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Going through the papers in his hand, the defense counsel removed several sheets. Walking over to his table, he returned the unwanted sheets to his colleague.

Standing in front of the defense table, Mr. Tappin said: "Professor, in your direct examination testimony, you indicated, I believe, that the Murchison meteorite contained 6 amino acids similar, in most respects, to amino acids occurring in living organisms. In addition, 12 other kinds of amino acids not found, as far as is known, in living organisms on Earth also were discovered in the Murchison meteorite. Is my recollection of this testimony correct?" asked the lawyer.

"Yes," Dr. Yardley confirmed.

"To the best of your knowledge, Professor," Mr. Tappin inquired, "has any recovered meteorite ever contained all twenty of the amino acids found in living organisms on Earth?"

"Not to my knowledge," the professor answered.

"Furthermore," continued the defense counsel, "you testified that the amino acids found in the 200,000 year old meteorite in Antarctica had optical properties which were opposite to the ones displayed by amino acids found in Earth organisms. Is this correct, Dr. Yardley?"

"Yes, it is," the professor responded.

"In addition, Dr. Yardley, I believe you stated earlier that in most cases outside of biological systems, amino acids tend to form racemic mixtures in which there are roughly equal numbers of left- and right-handed optical isomers. Is my understanding correct in this respect?" Mr. Tappin inquired.

"Yes," said the professor.

"Moreover, previously, you testified that only 5-6 percent of meteorites consist of carbonaceous materials and that organic materials constitute only a small part of this carbonaceous subset of meteorites. Is this right?"

"Correct," affirmed the professor.

"Finally, Dr. Yardley, isn't it the case that most of the organic material found in meteorites such as Murchison exists in the form of a complex kerogen-like polymer which is poorly defined and consists of a variety of aromatic groups, monocarboxylic acids and aliphatic hydrocarbons which may not have any positive implications for origin-of-life issues? In fact, isn't it true, Professor, that only a very small fraction - measured in parts per million - of the organic material found in meteorites contains molecules, such as purines and amino acids, which have any potential relevancy to issues concerning the origin-of-life?"

"That is right," the professor indicated.

"Well, Dr. Yardley," the attorney stated, "if we factor in all of the foregoing possibilities, we seem to be left with very uncertain, and possibly negligible, amounts of usable organic compounds from exogenous sources. In other words, given that organic materials form only a tiny portion of an already small subset of meteorites, and given that many of these exogenous organic materials exist in forms, or as kinds, which are not used by Earth organisms, and given that a considerable amount of this organic material may be destroyed through pyrolysis, hydrolysis, photolysis or impact, and given that we really don't know the rate or mass of carbonaceous chondrite influx during the Archean era, are not any statements about the amount and kinds of useable exogenous organic materials that arrive, and survive, very speculative and arbitrary?"

"Yes, I suppose so," Dr. Yardley admitted.

"Earlier," Mr. Tappin noted, "you mentioned, briefly, the possibility that hydrothermal vents may have played a role in the 'let the Earth freeze' model which arose in response to, among other things, the faint early sun paradox. Would you expand on this a little?" the lawyer requested.

"Some people," the professor said, "began to look seriously at hydrothermal vents as a possible locus for the origin-of-life when, a few years ago, rather extensive ecosystems were discovered to have developed around some of these vents. These ecosystems consisted of many exotic sorts of organism, including blind shrimp and giant tube worms.

"The food chains of these ecosystems were rooted in various kinds of microorganisms. These microorganisms were sulfur-eating life forms.

"Thermophilic, or heat-loving, microbial organisms also have been found living in the steam bath-like conditions of the hot springs at Yellow Stone National Park. In general, however, no one has discovered life forms on Earth capable of surviving in temperatures above 112 degrees Celsius."

"My understanding, Professor," indicated the lawyer, "is that these organisms are capable of living under such conditions because they possess specialized proteins which allow them, among other things, to dissipate heat. Apparently, there also are proteins, in various species of cold water fish, capable of binding to, and controlling the growth of, ice within the organism, and, as a result, helping the organism adapt to cold water conditions. Is this correct?"

"Yes," replied the professor. When he saw the defense lawyer signaling him to continue on with his discussion, he said: "Some researchers hypothesized that life may have originated with thermophilic organisms.

"Other scientists have hypothesized that life originated elsewhere. In time, however, these organisms may have migrated to the hydrothermal vents in order to seek resources exuded by the vents or as a protection from the extraterrestrial bombardment of the Archean era Earth, or, maybe, both.

"Presumably," reflected the defense counsel, "if organisms migrated to the vents, then, regardless of whatever forces drove organisms to, or induced them to seek out, these hydrothermal vents, nonetheless, in order to survive, these organisms would have to be adapted, in some minimally feasible fashion, to the thermal conditions of the vents. Is this not so, Dr. Yardley?"

"That's right," acknowledged the professor.

"But, the process of migration presupposes the existence of such organisms and assumes the existence of such adaptive capabilities. So, we are getting ahead of ourselves.

"Has anyone," Mr. Tappin asked, "devised a plausible theory of how life would have originated in the vicinity of the hydrothermal vents?"

"Not really," replied the professor.

"Dr. Yardley, in your direct examination testimony concerning the period of core differentiation of the Earth, you indicated some scientists believed the Earth's crust would have been relatively fragile at that time, and, therefore, conducive to the formation of these hydrothermal vents. Is this right?"

"Yes," responded the professor.

"Does the water in the ocean remain relatively static, or does it circulate?" Mr. Tappin asked.

"The water in the oceans of our day circulates extensively," the professor reported. "In fact, we believe any given volume of sea water eventually will circulate through every portion of the ocean."

"What about the Archean era ocean?" inquired the lawyer.

"I think the same scenario probably was the case," offered Dr. Yardley. "Between tidal forces and convection currents, of one sort or another, a circulatory system of some kind likely would have been present."

"If my information is correct," Mr. Tappin stated, "the temperatures associated with hydrothermal vents are in the vicinity of 350 degrees Celsius. What would be the effect," queried Mr. Tappin, "of hydrothermal vents on complex hydrocarbons that had dissolved in ocean waters and were brought into contact with these vents through the process of circulation?"

"A lot would depend on the extent, length and character of the contact," replied Dr. Yardley. "In general, the more direct, the longer, and the more extensive such contact, the more likely would be the tendency of any given complex hydrocarbon to denature or decompose."

"Would one be justified in arguing," asked the defense counsel, "that given some unknown number of hydrothermal vents on the bottom of the Archean era ocean, then the formation of a 300-meter ice layer above the ocean, due to the effects of a faint early sun, would not necessarily offer long-term stability to complex hydrocarbons which had, in one way or another, arisen?"

"As long as the molecules were able to stay in cold or cooler waters," Dr. Yardley pointed out, "then their average life times probably would be enhanced to some degree. On the other hand, to whatever extent such molecules could not stay in cold or cooler conditions, then the average length of life for such molecules would be decreased as a function of the different kinds of forces of decomposition, including temperature, to which these molecules were subjected.

"For example, one scientist has studied the effects of heat energy on the amino acid alanine. This molecule is one of the more stable amino acids.

"The researcher found that at a temperature of twenty-five degrees Celsius, the mean life of alanine is estimated to be 10¹¹ years. Yet, the mean life of this molecule is calculated to be just thirty years in length when the temperature is raised to 150 degrees Celsius.

"Less stable amino acids will break down more readily at such temperatures, and, therefore, they will have even shorter mean life times than alanine. In fact, less stable amino acids may begin to break down at temperatures somewhat lower than 150 degrees Celsius.

"Generally speaking, the more complex a hydrocarbon, the more unstable it tends to be in the presence of heat. For instance, proteins, DNA, and RNA all tend to denature and decompose when exposed to sufficient amounts of heat much more readily than may be the case with their component parts."

"Dr. Yardley," said the defense counsel, "I presume the aforementioned effect of heat on complex organic molecules would remain the same whether one is talking about hydrothermal vents or elevated surface temperatures caused by a super greenhouse effect. Is this presumption correct?"

"Yes, of course," remarked the professor.

"Therefore," Mr. Tappin observed, "all three theories which have been proposed as possible ways of resolving the faint early sun paradox, face, each in its own way, a potential problem with respect to decomposition of complex hydrocarbons as a result of potentially prolonged exposure to heat energy, either in relation to hydrothermal vents or to enhanced greenhouse effects. Would you agree with this assessment of the situation, Dr. Yardley?"

"In broad terms, I imagine this would be so," answered the professor."

Looking briefly at the papers in his hand, Mr. Tappin walked toward the witness stand. When he was a few feet away, he came to a standstill.

"Professor, earlier you testified that scientists believe there was little or no free oxygen in the early Archean era atmosphere. Given," postulated the defense counsel, "all the talk these days about holes in the ozone layer and how ozone absorbs ultraviolet radiation, and, in the process, protecting living organisms from the destructive effects of such radiation, I was wondering what the situation would be in the Archean era. More specifically, would the faint early sun lessen the presence of ultraviolet radiation?"

"Oddly enough," Dr. Yardley began, "although the overall, net luminosity of the early sun was lower than today's sun, nonetheless, on the basis of astronomical observations of young stars comparable to our early sun, the ultraviolet radiation of the early sun is considered to have been greater than is the case with our present sun. Consequently, in the absence of oxygen, the ultraviolet effect would be more pronounced than it is today, even in those areas, such as the Antarctic, where the ozone hole has grown to such a disturbing size."

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