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HOPES that life on Mars would have left a permanent record of its presence in
the planet鈥檚 sulphur isotopes are misplaced, say chemists in California.
Organisms preferentially collect the lighter sulphur-32 isotope, and the element
is abundant on Mars鈥攚hich 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鈥檚 atmosphere (Nature, vol 404, p 50). Harry McSween of the
University of Tennessee in Knoxville says the findings 鈥渃aution us not to fool
ourselves by too simplistic an interpretation of sulphur isotopes鈥�.