The Origin of Simple Organic Chemicals on Earth by Joe MacAvoy Billions of years of evolution and chemical happenstance have led to the complex organisms that exist on the Earth's surface today. RNA and DNA a nd the many complex proteins, the central constituents of life as we know it, are the result of years of reactions that began with the simplest of organic molecules, short carbon-chains and amino acids. These carbon-chains and amino acids may be considered the basic building blocks of life; without them, the more complex organic chemicals and life itself would not have developed and flourished on the surface of planet Earth (Horowitz 2-9). There is a dispute among scientists, however, as to where these simple organic molecules, the precursors to life, came from. Are they naturally produced by conditions on the surface of the young planet Earth? Are they a natural result of basic Terran chemistry and geology? Or did they come from some other source? When discussing the origins of simple organic compounds, scientists tend to fall into one of two main schools of thought: those who favor the terrestrial origin model and those who favor the extraterrestrial origin model. J. B. S. Haldane and Alexander Oparin, creators of the "primordial soup" concept, hypothesized that natural conditions on the young Earth's surface would lead to the development of simple organic molecules in the Earth's oceans and tidal pools -- a primeval "broth" of chemicals with the potential to become simple organisms. Various features of the young Earth (in particular, high volcanic activity, temperature, chemical composition, and the existence of lightning storms), they believed, provided the ideal conditions for simple organic chemicals to develop, flourish, and eventually become more complex (Goldsmith and Owen 189-191). The less conventional model of Louis Frank, Fred Hoyle, and Chandra Wickramasinghe among others, is one that involves the collision of extraterrestrial bodies into the Earth. They have suggested that organic molecules could form in great quantities in outer space, and could somehow be carried to the Earth on various solid interstellar bodies. Enough organic chemicals, they believe, could not have been produced by natural means on the planet's surface; an external source of such chemicals is needed to account for the large amounts of organic matter that must have existed on Earth for life to begin and flourish (Goldsmith and Owen 96-97, 195-196). In 1953, Stanley Miller and Harold Urey set out to test the merit of the Haldane/Oparin terrestrial model and answer, once and for all, the question of the origin of simple organic molecules. They set up an experiment to determine whether or not such molecules could be created from conditions mirroring that of the Earth's surface billions of years ago (see schematic diagram on page 4). First, they "recreated" the atmosphere of the Earth in a flask, filling it with the gases present on the planet billions of years ago: methane, ammonia, hydrogen, and water vapor. Then, a second flask filled with water was connected to the first flask to simulate the pools of water on the Earth's surface. Finally, electrical wires were connected to the apparatus to provide 60,000-volt high frequency sparks, which simulate an energy source (in the case of the young Earth, either ultraviolet radiation from the sun or lightning from storms). The electricity was then allowed to flow, and the experiment ran for several days. If simple organic chemicals were produced in the water during the experiment, Miller and Urey believed, they could conclude that conditions on the early Earth's surface were conducive to the production of both organic chemicals and life itself. Were they produced? Indeed, after several days, organic molecules formed in the water-filled flask - a great deal, in fact. Included among these (in addition to an amount of unidentified organic "goo") were acetic acid (C2H4O2), alanine (C3H7NO2), formic acid (CH 2O2), glycine (C2H5NO2), glycolic acid (C2H4O3), hydrocyanic acid (HCN), lactic acid (C3H6O3), and urea (CO(NH2)2). In particular, the presence of the amino acids glycine and alanine provided strong support to the terrestrial origin model; these are two of the most fundamental ingredients to life on earth, key in the production of proteins in all known organisms (Goldsmith and Owen 191-193; Sullivan 127-129). The Miller/Urey experiment and other experiments like it seem to provide definite evidence that the primordial soup model is correct. But, in fact, they do not; these experiments have several fundamental flaws. First, the conditions created in the flasks might not have been accurately representing those of the early Earth - scientists cannot say for certain what the exact conditions were and what actual chemistry was involved. There could be some important factor or factors they are omitting that would change the results. In particular, many scientists doubt the methane-ammonia content of Miller and Urey's experimental "atmosphere" - they propose that the Earth's early atmosphere might have been composed of mostly carbon dioxide, instead of the other compounds (Chyba and McDonald 220). The second major flaw is the fact that not all of the basic molecules necessary for life were present in the experiment's resulting organic "goo"; in particular, many of the various amino acids were missing, and there was no trace of anything similar to nucleic acids. If all the necessary organic molecules are not formed, then it is likely that life could not have formed on the Earth in the manner predicted by J.B.S. Haldane and Alexander Oparin. In other words, life could not have been created without all of the necessary "ingredients". This leaves the proverbial door wide open for additional sources of organic material to play a role in the production of life on Earth. If one considers the possibility of extraterrestrial sources of organic compounds, one must first ask the simple question, where else in the universe can these compounds be found? One of the answers, scientists have discovered, is in molecular clouds and nebulae, the dense dust-laden regions of outer space where stars are beginning to coalesce. The relative high density of these regions (millions of particles per cubic centimeter of space) provides an ideal situation for the formation of simple molecules. For example, in the molecular clouds of Orion, scientists have identified nearly 130 simple molecules, from basic two-atom molecules like CH, CN, and CO to large molecules containing over 10 atoms, like HC9N, C2H6O, and HC11N (Goldsmith and Owen 93-97). In all likelihood, many more molecules exist in the clouds that have, as of yet, been undiscovered. Some scientists, Fred Hoyle and Chandra Wickramasinghe being the most famous, have even suggested that complex polysaccharides (complex carbohydrate chains found in plants on Earth), various bacterial and viral diseases, and even life itself could have first been formed in nebulae (Klyce; Sullivan 95-101). Although this idea, part of the theory of "panspermia" that life exists in either spores or seeds throughout most of the universe and seeded life on Earth, seems rather far-fetched and lacking in any concrete evidence (most, if not all, of Hoyle and Wickramasinghe's theory is unsubstantiated), one cannot overlook the idea that simple organic chemicals in the nebulae could somehow be connected with the origin of life on earth. If the molecules from the clouds and nebulae did, in fact, somehow bridge the gap between the clouds of dust and the rocky planet Earth, an intermediary body must have existed, one that could have taken the molecules and carried them over vast distances. Scientists believe such bodies do exist -- comets, large chunks of dirty interstellar ice, and meteors, inter planetary rocks. In particular, comets seem like attractive carriers of organic matter. First, they traverse large distances in outer space while moving along their famous elliptical orbits. And second, if comets are made from the original dust and gas of the young universe as is the current belief, they should contain some of the organic chemicals and be able to preserve them in their icy core (Goldsmith and Owen 97, 259-265). One could consider a scenario where: 1) simple organic molecules form in an area of space within or relatively close to the solar system (perhaps in a molecular cloud similar to the Orion nebula/molecular cloud previously mentioned), 2) one or several comets form out of the dust and gases of the cloud, 3) the comet or comets take on an orbit that eventually puts them on a collision course with the Earth, and 4) the organic chemicals in the comet/comets are deposited on the Earth's surface. If this theory is to be considered viable, however, several issues need to be addressed. First, organic material must be proven to exist in comets. Second, it should be proven that collisions involving comets were frequent in the early history of the Earth. Third, some proof should be offered that the organic material could survive such a collision. The first issue, the question of actual proof that organic chemicals exist in comets, was resolved in the several spacecraft missions to Halley's comet several years ago; they have shown that Halley contains large amounts of carbon-based chemicals -- it is 25% organic by mass. This is a substantial quantity of organic matter, and is certainly significant enough to influence the conditions on Earth if the matter was somehow able to survive a collision. Also of note, the missions were able to show that Halley's comet is 40-50% water ice, which provides a suitable environment to protect the chemicals from frictional heating as the comet travels through space (Chyba and McDonald 227-228; Sagan 302-303). The second issue, the question of proof that collisions between comets and planets took place, is relatively easy to address. Evidence of planetary bombardment exists, most obviously, on the surface of the moon, where craters litter the surface. In the first hundred million years after the planets formed, scientists have concluded, collisions between comets, meteors, and planets must have been very frequent - all of the solid material in the solar system was crashing and banging together. Although the weathering of the surface and the active geology of the Earth, most notably the high volcanic activity and the shifting of land masses due to plate tectonics, covers most evidence (unlike the moon, whose lack of weather/significant geologic activity preserves the craters), collisions involving the Earth must have been very frequent (Goldsmith and Owen 267; Sagan 188). The third issue, whether organic chemicals could have survived a collision, is more difficult to address. Scientists have theorized that the most intense phase of the Earth's bombardment with comets and meteors would have had a drastically negative effect on the survival of organic compounds and on life's ability to emerge. Collisions of large objects would have literally blown off the planet's atmosphere. Collisions involving small objects would have, as Donald Goldsmith and Tobias Owen state, "created temporary atmospheres of vaporized rock, essentially heat-sterilizing the planet's surface" (p.195). Therefore, if organic chemicals from comets are to play a role in the origin of life on Earth, they must have come to the planet in comets that came to the Earth after the initial bombardment and after the formation of an atmosphere. Once the Earth developed a thick enough atmosphere (and, hence, a large enough atmospheric friction) to significantly slow down incoming objects, the organic compounds might have arrived intact on the Earth's surface. As David Deamer and Gail Fleischaker state: Meteorites of intermediate size, ranging from larger pebbles a few grams in mass up to boulder-sized objects weighing several hundred kilograms, lose their interplanetary velocity in the atmosphere and enter free fall, striking the ground at the same velocity as a stone dropped from an airplane. Although their surfaces briefly reach white heat from atmospheric friction during entry, the interior of such meteorites remains cold, thereby preserving their chemical and physical composition in essentially a pristine state (qtd. in Klyce). Thus, the interiors of meteors (which often contain some organic matter like comets do) can be preserved on atmospheric entry. The same condition s hold true for objects like comets. Therefore, at least some of the organic materials from extraterrestrial bodies could have survived a collision with planet Earth, despite the atmospheric friction and the physical impact. The evidence for organic matter coming to Earth in comets seems fairly good. The three main problems with the theory have been addressed: organic matter was proven to exists in comets, collisions between extraterrestrial objects and the young Earth were proven to be fairly frequent, and organic material was proven to be able to survive such collisions. Is the evidence conclusive, though? No - much like the evidence for the terrestrial origin model, much of the evidence is conjecture and lacks conclusive proof. Not all variables can be accounted for, and one cannot be sure that the situation occurred exactly as predicted. The question remains, which theory is correct? If one were to consider only the evidence previously discussed, one might reach the tentative conclusion that neither the primordial soup model nor the extraterrestrial origin theory is more likely than the other -- most likely, a combination of what the theories predict occurred. Perhaps, simple organic matter was able to form from the natural conditions on the surface of the Earth, and some organic matter was contributed from the periodic collision of comets into the Earth. Then, from this simple organic matter, life was somehow eventually able to form. This situation seems possible, if not probable, and reconciles all of the known information. There is, however, one more important piece of information. Just this year, the NASA Polar Spacecraft took some startling satellite pictures that may put to rest the origin question once and for all. The pictures from the craft clearly show that there are small objects entering the Earth's upper atmosphere that contain a lot of water. Analysis of the pictures by Louis Frank and other scientists at the University of Iowa reveal the fact these bodies from outer space are bombarding the Earth every day, creating a sort of bizarre "extraterrestrial rain". If the analysis is correct, then a new class of small comets up to 40 feet wide, previously unseen by astronomers, exists. Plus, these objects are amazingly common; if calculations are correct, these comets are striking the Earth at a rate of 15 million per year (Broad 1-2). If these "mini-comets" contain organic molecules and have been striking the Earth often and for billions of years back to when the Earth had just been formed, then an astonishingly large amount of cometary organic matter would have reached the planet's surface - much more than anyone could have previously imagined. In addition, because the comets are so small in size, they break up at heights of 600 miles to 15,000 miles above the Earth, before the onset of intense frictional heating from the atmosphere. This means that any organic chemicals in the small comets would face little or no high heat, allowing a great deal of the chemicals to survive en try into the atmosphere. The "mini-comets" are an ideal means for the simple organic matter from outer space to reach the surface of the Earth. If the evidence from NASA's Polar spacecraft proves true, then the question of the origin of simple organic molecules has virtually been answered: the extraterrestrial origin model must be the correct model. Although the terrestrial model may have played some small role (perhaps a small fraction of the organic matter was created from natural planetary conditions), an overwhelming majority of the organic material on Earth would have come from the millions of so-called mini-comets entering the atmosphere every minute. Comets, the dirty interstellar chunks of ice, are indeed the source of the simple organic matter that is needed for life to begin. Works Cited American Geophysical Union. "NASA's Polar Spacecraft Confirms Small Comets are Pelting the Earth." May 28, 1997. http://smallcomets.physics.uiowa.edu/www/may-1.html Broad, William J. 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