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Defunking ALH84001
This week's issue of the British journal Nature (387, 377; May 22, 1997) contains an article by Scott, Yamaguchi and Krot, University of Hawaii, entitled, "Petrological evidence for shock melting of carbonates in the martian meteorite ALH 84001." A preview summary appears at Nature's web site: www.nature.com in the "current issue" section. In essence, the authors argue that the carbonates could not contain fossils because they formed at high tempertature when carbonate, plagioclase and silica were melted and redistributed by the same shock event. Say it ain't so! However, an earlier article in Nature by Hap McSween and Ralph Harvey made a similar argument but did not attribute shock-melting as the heat source for the high-temperature origin. However, subsequent work by various members of the NASA team (Romanek, et al) bolstered the case for a low-temperature disequilibrium and possibly biogenic origin for the carbonates and cast considerable doubt on the previous findings by McSween and Harvey. The debate is far from over, but the Nature article will definitely be worth reading to see if any "new" evidence is presented.
Steve Excell
excell@cris.com