"Thank you, Dr. Yardley," said the defense lawyer, "I believe you have answered my question quite adequately. Now, let's see if I understand the overall character of this part of your position as stated in direct testimony.

"Earlier, you informed Mr. Mayfield and the court that researchers have concluded, based on lunar radiometric analysis, there were as many as 15-16 meteorite collisions on Earth which were greater than the impact creating the largest crater on the moon and, therefore, may have been sufficiently big to evaporate the oceans of early Earth. You further testified, Dr. Yardley, that researchers contend the last of these ocean-vaporizing events probably took place somewhere between 4.44 billion and 3.8 billion years ago. Is my understanding correct on both of these points, Professor?" inquired Mr. Tappin.

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

"On the other hand," the lawyer proceeded to say, "none of this would preclude any number of lesser collisions capable of sterilizing the photic-zone from having occurred. Presumably, the Yucatan crater serves as indirect evidence for such a statement since it was considerably larger than what is minimally necessary to boil away the photic-zone and, yet, here we are talking about it. Would I be correct, more or less, in asserting this, Dr. Yardley?"

"In general," replied the professor, "I would be prepared to go along with you except I would add one proviso to what you have said."

"Yes, Professor, what would this proviso be?" inquired the lawyer.

"If one had too many impacts capable of sterilizing the photic-zone," suggested the professor, "then this could prove to be as problematic, in its own way, to the development of life or to the evolution of prebiotic systems as were impacts of the ocean-vaporizing variety. Such impacts do occur, as the Chicxlub, Yucatan crater demonstrates, but we believe the available evidence indicates these kind of collisions, probably, were relatively rare events after 3.8 billion years ago, the time when the last of the ocean-vaporizing events is thought to have occurred."

"Yet, Dr. Yardley," the defense lawyer said, "the fact of the matter is there really is very little, if any, available evidence to indicate how many impacts there may have been, from, say, 3.8 billion to 3.5 billion years ago, which were capable of boiling away the photic zone. Is this not correct, Professor? Yes or no?"

"You would have ..." Dr. Yardley began to say. The defense attorney interrupted.

"Your Honor, I find the witness' answer non-responsive," Mr. Tappin stated.

"Dr. Yardley," Judge Arnsberger explained, "you must answer the queries of the defense counsel in accordance with the form in which the questions are being asked. In this particular case, your only options are 'yes' or 'no'"

"Thank you, your Honor," acknowledged Mr. Tappin. "Would you like me to repeat the question, Dr. Yardley?" asked the defense lawyer.

Shaking his head in a negative fashion, the professor sighed and said: "Yes."

"So, to restate the matter, Professor," the lawyer paraphrased, "statistically speaking, there might have been: no impacts, or one impact, or a few impacts, or more than a few impacts, of a size sufficient to boil away the photic zone of the ocean during the indicated period between 3.85 billion and 3.5 billion years ago. Is this correct?"

"Yes, that is correct," Dr. Yardley replied.

Flipping the page on his note pad, Mr. Tappin scanned the contents of the page for a few seconds, and said: "Professor, in your earlier testimony concerning indirect, isotopic evidence for the existence of life 3.85 billion years ago, which has been discovered at the Isau rock formation in Greenland, you mentioned, in passing, certain kinds of methodological counter-indications with respect to the previously stated interpretation of that evidence. Would you explain," requested Mr. Tappin, "at this time, a bit more about the nature of these possible counter-indications?"

"As I said earlier," noted Dr. Yardley, "during the fixation of atmospheric carbon dioxide, living organisms tend to discriminate against the carbon¹³ isotope and prefer its carbon¹² counterpart. This is due to the kinetic character of the enzyme responsible for the fixation of carbon in so-called C₃ plants - that is, plants in which a three-carbon acid is the first product of photosynthesis.

"Consequently, one will find organic sediments exhibiting depleted amounts of carbon¹³ relative to atmospheric CO₂. On the other hand, inorganic carbonate sediments, such as limestone, will tend to display elevated levels of carbon¹³ relative to atmospheric CO₂.

"If one encounters a sample which fits the depleted carbon¹³ profile, such evidence can be interpreted to mean that the profile was produced by a C₃-like plant which has a carbon fixing enzyme with this tendency. The issue, unfortunately, is not always straightforward.

"This is especially true in cases where the sample is drawn from a rock formation, such as Isau, where the rocks have, at some time, been subjected to temperatures in the range of 450 to 700 degrees Celsius. These sorts of high temperature may bring about what is referred to as a partial re-equilibrium of any carbon isotopes which are present in the rock formation.

"This partial re-equilibrium of carbon isotopes tends to elevate the carbon¹³ values for organic samples. At the same time, this process causes a lowering of the carbon¹³ value for the inorganic carbonate sample.

"When this happens, the results are skewed. Under such circumstances, one may not know if one is dealing with an inorganic carbonate with a lowered carbon¹³ value, or if one is dealing with an organic material with an elevated carbon¹³ value.

"Some people have interpreted the Isau carbon isotope evidence to mean that the samples in question were produced by a carbon-fixing enzyme similar in character to the enzyme existing in C₃ plants of today. Other investigators are not so sure if this interpretation is correct."

"What ramifications follow from these different interpretations, Dr. Yardley?" inquired the lawyer for the defense.

"If the first interpretation I mentioned is true - that is, if the Isau sample is actually organic in origin, then evidence would have been established which pushes back the earliest known life form to at least 3.85 billion years ago, several hundred million years, and change, prior to our previous oldest, fossil evidence drawn from the Warrawoona Group in Western Australia. If, on the other hand, the Isau sample turned out to be an inorganic carbonate with thermally skewed low carbon¹³ values, giving a false positive for the presence of life, then the oldest known evidence for the existence of life would stand at around 3.55 billion years ago, give or take thirty million years, or so."

"If," hypothesized Mr. Tappin, "the organic interpretation of the Isau isotope evidence is correct, then, presumably, this would suggest an upper boundary had been established for ocean-vaporizing meteorite impacts. In other words, given the catastrophic character of this kind of collision, as outlined by you previously, then, one would be hard-pressed to account for the continued existence of photosynthetic life forms like the proposed Isau organism. Would you agree with this, Dr. Yardley?"

"Yes, I concur," the professor indicated.

"On the other hand," offered the lawyer, "depending on circumstances, the location, the hardiness, and the luck of our hypothesized Isau organism, this photosynthetic autotroph might or might not survive an impact capable of vaporizing the photic zone. Is this correct?"

"Yes, I think so," stated Dr. Yardley.

"Now, Professor," continued the lawyer, "this approximate date of 3.85 billion years ago puts us at the upper, or later, limit of the period between 4.2 billion and 3.8 billion years ago that you earlier cited as the time during which the last of the 15-16 ocean-vaporizing meteorite collisions with earth is projected to have occurred. If one were to claim the final ocean-vaporizing impact were to have occurred some 4.2 billion years ago, then one has, approximately, 425 million years to play with in order to account for the origin-of-life. Is this right, Dr. Yardley?"

"Right," replied the professor.

"However," remarked Mr. Tappin, "on the one hand, there is no compelling evidence to suggest one would be justified in adopting the earlier 4.2 billion year bench mark as one's starting point. On the other hand, there is some evidence - namely, projected photic-zone vaporizing and ocean-vaporizing meteorite collision like the one near the Yucatan Peninsula some 65 million years ago, suggesting the 4.2 billion parameter may be a tad premature. Do you feel my characterization of the situation, Dr. Yardley, is unfair?"

"Not really," admitted the professor. "The starting point for origin-of-life scenarios has considerable theoretical and empirical looseness to it."

"If," Mr. Tappin conjectured, "scientists suddenly were to discover evidence indicating the incorrectness of the biological interpretation of the Isau sample, then, in your opinion Dr. Yardley, would the arbitrary nature of this starting point issue change much?"

"Yes and no," the professor responded.

"Would you please elaborate," requested Mr. Tappin.

"The fixing of a time frame which establishes a non-catastrophic period of time having conditions conducive to a prebiotic account of the origin-of-life always will have an element of arbitrariness about it. Nevertheless, using the later, 3.55 billion year Warrawoona date as the time when life initially had become firmly established, is more friendly to evolutionary models than is the Isau date of 3.85 billion years ago.

"The later, Warrawoona dating of life fits in more comfortably with the available data than does the earlier, Isau dating. By this, I mean the earlier dating of life has more problems to overcome in a shorter period of time than does the later dating of life.

"Among other things, the earlier, Isau dating of life is overlapping with the meteorite impact data, which we have discussed, much more than is the later, Warrawoona dating of life. There are more likely to have been both ocean-vaporizing and photic-zone vaporizing impacts associated with the earlier, Isau dating than with the later, Warrawoona dating of life."

"Still, Professor Yardley, wouldn't you agree," inquired the defense attorney, that one of the bottom lines in all of this is the following? In the light of the meteorite impact data, do we really have any non-arbitrary way to determine the amount of time with which, theoretically, we have to play around, so to speak, as far as providing a plausible evolutionary account of the origin-of-life is concerned?

"In other words, are we not merely guessing in relation to the basic question? Do we have any empirical means of pinning down how much historical or Archean time we actually have to work with in order to provide an account of the transition from prebiotic conditions to the first protocell or full-fledged organism which is plausible?

"Isn't one as justified in saying there was only 4,000 years- or less, say, between the last catastrophic meteorite impact and the laying down of the physical evidence, whether direct or indirect, for the first appearance of life on Earth, as one is claiming there was some 425 million years between these two points in history? Aren't evolutionary scientists arbitrarily selecting the latter time interval, during which life allegedly arose, simply because it proves to be less embarrassing and problematic for their theory than the 4,000 year scenario would be?"

"I believe," responded the professor, "there is a difference between making educated, empirically based conjectures about the origin-of-life and creating myths concerning those origins. I maintain there is a difference between, on the one hand, making conjectures with respect to which one can seek out evidence both for or against, and, on the other hand, developing systems of beliefs which are removed from empirical data as well as from rigorous demonstration."

"Dr. Yardley," interjected the defense lawyer, "one can agree entirely with what you just have said, but you haven't addressed the essential thrust of my previous line of questioning. Let me restate the issue in another manner."

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