91av

SCIENTISTS in the US and Europe say they have found 鈥渃onclusive evidence鈥� of
ancient life on Mars after taking another look at a 3.9-billion-year-old Martian
meteorite retrieved from Antarctica in 1984.

They have discovered long chains of magnetite crystals that could only have
come from living organisms, according to Imre Friedmann of NASA鈥檚 Ames Research
Center in Moffat Field, California.

But the findings, released as 91av went to press, have
reignited the controversy over whether traces in the rock are from Martian or
Earth bacteria, or some non-biological process. In 1996, NASA announced that it
had found the imprints of fossilised bacteria in the same meteorite. These
findings were widely disputed.

Recent studies suggested crystals in the rock were magnetite formed by
bacteria. On Earth, bacteria use them as tiny compasses. Now Friedmann and his
colleagues say they have found around a thousand long chains of magnetite in the
meteorite using a technique called high-power stereo backscattered scanning
electron microscopy. Five characteristics, such as uniform crystal size and
flexibility, show they were produced by a living organism, he says. 鈥淪uch a
chain of magnets outside an organism would collapse into a clump due to magnetic
蹿辞谤肠别蝉.鈥�

Other scientists claim it is impossible to be sure that Earth bacteria didn鈥檛
get into microscopic cracks in the rock while the meteorite lay in Antarctica.
Colin Pillinger at Britain鈥檚 Open University says a definitive answer as to
whether Mars once harboured life can only come from missions to the planet to
collect new samples.