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Prospects Dim for Fossils in Martian Meteorite
Thursday, March 14, 2002
By David L. Chandler
Sky & Telescope

David McKay (lower left) and his colleagues shook the scientific world in August 1996 when they announced finding possible signs of ancient microbes in a Martian meteorite.
Image Credit: Bill Ingalls -- NASA.

Still, the fossil proponents are far from throwing in the towel. An assessment led by Joseph L. Kirschvink (Caltech) concludes that up to half of the meteorite's magnetite grains are indeed truly biogenic.

Ever since it was trumpeted at a hastily convened press conference in August 1996, the subject of possible signs of life in the Martian meteorite ALH 84001 has remained intensely controversial. At the time, David S. McKay (NASA/Johnson Space Center) and his coauthors presented four lines of evidence suggesting that the 4-billion-year-old meteorite contains chemical or fossil traces of microbial life. In the years since, however, these signs have been disputed by other researchers, who ascribe them either to terrestrial contamination or to nonbiological processes on ancient Mars.

To many, the strongest remaining evidence for Martian microbes is the presence of tiny, uniform, chemically pure crystals of magnetite embedded in globules of carbonate — crystals that look remarkably similar to those produced by certain strains of terrestrial bacteria. Kathie L. Thomas-Keprta (Lockheed Space Systems) and her colleagues have continued to study the crystals and strengthen their argument that the tiny grains exhibit a suite of five characteristics found in biogenic crystals and never seen in magnetite produced by chemical and geophysical processes.

Not anymore, say two teams who will report tomorrow that they have independently synthesized magnetite crystals in the laboratory showing most of these same characteristics. The presentations will be made at the 33rd Lunar and Planetary Science Conference in Houston, Texas. One group, led by Dadigamuwa C. Golden (Hernandez Engineering) and Douglas W. Ming (NASA/Johnson), had previously produced perfectly formed, chemically pure magnetite crystals, thus matching two of the distinctive features of those in ALH 84001. Now, having completed 3-D examination of their fabricated crystals, Golden and Ming say these also share the distinctive shapes (termed truncated hexaoctahedrals).
(More: Sky & Telescope News Source)
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