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HOPES that life on Mars would have left a permanent record of its presence in
the planet’s sulphur isotopes are misplaced, say chemists in California.
Organisms preferentially collect the lighter sulphur-32 isotope, and the element
is abundant on Mars—which left some people wondering whether Martian life
left its mark in the isotopic record. However, chemists from the University of
California at San Diego have concluded that the unusual sulphur isotope ratios
found in Martian meteorites were caused by chemical reactions in the Red
Planet’s atmosphere (Nature, vol 404, p 50). Harry McSween of the
University of Tennessee in…