Life on Mars theory faces the final curtain

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The scientific debate over whether there was once life on Mars intensified yesterday, as new evidence was published suggesting that the meteorite hailed in August as containing the remains of extraterrestrial bacteria in fact offers no proof of past life.

Two papers, accepted by a scientific journal dealing with the chemistry of terrestrial rocks and meteorites, have given a thumbs down to the idea that tiny tubular structures in ALH 84001, a Martian meteorite discovered in Antarctica, offer evidence that some sort of life existed on Mars roughly four billion years ago.

Microscopic examination of the meteorite, and a comparison of its contents with those of rocks from the same area as it was found, both provide nonbiological explanations for the observations, say a group of American scientists.

The original claim was that the meteorite showed the results of biological action, because of the presence of polycyclic aromatic hydrocarbons (PAHs) deep within it, along with crystals of an iron compound called magnetite. Both are produced by some terrestrial bacteria, but the Nasa team argued that they were buried so deeply within the meteorite that they could not have been introduced from outside.

But New Scientist reports today that the journal Geochimica et Cosmochimica Acta will publish scientific evidence that the magnetite was formed by inorganic action, while the PAHs filtered in from the terrestrial surroundings.

Those claims though were swiftly rebutted yesterday by Ian Wright at the Open University.

"The magnetite particle that they observed for this was comparatively large," he said. "But the ones found with the evidence of bacterial microfossils are much smaller. So their refutation of that isn't a catchall.

John Valley, professor of geology at the University of Wisconsin, who is presently carrying out tests at the University of Edinburgh on the ALH 84001 meteorite, said "Even if they're right, it doesn't disprove the life hypothesis at all. I always thought the PAH evidence was the weakest link. But the overall hypothesis comes from multiple lines of evidence." He is performing tests on the mixtures of carbon and oxygen in the meteorite to see if they suggest past organic activity. He hopes to report the results next March.