"Given," began Mr. Tappin, "what you have been saying, Dr. Yardley, in response to my question, is one being unfair to the facts if one were to argue that the manner in which one pieces together those facts is very much dependent on, or driven by, the assumptions one makes concerning the nature of conditions in which one believes those facts are embedded?"

"No," indicated the professor, "someone arguing in the fashion in which you have suggested would not be treating the facts unfairly. Indeed, in science, one constantly should be examining the relationship between established facts and the assumptions surrounding one's use of, or interpretation of, those facts."

"Could one," asked the defense lawyer, "not also say the following? When the facts of a matter have not been established clearly, then the relation among assumptions, interpretation and 'facts' becomes, potentially, quite problematic?"

"Yes, I would agree with that," Dr. Yardley replied.

"Therefore, in the matter at hand, Professor - namely, the question of whether or not a 300-meter frozen zone would have formed near the surface of the Archean-ocean as a result of the dimness of the faint early sun - we appear to be faced with a rather problematic situation. This is so, because given, as seems to be the case, that we don't know such things as the composition, temperature and pressure of the Archean-atmosphere; or, the rate of Archean-ocean formation; or, the water vapor saturation levels of the Archean-atmosphere; or, the degree to which hydrothermal vents or volcanic activity are present, and so on; then, in a very real sense, except in extremely broad terms, we don't know the facts of the matter, do we?"

"No, we don't," confirmed Dr. Yardley. "This is one of the reasons theoretical models are constructed.

"Scientists take what is known about the laws of nature, together with whatever data may be available concerning the conditions surrounding a particular problem, such as the present issue of a frozen zone above the Archean era ocean. Then certain assumptions are made about how natural laws may be manifesting themselves under certain conditions.

"The implications of these assumptions are worked out in the form of a model. Essentially, the model says that if certain assumptions are true, then, under specified conditions, natural laws will generate certain kinds of predictable activity in the context of those given conditions and assumptions.

"At this point, if possible, controlled experiments are performed that focus on, or isolate, different variables shaping the problem being considered. By comparing the results of these experiments with the character of one's model, one has an opportunity, over time, to correct, eliminate, refine and/or confirm different facets of the model."

"We have before us, Dr. Yardley, three different ... models, I guess, ... or theories concerning the faint early sun paradox," noted the defense lawyer. "Is there an experimental way," the lawyer asked, "of deciding which, if any of these models, are an accurate reflection of what happened on Earth during the Archean era?"

"Not really," observed the professor. "Certain experiments may carry various kinds of implications and ramifications for such models that will have to be taken into consideration.

"Experimental results may raise questions about, or pose problems and challenges for, a particular model. Generally speaking, however, what happens is that researchers will merely modify their models in the light of the experimental data.

"Since we, to some extent, are working in the dark concerning what the precise nature of the conditions were during the Archean era, we frequently are limited to saying that different kinds of models are consistent with, rather than proved by, the known facts. Yet, the known facts may be, more or less, equally consistent with quite different models, depending on the assumptions one makes and how one chooses to interpret, and piece together, the available facts in the context of one's model.

"All models are conditional in nature. In other words, the accuracy or reflective capacity of a model, vis-a-vis & 'reality', or the facts, or one's field and laboratory experiences, is dependent on the rigor with which, and degree to which, one's assumptions can be shown to be plausible, or justified representations, of the prevailing conditions surrounding some issue or phenomenon.

"Modern scientists cannot recreate the Archean era conditions. At best, we can try to simulate certain facets of what, on the basis of the available data, we believe those Archean era conditions to have been.

"In the light of these simulations, we extrapolate and interpolate backwards to the Archean era. In this fashion, we try to link, as well as we can, our simulations, whether computer or experimental, to the available empirical data and known physical/chemical laws of nature.

"Many models will work in upper and lower boundaries as part of their conditional statements concerning the nature of reality. In other words, if certain variables operate at the upper boundary limits of the model, then certain things are said to follow. If, on the other hand, these same variable operate at the lower boundary limits of the model, other kinds of things may be said to follow.

"For example, quite a few simulation experiments in evolutionary theory concerning the Archean era are now, and have been for a number of years, examining the issue of organic synthesis under a variety of prebiotic conditions. The same experiment or simulation will be run a number of times under, say, a variety of conditions involving different atmospheric compositional packages.

"On one experimental run, a particular organic synthesis will be attempted with a methane/ammonia atmosphere. Other runs of the experiment will be done in the presence of, perhaps, different ratios of hydrogen and carbon dioxide gases.

"On the basis of these experimental results, a researcher will reach certain tentative conclusions. For instance, she or he may say: when the composition of the atmosphere consisted of a particular mixture of methane and ammonia, the synthesis went forward at such a rate and with such-and-such an efficiency yield. However, when the same synthesis was attempted with a certain ratio of hydrogen and carbon dioxide, the synthesis either did not occur, or it occurred at a reduced rate and with reduced efficiency yields of such-and-such a nature."

"Dr. Yardley, why don't we," suggested the defense counsel, "run some data by you and see how you handle it in the context of an evolutionary model? Perhaps, this exercise will help the court and the jurors to get a better feel for some of the issues which are, I believe, at the heart of the present trial."

The professor gestured a willingness to go along with such an exercise. He poured himself a glass of water and waited for the defense lawyer to begin.

"Let's return, for a moment," Mr. Tappin directed, "to the theory which assumes that the world froze, at some point, in response to the faint early sun. You indicated previously that one of the inspirations behind the construction of such a theory was to avoid the potential problems associated with a carbon dioxide dominated atmosphere in the Archean era.

"Presumably, one of these difficulties is that carbon dioxide has the potential to be highly reactive with complex hydrocarbons. As a result, CO₂ will help break the more complex molecules down into less complex and less interesting organic materials as far as the origin-of-life issue is concerned.

"Another difficulty posed by a carbon dioxide dominated atmosphere is the following. Experiments have shown that many kinds of organic synthesis are less likely to proceed, or do so in very limited fashion, in such an atmosphere.

"If the Archean era atmosphere were dominated by carbon dioxide, with very little, or no methane and ammonia, how would the 'let the world freeze' assumption avoid the ramifications of this kind of atmosphere? In other words, where would the simple hydrocarbons come from out of which more complex hydrocarbons are to be synthesized, and what sources of energy would underwrite this underwater synthesis?"

"If one were to assume," Dr. Yardley responded, "there were little, or no, atmospheric production of hydrocarbons, like hydrogen cyanide (HCN) or formaldehyde CH₂O, then one would have to look to other sources such as carbonaceous chondrites, interplanetary dust particles or interstellar dust clouds, for either these more complex kinds of hydrocarbons or their simpler precursors such as methane and ammonia. Another possibility might be through hydrothermal vents from which hot water, rich in dissolved materials, spills out into the ocean."

"If," posited Mr. Tappin, "the surface of the Earth is frozen over, how do extraterrestrial materials get to the underlying ocean?"

"One possibility," replied the professor, "is that these materials may have gone into solution during the earliest stages of ocean formation, prior to the establishing of a frozen zone near the surface of the ocean. Another possibility arises in conjunction with the asteroid impacts which, conceivably, could have provided a mechanism for mixing exogenous/extraterrestrial organic materials lying frozen on the surface with the oceans lying 300 meters below the frozen zone."

"Dr. Yardley, isn't the asteroid impact possibility a bit like dropping a hydrogen bomb on the Antarctic regions and seeing if anything interesting happens?"

"Objection, your Honor," proclaimed Mr. Mayfield. The question is argumentative."

"Sustained," stated Judge Arnsberger. "Rephrase the question, Mr. Tappin."

Starting again, the defense counsel asked: "Do we have any good reason to believe the impact of an asteroid sufficiently large to melt 300 meters of ice encircling the globe would have anything but destructive consequences for whatever residual exogenous organic materials might be lying frozen on the surface of the Earth?"

"No, I suppose not," answered Dr. Yardley.

"Is it fair to say, Professor," inquired Mr. Tappin, "that any conjectures concerning what may or may not have survived such a catastrophic event are quite presumptive and arbitrary in character?"

"Yes, I think that would be fair to say," Dr. Yardley acknowledged.

"Would you also agree, Professor," pressed Mr. Tappin, "that in view of the many uncertainties surrounding both the issue of the formation of the Archean era ocean, as well as the uncertain nature of the circumstances and conditions connected to the emergence of the 300-meter frozen zone, any conjectures concerning what had or had not entered into solution prior to the appearance of the frozen zone are equally presumptive and arbitrary?"

"I would have to offer a provisional yes to your question," Dr. Yardley stated."

"What is the nature of your qualifying provision?" inquired the lawyer.

"If," the professor hypothesized, "exogenous or extraterrestrial organic materials were reaching Earth through interplanetary dust particles or by the Earth's passage through interstellar clouds or by means of carbonaceous chondrites, then one would have to consider the possibility that these organic materials might be available to enter into solution should the opportunity arise."

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