"Where does ozone come from?" Mr. Tappin asked.

"When free oxygen is available," Dr. Yardley explained, "ultraviolet radiation tends to split oxygen molecules into separate atoms of oxygen which are quite unstable. These unstable atoms of oxygen will combine with oxygen molecules to produce O₃ or ozone.

"Studies have indicated there was no appreciable presence of atmospheric oxygen until some time between 2.1 and 2.03 billion years ago. As a result, between 4.55 billion years ago, and 2.1 billion years ago, there would have been no way for ozone to be manufactured in the Archean era atmosphere."

"What are the ramifications," Mr. Tappin inquired, "of this combination of enhanced ultraviolet luminosity, as a result of the faint early sun, and the absence of ozone, due to the absence of oxygen, as far as the development of increasingly complex hydrocarbons is concerned?"

"Ultraviolet light," replied the professor, "is like most forms of energy. They are all two edged swords.

"In the right amounts and for the right length of time, energy is capable of bringing about many kinds of chemical reactions among organic molecules. In the wrong amounts and for the wrong length of time, energy can be quite destructive in its effects upon hydrocarbon compounds.

"In limited doses, ultraviolet radiation can help underwrite, among other things, the synthesis of a wide variety of organic molecules. Beyond a certain limit, however, such radiation begins to have an adverse effect, even on those compounds which, originally, it may have had a hand in helping to synthesize.

"Photolysis refers to the breakdown or decomposition of materials by the action of light. Prolonged exposure to ultraviolet radiation brings about photolysis.

"These remarks notwithstanding, the results of photolysis sometimes can bring about reactions which have a potential, under the right circumstances, for building more complex hydrocarbons. In other words, the products of photolysis may recombine with other organic materials.

"For example, one team of researchers observed that when methane gas is subjected to photolysis, methyl (CH₃) and methylene (CH₂) radicals are produced. Subsequently, these two radicals were observed to enter into reactions which resulted in heavier hydrocarbons.

"These researchers calculated that the equivalent of one bar or atmosphere of methane gas could have been polymerized by means of ultraviolet radiation over a period of some 10⁶ to 10⁷ years - in other words, between one and ten million years. They further proposed that such heavier hydrocarbons would have precipitated out of the atmosphere and formed a layer of hydrocarbons on the surface of the Earth measuring anywhere from one to ten meters in thickness."

"Dr. Yardley," interjected the defense council, "in the light of our previous discussion about the nature of the atmospheric composition of the Archean era, couldn't one respond to the findings of this methane photolysis research in several ways? For example, if the Archean-atmosphere were methane-dominated, this finding might have some value in origin-of-life scenarios, but if the Archean-atmosphere consisted of little or no methane, their finding is meaningless as far as the origin-of -life issue is concerned. Would you agree with this assessment of the situation, Dr. Yardley?"

"Not entirely," the professor indicated. "Even if there were little methane in the atmosphere, the synthesis of important precursors - such as hydrogen cyanide, formaldehyde, and, maybe, a few amino acids, still is possible.

"A great deal would depend on the ratio of hydrogen (H₂) to carbon dioxide gas (CO₂) which existed in the Archean-atmosphere.

"As I testified previously, if the ratio were about 2, then some researchers feel this kind of atmosphere would have reducing properties comparable to a methane-dominated atmosphere.

"As the ratio of hydrogen gas to carbon dioxide drops, the production efficiency by ultraviolet light also will drop. As one approaches a ratio of, say, one-tenth of hydrogen to carbon dioxide, then production efficiency by ultraviolet light is calculated to drop by at least two magnitudes or by a factor of around 100.

"Researchers suggest hydrogen might have arisen through outgassing from Archean era volcanoes. Hydrogen also might have been generated through the photo-stimulated reduction of ferrous iron in the photic zone of the ocean."

"Doesn't this photo stimulated reduction of ferrous iron assume," observed the defense counsel," that the surface of the Earth has not been frozen over due to the effect of the faint early sun?"

"Obviously," the professor responded.

"In addition," continued the lawyer, "doesn't the temperature of the exosphere, some 400 miles above the Earth, have to be factored into the equation concerning hydrogen? Doesn't the rate at which hydrogen escapes from the Earth's atmosphere increase as the temperature of the exosphere rises?"

"Yes, that is correct," acknowledged the professor.

Turning over one of the papers in his hand, the defense counsel ran the fingers of his right hand down the page. At a point near the bottom of the page, he stopped and inquired: "Are you familiar with Shimizu's study on exospheric temperatures in a methane dominated Archean era atmosphere?"

"Vaguely, yes," Dr. Yardley answered.

"Shimizu had concluded," reported the lawyer, "that a methane dominated Archean era atmosphere would have had an exosphere whose temperature exceeded 1300 degrees Kelvin, or more than 1000 degrees Celsius. The study suggested these temperatures would have made an atmosphere of such composition very short-lived.

"If one were to assume," Mr. Tappin postulated, "that a super greenhouse effect in a carbon dioxide- dominated atmosphere also were capable of generating comparable kinds of exospheric temperatures, then might one conclude, with some degree of justification, that there could be a relatively high rate of exodus of hydrogen from such an atmosphere?"

"Possibly," Dr. Yardley offered.

"Moreover," Mr. Tappin countered, "irrespective of the kind of atmosphere in which organic materials may have arisen by means of ultraviolet synthesis, if such organic materials were to continue to remain in the same exposed condition to ultraviolet radiation, then they will, after a time, begin to break down or decompose through the process of photolysis. Is this right?" inquired Mr. Tappin.

"That's pretty much the upside and the down side of things," answered the professor.

"Let us assume," proposed the defense counsel, that a methane-dominated atmosphere, or its hydrogen/carbon dioxide equivalent, existed. Let us further assume that the equivalent of one atmosphere of methane gas, or its hydrogen/carbon dioxide equivalent, was polymerized to more complex hydrocarbons through ultraviolet photolysis over a period of some one to ten million years.

"Despite allowing such assumptions as given, one still would have to consider the following possibility. The one to ten meters of organic material which we are assuming had precipitated out would now be subject to one to ten million years of further photolysis, not to mention possible hydrolysis, and, depending on surface temperature, pyrolysis. Is this about right, Professor?"

"More or less," Dr. Yardley said.

"In addition," continued the defense counsel, "if there were an extraterrestrial event of sufficient magnitude to vaporize the ocean, or vaporize the photic zone, or the size of the Yucatan meteorite, then, the one to ten meter layer of hydrocarbon material which has been postulated by some, would be, shall we say, history. Would you agree with this?"

"Given your premise, that conclusion tends to follow," admitted Dr. Yardley.

Referring briefly to the paper in his hand, Mr. Tappin asked: "Professor, would one be correct in stating that only a small fraction of the light energy coming from the sun is in the form of ultraviolet wavelengths which are sufficiently small to be capable of being absorbed by molecules such as H₂O, CO₂, CH₄, and NH₃?"

"Yes," agreed the professor.

"Would one also be correct," inquired the lawyer, "if one said the following: when more complex molecules are formed, then the absorption profile or spectrum of these molecules shifts in the direction of longer wavelengths where a great deal more energy is available from the light being radiated from the sun?"

"Again, yes," the professor affirmed.

"Dr. Yardley," continued the defense counsel, "do most of the relatively low wavelength ultraviolet photochemical reactions take place in the upper or lower atmosphere?"

"The upper atmosphere," responded the professor.

"Is it possible," queried the lawyer, "that the compounds which formed in the upper atmosphere through low wavelength ultraviolet photochemical reactions, are now vulnerable to photolytic decomposition from a broader range of energies as the absorption spectrum of these more complex compounds moves in the direction of longer wavelengths?"

"Yes, this is a possibility," the professor acknowledged.

"In other words, Dr. Yardley," the defense counsel summarized, "a variety of compounds could have been synthesized in the upper atmosphere by means of low-wavelength ultraviolet photochemical reactions, and, then, these newly formed compounds could have been decomposed through the photolysis brought about by longer wavelength ultraviolet radiation to which these compounds had become susceptible by virtue of their greater complexity, and, this all could take place before the organic materials ever reached the ocean or surface of the Earth. Isn't this a very real possibility, Professor?"

"Yes, it is," Dr. Yardley stipulated.

"Seemingly," Mr. Tappin suggested, "there is something of a race between two opposing forces here: photolytic production of compounds and photolytic decomposition of organic materials. Which of these two forces dominates in a given context will significantly shape what does and does not get to the ocean. Is this correct Dr. Yardley?"

"I would say so," the professor confirmed.

Once again, Mr. Tappin went to the table for the defense and exchanged the papers in his possession for ones being offered by his colleague. Turning back toward the witness, the lawyer said: "Dr. Yardley, in your direct examination testimony concerning the coupling of shock wave energy to hydrocarbon synthesis, you cited a number of figures."

Reading aloud from the papers in his hand, the lawyer summarized the material. "One, meteorites entering the atmosphere with a mass between 10^-14 to 10² grams would generate, collectively, about 1.8 x 10¹⁵ joules per year. Two, carbonaceous chondrite airbursts of objects which had a radius less than, or equal to, 300 meters would generate, collectively, approximately 1.5 x 10¹⁴ joules per year. Three, the post-impact vapor plumes of meteorites striking the Earth's surface would produce, collectively, about 6 x 10¹⁷ joules per year. Are these figures correct, Dr. Yardley?" asked the defense lawyer.

"Yes," the professor indicated.

"What sort of a conversion factor is used to come up with these figures?" Mr. Tappin inquired. "In other words, what percentage of the total impact energy actually is believed to be directed toward, or available for, shock synthesis?"

"The conversion factor," replied the professor, "would be a function of the kind of assumptions one made in developing the thermochemical model one used to calculate energies, efficiencies and so on. The amount of total energy which is capable, potentially, of being converted to synthesis reactions starts at about twenty to thirty percent and works its way downward from there depending on the factors being taken into consideration."

"Presumably, then, Dr. Yardley," remarked the lawyer, "the figures you have cited are not cast in stone. The actual energies which may be directed toward synthesis reactions may be less - perhaps, even considerably so - than the figures you have cited. Would you agree with this?"

"To a certain extent," the professor responded. "At the same time, these figures are not randomly pulled out of a hat. They are the end result of quite a bit of rigorous reflection and take into consideration a great deal of scientific knowledge."

"I'm sure," admitted the lawyer, "that what you say is true, Dr. Yardley. However, the same thing could be said with considerable justification at almost every stage of science for the past several hundred years, and, yet, despite this, models have changed and calculations have been revised. Isn't this so, Professor?"

"This is the character of science," replied the professor.

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