Donald Goldsmith, The Hunt for Life on Mars (Dutton, New York, 1997). xvii + 267 pp. ISBN 0-525-94336-6.
A rock is on trial. It was found in Antarctica in 1984, though analysis showed it had been there for 13,000 years. For the previous 15 million years, it was found, from tests of cosmic ray bombardment, to have traveled through space from its original home of Mars, where it had been formed four and a half billion years ago, when the solar system was in its infancy.
The rock has been named ALH84001 (because it was the first meteorite found in the Allan Hills in 1984). It has been put on trial because a team of scientists headed by David McKay have accused it of harboring evidence for life long ago on Mars. If McKay is to be cast in the role of prosecuting attorney, author Goldsmith (who characterizes himself as a "scientist turned science popularizer") assigns himself the role of judge and asks his readers to be the jury.
Goldsmith sets this scene in his first chapter, where he lists four requirements to prove that life once existed on Mars:
(1) Establishing that a rock on Earth in fact came from the planet Mars.
(2) Demonstrating that the material inside that rock did not receive contamination from terrestrial forms of life during the thousands of years while it awaited discovery, while it was being collected, or at any time thereafter.
(3) Proving, by detailed analysis of matter in the rock, that it contains chemical compounds and structural forms that are characteristic of life.
(4) Eliminating the possibility that this chemical and structural evidence could have arisen through processes other than those performed by living creatures.On points one and two there is general agreement; on the last two points there is not. The second chapter iterates the history of ALH84001 since it left Mars, on which there is also general agreement.
Chapter three presents the case for the prosecution (with incorrect structural diagrams for aromatics on p. 89); chapter four presents the case for the defense. Like jurors in an actual trial, we must reach our conclusion from the evidence and argument presented on both sides of the case but are not allowed to interrogate those who have testified. Here I regretted that I could not ask the prosecution why, if laser extraction was used to insure that detected polycyclic aromatic hydrocarbons were not contaminations (p. 86), it was not used to identify the carbonates and magnetic minerals. In fact, in this "trial," not even cross-examination is allowed. The defense's question, "Why didn't the researchers attempt to determine the chemical composition of the nanofossils?" must also go unanswered.
But the reader members of the jury are entitled to background information, and it is provided in the next several chapters. Chapter five presents our present understanding of the origin of life on earth, chapter six considers whether Martian life could exist, and chapter seven assesses what could be learned from future expeditions to Mars.
Chapter eight, entitled "Science As a Way of Life," is in effect "judge" Goldsmith's charge to his jury of readers. Goldsmith counsels us that science is "organized skepticism." "Science has long been organized to reward not only the creation but also the rejection of new ideas," he writes on page 226. Though Newton stated in his "Rules for Reasoning in Natural Philosophy" that a theory must be accepted as true until proven false, nature does provide reality as a standard by which theories must pass the "doubt" test, and it is failure to pass this "doubt" test which leads to exclusion of "crackpot" and otherwise unsubstantiated theories from further consideration by the scientific community.
There is a tacit recognition that McKay's prosecution has not yet passed the "doubt" test. The jury is still out.
- John L. Roeder
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