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A ROCKY DEBATE - PART ONE - PART TWO - PART THREE - PART FOUR

The success of the Sojourner rover has blazed a new path for robotic exploration
Analyzed and Catalogued
by Bruce Moomaw
Cameron Park - April 28, 2000 - Indeed, James Ferris delivered a Conference talk describing the theory that life first consisted of RNA molecules arranged into ordered polymer sequences by their reactions with the surfaces of montmorillonite clay minerals -- in which case life first consisted of sheets of organic compounds stuck between microscopically thin layers of clay, rather than separate cells bordered by cell membranes.

According to him, RNA sequences only 50 molecules long might be sufficient to reproduce themselves, carry out protein synthesis and mutate into new but viable forms -- and sequences that long have already been produced by clay minerals in the laboratory.

Regardless of whether nanobacteria are real, though, objects that look like microbes absolutely must be chemically analyzed to confirm their identity as life.

Nealson proposed that the best procedure for identifying microbial fossils is to first locate areas within rocks that may contain them (using UV fluorescence, which is sensitive to organics, and perhaps even X-ray CAT scans of rocks to look for areas of peculiar density) -- then to examine these areas with various kinds of microscopy (whether optical or electron), and finally to try to analyze the composition of any microbe-like objects that turn up.

One technique that he and several other researchers at the Conference suggested was X-ray spectroscopy of possible microbial fossils, which can measure the percentages of various elements in them-- and thus clearly distinguish them from the ordinary minerals, produced by nonliving processes, in which they are embedded.

Perhaps the most promising new technique, though -- which drew great attention at the Conference -- is "Raman spectroscopy" (described by David Wynn-Williams in a talk), which makes use of the fact that when a substance is illuminated by a one-frequency laser beam, a very small fraction of its light is scattered at new frequencies whose spectrum is determined by the makeup of the substance.

This technique has turned out to be both very sensitive to small traces of organic compounds and capable of clearly identifying a wide variety of complex ones (including chlorophyll, nucleic acids, and amino acids); it does so without modifying the substance being examined; and it can easily be used in a microscope or a fiber optic probe of layers of rock or soil.

A tiny Raman spectrometer was supposed to be carried on the 2003 U.S. Mars lander, designed to analyze inorganic minerals but also capable of sensing traces of organic compounds in Mars rocks -- and while that mission has been cancelled, it seems certain that this instrument will be flown to both Mars and Europa in the near future, in forms more specifically designed to focus on the search for biological compounds.

Other life-detection techniques were also discussed.

Janice Bishop's poster referred to the fact (also noted by Mars expert Christopher McKay) that Mars' soil has turned out to be remarkably rich in magnetic iron minerals, one of which is thought to be maghemite -- and on Earth maghemite is rare and produced mostly by reactions with organic material.

(This is another reason for interest in the "hematite patch" which is now the favored landing site for the next U.S. Mars lander, and which may consist of lake-bottom minerals.)

Nealson stated that one of the best unambiguous techniques for proving the present or past existence of life is to measure how the composition of a layer of some substance -- whether rock or water -- changes with depth; as anaerobic microbes consume some chemicals and produce others, they produce variations in composition which cannot be copied by any nonliving process, and which are frequently preserved in "chemical-fossil" form in rock layers.

One scheduled talk at the Conference, by Benjamin Weiss, was to be on the degree to which subsurface Martian microbes might still survive by consuming the natural traces of hydrogen and carbon monoxide in Mars' atmosphere -- and the possibility of confirming their presence by detecting near-surface concentrations of the trace gases they may produce, such as methane or formaldehyde.

This talk was cancelled, but Weiss has recently published an article on the same subject in the Jan. 31 "Proceedings of the National Academy of Sciences".

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