Judge Arnsberger had entered the courtroom, and everyone had risen in concert with the command to do so given by one of the court officers. Again, in obedience to a directive, we all sat down.

"Mr. Tappin," stated the judge, "you may begin your cross-examination. Dr.Yardley, please remember, you still are testifying under oath."

Picking up a note pad from the table in front of him as he arose, Mr. Tappin approached the witness stand. Smiling at the professor, the defense lawyer said: "Dr. Yardley, I would like to commend you on an excellent presentation during direct examination."

The professor angled and dipped his head slightly in acknowledgement of the compliment. The smile on his lips was a tentative one, and the look in his eyes was wary in character.

The two looked like a cobra and a mongoose ready to do battle. Which was which was a toss-up.

Beginning the conceptual competition, Mr. Tappin briefly referred to the note pad he was carrying and stated: "In your discussion concerning meteorite impacts of the early Earth, Professor, you indicated that the scientific models dealing with what was happening on Earth, and when, were based on various studies conducted in relation to the lunar cratering data acquired through the Apollo space program. Is this correct, Dr. Yardley?" the lawyer asked.

"Yes, that's right," the professor answered.

"To the best of your knowledge," inquired Mr. Tappin, "what is the oldest time frame for which a radiometric date has been fixed in relation to the lunar samples?"

"That would be the Apollo 16 and 17 uplands data," Dr. Yardley responded. The radiometric dating process has established a time frame of between 3.85 and 4.25 billion years ago for the lunar samples taken from the craters in the areas of the two, aforementioned Apollo expeditions."

"Do the samples from the uplands represent the most heavily cratered areas of the lunar surface?" Mr. Tappin asked.

"No, they don't," the professor indicated.

"Therefore, Dr. Yardley, am I right in assuming that, at the present time, we don't have any radiometric data from these more heavily cratered areas of the moon?"

"Your assumption is correct," affirmed the professor.

"Then, this would seem to suggest," the lawyer stated, "that we don't know whether the more heavily cratered areas are older or younger than the lunar samples which have been brought back to Earth, or, perhaps, a bit of both - that is, some craters may be older, and some may be younger."

"Yes, at present, the age or ages of the more heavily cratered areas of the moon only can be estimated," the professor acknowledged. "More precise dates must come from radiometric testing of samples from those areas."

"How would one go about estimating the age of areas of the lunar surface for which we have no direct data?" Mr. Tappin inquired.

"Well, this is really not my specialty," pointed out Dr. Yardley, "but, I suppose, a lot would depend on one's choice of decay rates and how one fitted this to the available lunar cratering data."

"Dr. Yardley, would the choice of decay rates substantially affect one's conclusions, both with respect to amounts and times, in relation to the models of extraterrestrial bombardment of early Earth?"

"Whether or not one's conclusions would be affected substantially, depends on what one means by the word 'substantially'," the professor replied. "In general, however, the use of different methodological or radiometric starting points obviously will have some kind of impact on one's conclusions."

"If I understand you, Professor," Mr. Tappin said, "the choice of decay rates with respect to lunar cratering data could increase or decrease estimates of such variables as: how many meteorites, what size and when such meteorites collided with the Earth. Is this, essentially, the case?"

"In broad terms, yes," Dr. Yardley confirmed. "As I indicated in my earlier testimony, the model concerning the influx of meteorites into the Earth's atmosphere is largely a stochastic or probabilistic one.

"Consequently, a range of values is possible," indicated the professor. "The ones I have given to Mr. Mayfield are best-estimate projections based on carefully worked out models of probability which are believed to have governed what transpired on early Earth as far as meteorite activity is concerned."

"Dr. Yardley, in your direct testimony, I believe you stated many evolutionary researchers are of the opinion that much of the heavy meteorite bombardment of early Earth probably began to taper off somewhere between 4.44 billion and 3.8 billion years ago. Is this true?"

"Yes," the professor affirmed.

"You also testified, did you not Dr. Yardley, that many scientists contend an extremely large meteoric impact occurred on Earth approximately 65 million years ago off the Yucatan peninsula, and there is evidence to indicate this collision may have destroyed most of the species in existence on Earth at the time?"

"I gave such testimony, yes," admitted the professor.

"Was the Yucatan crater the result of a statistical anomaly?" asked the defense lawyer. "In other words, can we assume that between, say, 3.8 billion years ago and 65 million years ago, there were probably few, if any, large-sized meteoric impacts on Earth?"

"Such an assumption would be a reasonable one," the professor said.

"What makes the assumption reasonable, Dr. Yardley?" inquired the lawyer.

"Well, for one thing," Dr. Yardley answered, "the very fact life continues to exist, and, on the basis of paleontological data, has existed for over 3.5 billion years, indicates there cannot have been too many large-sized meteorite collisions with Earth. If there had been, we probably wouldn't be having this conversation."

"In your opinion, Professor, would living organisms have a better chance of surviving such a catastrophic event than various prebiotic arrangements of complex hydrocarbons?" Mr. Tappin asked.

At this point, Mr. Mayfield jumped up and firmly stated: "Objection, your Honor. The question is highly hypothetical and speculative."

"Mr. Tappin," probed Judge Arnsberger, "do you care to respond to the objection?"

"Yes, your Honor, I do," replied the defense lawyer. "On the basis of both direct testimony, as well as on the basis of evidence forthcoming from cross-examination to this point, the nature of science has been shown to involve, among other things, the use of assumptions, hypothesis, conjecture, probability, projections, estimates, interpolations and extrapolations. Therefore, I fail to see on what plausible grounds the prosecution could object to the defense's desire to explore certain hypothetical and speculative issues concerning the origin-of-life problem from a scientific perspective."

"Mr. Tappin has a point, Mr. Mayfield," the judge indicated. "I'm inclined to cut him some slack on this line of questioning, provided the attorney for the defense doesn't roam too far astray.

"Objection overruled. The witness should answer the question," she stated.

Turning his attention from the judge to the lawyer for the defense, Dr. Yardley replied: "In my opinion, the answer to your question would depend on quite a few variables. For example, one factor would concern whether the size of the meteor impact was sufficiently large to vaporize the ocean, or merely big enough to boil, to the point of evaporation, the 200 meter layer beneath the ocean's surface known as the photic zone."

"Excuse me, Professor," interrupted the defense lawyer, "what is the photic zone?"

"The 200 meter photic zone represents the depth to which light penetrates with sufficient energy to be able to sustain photosynthetic autotrophs. Photosynthetic autotrophs are organisms that synthesize their organic requirements by using sunlight as a source of energy to convert inorganic materials, such as carbon dioxide, to molecular forms capable of being used by the organism to sustain itself."

"Thank you," said Mr. Tappin, "please continue."

"The first kind of impact mentioned previously - that is, one capable of vaporizing the ocean, would involve, roughly speaking, about 5 x 10²⁷ joules of energy. This amount of energy would be delivered by an object which was around 440 kilometers in diameter and/or had a mass of 1.3 x 10²⁰ kilograms, travelling at approximately 17 kilometers per second.

"The second kind of impact - that is, one capable of boiling away the photic zone, would require about 4 x 10²⁶ joules of energy. The object would have a mass of approximately 1.1 x 10¹⁹ kilograms and a diameter of about 190 kilometers.

"The Chicxlub, Yucatan crater, by way of comparison, is calculated to have been created by an object some 300 kilometers in diameter. Thus, it is intermediate in size between meteorites capable of evaporating the ocean and meteorites able to boil away the 200 meter photic zone near the ocean's surface.

"If the size of the impact were of the ocean-evaporating kind, then neither living organisms nor various complex arrangements of hydrocarbons would have been likely to survive to any appreciable degree. To understand why this is so, one needs a few facts about the nature of the collision being discussed.

"With an impact of this magnitude, roughly a quarter of the energy arising from the collision would have been directed toward vaporizing the water of the ocean. Another quarter of the impact energy would have been radiated upward toward the atmosphere, and the remaining fifty percent of the energy would be buried in the vicinity of the impact.

"The heat generated at the point of impact would be sufficiently great to melt, if not vaporize, most of the crustal material ejected from the crater being formed by the force of the collision. The temperature of these materials probably would reach around 2000 degrees Kelvin or 1727 degrees Celsius.

"Furthermore, the heat released through these melting and vaporizing materials would have been radiated in at least two directions. There is a thermal wave of some 2000 degrees Kelvin that would have been generated upward toward the atmosphere, as well a thermal wave that would have been radiated downward.

"The rock vapor which radiated upward would have surrounded the globe for a period of time, raising the atmospheric temperature considerably. By the time the rock vapor had rained out, so to speak, from the atmosphere, half of the ocean would have existed in the form of a hot steam that would have added about 140 times of our present sea level pressure to the atmosphere.

"A short while after the rain out of the rock vapor, which would take several months, the uppermost portions of the steam atmosphere would have cooled enough to generate a relatively thick, moist zone capable of convectively reflecting substantial amounts of heat back to Earth. A number of researchers believe this would have led to the runaway greenhouse threshold, or beyond, at which time the rest of the ocean would boil away.

"There are a number of factors that could affect the character of the foregoing sequence of events. The amount of carbon dioxide in the atmosphere would be one consideration, especially given that the manner in which CO₂ is distributed among earth, atmosphere and the ocean is quite complex, with different greenhouse and temperature scenarios following from different modalities of distribution.

"In addition, the amount of cloud cover, as well as whether the cloud cover was at higher or lower altitudes, could affect the amount of infrared radiation which is absorbed and radiated back to Earth. On the other hand, cloud cover also could affect the amount of sunlight which might be reflected away from the Earth.

"Eventually, depending on the actual atmospheric temperature, pressure, and so on, the water content of the atmosphere would begin to precipitate out and fall back to Earth and, in this way, reform the ocean. This period of cooling and ocean re-formation would probably take between 2,000 and 3,000 years to be completed.

"The impact of a meteorite sufficiently large to boil away the 200-meter photic zone of the ocean also would have catastrophic results, although, obviously, not quite as pronounced as those which I have just described. For one thing, after an impact of the lesser kind now being addressed, the atmospheric disturbances and restoration of the ocean to relatively 'normal' conditions would take merely 300 years, rather than 2-3000 years as previously indicated for the larger kind of impact.

"If the nature of an existing ecosystem is such that it is dependent, ultimately, on photosynthetic autotrophs, then the sterilization of the photic-zone would wipe out the ecosystem. In other words, when the bottom link of the food chain in a given ecosystem disappears, then all of the heterotrophs higher up the chain which depend on that link also will disappear."

Professor Yardley noticed the expression on the face of the defense attorney. The professor seemed to reflect for a second on what he had just said.

Upon, apparently, intuiting the question about to be asked, he started to speak again. "Heterotrophs," he added, are organisms which depend on other life forms, usually photosynthetic or chemosynthetic autotrophs, to provide them with the organic materials that can be used to derive energy by which to synthesize their organic needs."

Mr. Tappin smiled in acknowledgement of Dr. Yardley's correct intuition. The defense attorney gave a slight motion of his hand indicating for the witness to proceed.

"However," pointed out the professor, "not all life forms live within the photic zone, and not all life forms necessarily are dependent on photosynthetic autotrophs in order to survive. There are chemosynthetic autotrophs, involving a few species of bacteria, which derive their source of energy for organic synthesis completely independently of light energy.

"These organisms accomplish this by means of the oxidation of various reduced inorganic compounds. For instance, some of these chemosynthetic autotrophs, like the colorless sulfur bacteria, have the capacity to generate energy by oxidizing hydrogen sulfide to sulfur, while other organisms, such as certain nitrifying bacteria, possess the ability to produce energy through oxidizing ammonia to nitrite.

"If these chemosynthetic autotrophs lived far enough below the photic zone, or lived sufficiently deep beneath the earth's surface, so as not to be affected by an impact large enough to vaporize the photic zone of the ocean, then such organisms might stand a very good chance of surviving this sort of catastrophic event. Similarly, complex, prebiotic hydrocarbons located out of harm's way in the same fashion as these chemoautotrophs also would be likely to survive a collision of this lesser kind."

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