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HIE ORIGIN OF LIFE IN THE UNIVERSE 



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Cyril Ponnamperuma 



Exobiology Division 
National Aeronautics and Space Administration 

Ames Research Center 
Mbffett Field 
California 



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Space Science Education Conference 
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June k, 196k 









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In the 1958 Reith Lectures, A.C.B. Lovell, Professor of Radio- 
astronomy of the University of Manchester and Director of the Jodrell 
Bank Experimental Station, described the problem of the origin of the 
universe as the greatest challenge the human intellect has ever faced. 
Along vith the problem of the origin of the universe, the question of 
the origin of life and the origin of intelligence may be regarded as 
the three most fundamental questions of all science. It is my purpose 
this morning to outline hov modern science is endeavouring to find a 
solution to the problem of the origin of life. 

While the problem of the origin of the universe is staggering to 
the human mind in its very concept, the solution to the problem may 
come from a surprisingly simple, one-shot observation or experiment. 
The theory based on the evolutionary model of a universe arising from 
Abbe Lemaitre's primeval atom will stand or fall vhen an astronomer's 
penetrating gaze has compared the spatial density of galaxies fifty 
million light years ago vith those of ten billion light years ago. The 
rival cosmological concept of continuous creation demands the appearance 




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of hydrogen at several "billion trillion tons per second in the observable 
universe. This concept will "be satisfactorily proved when a nuclear 
physicist can demonstrate that energy can he converted into hydrogen 
at the rate of one atom per year, in a volume as big as a New York sky- 



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scraper. 

When we contemplate the origin of life, the enormity of the problem 
is equalled only by the complexity of the possible solutions. "The 
evolution movement," wrote Bergson, "would be a simple one, and we 
should soon be able to determine its direction if life had described 
a single course like that of a solid ball shot from a cannon. But it 
proceeds rather like a shell, which suddenly bursts into fragments, 
which fragments, being themselves shells, burst in their turn into 
fragments, destined to burst again, and so on for a time incommensurably 
long. We perceive only what is nearest to us, namely, the scattered 
movements of the pulverized explosions. From them we have to go back, 
stage by stage, to the original movement." 

Even the formulation of this problem is perhaps beyond the reach 



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of any one scientist, for such a scientist would have to "be at the 



same time a competent mathematician, a physicist, and experienced 



organic chemist. He should have a very extensive knowledge of geology, 



geophysics, and geochemistry and, besides all this, be absolutely at 



home in all biological disciplines. Sooner or later, this task would 



have to be given to groups representing all these faculties and working 



closely together theoretically as well as experimentally. Such was the 
view professed by Bernal in 19^9* However, today we have reason to be 



more optimistic. For the first time in human history, the sciences 



which arose as separate disciplines are seen fused together, and our 



own generation has witnessed the birth of such sciences as biophysics 



and molecular biology. 



Three factors have made the scientific approach to the question 



"how. did life begin" possible, not only theoretically but also 



experimentally: 



a) astronomical discoveries of the century 



b) the triumph of Darwinian evolution 



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c) recent biochemical advances, 



The humanist may he indignant that a problem so profound should be 



regarded as belonging to the laboratory, but the experimental scientist 



is optimistic that his investigations will some day unravel this great 



mystery. 



The astronomical discoveries of the century have relegated our 



earth to the corner of a universe made up of billions of stars. The 



study of the heavens, by present-day telescopes, has revealed more than 
10 stars. Like our own sun, each one of these stars can provide the 



photochemical basis for plant and animal life. Two factors become 



abundantly clear: that there is nothing unique about our sun which 



is the mainstay of life on this planet, and that there are more than 
IQr® opportunities for the existence of life. In the light of numerous 



possible restrictive conditions, a conservative estimate made by Harlow 
Shapley shows that there must be at least 10" planetary systems suitable 



for life. The astronomer, Su-shu Huang, however, considers that five 

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per cent of all stars can support life: there are 10 possible sites 



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for the existence of life. In the light of these considerations, the 



question of the origin of life assumes cosmic proportions. 



This conclusion which astronomers have reached by the rigorous 



analysis of scientific observations was already prophetically described 
by the Italian, Giordano Bruno, in the l6th century: "Sky, universe, 
all-embracing ether, and immeasurable space alive vith movement — 
all these are of one nature. In space there are countless constellations, 



suns, and planets; we see only the suns because they give light; the 
planets remain invisible, for they are small and dark. There axe also 



numberless earths circling around their suns, no worse and no»less 



inhabited than this globe of ours. For no reasonable mind can assume 



that heavenly bodies which may be far more magnificent than ours would 



not bear upon them creatures similar or even superior to those upon 



our human Earth." 



The Space Science Board of the U.S. National Academy of Sciences 



in an authoritative document set the search for extraterrestrial life 



as the prime goal of space biology: "It is not since Darwin and, 



before him, Copernicus, that science has had the opportunity for so 



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great an Impact on the understanding of man. The scientific question 
at stake in exobiology is the most exciting, challenging, and profound 
issue not only of the century but of the whole naturalistic movement 

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that has characterized the history of western thought for over three 
hundred years. If there is life on Mars, and if we can demonstrate 
its independent origin, then we shall have a heartening answer to the 
question of improbability and uniqueness in the origin of life. Arising 
twice in a single planetary system, it must surely occur abundantly 
elsewhere in the staggering number of comparable planetary systems. 

If pursued thoroughly, this search for life elsewhere will inevit- 
ably demand that man must get into space himself. We shall, of course, 
get on with the job using remotely controlled life-detection systems 
even before this venture is fully possible. But we shall never be 
satisfied with negative results from our instrumental life-detectors 
because they are intrinsically hampered in their scope by our current 
ignorance of the nature of whatever extraterrestrial life there may be. 
Furthermore, should these preliminary sallies give positive results, 



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the urgency for man to get there will only increase. Therefore, while 



the intellectual appeal of the extraterrestrial life question stands 



out above all else in space biology, it seems inevitable that the size 
of the man-in-space project (in terms of dollars and manpower) will 



exceed that of all other aspects of space biology/ 1 



There is a distinct possibility of our finding an answer to the 



question of the existence of life in our own planetary system, by 



an inspection of the planets with our immediate or remote sensors. 



Outside our planetary system one way by which we can answer the question 



is by making radio contact with other civilizations in outer space. 



The odds against success in such an attempt are literally astronomical. 



"There is one race of men; one race of gods; both have breath of life 



from a single mother. But sundered power holds us divided, so that one 



is nothing, while for the other the brazen sky is established their sure 



x citadel forever ,r wrote Pindar in the sixth Nemean Ode. 



However, we have yet another possibility in the experimental 



approach to the problem. As the laws of chemistry and physics are 



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universal, the retracing of the stages "by which life appeared on 



earth vould give strong support to the theory of its existence else- 



where in the universe. Laboratory experiments on earth can reveal 



which materials and conditions available in the universe might give 



rise to chemical components and structural or "behavioral attributes 



of life as we know it. 



Ihe Darwinian theory of evolution has postulated the unity of 



the earth! s entire biosphere. According to Darwin, the higher forms 



of life evolved from the lower over a very extended period in the life 



of this planet. Fossil analysis has shown that the oldest known forms 



of living systems may be about two billion years old. Life, indeed, 



had a beginning on this planet. Geochemical data tells us that the 



earth is about four and one-half billion years old. A question 



Immediately arises as to the history of our own planet between its 



birth four and one-half billion years ago and the emergence of life. 



This idea was uppermost in the mind of the physicist !Cyndall, when in 



I87I he wrote in his "Fragments of Science for unscientific people": 



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"Darwin placed at the root of life a primordial germ, from which he 



conceived that the amazing richness and variety of the life now upon 



the earth's surface might have been deduced. If this hypothesis were 



true, it would not be final. The human imagination would infallibly 



look beyond the germ and, however hopeless the attempt, would enquire 



into the history of its genesis . ... A desire immediately arises to 



connect the present life of our planet with the past. We wish to know 



something of our remotest ancestry . ... Does life belong to what we 



know as matter, or is it an independent principle inserted into matter 



at some suitable epoch, when the physical conditions became such as 

to permit of the development of life?" The consideration of biological 



evolution thus leads us logically to another form of evolution, namely, 



chemical evolution. 



Recent biochemical discoveries have underlined the remarkable 



unity of living matter. In all living organisms, from the smallest 



microbe to the largest mammal, there are two basic molecules. Their 



interaction appears to result in that unique property of matter which 
is generally described by the word;, "life". These two molecules are 



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the nucleic acids and protein. While each one of these molecules is 
complex in form, the units comprising them axe few in number. The 



nucleic acid molecule consists of nucleotides strung together like 



heads along a chain. The nucleotides, in turn, are made up of a purine 



or pyrimidine base, a sugar, and a phosphate. In the protein molecule, 



twenty amino acids link up with one another to give the macromolecule. 



A study of the composition of living matter thus leads us to the 



inescapable conclusion that all living organisms must have had some 



common chemical ancestry. A form of evolution purely chemical in 



nature must of necessity have preceded biological evolution. 



The evidence which is available from practically every field of 



science, thus leads us to the idea that nature is a unity which can be 



divided into categories merely for human convenience. The division of 



matter into living and non-living is perhaps an artificial one, which 



is convenient for distinguishing such extreme cases as a man and a 



rock, but would be quite inappropriate when describing a virus particle- 
Indeed, the crystallization of a virus by Wendell Stanley almost thirty 



years ago precipitated the need for revising our definition of the 



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terms "life n and "living". These sentiments were powerfully expressed 
by Pirie in an essay entitled "The Meaninglessness of the Terms Life 



and Living" • He compares our use of the terms "living" and" non-living" 



to the words acid and base as used in chemistry. While sodium hydroxide 



is distinctly alkaline, sulfuric acid is a powerful acid. However, in 



between, there is a whole variation in strength. The chemist has 



overcome the confusion arising from the use of the two terms, acid and 



base, by inventing the nomenclature of "hydrogen* ion concentration". 



He is thus able to describe all the observed phenomena in terms of one 
quantity. Thus, a liquid may have : a pH of k or a pH of 8. We may have 



to invent a similar quantity in order to avoid any vagueness that might 
arise in applying the term "life" to borderline cases such as the virus- 



Chemical evolution may be considered to have taken place in three 



stages: From inorganic chemistry to organic chemistry, and firom organic 



chemistry to biological chemistry. The first stage of chemical evolution 



perhaps began with the very origin of matter. In a series of cataclysmic 



reactions during the birth of a star, the elements of the periodic table 



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must have been formed. About 15 billion years later, when the solar 



system was being formed, the highly reactive elements which occur in 



living organisms, probably existed in combination with hydrogen - 



carbon as methane, nitrogen as ammonia, and oxygen as water. Four 



and a half billion years ago, when the planet earth was being born 



from the primitive dust cloud, the rudimentary molecules, which were 



the forerunners of the complex biological polymers of today, were 



perhaps already in existence. Within this framework, life appears 



to be a special property of matter, a property which arose at a 



particular period in the existence of our planet and which resulted 



from its orderly development. 



The idea of life arising from non-life, or the theory of spontaneous 



generation, had been accepted for centuries. One had only to accept 



the evidence of the senses, though the ancients: worms from mud, 



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maggots from decaying meat, and mice from old linen. Aristotle had 



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propounded the doctrine of spontaneous generation in his "Metaphysics" 



He had traced the generation of fireflies to morning dew and the birth 



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of mice to moist soil. His teaching was accepted by the long line 



of Western thinkers who had turned to him as the final authority in 



matters metaphysical and physical. 



The ancient Hindu scriptures described life as having originated 



from non-living matter. Hie Big Veda, for example, pointed to the 



beginning of life from the primary elements, while the Atharva Veda 



postulated the oceans as the cradle of all life. 



Newton, Harvey, Descartes, van Helmont, all accepted the idea of 



spontaneous generation without serious question. Even the English 



Jesuit, John !Tiiberville Needham, could subscribe to this view, for 



Genesis tells not that God created plants and animals directly but 



that he bade the earth and waters to bring them forth. 



The world's literature is full of allusions to this popular 



belief in spontaneous generation. Virgil in his "Georgics" tells 



\ us how a swarm of bees arose from the carcase of a calf. Lucretius 



in "De Natura Rerum" refers to the earth as the mother of all living 



things. "With right 



It f olloweth then that earth hath won the name 



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Qf Mother, since from earth have all things sprung." 



Recall "Antony arid Cleopatra", Act II, Scene VII, where Lepidus tells 



Mark Antony "Your serpent of Egypt is bred ♦.. now of your mud "by the 



operation of your sun - so is your crocodile. 



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In the middle of the last century, Pasteur, by a series of 



brilliant experiments demonstrated that living systems could not arise 



out of non-living material. Pasteur dealt the death blow to the theory 



of spontaneous generation which was based on incompetent observation 



and the willingness to accept the superficial evidence of the senses. 

Unfortunately, Pasteur's work gave rise to the misconception that 
the problem of the origin of life could not be approached by scientific 
methods. The question of life's beginning was, therefore, considered 



to be unworthy of the attention of any serious scientific investigator. 



But a little thought makes it transparently clear that what Pasteur 



disapproved was the growth of microorganisms from sterile starting 



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material. It is indeed a very different thing from what we are con- 



cerned with: in chemical evolution - the gradual formation of organic 



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compounds over hundreds of millions of years and the slow emergence 

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of replicating systems. 

The story of Louis Pasteur is often told to beginning students 
in "biology as a triumph of reason over mysticism. But today we know 
it is perhaps the contrary. The reasonable view is to believe in 
spontaneous generation though in a restricted sense. 

Among those who speculated on the conditions necessary for the 
origin of life, Charles Darwin was a pioneer. In a letter to a friend 
he wrote: "If we could conceive in some warm little pond, with all 
sorts of ammonia and phosphoric salts, light, heat, electricity, etc. 
present that a proteine compound was chemically formed ready to undergo 
still more complex changes." This was too outrageous a declaration for 
the conservative thinking of Darwin's contemporaries. At the height 
of the controversey over the origin of the species, little or no 
attention was paid to the remote question of the origin of life. 
f^ ^ The great impetus, however, to the experimental study of the origin 

of life began with the Russian biochemist, Oparin. Already in 192**-, a 
preliminary booklet was published by him in Russian pointing out "that 



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there vas no fundamental difference between a living organism and brute 



matter. The complex combination of manifestations and properties so 



characteristic of life must have arisen in the process of the evolution 

of matter." According to Oparin, "at first there vere the simple solutions 



of organic substances whose behaviour vas governed by the properties 



of their component atoms and the arrangement of these atoms in the 



molecular structure. But gradually, as a result of growth, and increasing 



complexity of the molecules, new properties have come into being and a 



new colloidal chemical order was imposed on the more simple organic 



chemical relations. These never properties vere determined by the 



spatial arrangement and mutual relationship of the molecules. In this 



process biological orderliness already comes into prominence." 



Independently of Oparin, Haldane in 1928 had speculated on the 
early conditions suitable for the emergence of terrestrial life. "When 



ultraviolet light acts on a mixture of water, carbon dioxide and ammonia, 



a variety of organic substances are made, including sugars, and apparently 



some of the materials from which proteins are built up. Before the 



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origln of life they must have accumulated until the primitive oceans 



reached the constituency of a hot dilute soup # " 



Twenty years after the appearance of Haldane's paper, Bernal of 



/ the University of London theorized before the British Physical Society 



in a lecture entitled "The Physical Basis of Life." "Condensations 



and dehydrogenations are bound to lead to increasingly unsaturated 



substances, and ultimately to simple and possibly even to condensed 



ring structures, almost certainly containing nitrogen, such as the 



pyrlmidines and purines. The appearance of such molecules makes 



possible still further syntheses. The concentration of products is 



an absolute necessity for any further evolution. One method of concen- 



tration vould of course take place in lagoons and pools which are bound 



to have fringed all early coastlines, produced by the same physical 



factors of wind and wave that produce them today. A much more favour- 



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able condition for concentration, and one which must certainly have 



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taken place on a very large scale, is that of adsorption in fine clay 



deposits. It is therefore certain that the primary photochemical 



products would be so adsorbed, and during the movement of the clay 



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might easily "be held blocked from further possibly destructive trans- 



formations. In this vay relatively large concentrations of molecules 



could be formed." 



A starting point for any consideration of the origin of life 



must turn round the question of the cosmic distribution of elements 



Astronomical spectroscopy reveals that with surprising uniformity the 



most abundant elements in our galaxy are, in the order of rank, hydrogen, 
helium, oxygen, nitrogen, and carbon. Hydrogen, oxygen, nitrogen, and 



carbon are indeed the basic constituents of living systems. The table 



on the composition of the sun illustrates the distribution of these 



elements very clearly. (Figure l) 



The present rarity of the terrestrial noble gases vith respect 



to their cosmic distribution indicates that a primary atmosphere of 



the earth vas almost completely lost in early times, and that the 



present atmosphere is of secondary origin. The chemical composition 



of the secondary atmosphere must at first have been very similar to 



that of the primary atmosphere. Because of its high rate of escape, 






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-19- 



most of the free hydrogen must have been lost and the principal 



constituents of the atmosphere must have "been vater vapor, ammonia, 



and methane. It is this atmosphere of vater vapor, methane, ammonia, 



and small amounts of hydrogen which will he considered in this 



discussion as the primitive atmosphere of the earth. 



The energies available for the synthesis of organic compounds 



under primitive earth conditions are ultraviolet light from the sun, 



electric discharges, ionizing radiation, and heat. It is evident that 



sunlight was the principal source of energy. Photochemical reactions 



would have taken place in the upper atmosphere and the products trans- 



ferred by convection. Next in importance as a source of energy are 



electric discharges such as lightning and corona discharges from 



pointed objects. These occur close to the earth's surface and hence 



would more efficiently deposit the reaction products in the primitive 



oceans. A certain amount of energy was also available from the 
disintegration of uranium, thorium, and potassium *K). While some of 
this energy may have been expended on the solid material such as rocks, 



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- 20 - 



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a certain proportion of it was available in the oceans and the atmos- 
phere . Heat from volcanoes may also have been effective. In comparison 
to the energy from the sun and electric discharges, this vas, perhaps, 
not too videly distributed and its effect may have been only local, 
on the sides of volcanoes for example. 

Most of these forms of energy have been used in the laboratory 
for the synthesis of organic molecules. Simulation experiments have 
been devised to study the effect of ionizing radiation, electric dis- 
charges, heat, and ultraviolet light on the assumed early atmosphere of 
the earth. The analysis of the end products has often yielded, very 
surprisingly, the very compounds which we consider today as important. 
for living systems. 

Among the first experiments specifically designed to test some of 
the theories on the origin of life were those of Calvin and his associates 

in Berkeley. In 1951 they radiated water and carbon dioxide in the 

\ 

--^T" y Berkeley cyclotron and obtained appreciable yields of formaldehyde and 

formic acid. Although in this experiment carbon dioxide was used as 
the source of carbon, instead of methane, it established very clearly 



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-21- 



that materials of biological significance can "be synthesized non- 



biologically. It may "be pertinent here to recall that in 1829 Wohler 



synthesized urea from ammonium cyanide and disproved the theory long 



held by Berzelius and others that a "vital force" was necessary for 



the production of organic compounds. 



A classic experiment in this field was performed in 1953 by 



Stanley Miller who was then a graduate student of Harold Urey at the 



University of Chicago. When methane, ammonia, water and hydrogen were 



subjected to a high frequency electric discharge, some amino acids 



were produced. A more complete analysis shoved a variety of organic 



products. 



Miller's experiments on the mechanism of the synthesis of amino 



acids by electric discharges, indicated that a special set of conditions 



was not required to obtain amino acids. Any process or combination of 



processes that yielded the two very basic carbon compounds, formalde- 
hyde and hydrogen cyanide, would have contributed to the accumulation 
of amino acids in the oceans of the primitive earth. Therefore, whether 



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"■'JO" 



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the aldehyde and hydrogen cyanide came from ultraviolet light or 
from electric discharges is not of fundamental importance, since both 
processes would have contributed to the amino acid content. It may 
be that electric discharges were the principal sources of hydrogen 
cyanide and that ultraviolet light was the principal source of alde- 
hyde, and that the two processes complimented each other. 

The work of Sidney Pox of Florida State University has centered 
around the thermal model of biochemical origins. Although this model 
limits itself to a single form of energy, a somewhat coherent picture 
seems to emerge. 

When a mixture of methane, ammonia, and water in the gas phase 
is passed through a heated tube containing alumina at about 1000 and 
the reactants absorbed in water, amino acids are formed. Fourteen of 
the amino acids which commonly occur in protein have been synthesized 
by this method. 

If the eighteen amino acids usually present in proteins are heated 
to about 200 C polymers can be obtained. These random polymers have 



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-23- 



been described as proteinoids. When hot saturated solutions of these 



polymers are allowed to cool, huge numbers of uniform, microscopic, 



relatively firm and elastic spherules separate* These are usually 



1.5 to 3 microns in diameter. For each milligram of solid, approxi- 

rj ft 

mately 10' to 10 microspheres can be formed. Fox's work had thus 



led him to a theory of the origin of organized units. He considers 



them suitable models for the evolution of the cell. 



In the experiments in our ofai laboratory we have adopted the 



simple working hypothesis that the molecules which are fundamental 



now were fundamental at the time of the origin of life. We are 



analyzing rt the primordial soup" described by Haldane. The various 



forms of energy which are thought to have been present in the primitive 



earth have been used by us in a series of experiments. 



In the experiments with methane, ammonia, and water, electron 



irradiation was used as a convenient source of ionizing radiation 
simulating the IT on the primitive earth. The results of this 



investigation clearly establish adenine as a product of the irradiation 



™ **. -^ -*.— - nrffHinnm^-^^.^^^^^^.^^^ , ifi iih i Tt ^. ,„. . ^ma^^.^ ,^,,,,,, ^t fc rt ^j. ' ir nrt to » i m i t r. i 



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-24- 



of methane, ammonia, and water. It is the single largest non-volatile 



compound produced. The apparent preference for adenine synthesis may 
"be related to adenine's multiple roles in "biological systems. Not only 



is it a constituent of "both the nucleic acids DRA. arid RNA but it is 



also a unit of many important cof actors. (Figure 2) 



The apparatus used for studying the effect of electric discharges 



on a primitive atmosphere is illustrated in Figure 3. ■ "..'. . In a 
typical run of 150 hours 65$ of the methane was converted into organic 



material which could be recovered in ether and water solution. In the 



water soluble fraction, adenine was identified. 



As formaldehyde is formed by the action of electric discharges or 



ionizing radiation on a mixture of primitive gases, it was used as 



the starting material for synthesis in a further series of experiments. 



A preliminary separation into groups of sugars seems to indicate that 



by far the highest yield is of the pentoses and hexoses. Among these, 



Y • y ribose and deoxyribose, the two sugars present in RNA and DKA were 

identified. ^ 



In a third series of experiments, hydrogen cyanide was used as 



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-25- 



the starting material. This, again, is one of the primary products 



when a mixture of methane, ammonia, and water is exposed to electric 



discharges or ionizing radiation. 



The use of hydrogen cyanide as starting material is also strengthened 



"by the theory that comets may have been responsible for the accumulation 



of relatively large amounts of carbon compounds on the primitive earth* 



The CN hand is generally the first molecular emission to appear on the 



tails of comets during the travel of these bodies towards the sun. It 



is also the hand with the largest degree of extension into the comets 1 



heads. It is possible that the heads of comets contain frozen free 



radicals which are volatilized by radiant heat from the sun. It is 



also possible that they contain frozen molecules which are vaporized 



and photodissociated into radicals by solar radiation. 



About k-0 million comets are now reckoned to be present in the 



solar system, and it has been calculated that about 100 comets have 
collided with the earth since the formation of our planet some 5 x 10^ 



years ago. The amount of cometary material, trapped by the earth during 



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-26- 



its first tvo billion years can be calculated to be about a thousand 



billion toiis. Most of the cometary material must have been retained 



by the magnetic and gravitational fields of the earth. Hydrogen 



cyanide or its reaction products may thus have been found in fairly 



large concentrations either locally or distributed through the earth 1 s 



primitive atmosphere. 



When hydrogen cyanide is exposed to ultraviolet light a large 



number of organic molecules are formed. Among these we have identified 



adenine and guanine, which are constituents of the nucleic acid molecule. 



In the experiments already described we have established the 



formation of the purines adenine and guanine and the sugars ribose and 



deoxyribose. It was therefore of interest to see whether the same 



sources of energy which were responsible for the synthesis of the purines 



and sugars could be instrumental in the synthesis of nucleosides and 



nucleoside phosphates leading up to the synthesis of the energy source 



v* -! ^ adenosine triphosphate. 



It has been suggested that the earth's primitive reducing 



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V- 1' 



-27- 



atmosphere vas at least slightly transparent around 2600 A and that 



the activation of purines and pyrimidines by ultraviolet light in 



this region vas a possible step in the formation of nucleosides and 



nucleotides. In our laboratory we have satisfactorily duplicated 



these conditions and established the synthesis of adenosine, adenosine 



monophosphate, the diphosphate and ATP the energy source of all living 



systems 



Recent developments in the science of quantum biochemistry has 



thrown new light on some very significant aspects of chemical evolution. 



It is a striking fact that many of the molecules which are essential to 



living systems are conjugated systems exhibiting the phenomenon electronic 



derealization. In the nucleic acids, for example, the purines and 



pyrimidines are conjugated systems. Although the proteins do not, at 



first sight, appear to enjoy this property, a closer look shows us 



that the matrix of hydrogen bonding which exists in a protein molecule 



provides a certain measure of electronic derealization. In the high 



energy phosphates, there is interaction between the mobile electrons 



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-28- 



'/^ 



of one phosphoryl group with those of another. The porphyrins, for 



example chlorophyll and haem, which are of paramount importance in 



living systems are highly conjugated molecules, 



Even this meager consideration of electron derealization leads 



us to the following conclusions: 



(a) Evolutionary selection used the most stahle compounds, 



(b) On account of electron derealization these compounds were best 



adapted for biological purposes. 



(c) The possibility of life as we know it was made more probable by 



the appearance of these compounds 



The choice of conjugated systems is perhaps the most important quantum 



chemical effect in biochemical evolution. 



Carbon and silicon appear in the same group of the periodic table 



and both need k electrons to reach the configuration of the nearest inert 



gas. On account of this superficial and apparent similarity between 

* 

carbon and silicon the question of a "silicon biology" has often been 



raised in discussions on the origin of life. However, a careful 



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-29- 



consideration seems to indicate that such a prospect is very unlikely. 



One answer to the question is forthcoming from a consideration 



of cosmic abundance. Carbon is certainly more prevalent than silicon 



in the universe. Another reason arises from the fact that hydrogen, 



carbon, nitrogen, and oxygen have been utilized in living systems, 



since they are the smallest elements in the periodic table and can 



achieve the stability of inert gases by the addition of 1, 2, 3, and 



h electrons. Small atoms form tight and stable molecules. They can 



also form multiple bonds. In comparison to carbon, silicon forms 



weaker bonds with itself and other atoms. Silicon does not form multiple 



bonds, and the result is the formation of large polymers, like quartz, 



which are unwieldy and also remove any available silicon from circul- 



ation. A further reason for the unsuitability of silicon for life 



processes arises from the fact that silicon compounds are fairly 



^ unstable in the presence of water or oxygen. 



Optical activity has often been suggested as a very distinctive 



characteristic of molecules present in living systems. In living 



organisms all syntheses and degradations involve only one enantiomorph. 



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-30- 



Molecules axe either left handed or right handed. While a start with 



one form or the other would have been self -perpetuating, it is difficult 



to understand how the initial choice was made. Physical forces such 



as circularly polarized light, the surface of asymmetric crystals, or 



spontaneous crystallization can not account for the overwhelming 



tendency to produce only one form rather than the other. 



A reasonable explanation appears to be that the structural demands 



of large molecules required the use of one form rather than both. The 



use of one optical isomer rather than mixtures would undoubtedly 



confer great stability on the polymers. This still does not answer 



the question of how the initial choice was made. Professor Wald 



describes how he once discussed this matter with Einstein, and this 



was Einstein's reply: "You know, I used to wonder how it comes about 



that the electron is negative. Negative - positive - these are 



perfectly symmetric in physics. There is no reason whatever to 



prefer one to the other. Then why is the electron negative? I 



thought about this a long time, and at last all I could think was 



it won in the fight 



Tit 



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-31- 



The most plausible solution appears to be that the single 



optical isomers were selected on the basis of stability of the 



structures of higher order. The final choice -was arbitrary. This 



is a case of natural selection at the molecular level. It accords 



with the evolutionary scheme: "we are the products of editing rather 



than authorship." It will be most interesting indeed if the sampling 



of martian life reveals the presence of d - amino acids rather than 



1 - amino acids. If we were to sample all life in the universe we 



should hopefully end up with an equal distribution of 1 and d amino 



acids. 



The decrease in entropy produced when a highly organized system 



results from less organized matter has often been raised as an 



obstacle to the evolution of life from non-life. The second law 



of thermodynamics applies to chemical and physical systems which are 



isolated in the sense that energy does not cross the boundary of the 



system. In such systems, entropy tends to increase or the state of 



the system becomes progressively more random. 



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-32- 



A feature of the evolution of living organisms and of many 



processes taking place within living organisms is that in them entropy- 



appears to decrease at the expense of a greater entropy increase in 



the environment. This point was clearly made by Schroedinger in his 



hook "What is Life". Living systems are not isolated. Energy does 



cross the boundaries of the system. This state of affairs is consistent 



with the second lav. 



There is no reason to doubt that we shall rediscover, one by one, 



the physical and chemical conditions which once determined and directed 



the course of chemical evolution. We may even reproduce the intermediate 



steps in the laboratory. Looking back upon the biochemical understanding 



gained during the span of one human generation, we have the right to be 



quite optimistic. In contrast to unconscious nature which had to spend 



billions of years for the creation of life, conscious nature has a 



>. 



purpose and knows the outcome. Thus the time needed to solve our 



v ■■*> 



problem may not be long. It is unnecessary to belabor the difficulty 



of the task or the Immensity of the prospect for any man's philosophic 



ftjAb** \.-J*-cii 



F k ' r 



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-33- 



position. It is superfluous to discuss the sceptical and provincial 



viewpoint that would shrink from pursuing it, for what is at stake 



is the chance to gain a new perspective of man's place in nature - 



an entirely new level of discussion on the meaning and nature of life 



Over 500 years ago, Copernicus in De Revolutionibus Qrbium 



Coelestium reversed the scientific thinking of his time about man's 



place in the physical universe. A hundred years ago, Darwin's theory 



of evolution destroyed age-old beliefs of the uniqueness of man by 



tracing his origin from the brute. Today, we are gradually learning 



to accept the Oparin-Haldane hypothesis that life is only a special 



and complicated property of matter and that basically there may be 



no difference between a living organism and lifeless matter. 






-34- 



Figures 
Figure 1. A 3 ol0*6-21 

« 

Figure 2. Electron irradiation of methane, ammonia and 

vater A 31716 

Figure 3. Electric discharge through a mixture of gases 

resembling the earth's primitive atmosphere. A 32587 



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COMPOSITION OF SUN 



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HYDROGEN 

HELIUM 

OXYGEN 

NITROGEN 

CARBON 

MAGNESIUM 

SILICON 

IRON 
SULPHUR 

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0.002 
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