THE FORTNIGHTLY CLUB
OF REDLANDS, CALIFORNIA  - Founded 24 January 1895

MEETING # 1479

4:00 P.M.

NOVEMBER 1, 1990


The Origin of Life

howell4.jpg (108077 bytes)

by Charles D. Howell Ph.D.

Assembly Room, A. K. Smiley Public Library


Abstract

Early ideas of the origin of life were naive in believing the first life had to be autotrophic, i.e. capable of making the first organic materials. Oparin challenged this by conceiving that the first organic compounds need not have been made by living things but instead by physico-chemical action of energy on primitive earth gases. The organic substances so produced would have been washed into ponds on the earth, becoming more and more concentrated in time till the ponds became veritable soups. A very simple form of life, if it then arose, could have lived on this soup, as a saprotroph. But before all the soup was consumed, a mutation would have to have occurred, producing an autotrophic form of life, which could replace the lost organic matterials. M iller's classic experiments proved the soup-production theory possible. Further experiments revealed the fact that all the basic chemicals needed for forming life-chemicals could be produced without the aid of living matter. But the mystery of imparting life to them still eludes us.. . .


Biography of the Author

The author, Charles D. Howell is Robertson Professor of Biology Emeritus of the University of Redlands, and Volunteer Curator of Entomology at the San Bernardino County Museum in Redlands, CA. He was born in East Bangor, PA, brought up in Brooklyn, N. Y., graduated from Oberlin College in Ohio, and earned his Ph. D. in Zoology at the Johns Hopkins University in Baltimore MD. His special interest has been in physiology, but he has taught classes in many of the basic subjects of biology. He has published research on functions of the nervous system in earthworms, on the developoment of an abnormal heart in a calf, on inheritance of abnormal anatomy of a human family, and on cardio-vascular and respiratory physiology on dogs, and engaged in resarch with students, particularly on alligators, that produced more enthusaism than knowledge. In retirement he became an entomologist, trying to gain some insight into variations in species as seen in nature rather than in the laboratory, and has added publicatiions on insect taxonomy to his portfolio. He is a member of Sigma Xi, and a numbers of scientific societies and is a Fellow of the National Public Health Service. He has been active in community concerns, church work, Boy Scouts, and much that is forgotten.


The Origin of Life

by Charles D. Howell

Albert Einstein once wrote, "The eternal mystery of the world is its comprehensibility." During each generation this comprehension changes, but the mystery remains undiminished. We consider the earlier conceptions as reflecting the misconceptions of their time, nevertheless, in their times they were considered logical. How will future generations look upon our ideas?

Charles Darwin delayed the publication of his ORIGIN OF SPECIES many years, because so many questions he raised had elusive answers. One questions was therefore carefully ignored, namely, "How did life (species) begin?" Yet he had some very clear thoughts about this in relation to current thinking on the subject, as we will point out later.

Man's early conceptions of the origin of life and the origin of species were not related. This was because of the belief in the creation of all species, many simultaneously, and because there was no concept of the biological continuity of species. Furthermore, the spontaneous generation of species was a universal concept, confronting biologists even in the mid-twentieth century.

The use of the experimental method to verify conclusions about nature is relatively new in history, and in its short history has actually been practiced rather unevenly. Few individuals have been at the forefront testing hypotheses, and even they were often prone to accept what they had been taught in areas where they were not scientifically probing the truth. Imagination often superseded critical examination in men's thinking. So when farmers found hair-like worms in streams where horses abounded, it seemed logical to consider that they came from horse hairs shed into the water. This could not be readily disproved, as one cannot disprove a negative, but no one ever observed the event happening. It required a study of the life cycle of the worms to prove their true origin from parent worms in a positive manner.

The scientist's rational point of view is based on Faith in certain rules. First, he believes in the Law of Cause and Effect, in so far as the causes and effects are natural and reproducible in terms of objective reality. Secondly, he ~elieves in the Law of Continuity (Uniformitarianism). This states that the laws man derives from his present experiences are the same laws that were working before man was here to observe them, and the same as will work in the future. Thus these laws can be used to explain the past, and to predict the future.

Since we are, in this paper, trying to apply rational thought to life, we should be able to define life at the start. Biologists note that living things carry on metabolism, reproduce themselves precisely, have peculiar structural features symbolized in a "typical cell," and respond to stimuli in a manner displaying "irritability." This latter is quite different from the physical laws of reaction in which reactions are only equal to the applied force.

There are certain things that are obviously alive - a cat; and others which are obviously not living - atones. As you proceed progressivly from these cases to examples less alive or less dead, the certainty about a definition of life vanishes. A good borderline example is a virus. We may seriously debate whether a virus is living or non-living. It is reproduced by a cell which it parasitizes, and cannot reproduce outside, by itself. It lacks enzymes and so cannot carry on metabolism alone. It has a deficient cellular structure. To understand this we need to look at other kinds of living material at the cellular level.

To illustrate, let us examine diagrams of three objects of biological interest. This may give us some insight into what one needs to create, in order to give birth to life in a test tube or in any other pregnant laboratory device. -

howell1.jpg (89194 bytes)

 

Figure 1 is a diagram of a cell illustrating, grossly out of scale, significant features revealed by electron microscopic studies. The great revelation of this technique is that the cell is a mass of folded membranes: the cell membrane of the surface folding in to form the endoplasmic reticulum, and the membraneous covering of the nucleus, mitochondria, and the golgi apparatus. These replace many of the functions formerly assigned solely to colloids in the protoplasm.

 

 

 

 

howell2.jpg (14937 bytes)

 

Figure 2 is a diagram of a bacteriophage type of virus. It has a protein shell, but lacks a cell membrane There is no  nuclear membrane, nor membraneous inclusions such as mitochondria, with which oxidative metabolic enzymes are associated in a typical cell.

 

 

 

 

 

 

Figure 3 is a diagram of a stylized bacterium after Mazia and Tyler. It may be a bit advanced, as statements occur in the literature claiming bacteria lack infolded membranes, such as are seen here continuing inward from the cell membrane. However, the bacterium lacks a nuclear membrane and mitochondria or other cytoplasmic membrane structures. It does carry on its own metabolism and reproduce itself.   howell3.jpg (15702 bytes)

As a starting point, one could assume that the first true life was something nearer the bacterial structure than that of the virus. What protocells or prebiological structure were, remains to be clarified, and may be extrapolated back to their chemical origins. The following discussion may help in this extrapolation.

The progress of human thought on this subject is fascinating. One would not expect the earliest pronouncements of man to have shown an appreciation for the conception of life that even a high school freshman has today, nor of the problem of origins. To early men the origins of their own cultures, or even their cities, were already shrouded in mystery. The founding of cities was often attributed to gods. Cities seem to have sprung fullfledged without a past history. So with the origin of living things, they too were conceived of as arising without past history or with a non-rational history. Such an origin for living things has been referred to as spontaneous generation. According to it, rats were believed to arise spontaneously from the mud of the Nile River every Spring as flood waters rose. Meat when left exposed, spontaneously generated maggots. Out of tumors on trees, called galls, crawled wasps that presumably were spontaneously generated in the wood. By comparison with these illustrations the origin of the horse-hair worm almost assumes a rational aspect.

From earliest times men took for granted the conception of spontaneous generation. The idea seemed so obvious that it remained unchallenged until recent times, and is faithfully believed still in many parts of the world, even in rural U.S.A.

As W. K. Brooks, the eminent Zoologist, wrote in 1915: "Two hundred and fifty years ago no one thought of asking whether living beings ever arise out of dead matter, for all believed they never arise any other way."

A great experiment that should have challenged this idea was described by Franscesco Redi about 1668. He placed freshly carved meat into two separate jars. One jar was covered with gauze, and the second left open. Flies gathered in the second, and soon maggots appeared in its meat. But in the covered jar, no maggots appeared. Redi drew the strict logical conclusion from this, that meat by itself does not spontaneously generate maggots and flies. However, he continued to believe that galls on twigs of trees spontaneously generated gall-flies. He was on the verge of making a great discovery, the biogenetic law, but lacked the inductive capacity of a Darwin, and never imagined that gall-flies, like maggpots, had to have parents.

At this time the microscope was being developed. With its wider use, the center of the controversy shifted from large organisms to microscopic ones found in putrefying broths. These mysterious, tin:, wiggling forms were now considered to be spontaneously generated. The controversy that raged over this was stilled by the voice of Louis Pasteur during the latter half of the 19th century. His work assured scientists that broth, if rendered sterile, will not spontaneously generate even the tiniest microorganism.

But even as this great bacteriologist-chemist laid to rest the ghost of spontaneous generation, he was jarred by the thought, "How could the first life have arisen except in such a manner?" At least life was not arising with the swarming frequency claimed by the ancients, but was it possible for it to occurin a favorable spot somewhere on the earth? Wouldn't broth be favorable? Perhaps! But the occasion for the origin of life to occur in a pot of broth was regarded as being so remote that there would be little chance, if it arose, that a scientist would just happen to be present to make the observation.

Even Darwin thought of this. In a now famous letter written by him in 1871, but not brought to light until 1950, by Garret Hardin, Darwin wrote: "If (and oh!.what a big if!) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case.before living things were created.He points out that as things are today, if spontaneous generation ccurred in nature we would never observe it.

By the turn of the century, after 40 years oft the impact of Darwinism, a philosophy of belief in change was generally developing. The world of life had lost its former secure immutability in favor of progressive adaptation and evolution, leading toward optimal adaptation of form and function to environmental changes.

The history of this change is startling to many people, as each step caused certain spokesman of Science or Theology to become embattled and embittered. The development of knowledge of chemistry and biology uncovered successive features that were immediately seized upon as unique to living things alone.

For example, when carbon compounds were recognized as unique products of life, they were called "organic compounds", Vitalists then claimed only living things could make organic substances. No sooner was this proclaimed than Wohler synthsized urea, a body product, from inorganic chemicals. Whey Pasteur discovered that fermentation was caused by living yeast cells, the vitalists looked upon fermentation as a life-limited phenomenon. Promptly, Buchner ground up cells and showed that it was the chemicals in yeast, not the- life~that caused the fermentation process. Soon after this the German dye-industry arose, and synthesized untold number of new organic compounds.

 In the face of this, dare we say man will never produce a natural protein, or DNA, or life in the laboratory? Certainly the experience of the 19th century was shattering to vitalists.

In the early 20th century, the possibility of the "first life" arising by spontaneous generation was not discussed too openly in scientific circles. Many believed that the first life would have to be a form with powers of organic synthesis like those of green plants. Such a form would be able to carry on photosynthesis or chemosynthesis from the start, using inorganic sources of energy as soon as they arose. They would arise supposedly by "fortuitous concourse of atoms." The chances for the "fortuitous concourse of atoms" to bring together just the right chemicals was looked upon as a billion to one shot. This is what Le Compte du Nouy refers to as a statistical miracle: "The occurence of the improbable."

That the first life was of this type -- autotrophic -- was held by Vinogradski (1881). Perhaps some of the current hypotheses also support this possibility, e.g., Granick had a conception of the origin of a chlorophyllike-action through an impure crystal of iron ore called spinet.

The autotrophic point of view was not seriously challenged until the 1930s when the brilliant Russian scientist, A. I Oparin set forth his thesis that the first life was saprophytic. A saprophyte is a decay organism that lives on lifeless, dead, organic matter. It digests the material outside its own body, causing its decay.

If such an organism arose spontaneously, what would be the sources of the organic matter it required for its life? Oparin postulated they would have been created from available elements and the natural gases in the atmosphere during the earth's early history. He deduced that there was a time when the earth's atmosphere contained a different combination of gases than it now contains. Astro-chemists have postulated many different possible gases for those early times. Oparin's atmosphere was composed of ammonia, hydrogen, methane and water vapor. The earth was very hot. This atmosphere would be a reducing atmosphere, which is favorable for synthesis. Energy would be provided by ultraviolet light, and lightning,as well as heat. These gases contained the basic elements for organic molecules and would synthesize them in presence of the energy.

Eventually, in eons of time, the pools, and oceans of the earth would become a rich organic soup as organic chemicals poured into them from above. None of it would undergo decay, for there were, at first, no living things to digest and decay them. Large molecules would eventually develop and gather in colloidal masses with membranes around their globules. This was written in the heyday of colloidal chemistry.

Finally, the right combination would bring together those chemicals having the power to initiate the creative acts of life. The living organisms, so formed, would feed on the organic material in which they lay, and would reproduce. Their mode of nutrition was the saprophytic mode -- the way decay organisms live. Such organisms have no mouths, and do not carry on photoshythesis or chemosynthesis, which are much more complex processes.

Oparin postulated that luckily, before the soup was all consumed, the genetic material in these organisms mutated to produce enzyme systems that used chemicals and sunlight as energy sources to aid synthesis of organic matter. So photo- and chemo-synthesis wee born, and henceforth all life eventually became dependent mainly on photosynthetic forms to supply organic materials.

Photosynthesis needs carbon dioxide -- this gas was produced and put in the atmosphere by the metabolism of saprophytes. The photosynthetic organisms used the carbon dioxide and gave off the first oxygen to the atmosphere. Here then was the source of not only the first, but it is believed all the oxygen of our atmosphere. Life requiring oxygen, probably arose when the atmospheric concentration of oxygen reached between 0.1 and 0.2 of a percent (it is now 20 percent). The change to aerobic life would require a small change in the same type of molecule as that of which chlorophyl is composed. That is, small in the cosmic sense, but large in the difficulties of organic synthesis by man.

Oparin's saprophyte theory immediately supplanted the autotrophic theory. Astronomers, physicists, geologists, and chemists began looking at the galaxies and space between them for evidence of the possible nature of the atmosphere of a young earth-like planet. A discussion of the biological origin of life was still not considered entirely respectable -- it was mere theory. But this was soon to change. In the 50s, Dr. Harold Urey, who rose to eminence working on the problems of atomic fission and fusion, gave some thought to astro-chemistry. He postulated that an early atmosphere of the earth was something like what Oparin suspected. One of his graduate students, Stanley Miller, decided to test such an atmosphere. He combined the four gases CH4, NH3, H2O, and H2, and passed electric sparks through it to see if organic matter could be formed from simulated primitive earth conditions (P.E.C.).

It should be noted that he was no longer naive enough to say, "we will look for life." Instead, he would be content if a few organic chemical compounds were to appear. After running the apparatus for only a week, Stanley Miller took it apart, and began an analysis of the contents of the system. He could not isolate and analyze all he found, but he did find about 19 recognizable substances, including seven different amino acids, and urea. Control experiments were run. Checks were made for bacterial contamination, etc. In the end his results were confirmed. A valid synthesis of simple organic compounds had occurred in an experiment under P.E.C. Miller's work was first published in 1953.

Newspaper statements claiming he had produced life in the test tube were of course slight exaggerations. He had not yet produced even a protein, or any of the other macromolecules so important to life: polysaccharides, nucleic acids, lipids.  But the building blocks were there, and at once the subject of the origin of life became respectable for scientists to embark upon. A test had been designed and had verified what had once been a fantasy.

To understand the situation we might liken the process of building life or the body of organisms, men, animals, and plants to that of building castles. Every castle is a little or a lot different from every other one.- There are an infinite number of ways of arranging rooms, turrets, hallways, basements, windows and decorations. But it can all be done with a finite number of kinds of bricks, stones, pieces of wood, and mortar. So although there are over a million different species of plants and animals, they, too, are constructed of basically only a few simple bricks. For example, among these bricks we need only 20 different kinds of amino acids serving as the building blocks of proteins, the main structural framework of all protoplasm. These 20 amino .acids can be arranged in any permutation or combination so that an infinite number of different proteins could be formed.

And behind this there is even a greater simplicity. Today we know the hereditary code of the genes that guides the production of these proteins. It is composed of nucleic acids in the form called D.N.A. The framework of D.N.A. consists of only four different kinds of bricks: four N-bases. These four can be arranged three at a time to make 64 different triplet combina- -tions. Each combination keys out an amino acid. There are thus an adequate number of triplets to more than key out all 20 amino acids. So a simple key of four different things will key out the 20 amino acids. The different arrangements of 20 amino acids make possible an infinite number or proteins. Proteins are the warp and woof of protoplasm, and every species is different because its proteins are different.

Thus we arrive at million of species of organic life depending on the simplicity of only four different nucleic acids which code only 20 amino acids, which can be tied together in millions or billions of ways to make possible the creative living world.

Following Stanley Miller's work, numerous other workers immediately set about trying variations and additions to Miller's important experiment. Abelson alone tried out 20 combinations of possible gases that might have constituted an atmosphere of the earth at some primitive time or place. No combination was effective in synthesizing organic substances unless it was a reducing atmosphere. If hydrogen were part of the reducing atmosphere, its yield of products increased significantly.

We must realize that these experiments have a short duration. Life is short. Men want to look at things as soon as possible, not wait till they are old. They want to com~unicate-their discoveries to others. Few experiments therefore have run over a week's duration. By contrast nature carried the same thing out in the unhurried span of billions of years---plenty of time for the improbable to occur.

We must not forget that in nature much more happened than the mere passing of ultra violet light or electric sparks through gases. Things happened in the pools of water. They dried up some times. The products became powder at times. They were blown away, mixed with minerals, sometimes superheated in volcanoes, frozen at times, warmed gently at others, splashed over hot rock and cool soil. This continued for billions of weeks. But even so, the proper combination for life is so elusive that we can only stand in awe that life emerged at all by such a process.

J. B. S. Haldane also has tried to predict the probability of the occurrence of the right chemical combinations for life. Just to produce the simplest imaginable enzyme of 100 elements (much smaller than the smallest known enzymes) would take 103 trials to get one correct combination. This would require trving out one choice every minute for 108 (100,000,000) years. This is an incredibly low chance of success. That we are here, implies that success was achieved. But it might not happen very often even on other planets if they by chance developed the right conditions.

The experiments of Miller and others show how under P.E.C. the simple compounds basic to protoplasm could have arisen. I stress simple. Next, we might ask, could the more complex ones also possibly arise, and if so, howl That is, how could the simple acids, amino acids, aldehydes, etc. give rise to the macromolecules, such as proteins, DNA, lipids and polysaccharides that are in protoplasm?

Many scientists at once approached this problem. Some began with pre-supplied organic chemicals and mixed them in different combinations and subjected them to different conditions. That is, they did not always begin with primitive earth materials or conditions, but started one or two steps higher up in their efforts. They shortened natural nistory by perhaps millions of years.

Dr. Sidney Fox has, among other things, put dried amino acids on lava rock and poured hot water over them, simulating some volcanic situation. He has varied this with heating the amino acid solutions for prolonged periods. His main thesis is that heating tends to dehydrate compounds, and that dehydration furthers synthesis or causes polymerization. Sure enough, his experiments resulted in the union of amino acids into long chains of polypeptides. hone of them were naturally occurring proteins, but since proteins are polypeptides the Principle seems workable. Amino acids might thus be formed into large proteins.

Dr. Gerhard Schramm, of the Max Planck Institute, has discovered that additions of phosphate esters aids polymerization of simple sugars into complex sugars. Dr. Sidney Fox also tried this technique adding phosphate esters to his amino acids. He too found it produced greater yields of complex proteins. The theory here is that phosphates provide a unique chemical radicle for holding energy for relatively long periods, and for transferring it to further chemical reactions. This is the basis of ATP (adenosine tri phosphate) activity in our own bodies. ATP holds a great amount of energy in phosphate bonds. When a phosphate bond breaks, it releases energy for muscle contraction and other body-work. This reaction is the most basic in living things. It occurs also in photosynthesis, where the breaking of the same phosphate bond in ATP provides some of the energy for synthesis of sugars.

So we have the possibility of synthesis of proteins, and of complex sugars. What about synthesis of ONA, the complex nucleic acid so important in heredity? The heart of DNA is four nitrogen bases. None of these four were produced in Miller's original experiment. But many workers (Fox, Oro, Ponnamperuma) have produced N-bases after starting experiments with some of the simple products derived under P.E.C. The combining of cyanide (CN) with NH3 or succinic acid has produced most, if not all of the necessary nitrogen bases. It should be pointed out that ATP also has a N-base, and its synthesis provides the possibility of early synthesis of ATP under P.E.C.

Thus the possibilities for chemical synthesis, leading to some, if not all the major necessary products of protoplasm, seem within our grasp. What more do we need? Besides the proper combinations of chemicals at one time, we need membrane structures to contain, concentrate, and mobilize them into organized life activity. As Dr. Robert Young writes, "A major stumbling block in our knowledge of the origin of life is the enormous gap between chemical evolution and the first selfreplicating metabolizing unit which we might call a cell." Basic to this is perhaps the membrane system of cells and proteins.

What about the cell membranes and membranes within cells? Dr. Sidney Fox has made some modest progress along the line of evolution of membraneous materials. He has worked in the Institute of Molecular Evolution in Miami, mimicking volcanic conditions. We have mentioned how he obtained polypeptides from amino acids in hot water on lava rock. In these experiments his water suspension developed interesting globules. On microscopic examination they looked like tiny spherical (coccoid) bacteria, and were of the same size as such organisms. Taking time-lapse moving pictures of them, he believed he saw them undergo fision, or division of one globule into two. He called the coccoid objects proteinoids. He then examined them under the electron microscope. This revealed that these proteinoids possessed a membrane structure strikingly like that seen in cells. They lacked any endoplasmic reticulum or internal membraneous structure. Since they divided, one would ask, are they alive? His answer to this is no, they are not, for they do not contain an enzyme system and do not carry on metabolism. Also, DNA had not been incorporated into them, although they had some peculiar inclusions at times.

This work represents the nearest to cell framework achieved from a P.E.C. experiment. But it lacks all the chemicals reguired. By what principle are the framework and chemicals simultaneously organized into a life-like whole? We are along way from ascertaining this.

This is approximately where we find ourselves today. The incredible odds against "creating life" by synthesizing all the proper chemicals, at one time, in one place, with other factors, such as membrane structures, etc., still is just as awe-inspiring as ever to scientists. My guess is that there is a key-concept and if the key idea is found, it will prove to be incredibly simple, as other recent key ideas have proved to be. The frustration of the search for these key ideas has shaken our faith in the rationale of the physiochemical laws. Scientists are well aware of the dangers of departing from their faith in physicochemical principles. Yet many of them have speculated beyond the data of science. Le Compte duNouy gave us the concept that Being and Life are statistically so improbable that they may be -regarded as statistical miracles. Dr. Peter Mora, at the Conference on The Origins of Prebiological Systems at Wakulla Springs, urged scientists "to question the sufficiency of principles of physics applied to biology." At the same conference, Dr. Pattee of Stanford stated, "I think we agree that the chance hypothesis for the origin of life is unsatisfactory." Few eyebrows were raised over these remarks. The objective scientists pondered more than argued these ideas.

Dr. George Wald, reknowned zoologist, physiologist, and biochemist opened a "Cooperative Lectureship Institute" with these statements" "We live in a world of chance, but not of accident.... Probable things happen, but improbable ones don't.... God gambles, but he doesn't Cheat.... In a world of chance anything can happen, but things that repeat do so for a reason."

When we consider the possibility that all the universe might have come from hydrogen atoms alone, or from neutrons alone, or from four simple particles of physics: protons, electrons, neutrons, photons, antimatter, or quarks, the idea of creative evolution takes on new meaning.

Perhaps the very pulsing heart of the universe is creativity. New combinations of simple things create new, unexpected and beautiful complex things. Life may be a very natural and complex expression of this creativity, as also may be Mind.... And, most extraordinary of all is the whole man. [lere we sit, or stand, aware of each other, and of the universe, putting together ideas about the behavior of particles we know exist but cannot see, creating in our own minds a rational picture of our own origins which we can never witness. Here in man is a fathomless source of creativity.

No other known organisms possess such creative powers. Truly, if we consider man to be created in the image of God, I see hire more like God in his creativity than in his anatomy.


 BIBLIOGRAPHY

Bernal, J. D. 1957. The physical basis of life. London.

Barghorn and Tyler. 1965. Microorganisms from the gunflint cheat. Science 147:563-577.

Calvin, Melvin. 1961. Chemical evolution. U. of Oregon.

Fox, Sidney. 1965. The origins of prebiological systems and of their molecular matrices. Academic Press. 1965. A theory of macromolecular and cellular origins. Nature 205:328-340.

Haldanne, John S. 1923. Mechanism, life and personality. Dutton.

Kesosian, John. 1964. The origin of life. Reinhold.

Lewin, Roger. 1982. The thread of life. Norton.

Miller, Stanley L. and Leslie E. Orgel. 1974. The origins of life on the earth.

Oparin, A. I. 1938. The origin of life. Macmillan.

Pannamperuma, Cyril and Katherine Pering. 1966. Nature 209:979.

Schopf, J. William (Editor). 1984. Earth's earliest biosphere.


Home Page

Copyright © 2007 The Fortnightly Club of Redlands, California 
Website maintained by RedFusion Media