacent planets. This third factor, in Chamberlin’s view, is © 


AND ITS INHABITANTS 25 
regarded as very important and he believes this diffused 
matter contributed much of the earth substance, very slowly 

and in a dust-like form. This is one of the critical points 
in the details of the theory upon which turns much of the 
development of his following argument. 

Chamberlin conceives the earth to have been built up as 
a solid body, not to have been fluid or viscous at any time 
later than the early nuclear stage and to have begun to 
_hold an ocean by the time it contained 30 or 40 per cent 
of the present mass. Such liquid rock as was generated 
by compression or radioactivity during earth-growth is re- 
garded as having been kneaded and squeezed to the surface, 
where it solidified approximately as fast as it was formed. 
In earth-growth, the denser planetesimal dust, he argues, 
tended to be somewhat segregated into the primitive ocean 
basins and served to maintain in them, as the earth was 
built outward, a greater density than in the elevated zones 
between, establishing thus a relation between density and 
elevation. 

It seems a debatable question if such a large proportion 
of the added material was necessarily dust-like and capable 
of being weathered, sorted, and distributed by the primitive 
atmosphere and ocean. In fact, from this beginning of 
earth-growth the preponderance of the evidence appears to 
the writer to be against those sub-hypotheses which Cham- 
berlin has followed. This evidence, its bearings and con- 
clusions, will form the following parts of this article. It will 
be of ultimate value to both lines of argument that each may 
be weighed against the other. 


HYPOTHESIS OF EARTH-GROWTH BY RAPID INFALL OF 
PLANETOIDS 


Preliminary statement. Alternative views quite different 
from those which have been presented under the previous 


26 | EVOLUTION OF THE EARTH 
heading will now be discussed. It appears to the writer 
that the chemical character of the igneous rocks, the limited 
depth of density variations in the crust, the limited amount 
of salt in the sea, the rotation periods of the moon and 
planets,—all point to a molten condition of the earth at the 
completion of its growth. In the limited space available the 
more technical aspects of the arguments must, however, be 
omitted. The questions raised by this conclusion are: What 
mode of growth would have favored a molten state and 
how far did this precede the beginning of the geologic 
record, as given by the oldest rocks exposed at the surface 
of the globe? 

Up to this point the method of alternative hypothesis | 
has been pursued, and from the standpoint of scientific pro-— 
cedure it should be continued to the end. ‘The limitations — 
of space in a single essay, however, forbid. This subject, - 
which for complete analysis should be developed in a volume, — 
must be compressed into a few pages. ‘The judicial style 
must often be abandoned for the declarative. Descriptions — 
of some things which no eye has ever seen will be given 
graphically as though viewed by a witness. This change in 
method necessitated by limitations of space is, however, 
least objectionable in the closing parts of the subject, since 
the foundation hypotheses have been already presented ‘and 
the argument leads from them toward the established facts 
of the geologic record. 

Significance of the planetoids. The belt of asteroids, better 
called planetoids, appears to have remained more nearly in 
its original state than have other parts of the solar system. 
The lack of aggregation into a planet may be due in part to 
the absence of any dominating center. More than eight hun- 
dred of these bodies have now been discovered and listed and 
countless others must be so small that they will largely remain 
unknown. The diameters range from a maximum of 485 


: 


AND ITS INHABITANTS 27 
miles in increasing numbers down to 15 to 20 miles, the limit 
of telescopic visibility. 

At some diameter below the limit of visibility in the tele- 
scope, although the number may be increasingly great, the 
summation of their masses must begin to fall off, since other- 
wise the combined bulk would produce a perceptible glow in 
the sky. Furthermore, Leverrier demonstrated from the 
limited perturbations of Mars in its orbit that the whole 
amount of matter distributed between the orbits of Mars and 
Jupiter cannot exceed about one-fourth of the mass of the 
earth. It may be less. In fact, later calculations limit it to 
less than one-hundredth of the mass of the earth. The rate 
of increase in numbers in the smaller visible sizes suggests in 
connection with the limitation in aggregate mass that a con- 
siderable part, perhaps a larger part of the matter, is not in 
dust-like or molecular form but is in fragments of appreciable 
size ranging up to some miles in diameter. These masses, 
owing to their small diameters and weak gravitative force, 
would possess almost no power to grow by accretion. ‘They 
must retain almost the original state of the nebula, or better, 
the meteoritic swarm, and are perhaps as likely to have suf- 
fered occasional shattering and scattering by impact as to have 
grown from a lower order of size. Their evidence favors the 
hypothesis that the scattered matter which was added to the 
nucleus to form the earth was largely of such size that the 
individual planetoids would have plowed through a primordial 
atmosphere and ocean, if such existed, and have penetrated 
beneath the surface of the liquid or solid body below. The 
energy of impact from dust-like material would be absorbed 
at the surface and, as heat, quickly radiated into space. The 
‘accretion of dust would favor the growth of an earth solid 
throughout. Larger masses would, on the other hand, carry 
the energy of impact into the earth. They would not strike 
with the high velocities of the meteors which collide with the 


28 EVOLUTION OF THE EARTH 
earth, since the different planetoids were traveling in the same 
general direction, but nevertheless a state of incandescence and 
liquidity would be likely to result from the sizes of the masses 
involved. If in addition the infall of masses was sufficiently 
rapid to bury the heat of previous infalls before it could be 
dissipated by conduction to the surface, a general heating and 
liquefaction of the earth would tend to take place, both from — 
the increased compression of the deeper nucleus and the effects 
of impact at higher levels. 

The fact that the planets have cleared up the zones about 
them, whereas the planetoids have remained permanently in 
a scattered state, is an argument for holding that the existence 
of dominating nuclei determined the growth of the planets. 
It is likely that the nuclei were of various sizes, were clustered 
to various degrees, and many of them united by their impact. 
A somewhat limited number and considerable size of the units” 
as well as their grouping would be in accord with the lack of 
relation of the amount of eccentricity and inclination of orbit 
to the masses of the several planets. | 

Indications of primordial tidal retardation. The moon 
keeps the same face turned always toward the earth. Con- 
sequently, from a point in outer space, it would be seen to” 
rotate on its axis in exactly the same time that it completed its” 
orbital revolution. Mercury is known also to keep the same 
face turned always toward the sun and the same relation is” 
probably true of Venus. The other planets revolve many 
time on their axes during the period of revolution, the earth, 
for example, 366 times. The exact correspondence in the 
moon, Venus, and Mercury between their times of axial rota- 
tion and orbital revolution points.to some causal relation be- 
tween the two periods. That relation is one of tidal forces. 

The moon distorts slightly the earth’s figure, but as the tidal 
forces due to the moon are weak and the earth is very rigid, 
this distortion in figure is expressed mostly by the rise and 


AND ITS INHABITANTS 29 
fall of the earth’s fluid envelope. In so far as the body of 
the earth yields, it is an elastic yielding which involves no 
measurable expenditure of energy. The oceanic tidal waves 
tend to continually face the moon and the earth revolves be- 
“neath them, like a wheel revolving between two opposite 
‘brake-shoes. This generates tidal friction which tends to slow 
down the axial rotation of the earth. There is no question as 
to the correctness of this theory, but there is a very serious 
question whether the forces are not so weak as to be without 
any geologic consequences, at least under the present rigid 
condition of the earth’s interior. 

Some of the latest work has been given to measuring directly 
the retardative influence of the tides, if such exists. Mac- 
Millan has made an estimate of the loss of energy by friction 
of the oceanic tides. He used the formule employed by en- 
gineers for the loss of head due to friction and viscosity, and 
applied them to the ocean. His conclusion is that the day 
would be lengthened by one second in about 500,000 years. 
Even if this figure be in error tenfold or a hundred-fold it is 
still in great contrast with the conclusion of Adams in the 
_ middle of the last century, that the earth was losing time at the 
rate of 22 seconds per century, a figure raised to 23.4 seconds 
by Darwin and lowered to 8.3 seconds by Newcomb. Mac- 
Millan’s method brought to bear as a retardative agency prac- 
tically all the friction of the tides, irrespective of their positions 
or directions of motions, and seems to show that thé water 
tides do not have and have never had an appreciable effect on 
_the earth’s rotation.® 
_ Tidal retardation if it has ever been an important factor in 
_ planetary history must then be chiefly due to a body tide. In 
so far as there is a mere elastic yielding of the body no energy 


® MacMillan, W. D., “On the Loss of Energy by Friction of the Tides.” In 
“The Tidal and Other Problems.” Carnegie Institution of Washington, Pub. 
No. 107, 1909, pp. 71-75. 


30 EVOLUTION OF THE EARTH 
is consumed, but a viscous drag will produce retardation. 
Recent measurements of the rigidity of the earth under tidal 
stresses, both by the horizontal pendulum and by the water 
level in a horizontal pipe, show that the earth as a whole is” 
more rigid than steel and that under the exceedingly small tidal 
stresses the yielding is essentially elastic. he estimates of 
viscosity are so small that they are within the limits of error 
of the measurements. The smallness of the tidal strains in 
the earth may be appreciated by citing Darwin’s calculations. : 
According to this investigator, the tides raised by the moon - 
upon the earth generate a stress-difference of 16 grams per 
square centimeter at the poles, 48 grams at the equator, and 
128 grams at the center of the earth. Thus the earth is 
stressed by the lunar tidal forces even at the center to only 
about one part in fifteen thousand of the strength which 
granite has at the surface of the earth. 
The tidal force exerted by the earth on the moon is about © 
twenty-two times as great as the lunar tidal force on the earth, © 
and reaches about one part in six hundred or seven hundred of 
the strength of granite. If the moon were once nearer the ~ 
earth, the tidal stress-difference was much greater, varying 
inversely with the cube of the distance. ‘Tidal retardation must 
have acted efficiently upon the moon, nevertheless, until the 
moon was at its present distance and the stresses reduced to 
their present magnitude, in order to have reduced its period 
of rotation to the same value as its final orbital period about 
the earth. The action must have been that of a viscous body 
tide since the moon has never been able to hold to itself an 
ocean envelope. ‘The tidal force exerted by the earth upon 
the body of the moon consequently must have produced a : 
notable viscous yielding and continued to do this in spite of 
increasing distance of the moon and increasing rigidity. 
The far greater mass of the earth prevented such large 
effects of tidal retardation from being felt, but its period of © 


| AND ITS INHABITANTS 31 
‘ revolution compared. to those of Mars and the outer planets 
suggests that the tidal forces of the moon and sun have pro- 
_ duced a notable slowing down of the earth also. The largest 
planet, Jupiter, 86,500 miles in diameter, revolves the most 
rapidly, completing one revolution in 9 hours 55 minutes; 
Saturn, the next largest, revolves in 10 hours 14 minutes. 
Uranus also shows by the pronounced polar flattening of its 
disc that it revolves in some similar short period. Mars, with 
a diameter approximately half of that of the earth and a 
_ twentieth of that of Jupiter, revolves in 24 hours 37 minutes. 
These planets can never have suffered largely from tidal 
_ retardation and a rough rule appears to prevail that the larger 
the planet the more rapidly it rotates. Judging from its mass, 
the earth may consequently have originally rotated in a period 
- of between 15 and 20 hours. This argument is only of sug- 
_ gestive value, but it is in accord with other lines of argument. 
If the moon passed through a viscous state sufficiently pro- 
longed for it to respond completely to tidal control in its 
rotation period, the presumption is clearly that the earth, a 
larger body and better able to retain its heat, also passed 
through a similar stage of viscosity. The present rigid and 
elastic condition of the earth appears then to be a secondary 
feature and the present ineffectiveness of the tides cannot be 
safely used as an argument against the strong indications of a 
primordial tidal retardation. 

Significance of the oceanic salt. Sodium derived from the 
weathering of igneous rocks has been stored through all geo- 
logical time in the ocean as sodium chloride. The ocean has 
grown more salty since it first gathered on the earth, yet it is 
so far undersaturated that sea water must be nine-tenths 
evaporated before sodium chloride begins to be precipitated. 
Furthermore, the indications are that it never was saturated, 
even though in primordial times the sea water may have been 
less in volume. Concentration to a degree which eliminates 


ac > tee EVOLUTION OF THE EARTH 

part of the sodium chloride raises the percentage content of 
bromine, magnesium chloride, and magnesium sulphate, so 
that sodium becomes subordinate to magnesium and the ratio 
of bromine to chlorine is increased Subsequent dilution 
would not change this ratio and the introduction of new salts 
could never bring it back to the original composition. The 
evidence from the sea itself is substantiated by the testimony 
of the sedimentary rocks. The amount stored as impregna- 
tions or as salt deposits in the sediments is quantitatively 
negligible, either as compared to the volume of the sediments 
or the mass of the oceanic salts. Salt deposits, furthermore, 
so far as known, began to be present only in the Paleozoic, in 
the later half of geologic time, the great masses of earlier 
sedimentary strata being barren of them. 

It has been calculated that the total sodium in the ocean 
would be derived from the weathering and erosion over all 
the earth of a mantle of igneous rock of average composition 
only 2,300 feet thick, corresponding to 6,500 feet as the 
average thickness of erosion if restricted to the area of the con- 
tinental platforms, including the lands and extending out to 
a depth of 600 feet below sea-level. 

Daly has noted the significance of these facts upon the 
hypotheses of earth-growth.* Chamberlin supposes an ocean 
to have existed for long geologic ages upon the surface of 
the earth during its growth from a body about half of its 
present diameter and one-eighth of its present volume. The 
planetesimal material, he holds, was weathered and sorted 
into lighter and heavier portions, leading to the development 
of lighter protuberant and heavy depressed areas. The 
limited quantity of salt in the sea, however, is distinctly against 
such a hypothesis of oceanic antiquity and continental build- 
ing. The amount of erosion in evidence where the older 
rocks are exposed as crystalline masses and from the great 


® Daly, R. A., “Igneous Rocks and Their Origin,” 1914, pp. 159, 163, 164. 


AND ITS INHABITANTS 33 
uplifted tracts of later times is apparently about sufficient to . 
account for all the salt in the sea. In fact, the estimates of 
_ erosion through known geologic time based on the nature of 
rock exposures and the thickness of sediments have fully 
equaled or exceeded the amount given by the quantity of salt 
in solution. Weathering, erosion, and the accumulation of 
_ salt had therefore played no considerable part previous to the 
time recorded by the oldest rocks. ‘The earlier physical con- 
- ditions must have been very different from those which later 
_ prevailed. 


Ao 


FAVORED HyYPoTHESIs OF AN EARTH INITIALLY MOLTEN 


Indications of a primordial molten state. The indications 
_ of primordial tidal retardation and the limited amount of salts 
in the sea both point to the cgnclusi was molten 


at the completion of its growth. A molten state suggests a 
rapid earth-growth due to an original clustering of the matter 


whose convergence built up the planet. Larger nuclei hun- 
dreds of miles in diameter and smaller ones able to the 
planetoids moved in elliptic and nearly intersecting orbits. 
~_Mutual perturbations kept modifying these orbits and provid-_ 
ing new chances for collisions, union, and growth. Such colli- 
sions led to_a development _of energy of impact suthcienf fo 


_produce in the growing earth a molten state, at least in the 


_ outer portions. The earth kept growing at the same time 


—by sweeping up large quantities of finer material, but a molten 
_state suggests that the greater growth was due to the intall 


“ot Targer nuclei. Finally, but one outstanding nucleus, the 
“moon, was left beside the earth, and the earth-moon system 
attained a condition of stability and completed growth. 

If the composition of the earth as a whole is similar to 
that of the meteorites, those samples of matter which come to 
us from the heavens, the most abundent-material in the deep 
body of the earth is metallic iron. Now the blast furnace 


34 EVOLUTION OF THE EARTH 
/ i have el 
_ makes familiar the fact that slag is insoluble in iron and, 
being lighter, gathers in the upper part of the crucible, like 
cream upon milk. The slag is similar in composition to 
basaltic 1 igneous rocks. The density of the deep interior sug- 
ests that it is layered like the crucible of the blast furnace — 
and that the silicate rocks form an envelope some hundreds 
of miles thick, grading down into a great metallic core. The 
silicate envelope ultimately differentiated further, resulting 
in a rise of the more siliceous and lighter fraction into an outer _ 
layer, perhaps 50 to 75 miles in thickness. This in turn crys- 
tallized into a primordial, universal, granitic crust above a 
thicker basaltic shell below. | 
The primordial atmosphere. Granting the conclusions in | 
regard to the initial fluid state of the earth, let the primordial 
atmospheric conditions be pictured. A gaseous envelope exist- 
ing in equilibrium with rock magma would be dominantly 
water-vapor, followed in order of importance by carbon 
dioxide and carbon monoxide, chlorine and hydrochloric:acid, — 
with some nitrogen, but no free oxygen. 
The present atmosphere of nitrogen and oxygen penetrates 
by solution into the liquid envelope of water. The primitive - 
atmosphere of water-gas penetrated in the same manner by — 
solution into the ocean of molten rock. But such an admixture — 
of molten rock and water-gas is known to have a remarkable — 
effect upon the melting point of silicate magmas. Under dry 
fusion the exalted temperature of 1300° to 1500° C., 
dazzling white heat, is necessary to make granite thinly molten. 
But if the fluid rock has dissolved an abundance of water- — 
vapor the mixture stays fluid until it has cooled below a tem- 
perature of 800° C. ‘The surface of the earth when molten 
was perhaps no hotter than this. At such a comparatively 
low temperature and even at somewhat higher temperatures 
there would be but little dissociation of water into its com- 
ponent gases, and the earth would be capable of holding to 


' AND ITS INHABITANTS 35 
Tisclf, even in its molten stage, an envelope of water in the 
form of a deep and heavy atmosphere of water-gas. Such an 
envelope, including also an abundance of carbon dioxide and 
carbon monoxide, formed an effective thermal blanket, pre- 
nting a precipitous chilling one freezing at the surface of 
the ocean of molten rock. 
_ The effectiveness of the bis depended upon the pecu- 
arity of both water-gas and carbon dioxide in being opaque 
E the slow vibrations of dark heat, absorbing these near 
the bottom of the primitive atmosphere and reradiating them 
from higher levels as long, slow heat waves. Strong convec- 
tion currents carried up these heated gases from the super- 
heated base to the higher levels of the atmosphere. There the 
uilling condensed the water-vapor into a thick and universal — 
canopy of cloud, boiling up like thunder-heads from below, 
shedding continuously a downpour of acid rain, rain dissipated 
again into vapor as fast as the drops fell into the deeper and 
hotter strata of the atmosphere. The intensity of the vertical 
convection maintained a high electric tension. Incessant 
flashes of lightning linked as with living, fiery tentacles the 
cloudy heavens to the lurid molten earth. Tremendous re- 
verberations of thunder, unsensed by mortal ears, shook the 
atmosphere in the worldwide primeval storm. 
_ The sunlight of the Primordial Era illumined and was 
teflected from the outer side of the mantle of cloud. The 
planet shone brilliantly by this reflected light, having an ex- 
ternal appearance similar to that which Jupiter and Saturn 
still possess. Above the zone of cloud the carbon dioxide and 
other gases, with very minor amounts of water-vapor, ex- 
tended with diminishing density as an upper transparent 
envelope. 
_ During the more rapid growth-stages the molecular and 
dust-like matter swept up by the earth settled like a never 
ceasing cloud of volcanic ash. The planetesimals of sand and 


36 EVOLUTION OF THE EARTH 
gravel size were swept up by the earth many millions of times 
more abundantly than are meteors at the present time. Those. 
meeting the earth with the higher velocities were consumed by 
impact. Over the hemisphere of night the otherwise invisibl 
atmosphere above the cloud canopy scintillated with incessant 
flashes of light and trails of luminous dust. Bodies of larger 
size gave in their dissolution a still more brilliant display and 
penetrated to greater depths. At longer intervals, with titanic 
rush and roar, a greater projectile, tens or even hundreds of 
miles in diameter, cleaved through the canopy of cloud, leaving 
a tumultuous maelstrom behind, drove almost unchecked 
through the deep and dense atmosphere below, and, with 
worldwide commotion, was engulfed, with development of 
fervid heat, within the molten sea. | 


THE PASSAGE OF THE MOLTEN INTO THE RIGID EARTH 


Density stratification by fractional crystallization, The 
central parts of the earth were compressed during the growth 
stages by the increasing load above. This compression 
developed heat, but also raised the fusion point and made for 
a greater rigidity. It is not known, consequently, whether 
during earth-growth the center tended toward a liquid or 
solid state. The outer part, however, with a thickness of 
perhaps the outer quarter of the radius, comprising about one- 
half of the volume of the sphere, seems to have passed into 
a truly molten condition. | | 

The heavy atmosphere and canopy of cloud prevented a 
rapid radiation from the molten surface, probably sufficien 
during the highly liquid stage to prevent a crusting over of 
frozen rock. The method of solidification approached neare 
to that which occurs in a large reservoir of magma intruded 
into the crust than to the freezing of a modern lava stream in 
contact with the air. 


AND ITS INHABITANTS 37 
_ At last the rapid generation of heat by impact lessened, and 
the fluid sphere, seething with slow convection currents, began 
‘to cool. Certain compounds in the mutual solution of rock 
elements became insoluble and fractional crystallization was 
initiated. ‘The heavy basic crystals were the first to form: 
crystals of metallic sulphides, magnetite, hornblende or 
pyroxene, and olivine. These crystals, because of their high 
‘specific gravity, tended to work downward in the convective 
movement. At first they were dissolved again in the abyss, 
but as time went on they remained undissolved and accumu- 
lated in the deeper parts of the fluid zone. The remaining | 
magma was more siliceous, of lighter gravity, and in crystalli- 
zation gave to the upper shell a higher proportion of feldspar 
and quartz. The original crust of the earth was consequently 
a granite. [he process of fractional crystallization may, 
‘however, not be a sufficient explanation. An immiscibility of 
the complex mineral solutions may have developed upon the 
lowering of the temperature. In one way or the other or by a 
combination of several causes a density stratification is sug- 
gested by a number of lines of evidence as existing in the earth. 
The conclusion, then, is more than a mere inference from 
theories of crystallization. 

The gathering of the ocean waters. At last the ocean of 
molten rock had shallowed, crystallization went forward in 
separate basins, convection became hindered, the surface 
froze as in a lava'caldron. Then rain, ever descending from 
the shield of perpetual cloud, but never heretofore reaching 
the bottom of the atmosphere, at last began to splash on the 
hot surface of the earth. The raindrops at first were dis- 
‘sipated by contact and sent flying back as scattered molecules 
of gas. But, owing to the low conductivity of rocks, the tran- 
sition stage was very brief, and perhaps even in a few thousand 
years from the time when the crustal congelation of the earth 
had taken place a permanent ocean of acid water began to 


oo 


EVOLUTION OF THE EARTH | 
fest upon the surface. For a while the balance swung, as one 
section or another of the crust was broken through and lavas 
would pour out abundantly. Rapidly, however, from th 
geologic standpoint, as the surface cooled, the atmosphere of 
water-vapor condensed in a never ceasing deluge until an 
ocean, probably universal in its extent, had gathered to a meat 
depth of several thousand feet. The remaining atmospher 
was comparatively rare and cold. Carbon dioxide became thi 
dominant gas, and water-vapor subordinate. Solar heat begai 
to play the principal part in warming the equatorial zone. / 
system of planetary winds developed in accordance with the 
new order of nature. The cloud canopy became thin and 
broken, resolving itself into climatic belts. Sunlight for the 
first time began to pierce the lower atmosphere and illumin 
from without the surface of the earth. 

During the earlier time, when the water could exist only a 
gas in the atmosphere, the great pressure of this envelope ha 
kept much, perhaps most, of the gases in the molten rocks 
With the great fall in atmospheric pressure which accompaniet 
the gathering of the ocean, magmas which broke through the 
higher levels of the crust into the regions of this decreased 
pressure were able to give off great volumes of gases which it 
the earlier stage had been repressed. These gases, freed foi 
the first time, are termed juvenile and from this time forwar 
juvenile waters were added to the ocean. In the first age 
following the solidification of the earth the additions wer 
large in volume, but igneous action continues to bring ney 
magmas to the surface recurrently from age to age. Thes 
give off the gases which have been repressed in them sine 
the origin of the earth. Thus, in intermittent and lessenec 
rate, the surface waters have increased through geologic time 
As Suess has said, the body of the earth has given forth its 
oceans. : 


a i 


AND ITS INHABITANTS 39 


THE ORIGIN OF OCEAN BASINS 


_ The relations of crustal density to ocean basins. The fluid 
‘earth had a surface as level as the ocean, and the process of 
‘solidification which has been outlined does not account for 
those marked variations in density and in surface form which 
‘are expressed by the outer crust of the solid earth being divided 
into continents standing high above the ocean floors. A sketch 
of the formative period is therefore not complete unless the 
processes are briefly discussed which are thought to have 
‘shaped the earth’s surface, giving rise to the existence of lands 
even before the period of the oldest known rocks. 

Reasons will be given below for holding that the ocean 
basins have been formed by subsidence of broad areas of the 
crust, owing to the weight of magmas of high specific gravity 
rising widely and in enormous volume from a deep core of 
greater density into these portions of an originally lighter 
crust. This regional subsidence was especially characteristic 
of primordial times, but the process did not wholly cease then; 
since certain lines of evidence suggest that some ocean basins 
have been extended in later geologic ages, breaking into once 
wider continental platforms. ‘The resultant increase in the 
volume of the ocean basins has led to a drawing off of the. 
ocean waters from the continental areas, and a marked diminu- 
tion of the shallow seas of earlier ages. 

The cause of the continued generation of new bodies of 
molten rock in the sub-crustal shell, adequate to account for 
the observed results of later geologic time, is thought to Ife 
in the slow accumulation of heat from radioactivity in these 
depths below the crust. ‘This is discussed in the subsequent 
topic on the rise of basic magmas. 

Some very thick bodies of intrusive rock are observed to 
be more dense and basic below, lighter and more siliceous 
above. The lower part is a gabbro, whereas the upper may 


40 EVOLUTION OF THE EARTH 
be a granite. The separation has taken place after the in- 
trusion of the magma, the denser material sinking, the lighter 
rising. ‘There are indications that the process goes forward 
ona larger scale also, a scale so large that the dark and heavy 
base is never seen, erosion of later ages being restricted en- 
tirely to the granite zone. Such a splitting in composition is 
indicated in that the earlier intrusions in a period of igneous 
activity are intermediate or basic and the later products are 
vast bodies of granite. The greater density in the earth’s 
interior suggests a primal density stratification on even a larger 
scale, which has been discussed under a previous topic. 

But in the outer shell, 50 to 75 miles thick, the density is 
far from being uniform. In recent years it has been proved 
by means of precise geodetic measurements on the local in- 
tensity of gravity and deflections of the vertical that the crust. 
beneath the continents is notably less dense than that beneath 
the oceans. The most of this difference in density exists prob- 
ably within the outer 50 miles. The continents stand high, 
consequently, for the same reason that an iceberg rises above 
the surface of the sea: it is the position of equilibrium. At a 
certain depth the downward pressures given by the thicker 
continental and the thinner oceanic crust are the same and a 
condition of hydrostatic equilibrium prevails in the sub-crustal 
shell. 

This condition of equal pressures at a certain depth is called 
isostasy. It is not inconsistent with a solid and rigid condi- 
tion of the earth, but does mean that at a greater depth, 
apparently from 50 to 300 miles or more, hot but solid rock 
can slowly yield and flow by recrystallization. ‘The process 
is physically the same as that by which a glacier flows under 
the slight stimulus of an almost level surface slope. The condi- 
tion for such ready recrystallization is found in temperatures 
which are close to those of fusion. At such temperatures 
molecules under strain pass readily from the solid to the liquid 


‘sa1aydstwiay U19}sva pue UIIIsAM BY —"T] ILVIg 


AND ITS INHABITANTS 41 
state, shift into positions which ease the strain, and again enter 
into a crystalline solid condition. The proof that such a pro- 
cess exists in the earth is based on several lines of evidence. 

First, evidence of a broad isostatic equilibrium notwith- 
standing the agencies of mountain folding, of erosion, and of 
sedimentation, all of which work through geologic time tend- 
ing to destroy those relations of elevation which are needed 
to maintain isostasy, giving equal pressures by broad crustal 
areas of unlike density upon the yielding zone below. 

_ Second, the evidence of increasing temperature with depth, 
giving temperatures close to those of fusion at depths below 
40 to 50 miles. | 

_ Third, the evidence from tides and earthquakes that the 
earth as a whole is more rigid than steel and cannot possess a 
fluid shell beneath the crust. 

Fourth, the physical principle that at temperatures close 

to fusion a crystalline substance is incapable of supporting 
permanent shearing stresses, but yields slowly by recrystalliza- 
tion, notwithstanding the fact that under short stresses the 
same substance may be as rigid as steel. 
_ The conclusion to which this argument leads is that an outer 
crust or lithosphere, the rock sphere, 50 to 75 miles thick and 
very strong, is marked by broad variations in density amount- 
ing to as much as 5 per cent, and more local variations up to 
IO per cent, which correspond to the broader relief of the 
earth’s surface. Below this lies a thick, hot, basic, rigid yet 
weak shell which the writer has named the asthenosphere," 
the sphere of weakness. The problem of the origin of the 
ocean basins and of continental platforms resolves itself con- 
sequently into the origin of the density differences in the 
lithosphere and the maintenance of the heated and weak con- 
dition in the asthenosphere. 


TBarrell, Joseph, “The Strength of the Earth’s Crust.” Jour. Geology, vols. 
22, 23, 1914, 1915. 


42 EVOLUTION OF THE EARTH | 
Rise of basic magmas from the asthenosphere. ‘The series 
of radioactive elements slowly break down into elements of 
lower atomic weight and give off in the process enormous quan- 
tities of energy. Uranium, in degenerating through radium to 
the stable element lead, develops more than a million times | 
the heat given by the combustion of an equal weight of coal, 
but the disintegration of the element and the liberation of its 
heat are so slow that the whole duration of geologic time has” 
not sufficed to eliminate uranium from the crust of the earth. 
Therefore it has acted as a permanent generator of heat in 
the rocks which contain it. | 
Uranium and thorium, the parents of the radioactive series, 
are widely though sparsely diffused through the lithosphere. 
It has been calculated that, if they extend in their surface 
amount to a depth of 40 miles, they must supply heat to the 
surface as fast as it is lost by radiation into space. The earth 
therefore appears not to be growing colder, though losing heat. 
The small content of’ radioactive elements in the basaltic 
shell below the granitic crust of the continents would then 
supply that slow increment of heat which is necessary to 
generate new molten rocks. The granitic shell above, though 
somewhat richer in radioactive elements, is sufficiently near 
the surface to lose its excess heat by conduction. ‘The excess 
heat generated in the asthenosphere is, on the contrary, so” 
deeply buried that it cannot escape in that manner but must 
slowly transform some of the solid rock into liquid form. 
Reservoirs gather, until their mass, combined with their de- 
creased density in the fluid form, enables them to work their 
way through the crust above and demonstrate their existence 
in igneous activity at the surface of the earth. The magma 
which thus comes from the greatest depth and in greatest 
volume would, because of the initial density stratification, 
produce a notable increase in the density of the outer crust. 


AND ITS INHABITANTS 43 

In order to reéstablish isostatic equilibrium such a region must 
subside. 

Most of the igneous rock of later geologic ages which has 

been intruded into the outer continental crust clearly has aot 


_ increased the density sufficiently to produce a foundering and 


would appear therefore either to have come from somewhat 


higher levels or to have risen in lesser quantity. In some 


~ 


regions, however, as in that of the Lake Superior basin, large 


masses of basic magma do seem to have overweighted the crust 


in an early geologic period and produced a tendency to settle 


as a basin. The same effect may have taken place to even a 
larger degree in some regions of notable subsidence, as in the 
Mediterranean basins. In the earliest times, following the 


_ solidification of the earth, the forms and relations of the ocean 


basins suggest that dense’ molten matter from the depths of 
the earth broke into or through the outer crust, on a gigantic 
scale, eruption following eruption until the widespread floods 
had weighted down broad areas and caused their subsidence 
into ocean basins. | 

As seen in the lava plains of the moon, such an action, once 
started at a certain point, is conceived to have gone forward 
with widening radius, leading to the origin of the many rudely 
circular outlines characteristic of the ocean basins. The 
process left great angular segments of the original lighter crust 
as continental platforms standing in relief between the coales- 
cent basins. The waters gathered into the basins and the 
continents emerged. 


THE REIGN OF SURFACE PROCESSES AND BEGINNING OF THE 
ARCHEAN 


It is possible that shallow ocean basins began to form nearly 
as fast as the waters gathered, tending to maintain some land 
areas above the level of the primordial sea. Or the lands 
may have emerged later, as the ocean basins spread and deep- 


44 EVOLUTION OF THE EARTH | 
ened. With the separation of the lands from the seas, ero- 
sion began, carbon dioxide was abstracted from the atmosphere ) 
to make carbonates, and a further cause of atmospheric 
depletion was initiated. Thinner, rarer, and colder grew the © 
gaseous envelope, until an oscillating balance was established — 
between the supplies of new gases from the uprising molten — 
rocks and the losses involved in the weathering of their solid 

forms. Nitrogen was at first relatively small in quantity and 

oxygen not present in more than a trace. An evolution in 

atmospheric composition had still to go forward through © 
following ages to transform it into a gaseous medium for the 
support of the higher life. But even in the early periods 
following the gathering of the oceans and the emergence of the - 
lands, the sun warmed the atmosphere and earth. An environ- | 
ment suitable for the lowest organisms had arisen and the 
earliest forms of life may not have been long in coming into 
existence. The reign of the surface processes had begun, but, 
at age-long intervals, the still youthful energies of the interior © 
broke forth. Magmas in great volume ascended, now seen as ~ 
the most ancient granite-gneisses. In the great crustal over-— 
turning of these earliest revolutions the foundation rocks ap- 
pear to have been everywhere destroyed. The oldest rocks pre- 
served are mashed and crystallized sediments and lava sheets 
resting as fragments of a cover on the reservoirs of younger 
magma. Such sediments, altered and intruded, are the 
oldest Archean rocks. It is not known how close they stand 
in point of time to the formative processes whose description 
has been attempted. With these oldest rocks, the dimly 
known, heroic and mythical eon of the earth is closed and the 
first historic eon opens as the remote and long enduring 
Archean division of geologic time. 


CHAPTER II 


THE EARTH’S CHANGING SURFACE AND CLI- 
MATE DURING GEOLOGIC TIME 


CHARLES SCHUCHERT 
PROFESSOR OF PALEONTOLOGY IN YALE UNIVERSITY 


UNIFORMITY OF NATURE. The previous lecturer in this course 
had to seek for the probable origin of the earth in far-off space 
among the stars, examining them through the great telescopes 
of our time, through the light-sensing chemical plate of the 
photographic camera, and through the even more wonderful 
spectroscope. With this knowledge in hand, postulate upon 
_ postulate has been tried out through that talismanic study, 
mathematics, and so through astronomy and the science of 
numbers there is revealed an earth evolution still hazy, to be 
further established through geodesy, mechanics, and chemistry 
before the geologist comes to be its interpreter. “Then, hand 
in hand with the geologist, the paleontologist, or student of 
ancient life, reveals the organic hordes that have gone on and 
through whose fossil remains is unraveled the history of the 
earth. In all of this we see the brotherhood of the sciences 
_ and the fundamental postulate of the uniformity of nature. 

The geological time-table. As some geologic terms must 
be used in this lecture, it is desirable to define them here. The 
geologic history of the earth is now divided as follows: 

Present time. 

_ Psychozoic era. Age of man or Age of reason. 

ncludes the present or ‘‘Recent time,’”’ and the time 


during which. man attained his highest civilization, 
estimated to be probably less than 30,000 years. 


46 EVOLUTION OF THE EARTH 


Geologic time. 
Cenozoic era. Age of mammal dominance. 
Glacial or Pleistocene time. Last great ice age. 
Late Cenozoic or Pliocene and Miocene time. Rise of 
higher primates: apes and man. 
Early Cenozoic or Oligocene and Eocene time. Rise 
of higher mammals, including primates. 
Mesozoic era. Age of reptile dominance. 
Cretaceous period. Rise of archaic mammals. 
Comanchian period. Rise of flowering plants and — 
higher insects. 
Jurassic period. Rise of birds and flying reptiles. 
Triassic period. Rise of dinosaurs and primitive mam- 
mals. 
Paleozoic era. Age of fish dominance. . 
Permian period. Rise of reptiles. Another great ice — 
age. 
Pennsylvanian period. Rise of insects and first time — 
of marked coal accumulation. 
Mississippian period. Rise of marine sharks. 4 
Devonian period. First known amphibians and marine 
fishes. | 
Silurian period. First known land floras. 
Ordovician period. First known fresh-water fishes. . 
Cambrian period. First abundance of marine fossils, — 
and dominance of trilobites. 
Proterozoic era. Age of invertebrate dominance. An 
early and a late ice age. 
Archeozoicera. Originof protoplasm and of simplest life. — 
Cosmic time. 
Formative era. Birth and growth of the earth out of 
the spiral nebula of the sun. Beginnings of the atmos-— 
phere and hydrosphere, and of continental platforms — 
and oceanic basins. No known geological record. 


Origin of the sun and earth. Professor Barrell, in the pre- 
vious lecture, pointed out that the sun is a star, and one of the” 
smaller among the countless millions seen through the tele- 
scope. It may have had its origin in a diffuse nebula like 
Orion, and, according to the disruption hypothesis of Cham-— 


AND ITS INHABITANTS 47 
berlin and Moulton, had a long antecedent history before it 
gave birth to its planetary system. ‘Therefore before there 
_ was an earth, the sun had been condensing and moving undis- 
turbed in space for countless ages, until it came within the 
influence of another and a greater star. The gravitative 
influence of this mighty passing intruder acted catastrophically 
upon the sun and caused its partial disruption. As a conse- 
quence, from opposite sides of the sun there streamed rapidly 
outward materials of its own mass that soon arranged them- 
selves into a two-armed luminous spiral nebula. The mass 
which was so extruded, and which did not fall back again into 
_ the sun, was less than 1 per cent of the sun’s mass, and yet it 
_ gave rise to the planetary system which encircles the parent 
body. From this we also the more readily appreciate the 
great size of the parent sun, whose volume is 1,300,000 times 
greater than that of the earth. 

Growing earth during the Formative era. In the solar 
nebula there existed eight knots of more or less loosely aggre- 
gated denser and hotter matter, the nuclei of the future minor 
and major planets and their satellites, and these in the course 
of time attracted to themselves most of the surrounding nebu- 
lous material, usually spoken of as the planetesimals. The 
earth-knot, it is estimated, may have had an original diameter 
of about 5,500 miles, and the moon-knot perhaps half its 
_ present diameter of 2,162 miles. In the course of cosmic time, 
the earth and moon, revolving as companions about the sun, 
gathered into themselves the planetesimals that lay within 
_ their spheres of influence. 

The speaker holds to the postulate of Barrell that the plan- 
_ etesimals conceived by Chamberlin to have been of the size of 
sand and dust were probably for the most part much larger 
and more like the planetoids in dimensions. From time to 
time, as one or more of the planetoid-like bodies, singly or in 
combination, plunged in upon the earth with velocities up to 


48 EVOLUTION OF THE EARTH 
tens of miles per second, their impact with and engulfment by 
the earth engendered much additional heat. In fact, they 
liquefied themselves and their earth surroundings as a result 
of their great impacts. Furthermore, the high internal heat 
of the earth was accentuated by the condensation accompany- 
ing the increase of mass from an original earth diameter of - 
5,500 miles to one initially larger than 8,100 miles. At no time, | 
however, does it appear that the earth was necessarily in an 
astral condition, shining like a star. : 

The present diameter of the earth is 7,918 miles, but at the 
close of the growing period it must have been 200 and possibly 
even 400 miles greater, for it is well known to geologists that 
throughout geologic time it has been losing volume, due in. 
part to the loss of heat into space, but probably in greater 
degree to internal molecular rearrangements. It is now known © 
that the earth does not shrink all the time because of these - 
changes, but does so only periodically, and at these times the » 
surface of the planet becomes wrinkled, giving rise to more or 
less high ranges of mountains. Even though the earth has _ 
been dissipating its inherited and derived energy for at least 
some hundreds of millions of years, and in so doing repeatedly 
giving birth to new series of mountains, our mundane sphere © 
is still far from having attained the internal stability that will, - 
when achieved, result in a featureless earth, an ie 
devoid of the carbon dioxide that is the basis of life, and a 
universal lifeless ocean—the facial expression which the earth | 
will have in its old age. 

Volcanism during the Formative era. While the earth was : 
internally very hot and viscous, the body-mass was in slow 
movement, with the heat ever rising toward the surface. | 
These movements simulated a slow boiling process, and the 
upwellings of the molten matter repeatedly broke through the 
outer cold shell and engulfed it. As the cold crustal masses 
descended, they liquefied, and in expanding brought about 


| 
: 


— 


| 
: 


| AND ITS INHABITANTS 49 
increased pressures that again found relief in the rising tongues 
‘of heated matter. This condition is believed to have continued 
for a very long time, and to have been particularly active 
during the last half of the Formative era and the first era of 
_ geologic time, an age that may have. endured for one-eighth 
to possibly one-fourth of the earth’s entire history. The 
boiling process not only disseminated the internal heat, but also 
‘brought about an irregular sorting out of the heavier and 
lighter substances, so that the more basic and metalliferous 
materials as a rule sank to ever lower levels, while the less 
heavy acidic ones rose as granitic rocks toward the surface of 
‘the earth. Finally, at the close of this first era, the Archeo- 
zoic, the lithosphere or outer rocky and more or less rigid 
shell may have had a thickness of 50 miles. Through such a 
_ rocky mass little of the internal heat rises to the surface, and 
life would be impossible on the earth if it were not for the 
constant flow of the sun’s radiant warmth, made equable and 
usable by the atmosphere. These conditions were already 
present in the Archeozoic era. 

Origin of continents and oceanic basins. It is well known 
to geodesists and geologists that the continents are built of 
lighter materials, essentially of granites, while the greater 
Oceanic areas have the heavier basaltic rocks beneath them, 
and that the difference in specific gravity amounts to about 
3 per cent. We have seen that these differences came about 
seemingly as a result of the internal boiling process that pre- 
vailed during the Formative era and the Archeozoic, and so 
it appears that the higher continental masses and the depressed 
Oceanic basins came into being very early in the history of 
the earth. The same interrelation of masses is also to be 
seen in the moon. 

This is the igneous theory of the origin of oceanic basins 
and continental platforms of Barrell, and it holds that the 
differentiation took place after the earth had attained its com- 


50 EVOLUTION OF THE EARTH 
plete growth, in other words during the closing time of the 
Formative era and during the Archeozoic era. ‘The differ- 
ences between the densities of the lands and oceans are held © 
by Barrell to be only skin deep—in the outer one-fiftieth of — 
the earth’s present diameter, or in the outer shell of about — 
150 miles in thickness. 

On the other hand, it is true that the lands throughout 
geologic time ‘have repeatedly gone down as well as up, but 
the sum of their movements has been upward,- and for this — 
reason geologists speak of them as the positive areas of the 
earth’s surface. In the same way, the lower-lying fields have 
also risen locally at times, but their movement has in the 
aggregate been downward, bringing about the increasingly 
greater oceanic basins, the negative areas, by far the largest 
of the earth’s surface. We shall see later on that the oceanic” 
fields have become larger at the expense of the lands to 
accommodate the ever increasing volume of water, and it~ 
therefore naturally follows that the continents in former geo- | 
logic times were considerably larger than they are now, pos- 
sibly even 25 per cent larger. But the newer geology no™ 
longer holds to the theory that the oceans and lands have 
repeatedly changed places; quite the contrary, we agree with 
Dana that the present positions of the land and water areas 
have been more or less permanent throughout geologic time. 

Origin of the atmosphere. It was not so long ago that 
most geologists held with the French astronomer Laplace 
and with Dana that the earth was originally very hot, and that 
all of the water of the hydrosphere, the salts of the oceans, 
and the carbon dioxide of the air and oceans had been parts 
of the primal gaseous envelope. Not only this, but that the 
latter also included all the carbon locked up in the rocks, 
estimated to be 30,000 times greater than the amount now in 
the atmosphere. Accordingly, as the earth was held to have 
been cooling throughout its history, it was thought that only 


AND ITS INHABITANTS 51 
recently, geologically speaking, was the present thin condition 
of the atmosphere brought about. 

_ Even though more than sixty years ago a few English 
geologists who were familiar with the geology of India and 
Africa began to point out that the earth had passed through 
-acold period toward the close of the Paleozoic era (see Figs. 
4and 5), this discovery did not at once break down the teach- 
ings of Laplace and Dana. When, however, still older glacial 
periods began to be discerned in the stratified rocks and espe- 
cially in the oldest ones near the beginning of the Proterozoic 
era (see Figs. 7 and 8)—a record that is remarkably well 
preserved in Canada—the final straw was at hand to break 
down the theory that the climates of the earth had passed 
progressively from an astral through a torrid to a temperate 
condition, along with a slow clarifying of the atmosphere (see 
Figs. 3-8). 
_ The newer geology holds, with Chamberlin, that the grow- 
ing earth was originally too small in mass to hold an atmos- 
phere and accordingly there was a time when our planet had 
|mone. As it grew in diameter, the earth was more and more 
| able to hold an atmosphere and a hydrosphere, and during 
| the long growing period there was finally originated an atmos- 
| phere probably not much unlike the present one, which in a 
| roughly approximate way may be said to be composed of 
| four-fifths nitrogen and one-fifth oxygen. It should, however, 
| be noted here that at first the atmosphere had but little oxygen. 
| Since life came to be, using the carbon and freeing most of 
the oxygen of the carbon dioxide of the atmosphere, the 
quantity of oxygen has more or less steadily increased, though 
| at all times much of it has been consumed in the oxidation 
| processes of the rocks and minerals. 
| The most constant accessory constituent of air is carbon 
dioxide, one of the three fundamental materials at the basis 
| of life. In the present atmosphere there are about three vol- 


52 EVOLUTION OF THE EARTH 
umes of this gas to 10,000 of air, and there is as much more 
in living things as there is in the atmosphere. On the other 
hand, there is in the oceans of today, according to F. W 
Clarke, the geochemist, from 18 to 27 times more carbor 
dioxide than in the air (Johnston and Williamson say that 
at 15° C. there is about 70 times more), while the still vaster 
volumes locked up in the sedimentary rocks and in the fuel 
and carbonaceous deposits of the earth are computed to be 
30,000 times greater than the volume in the present atmos 
phere. These facts are brought forward at this time to shoy 
that the constituents of the atmosphere have always variec 
because of the constant loss of carbon dioxide and oxygen to 
the sedimentary rocks, but that at the same time there ha: 
always been a resupply of carbon dioxide through the e 
active volcanoes and the mineral springs, and of oxyger 
through the life activities of plants. Holmes says:* “Ever 
now, the outer 70 miles of the earth’s crust would be competent 
to supply all the nitrogen of the atmosphere, the water of tl 
oceans and the vast quantity of carbon dioxide represented br 
limestones and carbonaceous deposits.”’ 

It has been well said that if volcanism should cease it would 
not be long before the existence of life would be impossible 
because of the absence of carbon. We should add here that 
if there were again as much life as there is at present, all the 
carbon of the atmosphere would be in the living plants ane 
animals, and, if such a condition were possible, death woulc¢ 
come to them all. Therefore life and its abundance at an} 
time are conditioned by the amount of this gas present in th 
atmosphere. a 

Climates of the past. The quantity of carbon dioxide i 
the atmosphere is to a certain extent also a climatic regulator, 
though the greater factor in this matter is water-vapor, whicl 
is also the most variable constituent of the atmosphere. Witl 


1 Holmes, A., “The Age of the Earth,” 1913, p. 30. 


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54 EVOLUTION OF THE EARTH a 
a greater abundance of both, and especially of aqueous vapor, 
there results a thickened atmospheric blanket that not only a 
holds in more of the earth’s warmth but takes up greater 
amounts of the sun’s radiations, and when there is less of this j 
gas and of water-vapor the climates are thinner and cooler. 
The amount of carbon dioxide and water-vapor in the atmos- 
phere has varied much throughout the geologic ages. “a 
Huxley in his interesting book Physiography has well saic 
that without the sun ‘“There could neither be rain nor rivers. 
. Rain is dependent for its distribution upon ae 
the atmosphere, but these currents are due to disturbances of 
equilibrium which are brought about by means of solar heat. 
Without the sun, then, there could be no winds.” The currents 
of the sea in their final analysis are also due to the heat of 
the sun. Therefore through the radiant action of the sun, 
water-vapor is added to the atmosphere, and the amount of 
it is at present and always has been the latter’s most variable 
constituent, and, as rain, is of the greatest importance geologi- 
cally. Clarke states? that water “is not merely a solvent anc 
disintegrator of rocks, but it is also a carrier, distributing othet 
substances and making them more active. To the circulatio n 
of atmospheric moisture we owe our rivers, and through them 
erosion is effected. The process of erosion is partly chemical 
and partly mechanical, and the two modes of action reénforet 
each other. By flowing streams the rocks are ground to sand 
and so new surfaces are exposed to chemical attack. On thi 
other hand, chemical solution weakens the rocks and render 
them easter to remove mechanically. . . . It is through the 
agency of rain or snow that the atmosphere produces its grea 
est geological effects. . . . Aqueous vapor dissolves and es 
centrates the other ter eeuicnts of air, and brings them to 
ground in rain.’ a 


: k 
2 Clarke, F. W., “The Data of Geochemistry.” U.S. Geol. Survey, Bull. 49 
1911, p. 48. 


Fic. 4.—Glacially striated diabase, made in early Permian 
time. Vaal River north of Kimberley, South Africa. 
Photograph by W. M. Davis. 


Fic. 5.—Lower Cambrian quartzite, striated in early 
Permian time. Inman Valley, South Australia. 
Photograph by T. W. E. David. 


Ce : , 
Sp Aart PS wie ae 
at 

“> 


eke: OA 


iss 


a 


s/h 


“ 


Si 


a: 


a 
Da 
se 
% 


a AND ITS INHABITANTS 55 
_ Weare living at a time when the earth has marked climatic 
differences, varying between icy polar climates and hot moist 
__ or dry tropical conditions. This has, however, not always 
been the case, for not long ago geologically the temperature 
of the entire earth was even colder than it is now, although 
| most of the climates of the past have been warm and fairly 
| equable the world over (see Fig. 3). ‘The ancient plants and 
animals are “self-registering thermometers” with regard to 
the climates of the past, and they indicate that warm climates 
persisted during long geological ages, and that even though 
there were at all times zonal belts and fluctuations in the tem- 
perature, the polar areas were usually inhabited, as is now 
well known, by plants and animals of kinds that were adjusted 
‘to winterless environments. [hese temperature fluctuations 
were greatest during the closing and opening stages of the 
periods and eras. 

The very long warm times were separated by short periods 
of cool to cold climates. Geologists now know of seven 
periods of decided temperature changes (earliest and latest 
Proterozoic, Silurian, Permian, ‘Triassic-Lias, Cretaceous- 
Eocene, and Pleistocene), and of these at least four (those in 
italics) were glacial climates). Cooled climates occur when 
the lands are largest and most emergent, during the closing 
stages of periods and eras, and cold climates nearly always 
exist during or immediately following the times when the 
‘earth is undergoing most marked mountain making (see 
Fig. 3). 

Origin of the earth’s waters. ‘There was a time when the 
earth was too small in mass to hold a hydrosphere, the 

envelope of water that lies beneath the atmosphere and above 
the rocky surface of the planet. As the earth grew in mass, 
it became more and more possible for it to have standing 
bodies of water and clouds of water-vapor floating with the 
winds of the atmosphere. All of this water, the newer geology 


56 EVOLUTION OF THE EARTH 

thinks, came forth out of the earth itself, through volcanic 
activity and thermal springs. Even though some of the sur+ 
ficial waters vanish through soaking into the cold earth-shell, 
their volume has increased throughout geologic time; the 
greatest amount was added during the later part of the long 
growing period of the earth and during the Archeozoic era, 
when from 25 to 50 per cent of the present volume is believed 
to have come into existence. The rest has been added during 
subsequent geologic time. 

Source of the salts of the oceans. It is well known that the 
seas and oceans are salty, and that on the average there are 
3.5 pounds of saline matter to every 100 pounds of marine 
water, and in each 100 pounds of sea salts there are nearly 78 
pounds of sodium chloride or our table salt. Clarke has esti- 
mated that if all of the saline matter of the oceans were con- 
centrated, and the volume placed on the United States, its 
surface would be completely covered to a depth of 1.6 miles. 
As all of this saline matter has been leached out of the rocks 
of the dry lands since the earth has had rains, and as very little 
of it, comparatively, has been taken out of the ocean by the 
accumulating rocks, it has been further estimated that it repre- 
sents the breaking down of a mass of average igneous rock 
equal to at least 6,900 feet in thickness over all the continental 
platforms. Probably it is more correct to state that the con- 
tinents have suffered erosion of igneous rocks amounting to 
between 1 and 2 miles of average depth. Of course all 
erosion throughout geologic time was far greater, perhaps, 


as Barrell states, from 50 to even 100 per cent higher. It 
included the reworking of older materials, igneous and-sedi- 


mentary. Furthermore, ° ‘more than a half, perhaps four- 
fifths, of the erosion of igneous rocks was accomplished before 
the beginning of the Paleozoic” (Barrell). 


Various computations have been made as to how long it 


has taken the salts in the oceans to accumulate and the best 


ge ne Ca oe 


Fic. 6.—Glacial bowlder beds beneath thick formations of 
dolomite on the upper Yangtse River, China, in latitude 
31°. N. Age of till, late Proterozoic. Photograph by 
Bailey Willis. Published in ‘‘Researches in China,”’ 
Publication No. 54, Vol. I, 1907, of the Carnegie 
Institution. 


Fic. 7.—Eroded exposure of the oldest known glacial deposits (Lower Huronian), 
near Cobalt, Ontario. Photograph by A. P. Coleman. 


Fic. 8.—Striated bowlder.taken from the oldest known glacial deposits. 
Photograph by A. P. Coleman. 


ee a , 


: 


AND ITS INHABITANTS 57 
: of the calculations arrive at about 100 million years. This 
~ figure is based on the postulate that the present rate has been 
‘continuous throughout geologic time; this rate, however, 
‘appears to be excessive, and renders the postulate erroneous. 
The rate was highly variable during geologic time, as will be 
-seen from the evidence throughout this chapter, so that the 
Tatest calculation of Holmes*® gives the time as between 210 
and 340 million years, with the warning that these high figures 
“must not be supposed to possess any serious value. 


a For the present we can only conclude that our knowledge of 


the part played by sodium and chlorine in the constant redis- 
3 Bee ution of the materials of the earth’s crust is still lamentably 
imperfect, and that quantitative deductions drawn from it 

~ must be regarded as being purely provisional.” 

Origin of the sedimentary strata. ‘The great variability of 
geologic climates also leads to variations in the power of the 
atmosphere to weather and break down the high places of 
the lands. The earliest atmosphere, far richer in carbon 
monoxide and carbon dioxide than subsequent climates, was 
a most active weathering agent in dissolving and breaking up 
the oldest rocks of the lithosphere, the igneous basaltic and 
granitic rocks. Then, too, there had not yet developed a 
vegetation on the most ancient lands to hold the fast-forming 
soils, and these conditions made it inevitable that all of this 
loose and solvent material should be rapidly washed by the 
rains and rivers into the oceanic basins. Therefore the strati- 
fied or water-laid rocks accumulated during the earlier geologic 
eras more quickly than in the later ones. On the other hand, 
the erosive power of both air and water has varied much 

_ throughout geologic time because of the periodically varying 
height of the land and the ever changing humidity and tem- 
"perature of the air. Accordingly, the rivers carry their loads 
of sediments for long times very slowly and at others much 


% Holmes, A., op. cit., pp. 74-75, 


58 EVOLUTION OF THE EARTH 
more quickly. If the erosion on the land is rapid and the 
rivers are not long, the land débris is apt to be coarser in grain 
and less well assorted, but of whatever nature the waste of — 
the lands is, the rivers finally deliver it to the seas and oceans; 
and here the materials are subjected to a long process of re-— 
working and assorting into muds and sandstones. As all of 
this work is done in waters, as the character of the sediments © 
varies, and as the wave-power is variable with the winds from . 
day to day, it follows that the materials must be laid down in 
horizontal sheets of different kinds of rock that make up the — 
strata of the stratified rocks. From this it is apparent why 
the sedimentary rocks of the earth’s outer shell not only are . 
of different kinds, but why they so often occur in more or less - 
long cycles of deposits that begin with coarse sandstones or 
even conglomerates and pass upward into the much finer-— 
grained mudstones and finally into limestones. The limestones 
are in the main the deposits due to the chemical activities of : 
organisms or the accumulating debris of plants and animals. 
Geologists therefore speak of limestones and chalks as organic 
deposits. So throughout the geologic ages, cycle upon cycle” 
of sedimentation succeeded one another, the débris of suc- 
cessive ranges of once majestic mountains, and in this orderly 
sequence of deposits lies buried much of the life of the past. 
The United States Geological Survey stated in 1912 that 
the surface of the United States is being removed by solvent 
denudation at the average rate of .o013 of an inch a year, 
or I inch in 760 years. This means a removal by the streams 
of over 270 million tons of dissolved matter and 513 million - 
‘tons of suspended matter annually. In other words, there is” 
delivered into the seas and oceans each year from the area | 
of the United States alone 783 million tons of rock materials. 
The amounts removed from different drainage basins show 
interesting comparisons. In respect to dissolved matter, the 
southern Pacific basin heads the list with 177 tons per square 


AND ITS INHABITANTS 59 
mile per year, the northern Atlantic basin being next with 130 
tons. The rate for the Hudson Bay basin, where the topog- 
raphy is nearly flat and the rocks are mainly granites, is lowest, 


with 28 tons. 


‘Holmes states* that the known denudation rates vaiy be- 
tween I foot in 400 years (Irawadi basin) to 1 foot in 47,000 
years (Hudson Bay region). For North America the rate 
for solvent denudation is 1 foot in 30,000 years, and for 


~ mechanical removal 1 foot in 12,000 years. ‘Taking both 


——————— tlie te 


together, the average rate of denudation is found to be 1 foot 


in 8,600 years.” 
The ancient life is known to us in the countless fossils of 
the rocks, for they are the remains of plants and animals 


living on the lands and in the seas at the time when the sedi- 


ments were accumulating. Most of them, like the shellfish, 
lived on or in the bottom of the seas, other active forms swam 
about in the water, while the remains of the plants and animals 
of the lands were drifted by the streams into the marine areas, 
where they eventually sank to the bottom and came to be 
covered over—buried—by the accumulating sands, muds, or 
limestones. It should, however, be added that but little of 
the life of any time is preserved as fossils, for much of it is 
too soft to be preservable, or it is eaten or destroyed by other 
organisms or reduced by the solvent powers of bacteria and 
the acids of the waters. 

The record of the physical forces which automatically en- 
tomb the successive upwellings of life is found upon all the 
continents, but is woefully incomplete in any one. For many 
cycles the marine record is best in North America, at other 
times in Europe or the Mediterranean countries or .in Asia. 
The land or fresh-water record is even more scattered and 
imperfect, with the longest deposition in Africa, a .continent 
that, south of the Sahara desert, has been invaded but little 


_*Holmes, A., of. cit., p. 57. 


60 EVOLUTION OF THE EARTH 
by the ancient oceans. Out of all these widely scattered 
records the geologist pieces together the geological column, 
embodying the history of the earth, and yet at best we seem 
to have recovered far less than half of it. The record may 
be complete in the oceanic basins, but here it is forever hidden 
from hammer and mind. However, if we piece together all of 
the thicker known geological formations of sandstones, mud- 
stones, and limestones into a superposed sequence, we get a 
pile of about 53 miles in thickness as a mean estimate, with 
the maximum thicknesses attaining to over 67 miles (Sollas 
gives a maximum of 63.5 miles). This means the more or 
less rapid wearing away almost to sea-level, one after another, 
of more than twenty ranges of mountains like the present 
European Alps or the American Rockies. During the in- 
credibly long intermediate times, when the lands were planed 
to a low relief, there was very little erosion. 

Ratios of muds, sandstones, and limestones. We have seen 
that the continents have lost through atmospheric erosion a 
layer of igneous rock between 1 and 2 miles thick in the 
course of geologic time. ‘This amount of eroded average 
igneous rock should theoretically resolve itself into 30 per cent 
of solution materials and 70 per cent of detritals, or 80 per 
cent of mudstones, I1 per cent of sandstones, and 9 per cent 
of limestones. Holmes gives 70 per cent of shales (20 per 
cent quartz), 16 per cent of sandstones (75 per cent quartz), 
and 14 per cent limestones (75 per cent calcium carbonate). 
However, actual observations of the stratified rocks of Amer 
ica and Europe show quite different percentages for these three 
categories of water-laid sediments, and the difference is dut 
to a great increase of pore-space in the fragmented material 
and to the addition of material extracted out of the atmos 
phere and hydrosphere during the weathering processes 
Accordingly, Leith and Mead*® have shown that the cubica 


5 Leith, C. K., and Mead, W. J., “Metamorphic Geology,” 1915, pp. 59-97. 


AND ITS INHABITANTS 61 
content of average igneous rocks thus increases in volume by 
at least 28 per cent, and that on the continents we appear to 
have 48 per cent of mudstones, 32 per cent of sandstones, and 
20 per cent of limestones. This marked difference between 
‘chemical theory and actual presence is further explained by 
the unknown quantitative loss from the continents of the finest 
muds, sands, and solvent materials that the lands have per- 
manently contributed to the oceanic basins. On the basis of 
the circulation of radium, Holmes estimates that the loss from 
the lands to the deep-sea deposits is about one-thirtieth of all 
the material eroded, i.e., about 300 million tons of the 9,000 
| million tons annually. 

_ Distribution of the sedimentary rocks. We have seen that, 
according to theory, all of the continents have lost a layer of 
original i igneous rock that is on the average between 1 and 
2 miles in thickness, and it is this material, removed and 
reworked time and again by the weathering processes and the 
| further chemical and assorting agencies of the rivers and 
| Oceans, that has gone into building the known geological 
column, with its maximum summation thickness of 67 miles. 
| In no one place, however, can be seen more than a small 
| part of this record, for usually the local thickness is under 1 
| mile, though there are limited regions where as much as 20 
miles of it is present. This is because the deposition of the 
geologic formations in the periodically rising and flooding 
| oceans, as described later in this lecture, takes place at any 
| given time in very limited areas, most commonly, as at 
| present, along the margins of the continents, or in long and 
| Marrow troughs—the geosynclines (see Fig. 9)—within the 
continental borders, and only periodically over the wider inner ~ 
portions of the lands. We may add that over the surface of 
one-third of North America the rocks are all of igneous or 
crystalline character, that. over more than one-half of it the 
thicknesses of the sedimentary rocks are under 1 mile, and 


LW 
4 
» 
Dp 
A 
eset ts, 


LANDS, GEOSYNCLINES, 
AND EPEIRIC 
SEAS OF N. AMERICA. 
CHARLES SCHUCHERT 
@CALE OF STATUTE MILES 


100 0 | 200° 400 600 


positive elements, and in lightest shading the extensive neutral medial area of 
continent. ‘The two heavy black lines indicate the Cincinnati and Ozark ( 


kakee) uplifts. From the Pirsson-Schuchert ‘“Text-book of Geology,”’ publishe¢ 


by John Wiley & Sons, Inc. 


— 


AND ITS INHABITANTS 63 
that over the remaining small portion they vary from 1 to 
20 miles; yet the greater depths do not cover more than one- 
eighth of the continent, and they occur in the long and narrow 
troughs of sedimentation, of which the two best known lie in 
the Appalachian and Rocky Mountain regions (see Fig. 9). 

_ Eras of geological time. Now let us see how geologists 
divide this great pile of at least 53 miles of sediments and 
_ their included fossils. (A synopsis of geologic time is pre- 
| sented on page 46, and in Fig. 3.) The first era, or Archeo- 
‘zoic time, with the oldest known strata, has no proved fossils, 
though a very low form of water-living alga appears to have 
been present. Even if we exclude the probable fossil evidence, 
the presence in Ontario of 18 miles of sediments, of which 
about one-half is impure limestone along with much graphite, 
indicates unmistakably that life was already in existence. As 
"we are treating of the oldest known time in the history of the 
earth, this is the place to emphasize what results were then 
attained and what natural processes were at work. 
At the very beginning of the Archeozoic era, the earth had 
‘a rocky and fairly stable exterior known as the lithosphere, an 
atmosphere and a hydrosphere; protruding continents, and 
oceanic basins that were filled with slightly saline water; twice- 
daily tides, wear and tear of the ocean waves against the 
| lands, reduction of the high lands by the atmosphere, and, 
through the rains, washing of the soil and solution materials 
into the seas and oceans. ‘The sun shone then as now and, 
made life possible, and the man in the moon was as clearly 
developed as he is today, remaining so ever since because this 
satellite has had neither atmosphere nor water to wash away, 
his face. We therefore see that the earth was then very much 
‘as it is now, with these great differences, that at first the 
atmosphere was almost devoid of free oxygen and probably 
richer in carbon dioxide, that the lands were not covered with 
verdure, and that what there was of life was of a very low 


64 EVOLUTION OF THE EARTH 
order and possibly more prevalent on the lands than in the 
oceans. 

Then follows the second era of geologic time, the Protero- 
zoic, with a thickness in south-central Canada of nearly 14 
miles of coarse sediments almost devoid of fossils, and 4 miles 
of lavas. Probably more than three-fourths of this mass is 
of fresh-water and volcanic origin, and less than one-fourth 
may be of marine origin. In the Rocky Mountains there are 
upwards of 7 miles of less coarse sediments that include about 
1.5 miles of possibly marine limestones. In this connection it 
should also be noted that one of the remarkable recent dis- 
coveries in geology is that we know very little of marine Pro- 
terozoic sediments (in the sense of marine and fossiliferous 
Paleozoic formations) and that there is as yet even no hint 
as to where geologists are to look for them. 

The Archeozoic and Proterozoic eras have the most ancient 
strata of the earth and their combined thickness is 32 miles as 
against about 21 miles for all subsequent, fossiliferous strata. 
In this we discern the astounding fact that at least one-half 
of geological time and the greater part of the earth’s history 
had passed before organisms became sufficiently endowed with 
hard parts to be abundantly preserved as fossils in the sedi 
mentary rocks. It also means that the evolution of life for a 
incredibly long time was exceedingly slow in rising from the 
simple unicellular forms into the multicellular forms of plants 
and animals. It may be that the Archeozoic was entirely 
occupied in originating only the unicellular plants and animals, 
In the Proterozoic, organic differentiation appears to have 
gone on faster, because at the very beginning of the Paleozoic 
era are found all of the main kinds of marine animals other 
than fishes. The subject of the origin and progress of life 
from the unicellular forms to the most complex modern verte’ 
brates will be developed by Professors Woodruff and Lull 1 in | 
subsequent lectures. 4 


AND ITS INHABITANTS 65 
The third era of geologic time, the Paleozoic, is based upon 
a thickness of about 4.75 miles of muds and sands and 3.4 


miles of limestones. These thicknesses are in the Appalachian 
“region, and form one of the most complete of all known 
Paleozoic records. In the Cordilleran area, where the record 
is far less complete, there are about 2 miles of coarse deposits 
and 3 miles of limestones. Toward the medial regions of the 


continent the thick lateral sections thin down to about 1 mile, 


essentially of limestones. 


Shortly after the opening of the Paleozoic appear the fishes, 


_ the first of the vertebrates, and now, surprising as it may seem, 
in the fresh waters of the land and not inthe seas. Before half 
_ of the Paleozoic is gone, double-breathing is perfected, and 
‘the amphibia begin to people the dry lands, and long before 


the close of the era give rise to the reptiles. It is also in the 


_middle Paleozoic that the most primitive land floras arise, 


and not long afterward, in the Coal Measures, their remains, 
falling into great swamps, create the world’s greatest supply 
of fuel in the soft and hard coals (see Fig. 10). 

The fourth era, known as the Mesozoic, has, in western 
North America, about 7.5 miles of sediments, of which not 
more than 1.25 miles are limestones. On the other hand, in 
the lands bordering the Gulf of Mexico and chiefly in Mexico 
there are less than 3 miles of Mesozoic sediments, but here 
the limestones make up more than one-half of the total 
thickness. 

The Mesozoic is the Age of Reptiles, and yet the little 
mammals and the toothed birds are storing up intelligence and 
strength to replace the reptiles when the cycads and conifers 
shall give way to the higher flowering plants. Then follows . 


the Cenozoic era, the Age of Mammals, with a thickness in 


California of about 5 miles of coarse sediments, contrasting 
with about 4 miles of fresh-water detritals in the Rocky 


Mountain area, and in these rocks occurs a most wonderful 


66 EVOLUTION OF THE EARTH 
array of modernized animals. The era closes with a very 
decided glacial climate and another marked change in the 
animal world, out of which man rises to his present primacy 
among organisms. Geologists therefore call the present time 


the Psychozoic era or the Age of Reason. 


Fic. 10.—The marine inundation in Pennsylvanian time. Coal 
swamps in partially marine areas indicated by broken lines. 
From the Pirsson-Schuchert ‘“Text-book of Geology,’’ pub- 
lished by John Wiley & Sons, Inc. 


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68 EVOLUTION OF THE EARTH 

Relative duration of the eras. The preceding table gives 
the generalized thicknesses of the sedimentary rocks of North | 
America in terms of the detritals (muds and sands) and the 
solution materials (limestones and dolomites). To attain 
more clearly to the relative duration of each of the eras it is” 
desirable to restate the probable time taken by the far more | 
slowly accumulating solution materials in terms of those of 
the detritals. Geologists differ greatly as to the time required 
to deposit any kind of sediment, but most of them will agree 
that limestones take from four to ten times longer than the 
coarser materials. On the other hand, the rate of deposition 
is exceedingly variable from place to place and from time to 
time. Further, the limestones of pre-Cambrian time are on 
the average far less pure than those of the later eras. Ac- 
_ cordingly, on the basis of per annum rate of sedimentary accu- 
mulation there are as yet no reliable estimates, and as we are 
just beginning to appreciate that the geologic record is very 
incomplete, any percentages given at present must be taken as 
only suggestive of geologic time. A far more reliable stan- 
dard is that of the rate of disintegration of radioactive 
minerals, though here the estimates of geologic time, of not 
less than 1,600 million years, appear to the writer to be 
excessive by 50 per cent. 

Now let us compare the above results with the ratios ob- 
tained by other geologists, but before doing so it should be 
said that their statements relate almost always to post 
Proterozoic time. If, however, we follow Dana’s ratios, it 
is clear that he held in his famous text-book that about one: 
half of geologic time lies back of the Cambrian. It is on this 
basis that the following table has been prepared, and th 
figures in parentheses restate the ratios in percentages of al 
geologic time. 


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70 EVOLUTION OF THE EARTH 

Periodic reélevation of the lands. We have thus far pre- 
sented the sedimentary evidence in the main as if it had con- 
tinuously and regularly formed, without stoppages or “‘breaks.” 
The geologic record, however, was not laid down in this way, 
because the surface of the earth does not remain stationary. 
Even though to humanity the “everlasting hills” appear to 
be permanent features of the earth’s surface, they are all 
doomed to be carried away by the rain and transported by the 
rivers into the seas and oceans. Erosion of the land goes on 
until all is worn to near sea-level, and then there is but a very 
sluggish run-off of the rain that falls upon the planed con- 
tinents. The earth has repeatedly had such a low relief; in 
fact, this has been the condition during the greater part of 
its history. . 

The continents are repeatedly reélevated in relation to th 2 
strand, and this goes on many times in a small way and less 
often on a large scale (see Fig. 3). We have said that in the 
course of the geologic ages the earth has shrunk at least 200 
and possibly 400 miles in diameter. The earth is still shrink- 
ing all the time, and this gives rise on the surface to small 
warpings whose difference of elevation is usually not more tha 
a few hundred feet. These are but surficial symptoms, due to 
internal readjustment, remarkable as it may seem, in an earth 
as rigid as steel—local accommodations of the earth’s mas 
to loss of heat and molecular rearrangements. ‘These altera 
tions finally set up strains in the. lithosphere which are tot 
great for its strength to bear, and then there is a time 6 
breaking and greater readjustment between the relativel} 
settling and rising masses. At these times ranges of moun 
tains are slowly raised up near the margins of the continents 
due to the shortening, folding, and breaking of the earth's 
crust, and the ranges have lengths of between 1,000 and 1,50% 
miles. ‘These are the minor shrinkage movements, the “di 
turbances,” which are coming more and more to be regardet 


AND ITS INHABITANTS 71 
as the basis for dividing the eras into periods of time, and how 
often they occurred is one of the things that geologists are 
trying to ascertain. In North America we know of at least 
eight of these minor crustal readjustments, but in all the world 
there are many more than this. 

Finally, there comes a time of major shrinking that adjusts 
all of the strains and stresses set up in the earth’s mass by the 
minor, incompletely adjusted shrinkages. The earth has just 
passed through one of these major readjustments, and accord- 
ingly we see all of the continents standing far higher above 
sea-level than has been the rule throughout geologic time, and 
in many of them rise majestic ranges of mountains (see 
Fig. 3). A grander, more diversified, and more beautiful 
geography than the present one the earth has never had; this 
statement is made advisedly and with the knowledge that our 
planet has undergone at least six of these major readjustments 
of its mass. These greater movements are the “revolutions” 
that close the eras. Because the lands are then high they are 
subject to more active erosion and in the last analysis all of 
the broken-up detrital and dissolved material is carried away 
by the streams to the oceans. At these times the continents are 
also largest and the materials received by the oceans are laid 
down on the outermost edges of the lands, where subsequent 
transgressions by the sea cover and hide them from our 
observation. After a long time the sea again comes to press 
further and further upon the land and spreads more forma- 
tions of stratified rocks over those left by the previous flood- 
ings, the older geologic formations (see Fig. 11). Therefore 
there is upon the present continents between each two such 
successive formations a ‘“‘break’’ in deposition, a hiatus in the 
geologic record, a “time interval” when no record other than 
erosion is at hand. These ‘breaks’? in sedimentation are 
representative of loss of record and are called ‘“‘intervals”’; 
they are regarded as the closing times of the eras. 


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AND ITS INHABITANTS 73 
During these intervals when the continents are highest and 
largest, the oceans are smallest in areal extent, the separate 
continents are often united by land-bridges as Panama unites 
the Americas, such bridges alter the direction of the great 
ocean streams like the Gulf Stream, the high mountain ranges 
alter the directions of the air currents and take out of them 
their moisture so that great desert areas arise like our inter- 
Rocky Mountain country, and because of these vast changes 
nearly all of the major movements are accompanied by glacial 
climates. Such mighty changes in the geography, topography, 
and climate of the earth react strikingly upon the life of the 
polar and temperate belts and so disarrange it that the major 
“«ntervals” following the ‘revolutions’ are spoken of as the 
critical times in the earth’s history—critical not only for the 
geography, separating or uniting continental masses, but also 
for life, since as a result of the lands then becoming high and 
cool to cold in places and elsewhere moist or dry, vast domains 
of organisms are forced to adapt themselves to the altered 
conditions, or to migrate into more favorable areas, or to die 
out and make room for the rising hordes of fitter types. 

In this way cycle after cycle of organisms appear and vanish, 
and their coming and going is brought about by the changing 
environment. ‘Thus in the Mesozoic era, we see the lands 
mastered by the cycads and conifers among the plants and the 
dinosaurs among the animals, the air by the flying dragons, 
and the seas and oceans by other reptiles and hordes of ammo- 
nites and squid-like molluscs. The Great Reaper then steps in 
and through struggle and the elimination of countless organ- 
isms, resulting in regressive and progressive evolution, the 
lands in the Cenozoic begin to bloom with more and more 
flowering plants and grand hardwood forests, the atmosphere 
is scented with sweet odors, a vast crowd of new kinds of 
insects appear, and the places of the once dominant reptiles 
of the lands and seas are taken by the mammals. Out of these 


74 EVOLUTION OF THE EARTH 
struggles there rises a greater intelligence, seen in nearly all © 
of the mammal stocks, but particularly in one, the monkey- 
ape-man line. Brute-man appears on the scene with the intro- 
duction of the last glacial climate, a most trying time for all © 
things endowed with life, and finally there results the domi- 

‘nance of reasoning man over all of his brute associates. : 
The Cenozoic era was a time of especially marked geo- 
graphic alteration, as is especially well seen in the evolution 
and spread of the elephant stock or Proboscidea. ‘These 
animals arose in Africa early in the era, but there was no 
means by which they could spread into other continents, because 
Africa remained isolated. At about the middle of the Ceno- 
zoic, the Alps were rising and these crustal alterations also 
gave birth to a land-bridge across the Mediterranean connect- 
ing Europe and Africa. Across this bridge the long-faced - 
elephants, now all gone, spread first into Europe and thence 
into Asia. A little later much of Asia began to rise, and the 
culmination is seen in the grandest of all mountains, the present 
Himalayas. ‘These alterations permitted the elephant stock 
to spread across Asia and the Nome bridge into Alaska and 
wider North America, and they had no sooner arrived there 
than they were on their way across the newly arisen Panama _ 
bridge, thence to spread all the way south into distant Argen- 
tina. North America was then peopled with many kinds of — 
camels and horses, and they, along with many other animals, 
migrated into South America. Wanderlust was upon the 
world, and from South America there migrated into our coun- 
try great sloths, a claw of one of which was found by Thomas 
Jefferson in Virginia, and described as that of a huge lion. 
The great Democrat may be excused for his error, since in 
those days fossil sloths were unknown in North America; 
rather should he be praised, for he is the only president who 
has described a fossil, other than live ones! | 
Times of volcanic activity. In all that has been said we 


AND ITS INHABITANTS 75 
see the periodic rejuvenation of the lands and the renewal of 
active erosion. During these times of crustal unrest and 
subsequent internal readjustment the molten portions deep 
lown in the lithosphere are forced to rise as great hot tongues 
into the cores of the mountain ranges, and in many places they 
break through and give rise to active volcanoes. Beneath lie 
great and highly heated masses that subsequently cool into 
granitic rocks, and when long afterward the mountains are 
worn away we discern among their roots these cores of granite. 
However, during all the time of crustal rising and readjust- 
ments the volcanoes are more or less active, spewing violently 
01 quietly into the atmosphere tremendous volumes of rocks 
lown into volcanic ashes and of lavas, and great quantities of 
ises that increase the volume of the atmosphere, and much 
avenile water is added by them and the thermal springs to the 
adose water of the hydrosphere. Even though the litho- 
\ <a absorbs much vadose water through soaking and min- 
zation, the oceans are yet constantly growing in volume 
through this accession of juvenile water. In the same way, 
even though vast quantities of carbon are taken out of the 
atmosphere by organic agency and buried in the rocks, there 
to be transformed into natural gases, petroleum, asphalt, peat, 
and coal, the air is periodically resupplied by the volcanoes 
and by the hot-water springs. 
_ Periodic spreading of the oceans. So far we have been 
describing the alterations that take place in the dry land; let 
jus now turn to the realms of Neptune and note briefly the 
areal fluctuations of the oceanic waters during the latter half 
|of geologic time. The geography of the earlier times we have 
not as yet deciphered and therefore cannot relate the move- 
|ments of the oceans. It has been stated that when the earth 
the lands rise in relation to the strand-line, and that 
|this is especially true at the times of major crustal alterations. 
\It is now definitely known that at the close of all the eras the 


{ew Seger 


76 EVOLUTION OF THE EARTH 
continents were largest and at some of these times were even 
larger than they are now. On the other hand, the present 
oceans are more than full and for some time have been spilling 
over the outer edges of the continental platforms, apparently 
to the extent of nearly ten million square miles or about 5 per 
cent of the earth’s surface. In other words, the present con- 
tinental platforms occupy 35.5 per cent of the lithosphere, 
while the total water areas are equal to 69.6 per cent of the 
earth’s surface. | 

The mean height of the present continents above the sea is 
given by Sir Archibald Geikie as about 2,400 feet, and if these 
protuberant masses were deposited in the sea, as they surely 
will be by the future rivers, the ocean waters would be dis: 
placed to the extent of raising the strand-line about 650 feet. 
We see therefore that the ocean level is also inconstant, anc 
accordingly, even though the North American continent should 
remain stationary, about half of it would be covered by the 
displaced seas to depths of several hundred feet. | 

Between the comparatively short intervals of mountair 
making and crustal unrest occur the long quiet times of erosion 
when the lands are planed down to near the sea-level. Thi: 
transference of rock leads, as has already been stated, to mor 
or less flooding of the continents by the oceans (see Fig. 12) 
During the Paleozoic, Mesozoic, and Cenozoic eras, Nort 
America, and especially the United States, was widely floodes 
by warm and shallow marine waters at least sixteen time 
—Waucobian, Croixian, Canadian, Chazyian, Mohawkian 
Cincinnatian, Silurian, Devonian, Mississippian, Pennsylva 
nian, Permian, Triassic, Jurassic, Comanchian, Cretaceous 
and in an oscillatory and marginal way during the Cenozoi 
(see Fig. 13). These shallow-water spreadings begin in- 
small way, grow to greater dimensions throughout a very lon 
time, and then, declining, recede more rapidly than they came 
(see Fig. 11). They vary in areal extent up to 4,000,000 


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78 EVOLUTION OF THE EARTH 
square miles. The greatest floods have spread from the Arctic 
Ocean, others from the Pacific, and those of least amount from 
the Atlantic. On the other hand, the number of floods was 
greater from the south than from the north, and the waters 
were most persistent in the Appalachian, lower Mississippi, 
and Rocky Mountain areas. Where the greatest thicknesses 
of sediments accumulate, out of this continental débris there 
will arise, phcenix-like, a future mountain range. After about 
40,000 feet of strata had been deposited in the Appalachian 
trough, there arose near the close of the Paleozoic era the 
majestic Appalachian Mountains, some of which may have 
towered to at least 20,000 feet above the sea. In fact, the 
original mountains were destroyed by erosion during the Meso 
zoic era and the reélevated Appalachians of today are due te 
later uplifts of more than 2,000 feet; subsequent erosion ha 
developed them into their present interesting forms. Toda 
one may travel comfortably over the roots of these once gran 
mountains by way of the Pennsylvania, the Baltimore anc 
Ohio, and the Chesapeake and Ohio railways. 

Areal variability of organic habitats. We have seen tha 
the dry lands become alternately larger and smaller, and in th 
same way the shallow-water areas of the oceans are vasth 
increased when they spread over the lands, and are agai 
greatly decreased when the land areas increase in size. Thv 
when the lands are widely flooded there is a great increase 1 
the quantity of marine life, but little is originated that is ney 
while on the lands the climate becomes insular, warm af 
moist, and productive of the greatest amount of life in th 
then restricted areas. On the other hand, when crustal reat 
justments occur, the lands are largest, driest, and coolest, ar 
these changing environments react on the life and bring abot 
great alterations in the composition of the floras and fauna 
At these times the shallow-water marine areas are smalle 
and most variable in turbidity and salinity—conditians that 


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80 EVOLUTION OF THE EARTH 
set up renewed evolution, resulting in the rise of new stocks 
In these various periodic physical changes we see the stimulus 
that quickens organic evolution. Each cycle begins and closes 
with a comparatively short time of accelerated evolution, while 
the far longer intermediate tranquil periods lead to but little 
that is striking in the way of new organisms. 


CONCLUSION 


From this summary of the earth’s changing surface and 
climate during geologic time the following facts may bk 
selected for emphasis: 

First, geologic time is very, very long, indeed so vast as te 
be beyond human comprehension. No geologist today thinks 
that the evolution of the earth and its life could have taker 
place in less than 100 million years. My own view as a st 
dent of Historical Geology is that geologic time endured abou i 
800 million years. In all of this we perceive how slowly th 
physical and organic processes bring about the results of nature. 
Second, the constant shrinking of the earth leads to an in 
stability of surface that brings about periodic changes, no 
only in the areal space relations of the water and land, bu 
in the shapes and heights of the lands as well. Third, 
sooner are the lands elevated above the sea-level than thi 
weathering processes become more active and through tht 
agency of the rain and wind all high places are, according t 
human standards, slowly but surely moved into the seas an¢ 
oceans. Fourth, as a result of the transference of the high 
lands into the water areas the latter are to a certain exte 
displaced and periodically flood more or less of the land 
Fifth, due to these surficial changes the atmosphere and th 
climate are constantly changing in a small way, but every now 
and then when the lands are largest, highest, and driest, a col 
period appears and disarranges the entire organic world, bot 
on the lands and in the waters. Sixth, when these ‘‘critica 


AND ITS INHABITANTS Sr 
periods” are upon the world, the face of the earth is scenically 
grand and beautiful and at the same time the struggle for 
existence among the living is most intense. The rulers of 
the various domains find themselves overtrained and over- 
specialized, and succumb one after another to the changing 
environment. Their places are taken by the small, less 
specialized, and heretofore little known stocks, which quickly 
adapt themselves to their environments and become the 
dominators of the organisms about them. In all of this un- 
ceasing organic struggle most of the unadaptive families fail 
to continue; others are pushed by the pulse of life into the 
less desirable places, where they continue to exist as the static 


| forms—the living fossils that tell us so much that is most 


interesting of once prominent stocks of plants and animals; 
but at all times much of life quickly responds to the changing 
environment and is remolded into the more fit, active, and 


| alert types. The experiences thus gained are passed on to 


successive generations, and so the organic world as a whole 


| advances to ever better living mechanisms endowed with higher 
| and higher mentality. 


The greatest mentality in the sea has been repeatedly de- 


| rived from the continents, first in the fishes, then in the reptiles, 
| and lastly in the mammals, and they have adapted themselves 
| to the sea because of the ease with which they can there prey 


upon the less alert and intelligent. Such adapted stocks in the 
course of geologic time grow larger and larger, as, for 
instance, the whales of today. Out of them, however, comes 
no higher mentality. They represent an adaptation in the 
wrong direction, that is, to an easier life, for the highest 
Organisms with the greatest mentality have been developed 
only on the land where the struggle for existence is fiercest 
because of the constant necessity of adaptation to an environ- 
ment subject to intense changes. Organic supremacy is at- 
tained only through constant vigilance. 


CHAPTER III 
THE ORIGIN OF LIFE? 


LORANDE LOSS WOODRUFF 
PROFESSOR OF PROTOZOOLOGY IN YALE UNIVERSITY 


PROTOPLASM. ‘The phenomena: to: which we apply the term 
life have as their physical basis an inconceivably compl 
physicochemical organization called protoplasm. The con- 
ception of a common basis of all vital activities—that all living 
nature is one—was the culmination of a long series of re- 
searches during the first half of the nineteenth century, and 
forms the corner-stone of modern biology. At the presen 
time biology is the study of the properties of protoplasm 
because to it, in the last analysis, the multifarious activities 0: 
animals and plants must be referred. | 

Since we are only familiar with life as a manifestation of 
protoplasmic activity, the problem of the origin of life natu 
rally resolves itself into the problem of the origin of proto- 
plasm, and it is obviously impossible to discuss the origin 0! 
living matter without an insight into its composition anc 
organization. ‘The crude attempts of the alchemists of the 
Middle Ages to produce artificially in crucible or retort ai 
homunculus complete, though they had not the slightest com 
ception of its composition, affords, in contrast with the 
present trend of intensive analysis of protoplasm, a vivid illus 
tration of the progress of scientific method in the interi 
Obviously, analysis must precede synthesis even though tht 
latter may never be achieved. 


1 This lecture is published cenentinily as it was presented to a general uni 
versity audience except that some of the more important references to th 
literature of the subject have been inserted as footnotes. 


_— ee a ee ee ee eee 


a 


Fae 


AND ITS INHABITANTS 83 
From one point of view it is impossible to analyze proto- 
plasm because the least disturbance of its fundamental organi- 
zation results in a cessation of those phenomena characteristic 
f life, leaving matter in the non-living state before us. How- 
er, since in the transformation of matter from the living to 
he lifeless condition there is certainly no loss of weight, it 
‘follows that the complete material basis of protoplasmic 
‘organization remains for examination, and we may assume, 
as a working hypothesis, that the properties of protoplasm are 
a resultant of the properties of its constituent elements. But 
it may be noted in passing that an analysis of the débris from 
a destroyed factory probably would give one very little insight 
in 0 the modus operandi of the intact organization. 
_ Physical characteristics of protoplasm. Since the funda- 
ie activities of all forms of protoplasm are of the same 
nature, biologists have naturally tried to discover a correspond- 
ing fundamental physicochemical basis in all living matter, 
and thus far research, broadly speaking, indicates that such 
exists. Living protoplasm ordinarily appears under a moder- 
ately high power of the microscope as a viscid, granular fluid. 
en studied with the highest magnifications, usually after 


ee 


being killed and stained, it often exhibits an extremely complex 


structure which, however, cannot be briefly described, as it is 
subject to considerable variation not only i in the protoplasm of 
different organisms and tissues, but in the same microscopic 

t mass under varying physiological conditions. Most fre- 
e though, it seems to present a foam-like appearance, 
due perhaps to closely crowded minute drops of a liquid alveo- 

substance suspended in a continuous interalveolar substance, 
also liquid but of a different physical nature. But it seems 
clear, since studies of protoplasmic structure have revealed by 
no means a complete correlation between its morphological 
organization and its activities, that the key to the latter must 
lie i in an ultra-microscopic architecture whose varying phases 


84 EVOLUTION OF THE EARTH 
are as it were reflected in the changing picture which the micro- 
scope is capable of resolving. : 

Chemical characteristics of protoplasm. Chemical analysis 
shows that protoplasm is a colloidal complex comprising chiefly 
the elements carbon, hydrogen, oxygen, nitrogen, sulphur, 
phosphorus, potassium, calcium, sodium, chlorine, iron, and 
magnesium—all of which are commonly found in the inor- 
ganic world. Indeed, there is no chemical element present 
which is peculiar to living matter. 4 

But there are combinations of elements which are distinctly 
characteristic of protoplasm, not being found in nature except 
as the result of protoplasmic activity. “These chemical com- 
binations are the proteins, carbohydrates and fats, and of 
them the proteins are the most significant because they are 
universally present as a part of all living matter and form 
quantitatively its chief organic constituent. Proteins invari- 
ably consist of the elements carbon, oxygen, hydrogen, nitro- 
gen, sulphur, with sometimes phosphorus or iron; the nitrogen, 
however, particularly distinguishing them from the othet 
organic compounds of the living complex. Although the 
stereochemical composition of a protein molecule has not been 
determined, analyses show that it may be split up into a large 
number of simpler, though still very complex molecules, anc 
it is evident that its few elements may be represented by hun 
dreds and even thousands of atoms. As Underhill has said 
“Viewed from the chemical standpoint protein is seen as a hu g 
molecule, complex in structure, labile in character and there 
fore prone to chemical change. So large and intricate is tht 
make-up of the molecule that chemists for generations havi 
been baffled in their attempts to gain any adequate conceptio 
of its nature. At the present stage of our knowledge it i 
impossible to form any satisfactory definition of a protet 
based either on its chemical or physiological properties.’ 


2 Underhill, F. P., “The Physiology of the Amino Acids,” 1915, published 
Yale University Press. 


ee ee 


AND ITS INHABITANTS 85 

_ It must suffice then to emphasize that it is the presence of 
Broteins and the power of forming them which is the diag- 
sti chemical characteristic of matter which is alive. It will 


be recognized, of course, that proteins are not “‘alive,” and even 


if the biochemist should succeed in artificially synthesizing a 


; rotein, which has not thus far been accomplished, by group- 


g together amino acids, which already have been made syn- 
etically, this would not be in any sense the artificial produc- 
on of life. But since proteins are the one molecular system of 


which we are aware which is diagnostic of protoplasm, we have 


e right to assume, for the present at least, that they represent 
in a way the quintessence of that arrangement of matter which 
exhibits life, while clearly recognizing that they are but an 
integral part of the more complex, physicochemical structure 
of protoplasm. Protein is, as it were, “the chemical nucleus 
or pivot around which revolve a multitude of reactions char- 
acteristic of biological phenomena.” 

_ The vehicle of life manifestations is thus clearly a physico- 


chemical complex and one of its most conspicuous and funda- 


mental phenomena is what has been described as “energy 
traffic” or the function of trading in energy. This consists in 
appropriating energy from the environment, storing it in a 
state of higher potential and later expending it in the kinetic 
form. The lability of many of the molecular aggregates of 
protoplasm, that is, their tendency to change in composition 
toward greater or less complexity, coinciding with deoxidative 
and oxidative processes, is an important characteristic and one 
which endows the protoplasmic system as a whole with its 


perennial plasticity—‘“‘its peculiar proneness to change its com- 


position under the stimulus of slight changes in the energy- 
equilibrium between itself and its surroundings.’ 
Definitions of life. This continual flux, which is now em- 


8 Allen, F. J., “What is Life?” Proc. Birmingham Nat. Hist. and Philos. Soc., 
vol. 11, pp. 44-67, 1899. 


86 EVOLUTION OF THE EARTH | 
phasized as characteristic of protoplasm, was recognized as 
a characteristic of organic individuals long before it wat 
recognized in their physical basis, and is expressed 1 in neark 
all definitions of life. Aristotle described life as “the asse 
blage of the operations of nutrition, growth and destruction” ; 
Bichat as “‘the sum total of the functions which resist . death” 
De Blainville as “the twofold internal movement of composi 
tion and decomposition, at once general” and continuous” 
Lewes as ‘“‘a series of definite and successive ance both o: 
structure and composition, which take place within an indi 
vida without destroying its identity”; while’Spencer defines i 
“the definite combination of heterogeneous changes, dot! 
simultaneous and successive, in correspondence. with exter 
coexistences and sequences’ “and as “‘the Sontmuaas “ad aaa 
of internal relations to external relations.” 
Obviously these statements are far from satisfactory, bu 
no adequate, concise and yet comprehensive definition of lif 
ever has been formulated, though it has been. essayed b 
the best minds for generations. The fact is that life is to 
complex to be described concisely, and so unique that it i 
impossible to resort to the lexicographer’s trick of comparin 
it with something else. Although many physicochemic: 
phenomena contribute to life, not one of them will serve ¢ 
a criterion and all of them collectively do not offer, as yet, 
satisfactory explanation. Whether behind the physical ph 
nomena there are intangible metaphysical factors is a questic 
outside the realm of biology. Since the limitations of ot 
senses confine our perception to that part of our environmen 
perhaps a very small ‘part, denoted by the fundamental co 
cepts of science, matter, and energy acting in space and tim 
we are forced to interpret, in so far as we are able, the li 
processes in these terms. Thus far, however, the study 
protoplasm has given no reason for abandoning the productiy 
working hypothesis that life phenomena are an expression ¢ 


AND ITS INHABITANTS 87 
a complex interaction of physicochemical laws which do not 
differ fundamentally from the so-called laws operating in the 


jnorganic world. 


Individuality of organisms. We have seen that, although 
all protoplasm has a similar fundamental physicochemical 


basis, nevertheless there is a considerable, indeed a great, di- 


versity in the minor details of its composition, not only in 
different species of animals and plants, but also in the various 
parts of the same animal or plant. In fact, organisms are 
organisms because of specific local differentiations in the imme- 
diate substratum of their vital activities. 


_ This specification of protoplasm is rendered possible by the 


fact that the structural units of all organisms are microscopic 
masses of protoplasm, termed cells. The bodies of all higher 
animals and plants are congeries of millions of these proto- 
plasmic units, while many of the simpler forms of life consist 


| of but a single one. Therefore it is apparent that a funda- 


mental characteristic of organisms as we know them today is 
not only that the material basis of their activities which we 
call life is the somewhat protean, though no less real, proto- 
plasm, but also that this physical basis is individualized into 
structural moieties, the cells. It is not an overestimation to 
say that the recognition of this dual similarity of physico- 
chemical and morphological organization of all living things 


must be considered the greatest single generalizatioa which 


biological science has attained, and must be ranked with the 
theory of organic evolution, of which it is the corner-stone, in 
its far-reaching bearings.‘ 


*See Allen, F. J., op. cit. 
Minchin, E. A., “The Evolution of the Cell.” Amer. Nat., vol. 50, 1916, 
pp. 5-38, 106-118, 271-283. 
_ Conklin, E. G., “The Basis of Individuality in Organisms from the 
_ Standpoint of Cytology and Embryology.” Science, new ser., vol. 43, 
1916, pp. 523-527. 
Driesch, H., “The Problem of Individuality,” 1914. 


88 EVOLUTION OF THE EARTH 

Obviously, then, the biologist in dealing with living sub- 
stance has it only in the form of cells, and these, singly or col- 
lectively, constitute individual organisms. Thus in the final 
analysis protoplasm is known to us only in the form of living 
individuals, and the expressions ‘“‘protoplasm”’ and “‘life” are 
merely abstractions, one indicating that all individuals have 
to a certain extent a common organizational foundation and 
the other that they exhibit certain characteristic actions and 
reactions. The living organism is a microcosm which exhibits 
a permanence and continuity of individuality correlated with 
specific behavior, and this it transmits to other matter which 
it makes a part of itself and to its offspring in reproduction. 

It is apparent that the phenomena which we call life are 
dependent upon the interplay and interchange between the 
highly organized protoplasmic complex and its environment. 
Although the organism, whether animal or plant, is an indi 
vidual, still it retains its individuality—lives—solely by its 
powers of developing and maintaining exquisite adjustments to 
its surroundings, and therefore the concept protoplasm has 
little or no content unless environmental relations are included. 
This fitness of the organism, as Henderson has recently empha- 
sized, is but one part of a reciprocal relationship of which 
the fitness of the environment is the other. ‘The fitness of the 
environment results from characteristics which constitute a 
series of maxima—unique or nearly unique properties of 
water, carbonic acid, the compounds of carbon, hydrogen, 
and oxygen and [for primordial life] the ocean.” ‘No other 
environment consisting of primary constituents made up of 
other known elements, or lacking water and carbonic acid, 
could possess a like number of fit characteristics’ for proto- 
plasmic phenomena. The properties of matter and the course 
of cosmic evolution are intimately related to the structure of 
the living being and to its activities. Indeed, ‘‘the whole evolu- 
tionary process, both cosmic and organic, is one, and the biolo- 


AND ITS INHABITANTS 89 
_ gist may now rightly regard the universe in its very essence as 
_biocentric.’”® 
\ History of the establishment of biogenesis. The previous 
lectures in.this course have described the theories in regard to 
the origin of this environment on the earth, so we turn now 
“to the question of the origin of life—that primeval question 
_ which has been asked by all ages and the answers to which, if 
_ they do no more, at least epitomize the philosophic and scien- 
; " tific perspective of the times. 
_ One of the greatest intellectual characteristics of the Greeks 
_ was their scientific curiosity, and therefore it is not strange 


_ that the first biological question which they propounded was 


_ in regard to the origin of life. Even to the best minds of the 
ancients there was little incongruity’ in the idea of animals 
and plants arising de novo from earth or water. Although 
Aristotle, whose scientific studies formed the foundations of 
natural history, devoted a great deal of thought and ingenuity 
to the subject of the origin of animals, he apparently accepted 


| with little reservation the statements that even such highly 


developed organisms as worms, insects, and some fishes could 
come into being from mud. Such ideas are voiced over and 
over again through more than twenty centuries by philosopher 
and poet, theologian and layman. 
Lucretius, in his De rerum natura, says that “with good 
reason the earth has gotten the name of mother, since all 
things are produced out of the earth, forming in rain water 
and in the warm vapors raised by the sun.”’ Virgil in the 
fourth Georgic, which is devoted to a discussion of bees, 
graphically describes a simple method used in Egypt for obtain- 
ing bees from the dead bodies of bullocks. 
Coming to the medieval period and later we find Cardan 
stating that water engenders fishes and that various types of 
animals arise from fermentation. Swan in his Speculum mundi 


_ 5 Henderson, L. J., “The Fitness of the Environment,” 1913. 


go EVOLUTION OF THE EARTH 

says that a dead horse breeds wasps, a mule produces hornets, 
while from an ass arise bumble bees. Van Helmont, one of 
the founders of chemical physiology, gives particularly specific 
directions for the experimental production of scorpions and 
mice, while Kircher actually figures animals-which he avers 
arose under his own eyes through the influence of water on 
the stems of plants; an instance, perhaps, not of spontaneous” 
generation but of the transformation of plant into animal, 
which was also a ‘notion prevalent at the time. The ironical” 
reflections of one Ross, aroused by the scepticism of Sir 
Thomas Browne in regard to mice arising by putrefaction, are 
quite typical of seventeenth-century opinion. He says: “So 
we may doubt whether in cheese and timber worms are gen- 
erated, or if beetles and wasps in cow-dung, or if butterflies, 
locusts, shellfish, snails, eels, and such life be procreated of 
putrefied matter, which is to receive the form of that creature 
to which it is by formative power disposed. ‘To question this 
is to question reason, sense, and experience. If he doubts 
this, let him go to Egypt, and there he will find the fields — 
swarming with mice begot of the mud of Nylus, to the great 
calamity of the inhabitants.” 

That such ideas of the origin of life were prevalent and their 
truth untested by experiments is an eloquent commentary on 
the general state of the scientific method before the Renais- 
sance. It was Francesco Redi, an eminent Italian scholar, — 
physician, and naturalist, who, not content with tradition, but 
with great faith in observation, made a study of the origin © 
of maggots in decaying animal matter. By the simplest of 
experiments he found that maggots never developed in meat ~ 
to which flies were not allowed access and that the seeming 
transformation of meat into maggots was the result of flies 
laying their eggs on the meat. When this was prevented, no — 
matter how he varied the materials of his experiments, he 


obtained the same result, and naturally concluded that the sup- — 
B 


2. i rr ———————e 


AND ITS INHABITANTS gI 


posed appearance of life where life had not been previously 


was due to the introduction of foreign living material.® 


One may imagine that the practical man of affairs, who 


scofied at Redi toiling under the Italian sun with meat and 
“maggots to satisfy a scientific curiosity, little dreamed that 
the practical results which germinated from this folly would 
be among the most important factors in twentieth- -century 
‘civilization. Indeed, it is difficult to overestimate the i impor- 


tance of Redi’s conclusion from either the theoretical or prac- 


tical viewpoint, for with it was definitely formulated the theory, 
which has gained content and impetus as the years have rolled 
‘on, that matter does not assume the living state, at the present 
time at least, except under the direct influence of preéxisting 


living matter. 

The influence of this work gradually became apparent in 
scholarly literature; Derham, for instance, stating that ‘‘Spon- 
taneous generation is a doctrine so generally exploded that I 
shall not undertake to disprove it. It is so evident that all 
animals, yea and vegetables, too, owe their production to 


parent animals and vegetables, that I have often admired at 


the sloth and prejudices of the ancient philosophers in so easily 
taking upon trust the Aristotelian, or rather A‘gyptian doc- 
trine of equivocal generation.’” Another writes: “I would 
as soon say that rocks and woods engender stags and ele- 
phants as affirm that a piece of cheese generates mites. Stags 
are born and live in woods, and mites in cheese, but they both 


owe their being to that of other animals.’ And again, Henry 
Baker, the versatile microscopist of the Royal Society, says: 
“Nothing seems now more contrary to reason, than that chance 


and nastiness should give a being to uniformity, regularity 


and beauty . . . and create living animals. . . . This, however, 


© Redi, F., “Esperienze Intorno Alla Generazione Degl’ Insetti,” 1668. Eng- 
lish translation by M. Bigelow, 1909. 
*Derham, W., “Physico-Theology,” 1713, 


92 EVOLUTION OF THE EARTH 
was the opinion not only of the ignorant and illiterate, but off 
the most learned grave philosophers of preceding ages; and 
would probably still have been taught and believed had not 
microscopes discovered the manner how all these things are 
generated, and restored to God the glory of his own = 
work.’’® | 

Although it is relatively easy to follow when one’s eyes are 
opened, it is not to be imagined, of course, that one experiment, 
or even the long series of studies made by Redi, could annihi- 
late a time-honored belief. Indeed, the history of the establish- 
ment of the theory extends down even to the present time, 
for no sooner had experiment apparently disposed of it com- 
pletely than it arose again, pheenix-like, with fresh vigor in 
a slightly different phase demanding further study. | 

Among others, a Scotch priest, ‘Turbervill Needham, studied 
the problem and believed that various minute organisms, 
which improvements in the microscope were bringing to the 
fore, appeared spontaneously in infusions which he boiled ane 
corked up in flasks.®° His results attained considerable noto- 
riety, since Buffon, the famous French naturalist, found in 
them a substantiation of his theory that all organisms are 
aggregates of indestructible units, which upon the death of 
the individual are disseminated in nature and later are e 
ployed as moieties in the organization of arising generations 

Needham’s results, however, were soon shown by Lazzar 
Spallanzani* to have been obtained by inadequate sterilizatio: 
and sealing of the infusions which he studied; but at this poin 
objections came from another source—the chemists who had 
recently discovered oxygen and the importance of this elemen 


8 Baker, H., “The Microscope Made Easy,” 1742. 

9 Needham, T., “A Summary of Some Late Observations upon the Generation, 
Composition, and Decomposition of Animal and Vegetable Substances.” Philo: 
Trans. Roy. Soc. London, 1748. ¢ 

10 Spallanzani, L., “Expériences pour Servir a l’Histoire de la Génération de 
Animaux et des Plantes ” 1786. 


. 
4 
; 


AND ITS INHABITANTS 93 
in the free state for the processes of life and for putrefaction 
and fermentation of organic matter. The treatment to which 
Spallanzani subjected his infusions might well have so changed 


‘the organic matter, they argued, that it was incapable of pro- 
‘ducing life. This objection was met by a series of experiments 
by various investigators during the first half of the last 
Bentury, which showed conclusively that thoroughly sterilized 


fusions never developed living organisms when air was 


admitted which had. been rendered sterile by heat or by having 


all suspended matter removed, while the studies of Schwann 
and Cagniard de la Tour intimated that fermentation and also 
putrefactive changes in organic infusions are themselves the 
result of micro-organisms. 

So far it was clear that organic infusions in which no life 


is present do not develop living organisms except when con- 


taminated with material from an extraneous source, which is 
ordinarily the atmosphere, but it remained then to be shown 
that living organisms are practically ubiquitous in the atmos- 
phere and thus are available for the initiation of the micro- 
flora and fauna of infusions. This was put upon a broad 
empirical basis chiefly by the labors of Pasteur. Tyndall, 
who himself made a notable contribution to the solution of 
the problem by researches in experimental physics, confidently 


| asserted that there seems to be no flaw in the reasoning, and 


it is so simple as to render it unlikely that the notion of life 


| developing from dust can ever again gain currency among the 
| members of a great scientific profession. 


’ We thus reach the general conclusion that, so far as human 


| observation and experimentation go, no form of life arises 


today except from preéxisting life. But since life is present on 
the earth now and the paleontological record indicates that it 
has been present without interruption for some hundreds of 
millions of years, we have to consider the following alterna- 


| tive: Either life was transported to this planet from some 


| The magnitude of the problem may be inferred from a recent 
statement by the dean of American biologists that ‘‘the study 


94 EVOLUTION OF THE EARTH 
other part of the universe; or life arose spontaneously from 
non-living matter at one period at least in the past as a natural 
result of the evolution of the earth and its elements. 


THEORIES OF THE ORIGIN OF LIFE Ss 

It will be useless to offer any extended discussion or specific 
criticisms of the individual theories of the origin of life, for 
each one rests on many uncertain postulates, which have < 
greater or less degree of probability dependent, to a con- 
siderable extent, on the personal equation of the critic. It 
should be said, however, in justice to the authors of the theories 
which we shall outline, that the theories are not advanced as 
final solutions of the problem of the origin of life, but rather 
as gropings toward a formulation of the conditions which con- 
ceivably might have attended and contributed to its genesis. 


of the cell has on the whole seemed to widen rather than to 
narrow the enormous gap that separates even the lowest forms 
of life from the inorganic world.’’™ 

Vitalism. ‘The vitalistic conception that life phenomena are 
in part at least the resultant of manifestations of matter and 
energy which transcend and differ intrinsically in kind from 
those displayed in the inorganic world—a denial, as it were, 
in the organism of the full sufficiency of known fundamenta 
laws of matter and energy—has arisen many times in th 
development of biological thought, either as a reaction against 
premature conclusions of the nascent sciences or from af 
overwhelming appreciation of the complexity of life phe 
nomena. Vitalism goes back as far as ‘the history of science 
is recorded, but it attained its most concrete formulation as a) 
doctrine during the early part of the eighteenth centu 
in opposition to the obviously inadequate explanations which 


11 Wilson, E. B., “The Cell in Development and Inheritance,” 2d ed., 1900; 
“The Problem of Development,” Science, new ser., vol. 21, 1905, pp. 281-294. 


4 


] AND ITS INHABITANTS 95 
chemistry and physics could offer for the phenomena of irrita- 
bility of living matter then prominently before the professional 
biologist. The vitalists at that period abandoned almost 
- os : 
completely all attempts to explain life processes on a physico- 
chemical basis and assumed that an all-controlling, unknown, 
-and unknowable, mystical, hyper-mechanical force was re- 
sponsible for all living processes. It is apparent, of course, 
that such an assumption in such a form is a negation of the 
scientific method, and at once removes the problem from the 
realm of scientific investigation. No biologist at the present 
day subscribes to vitalism in this form; some uphold vitalism 
(if it must still be called vitalism) in its modern aspect, while 
all will undoubtedly admit that we are at the present time 
“utterly unable to give an adequate explanation of the funda- 
“mental life processes in terms of physics and chemistry. 
Whether we shall ever be able so to do is unprofitable to 


7 


‘speculate about, though certainly the twentieth century finds 
relatively few representative scientists who really expect a 
“scientific explanation of life ever to be attained or who expect 

that protoplasm will ever be artificially synthesized. But, 
“In ultimate analysis everything is incomprehensible, and 
the whole object of science is simply to reduce the fundamental 
incomprehensibilities to the smallest possible number.’ 

Cosmozoa theory. ‘The establishment of the fact that, so 
| far as we can determine, life does not arise except from 
| preéxisting life at the present time, and the dawning realiza- 
tion of the intrinsic and unique complexity of the architecture 
of matter in the living state, which has thwarted the attempts 
of alchemist and biochemist to synthesize even one of its chief 
| molecular aggregations, have led several scientists to suggest 
and elaborate the hypothesis that life has never arisen de novo 
on the earth but has been transported hither from elsewhere 
in the universe. 


) 
) 


12 Huxley, T. H., “Darwiniana.” “Collected Essays,” vol. 2, 1893, p. 165. 


~ 


96 EVOLUTION OF THE EARTH : 

Such an idea was advanced by Richter, and later inde- 
pendently suggested and discussed by Helmholtz and Kelvin.* 
On the assumption that some of the heavenly bodies have 
always been the abode of life, and from the fact that smal 1 
solid particles, which presumably have formerly been an 
integral part of such bodies, are moving everywhere in space, — 
Richter pictures these particles as the vehicles which dis- 
seminate the simplest forms of life through interstellar space 
to find lodgment and development upon such planets as afford 
a suitable environment. Clearly, from this point of view, life 
is as old as the universe itself—living matter has never 
originated but has been transported from world to world. 
Hence the acceptance of this permanent dualism of living and 
lifeless matter does not answer the broad question as to the 
origin of life, but transfers its origin to a ‘“‘conveniently inac- 
cessible corner of the universe where its solution is impossible.” 
However, the question before us is the origin of life upon the 
earth, and the plausibility of this cosmozoa theory depends on 
two assumptions—that life exists elsewhere in the universe 
and that life can be maintained during the interstellar voyage. 
Neither assumption has, of course, any empirical foundation 
whatsoever, though the second offers at least something 
tangible for discussion. J 

Many of the lower forms of life, such as the bacteria anc 
protozoa, have the power of developing, particularly unde: 
the influence of unfavorable environmental conditions, pro 
tective coverings of various sorts about themselves and of 
assuming a resting condition in which all the metabolic activi 
ties characteristic of active life are reduced to the lowest ebb 
In this spore or encysted state they are immune to extremes 0 
temperature and desiccation to which they readily succuml 
during vegetable life. It has recently been found, for example 


13 Verworn, M., “Allgemeine Physiologie,” 5th ed., 1909. English translatio 
of 2d edition by F, S. Lee, 1899. 


AND ITS INHABITANTS 97 
that certain types of bacteria can successfully endure a 
temperature of nearly —200° C. for six months, and about 
—250° C. for shorter periods, that is, a temperature con- 
| siderably lower than that at which any chemical reactions 
are known to occur; and again the spores of other bacteria 
can withstand a temperature as high as 120° C. for a short 
| time. The cysts of some relatively highly specialized protozoa 
‘can retain their vitality for at least fifty years, and the seeds 
‘of the higher plants, particularly those with a thick and im- 
permeable integument, have been found to retain the power of 
germination for nearly a century, though the statement that 
grain from Egyptian tombs still maintains its power of growth 
has been disproved. The ability to continue dormant life 
clearly seems to depend to a large extent on the presence 
‘of a dry enclosing membrane, since under these conditions the 
entrance of gases is impossible and the chemical processes 
within are at a minimum. Thus it is apparent that certain 
Organisms may survive unfavorable conditions for a long 
period, and we have no reason for believing that the limits of 
endurance of other forms do not greatly exceed that of the 
few which have thus far been studied. 

On the other hand, the exigencies to which living matter 
would be exposed when started on its interstellar journey are 
not inconsequential. Meteors in their fall through the earth’s 
atmosphere become incandescent and, if they are the vehicle 
of transfer, it would only be conceivable for life to survive 
far below the surface where the temperature is lower. To 
avoid this and other difficulties it has been suggested by 
Arrhenius that the radiation pressure of light is sufficient to 
Overcome the attraction of gravitation for particles of the 
extraordinary minuteness of some of the lowest forms of life, 
and that isolated germs might make the journey to the earth. 
But on the assumption that such an individual organism were 
forced out into space by the mechanical pressure of the light 


98 EVOLUTION OF THE EARTH 
waves from the sun of the nearest solar system, it would re- 
quire many thousand years to reach the earth. Only on the 
view that cells are potentially immortal and can remain in a 
dormant condition nearly indefinitely can we believe that lif 
has reached the earth from other planets. Arrhenius maintains 
that this is possible owing to the exceedingly low temperature 
and absence of water-vapor which must prevail in cosmic space; 
and Loeb states that there is no reason why spores should lose 
appreciably more of their germinating power in ten thousand 
years than in six months.** ; 

Without further discussion it is apparent that the theory is 
one which cannot be proved or disproved. At first thought, 
and as first outlined by Richter, it commanded little serious 
attention; but with its strictly scientific formulation by later 
physicists and biologists, and especially in view of our increas- 
ing appreciation of the potentialities of life in the latent state, 
we are justified perhaps in seriously questioning, with Helm- 
holtz, ‘‘whether after all life has ever arisen, whether it maj 
not be even as old as matter, and whether its germs, passing 
from one world to another, may not have developed where 
they found favorable soil.”” But the majority of biologists 
doubtedly would agree with Schafer that, ‘knowing what we 
know, and believing what we believe, as to the part played by 
evolution in the development of terrestrial matter, we are, 
without denying the possibility of the existence of life in othe 
parts of the universe, justified in regarding these cosmic theories 
as inherently improbable—at least in comparison with the solu 
tion of the problem which the evolutionary hypothesis offers.’” 


14 Arrhenius, S., “Worlds in the Making.” English translation by H. Borns 
1908. 

Loeb, J., “The Organism as a Whole from a Physicochemical Viewpoint,’ 
1916. 
Woodruff, L. L., “A Pedigreed Race of Paramecium.” Proc. Soc. Exp. Biol 

and Med., vol. 9, 1912. 

15 Schafer, E. A., “Life: Its Nature, Origin and Maintenance.” Presidentia 
address, Brit. Assoc. Adv. Sci. Science, new ser., vol. 36, 1912, pp. 289-312, 


a AND ITS INHABITANTS 9 
_ With this in mind we may briefly survey some of the modern 
scientific conjectures which attempt to formulate the phe- 
nomena attendant upon the evolutionary origin of matter in 
the living state from the inorganic upon the earth. 

| Pfliiger’s theory. Assuming that the surface of the earth 
was once incandescent, Pfliiger has offered a suggestive theory 


‘the crucial points of which turn on the chemical characteristics 


of the proteins. He emphasizes that there is a fundamental 
difference in the nitrogenous radicals of what he terms “‘dead” 
proteins, as egg albumin, and “living” proteins taking an active 


part in the economy of protoplasm, since the nitrogenous 


omposition products of the latter either contain the cyano- 


a ; a radical or can be artificially produced from compounds of 


cyanogen by atomic rearrangement. ‘This suggests to Pfliiger 
the probability that the cyanogen radical is an integral part 
of the molecular complex of living proteins and since in the 
formation of cyanogen a large amount of heat is absorbed, it 
follows that this radical possesses a large amount of internal 
energy and thus with it there is “introduced into the living 
‘matter energetic internal motion.’ 

Pfliiger’s idea that the protein molecules of living proto- 
plasm owe their diagnostic characteristics, in particular their 
bility, to cyanogen is supported, be believes, by certain 

analogies, which we need not consider, between cyanogen com- 
pounds and “‘living’’ proteins. Indeed, he says, the “‘similar- 
‘ity i is so great that I might term cyanic acid a half living mole- 
cule.” “When we think of the beginning of organic life, we 
must not think primarily of carbonic acid and ammonia; for 
they are the end of life, not the beginning.” ‘The beginning 
lies rather in cyanogen.” Pointing out that cyanogen and its 
compounds arise only in an incandescent heat, he holds that 
“life is derived from fire, and its fundamental conditions were 
laid down at a time when the earth was still an incandescent 
ball.” Thus living material owes its genesis to cyanogen com- 


100 EVOLUTION OF THE EARTH 
pounds which, on account of their tendency to decomposition, 
entered into relations with carbon compounds arising at similar 
temperatures. When the temperature conditions of the earth’s | 
surface permitted the precipitation of water, this with the 
salts and gases in solution joined the growing cyanogen- 
carbon complex and gave rise to the highly labile protein. 
molecules so characteristic of protoplasm. Thus, according to 
Pfliiger’s hypothesis, arose a relatively simple, homogeneous 
material from which has been evolved the highly differentiated 
PROLOE aa masses or cells of organic life today.*® 

Moore’s theory. Moore essays to picture with rather bold 
strokes the origin of life from the inorganic elements of the 
cooling earth, by a continuation of the slow process of com- 
plexification which he sees inherent in matter. ‘This note,” 
he says, “‘cannot be too strongly sounded that as matter is 
allowed capacity for assuming complex forms those complex 
forms appear. As soon as oxides can be there, oxides appear; 
when temperature admits of carbonates, then carbonates are 
forthwith formed. . . . Next in order of development prio 
to life inorganic colloids begin to appear in solution, or sus- 
pension, in the waters of the cooling globe, alumina and silica 
deposited in colloidal form are seen in many sedimentary 
rocks. Single molecules existing in solution, and capable of 
forming colloids, with alterations in temperature, and in 
chemical reaction of the environment, begin to form com-) 
plexes, or solution aggregates, in which the unit of chemical 
structure passes from the atom to the molecule.” | 

Accompanying these structural changes, the energy types 
and phases inhabiting the unit of structure also vary. The 
rates of vibration or of phasic activity in the colloidal aggre= 
gates become slower than in the simpler molecules of the 


16 Cf. Verworn, of. cit. 
Pfliger, E., “Ueber die physiologische Verbrennung in den lebendigen 
Organismen.” Arch, f. d. ges. Physiol., vol. 10, 1875. q 


? AND ITS INHABITANTS IOI 
cr stalloids. The characteristics of colloids, slowness of 
reaction, metastable equilibrium, delicacy of union, and in- 
= reactivity of specific type, become present in the forms 


‘yironment. As the complexity of structure increases, the 
ature of the equilibrium in the colloidal aggregates ap- 
proaches more and more towards that labile, easily destroyed, 
but also more readily constructive condition which is char- 
acteristic of life. 
_ Moore then states in a general way as a “law universal in 
Ml ts application to all matter, although varying in intensity in 
‘different types of matter, and holding throughout all space as 
“generally as the law. of gravitation—a law which might be 
called the Law of Complexity—that matter so far as its energy 
‘environment will permit tends to assume more and more 
complex forms in labile equilibrium. Atoms, molecules, col- 
loids and living organisms arise as a result of the operations 
‘of this law, and in the higher regions of complexity it induces 
organic evolution and all the many thousands of living forms.” 
Tn this manner he conceives that the hiatus between non-living 
and living things can be bridged over, and that life arose as 
an orderly development, which comes to every earth in the 
universe in the maturity of creation when the conditions arrive 
within the suitable limits.*’ 
_ Allen’s theory. We may now consider certain theories 
which conform with the primal earth conditions as postulated 
by the planetesimal theory of its origin. Allen, for example, 
maintains that it is simplest to believe that the circumstances 
which support life would also favor its origin and that if life 
| formerly existed actively outside the range of the freezing 
and boiling points of water, it must have been quite different 
from that which now exists. Life then arose at the period 
when the physical conditions of the earth came to be nearly 
1, Moore, B., “The Origin and Nature of Life,” 1912. 


102 . EVOLUTION OF THE EARTH 
what they are at present. At such a time, as now, dis- 
charges of lightning passing through the damp air produced 
ammonia and oxides of nitrogen, which were carried down by 
rain into the streams and pools. If this process went on un: 
modified, the result would be a large accumulation of nitrogen 
compounds in the terrestrial waters, which would also contain 
carbon dioxide probably in larger amounts than the waters o: 
the present day, because since that time much carbon dioxide 
has been withdrawn from the air and water and locked up in 
organic matter. In the same waters the usual metallic ele- 
ments, in the form of chlorides, sulphates, phosphates, etc., 
would also be present. 

Thus there must have been brought together an abundance 
of such raw materials as are required for the production of 
living matter, and, provisionally, Allen imagines some suck 
reactions as the following to have occurred: solar energy 
acting on the water or damp earth containing the raw material; 
just mentioned, caused dissociation and rearrangement of thé 
atoms, the nitrogen abstracting oxygen from its compound 
with carbon, hydrogen, sulphur, and other elements and de: 
livering it to the atmosphere. Not much energy would bi 
absorbed by a transparent liquid; but such actions as th 
above would occur particularly in water containing compound 
of iron in solution or suspension since these compounds woul 
absorb the solar energy. In this way compounds of nitroger 
carbon, etc., accumulated in the water or damp earth; an 
further reactions, anabolic and catabolic, occurred among ther 
by virtue of the lability of the nitrogen compounds. Life a 
this stage was of the humblest kind since there were no defini 
organisms, only diffuse substances trading in energy, an 
between this stage and the evolution of cellular organisms 4 
immense period probably elapsed. | 

Allen questions whether the earliest organisms were able ; 
utilize the energy of sunshine or whether their whole energ 


q 


AND ITS INHABITANTS 103 

was derived from the nitrogen compounds produced in the 
atmosphere by lightning, but in any case he thinks the faculty 
of appropriating the energy of sunshine must have developed 
at an early period, if not at the very beginning. In the func- 
tions of life, constructive process precedes destructive, and it 
therefore seems. reasonable to suppose that the earliest forms 
| of life were concerned more in accumulating than in dispersing 
energy, and that the energy-dispersing organisms, like bacteria 
and fungi, have had a comparatively late origin. 
_ Allen’s view of the origin of life “implies that the first 
attempts at life are still continuing, and that if by chance all 
life were wiped out, another cycle would begin.” Such he be- 
lieves to be the case, and to the question, ‘‘Why do we not find 
evidence of these processes in the form of primitive vital sub- 
stances in water or elsewhere ?”’ he answers that as soon as any 
such substances begin to be formed, they are seized and assimi- 
lated by the already developed organisms.* 

Troland’s enzyme theory. With the increasing realization 
of the importance of enzymes in the economy of organisms it 
is not strange that in these chemical bodies has been sought 
the key to life’s origin, and accordingly we find Troland stating 
that life is something which has been built up about the 
enzyme. This author assumes that, at some moment in earth 
history, a small amount of a certain autocatalytic enzyme 
suddenly appeared at a definite point within the yet warm 
ocean waters which contained in solution various substances 
reacting very slowly to produce an oily liquid immiscible with 
water. If, when this occurred, the enzyme became related to 
the reaction in such a way as to greatly increase its rate by 
reducing the chemical friction involved, Troland believes it is 
obvious that the enzyme would become enveloped in the oily 
material resulting from the reaction, and the little oil drop 
| would increase until it was split into smaller globules by water 


48 Allen, F. J., of. cit. 


104 EVOLUTION OF THE EARTH 
currents, provided the original substances which combined 
were soluble in oil as well as in water. Thus arose, according 
to his theory, the first and simplest life-substance, possessing 
the power of indefinitely continued growth, by virtue of the 
postulated autocatalytic character of the initial enzyme. Tro- 
land is convinced that this theory of the origin of life satisfies 
most of the objections which have been advanced against 
ordinary chemical hypotheses, since the characteristic catalytic 
power of the enzyme accounts for the elevation of the rate of 
synthetic action from, practically zero to one making possible 
rapid growth of the protoplasmic mass. The same catalytic 
property explains the localization of the reaction in a definite 
region, for catalysis can occur only where the catalyzer itself 
is present. ‘The theory also provides a basis for the per- 
manent growth of the primitive organism—if such we dare to” 
call it—as well as for its reproduction, without, in general, the 
loss of its specific individuality.” Troland suggests that the 
most fundamental objection which can be raised against’ his 
ideas is the fortuitous formation of the original enzyme; but 
he insists that since only a single molecule of the enzyme was 
required, and since multitudinous chemical reactions undoubt- 
edly took place in the primordial ocean, this objection of 
improbability is almost absurd.*® | 

Osborn’s theories. The most recent consideration of the 
origin of life is that by Osborn, published during the past year. 
Starting with the postulate that “the primal earth, air, and 
water contained all the chemical elements and three of the 
most simple but important chemical compounds, namely, 
water, nitrates, and carbon dioxide, which are known to be 
essential to the prechlorophyllic and chlorophyllic stages of 
the life process,” Osborn suggests that an initial step in the” 
origin of life was the codrdinating or bringing together of 

19 Troland, L. T., “The Chemical Origin and Regulation of Life.” Th 
Monist, vol. 24, 1914, pp. 92-133. { 


ae gn 


AND ITS INHABITANTS 105 


_ these elements, which, so far as we know, had never been in 
- combined action before. He states that the thermal condi- 
tions of present-day living matter point to the probability that 
this codrdinating of the ‘“‘life elements’ was initiated when 
‘portions at least of the earth’s surface and waters had tem- 
_ peratures of between 6° and 89° C. and before the atmospheric 


vapors admitted a regular supply of sunlight. The earliest 
' function of living matter appears to have been to capture and 


_ transform the electric energy of the chemical elements char- 
acteristic of protoplasm, and this power probably developed 
2 only in the presence of heat energy derived from the earth or 
_ from the sun. Frankly admitting, however, that both the time 


_and place of the origin of life is a matter of pure speculation, 


-in which we have as yet no observations or uniformitarian 


_ reasoning to guide us, Osborn advances five hypotheses in 
regard to it as follows: 


An early step in the organization of living matter was the 


assemblage of several of the chemical elements essential to 


life. Of these the four most important elements were ob- 
tained from their previous combination in water, from the 
nitrogen compounds of volcanic emanations or from the 
atmosphere, consisting largely of nitrogen, and from atmos- 
pheric carbon dioxide. The remaining elements came from 
the earth. 

Whether or no there was a sudden or a more or less serial 
grouping of these elements, one by one, Osborn is led to a 


second hypothesis that ‘‘they were gradually bound by a new 


form of mutual attraction, whereby the actions and reactions 
of a group of life elements established a new form of unity in 
the cosmos, an organic unity or organism quite distinct from 
the larger and smaller aggregations of inorganic matter pre- 
viously held or brought together by the forces of gravity.” 
This leads to the hypothesis that since all living cells are 
colloidal the grouping of the ‘“‘life elements” took place in a 


106 EVOLUTION OF THE EARTH 
state of colloidal suspension, for it is in this state that the — 
life elements best display their incessant action, reaction and 
interaction. 

With this assemblage, mutual attraction, and colloidal con- | 
dition, a fourth hypothesis is that there arose the rudiments of ~ 
competition and selection. ‘‘Was there any stage in this group- — 
ing, assemblage, and organization of life forms, however ~ 
remote or rudimentary, when the law. of natural selection did — 
not operate between different unit aggregations of matter? 
Probably not, because each of the chemical life elements pos-_ 
sesses its peculiar properties which in living compounds best 
serve certain functions. ‘This codperation was also an appli-. 
cation of energy new to the cosmos.’ In other words, every 
“life element”’ has its single and multiple services to render to 
the organism. . 

And as a fifth hypothesis relating to the origin of organisms, 
Osborn advances the idea that the evolution and specialization — 
of various enzymes has proceeded step by step with the evolu- | 
tion of plant and animal functions, ‘‘since in the evolution from ~ 
the single-celled to the many-celled forms of life and the multi- 
plication of these cells into hundreds of millions, into billions, — 
and into trillions, as in the larger plants and animals, bio- 
chemical coédrdination and correlation become increasingly 
essential.’’?° : ' 

Conclusion. Such are the principal attempts of modern 
biologists to formulate in some concrete way the evolution of 
matter in the living state from the elements of the earth. 
Their consideration is valuable in that it indicates the uni- 
formitarian trend which, at the present day, biological thought - 


follows in this field, and also the diversity of results arrived 7 


at by the scientific imagination when it is largely untrammeled 


20 Osborn, H. F., “The Origin and Evolution of Life upon the Earth.” Scien-_ 
tific Monthly, vol. 3, 1916, pp. 5-22, 170-190, 289-307, 313-334, 502-513, 601-614. 


AND ITS INHABITANTS 107 
by facts. One, however, cannot but admire the scientific 
caution of Huxley when he said: 

_ “Looking back through the prodigious vista of the past, I 


‘find no record of the commencement of life, and therefore I 


“am devoid of any means of forming a definite conclusion as 
‘to the conditions of its appearance. Belief, in the scientific 


sense of the word, is a serious matter, and needs strong founda- 
tions. To say, therefore, in the admitted absence of evidence, 
that I have any belief as to the mode in which existing forms of 
life have originated, would be using words in a wrong sense. 
But expectation is permissible where belief is not; and if it 
were given to me to look beyond the abyss of geologically 
recorded time to the still more remote period when the earth 
was passing through physical and chemical conditions, which it 
can no more see again than a man can recall his infancy, I 
should expect to be a witness of the evolution of living proto- 
plasm from not living matter. I should expect to see it appear 
under forms of great simplicity, endowed, like existing fungi, 
with the power of determining the formation of new proto- 
plasm from such matters as ammonium carbonates, oxalates 
and tartrates, alkaline and earthy phosphates, and water, 
without the aid of light. That is the expectation to which 
analogical reasoning leads me; but I beg you once more to 
recollect that I have no right to call my opinion anything but 


an act of philosophical faith.”” 


Thus since biologists are at the present time absolutely 
unable, and probably will be for all time unable, to obtain 
empirical evidence on any of the crucial questions relating to 
the origin of life on the earth, their endeavors are and must 
be directed chiefly toward an intensive analysis of life mani- 
festations as exhibited in the physical basis of individual 


21 Huxley, T. H., “Biogenesis and Abiogenesis.” Presidential address, Brit. 
Assoc. Adv. Sci. 1870. “Collected Essays,” vol. 8. 


108 EVOLUTION OF THE EARTH . 
organisms, in their bionomic relations, and in the kaleidoscopic 
panorama which geological history presents of their evolution 

In the closing words of Darwin’s Origin of Species: . 

“Tt is interesting to contemplate a tangled bank, clothed with 
many plants of many kinds, with birds singing on the bushes, 
with various insects flitting about, and with worms crawling 
through the damp earth, and to reflect that these elaborately 
constructed forms, so different from each other, and dependent 
upon each other in so complex a manner, have all been pro- 
duced by laws acting around us. . . . There is grandeur ir 
this view of life with its several powers, having been originally 
breathed by the Creator into a few forms or into one; anc 
that, whilst this planet has gone cycling on according to the 
fixed law of gravity, from so simple a beginning endless forms 
most beautiful and most wonderful have been, and are being 
evolved.” | 


t CHAPTER IV 
THE PULSE OF LIFE 


RICHARD SWANN LULL 
PROFESSOR OF VERTEBRATE PALEONTOLOGY IN YALE UNIVERSITY 


THE stream of life flows so slowly that the imagination fails 
‘to grasp the immensity of time required for its passage, but 
like many another stream, it pulses as it flows. There are 
‘times of quickening, the expression points of evolution, and 
these are found to be coincident with geologic change. These 
coincidences are so frequent and so exact that the laws of 
‘chance may not be invoked to account for them. They stand 
to each other in the relation of cause and effect. 

This does not imply the acceptance of any one philosophical 
factor of evolution, for whether the creature is directly modi- 
fied by environmental change, or indirectly through induced 
habit, or whether nature merely sets a standard to which the 
Organism must attain if it would survive, matters not; the 
fact remains that changing environmental conditions stimulate 
the sluggish evolutionary stream to quickened movement. 
Whenever it has been possible to connect cause and effect, the 
immediate influence is found to be generally one of climate, ! 
back of which lies, as the main cause, earth shrinkage and a | 
‘consequent warping of the crust, with the elevation and spread 
‘of the lands and the formation of mountain ranges. In addi- 
tion to this mundane cause, there are the complex rhythms in 
solar energy and the consequent variation in the amount of 
solar-derived heat. For example, the most generally accepted 


I10 EVOLUTION OF THE EARTH | 
single cause of the last or Pleistocene glacial period is the 
great continental elevation which formed the Cascadian reval 
lution, but, so far as our knowledge goes, that would not 
account for the successive advances and retreats of the ice 
mantle, with the attendant climatic variation; and some other 
factor such as the rhythms of solar energy must be invoked as 
of supplemental influence. - Nevertheless, the ultimate source 
of profound and far-reaching crises in the evolution of the 
organic world may have been, geologically speaking, of a very 
simple character. 

Through the collaboration of my colleagues, Professors 
Schuchert and Barrell, the appended chart, Figure 14, has 
been prepared to show the relation between the changing con- 
tinental elevation and climate. To this I have added a curve 
representing the consequent acceleration and retardation of 
the evolutionary stream. ‘The climatic records of pre-Paleo- 
zoic time are so vague and unreliable that it was not thought 
wise to include the vast Archeozoic and Proterozoic eras 
within the scheme. The time values of the several included 
eras are not proportionally indicated, too much, space by far 
being given to the Cenozoic because of its biologic interest. 
As a matter of fact, its duration is more nearly comparable 
to that of Permian time. a 

The curves are necessarily Cater for there was 
neither space nor necessity for greater detail. In the altitu- 
dinal curve, the upslope of the diastrophic peaks signifies 
rising diastrophism; the downslope, the period of erosion 
before the continents are low enough to have mantles of sedi- 
ment spread upon them. A greater or lesser part of the peak 
and downslope represents, therefore, the unrecorded interval 
between eras or periods, as the case may be. The tangential. 
lines drawn to the diastrophic peaks show the relation of a 


revolutions. Were the Cenozoic compressed into its normal 


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ries ¢ EVOLUTION OF THE EARTH 
relative length, the slope of the tangent drawn to its peaks 
would correspond more nearly to those of the Paleozoic. 

In the climatic line, the minor undulations indicate in a very 
general way the climatic oscillations which must have existed 
but of which we have as yet no very exact data; the larger 
movements, on the other hand, are based upon observed fact. 
The optimum embraces a normal range of temperature and 
degree of moisture; a rising curve, increased aridity; its de- 
pression, a lowering of temperature. Where the line is single 
there is a supposed uniformity of conditions the world over; 
where it splits, aridity and cold are differentiated. It is highly 
probable that with more detailed knowledge the divergence of 
the moisture and temperature curves will be more extensive. 

The life line is dotted where theory precedes the recorded 
fact, solid when actual fossils attest the truth of the assumed 
evolution. The numbers indicate the times of these first 
records as follows: 1, first vertebrates; 2, lung-fishes; 3, verte- 
brate footprints; 4, reptiles; 5, dinosaurs; 6, mammals; 7, 
birds; 8, amphibious dinosaurs; 9, archaic mammals; 10, mod- 
ernized mammals; 11, man. (Vide infra, page 144.) 


Crises OF EVOLUTION ~ q 

Origin of life. The first great crisis in the evolution: of 
organic beings was the origin of life: the marvelously subtle 
combinations attained by certain very familiar inorganic ele- 
ments, increasing their molecular complexity until a substance 
was produced endowed with the attributes of life. Of this 
momentous event we have no record, nor.does the geologic 
cause come either within the scope of our knowledge or con- 
jecture, for the time was too remote and the first living sub- 
stance too delicate to leave any decipherable record upon the 
rocks. All we can say of it is that in the fullness of time, when ~ 
the earth had, in the course of its physical evolution, become 
adapted as the abode of life, living substance came into being. 


f 
, 


t AND ITS INHABITANTS 113 
rs Establishment of the lime-secreting habit. The first re- 
corded crisis, that of the assumption of the lime-secreting 
habit—perfected by animals in the Upper Cambrian, by plants, 
“marine alge, much earlier—has again no accepted geologic 
‘cause. The importance of this crisis is doubtless not as great 
as that of many unrecorded ones which had gone before, its 
Seeenncance lying mainly in the fact that the development of 
yard parts enabled the organisms which bore them to write 
re mperishable records of their existence upon the rocks. Pre- 
vious to this, the indications of life are indirect, such as the 
accumulation of graphite, which is never produced in nature 
except as the result of organic activity; or the records are in 
the nature of the rare fossils of algz, of Protozoa (Radio- 
aria), and of the burrows of annelid worms. It may be 
"assumed that the presence of Protozoa, on the one hand, and 
of Annelida, on the other, in late Proterozoic sediments implies 
‘the existence of all the intermediate phyla of inverte- 
brates—sponges, celenterates, flat and round worms—and the 
probabilities are that all the other invertebrate groups except 
the Arthropoda were also present. 
_ The culmination of this crisis, like several which are yet to 
be discussed, did not come until long after its inception, for 
while certain creatures like the Archeocyathine (probable 
corals) and brachiopods show limy skeletons in the early 
Cambrian, others were as yet chitinous, and it is not until the 
“Middle Ordovician that the process is entirely complete. 

The definite fossil record thus established shows us that 
the evolution of great invertebrate groups occurred largely 
‘before the close of the Proterozoic, hence we may not speak 
| confidently of cause and effect. Vertebrate evolution, on the 
| other hand, lies within the period of recorded evolutionary 

history, and while there is little direct evidence regarding the 
| origin of this important phylum, the evolutionary crises 
through which it passed are entirely within the scope of our 


114 EVOLUTION OF THE EARTH 
observation. That the invertebrates also have advanced si 
the Proterozoic is certainly true, but their evolution is lar 
one of detail and does not represent the establishment of ; 
new principle or type, that is, if we except the insects. Wy 
the vertebrates, however, this is not true, for some of 1 
most momentous advances in the evolution of higher for 
lie within the range of their fossil record. 
Origin of vertebrates. ‘The distinction between the ve 
brates and invertebrates is largely dynamic, for the former 
principally motor types, the latter largely quiescent, slugs 
forms, often actually sedentary, that is, fixed in their mode 
life. A review of invertebrates, especially the aquatic for ort 
will serve to emphasize this point. The sponges are enti 
sedentary, while the celenterates are either fixed focal 
the corals or capable of very slight creeping locomotion 
the sea-anemones; or are feeble swimmers like the jelly-fisk 
subject to the whim of tidal and other marine currents, or 
the turmoil of a wind-swept sea. Of the worms, using the te 
in its old collective sense, some again are fixed, some crawlt 
some feeble swimmers, and the same is true of echinode 
and many molluscs. The arthropods are perhaps the m 
venturesome of marine invertebrates except the cephalo 
molluscs, but even to them do the same three condi 
fixedness, crawling, or none too effective swimming < 
Such as are pelagic are, like the jelly-fish, so non-resistan 
to be largely the victims of circumstance. [ 
Of all aquatic invertebrates, the cephalopods alone | 
developed locomotive powers of marked significance, but t 
locomotion is strikingly different from that of a vertebrat 
that it is the perfection of a method of jet propulsion w 
other invertebrates have also developed, although none 
carried it so far. Briefly, the perfected cephalopod, suc 
the squid (see Fig. 15), has an elongated, spindle-sh; 
body, at the hinder pointed end of which are two horizo 


rt 


AND ITS INHABITANTS IIs 
stabilizing fins that may be used for slow forward swimming 
by means of wave-like undulations. The body is enclosed in 
a muscular fold of the body-wall known as the mantle, but 
dees not fill it, leaving a space beneath known as the mantle 
cavity. There is on the under side of the well-developed 
head, with its huge eyes and long tentacles, a tubular funnel 
(Fig. 15, f) whose larger end connects with the mantle 


Fic. 15.—Squid, Lo/igo sp., capturing a fish: f, funnel. After Doflein, from 
Lull’s ‘‘Organic Evolution,’’ published by the Macmillan Company. 


cavity, the smaller one pointing forward beneath the head. 
Relaxation of the mantle permits the ingress of water into'the 
cavity; closure of the muscular margin around the animal’s 
neck, on the other hand, prohibits its egress except through 
the funnel. A forcible contraction of the entire mantle forces 
the water out in a sharp jet which impinges against the sur- 
rounding water and thus drives the creature backward at a 
very rapid rate. As compared with the easy undulatory move- 
ments of an aquatic vertebrate, however, this jet propulsion 
mode is.highly costly of effort, and its adoption by mankind 
for steam-propelled craft was to meet peculiar conditions of 
short choppy seas and a disastrously ‘“‘racing’’ screw propeller 
rather than because of any inherent virtue in the basic idea. 
Its rejection from ordinary usage is due largely to its extreme 
lack of economy. 

The cephalopods, being predaceous forms, must overtake 
their prey, and in turn must flee from devouring Cetacea for 
which they form a principal dietary staple, hence their urgent 
need of locomotion; but for the great host of invertebrate 
forms their static habitat places no premium upon locomotive 


— 


116 EVOLUTION OF THE EARTH ! 
powers, and the evolution of so marked an’ attribute as high 
speed must have some powerful incentive. The thesis has been 
advanced therefore that the main distinction between verte- 
brate—or more properly chordate—and invertebrate is largely 
a response to habitat, the invertebrate being the product of 
static waters, marine or sluggish terrestrial, where an effort 
less existence, carried hither and yon by wave and tide, wouk C 
not remove it from the environment. The chordate, on the 
other hand, is the outcome of dynamic or flowing terrestria al 
waters which enforced swimming powers as the only means of! 
resisting eviction from the realm. ‘The distinction is not on ; 
of contour, for the fusiform shape of the speedy animal is th 
result of swift movement through a more or less resista 
medium, whatever the motive power; but the segmental body 
muscles, the internal resistant axis, and the fin-like expansions 
to resist the thrust of the muscles, all are the direct outcome 0 
the mode of locomotion, that by lateral undulation of a primi. 
tively elongated body. (See Fig. 16.) ‘That this locomotive 
device might have been developed in static waters is not denied, | 
for some marine worm-like organisms swim by a wriggling 
movement, though invariably in the dorso-ventral plane, a 
there is in the sea little incentive to enforce its rapid perfec. 
tion, such as dynamic waters would produce. Hence thi 
assumption that the vertebrates are the outcome of terrestrial 
waters. To illustrate the means whereby the evolution wa: 
initiated, Chamberlin’ has discussed the peculiar habit of a 
stream-borne lamprey, Petromyzon (Fig. 16, E, left-hand eel) ' 
which adheres to the bottom by its suctorial mouth and allow: 
its body to undulate in the pulsating current as a flag is is 
whipped in the breeze or a rope of grass in the stream. Unles: 
the stream be very shallow so as to cause distinct vertical dis 
placements of the water, this undulation is always lateral o 


1 Chamberlin, T. C., “On the Habitat of the Early Vertebrates.” Jo ur. 
Geology, vol. 8, 1900, pp. 400-412. . 


1G ee —Fish forms. From ‘The Origin and Evolution of Life,’? by Henry 
_ Fairfield Osborn; copyright, 1917, by Charles Scribner’s Sons. 


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AND ITS INHABITANTS 117 
1 ‘the horizontal plane, as that is the direction of least re- 
ce because of the inhibitive force of gravity. When the 
mprey wishes to swim to maintain its position in the current, 
_ simply reproduces i in the active voice the motions imparted 
© it in the passive voice by the stream itself. More forcible 
ction drives it ahead. Such motion, consisting as it does, of 
“series of reversed curves, requires segmented muscles on 
ither side, along which alternating waves of contraction may 
ass. An axial stiffening to resist the longitudinal compres- 
on of such muscles is also necessary. This is first a pliant 
ellular membrane rendered resistant by being tensely filled 
ith liquid, next a supple rod of cartilage, and finally a bony 
xis, segmented for the sake of flexibility. The economic eff- 
a y of this undulatory mode of progression as compared 
h the jet propulsive method of the cephalopod is evident to 
yone who has observed the quick dart of a trout or the 
; n: marvelously effortless progress of a school of porpoises at the 
_ bow of a ship. 

DAs time went on, the assumption of the compact spindle 
pape of a swiftly swimming fish became, as we have argued, 
rely a speed response and not necessarily an exclusively 
am-borne attribute. Depressed grovelling forms (see Fig. 
6, C), or compressed highly specialized forms, are, however, 
sither marine or static fresh-water in habitat, never stream 
wellers. 

Tt has been argued that as the most primitive existing 
lordates, Amphioxus, the tunicates, and the adelochordates 
Balanoglossus), are marine, the ancestral chordates must 
ave been also, but their distribution corroborates the hy- 
ithesis of fresh-water origin instead of denying it, for as 
Matthew” has shown, the most ancient members of a group 
re not to be found at the old center of, evolution, but rather 


2 Matthew, W. D., “Climate and Evolution.” Ann. New York Acad. Sci., vol. 
, 1915, p. 180. 


118 EVOLUTION OF THE EARTH F. 
at the periphery of their migratory area. This is certainh 
true of these protochordates which, save for a few pelag 
forms, are all found near the continental margins in t 
shallow seas. They are all degenerate and more or les 
sedentary, and hence could not maintain themselves in thei 
fluviatile habitat and were swept into the sea—descendants o 
the unsuccessful early tyros in the art of undulatory swimmin; 
But all of this requires as an impelling cause a change ¢ 
habitat on the part of the invertebrate progenitors, eithend 
a migration of the stock from static to dynamic waters, or | 
a change in the character of the waters themselves. T 
former view entails the necessity of some force to impel tl 
migration, either the need for safety or food or the lack 
salinity on the part of flowing waters, none of which seer 
adequate to compel so radical a change, and one along a li 
of so great resistance as the evolution of the invertelam 
ancestor into the chordate implied. On the other hand, mig 
tion from the sea into sluggish terrestrial waters is mi 
readily imagined, .but affords no stimulus for chordate ev al 
tion. The picture of the Laurentian peneplain (see Fig. 17 
with its low-lying lands and slow drainage, shown by glac 
lakes, the result of recent choking of sluggish streams, s st 
gests the solution, for while intermigration under such 
ditions would doubtless be relatively easy, it would n i : 
have stimulated chordate evolution. Geology records a gr 
diastrophic movement toward the close of the Protenaaa 0 
the so-called Grand Canyon revolution, partial evidence f 
which may be seen in the 8,000 to 12,000 feet of sedi nent 
more or less conglomeratic, which were swept from mount uit 
to the eastward and accumulated in the southern Appalach uu 
region during the early part of Lower Cambrian time. ; 
great upheaval changed the face of nature in many reg 
and quickened the static terrestrial waters to rapid and w 
spread movement over all the uplifted lands. Such inver 


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AND ITS INHABITANTS 11g 
_brate stocks as could neither cling to the bottom nor stem the 
Muickening current were swept to the encircling sea and lost 
to the limnobiotic fauna; such as could, remained to people the 
fluviatile realm with creatures of a markedly higher sort. 

5 The first recorded chordate comes from the Ordovician, but 
is an armored fish-like form, an ostracoderm, of groyvelling 
abit and implied quiescent habitat (see Fig. 16, C). Such 
“types, Patten* to the contrary, can hardly be considered as the 
first expression of chordate evolution, much less annectant 
forms between the vertebrates and the higher arthropods 
which they so closely resemble; but they were rather a highly 
specialized offshoot of the primitive chordate stem, derived 
after the physical stimulus of quickened drainage had spent its 
force and times of quiescent waters had again appeared. 

The evidence points, therefore, to Chamberlin’s conclusion, 
that the place of chordate origin was the flowing land waters, 
to which may be added as the impelling cause a diastrophic 
movement which quickened the drainage, and, as the time of 
its inception, the Epi-Proterozoic interval. This crisis is there- 
fore the direct outcome of earth movement without the inter- 
vention of the climatic factor. 

_ Emergence of terrestrial vertebrates. The waters, while 
‘a very necessary stimulus to early chordate evolution, afford 
too restricted an environment for the evolution of higher 
forms, and as a consequence all vertebrates whose ancestry 
‘can be traced back through an unending line of water inhab- 
itants since the beginnings of life on earth are but fishes, and 
no matter to what degree they may have been specialized, 
they could not have risen nor can they ever rise to a higher 
plane. The emergence from the limiting waters to the limitless 
air was absolutely essential to further development and consti- 
tuted one of the greatest crises in organic evolution. 

To know the route of. such migration is of the utmost im- 


*Patten, W., “The Evolution of the Vertebrates and Their Kin,” 1912. 


120 EVOLUTION OF THE EARTH 
portance if we would find a cause. In search of this, the mind 
turns at once to the land-encircling strand or tidal zone, stretch- 
ing as it does over the many thousands of miles of the coast, 
the omnipresent frontier between land and sea. Here th 
conditions are varied, here there is food and light, and heral 
the stimulus to double-breathing is enforced by the twice daily 
baring of the zone and its consequent transition from aquatic 
to terrestrial condition and back again. with monotonous regu 
larity. But in spite of its convenience, few indeed have beer 
the stragglers of the vast army of aquatic life which have ever 
essayed its passage—land crabs and other crustaceans, certain 
molluscs, a few of the higher fishes such as the mud-skippers 
Periophthalmus and Boleophthalmus, all of which are impelled 
to a temporary or permanent migration shoreward by the nee d 
of food. And while they have developed accessory respiratory 
devices, the latter are merely spongy or other extensions of 
modifications of the water-breathing gills, and in no instance i 
there developed anything comparable in structure or ultimate 
efficiency to the terrestrial vertebrate’s lung. Such structures 
as the latter have been developed only in fresh waters, al 
fishes which show it or its homologue, the swim-bladder, being 
either fresh-water or the descendants of fresh-water forms. 
The sharks forsook their ancestral waters before or when the 
need of such a structure was felt and have never developed it: 
on the other hand, all other fishes except the cyclostomes eithet 
have it or have lost it through specialization. In the moderr 
fish, the swim-bladder has a hydrostatic function in that i 
serves to alter the specific gravity of the creature and thu 
enables it to maintain any given level in the water without 
further effort. As such, it is analogous to the water ballas 
tanks in a submersible ship, although the mechanism whereby 
the effect is produced naturally varies. ‘ 

The lungs of higher vertebrates are therefore identical with 
the swim-bladder of the fish and have retained and vastly im. 


AND ITS INHABITANTS 121 
Bproved the primal function of air breathing. This function 
is inconceivable as a prime requisite to marine life, and could 
- only have arisen in terrestrial waters beyond the limits of the 
tidal zone,* where, due to increasing aridity of climate, the 
waters became reduced to stagnant pools which had neither 
| sufficient flowage nor wave action to renew the supply of 
respirable air exhausted by the contained life. Such conditions 
prevail today in Australia, where the recurrent droughts cause 
the rivers to dwindle until only isolated pools are left. Within 
certain of these rivers, the Mary, Burnett, and Dawson, dwells 
an ancient relic form, the lung-fish or dipnoan Neoceratodus, 
which in times of habitat stagnation rises to the surface, gulps 


SRE ane 


ee ee 
(eb Re Sets Me 7 


+ Fic. 18.—Lung-fish, Neoceratodus, breathing. After Dean. 


air (Fig. 18) into its lung, a highly vascular outgrowth or 
diverticulum of the alimentary canal, and thus aérates the 
. contained blood. Other dipnoans also exist, as the African 
lung-fish, Protopterus, of the Nile, which, during times of 
_ drought, forms for itself a cocoon-like case of slime-hardened 


*See Barrell, J., “Influence of Silurian-Devonian Climates on the Rise of Air- 
_ breathing Vertebrates.” Bull. Geol. Soc. America, vol. 27, 1916, pp. 387-436. 


122 EVOLUTION OF THE EARTH 

mud in the river bottom and estivates therein; and the South - 
American lung-fish, Lepidosiren, of the Amazon River and its 
affuents, which lives near the margin of the water, using its 
lung almost with the regularity of a mammal, and also forming — 
a burrow for its habitation during the dry season. Of these 
dipnoans the latter two belong to a group of which we have 
no fossil record; Neoceratodus, on the other hand, is a relic 
of what was formerly a large and widespread group. Yet 
another order of fishes in which the air-bladder has a respira- 
tory value is the Crossopterygii, or fringe-finned ganoids, again 
an important and numerous group in the geologic past but now 


are WA CMe Le) Ke LLLE Z 
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Fic. 19.—African fringe-finned ganoid, Polpterus delhexi. After Jordan, from 
Lull’s ‘‘Organic Evolution,’’ published by the Macmillan Company. 


represented by but two genera, Polypterus (Fig. 19) and- 
Erpetoichthys, both tropical African in distribution. While 
these living genera have not so effective a respiratory device 
as the dipnoans, nevertheless they present fewer anatomical 
difficulties to stand in the way of relationship with the am- 
phibia. Without rehearsing the technical arguments, it may 
suffice to say that the generally accepted view is that the terres- 
trial vertebrates were derived either from ancient crossop- 
terygians or from a group ancestral to both them and dipnoans. 

The geologic cause which lies back of the emergence is 
apparent. Diastrophic movement during the Silurian period 
( see Fig. 14) initiated a widespread aridity which culminated 
in the latter part of the period, continued with varying intensity 
into and through Devonian time, and rose again to greater 


AND ITS INHABITANTS 123 


‘severity in the latter part of that period. This meant, as in 


Australia today, the reduction of rivers and other bodies of 


fresh water and the entailed concentration of their fauna, 
which is borne out by the mode of occurrence of the Lower 
Devonian (Old Red Sandstone) fishes—innumerable speci- 
‘mens in very restricted areas. Add to this the diminution of 


aération of these waters and it will be seen that a high premium 
would be placed upon powers of air breathing or of zstivation. 


Still further desiccation would necessitate some sort of activity 
‘during the increasingly long droughts, for the periods of torpor 


_would otherwise bear too great a ratio to the creature’s life 
span. Thus a premium would be placed upon ability to crawl 


poe ee 


=” 


ashore and maintain an active life, while the less fit would sleep 


the sleep that knows no waking, to their racial extinction. 

Aridity, therefore, would place a premium, first upon lung 
breathing, ‘the first recorded lung-breathing fish appearing in 
the Lower Devonian, although they must have existed in the 
Silurian; and later upon emergence, the entire process up to the 
perfection of the terrestrial limb covering more than the whole 
Devonian period, as the earliest known footprint of a terres- 
trial vertebrate is found in Upper Devonian rocks. 

Evolution of the terrestrial foot. The question of the evo- 


| lution of the pentadactyl hand and foot, which is the vertebrate 


standard, from the ancestral fish fin is not fully solved, but 


| much light is thrown upon it by the above-mentioned footprint, 


known to science as Thinopus antiquus and preserved in the 
Peabody Museum at Yale. The slab of sandstone bears a 
single track (Pl. III), that of a right foot having two well- 
developed digits with distinct phalangeal impressions. On the 
outer side of the second digit is a budding third, while lower 
down on the side of the foot may be seen the rudiment of a 
fourth. Rabl> has shown that the developing foot of the 


5Rabl, C., “Gedanken und Studien tiber. den Ursprung der Extremitaten.” 
Zeits. fiir wiss. Zoologie, vol. 70, 1901, pp. 474-558. 


ONG 
Fic. 20.—Development of the hind foot of a 
salamander, Triton teniatus. After Strasser, 
from. Lull’s “Organic Evolution,’’ published 
by the Macmillan Company. 


Fic. 21.—Foot of a reptile, Ranodon 
sibericus: f, fibula; 4, femur; 4, 
tibia; I, Ii, II, IV., digits 1-5. 
After Wiedersheim, from Lull’s 
‘*Organic Evolution,”’ published by 
the Macmillan Company. 


PLaTE III.—Cast of the oldest known fossil footprint, Thinopus 
antiquus, from the Upper Devonian of Pennsylvania. Original 
in the Yale University Museum. 


AND ITS INHABITANTS 125 
embryonic amphibian, Triton (Fig. 20), passes through a 
series of stages of which one corresponds precisely to the 
degree of development of the Devonian track, which, from 
E size, is probably that of an adult although yet in the 
dolescence of its race. Comparative anatomy corroborates 
this belief and completes the tale of evidence (Fig. 21), in 
that the principal axes of the foot, as shown by the distribution 
of nerves and blood-vessels, lie in the first and second digits, 
the lesser axes of digits III, IV, and V arising as lateral 
branches from that of digit II. 
With the opening of Mississippian time came increased 
moisture and in the succeeding widely extended swampy forests 
of the coal period, amphibia throve mightily and developed 
into the many sorts of so-called Stegocephalia or armored 
forms. That they still returned to their ancestral waters to 
bring forth their young, and that the latter bore gills upon the 
eck for aquatic respiration is evidenced by the actual traces 
f such structures in many fossil forms. 


Fic. 22.—Restoration of the Permian stegocephalian, Cacops 
aspidephorus. After Williston, from the Pirsson-Schuchert 
**Text-book of Geology,’’ published by John Wiley & 

Sons, Inc. 

Origin of reptiles. During the latter half of ‘the Mississip- 
pian, however, came a diastrophic movement with a wave of 
aridity, making the return to the natal waters increasingly 
dificult until many forms were forced to abandon it forever, 
and the reptiles came into being. There are today well- 
recognized criteria whereby a reptile may be distinguished 


126 EVOLUTION OF THE EARTH 
anatomically from an amphibian, but with certain forms, such 
as Cacops (Fig. 22) from the Permo-Carboniferous red beds 
of Texas, the distinction is by no means so clear, for such as 
this were transitional, Cacops being:‘yet on oe ape side 
of the frontier. | 
The change of habit induced by this ire meant a radical 
change in the character of the vertebrate egg, with the develop- 
ment of certain membranes (Fig. 23) whereby the contained 
young could respire air, unnecessary in the water-laid egg. 
Thus the terrestrial egg, typified by that of bird or reptile, is 
large, with an abundance of nutrient “‘yolk”’ for the developing 
embryo, and enclosed in a protective though porous shell. 
Two membranes are developed, the first of which, the amnion, 
is merely protective, in that the cavity between its two layers 
contains a fluid which serves to absorb mechanical shocks and 
to guard the embryo against too rapid temperature changes. 
The other membrane is known as the allantois (see Fig. 23). 
This, when fully developed, lines the inside of the shell and 
is abundantly supplied with blood-vessels, veins, arteries, and 
capillaries, which connect with the embryonic circulation. 
This is the respiratory device, for the blood coursing through 
the allantoic capillaries is thus in close osmotic relationship. 
with the air which penetrates the porous shell, and thus the 
blood is purged of its carbonic acid gas and other volatile 
impurities and receives its life-sustaining supply of oxygen. 
Such an egg must be laid on land or retained within the mother: 
until it hatches, for the contained young would drown if the 
egg were submerged, as surely as would the adult. ! 
But the development of these membranes has a still deeper 
significance, because the allantois through an added function 
becomes the intermediary between the unborn young and its” 
mammalian mother, and hence its development, due to that 
far-off climatic change, has rendered possible the highe 
(placental) mammal with all which that implies to humanity. ~ 


i AND ITS INHABITANTS 127 
_ Origin of warm blood. ‘Toward the close of the Pennsyl- 
_ yanian commenced that series of earth movements which was 
; to culminate in the Appalachian revolution and the passing of 
’ the Paleozoic, and as attendant phenomena came increasing 
i aridity and, early in Permian time, glaciation, which, in the 
southern hemisphere, exceeded in intensity and extent the 
_ so-called glacial period of the Pleistocene. 
; Aridity has its influence upon terrestrial types, at any rate 
— upon the more progressive of them, in that it places a premium 
upon traveling powers, especially upon speed, for not only 
are food and water scarce and far between, but the strife 
_ between the pursuer and pursued becomes intensified—neither 
can afford to be outdistanced by the other. This means in- 
creased metabolism, which in turn generally implies not only 
_ greater motive powers but higher temperature. With in- 
_ creasing cold a premium would be placed upon such creatures 
_ as could maintain their activity beyond the limits of the shorten- 
ing summers, and this could only be accomplished by the de- 
_velopment of some mechanism whereby a relatively constant 
temperature could be maintained within the animal regardless 
_ of external conditions; in other words, warm, as opposed to 
‘cold (really variably temperatured or poikilothermous) blood. 
_ This crisis means much, for the cold-blooded reptile has its 
most decided limitations. On the other hand, the evolution of 
the bird and mammal, the latter particularly, was rendered 
- possible by the concurrence of these two factors, aridity and 
cold. Thus while actual recorded mammals (Upper Triassic) 
and birds (Upper Jurassic) are younger in time, their incep- 
tion could hardly have been later than the Permian. Not that 
warm blood was at once attained, for that we believe to have 
_been a relatively slow process, just as was the emergence. 
Indeed, in the existing egg-laying monotreme mammals the 
blood still ranges in temperature through at least 30° F., so 
‘ with them the mechanism is not yet perfected. 


128 EVOLUTION OF THE EARTH 

Origin of mammals. ‘These forms are clearly derived from 
a reptilian stock known as the cynodonts or theriodonts (Fig 
24), in which the dentition has become differentiated as in the 
mammals into incisor, canine, and molar teeth. The reptiles 
differ from the mammals in that the lower jaw is still a 
complex of several bones, while in the mammal there is but 
one on either side. Many cynodonts were long of limb and 
must have traveled with the body well off the ground, whict 
seems to have been a prerequisite to the development of warm 
blood. ‘These cynodonts are widespread, but the evidence 
points to certain of those of Africa as nearer the direct an - 
tors of the mammals; the record of the actual transition 
however, is as yet unrevealed. 


Fic. 24.—Skull of cynodont reptile, Nythosaurus 
larvatus. Note the mammal-like tooth differ- 
entiation, but complex reptilian jaw. After 
Broom, from the Pirsson-Schuchert ‘*Text- 
book of Geology,’ published by John Wiley 
& Sons, Inc. . 


Origin of birds. Birds, on the other hand, came from 
another, unrelated reptilian stock, that which also produced 
the dinosaurs. ‘True flight, such as that which the birds de- 
veloped, has been thrice evolved among the vertebrates and 
once among the invertebrates. In the two other vertebrate 
groups, however, the flying mechanism involves not only ni 
fore limbs, as in the bird, but also the hinder pair. With th 
birds, moreover, the hind limbs, as in dinosaurs, show a dis- 


or 
Ppietea 


ty 


ton 
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Es wr 3 
\ htt 
z St 
ie 
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z it a 
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we 
s 


Fic. 23—Diagram showing the relation of the extra- 
embryonal membranes. A, bird or reptile, with 
functional yolk-sac and respiratory allantois; B, 
mammal with functionless yolk-sac and with the 
allantois converted into an umbilical cord and 
placenta. From Wilder’s ‘‘History of the Human 
Body,’’ published by Henry Holt & Company. 


aa AND ITS INHABITANTS 129 
‘tinct adaptation of another sort, that for swift movement, 
sence the bird-like hind limbs of the dinosaur—or perhaps the 
“converse of this statement would be more nearly true. Swift 
“movement, which in this instance implies bipedality, evidently 
receded flight, and its impression on the bird was so great 
hat it has never been entirely relinquished despite the attain- 
ment of the higher faculty. Whether birds passed through an 
rboreal condition or whether they arose direct from cursorial 
ypes is unknown. It hardly seems probable, however, that 
“more than one evolution occurred. We may conceive of a 
‘proavian as being at least partially arboreal and launching 
itself into the air from a convenient tree, sustained for a brief 
‘soaring glide on motionless fore limbs and tail, the scales of 
which had metamorphosed into buoyant feathers (see Fron- 
‘tispiece, A). But the first recorded instance, Archeopteryx 


long lizard-like tail of its reptilian forebears, had already 
ained the power of sustained flight, though by no means so 


Origin of dinosaurs. The same primal influence—aridity— 
| which produced the bird also gave rise to the dinosaur. 
Whether the latter came within the further influence of glacial 


cold and evolved a constant temperature of blood is not known; 
the total absence of any heat-retaining clothing in the dino- 


That their temperature rose decidedly during their periods of 
| activity is, however, a reasonable assumption. Possibly the 
| early dinosaur-like forms which dwelt within the influence of 

‘the Permian cold became the birds, while those beyond its 
influence remained dinosaurs and as such were destined to 


‘dominate the lands as no creatures before them had ever done. 


130 EVOLUTION OF THE EARTH 
of the far-famed Connecticut Valley,* for here there is a pro- 
fusion of trails of creatures great and small, quadrupeds and 
bipeds, may of which were long of limb, compact of foot, and 
impress one as being concerned with weighty matters—ques- 
tions of food or safety which would brook no delay. In 
several instances the quadrupedal resting posture is clearly 
indicated by a creature whose normal gait is that of a biped, 
but in no instance is the impressed hand that of a carnivorous 
or theropod dinosaur, whose sharply curved grasping talons 
borne on the fore limbs would have left a highly characteristic 
impression such as is never seen. That carnivores were pres- 
ent is an irresistible conclusion, and the inference is that certain 
numerous footprints made by the hind feet only, in which the 
claws, including that of a grasping hallux, were comparatively 
sharp, are attributable to such forms. That aridity does give 
rise to bipedality is evidenced by the present existence of 
several bipedal lizards, notably in our own Southwest, and in 
Australia where the frilled lizard, Chlamydosaurus, reaches 
a length of five feet and is exceedingly swift of foot. | 
Rise of sauropod dinosaurs. Climatic oscillation during the c 
Jurassic gave rise to humid conditions and this, coupled witt 

extensive low-lying delta lands along the shores of shallow 
seas, tempted certain of the increasingly large Theropoda te 
forsake the strenuous life of a carnivore for the slothful ease 
of an amphibious herbivore. These huge creatures, because 
of the increased burden of the flesh, had reacquired a quad. 
rupedal gait as had the armored dinosaurs (stegosaurs). 
They suffered no very great alteration in their dental battery, 
the teeth of which became spoon-like (Brontosaurus) or, col 
lectively, rake-like (Diplodocus), fit only for securing some 
sort of abundant vegetation, not for the rending of flesh. The 
fate of these forms and that of the armored Stegosaurus wer 


8 See Lull, R. S., “Triassic Life of the Connecticut Valley.” Connecticut Stag 
Geol. Nat. Hist. Burect: Bull. 24, 1915. 


3 AND ITS INHABITANTS 131 
curiously linked together, for although unrelated, their habitat 
and habits seem to have been very similar and their extinction 
as apparently simultaneous. What was the physical cause 
of this extinction, which is believed to have occurred in the 
‘Comanchian, we do not know, for there is little evidence of 
‘climatic change. It may have been a temporary restriction 
of habitat, but curiously enough, these dinosaurs managed to 
‘survive the uplift at the close of the Jurassic, but are ap- 
P oped unknown, with a possible exception in Patagonia, 
after the much less extensive Comanchian movement. 
All of the most impressive characteristics of both Sauro- 
‘ F oda and Stegosauria, huge size, small brain, deficient teeth, 
and, in the latter, huge upstanding plates and spines, are to 
_ the paleontologist indications of the overspecialization which 
1 he interprets as racial senility. With such forms these char- 
f cteristics, when coupled with a long period of adolescence 
and the consequent slow breeding which may safely be in- 
} Wecred, render their extinction imminent. 
__ Gadow,’ in speaking of the habits of recent crocodiles, says: 
y q “In cooler countries they hibernate in the ground; and in hot 
_ countries, which are subject to drought, some kinds estivate 
ze in the hardened mud; or they migrate. When, during a pro- 
longed drought on the island of Marajé, at the mouth of the 
Amazon, the swamps and lakes were dried up, the alligators 
‘migrated towards the nearest rivers, and many perished in the 
‘ a empt. On one farm were found 8,500 dead, and at the end 
_ of Lake Arary more than 4,000. Such occurrences in bygone 
times may perhaps explain the masses of bones found here and 
are in a fossil state.” 
_ From this it will readily be seen how small a climatic change 
“might account for the serious depletion of an army of huge 
_ forms, perhaps never very numerous as to individuals, and 


17 Gadow, H., “Amphibia and Reptiles.” Cambridge Natural History, vol. 8, 
1909, p. 447. 


> 
eat 


rae 


ee a aoee 
oe » 


I 42 EVOLUTION OF THE EARTH . 
this may have been just enough to give the final death blow to 
an expiring race. 

Final extinction of dinosaurs. In the later Cretaceous t ie 
amphibious habitat was again widespread, if indeed it ke 
ever seriously diminished after its first expansion in the Juras- 
sic, for here we find the final eflorescence of dinosaurs. The 
Sauropoda and Stegosauria had gone, but in their place were 
unarmored duck-billed dinosaurs or trachodons, fairly rapid 
runners ashore but, judging from webbed feet and compressed 
tail, as quick as crocodiles when circumstances forced their 
retreat to the waters. Heavily armored dinosaurs, the nodo- 
saurs (ankylosaurs) were present, as were the horned Ceratop- 
sia, some of which were highly grotesque beings. And to main-. 
tain the balance of power there were carnivores, both small and 
great, the latter the mightiest beasts of prey which ever walked 
the earth. Then comes their dramatic extinction, the world 
over, although they may have lost their world-wide dominance 
some time before, as we only know these late Cretaceous forms 
doubtful Patagonia excepted, from a few European localities 
and from western North America; but there they were in ng 
climax of their grandeur and there is little save the tendency y 
to overspecialization once more to warn the observer of their 
coming dissolution. But so far as our records go, not one 
dinosaur of all the hosts that were survived the Mesozoic, for 
undoubted post-Cretaceous rocks have not yielded a fragmiegy 
of their remains. 

Why they became extinct no one knows. Our chart show: 
a lowering of temperature toward the close of the Cretaceous 
and to such climatic changes reptiles are highly sensitive. 
However that may be, the great Laramide revolution which 
marks the close of the Mesozoic must have brought in a long 
chain of attendant events in consequence of which the dinosaurs 
perished. Of all factors of which we have knowledge, th 
draining of the low-lying coastal lands, with a consequent 


Fic. 25.—Tooth of a carnivorous dinosaur, 
Allosaurus, and (below) jaw of a contem- 
porary mammal, Diplocynodon. Originals 
In Yale University Museum. From Lull’s 
“Organic Evolution,’’ published by the 

| Macmillan Company. 


— |) AND ITS INHABITANTS 133 
obliteration of the amphibious habitat, seems to have been the 
most significant. Dinosaurs have been spoken of as associated 
vith peneplanation and the times of their expansive evolution 
seem to be coincident with periods of degradation rather than 
vith diastrophism, the latter having a restrictive influence. 
_ Rise of mammals. Perhaps the most remarkable thing 
thich the history of the Mesozoic brings forth is the immense 
fetiod of evolutionary stagnation on the part of the mammals. 
T ey 2re first actually recorded in the Upper Triassic rocks 
f three rather remote localities, North Carolina, Germany, 
ind South Africa, and are already differentiated in dietary 
Bravics. _ During the Mesozoic, they develop in numbers and 
ee certain extent in tooth specialization. They do not, how- 
ever, increase markedly in size, but are humble folk, so far 
ri as our records have revealed them, until the extinction of the 
enosaurs has been accomplished. One cannot but associate 
the idea of mammalian suppression with that of dinosaurian 
| ¥ ‘dominance in the relation of cause and effect, unless it shall 
| “tome day be revealed that the mammals were undergoing a 
marked evolution beyond the temperature-limited habitat of 
the reptiles. That the former showed no marked evolutionary 
advance in the place where the dinosaurs actually occurred is 
an attested fact, and the significance of the dinosaurian check 
4 is no more graphically shown than by two specimens in the 
Yale Museum. These are both of Morrison age, from what 
is known i in our records as Quarry 9 at Como Bluff, Wyoming, 
| Beccary which has produced a number of the rare mammalian 
“specimens. The striking thing, however, is the association of 
i. jaws, especially the type of Diplocynodon Marsh, with 
‘the tooth of a carnivorous dinosaur, possibly A/losaurus. The 
‘figure here reproduced (Fig. 25) is from a simultaneous 
photograph of these two specimens, which are therefore on 
exactly the same scale. The single dinosaurian tooth greatly 


¥ 
L 


‘exceeds not only the tooth of the mammal, but the containing 


ate ea 


134 EVOLUTION OF THE EARTH 
jaw or even the entire creature as the imagination conjures 
it up. 

The archaic mammals. Dinosaurian extinction heralded 
the expansion of the mammals, and-thus the basic cause of the 
overthrow of the reptilian dynasty, the Laramide revolution, 
was the enabling act in the evolution of the higher race. 
Nature now began once more to people land and sea with 
beasts of diverse sorts, both small and great; but it was onl 
the warm-blooded furry forms whose privilege it was thu 
to expand. 

The first attempt, following hard upon the dinosaurian ex 
tinction, proved to be brief of duration, as though Nature tool 
the stock she had at hand without waiting for the coming o 
more plastic types. These creatures of the first mammaliar 
expansion have been called archaic, in that while capable of 
certain degree of specialization, they were more or less stati 
in three very essential structures, feet, teeth, and brain. Ce 
tain of them were herbivores, some light-limbed, fairly speedy 
suggestive of the later cursorial ungulates, although neve 
attaining perfection as speed-adapted types. These were th 
condylarths (Pl. IV, A). Others were slow-moving, ponde: 
ous forms relying upon weapons rather than upon fleetness for 
defense. Among these latter, the amblypods, were the swarm 
dwelling Coryphodon (Pl. IV, B) and the later Dinocera 
(Pl. IV, C), with conservative molar teeth and feet andl 
surdly small brain, coupled with elephantine bulk and propo 
tions of body and limbs, but with what was superficially 
highly specialized skull having many horn-like prominenc 
and sabre-like canine teeth—a veneer of specialization over 
primitive type. q 

The flesh-eaters were in some respects better equipped h 
their plant-feeding contemporaries, but they, like the other: 
were, if one may judge from skull capacity, notoriously dull al 


| 
} 


AND ITS INHABITANTS 135 


stupid compared with the shrewdness of their modern sup- 
planters (Fig. 26). 

iv Incursion of the modernized mammals. The archaic mam- 
mals barely survived the Eocene, only one group, the hyzno- 
.. being found in Oligocene rocks: Early in the Eocene, 


“however, are seen the vanguard of an army of invaders, none 


_ of which seem directly related to the native mammals. Their 


Fic, 26.—Restoration of the creodont, Dromocyon. After Osborn, from 
Lull’s ‘Organic Evolution,’’ published by the Macmillan Company. 


| simultaneous appearance in North America and Europe 


points to a contiguous center of evolution somewhere to the 
north, either a circumpolar land or the northern part of what 


| isnow Asia. Here they underwent their primal evolution and 
| here they were endowed with the highest potentialities along 
| the three directions wherein the archaic mammals failed. 
| Climatic oscillation in the north in the early Tertiary drove 
| these modernized mammals south along the three continental 


radii, not all at once, but in a series of drives, until the competi- 


136 ~ EVOLUTION OF THE EARTH 


tion became too severe for the native inhabitants to endure. — 
Assimilation of the native stocks by such an invading army is 
impossible among animals, however it may be with mankind. | 
The archaic mammals, therefore, had but little choice. Some 
lingered on, enduring the competition until it became greater 
than they could bear, others may have migrated still farther 
south to find asylum, which served to postpone their inevitable 
fate. Yet others, a very few, may have evolved into higher 
types, such as the family Miacide of the archaic carnivores, 
although whether they deserve the stigma of genetic relation- 
ship with the other archaics in view of this potentiality is 
somewhat doubtful. | ! 

Rise of grazing mammals. The modernized invaders are 
now established in their kingdom; they are the early odd- 
toed ungulates—horses, rhinoceroses, tapirs; the even-toed un- 
gulates, such as camels, deer, and swine; the rodents; the carni- 
vores, insectivores, and primates; and in the Old World the 
proboscideans or elephants and mastodons. Continental ele- 
vation in Europe and more especially in Asia during the 
Miocene brought in its train a marked increase in aridity which 
in turn had a more or less profound effect upon the flora of 
the temperate zones, for it meant a diminution of shrubby 
and herbaceous plants and a wide expansion of the harsher 
grasses, which now become the dominant note in the world’s 
flora. ] 

This could not but affect the mammals most profoundly, 
especially the hoofed forms. Floral differentiation during the 
Oligocene had already made its impress upon certain groups, 
such as the horses, so that they in turn were differentiating 
along several lines, some with short-crowned teeth suited te 
tender herbage, others with grinders whose length and com 
plexity forecast the grazing teeth of their successors and whos 
dietary choice led in the direction of the coming grasses. Ther 
came the floral change of the Miocene and with it a rapid 


ys , 
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eet ea = > =e 
f/ j XS: s > ‘ 
> = ws > al 
ei “Ss FF ‘ 
NU r f * 2 tZB ’ 
. ; TSF Z " 
Wog ‘: : oA 1 ois 
2 2 
Xf i } ES ~ eee “8. 4 4 
47, ANS 1 b= " ‘ 
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Kony eye aie, 


SIA 


Fic. C. 


PLate IV.—Restorations of archaic mammals. A, cursorial type, Phenacodus 
primevus; B, swamp-dwelling amblypod, Coryphodon; C, four-horned 
amblypod, Dinoceras, the culmination of its race. After Lull. 


we 


AND ITS INHABITANTS 137 
‘expansion of grazing forms—horses, camels, deer—and the 
Meescriction and often the extinction of browsing types. It is 
_ true that browsing forms are still extant, but not in their old 
_ profusion nor in their old homes, while the grazing forms are 
‘numerous and characteristic of the widespread steppes the 
world over. | 
5; Origin of man. We have observed the influence of geologic 
‘change in the evolution of the brute, and we have now to 
i aquire whether mankind in his long upward course has been 
| "amenable to those same laws or whether he has been a thing 
“4 part from other forms of life, whose development has been 
controlled by other influences. As the primates, the group to 
ipbich mankind belongs, are to be classed with the modernized 
‘mammals, their course of evolution up to the point of their 
d differentiation as primates must have been one with all the 
‘test and hence the result of the same chain of causes. And 
4 their differentiation from the other mammals when they came 
tC 0 the parting of the ways seems to have been due to the de- 
parture of the latter from their primal mode of life and 
structure rather than to any special evolution of the primates 
‘themselves, for in many ways they are among the most primi- 
tive of the modernized hosts, and their tree habitations may 
well have been a very ancient habitat of the whole mammalian 
_race.® 
They throve in their northern home just as did their other 
| compatriots, and like them drove southward along the several 
~ continental radii, the rear guard drawing in toward the equator 
| with the northern limits of the tropical forests within which 
| they dwelt and upon which, with rare exceptions, they are 
| _ dependent to this day for food and safety. They reached 
' North America, as the map (Fig. 27) indicates, early in 
* Eocene time (Wasatch) and became so abundant as to form a 


|< 8 Matthew, W. D., “The Arboreal Ancestry of the Mammalia.” Amer. Nat., 
vol. 38, 1904, pp. 811-818. 


138 EVOLUTION OF THE EARTH 

high percentage of certain fossil faunas. Here they throve 
until the close of the Eocene, when they died out, and North 
America knew no more primates until the coming of man. 
They had, however, crossed the isthmian land-bridge or its 
equivalent into South America, where they still persist. 


DISTRIBUTION OF PRIMAT 


ES Movern Anturopoinea {Mont ys APES BAB 
Tn ” Lemuropta (LEMURS ,LORIS, TARSIER 
E, Eocene (ano Oligocene Lemuroins 
0, Oricocene AntHropoins 
| M, Miocene 

P, Puocene ” 


Fic. 27.—Map showing the geographical distribution of the primates, living 
and extinct, and their indicated dispersal from Holarctica. After Matthew, 
from ‘‘Problems of American Geology,’’ 1915, published by Yale Uni- 
versity Press. 


In Europe, the history of primates below man was similar — 
to that in North America, marked by Eocene abundance and — 
synchronous extinction, but during the Miocene, at the time — 
of the proboscidean migrations, they reappeared, probably ~ 
from Africa, to suffer a second extinction during the Pleisto- 


AND ITS INHABITANTS 139 
zene. While the sub-human primates are now extinct on the 
“Asiatic mainland north of the great Himalayan uplift, they 
till persist in tropical Asia, in India, Indo-China, the East 
indies, Japan, and the Philippines. ‘ted are also extant in 
ropical Africa. 
_ Anthropoid apes. Man’s nearest blood relatives, whatever 
lay be his prejudice in the matter, are the so-called anthropoid 
i‘. man-like apes: the orang, chimpanzee, gorilla, and gibbon, 
i descendants from the same stock which gave rise to hu- 
lanity and perhaps fallen to their present condition through 
being the victims of circumstances. That man owes his higher 
estate, at least in part, to his past environments we shall 
‘endeavor to show. 
% eof the great apes, the orang-utan is one of the most familiar, 
or it and the chimpanzee are the kinds most frequently seen 
| n captivity. The orang is readily distinguished, however, by 
its reddish hair. It is rarely more than four feet tall but is 
C elatively of great girth, which, together with an arm spread 
: f upward of seven and a half feet, gives it a remarkable 
ppearance. ‘The jaws are powerful, with large canine teeth, 
but the hands are the chief weapons of defense. The great 
of the orang renders it less agile than the gibbon, for 
4 : ance (see page 140), and it climbs somewhat laboriously as 
does a man. It is highly intelligent but sluggish, stirred to 
r ction only by some powerful incentive such as hunger. 
‘Orangs are today confined to the dense somber forests of 
Bomeo and Sumatra, but the fossil remains of their ancestors 
some from the Siwalik Hills on the Asiatic mainland and thus 
| etray the course of their migration. 
, B The chimpanzee and gorilla are both African in distribution, 
| alt hough also of Asiatic stock. ‘They are perhaps the nearest 
to mankind in blood relationship. The chimpanzee may 
readily be distinguished from the orang by its black hair. It is 
so taller, although never exceeding five feet, and is less bulky 


as 
im 


= ina = J 
. 


140 EVOLUTION OF THE EARTH 
and hence more active, swinging from tree to tree by the han¢ 
with great agility. They rest in the sitting posture, sometim 
stand or walk, but run on all fours. Jaws and teeth are * 
chief defense. 

The gorilla (Fig. 28) is by far the most. formidable of 4 
the great apes, for its huge size and strength and its unparz 
leled ferocity make it a veritable terror. An authentic rf 
corded size makes the gorilla five feet one and one-half inche 
tall and 418 pounds in weight. Its lower limbs, whi 
enormously powerful, are disproportionately short. If 
limbs bore a human proportion to the torso, the creatur 
would stand at least seven feet in height, with a weight 1 
half a thousand pounds! The huge size of this ape has fore 
it to become partially terrestrial, but instead of becomi 
more man-like as an adaptation to ground-living, it has tak 
a yet more brutal aspect, more like a bear than a human bein 

All of these apes, the orang, chimpanzee, and gorilla, ; 
degenerating from the higher condition of their comm 
ancestor with mankind, the chimpanzee least, the gorilla me 
of all. The gibbons (Fig. 29), however, of which there ar 
several species, while the most remote from mankind in actt 
relationship, have probably retained in greater degree th 
any others the habits and development of the anthropoid stem 
form. They are wonderful acrobats, their relatively small siz 
and immensely long and powerful arms lending themselves t 
the full measure of arboreal progression. The gibbons ar 
oriental in distribution, living in the wooded regions of south 
eastern Asia and the islands of Sumatra, Borneo, and Java. _ 

It were well to dwell for a moment upon the locomotiy 
methods of these apes which, instead of running upon th 
upper side of the branches, as do most arboreal forms, swim 
beneath them by means of their hands. This method of loce 
motion has been called brachiation (Lat. brachium, arm) am 
in all probability took its rise with the earliest anthropoids 


Fic. 28.—Gorilla, Gorilla gorilla. From ‘“The 
American Natural History,’? by William T. 
Hornaday; copyright, 1904, 1914, by William 
T. Hornaday; published by Charles Scribner’s 
Sons. 


AND ITS INHABITANTS EAI 
aching its highest development in the modern gibbon. On 
1e ground, the gibbon walks erect, either touching the knuckles 
f the hands to the ground or with the arms held above the 
ead. The gait is quick, waddling, with no elasticity of step, 
nd they are soon overtaken. But in the trees they are virtu- 
lly transformed, for their hand leaps are prodigious, twelve, 
ighteen, one authority says no less than forty feet being 
eared, and that for hours at a time. Fully to appreciate 
hat this means one should compare it with the precise 
iechanical stride of a racehorse, for whereas in the horse 
tere is a practical uniformity of conditions stride after stride, 
vith the gibbon no two hand leaps can be the same, and each 
me such a thing is essayed a problem must be solved, for in 
rder neither to over- nor under-shoot the mark, the right 
+ oo of force must be used, and this varies with the distance 
ind the ability of the objective branch or branches to bear 
&. creature's weight. Thus, as with a gun pointer, the aim, 
stance, trajectory, windage, and in addition the varying 
force, all must be taken into consideration; in the present 
instance, moreover, the problem must be solved and its prac- 
tical application brought about instantly, and the penalty for 
error either in solution or application may be death. Even 
though the process becomes automatic, the result of much 
i experience, there is, nevertheless, a high premium placed upon 
ee tal acuteness, and the weeding out of the unfit is ruthless. 
A \dd to this the fact that the hands may be used to bring objects 
before the face for examination, thus inciting the powers of 
Observation, and two great stimuli to higher mentality are 


- tained There is reason to believe that the human precursor, | 


| before leaving the sheltered life of an arboreal primate, pro- 
4 ressed and acted much as do the gibbons, with a consequent 
kening of intellect as time went on. 

| Descent from the trees.. But while tree-life had much to do 
witl the prehuman evolution of our ancestors, the arboreal 


142 EVOLUTION OF THE EARTH 
is, after all, a limited environment and the descent to the tet 
restrial habitat was as necessary to further evolution manwards 
as was that older emergence .upon land on the part of ou 
piscine ancestry. In the former case as in the latter, the actual 
attainment of the terrestrial habitat is supposed to have been 
forced by geologic change of a very similar character. Th 
presumption is that central Asia was the evolutionary cente 
of the anthropoids and so far as our records go this is born 
out by the fossils, the oldest of which are found in the Siwali 
Hills of northern India in rocks of Lower Pliocene age. Fr on 
this center of radiation these primates took their departure 
the gorilla and chimpanzee southwestwardly toward the Darl 
Continent, while the gibbons and orang went toward the south 
east. The prehuman, on the other hand, remained in centra 
Asia nearest the dispersal center, which, we have seen, 1 
generally true of the latest and most highly specialized of 
race. The forms which migrated southward felt the enerva 
ing languor of the tropics and remained static, if they did no 
actually retrogress, whereas the prehuman in the more invig 
orating and variable climate progressed in his evolution towar 
a higher type. Central Asia has proved to be the theate 
wherein the highest mammalian evolution could be attainec 
for here the forms which man has chosen for his companion 
the domestic animals, almost without exception attained thei 
evolutionary completion. 

The actual descent from the trees seems to have been dt 
to a chain of events which in many ways parallel those which 
impelled the emergence.? The Miocene uplift, with the co 
sequent aridity, has been mentioned. As a direct result, th 
stupendous barrier of the Himalayas began to arise, cuttif 
off the forests of central Asia from their old-time contin 
with those in India, and thereby severing the lines of com 


® Barrell, J., “Probable Relations of Climatic Change to the Origin of t P| 
Tertiary Ape-man.” Scientific Monthly, January, 1917, pp. 16-26. = 


Fic. 29.—Gibbon, Hylobates lar. 


Fret ect mag 


| AND ITS INHABITANTS 143 
munication by which the anthropoids had left the cradle of 
their evolution. Miocene and Pliocene aridity diminished the 
northern forests, as Devonian aridity had diminished the 
terrestrial waters, until finally there were detached wooded 
areas within which the contained primates were as isolated as 
is the orang on sea-girt Borneo and Sumatra today. Further 
diminution compelled the descent to the ground on the part of 
the larger and more intelligent forms among them and the 
destruction of such as could not meet terrestrial competition. 
Thus a man-like tree-born primate became an earth-borne 
creature which from sheer necessity ultimately arose to man’s 
estate. This meant the assumption of the erect posture and 
the lengthening and strengthening of the lower limbs for speed, 
while the hands, released from the fetters of their earlier loco- 
otive function, became the organs of the mind. Now man 
had to compete with the mighty carnivores, and as nature had 
ill endowed him with defensive weapons he had to devise crude 
armaments of stick or stone with which to insure his survival. 
[he dwindling forests, especially as their tropical character 
nad gone, no longer supplied an easily gained livelihood, and 
sustenance had to be sought from other sources, mainly from 
among the feebler of man’s fellow creatures. It is probable 
at he also utilized the seeds of grasses which grew along 
the margins of the forests, the ancestors of our domesticated 
2ins. 
Increasing severity of winters, prophetic of the Glacial 
Period, necessitated some further means of keeping warm, 
and man utilized for clothing the skins of beasts which he had 
slain and later harnessed fire to his use. In common with the 
other primates, the precursors of mankind were doubtless 
gregarious, probably submitting to the leadership of such as 
iby strength or cunning could enforce their authority, but not 
jantil the terrestrial life was attained was the higher communal 
ife with codperative division of labor possible. 


144 EVOLUTION OF THE EARTH 
By means of this codperation and his individual prowes 
man has attained dominion over the organic world, whil 
through his subduing of nature’s forces he conquers all o: 
her varied realms from the equator to the poles, adapting him 
self to environments which mold their creature denizens most 
profoundly and through which he passes unimpressed by the 
laws which compel their adaptation, for he is swifter than th 
eagle in his flight and he passes through the waste of the 
waters unscathed by nature, a victim, if such he be, only t 
others of his own kind (Fig. 30). 
SUMMARY 4 
As the physician, by a clever device, can record graphically) 
the pulsations in the blood stream which are synchronous wit 
the throbbing of the human heart, so I have drawn a curve te 
show the correspondence between the pulse of life and thi 
heavings of the earth’s broad breast. In this curve (Fig. 14) 
the evolutionary crises and periods of expansive evolution ar 
represented by upward movements, while extinctions are indi 
cated by the downward plunge of the racial line. ‘This curve 
is broken where as yet we have no tangible evidence to validat 
our theory, solid when the fossil record changes theory int 
fact. if 
Thus the first recorded crisis, the origin of vertebrates, i 
drawn coincident with the revolution at the close of the Pro 
-terozoic era, but the actual vertebrate record begins in mid 
Ordovician time at the numeral 1. The development of lung 
is connected with the disturbance at the close of the Siluriai 
uplift, the first recorded lung-fishes appearing at the numeral 2, 
in the Lower Devonian, while the first footprint at 3, in th 
Upper Devonian, completes the evolutionary movement. Th 
Mississippian is a time of expansive evolution of the stego 
cephalians, while the establishment of the reptiles was th 
result of aridity toward its close, hence synchronous with th 


° 


Fic. 30.—Photograph of a submarine, 
twenty feet below the surface, taken 
from the aeroplane whose shadow is 
shown in the picture. From London 
Illustrated News. 


iL AND ITS INHABITANTS 145 
uachita uplift. The culmination of the wide disturbances at 
the close of the Pennsylvanian brought on aridity and glacia- 

on in the early Permian, with the beginnings of the warm- 
ooded stocks, birds and mammals, although the first recorded 
rd at 7 is Upper Jurassic and the first known mammals at 6 
rp per Triassic. Aridity has been regarded as the chief incen- 
tive to dinosaurian evolution, the actual record at 5 beginning 

in the Lower Trias. The differentiation of the Sauropoda, a 
res ponse to the expansion of the amphibious aquatic realm, may 
uve been Triassic, but in greater probability the subsidence 
hich followed the Palisade diastrophic movement late in 
le Triassic may be nearer to the actual time. They first 
& | spear in the Lower Jurassic, but do not culminate until early 
omanchian, shortly after which they suffer extinction from 
own causes, geologically speaking. The other dinosaurs 
radually i increase in numbers, size, and specialization, until 
th oe of the Cretaceous, when, with the movements which 
ninate in the Laramide revolution, en plunge into extinc- 


#1 


Nn. 
| The curve of mammalian evolution is perhaps the most 
striki ing of all, consisting as it does of minor fluctuations which 
nay represent accident of preservation and recovery rather 
periods of evolutionary expansion, as is equally true of the 
z osaurian curve. Then with the Laramide revolution and 
he coincident dinosaurian extinction comes the rapid mamma- 
Tian deployment, the archaic mammals, first known in the basal 
cene at 9, becoming fewer and less important, although 
er casing in specialization until their final extinction in the 
Middle Oligocene. With the fluctuating climate of the north- 
ern area come the modernized forms, first known in the Lower 
Eocene at 10, then the differentiation of browsing and grazing 
for s, followed by a restrictive evolution of the former and 
wide expansion of the latter consequent upon the Miocene 
lift and its resultant aridity. While the primate line is solid, 


146 EVOLUTION OF THE EARTH |. 
the derived human line is broken to the point 11, the 
actual record of man; the descent from the trees is, howeve 
made coincident with the Himalayan uplift and with the i 
creasing aridity of the Miocene. 

Man’s intellectual and spiritual rise and his dominanen ove 
the forces of nature and over the brute creation are shor 
graphically by the height to which his line ascends above the 
highest crest of the evolutionary crises which have gone befor 
For this dominance the Cascadian revolution with its recur e 
periods of devastating cold, out of which we are emergin 
must be looked upon as a contributory cause. 7 

Thus time has wrought great changes in earth and sea, a 
these changes, acting directly or through climate, have alw 
found somewhere in the unending chain of living beings cert: 
groups whose plasticity permitted their adaptation to the ne) 
arising conditions. 3 i 

The great heart of nature beats, its throbbing stiniul eee : 
pulse of life, and not until that heart is stilled forever will t 
rhythmic tide of evolution cease to flow. 


CHAPTER V 


CLIMATE AND THE EVOLUTION OF 
CIVILIZATION 


ELLSWORTH HUNTINGTON 
RESEARCH ASSOCIATE IN GEOGRAPHY IN YALE UNIVERSITY 


FACTORS IN HUMAN PROGRESS 


N progress depends upon three great factors. The 
I taherent mental capacity, the second material resources, 
oh third energy. If any of these is lacking, civilization 
lates or even retrogrades. Where all are present civiliza- 
| | moves onward. How far do these three depend upon 
sical environment? How far does man’s higher evolution 
’ with the evolution of plants and animals discussed in 
vious lectures? At first sight it appears as if there were 
teat gap between the evolution of man’s body which this 
rse of lectures has thus far considered, and of the mind 
ich is the subject now before us. In one sense there is 
oubtedly such a gap. Yet the more we study the matter, 
more we see that from the lowest protozoan to the highest 
osopher a marvelous unity pervades all nature. 
ll progress in civilization, whether material or moral, 
arises from ideas in the minds of individuals. Therefore the 
st requisite of any advance is men with unusually gifted 
minds. Some races seem to be capable of producing such men 
jn far greater numbers than do others. We rightly think of 
me¢ient Greece as preéminent in this respect. Galton, the 
founder of modern eugenics, has said that the average Athe- 


eS a = «an = = ee 


148 EVOLUTION OF THE EARTH 
nian in the age of Pericles was as much superior to the averag 
Englishman of today as the Englishman is superior to th 
African. Although a few students still claim that all race 
possess equal possibilities if given equal opportunities, thei 
conclusions lack statistical foundation. Judged by thei 
achievements and by all the exact tests yet available, race 
differ as do individuals, although not to so great an extent. — 
What causes these racial differences? We cannot answe 
until the biologists give us more light on the origin of the ney 
forms called mutants. If it be asked, however, what pr 
serves the mutants and thus gives rise to new racial qualitie: 
we can answer with considerable certainty. Environment b 
means of natural selection allows some types to perpetuat 
themselves indefinitely, while it rigidly exterminates other 
Among the various environmental factors, climate is appar 
ently the most important. As Professor Lull has said in 
previous lecture: “Changing environmental conditions stim 
late the sluggish evolutionary stream to quickened movemen 
Whenever it has been possible to connect cause and effect, 
the immediate influence is found to be generally one of 
climate.” e 
Inherent mental capacity. The American Indians seem t 
furnish one of the best examples of the influence of clima 
upon mental capacities. Practically all authorities agree that 
the Indian is endowed with a relatively conservative type « 
mind. He has great powers of observation, of patience, 
endurance, and also of action when some crisis suddenly sti 
him. He is lacking, however, in originality, in the power | 
adaptation, and in the quick insight and inventiveness whit 
make the Japanese so competent in seizing what they want 
European civilization. It has been suggested that the mental 
capacities and traits of the Indians have been modified by t 


1 For a fuller discussion of this matter see “The Red Man’s Continent,” vale : 
University Press, 1918. 


z AND ITS INHABITANTS 149 


yay of Bering Strait. If that is the case, they must have spent 
many generations in the extremely trying environment of the 

ar North where the January temperature averages 10° F. 
below zero, and where the winter night lasts months. Such an 


upon itself and in time gives way. ‘The type that survives is 
the phlegmatic man who can sit idly for weeks inside his stuffy 
hut, and not care whether anything happens or not. When 
they left the primitive home of man in Asia, the ancestors of 
the Indians presumably had minds like those of their neighbors 
who became the fathers of other races. When they emerged 
from their long sojourn in the Far North, however, they had 
lost some of their most valuable qualities. 
_ In the same way the European Nordics possess the type of 
mind to be expected of a race that has always lived in a stimu- 
lating climate. The Japanese show similar characteristics to 
an almost equal degree. It is significant that although these 
two races pushed out from central Asia in opposite directions, 
neither was ever forced far to the north or south, and each 
finds its present home in one of the world’s best climates. 
Neither race, however, has evolved in a uniform climate, for 
changes due to the Glacial Period, especially in Europe, have 
forced them to endure repeated epochs of stress. The stress, 
however, was of a stimulating kind because it was apparently 
characterized by variability and not by the monotonous uni- 
formity of the Far North or the equator.. The African 
negroes, on the other hand, have by no means been so fortu- 
nate. Because their migrations led them into southerly regions 
|they suffered a repressive evolution much like that of the 
Indians. In tropical regions the energetic types unfortunately 


150 EVOLUTION OF THE EARTH 
kill themselves by overexertion. Activity accelerates the pro 
esses of metabolism and generates toxic poisons. In the right” 
kind of climate these are eliminated during periods of rest. 
a warm climate, however, the high temperature appears to’ 
cause excessive chemical activity of the protoplasm just as does 
exercise. Hence people feel tired even without exertion. When 
bacteria attack such people, they find a ready prey, and when 
the effects of activity and of heat are combined the result is often - 
fatal. The exact mechanism of the process has not yet been de- 
termined, but some such poisoning of the system and consequen 
elimination of unduly active types appears to be one of thx 
reasons why the negro has acquired a comparatively indolen 
character. 
Among the backward natives of Australia the elimination o 
energetic, nervously alert people has gone farther than among 
the negroes. The Australians in crossing the torrid zone were 
subjected to all the evils which have weakened the mental 
powers of the negroes. They also suffered a terrible handicap _ 
because their tropical experience was the precursor of af 
equally strenuous repression by the desert. There sudden and 
intense activity is at a premium when the water dries up and 
a long march must be made to a new supply. The most 
essential of all qualities, however, is the ability to endure | 
hunger, thirst, and heat indefinitely, a kind of endurance which | 
is much harder on people with alert nerves than upon those 
of stolid disposition. Moreover, mental alertness loses muc 
of its importance as a factor in natural selection when th 
environment becomes so poor that there are almost no materia 
resources. It is by no means strange, then, that the Aus 
tralian bushmen, even more than their fellow sufferers, t 
Hottentots of South Africa, show, as it were, the combi 
weaknesses of the tropical negroes and of the desert peop 
of Arabia. One might go on to discuss this theme in relatio 
to all the races of the earth. Such a discussion would appat 
ently strengthen the conclusion that while the mental inhe it. 


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OS SS a TN aD aN eal 


AND ITS INHABITANTS 151 


‘tg nce of an individual may show no apparent relation to his 


4 ipress of the ieatit environments through which his race 


has passed. 
Material resources. Material resources are no less im- 
portant than innate capacity in their effect upon civilization. 


1 hey are, if anything, still more closely connected with climate. 


A Socrates with no resources except the sands of Arabia to 
support himself and his ideas would never have been heard of. 
ohammed had to live in an oasis and not in the sand. His 
religion would not today dominate nearly a seventh of man- 
kind if it had not speedily spread to places with abundant 
material resources. The Eskimos show the importance of 
material resources still more clearly. Though possessing the 
same power of passive, nerveless endurance which is character- 
ow of the Indians, these people of the snow and ice seem to 
“have a strain of inventive ability. Their stone lamps, their 
drills for lighting a fire by twirling one stick upon another, 
_their clever boats which make a man and his canoe parts of 
a single watertight structure, all show the earmarks of in- 
‘genious minds. Nevertheless, civilization has not made prog- 
“ress among the Eskimos. Even if they were not afflicted with 
the inertia of the North, the absence of material resources 
almost forbids a high civilization. Here, as in so many other 
“cases, climate is the factor which mainly determines the re- 
“sources. No crops will grow and even the reindeer does not 
thrive i in many parts of the Eskimo coasts, hence hunting is 
- the only possible mode of life. Hunters must be nomadic. 
‘They cannot accumulate any large amount of the material 
Bessources which are needed as aids to progress. If the white 
“man with his claims to superiority were placed in the home 
“of the Eskimos with no outside resources, would it be more 
than a few generations before his mode of life and manner of 
thought would be much like theirs? The retrogression of the 


oo 


| 


2 


Teo EVOLUTION OF THE EARTH | 
white fishermen in northern Newfoundland and Labradoi 
where the conditions are much better than in the home of the - 
Eskimos, is a pointed answer to this question. | 

The effect of climate upon material resources and of ma- | 
terial resources upon civilization is well illustrated by a com- — 
parison of the Indians of California and Utah with a 
Pueblo neighbors in New Mexico. The pre-Columbian in- 
habitants of California and Utah were abject savages. a 


| 


dwelt in flimsy brush huts, and ate rabbits, lizards, grass- 
hoppers, acorns, and other equally poor kinds of food. 
Because food was so scanty they lived in very small comma 
ties, and were forced frequently to move from place to place. | 
Because of their wandering, isolated life they had only the 
rudiments of social and political organization. All in all, 
they were well-nigh the lowest of the American aborigines. 
The Pueblo Indians, on the other hand, had risen far beyond 
mere savagery and were well along in the stage of culture - 
known as barbarism. They had an excellent diet of corn, 
beans, and squashes, with enough meat to keep them in health. | 
Not being obliged to wander, they lived in compact, well-made 
adobe houses. Their villages were large enough and neal 
enough to one another so that intercourse was frequent, hence 
they had a highly organized social and governmental system. 
They had also developed a series of complex religious cere- 
monials that did much credit to their mental powers. Among 
the aboriginal people of America they stood not far from | 
the top. é | 
The contrast between these two neighboring types was ap- : 
parently not due to racial differences. The Hopis, who were — 
among the most advanced Pueblo people, were apparently _ 
of the same race as the Utes, who were among the lowest of — 
the other type. Material resources seem to have been the _ 
main cause of the contrast. ‘The Pueblos had behind them | 
the resources of agriculture, while their savage neighbors — 


bey 
f 


: AND ITS INHABITANTS 153 
could not raise crops. This difference was due to climate. At 
‘first sight the climates of the two regions appear closely 
similar. Both are dry. Salt Lake City, in the home of the 
| Utes, for example, has an average rainfall of sixteen inches 
per year. Los Angeles, where lived some of the lowest Cali- 
fc ornia Indians, has the same. Santa Fé, in the center of the 
_ Pueblo district, receives a yearly average of nearly fifteen 
inches. Why, then, was agriculture and hence civilization so 
different in the two types? The answer is found in the 
_ season of rainfall. At Santa Fé the months of June, July, and 
August have an average of 8.4 inches of rainfall, whereas at 
- Salt Lake City the same months average only 2.2 inches, and 
_ at Los Angeles are practically rainless. 
| s _ Today the greatness of California depends upon its farms 
more than upon any other material feature; and the farms of 
Utah are also by no means to be despised. It must be remem- 
yered, however, that wheat, barley, beets, grapes, oranges, and 
Bother orchard fruits are the staples of agriculture in these 
} # ‘regions. They are raised largely by means of elaborate sys- 
_ tems of irrigation which utilize the winter snows upon the 
mountains. Where irrigation is not practised, cattle are the 
‘great agricultural resource. The other foundation of pros- 
perity is mining. All these things are essentially European. 
The crops which place parts of California and Utah among 
‘¢ he world’s garden plots are not indigenous to America. The 
_ cattle and horses which browse on a thousand brown hillsides 
5 had no counterpart in the New World before Columbus. Since 
iron tools were unknown, the art of mining was impossible. So 
¢ ar as anyone has yet pointed out, the poor Indians had no 
& plants that would serve in place of those with which the early 
¥ people of the Old World were blessed. The absence of sum- 
ia mer rain which is typical of all subtropical climates caused the 
" vegetation to be scanty, and hence wild animals, wild seeds, and 
fruits were also scarce. Thus the people were condemned to be 


154 EVOLUTION OF THE EARTH 
nomadic hunters and to remain in the lowest stage of civiliza- 
tion. : 

Turn now to the Pueblo region. A rainfall of six or eight — 
inches in the three summer months seems insignificant. Yet 
it made all the difference between savagery and barbarism. _ 
In its absence the Utes and the California Indians were 
as much below the Hopis and the other Pueblo tribes as the _ 
Pueblos are below modern Europeans. The one great cereal 
of the New World is Indian corn. The two other staple — 
crops capable of being raised in the dry regions of pre- | 
Columbian America were beans and pumpkins. All of these — 
can grow where there is moisture in summer, but not otherwise. _ 
To raise them by irrigation in places like Utah and California — 
is practically impossible for primitive people. On all except 
the larger streams, whose control is beyond the power of — 
beginners, the floods come to an end long before the time when — 
the crops most need them. Where the Pueblos live, however, — 
the summer rains produce floods just when the corn, beans, — 
and pumpkins are most eager for water. Hence these crops 
provided the early Americans with the basis for a well- 
developed system of agriculture, and progress was assured. | 
Even if the Utes and the Indians of California had been more _ 
inventive than the Pueblo Indians and had produced men with _ 
minds of unusual brilliancy, the lack of material resources — 
adapted to the early stages of development would probably © 
have kept them permanently in savagery. 5 

The material resources thus far mentioned depend upon 
climate. In this they are like nine-tenths of the world’s re- 
sources. All kinds of food, all kinds of clothing, and a large 
part of the materials used for shelter depend absolutely upon 
climate. Perhaps there is some exception to this statement, 
but I have searched for it in vain. . The fish of the sea, the 
fowl of the air, and the beasts of the field, even though they | 
may prey upon other animals, are in the last analysis wholly } 


e AND ITS INHABITANTS 155 
_ dependent upon the vegetation which feeds either them or 
_ their prey. Vegetation is absolutely dependent upon tempera- 
' ture, rainfall, winds, ocean currents, and other climatic con- 
_ ditions. Soil, to be sure, is of much importance, but all soils 
_ would be moderately fertile if they had never been subjected 
to any except a favorable climate. There would be no great — 
__wastes of sand, salt, gravel, or naked rock, for these arise 
_ only under aridity, glaciation, high wind, or other extremes. 
; In spite of the overwhelming preponderance of climate in 
_ determining the nature of material resources, certain articles, 
__ such as iron and coal, occur with little reference to heat or cold, 
_ moisture or drought. Their use, however, depends largely 
upon climatic conditions. Iron was well known in Mediter- 
_ ranean lands at the time of their highest civilization. Never- 
theless, its use was strictly limited by the scarcity of fuel in a 
_ subtropical climate. Only when iron was smelted in countries 
like England where the climate fostered dense forests did its 
__use increase rapidly. When the value of coal was at last 
realized it added wonderfully to man’s material resources. 
_ Yet even here the limitations of climate are strict. In Alaska 
_ today the presence of coal does little to advance civilization. 
"It brings a group of coal miners whose chief desire is to make 
P money enough to enable them to get home again. Because 
_ Alaska is so cold and inhospitable the regions with better 
| i climates farther south are the ones that profit by its coal. So, 
__ too, with the iron mines of Gellivara in northern Sweden. A 
. _ few small towns have sprung up, but the places chiefly benefited 
4 are the cities of southern Sweden where the climate is less 
_ Severe. Thus it appears that all kinds of resources are strictly 
| limited by climate either in their occurrence or in their use. 
| Energy. The importance of energy in advancing civiliza- 
tion is not so well understood as that of inherent mental 
v "capacity and material resources. Darwin says that the latent 
_ capacities with which most men are endowed are so great 


en -z 0 . 


156 EVOLUTION OF THE EARTH 
that inherent ability is less important than the zeal and deter- 
mination, or in other words, the energy with which that ability — 
is used. In our own experience have we not scores of times — 
had good ideas—perhaps revolutionary ideas—with which we — 
toyed for an hour or a day, only to forget them because we had ~ 
not the energy to undertake the hard work necessary to bring — 
them to fruition? Such energy is needed not only by the indi- — 
viduals of unusual capacity who make the great inventions, — 
but also by the people around them who must put the new — 
ideas into effect. ‘We have but partly solved the mysteries © 
of the progress of civilization —when we have pointed out — 
that each tangible stage of progress owed its initiative to a — 
new invention or discovery of science. To go to the root of — 
the matter we must needs explain how it came about that a 
given generation of men was in a mental mood to receive the — 
new invention or discovery.” The necessary mental mood 
is ‘alertness,’ which is merely a manifestation of energy. 
Therefore it would seem that in the march of civilization — 
energy is quite as important as either inherent mental capacity _ 
or material resources. Energy is partly the result of proper — 
food, clothing, and shelter, partly the result of inherited 
ability, and partly the result of freedom from specific disease. _ 
All these things depend in large measure upon climate. Back — 
of all, however, lies something else. Everyone knows that | 
he may be well fed, well dressed, well housed, of good ancestry, — 
and free from specific disease, and yet may not feel like wor 
even when he has no special occasion to be tired. Apparently 
the thing that is needed is the stimulus of the right kind of — 
climate. Health is one thing; full efficiency is quite another. 

Effect of climate upon man’s efficiency. This matter is so 


AND ITS INHABITANTS 157 
merable indirect effects through inheritance and material re- 
ssources. In this he appears to be like all other organisms. 
For every species of living being there is apparently a certain 
optimum or most favorable condition. As the temperature, 
humidity, or other climatic elements depart more and more 
widely from the optimum, the animal’s reproductive rate 
diminishes, its general strength declines, it becomes more 
susceptible to disease, and its life is shortened. Between the 
optimum conditions and those which cause death there may be 
| a wide range in which life and even health are possible, but 
in which the organism is not at its best. 
One of the great lessons of biology is that man’s physio- 
logical nature is essentially the same as that of the lower 
animals. A law which applies universally to them applies also 
to him. This is eminently true in respect to climate. By 
a easuring the rate of reproduction of infusoria, the rate of 
growth of plants, the amount of oxygen consumed by crayfish, 
or the length of life of the boll weevil we can arrive at an exact 
estimate of the effect of climate upon these various organisms. 
Inthe same way we can measure man’s response to climate and 
find out just what conditions are the best and how much harm 
is done by departures from the ideal. Thus far man’s physical 
relation to climate has been tested chiefly in the following 
ways: (1) by frequent measurements of the weight of healthy 
ersons or of those suffering from tubercular or other diseases, 
(2) by daily or weekly tests of people’s strength, (3) by 
_ €xamination of the amount of work done by specially chosen 
subjects or by piece workers in factories day after day 
throughout long periods, (4) by measuring the amount of 
tarbon dioxide given off in the breath of people who are at 
fest under various climatic conditions, (5) by tabulating 
| people’s estimates of their own feelings of comfort or dis- 
Bemfort at different temperatures and humidities, and (6) by 
ertaining the amount of sickness and death at different 


158 EVOLUTION OF THE EARTH 
seasons and comparing these with the weather. All of these 
methods yield substantially the same results. So far as 
temperature is concerned they indicate that people’s health is 
best and their physical energy greatest when the average 
temperature for day and night together is from 60° to 68° F., 
which means when the noon temperature ranges from about 
65° to.7E". 5 
Among the methods mentioned above the study of deaths 
seems to be the best thus far employed. As this method has 
never before been used on a large scale, it may be well to con- 
sider it somewhat fully. Death is one of the few occurrences - 
which takes place in all parts of the world and can easily be 
reduced to accurate statistics. Such statistics are kept by all 
of the more advanced governments, so an enormous body of 
valuable facts is easily available, and needs only to be tabulated - 
in order to give most significant results. Accordingly, I shall 4 
here give a résumé of the detailed study of about 9,000,000 
deaths in Italy, France, and the United States, and of the more 
cursory but no less exact study of a much larger number in- 
Belgium, Germany, Sweden, Finland, and Japan. The most 
important result of these studies is a series of “climographs” 
like Figures 31 to 33. Figure 31 is based on 2,500,000 deaths | 
in the part of the United States north of the fortieth parallel | 
and east of the Missouri River during the years 1900-1912. 
Figure 32 is based on 2,200,000 deaths in France from 1901 | 
to 1910, and 1,500,000 in Italy from 1899 to 1913. Figure’ 
33 is based on 142,000 deaths in four California cities, namely, | 
San Francisco, Sacramento, Los Angeles, and San Diego, from) 
1900 to 1912. The diagrams show to what extent the deaths 
during months with any specified temperature and humidity 
fell short of or exceeded the normal. Temperature is indi- 
cated at the left and humidity at the top. The heaviest shad-) 
ing means that on an average the deaths during months having 
the conditions included within its area were at least 10 per cent 


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a ee , a of. : e eo ae = ara i | ee ee a --—s 

“ . es °r ' - as . pe eee , - 4 — eos ow oo 
Ll T 


re ee Bee ae ee ee 
See . ant <a 
. tw eo 
oOo oO 
¥ T T T 


es 


Humidity 
50 60 70 


- la 
90 I ’ l e a ee ! ! 
France and Italy 
(1899-1913) 
6 3,700,000 deaths 
3° 20 
’ TTS} 
&0 


20 


G7) 


3025 20 15 
Deaths in Relation to Temperature 
i ij and Humidity : 


Fic. 32.—Climograph of France and Italy. Based on 3,700,000 deaths, 
1899-1913. q 


“Temperature 


Beco 
60 


60 


50 60 sty FO 30) 90 
South Pacific Coast. 
(1900-1912) 
142,000 deaths 
-10 
5 ~-10 
0 
5 
= 10 LY 
15 \ Vy, YY \\ - 
\Y aU) Yf 0 
Jan. 5 
a A S\N 
10 
lok 
30F 
Deaths in Relation to Temperature 
and Humiditys 
(Graph for Los AnfeTes) 
1 { F l P | j 


20 


Humidity 


| —sCWF. 33.—Climograph of Southern California. Based on 142,000 deaths at 


San Francisco, Sacramento, Los Angeles, and San Diego, 1900-1912. 


162 EVOLUTION OF THE EARTH 
less than the normal. The less heavily shaded area between 
the 10 per cent line and the zero line means that on an average 
the deaths in months having any of the combinations of tem- — 
perature and humidity falling between these lines range from 
the normal to not more than 10 per cent below it. The next i 
lighter strip indicates conditions under which deaths range — 
from normal to 10 per cent more than the normal, and so st 
The lighter the shading the greater the number of deaths, and 
the less the vitality and energy. The practical use of the 
diagrams may be illustrated by an example. Suppose, for — 
instance, that we want to find what degree of health we may — 
expect in a month having an average temperature of 50° for : 
night and day together and a mean humidity of 70 per cent. 3 
In Figure 31 find 50° in the scale on the left. Follow this q 
level to the right to a point in line with 70 per cent as marked © 
at the top. This point lies a trifle above the zero line and ; 
about one-fifth of the way toward the minus 5 per cent line . 
Therefore we infer that on an average the months with a 
mean temperature of 50° and a relative humidity of 70 per — : 
cent have 1 per cent less than the normal number of deaths. 
Such a month in spring after a hard winter may have 10 per 
cent more than the normal deaths, while in the fall after a — 
cool summer it may have 12 per cent less than the normal, but © 
the average is 1 per cent below normal. a 
The method of preparing these diagrams is as follows. — 
Certain cities were first selected to cover all parts of each | 
region, namely fourteen in France, fourteen in Italy, twenty- 
two in the northeastern quarter of the United States, and four 
in California. For each place tables were prepared showing — 
the mean temperature, mean relative humidity, and number — 
of deaths for each month. Next the yearly deaths in the first 
and last halves of the period under discussion were averaged _ 
to see how rapidly the number was increasing or diminishing. 
On the basis of these figures, and assuming that the change in ~ 


AND ITS INHABITANTS 163 
je number of deaths due to increasing population and to im- 
roved sanitation progresses uniformly, the normal for each 
ionth was obtained. Allowance was made for the varying 
umber of days in different months. Then for each month 
ie departure of the death-rate from the normal was calculated 
| percentages. These departures were next tabulated accord- 
@ to temperature and humidity. Contagious diseases were 
f necessity included and cause some irregularities which have 
een smoothed out in the diagrams here presented. It must 
e clearly understood, however, that the irregularities are 
light, and their effect is merely to cause the lines separating 
he different zones to be wavy instead of smooth. As a matter 
f fact, contagious diseases are in general worst under the same 
onditions which are worst for other diseases. 
By the method described above, each place is compared 
only with itself. This avoids the serious difficulty which arises 
4 actual death-rates are employed, and if all places are com- 
pared with the same standard. The death-rate of one town 
nay be high because of poor sanitation, or because a great 
umber of people work in factories. In another it may be 
yw because a large number of young people have migrated 
lither or because the occupations are unusually healthful. 
herefore comparisons of the death-rate of different places 
re misleading. According to the method here employed, 
dwever, it makes no difference what the actual death-rate is. 
Ve deal simply with the degree to which the deaths fall above 
r below the normal for the particular place and period in 
uestion. 
9 It will readily be seen that diagrams 31 to 33 present the 
Same general features. This would be much more evident if 
le range of temperature in California and of humidity in the 
astern United States were not so small. Nevertheless, in 
ach diagram the outstanding feature is a central heavily 
1aded area of few deaths and high physical energy. When 


164 ~ EVOLUTION OF THE EARTH | 
the weather conditions are like those included within this area, 
the number of deaths averages at least 10 per cent less than the © 
normal. In Figures 31 to 33 and in others of similar char. 
acter not here reproduced the favorable conditions when 
deaths are more than 5 per cent below normal range as follows: 


Mean Temperature at Which Deaths Are More than 5 rs 
Cent Below Normal 


. The northeastern quarter of the United States 51° to 71 ; 


I 

2. France and Italy’ .,,\. 323 Vvere date ema 51° to 74° 
3. Califormian oer. oi Gis tea eee 55° to 7am 
4. The southeastern United States ........... 60° to 63° 
5. The dry interior of the United States ....... 57° to 7am 
6. Colored people in the United States ........ 53° to 7am 


In each of these cases the central part of the area of high 
vitality lies not far from a mean temperature of 64° andam ’ n 
relative humidity of 80 per cent or 85 per cent. In each case 
there is a tendency for the lines to converge toward the righ an 
at high temperatures, which means that hot and very damp 
weather is not favorable, as everyone knows. To the left) 
is also a similar tendency toward convergence which indicates | 
that although a certain degree of dryness may be favorable 
in hot weather, too much is bad. Another notable feature is | 
that toward the top of the diagrams above the area indicating | 
most favorable conditions the lines are closer together than) 
they are toward the bottom. In other words, temperatures | 
that are too high have a worse effect than those that are too | 
low. Again it is noticeable that at lower temperatures the lines | 
tend to swing from a horizontal position on the left to a) 
vertical position on the right. This means that in cool weather 
moist conditions are decidedly better than dry. In this respect) 
the diagrams are surprising, for it is rarely realized that there | 
is any such pronounced difference between cold damp weather | 
and cold dry weather. In fact, the vast majority of persons, 


i AND ITS INHABITANTS 165 
‘myself among the number, have always supposea that dry 
‘weather is the best. There is no questioning the diagrams, 
however, for, as has already been said, they are based on 
millions of deaths. Moreover, the same features appear in 
‘ie ch of the five areas into which the United States is divided, 
and in France and Italy when taken separately as well as 
together. 
_ One of the most striking features of the diagrams is that 
although their general form is alike and although they all 
show substantially the same optimum, the lines are far apart 
in Figure 31, the diagram for the northeastern United States, 
nearer together in Figure 32 for France and Italy, and nearest 
of all in Figure 33 for California. This means that while 
people in all these regions are strongest and most energetic at 
essentially the same temperature and humidity, a departure 
from these apparently ideal conditions does much more harm 
‘in France and Italy than in the northeastern United States, and 
‘still more in California. We might add that between the 
northern and southern parts of France and Italy there is the . 
same sort of difference as between Figures 31 and 32, or 32 
and 33. This at first sight seems puzzling. The climates that 
re generally considered best for invalids actually show 
2 eater extremes in the death rates than do the more rugged 
northern climates. This happens not only in southern Cali- 
fornia where there are many invalids, but in San Francisco 
_and southern Italy where there is no influx of such people. 
_ The explanation is apparently found in the variability of 
‘the different climates. Measurements of factory work and 
studies of the marks of students show that changes of tempera- 
ture, especially a moderate drop, are distinctly stimulating. 
Other evidence also indicates that variability, both from season 
_to season and from day to day, is much better than uniformity. 
pparently people who live in variable climates acquire a 
power of resistance unknown among those where relative 


& 
¢ 
i 


- 


+ 


166 EVOLUTION OF THE EARTH | 
uniformity prevails. ‘The effect is like that of exercise. The 
people whose bodies are exerciséd by frequent transitions from 
one set of weather conditions to another are more healthy and 
energetic than those who live where there are no changes. 
The benefit of a climate like that of southern California comes 
not from staying there year after year, but from going there. 
Since the temperature never departs far from the optimum, 
people who come from other regions usually experience a help- 
ful change. It is like what they experience in their own homes 
during the favorable months of spring and fall, but it has the 
added advantage of rest, novelty, interesting scenery, and 
out-of-door life. z 

Since storms are the chief cause of variations of weather 
from day to day, they appear to be a most valuable stimulant. 
Hence they have much to do not only with human energy but 
with civilization. In the trying winters of the northeastern 
United States, to be sure, the most stormy months have about) 
6 per cent more deaths than do those with only a moderate 
number of storms. Months with almost no storms, however, . 
are not so good as those with a moderate number. Even in the 
mild winters of California the same is true. ‘There at tem- 


1900 to 1912: 


1. In months of practically no storminess, the deaths, 
which numbered 27,700, were 6.1 per cent more than the 
normal. | | 

2. In months with a medium number of storms, the deaths 
(11,920) were 5.3 per cent more than normal. 4 

3. In months of great storminess, the deaths (13,200) 
were 7.3 more than normal. 


In warm weather, on the other hand, the most stormy 
months are the most favorable. In the northeastern quarter 


‘ AND ITS INHABITANTS 167 
i. In months having no storms (17,800 deaths), the rate 
s 8.6 per cent Jess than the normal. 

2. In months having slight storms (3,000 deaths), the 
ate was 6.1 per cent Jess than the normal. 

3: In months having moderate storminess (1,700 deaths), 
ue rate was 13.8 per cent /ess than the normal. 

Jn the basis of these figures and of others in other parts 
f the country the bad effect of great storminess in cold 
eather appears to be balanced by the good effect in warm 
cathe To this, however, must be added the significant fact 
hat storminess, as has already been explained, Seperate to 
ncrease people’s vitality and energy at all seasons.* 

4 * What has all this to do with civilization? Much, as we 
hall shortly see. Thus far we have been dealing only with 
seople of European races. We have seen that whether in 
rance, Italy, or any one of five sections of the United States, 
he best health and greatest energy are found under essentially 
he same conditions. Less intensive studies of Belgium, 
Finland, Germany, and Sweden indicate that so far at least 
$ temperature is concerned the response is the same as in 
‘rance, Italy, and the United States. This is evident from 
following table: 


Optimum Temperature on the Basis of the Death-Rate 
in Foreign Countries 


| 
; 


Years Pegs 
fin, : 1861-1910 above 63° 
Finland, 1900-1912 above 61° 
sermany, | Ig12 64° 
“aapan, 1899-1908 64° 
Stockholm, 1906-1914 60° 
_ Average, 62.7° 


e $For a further discussion of this matter see the author’s volume on “Civiliza- 
tion and Climate,” 1915, published by Yale University Press. 


1 gh IS ONE Ot ag? ME igh SI 
erature 
on ~ a 
© 


* 3 7 T a r 


‘ lf 
| py 


170 EVOLUTION OF THE EARTH | 
Belgium and Finland are so cool that no entire month has _ 
a mean temperature as high as the optimum. Stockholm 
happens to show a low optimum, but this is not significant, for 
accidental circumstances such as epidemics may cause the 
figures for a single city to depart from the true normal.* » 
From the facts now before us it appears to make little 
difference whether we are dealing with Finns of semi-Mongo- 
loid stock in the Far North, with Nordics in central Europe 
and America, with people of Mediterranean stock in southern : 
Italy and Sicily, or with Japanese in the Far East. In all 
cases, the highest energy is found where the average tempera- 
ture for day and night together is between 58° and 71° F. 
In general it varies only a little above or below 64°. It is 
surprising enough to find such an agreement among all these 
races of Europe and Asia. It is still more surprising to find 
that in the United States the deaths of whites and of negroes, 
so far as they are available in the figures of the United States” 
Census from 1912-1915, show essentially the same response. 
This is illustrated in Figures 34 and 35. Figure 34 is based 
on all the reported deaths of colored people from non-— 
contagious diseases in the states of Maryland, Virginia, | 
North Carolina, and Kentucky, together with all the cities, 
both north and south, where deaths of negroes are reported in 
the Census tables. The negro deaths number only 167,000, — 
or so few that accidental and local circumstances cause great 
irregularities. Nevertheless, it is clearly evident that the zone 
of fewest deaths ranges from about 53° to 78°, which is essen- 
tially the same as in Figures 31 to 33. Light areas indicating 
many deaths are increasingly prominent at low temperatures 
and low humidities, and also at high temperatures and high 
humidities. 
Figure 35 is based on exactly the same places as Figure 34, 


4For a further discussion of this subject see Huntington, Ellsworth, “World- | 
Power and Evolution,” New Haven, 1919. 


i 


AND ITS INHABITANTS 171 
but it illustrates white deaths instead of colored. It differs 
f from Figure 34, however, because the number of deaths is 
feuch greater, being about 921,000. Moreover, the relative 
importance of different places varies much. For instance, in 
New York City there are only about 2,500 colored deaths per 
year, while white deaths number nearly 70,000. In North > 
Bolina, on the contrary, the white and the colored deaths in 
the towns for which statistics are available each amount to 
about 4,000 per year. In spite of this, the two diagrams show 
the same general features. This.is highly significant. It 
‘shows that in spite of the great outward difference between 
y whites and negroes, the two races are fundamentally alike in 
their climatic response. Even though his ancestors lived in 
Africa for thousands of years, the negro appears to have 
acquired little more than an external adaptation toa hot climate. 
His case is even more striking than that of the Finn, who has 
lived in a cold climate for many generations. The average 
temperature in the places wherethese two races have spent most 
of their lives differs by about 40°. Nevertheless, the tempera- 
ures at which each is most healthy and energetic differ by no 
more than 4°. It appears that not only the Nordic, Mediterra- 
nean, and Mongoloid races are (almost) alike in their response 
to climate, but even the negro joins them. It seems scarcely 
going too far to query whether all mankind may not shownearly 
the same adjustment to one special kind of climate. Men may 
have black skins to protect them from the heat of the tropics, 
or fair skins adapted to a cloudy, northern home, but so far as 
actual temperature and humidity are concerned they may not be 
essentially different. Possibly man’s adjustment to climate is 
somewhat like the temperature of the blood, which is almost 
unchangeable, no matter in what climate man may live. Pos- 
sibly this seeming uniformity in man’s adaptation to climate 
may indicate that the conditions under which he is now at 
his best are those under which he took the most important 


172 EVOLUTION OF THE EARTH 
steps in his final physical evolution, and acquired his present 
invariable inner temperature. 

In this connection it is important to note that among white 
men the best conditions for mind and for body do not appear 
to be quite the same. Variability seems, if anything, to be 


> J aaa 


even more stimulating to mental than to physical activity. | 


Tests of school children made by Lehman and Pedersen in 
Copenhagen and my own study of.the marks of about 1,600 
students at West Point and Annapolis indicate that mental 
activity is greatest at a temperature decidedly lower than the 


optimum for physical energy. For negroes the difference, as _ 
indicated by daily tests of twenty-two students at Hampton 


Institute for sixteen months, is much less. Perhaps this indi- 


cates that after the separation of the white and negro races 
there came a period of low temperature and of climatic stress 
which modified the white man’s mental response, but did not 
affect the negro because he had gone too far south. 

If the conclusions here presented are sound, a knowledge of 
the temperature, humidity, and variability of any region enables 
us to determine what effect its climate would have upon the 
_physical and mental energy of all mankind. It is thus possible 
to prepare a map showing the distribution of either kind of 
energy or of the two combined. Such a map, in which physical 
and mental energy are regarded as of equal importance, is 
shown in Figure 36.5 The map is subject to correction when 
fuller data are available, but that will not change its main 
outlines. The heavily shaded areas are those of great energy. 
The agreement of these areas with the places where civiliza- 


tion is highest is too marked to escape notice. In order to © 


bring the matter more clearly before us, Figure 37 has been 
prepared. This is a map showing the distribution of civiliza- 
tion according to the opinion of fifty competent judges in 
fifteen different countries. The judges have been grouped in 


5'The map is fully discussed in “Civilization and Climate.” 


700 120 140 


60 


20 40 60 


o. 


. 
. 
SS ee 


te. 


ima 


Fic. 36.—The distribution of human energy on the basis of cl 


From ‘‘Civilization and Climate.’’ 


140 160 


120 


Es 
Re 
Ne 


: 


1S > . 


e 


Y) 


ue pany 


— ee ee le ee ST 


De es aes cw dee ‘acs PEaiveibicie Se. sepns ease akon 


te.”” 


From ‘‘Civilization and Cli 


Fic. 37.—The distribution of civilization. 


174 EVOLUTION OF THE EARTH 


such a way that the opinion of each of five groups, namely ~ 
Americans, British, Teutonic Europeans, Latin Europeans, and 
Asiatics, has equal weight. The agreement of the two maps 
is surprising. It indicates that at the present time the distribu- — 


tion of climatic energy and of civilization is almost identical. 


Such differences as are discernible occur almost wholly where - 
exact information is lacking or where the presence of Euro- — 
peans as colonial rulers raises the apparent standard of 


civilization. 
This brings us to the climax of our discussion. At the 


beginning of this lecture we saw that human progress, that is, — 
the growth of civilization, depends in apparently equal measure © 


upon inherent mental capacity, material resources, and energy. 
We then saw that although inherent capacity has no relation 


to present climatic conditions, it is closely intertwined with — 


those of the past. We also saw that although some resources 


like the metals and coal occur without respect to climate, their — 


utilization is largely controlled by climatic conditions, while 
the vast majority of resources depend directly upon climate 


through its effect on vegetation. Finally we have seen that — 
human energy, even more than either of the other conditions, — 
appears to be dependent directly upon the physiological effect — 
of climate upon man’s body. Thus in the evolution of civiliza- — 
tion, as in the broader field of the evolution of life, the most ~ 
obvious controlling factor, although by no means the only one, © 


appears to be climate. 


STEPS IN THE EVOLUTION OF CIVILIZATION 


Invention of tools and speech, and discovery of use of fire. © 
In the light of this conclusion let us briefly examine some of | 
the great steps in the evolution of civilization. Three of the 
earliest and greatest steps were the invention of tools, the in- — 
vention of speech, and the discovery of the use of fire. As to © 
the relation of tools and speech to climate, nothing definite — 


_ 


ag a ee ee ee ee ee ee 


. . 


1 a aie sr a ie ae Sa Tid Pie a ete aioe te seg Se eye 


i AND ITS INHABITANTS 175 
a can be said. They probably became a part of man’s cultural 


| inheritance so early that he still lived in his primeval home, 


and had perhaps not begun to differentiate into races. If that 
is the case, the climate was presumably of the kind which we 


_ have found to be most stimulating. That is, it had a tempera- 


_ ture about like that of modern Greece, but with much more | 
_ variability from day to day. As to fire, the conditions of its 

_ discovery were probably like those of the first use of tools 
_and of speech. In this case, however, we can go farther. 
_ Presumably after man discovered that he could produce fire 
artificially he first employed it primarily as a source of heat. 
_ Only in a climate which had a distinct cold season would the 
incentive to its use be great. Only in a climate where there 
_ was plenty of wood and also a dry season to prepare the wood 


for fuel would he find it easy to use the new discovery. More- 
over, only in a relatively stimulating climate would early men 
| probably have had the energy to develop the highly laborious 
art of firemaking, for few things require greater determination 
_ and persistence. When some happy accident taught man the 
' value of heat in cooking food, the discovery doubtless spread 


_ to warm regions, but it seems no great stretch of the truth to 


_ infer that tropical man, if left to himself, would never have 
_ become a user of fire. 


| Discovery of use of iron. One of the next great steps in 
_ human progress was the discovery of the use of iron. This 
discovery required the concurrence of four important con- 


ditions, all of which are much less likely to occur within the 
_ tropics than without. First, there must be bits of ore lying 


_ about where fires are likely to be made. Of course this may 
occur in any part of the world, but it is far less likely to happen 
_ within the tropics than farther north because the tropical soil 
is generally so deep that rocks are rare. In the next place the 


fires must be hot enough and of long enough duration to melt 
the ore. This, too, may occur within the tropics, but is much 


176 EVOLUTION OF THE EARTH . 
less common there than in colder climates. In warm regions 
cooking is apt to be done over small fires that do not make 
people uncomfortable, or else in pits dug in the hot ashes; 
and the temperature is rarely high enough to melt iron ore. 
Farther north, however, where the winters are chilly, huge — 
fires must have been common from the earliest times. There, — 
too, in the fairly dry areas many stones lie on the surface 
almost everywhere. The next necessity is that when some bits — 
of ore happened to be in a particularly hot fire a man of 
unusual genius should be present and observe the molten ~ 
metal. This might occur anywhere, but we have already seen — 
reasons for believing that quickness of intellect is fostered in 
some climates more than in others. Finally, the fourth requi- 
site, and much the most important, is that the man of genius 
have the zeal and determination, as Darwin puts it, to bring — 
to fruition the ideas engendered by his observations. A singl | 

mind, however, was not enough to consummate the great dis- 
covery. It was necessary that the generation of men who 
lived with the genius should be ‘in a mental mood to receive 
the new invention or discovery.” ‘That mood, together with ; 
the necessary energy on the part of the genius, is rarely found 4 
within the tropics. It is common in regions blessed with a | 
stimulating climate. ‘Thus each of the conditions controlling 
the discovery of the art of smelting is so much stronger outside 
the tropics than within them that it seems highly probable | 
that the art arose in a stimulating extra-tropical climate. It — 
is generally supposed that the use of iron originated in North © 
Africa perhaps 6,000 years ago. This is eminently consiste - ii 
with our conclusions. At that time, as is almost universally — 
admitted by geologists, the climate of the world was inter- 
mediate between that of the Glacial Period and the present. “4 } 
Therefore North Africa was then a decidedly more stimulat-— 
ing place than it is today. This same line of reasoning applies 
to other great steps in the early development of civilization, | 


AND ITS INHABITANTS 177 
for many of them were influenced by the glacial stages or minor 
( epochs which succeeded the last glacial epoch. 
; Taming of wild animals. The taming of wild animals was 
_ one of these steps. The dog was apparently the first domestic 
animal. His contribution to civilization, however, is slight, 
i for instead of lifting man out of the hunting stage, he pre- — 
; serves it. If the hunter becomes a tiller of the soil he does not 
f want dogs, for he no longer has a frequent surplus of meat 
_ which will spoil if the dogs do not eat it. While he remains a 
§ hunter, however, the dogs not only help their master to find 
_ wild animals, but serve as a reserve supply of food in times of 
( scarcity. Among the American Indians no delicacy was for- 
merly more esteemed than a fat young puppy. The taming of 
| the dog was in itself no great feat. It was easy to bring home a 
: wild puppy, which grew up as tame as though its ancestors 
_ had long been domesticated. This, however, was the step 
_ which apparently led to the domestication of other and more 
_ useful animals. It probably did not occur within the tropics, 
_ for today the wolf-like creatures from which the dog is sup- 
4 posed to be descended do not appear to be found within twenty- 
_ five degrees of the equator. 
_ Other domestic animals far surpass the dog in utility. 
_ Lowest among these stands the pig. This creature is highly 
useful as a source of food, but cannot easily be domesticated 
unless the art of agriculture is well developed, for it is not 
readily herded, and its food is primarily the products of agri- 
culture rather than grass. Therefore, though the pig might 
have helped civilization, it never had the chance, because be- 
fore it was kept in large numbers the tillage of the ground had 
_ already done all, and more than all, that the pig could do in 
' this line. So far as climate goes it might have been domesti- 
_ cated almost anywhere from the equator to the temperate 
_ zone. 
The horse, the ox, and the sheep stand in a different cate- 


7 


1 
% 


178 EVOLUTION OF THE EARTH 
gory from the dog and the pig. Aside from agriculture — 
nothing did more than their domestication to give man that 
sense of ownership and feeling of responsibility which are — 
among the most essential prerequisites of high civilization. As — 
soon as herds were in his care, man was compelled to watch 
them day by day. Carelessness was fatal. He must defend 
them from wild animals, drive them to new supplies of grass 
and water, and plan to sustain them through the winter. Not ~ 
only did man thus become a property owner by reason of his — 
beasts, but he himself was able to increase in numbers to a 
degree utterly impossible while he still depended on the chase. 
Therefore the contact of family with family greatly increased. 
That necessitated either war and destruction, or some kind of 
mutual agreement whereby was laid the basis of a rudimentary 
social and political organization. As to the climate under 
which domestication of the grass-eating animals took place, itis — 
almost certain that the horse, ox, and sheep all were first tamed _ 
in the subtropical grasslands of central Asia thirty or forty 
degrees from the equator. Since this occurred during the ~ 
change from the last glacial epoch to the present, it presumably | 
took place in a climate closely resembling that which we have 
found to be ideal. Two other animals, the llama and the | 
camel, have been domesticated under less favorable circum- ~ 
stances, but neither is truly tropical. The llama of Peru lives 
where it is decidedly cool. The camel may frequent the hot ~ 
desert, but the only known wild camels are in the deserts of 
central Asia where the winter temperature may be 20° below 
zero. Neither of these animals can vie with the horse, ox, 
and sheep as contributors to civilization. In the case of the € 
llama this may be due to small size, but probably in both cases 
a more important factor is the fact that neither animal flour- ~ 
ishes in the kind of climate in which man is at his best. ft 
Rise of agriculture. During the whole course of human ~ 
history probably no one thing has had a greater influence upon © 


AND ITS INHABITANTS 179 
civilization than has the art of agriculture. It is impossible 
‘to say exactly where agriculture arose. Perhaps it developed 
‘in different ways in many different regions. The great staples 
of agriculture are the cereals—wheat, barley, rice, millet, 
maize, rye, and oats. The majority of these are of subtropical 
origin. Rice, however, which supports more people than any 
~ other one kind of food, is probably of tropical origin. The 
same may be true of maize. This conclusion, however, is mere 
guesswork, for that grain has never been found in its indige- 
nous form. Millet, which well-nigh rivals maize in the num- 
ber of people it supports, is of great importance within the 
‘tropics, but apparently it originated farther north in a sub- 
tropical climate, such as that of Egypt. The other grains all 
appear to have originated in regions well beyond the limits 
of the tropics. 

_ Whatever may be said of the origin of agriculture, it needs 
‘little demonstration to show that its effect in advancing civiliza- 
| tion has been far greater in relatively cool climates than in 
' those that are warm. It is a commonplace of history that 
_ the great civilizations of early times arose in fertile plains 
| where agriculture was carried on by means of irrigation. 
_ These were located more than twenty-five degrees from the 
" equator, as we see in Egypt, Mesopotamia, northern India, 
and China. It is hard to overestimate the effect of irrigation 
upon the early progress of civilization. Because of the neces- 
» sity of making ditches and reservoirs, and of having everything 
"ready when the water is turned on a field, the power to pre- 
pare consciously for the distant future is enormously stimu- 
lated. The man who depends on irrigation cannot neglect his 
fields, for a week of carelessness may cost his whole crop. 
He must learn, too, to live at peace with his neighbors. If 
men who use the same stream for their water-supply quarrel 
with one another and break down one another’s dams and 
ditches the chances are that all will suffer famine. They must 


; 


o 
h 


180 EVOLUTION OF THE EARTH 
agree, and therefore must organize a well-regulated system 0 
government. The fact that in irrigated regions many p 20 
ple live close together on a small area also tends to caus 
society to be thoroughly and wisely organized. Moreove ver 
the mere fact that water is precious leads to economy in its ust 
and to intensive agriculture. Hence man’s faculty for planning 
and for devising new schemes to increase his crops is constantl 
stimulated. The Hopis, whom we have already cited, are a 
admirable example of this. Could there be any ai 
velopment of agricultural science than their way of putting 1g 
seed into the midst of a ball of wet clay and burying it in tl 
dry sand? The stalk of corn that grows from such a seed m r 
be only a foot or two high, but it bears an ear with a hund: rc 
grains to replace the one grain that was planted. i 
it need hardly be said, is rarely practised in tropical countri 
So far as it exists there it is either a relatively late develll 
‘ment as in Java, or is confined to the highlands as in Peru, ¢ 
to certain dry regions as in India. Everywhere it is a ana 
response to special types of climate. 

So it is with all agriculture. Its type depends upon the kin 
of climate. After man has reached a fairly high stage o 
culture the most stimulating of all kinds of agriculture appe ar j 
to be that which prevails in temperate regions where the a is 
rain at all seasons. There each farmer lives on his own ind 
pendent farm. He may not have the stimulus of close conté 
with his neighbors which is found in irrigated vubceail 
regions, but he has the great stimulus of being wholly ind 
pendent and of being constantly urged to meet his own needs. — 
Moreover, he must be industrious and alert to a degree d 
manded of no other kind of farmer. The constant variety 
weather to which he is subjected demands that he shall 
ready to cut or harvest his hay instantly when the right tin 
comes. He cannot put off cutting his grain as can the st 
tropical farmer, for when once it is ripe the rain may cor 


i" AND ITS INHABITANTS 181 
-andruinit. In the fall, no matter how tired he is, he is forced 
to gather his crops before a sudden frost comes and spoils 
some of them. Thus while tropical agriculture is a help 
_ toward civilization, that which prevails in subtropical regions 
is far more helpful, while that of the stormy temperate zone is 
still more so. 
Invention of writing. We come now to the invention of 
writing, the great step which marks the boundary line between 
_ barbarism and civilization. Twice at least this step has been 
taken, once among the Mayas in Guatemala, and once in Asia. 
' Perhaps the writing of the Chaldeans may be of different 
origin from that of the Chinese, although we cannot speak 
_ with certainty. At least the line of development of the western 
- forms of writing in Mesopotamia, Egypt, and the adjacent 
" lands, has been very different from that on the eastern side of 
_ the continent. However this may be, it seems certain that 
_ writing was invented in regions with a variable and stimulating 
climate, as will soon appear more fully. The invention marks 
an era in man’s development as truly as does the discovery of 
pene use of fire or the invention of the art of smelting iron. 
When man learned to speak, the individual thereby became 
able to avail himself of the experience of all the people around 
him and of many people whose experiences had been handed 
‘down in memory. When he learned the art of writing he no 
' longer needed to trust to memory. The minds of all the ages 
_ became available to the mind of today. During.the hundreds 
_ of thousands of years of the previous existence of the human 
ace many a great man must have lived in vain, because among 
his immediate associates there was none to comprehend and 
carry out his ideas. When writing was invented, it enabled 
such men to spread their thoughts a hundred times more 
"widely both in place and time. Who knows how greatly our 
modern discoveries are influenced by thoughts recorded by the 
ancient Greeks and Egyptians? 


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182 EVOLUTION OF THE EARTH 
Contribution of tropical countries. In these later days sine 
historical records have been kept, the contribution of tropica 
countries to civilization has been as meager as appears to ha 
been the case in the remote past. So far as we are aware, 7 
truly great man except Mohammed has arisen within twenty 
five degrees of the equator. Gautama, the founder of Buc 
dhism, lived north of this limit. Moreover, his home y 
among the mountains where the climate is more stimulatir 
than in the lowlands. Mesopotamia had its great men whos 
names are still known, but that country, though hot in su a 
lies from thirty to thirty-five degrees north of the equator. Ss 
too with Egypt, for its great men almost without exceptiot 
lived from Thebes northward, and the latitude of Thebes i 
more than twenty-five degrees north. In modern times it t 
even harder than in the past to find great men who lived i 
tropical or even in warm countries. Diaz in the high, coo 
but nevertheless tropical plateau of Mexico may be cited as a 
example, but a hundred years from now only the special stu 
dent will have heard of him, while men like Lincoln, Pasteur 
and Humboldt will still be admired by thousands, yea, millions r 
of people. Even if we go back to Mohammed as an exampl 
of a truly great man arising within the tropics, we find : 
his ideas came to fruition only when they were carried no ‘ 
ward to a place where the minds of that generation were mor 
alert than in southern Arabia. [ 
We have now seen that civilization is today highest in place 
where climatic energy is also high. We have likewise seen na 
in the past no great steps in human progress seem to have beet 
taken in tropical countries, nor do great men appear to hay 
sprung up there in appreciable numbers. These consideration 
apparently lead to the conclusion that when the progress « 
human civilization is viewed in the broadest light its grea 
movements depend upon climate almost as closely as do the 
pulsations of the evolutionary stream in geological times. On 


fy 


AND ITS INHABITANTS 183 
great objection, however, has hitherto seemed to controvert 
any such conclusion. ‘Tropical countries may indeed have 
_ made no appreciable contribution to civilization at any time, 
but no later than two or three thousand years ago many 
_ countries where climatic energy is now comparatively low were 
the seats of the highest civilization. How was this possible? 
; The answer is that a great mass of evidence seems explicable 
_ only on the hypothesis of pulsatory changes of climate during 
historic times. This evidence has been discussed so fully in 
other publications that it seems unnecessary to repeat it here.° 
| It will be enough to state the main conclusions with almost no 
' details of proof. With these in mind we can apply them to 
_ concrete instances and see how climate appears to have been 
related to historic crises. 


HIsTORICAL CHANGES OF CLIMATE 


_ During the past few decades the opinion of geographers as 
_ to historical changes of climate has followed a course almost 
identical with that of geologists as to earlier and greater 
_ changes. Formerly climatic uniformity was supposed to be 
_ the “normal” condition and variations were supposed to be 

rare and exceptional. Today geologists universally believe 
_ that glacial periods have occurred irregularly from the earliest 
times to the most recent, and that these have been broken into 
_ alternate glacial and interglacial epochs, while other less ex- 
_ treme changes have been frequent. Coming to historical times 
_ a belief in similar but smaller climatic pulsations is now almost 
- universal among American geographers, as is indicated by 

® See “The Pulse of Asia,” 1907; “Palestine and Its Transformation,” 1911; 
and “The Climatic Factor,” 1914. Briefer treatments embodying further modi- 
fications of the original hypothesis, together with replies to certain criticisms, are 
found in “The Solar Hypothesis of Climatic Changes,” Bull. Geol. Soc. America, 
vol. 25, 1914, pp. 477-590; in “Civilization and Climate,” 1915, ch. XI; and in 


“Climatic Change and Agricultural Decline as Elements in the Fall of Rome,” 
Quart. Jour. Econ., vol. 31, 1917, pp. 173-208. 


184 EVOLUTION OF THE EARTH 
the answer to a series of questions recently sent out by the 
writer. As Dr. W. D. Matthew, one of the most careful stu- 
dents of the matter, says, “‘I should demand proof before I~ 
would admit that there has been uo change within 2,000 
_years.”’ 

The weakness of the hypothesis of climatic uniformity is 
indicated by a consideration of the strongest argument in its 


favor. It runs thus: The palm and the vine grow together _ 


only within a most limited range of temperature. Today they ~ 
grow together in essentially the same places as 2,000 or 3,000 © 
years ago. Hence no change of temperature and no change 
of climate. This argument is weak in two respects. In the 
first place, students of the Glacial Period agree that at the 
height of the last epoch of advancing ice, perhaps 30,000 years 
ago, the mean temperature of the earth was only about 10°, or ~ 
at most 20° F., lower than now. On that basis an historic — 
change of climate one-tenth as great as the enormous change 
since the height of glaciation would mean a change of only one 
or two degrees in temperature, an amount too small to detect 


by means of vegetation. In the second place, the fact that 


there has been no appreciable change of temperature in his- 
toric times does not mean that there has been no change in the | 
distribution of rainfall. The records of the United States 
Weather Bureau show that during the years 1875 to 1884 the 
region from Galveston to New Orleans had 40 per cent more ~ 
rainfall than during the ten years from 1890 to 1899. The ~ 
difference in temperature between these two periods was only 
0.42° F. Curiously enough, the wet period was the warmer, 


although in other cases the reverse has been true. If such , 
important changes in the distribution of rainfall can occur in 


our own day with almost no change in temperature, there is — 
no reason why much larger changes may not have occurred © 


similarly in the past. That such changes have occurred is indi- 


cated by almost innumerable waterless ruins like those which 


ea AND ITS INHABITANTS 185 
everywhere dot the country from Mongolia through Turkestan 
and Persia to Turkey and North Africa, and also in our own 
Southwest. In the deserts, roads too dry for caravans, but 
known once to have been much used, also point to a change in 
rainfall. So, too, do abandoned springs and the scanty supply 
_of water in many aqueducts. One of the most significant pieces 
of evidence is the amount of salt dissolved in the waters of | 
Owens Lake in southern California, and of Pyramid and Win- 
-nemucka lakes in Nevada. This, as Gale has shown, indicates 
that from 2,000 to 4,000 years ago these lakes must have been 
so high that they overflowed and were fresh. About 2,000 or 
2,500 years ago Owens Lake appears to have been two and 
one-half times as large as now and to have stood 180 feet 
above its present level. 
" It is not enough to conclude merely that the climate of the 
_ present is different from that which prevailed 2,000 or 3,000 
‘Years ago. We must know the nature of the change. Geolo- 
_ gists formerly thought that climatic changes proceed very 
slowly and uniformly in one direction. They now believe 
_ that they are highly irregular. Even when the general change 
during thousands of years is decidedly in one direction, it is 
_ marked by great irregularities. There is now a general con- 
viction that the same is true of historic times. Pulsatory 
changes have apparently occurred whereby certain centuries 
_have been moister than the present and others drier. No 
_ other hypothesis seems adequate to explain the fact that lakes 
_whose waters are known to have stood many feet above their 
_ present level also contain ruins buried beneath their waters. 
Equally strong evidence is afforded by the fact that the growth 
; of the big trees of California indicates constant pulsations 
whose main features agree with those inferred from other 
kinds of evidence in Mediterranean regions and central Asia. 
In our own day exact records show an unmistakable harmony 
_ between spring rainfall and tree growth in California on the 


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1600 1800-2000 


1400 


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1200 


1000 


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eeee ewe eee ced it ee 


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growth of trees in Cali 


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Fic. 38.—Changes of climate in the subtropical zone during historic times, on the basis of the 


: 


13001 1000 800 600 400 SHO RGAD. 20 400 600-800 


1606 


* AND ITS INHABITANTS 187 
one hand, and Mediterranean rainfall on the other. Hence 
‘it seems legitimate to infer that the main fluctuations in tree 
growth, which are portrayed in Figure 38, represent climatic 
_ pulsations of world-wide extent. 

Even yet we have not fully explained the nature of climatic 
changes. They appear to have been not only pulsatory, but to 
have produced different effects in different parts of the world. 
It is an interesting coincidence that independently and on 
wholly different lines of evidence the German glaciologist, 
Penck, and the writer at almost the same time announced the 
‘conclusion that climatic changes are the result of an alternate 
_ equatorward and poleward shifting of the climatic zones. The 
” matter seems to be even more complicated than this, however, 
’ for changes in the interior of continents seem to be different 
’ from those on their borders or over the oceans. The net 
" result is that when such regions as the subtropical zone which 
embraces California and the Mediterranean lands enjoy un- 
usually abundant rainfall, the northern border of the zone of 
equatorial rains becomes drier. The chief basis for this con- 
' clusion, so far as historic times are concerned, is the fact that 
the Maya ruins in the dense forests of Central America seem 
to indicate periods of relative dryness at the times when tree 
growth in California indicates unusual moisture, and vice 
versa. 

_ One more point needs emphasis if we would understand the 
“nature of these pulsatory shiftings of the climatic zones. 
Apparently the most essential feature is a change in the tracks 
of storms. At certain periods the total number of storms 
appears to increase. Of even greater importance, however, is 
the fact that at such times the storms show a tendency to follow 
two belts instead of the one to which they are now largely 
confined. The present belt of storms is well known. From 
British Columbia it runs as a band hundreds of miles wide 
centering along the international boundary line, but with a 


188 EVOLUTION OF THE EARTH ' 
southward tendency. Its center sweeps across the Great Lakes 
and then swings northeastward down the St. Lawrence Rive: 
to the Atlantic south of Newfoundland. It crosses the Atlant nti 
to Europe, where it splits up, and almost dies out in Siberia a 
central Asia. On the eastern border of Asia it is joined 
an important and vigorous branch from Japan, and then s 
the Pacific coast of North America to British Columbus It 
course may be judged from Figure 36, where in general th 
dark areas of high energy are also stormy areas. The other 
or minor storm belt, appears to start in California, cros 
Arizona and New Mexico to the Gulf of Mexico, and thet 
swing. northeastward into the Atlantic Ocean. In the Ol 
World its course lies along the Mediterranean, beginning a ap- 
parently east of Spain. Beyond the Mediterranean it passe 
across Syria to Mesopotamia and Persia, and then in an attenu 
ated form to India. It probably revives again in China an 
joins the strongly developed Japanese area of storms. In ch 
past, at times when rainfall has been abundant in Mediterra 
nean lands, many storms appear to have followed this soutlay “I 
belt. Thus increased rainfall and increased variability 0 
curred during certain centuries, while the opposite occurr ec 
in others. The centuries which saw increased rainfall in hi 
subtropical belt saw decreased rainfall farther south in place 
like Yucatan, on the northern border of the torrid zone, bu 
with this decreased rainfall also went greater variability be 
cause of the storms whose centers passed a little farther nortl 
Hence it appears that not only in our own day, but throughow 
historic times the highest civilization has been found in th 
regions of greatest climatic energy. | : 

The possible exceptions to this conclusion are the areas 
high civilization within twenty-five degrees of the equator. 
These include Central America, the highlands of Peru, Yemi 
and Rhodesia, Indo-China, and some of the East Indies lik 
Sumatra and Java. None of these places, however, made any 


f AND ITS INHABITANTS 189 
great impression on the world. In the plateaus of Peru, 
Yemen, and Rhodesia, civilization took a few steps and then 
halted. This corresponds closely with their climate. In mean 
‘temperature and humidity they are admirable. Therefore to 
that extent they are stimulating. A competent race migrating 
to any one of them would be invigorated and would be led to 
‘make important advances. There is no evidence, however, 
‘that any of them ever enjoyed any great degree of climatic 
variability due to strong seasonal changes and frequent storms. 
Therefore they lacked the stimulus needed to keep them 
ie steadily progressing. 
_ The only tropical center of civilization which developed 
any really remarkable ideas was Central America, where the 
“Mayas evolved a decidedly high type of architecture, a re- 
markably accurate calendar based on extensive astronomical 
knowledge, and a system of writing more advanced than that 
which the Chinese have even yet attained. It is perhaps sig- 
' nificant that the center of Maya culture in Yucatan and Guate- 
mala lies in the longitude where storm tracks today swing 
farthest south and where they apparently swung much farther 
: Roach in the past. To this day the Yucatecan descendants of 
the Mayas say that they work fastest when the temperature is 
lowered by the “‘northers” which follow in the wake of storms 
whose centers pass farther north. In the past such northers 
Were apparently much more frequent than now. Hence it 
looks as if the relatively active Maya civilization were asso- 
ciated with variability anal as are the high civilizations of 
today." 
As to the cultural center in southeastern Asia, we cannot 
; Deak with much certainty. It never showed anything like the 
Sriginality of the Central American center, for most of its 
deas were borrowed from places farther north. It did not 


7 This subject is fully discussed in the author’s volume, “The Climatic 
| Factor.” Pub. No. 192, Carnegie Institution of Washington. 


190 EVOLUTION OF THE EARTH q 
last so long as the other. It is worth noting, however, — 
relation to the continent of Asia is almost the same as tl 
relation of the Maya Civilization to the continent of Americ 
There is some reason to think that when the southern sto rrr 
belt was intensified even this region, like its American coun’ 
part, may have had a more variable climate than at preseiell 

Effect of climate upon Roman history. The ca 
Rome furnishes a good example of the way in which clim 
changes appear to influence the march of history.* The gold de 
age of Rome occurred 400 or 500 years B. Cc. In the fourt t 
century B. C., as appears in Figure 38, storms and rainfal 
seem to have been abundant in subtropical lands like Cali 
fornia and Italy. In Rome five acres of land was then cor n 
sidered enough to support an average family, although tl 
presumably does not include the land used for pasturage. Gu 
tivation, as we know from numerous classical accounts, . 
highly intensive, so that the most advanced methods of 
culture were developed. ‘The crops rarely failed and the 
was widespread prosperity. “The farmers were iidepedill 
and sturdy, and the difference between rich and poor was sligh 
The towns were small and the conditions were all highh 
favorable to a strong democratic form of government. ’ 

Turning back to Figure 38 we see that during the thir 
century B. Cc. there was a marked diminution of rainfall. I 
Rome this was accompanied by two occurrences of siniste 
omen. One was a serious decline in agriculture. The smal 
tracts of land which had hitherto been the rule were no longe 
large enough to furnish a living for the farmer and his famil 
Crops that had previously been profitable ceased to be wort 
while. Hence there arose much discontent and the agraria 
troubles with which the names of the Gracci are closely asso=— 


8 See Simkhovitch, V. G., “Rome’s Fall Reconsidered,” Pol. Sci. Quart., J ar 
1916; and Huntington, Ellsworth, “Climatic Change and Agricultural Exhav 
tion as Elements in the Fall of Rome,” Quart. Jour. Econ., vol. 31, 1917, pp. 17: 3 
208. c 


| AND ITS INHABITANTS IgI 
ciated. The other sinister event was an increase in malaria, 
which Jones® has shown to have played an important part in 
_ diminishing the vigor of both the Greeks and Romans. Its 
increase was apparently due to the fact that the decline in rain- 
fall caused a diminution in the amount of vegetation on the 
mountains. Hence the streams washed down an undue amount 
of silt which filled up their beds in the lowlands and caused 
+hem to wander widely and form great swamps. These were 
ideal breeding places for the anopheles mosquito which is the 
carrier of malaria. 

_ After the period of depression in the second century B. C., 
_ Rome recovered somewhat during a period of favorable 
_ climate culminating about the time of Christ. Yet she never 
was quite restored to her former energy and glory. A century 
_or two later, in the early part of the Christian era, there began 
a climatic decline which culminated in the seventh century. 
' Since crops were no longer profitable, the land was used for 
_ grazing purposes, the methods of agriculture became slipshod 
and unprofitable, and the farms fell into the hands of a few 
large owners. The great number of sheep and goats not only 
_added to the difficulties of agriculture by their ravages upon 
the fields, but ate up the seedling trees and thus prevented the 
_ growth of new forests. Hence the soil was washed away from 
the hillsides, with distressing consequences. 

_ With this agricultural decline there arose political diff- 
culties. Taxes which had previously been easily paid became 
‘onerous. Agrariart reforms were even more necessary than in 
_ the days of the Gracci, but they were much harder to make. 
~ The people flocked to the city in order to get work and thereby 
_ share in some of the wealth which came to Rome because of 
her conquests. This, however, only increased the evils. 
Democracy gave place to plutocracy, and thus to despotism. 
At this same time the nomads in the drier parts of the lands 


9 Jones, J. H. S., “Malaria, a Neglected Factor in History.” 


7 
ey 
ay 


192 EVOLUTION OF THE EARTH 7 
surrounding the Roman Empire were also suffering fro 01 
drought and famine. Therefore they began to make rai 
which set more prosperous people also into motion, and soc 
barbarian invasions threatened the very existence of | th 
Roman Empire. If the climate had remained favorable then 
might have been an occasional raid, but there is no reasaay 
think that there would have been the great disasters whic 
finally became so terrible. 

Worst of all, the climatic changes seem to have had a 
effect upon the energy of the Romans themselves. We hay 
already seen how close is the connection between climate an 
energy. As the variability of the Italian climate decreased 
because the storms diminished in. number, the energy of th 
people seems also to have declined. This was particularh 
unfortunate because special energy was needed to resist the 
ravages of malaria, to overcome the agricultural difficulties, tc 
engender the self-control and patience which are essential when 
political difficulties arise because of undue. taxation or other 
causes. Most of all, energy was needed to resist the ovasiel 
of barbarians, but instead of this the people’s energy declined. 
They became prone to sit still and wait for someone to feed 
them, prone to think only of pleasure, and hence ready for 
the disaster which finally overtook the Roman Empire. 

It would be interesting to carry this discussion farther ang 
see how these same principles apply to almost every countr 
It is easy to attribute too much to climate, and I am well aware 
that many of my hearers will think that I have done so in thi 
lecture. It must be remembered, however, that this is meni 
a brief attempt to show the importance of one of the great : 
factors in the evolution of civilization. The fact that the 
importance of climate is here emphasized does not mean that _ 
I deem it a whit more important than the other factors. 50 
far as inherent mental capacity is concerned climate is in one __ 
sense a minor factor. It is more important as regards material 


\] AND ITS INHABITANTS 193 
resources, but is far from being the sole factor. Even where 
energy is considered, the effect of climate may readily be neu- 
tralized by several other factors such as lack of resources or 
lack of ability. The point to be emphasized is that climatic 
energy is one of the great factors which must be reckoned with 
in any attempt to understand the evolution of civilization. 
Hitherto, its importance has not been realized. Therefore 
today we must emphasize it until it takes its true place with 
inherent mental capacity and material resources. It is not a 
‘determiner of civilization, but a condition which prevents 
| civilization from advancing i in some places and stimulates it to 
_ the greatest activity in others. Without an understanding of 
‘its part in evolution we cannot rightly comprehend our own 

‘present development in any of the great branches of human 
_»progress. | 


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ctivity, mental, optimum temperature 
for, 172 

_ physical, optimum temperature for, 
172 
_Adelochordates, 117 

Africans, 148, 149 

Agriculture, 153, 154, 177, 178, 180 
\ir currents, changes in, 73 

Alaska, coal in, 155 

Alchemists, 82, 95 

Alge, 63, 113 

 Allantois, 126, 128 

Allen, F. J., 101 

Allosaurus, 133 

a Centauri, 7, 8 

Alps, rise of, 74 

Alumina, 100 

Alveolar substance, of protoplasm, 83 
Amblypods, 134, 136 

American Indians, 148, 151, 153, 177 
Amino acids, 85 

Ammonia, 99, 102 

Ammonites, 73 

Ammonium carbonates, 107 
Amnion, 126, 128 

origin of, 65, 111 

Amphioxus, 117 

Animals, domestic, 177, 178 
-lime-secreting, 113 

wild, taming of, 177 

Ankylosaurs, 132 

Annelids, 113 

pes, anthropoid, 139, 141 

origin of, 111 

Appalachian Mts., 78 

_ revolution, 111, 127 

trough, 78 

rabians, 150 


. _ INDEX 


Arboreal habitat, forsaking of, for 
terrestrial, 142 
Archzocyathine, 113 
Archaeopteryx, 129, frontispiece 
Archean, beginning of, 43 
Archeozoic era, 46, 49, 50, 56, 63 
era, time ratio of, 69 
sediments, thickness of, 63, 67 
Arctic climate, effect of, on man, 149 
Aridity, 123, 126, 127, 129, 136 
Devonian, 143 
Miocene, 143, 146 
Mississippian, 145 
Permian, 145 
Pliocene, 143 
Aristotle, 86, 89, 91 
Arrhenius, S., 97, 98 
Arthropods, 114 
Asia, as home of domestic animals, 178 
as primitive home of man, 149 
as theater of mammalian evolution, 
142 
Asteroids, see planetoids 
Asthenosphere, 41 
Athenians, 147 
Atmosphere, 54, 57, 75, 80 
in Archeozoic, 63 
of growing earth, 51 
of water-gas, 35 
origin of, 50 
primordial, 34 ’ 
Atmospheric blanket, of earth, 54 
Atoms, 100, 101, 102 
Australians, native, 150 
Azoic era, time ratio of, 69 


Bacteria, 96, 97 
Baker, H., 91 
Balanoglossus, 117 


196 
Barbarism, 152, 154 
Barrell, J., 47, 49, 50, 56, 67, 69, 110 
Beans, 154 
Bees, 90 
Beetles, 90 
Belgium, optimum temperature in, as 
shown by death-rate, 167-169 
Bichat, M. F. X., 86 
Biochemists, 85, 95 
Biogenesis, history of, 89 
Biology, 82 
Bipedality, cause of, 129, 130 
Birds, evolution of, 127 
first recorded, 111, 129 
origin of, 111, 128, 145 | 
toothed, 65, 129, frontispiece 
Blainville, D. de, 86 
Boleophthalmus, 120 
Brachiation, 140 
Brachiopods, 113 
Breaks, geologic, 70, 71 
Brontosaurus, 130 
Browne, Sir Thomas, 90 
Browsing mammals, origin of, 111 
Buffon, Comte de, 92 “ 
Butterflies, 90 


Cacops, 125, 126 
California, agriculture of, 153 
deaths in, 158, 161, 164, 165 
Indians of, 152, 153, 154 
rainfall in, 187 
rate of growth of big trees in, 185, 
186 
southern, climate of, 166 
storms in, 166 
Cambrian period, 46, 79, 111, 113, 118 
Camels, 74, 136, 137, 178 
Campbell, W. W., 11, 21 
Canadian period, 76 
Carbohydrates, 84 
Carbon, 75, 102 
compounds, 100 


INDEX 


Carbon dioxide, 34, 35, 38, 44, 50, 
52, 54, 57, 102, 104, 105 . 
dioxide, as climate regulator, 52_ 
dioxide, in Archeozoic, 63 a. 
dioxide, resupply of, throuaig 
canoes, 52 i 
monoxide, 34, 35 “ 
Carbonic acid, 99 
Cardan, G., 89 
Carnivores, 136 B= 
Cascadian revolution, 110, 111, 146 
Catalysis, 104 ; 
Cells, 87, 94, 102, 105, 106 
potential immortality of, 98 a 
Cenozoic era, 46, 65, 73, 74, 76 Ry 
110, 111 Bt 


~| ao 
oe 


era, time ratio of, 69 ix 
sediments, thickness of, 65, 67 
Central America, 187, 188, 189 
Cephalopods, 114, 115 
Ceratopsia, 132 
Cereals, 179 
Cetacea, 115 
Chaldeans, 181 
Chalks, 58 
Chamberlin, T. C., 21, 24, 25, 47, 5 5 
116, 119 | 4 
Chamberlin and Moulton, on the nebi 
lar hypothesis, 12 2 
planetesimal hypothesis of, 13, 
Chazyian period, 76 , 
Chemical elements, essential to d 
105 I 
Chimpanzee, 139, 140, 142 
China, 179 
Chinese, 181 
Chlamydosaurus, 130 
Chordates, evolution of, cause bs 
first recorded, 119 
origin of, according to Chambe erli 
119 a, 
Cincinnati uplift, 62 
Cincinnatian period, 76 


y! 
Dy " 


Civilization, distribution of, 173 

- evolution of, 147, 174 

high, areas of, 188 

Civilizations, early, 179 

Clarke, F. W., 52, 54, 56 

Climate, arctic, effect of, on man, 149 

as factor in racial differences, 148 

_ changes in, 53, 78, 80, 111 

_ changes in, as cause of extinction, 

131 

_ changes in, causes of, 187 

changes in, effects of, 187 

changes in, evidences for, 184, 185 

changes in, historical, 183, 186 

_ Cretaceous, 55, 132 

effect of, on clothing, 154 

: effect of, on death-rate, 158 

effect of, on discovery of use of fire, 

= 175 

effect of, on energy, 156 

effect of, on food, 154 

__ effect of, on man, 153 

3 effect of, on materials for shelter, 

154 

. effect of, on Roman history, 190 

_ Eocene, 55 

_ Liassic, 55 

- Permian, 51, 55, 127, 129, 145 
Pleistocene, 55, 66, 110 


_ Triassic, 55 

_ tropical, effect of, on man, 149 

Climates, ancient, 51, 52, 55 

- glacial, 55, 66, 73, 110, 127, 143 
limographs, 159-161, 168, 169 

Clothing, dependence of, on climate, 

154 

effect of, on energy, 156 

“necessitated by Glacial period, 143 

Yoal, 65, 66, 155, 174 

Jelenterates, 113, 114 

Sold, increase in, influence of, 127 


INDEX 


197 
Collisions, among planetary nuclei, 33 
among stars, 23 
Colloidal suspension, life elements in, 
106 
Colloids, 100, 101 
characteristics of, 101 
Comanchian period, 46, 76, 79, 111, 
131, 145 
Communal life, 144 
Complexification, in matter, 100 
Complexity, law of, 101 
Condylarths, 134, 136 
Conglomerates, 58 
Conifers, 65, 73 
Connecticut Valley footprints, 130 
Continents, areal variability of, 78 
elevation of, 71, 73, 75, 136 
in Archeozoic, 63 
origin of, 49 
permanency of, 50 
when largest, 73, 76 
Convection currents, 35, 37 
Coérdination, biochemical, 106 
Corals, 114 
Coryphodon, 136 
Cosmic time, 46, 47 
Cosmozoa theory, 95 
Crabs, land, 120 
Creator, 108 
Creodonts, 135 
Cretaceous period, 46, 76, 79, 111, 132, 
145 
period, climate of, 55, 132 
period, in North America, 77 
Critical periods, 73, 81 
Crocodiles, 131 
Croixian period, 76 
Crops, of early Americans, 154 
Crossopterygii, 122 
Crust of earth, granitic, 34 
Crustaceans, 120 
Crustal density, relation of, to ocean 
basins, 39 
Crystallization, fractional, 37 


198 

Crystalloids, 101 

Crystals, basic, 37 

Culture, centers of, 188, 189. 
Cyanogen, 99 

Cycads, 65, 73 

Cyclostomes, 120 

Cynodonts, 128 

Cysts, 96, 97 


Daly, R. A., 32 
Dana, J. D., 50, 69 
Darwin, C. R., 108, 155 
Death-rate, cause of differences in, 163 
effect of storms on, 166 
effect of temperature on, 164 
Deaths, statistics of, 158, 159, 160, 161 
Deer, 136, 137 
Denudation, 58 
rates of, 59 
Deposition, rate of, 68 
Deposits, cycles of, 58 
glacial, 54, 56 
organic, 58 
salt, 32 
Derham, W., 91 
Deserts, 73, 185 
effect of, on man, 150 
Devonian, Lower, 123, 144 
period, 46, 76, 79, 111, 122 
period, aridity in, 143 
period, diastrophism in, 122 
Upper, 145 
Diastrophism, 50, 110, 118, 133 
Devonian, 122 
Miocene, 146 
Mississippian, 125 
Pennsylvanian, 127, 145 
Silurian, 122, 144 
Diaz, 182 
Dinocerata, 136 
Dinosaurs, 73 
ankylosaurs, 132 
armored, 130, 132 
associated with peneplanation, 133 


INDEX 


Dinosaurs, bipedal, 129 
carnivorous, 130, 132 
Ceratopsia, 132 
duck-billed, 132 
effect of, on mammals, 133 

evolution of, 145 
expansion of, 145 
extinction of, 131, 132, 134 
nodosaurs, 132 
origin of, 111, 129 
Sauropoda, 111, 130, 132, 145 
Stegosauria, 130 
Theropoda, 130 
trachodons, 132 
unarmored, 132 

Diplocynodon, 133 

Diplodocus, 130 ‘9 

Dipnoans, 121, 122 a 

Disruption hypothesis, of Chamberlin 

and Moulton, 46 'y 

Disturbances, 70 a 

Dog, 177 | 

Double-breathing, 120 

Dromocyon, 135 


- 
a 
?, 
ry: | 
as 
we 
nab 


Earth, 105 

age of, 57 

as a planet, 5 

atmospheric blanket of, 54 

crustal readjustments in, 78 

diameter of, 48 

effect of moon on, 28 

effect of, on moon, 30 

evolution of, 45, 94 

granitic crust of, 34 . 4 

growing, atmosphere of, 51 3 

-growth, by rapid infall of plan- 
etoids, 25 -_ 

-growth, by slow accretion of plat - 
etesimals, 24 e 

-growth, in Formative era, 47 

internal heat of, 48, 49 

-moon knot, 19 

negative areas in surface of, 50 


‘Earth, origin of, 46 
outer shell of, 40 


state, 36 
place of, in universe, 4 
positive areas in surface of, 50 
primordial molten state of, 26, 33 
 readjustments in, 70, 71 
shrinkage of, 48, 70, 71, 80, 109 
sub-crustal shell of, 40 
_ tidal strains in, 30 
_ warping of, 70, 109 
Echinoderms, 114 
Eels, 90 . . 
Efficiency, effect of climate on, 156 
Eggs, 126 
Egypt,-90, 97, 179, 181, 182 
Elephants, see Proboscidea 
Energy, as factor in human progress, 
147, 155, 173, 174, 192 
distribution of, on basis of climate, 
173 
electric, of chemical elements, 105 
heat, 105 
to what due, 156 
“Energy traffic,” 85, 102 
~ England, iron in, 155 
- Englishmen, 148 
' Environment, changes in, 73 
_ fitness of, 88 
Enzyme theory, of Troland, 103 
Enzymes, autocatalytic, 103 
catalytic power of, 104 
evolution of, 106 
Eocene time, 46, 111, 137, 138, 145, 146 
time, climate of, 55 
Eopaleozoic time, 79 
_Epi-Proterozoic interval, 119 
Eras, duration of, 67, 68 
Erosion, 32, 40, 54, 56, 57, 58, 60, 70, 
76, 78, 110 
Erpetoichthys, 122 
Eskimos, 151 
Europeans, modern, 154 


- INDEX 


passage of, from molten into rigid © 


199 
Evolution, 73, 98 


crises of, 112 
cycles of, 80, $1 
organic, 101 


Fats, 84 
Finland, optimum temperature in, as 
shown by death-rate, 167, 169 
Finns, 169, 171 
Fire, discovery of use of, 174, 175 
life derived from, 99 
Fish forms, 116 
Fishes, $1, 89, 119, 123 
Age of, 46 
origin of, 65 
Flight, true, evolution of, 128 
Floras, origin of, 65 
Flying dragons, 73 
Food, dependence of, on climate, 154, 
155 
effect of, on energy, 156 
use of fire in cooking, 175 
Foot, reptilian, 124 
terrestrial, evolution of, 123 
terrestrial, origin of, 111 
Footprint, earliest known, 123, 124, 
144 
Footprints, Connecticut Valley, 130 
Upper Triassic, 129 
Formative era, 46, 47, 49, 50 
era, earth-growth in, 47 
era, volcanism in, 48 
Fossils, 59 
living, $1 
France, deaths in, 160, 164, 165 


Gabbro, 39 

Gadow, H., 131 
Galaxy, see Milky Way 
Gale, H. S., 185 
Galton, F., 147 
Ganoids, 122 

Gautama, 182 


200 
Geikie, A., 76 
Generation, equivocal, 91 
spontaneous, 90, 91 
Geologic column, 60, 67 
history, 108 
record, 70 
time, eras of, 63 
time, length of, 80 
time, ratios of, 69 
time-table, 45 
Geosynclines, 61, 62 
Germany, optimum temperature in, as 
shown by death-rate, 167 
Gibbon, 139, 140, 141, 142, 144 
Gills, 120 
Glacial deposits, 54, 56 
period, 46, 184 
period, effect of, on man, 149 
periods, 55, 183 
Gorilla, 139, 140, 142 
Grand Canyon revolution, 111, 118 
Granite, 37, 40, 49, 75 
Graphite, 63, 113 
Grasses, expansion of, 136 
used for food by man, 143 
Gravitation, 97 
Grazing mammals, expansion of, 137 
mammals, origin of, 111 
mammals, rise of, 136 
Greece, 147, 175 
Greeks, 89, 191 


Habitats, organic, variability in, 78 
Hands, as organs of the mind, 143 
Haughton, S., 69 
Health, best climatic conditions for, 
158 

effect of storms on, 166 
Helmholtz, H. L. F. von, 10, 96, 98 
Helmont, J. B. van, 90 
Henderson, L. J., 88 
Herds, 178 
Himalayan uplift, 146 
Himalayas, 74 


INDEX . 


Imagination, scientific, 106 


Holmes, A., 52, 57, 60, 61 
Homo (Eoanthropus) dawsoni, 142 
Hopi Indians, 152, 154, 180 
Hornets, 90 

Horses, 74, 136, 137, 177, 178 
Hottentots, 150 

Human progress, factors in, 147 
Humboldt, A. von, 182 

Hunters, 151, 154, 177 

Huxley, T. H., 54, 107 
Hydrogen, 102 

Hydrosphere, 50, 51, 55, 63, 75 
Hylobates lar, 144 


Ice age, Permian, 51 
age, Proterozoic, 51 
Igneous rocks, 43, 75 | 
rocks, as source of oceanic salts, 56 — 
rocks, erosion of, 32 


Impact, effects of, 28 
India, 179 
irrigation in, 180 
Indian corn, 154 
Indians, American, 148, 151, 153, 177 : 
California, 152, 153, 154 
Hopi, 152, 154, 180 
New Mexico, 152 
Pueblo, 152, 154 
Utah, 152 
Ute, 152, 153, 154 
Indo-China, 188 
Infusions, organic, 93 
sterilization of, 92 
Insectivores, 136 
Insects, 73, 89 
Intervals, time, 71, 73 
Invertebrates, distinguished from ver- — 
tebrates, 114 | 
evolution of, 114 
Iron, 155 
compounds of, 102 
discovery of use of, 175 ; 
limits to use of, 155 


INDEX 


Irrigation, 153, 154, 179, 180 
Irritability of living matter, 95 
Isostasy, 40, 41 

Italy, deaths in, 158, 160, 164, 165 


Japan, optimum temperature in, as 
shown by death-rate, 167 
Japanese, 149, 169 
Java, 188 
irrigation in, 180 
Jefferson, Thomas, 74 
Jelly-fishes, 114 
Johnston and Williamson, 52 
Jupiter, 5, 6, 31, 
Jurassic, Lower, 145 
period, 46, 76, 79, 111, 130, 131 
Upper, 127, 129, 145 
Juvenile waters, 38, 75 


Kankakee uplift, 62 

Kant, hypothesis of, concerning evolu- 
tion of solar system, 10 

Kelvin, 96 

Kircher, 90 


Labrador, fishermen of, 152 

Lamprey, 116 

Land-bridges, 73, 74, 138 

Land waters, as place of chordate 

origin, 119 

Lands, contributions of, to oceans, 61 
elevation of, 70, 109, 110, 111 

Lane’s law, 15 

Laplace, P. S. de, 10, 50 

Laramide revolution, 111, 132, 134, 145 

La Tour, C. de, 93 

Laurentian peneplain, 118 

Lava, 2, 38, 44, 75 

Lavas, of moon, 43 
Proterozoic, 64 | 

Law of Complexity, 101 

Lehman and Pedersen, 172 

Leith and Mead, 60 

Lepidosiren, 122 


20I 
Leverrier, U. J. J., 27 
Lewes, 86 
Lias, climate of, 55 
Life, 88 
ancient, 59 
Archeozoic, 63 
as manifestation of protoplasmic. 
activity, 82 
changes in, 73 
chemical elements essential to, 105 
chemical elements of, grouping of, 
105 
communal, 144 
cycles in, 73 
definitions of, 85 
dormant, 97 
elements, coérdination of, 105 
elements, grouping of, 105 
elements, in colloidal suspension, 106 
evolution of, 64 
fresh-water record of, 59 
land record of, 59 
marine, increase in, 78 
marine, record of, 59 
materials at basis of, 51 
origin of, 63, 82, 94, 112 
paleontological record of, 93 
pulse of, 81, 109, 111, 144, 146 
scientific explanation of, 95 
thermometers, 55 
transportation of, through space, 96 
vehicle of manifestations of, 85 
Light, radiation pressure of, 97 
Lightning, 102, 103 
Limbs, change in, in primates, 143 
Lime-secretion, establishment of, 113 
Limestones, 58, 60, 61, 67, 68 
Lincoln, A., 182 
Lithosphere, 41, 49, 50, 75, 76 
density differences in, 41 
Lizards, bipedal, 130 
frilled, 130 
Llama, 178 
Locusts, 90 


202 

Loeb, J., 98 

Loligo, 115 

Los Angeles, deaths in, 158, 161 
rainfall at, 153 

Lucretius, 89 

Lull, R. S., 148 

Lung-breathing, first recorded, 123 
place of origin of, 121 

Lung-fishes, 121, 122 
first recorded, 144 

Lungs, development of, 144 
of higher vertebrates, 120 
origin of, 111 


Maggots, 90 
Magmas, 2, 34, 37, 38, 39, 40, 42, 43, 44 
Maize, 179 
Malaria, 191 
Mammals, 65, 73, 81 
Age of, 46 
archaic, 111, 134, 135, 136, 145 
browsing, origin of, 111 
evolution of, 127, 145 
expansion of, 134 
fate of, 136 
first recorded, 111, 127 
grazing, rise of, 111, 136, 137 
modernized, 135, 145 
modernized, origin of, 111 
modernized, source of, 135 
origin of, 111, 128, 145 
placental, 126 
rise of, 133 
Man, Age of, 45 
best climatic conditions for, 158 
brute-, 74 
dominance of, over organic world, 
144, 146 
increase of, dependent on domestic 
animals, 178 
origin of, 111, 137 
physiological adjustment of, to cli- 
mate, 156 
reasoning, 74 


INDEX 


Miacida, 136 


Man, response of, to climate, 157, 74 
rise of, 146 
Mars, 5, 27, 31 
Material resources, as factor in hun 
progress, 147, 151, 152, 154, 18 5, 
174, 193 
resources, limited by climate, 155 
Matter, complexification in, 100 
evolution of, 106 
living, irritability of, 95 
Matthew, W. D., 117, 184 
Mayas, 181, 187, 189 
Mediterranean lands, iron in, 155 
lands, rainfall in, 187, 188 
peoples, 169,171. a 
Membranes, extra-embryonal, 126, 12! . 
Mental activity, optimum temperaturs 
for, 172 a 
alertness, a manifestation of ener zy 
156 . 
alertness, effect of lack of materia 1 
resources on, 150 om 
capacity, as factor in human prog- 
ress, 147, 148, 174, 192 
Mentality, 81 
Mercury, 28 
Mesopotamia, 179, 181, 182 . 
Mesozoic era, 46, 65, 73, 76, 78, 79, 111, a 
132, 133 1 
era, time ratio of, 69 
sediments, thickness of, 65, 67 
Meteorites, 33 
Meteors, 27, 97 


aoe: 
A 
ag 
” 


ee 
Fi ota i 


SN cota 


Se es 


Mice, 90 

Microcosm, organism as, 88 

Milky Way, 8 

Millet, 179 

Mining, 153 

Miocene time, 46, 111, 136, 138 
time, aridity in, 143, 146 
time, diastrophism in, 142, 146 Tae 

Mississippian period, 46, 76, 79, a“ 

125, 145 


‘ 


INDEX 


Mississippian period, aridity in, 145 
period, diastrophism in, 125 

Mohammed, 151, 182 

Mohawkian period, 76 

Molecules, 84, 100 


_ Molluscs, 114, 120 
_ Molten stage, in earth’s history, 26, 33 
- Mongolia, 185 


Mongoloid races, 171 
Monotremes, 127 


- Moon, 2, 5, 13, 28, 30, 33, 43 


effect of earth on, 30 
effect of, on earth, 28 
in Archeozoic, 63 


- Moon-knot, 47 
Moore, B., 100 
- Moulton, F. R., 12, 18, 19 
_ Mountain-making, 53, 70, 78, 109 


Mountains, 71 
cycles of, 60 
origin of, 48 

Muds, 58, 60 


a Mud-skippers, 120 


Mudstones, 58, 61, 67, 68 


Mutants, 148 


_ Nature, uniformity of, 45 


Nebulz, 8 
irregular, 8 
planetary, 8 
ring, 9 
solar, 21, 47 
spiral, 8, 9, 13, 18, 20, 21, 47 
stellar, 9 


~ Nebular hypothesis of Laplace, 10 


hypothesis of Laplace, modifications 
of, 11 


_ Needham, T., 92 


Negative areas, in earth’s surface, 50 
Negroes, American, adaptation of, to 
_ climate, 171 
death-rate of, 164, 168, 169, 171 
effect of tropical climate on, 149 


Neoceratodus, 121, 122 


203 
Neogene time, 79 
Neopaleozoic time, 79 
Neptune, 4, 5, 6 
Neutral medial area of North America, 
62 

New Mexico, Indians of, 152 
New York City, death-rate in, 171 
Newfoundland, fishermen of, 152 
Nitrogen, 44, 102, 103 

compounds, 104, 105 

in primordial atmosphere, 34 
Nodosaurs, 132 
Nome land-bridge, 74 
Nordics, 149, 169, 171 
North America, in Paleozoic time, map 

of, 62 

North Carolina, death-rate in, 171 
Nuclei, planetary, 19, 33 
Nythosaurus larvatus, 128 


Oceanic basins, 43 
basins, in Archeozoic, 63 
basins, increase in volume of, 39 
basins, origin of, 39, 49 
basins, relations of crustal density 
to, 39 
currents, 54 
currents, changes in, 73 
floodings, 61, 71, 75, 76, 79 
floodings, Cretaceous, 77 
floodings, Pennsylvanian, 66 
floodings, Silurian, 72 
level, inconstancy of, 76 
salts, 31, 50, 56 
waters, gathering of, 37 
waters, increase in volume of, 50 
waters, origin of, 55 
Oceans, carbon dioxide in, 52 
increase in area of, 78 
origin of, 37 
when smallest, 73 
Oligocene time, 46, 111, 135, 136, 145 
Orang, 139, 140, 142 
Orbits, planetary, 5, 19 


204 


Ordovician period, 46, 79, 111, 113, 


119, 144 
Organic deposits, 58 
habitats, areal variability in, 78 
Organism, 105 
Organisms, bionomic relations of, 108 
individuality of, 87 
origin of, 106 
Orion, 8 
Osborn, H. F., 104 
Ostracoderms, 119 
origin of, 111 
Over-specialization, indications of, 131 
Owens Lake, 185 
Ox, 177, 178 
Oxalates, 107 
Oxides, 100 
Oxygen, 44, 51, 102 
importance of, for life, 92 
in primordial atmosphere, 34 
Ozark uplift, 62 


Paleogene time, 79 
Paleogeography, 66, 72, 77 


Paleozoic era, 46, 64, 65, 76, 78, 79, 


111, 127 
era, North America in, 62 
era, time ratio of, 69 
sediments, thickness of, 65, 67 
Palms, 184 
Panama land-bridge, 74 
Pasteur, L., 93, 182 
Patten, W., 119 
Peabody Museum of Yale University, 
123, 133 
Penck, A., 187 
Peneplanation, 76 
Pennsylvanian period, 46, 66, 76, 79, 
111,..127 
period, diastrophism in, 127, 145 
period, North America in, 66 
Periodicity, 70, 75 
Periophthalmus, 120 


INDEX | 3 


=! 
“~— 


Permian period, 46, 76, 79, 111,127 _ 
period, aridity in, 145 Z 
period, climate of, 51, 55, 127, 

145 a , 

Persia, 185 

Peru, 180, 188, 189 

Petromyzon, 116 ~ 

Pfliiger, E., 99 ae 

Phasic activity, 100 a 

Phenacodus primavus, 136 

Phosphates, 107 

Physical activity, optimum ‘temy 


ture for, 172 — 
Pig, 177 3 
Planetary nuclei, 19, 33 a 
system, 47 Sa 
Planetesimal dust, 25 . , 


hypothesis, 13, 101 
hypothesis, outstanding difficulties @ 
20 
material, 32 
Planetesimals, 35, 47 
earth-growth by slow accretion o: 
24 z 
Planetoids, 4, 5, 26, 28 
earth-growth by rapid infall of, 26 
significance of, 26 
Planets, 4, 5, 13, 18, 19, 24, 28, 31 
relations of, 5, 6 
Plants, flowering, 65, 73 
herbaceous, 136 
lime-secreting, 113 
Pleiades, 8 
Pleistocene time, 46, 111, 138 
time, climate of, 55, 66, 110 x 
Pliocene time, 46, 111 4 
time, aridity in, 143 
Polypterus delhezi, 122 
Positive areas, in earth’s surface, 50 — 
areas, in North America, 62 = 
Posture, erect, assumption of, 143 
Primates, 136, 137, 143 
American, 137 
descent of, from trees, 143, 146 


INDEX 


Primates, distribution of, 138, 139 
Eocene, 137 
European, 138 
evolution of, 146 
origin of, 111 
radiation of, 137, 138, 142 
Proavian, 129, frontispiece 
Proboscidea, 74, 136 
Proteins, 84, 85, 99, 100 
Proterozoic era, 46, 113, 118, 144 
era, climates of, 51, 55 
era, time ratio of, 69 
lavas, 64 
sediments, thickness of, 64, 67 
Protochordates, 118 
Protoplasm, 82, 88, 99, 100, 105 
alveolar substance of, 83 
chemical characteristics of, 84 
combinations of elements in, 84 
lability of, 85 
living, evolution of, 107 
physical characteristics of, $3 
variation in, 87 
Protopterus, 121 
Protozoa, 96, 97, 113 
Psychozoic era, 45, 66 
Pueblo Indians, 152, 154 
Pulse of life, 81, 109, 111, 144, 146 
Pumpkins, 154 
Pyramid Lake, 185 


Rabl, C., 123 
Racial differences, causes of, 148 
Radioactive elements, 42 
minerals, rate of disintegration’ of, 
as basis for computing geologic 
time, 67, 68. 
Radiolaria, 113 
Rain, 54 
first, on earth, 37 
Rainfall, 153, 154, 184 
Ranodon sibericus, 124 
Recrystallization, 40 
Redi, F., 90, 91, 92 


205 
Reptiles, 65, 73, 81, 132, 145 
Age of, 46 
foot of, 124 
origin of, 65, 111, 125 
Revolutions, 71 
Rhinoceroses, 136 
Rhodesia, 188, 189 
Rhythms, in solar energy, 109 
Rice, 179 
Richter, 96, 98 
Rivers, 54, 57, 76 
Rocks, acidic, 49 
basaltic, 49 
basic, 49 
granitic, 49 
sedimentary, 57, 61, 67, 68 
stratified, composition of, 60 
Rodents, 136 
Roman history, effect of climate on, 
190 
Ross, 90 


Sacramento, deaths in, 158, 161 
Salamander, foot of, 124 
Salt deposits, 32 
evidence of, for climatic change, 185 
oceanic, derivation of, 32 
oceanic, significance of, 31 
Salt Lake City, rainfall at, 153 
San Diego, deaths in, 158, 161 * 
San Francisco, deaths in, 158, 161 
Sandstones, 58, 60, 61, 67, 68 
Santa Fé, rainfall at, 153 
Satellites, 6, 19 
Saturn, 5, 6, 31 
Sauropoda, 111, 130, 132, 145 
characteristics of, 131 
Savagery, 152, 154 
Schafer, E. A., 98 
Schuchert, C., 110 
Schwann, 93 
Scorpions, 90 
Sea-anemones, 114 


206 
Sedimentary rocks, distribution of, 61 
rocks, origin of, 57 
rocks, thicknesses of, 61, 67, 68 
Seeds, 97 
Selection, natural, 106 
Sharks, 120° 
Sheep, 177, 178 
Shellfish, 90 
Shelter, dependence of, on climate, 154 
effect of, on energy, 156 
Silica, 100 
Silurian period, 46, 76, 79, 111, 122, 123 
period, climate of, 55 
period, diastrophism in, 122, 144 
period, North America in, 72 
Sloths, fossil, 74 
Snails, 90 
Snow, 54 
Socrates, 151 
Soil, 155 
Solar energy, 102 
energy, rhythms in, 109 
prominences, 16 
system, elements of, 5 
system, Kant’s hypothesis of evolu- 
tion of, 10 
system, Laplace’s theory of origin of, 
10 
system, plantesimal hypothesis of 
origin of, 13 
Sollas, W. J., 60 
Space, interstellar, transportation of 
life through, 96 
Spallanzani, L., 92 
Speech, invention of, 174 
Spencer, H., 86 
Sponges, 113, 114 
Spontaneous generation, 90, 91 
Spores, 96, 97, 98 
Squids, 73, 114, 115 
Star streams, 7 
Stars, 6, 13, 15, 23 
chances of close approach among, 22 


INDEX y 


‘" 


Stars, mode of tidal disruption in, 15 x 
new, 9 
Wolf-Rayet, 9 4 

Static forms, $1 

Stegocephalia, 125, 145 

Stegosauria, 130, 132 
characteristics of, 131 

Stegosaurus, 130 

Stellar system, sun a member of, 6 — 

Stockholm, optimum temperature a 

as shown by death-rate, 167, a | 

Storms, changes in track of, 187. 
effect of, on human energy, 166 


present belt of, 187 B - 
Strand-line, 76, 120 ) 
Stratification, density, 36 , a 


Struggle for existence, 73, 81 ag 
Suess, E., 38 or ,, 
Sulphur, 102 
Sumatra, 188 4 
Sun, 4, 10, 12, 13, 19, 20, 44, 98, 1¢ 5 
ancestral, tidal disruption of, 16 5 
as life factor, 54 es 
as member of stellar system, 6 i. 
critical velocity of, 17 om 
origin of, 46 a 
prominences shot out from, 16 
rotation of, 20 
Sunshine, 102 
Surface processes, in earth, 43 
Swan, 89 . 
Sweden, iron in, 155 ne 
Swim-bladder, 120 a 
Swine, 136 . 


Tapirs, 136 
Tartrates, 107 a 
Temperature, changes in, effect of, 
165, 172 4 
effect of, on death-rate, 163, 164, 165. 
optimum, 167 
Terrestrial foot, evolution of, 123 
foot, origin of, 111 
types, influence of aridity on, 127 


' 


ea em 


i aan ae 1a 
a 4 : 


——- 
De x 


Re 


INDEX 


Terrestrial types, influence of increas- 
ing cold on, 127 
vertebrates, eggs of, 126 
vertebrates, emergence of, 119, 122 
waters, as place of chordate origin, 
119 
waters, as place of origin of lung- 
breathers, 121 
Tertiary, climatic oscillation in, 135 
Theriodonts, 128 
Thermal springs, 56, 75 
Theropoda, 130 
Thinopus antiquus, 123, 124 
Thorium, 42 
Tidal disruption, forces of, 13, 14 
disruption, in ancestral sun, 16, 17 
disruption, mode of, in stars, 15 
force, of earth on moon, 30 
retardations, 28 
strains, in earth, 30 
Tide-generating force, 16 
Tides, body, 29 
in Archeozoic, 63 
loss of energy due to, 29 
Tools, invention of, 174 
Trachodons, 132 
Trees, growth of, as evidence of cli- 
matic change, 185, 186 
Triassic period, 46, 76, 79, 111 
period, climate of, 55 
Upper, 127, 129, 133, 145 
Triton, 124,125 
Troland, L. T., enzyme theory of, 103 
Tropical climates, effect of, on man, 
149 
Tropics, contribution of, to civiliza- 
tion, 182 
Tunicates, 117 
Turkestan, 185 
Turkey, 185 
Tyndall, J., 93 


Underhill, F. P., 84 


Ungulates, 136 


207 
Uniformitarian trend, of biologic 
thought, 106 
United States, eastern, deaths in, 158, 
159, 161, 164, 165, 168, 169, 170, 
171 
northeastern, storms in, 166 
southwestern, ruins in, 185 
Weather Bureau, 184 
Uranium, 42, 67, 69 
Uranus, 4, 5, 6, 31 
Utah, 152, 153, 154 
Indians of, 152 
Ute Indians, 152, 153, 154 


Vadose water, 75 
Vegetation, dependence of, on climate, 
155 
Venus, 5, 28 
Vertebrates, distinguished from in- 
vertebrates, 114 
egg of, change in, 126 
evolution of, 113 
first recorded, 144 
origin of, 111, 114, 144 
terrestrial, emergence of, 119, 122 
Virgil, 89 
Vitalism, 94 
Volcanic activity, as source of earth’s 
water, 56 
activity, times of, 74 
ashes, 75 
Volcanism, in Formative era, 48 
Volcanoes, as source of carbon dioxide, 
52 


Walcott, C. D., 69 
Warm blood, origin of, 111, 127, 145 
Wasps, 90 
Water, precipitation of, 100 
Water-vapor, 54, 98 
-vapor, as climate regulator, 52 
-yapor, in primordial atmosphere, 
34, 35, 38 
Waters, juvenile, 38, 75 


; Waters, anit? as place of chordate 


origin, 119 
oceanic, gathering of, 37 
- vadose, 75 
Waucobian period, 76 
Weathering, 32, 33, 80 
Whales, 81 
Williams, H. S., 69 
Wilson, E. B., 94 


Ar 


Wd oa el Pe ee 
Winnemucka Lake, 185 : 
| Worms, 89, 90, 113, rr 


ng ees 
4 ‘a 


Writing, invention of, 11 


Yemen, 138, 189 me 
Young, ClAns, | 
Yucatan, rainfall i in, 188 


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