2001-11-26 11:40:38 -- A group led by Peter R. Buseck of Arizona State University said that the NASA researchers have inadequate evidence showing that tiny crystalline structures in Mars meteorite ALH84001 were formed by bacteria billions of years ago as the rock was sitting on the Martian surface.
A study with Buseck as the first author appears Tuesday in the Proceedings of the National Academy of Sciences (news - web sites).
Buseck said that NASA-supported researchers claimed in February that crystals found in the meteorite are identical to crystals formed on Earth by bacteria. The material, known as magnetite, is formed by some bacteria that live on the bottom of lakes. The magnetic crystals act as a sort of compass to allow the bacteria to orient themselves as they move along the lake bottom.
Buseck said there was inadequate similarity between Earthly magnetite and that found in the Mars meteorite to prove that the material was formed by a living organism.
``We find that there is much more uncertainty than they seem to believe,'' said Buseck, referring to the NASA researchers.
The Arizona State researcher said there are computer-driven electron microscope techniques that can be used to determine if the NASA researchers are correct. He said he plans to do such a study.
Everett Gibson, a NASA researcher who was among the group that first proposed that ALH840001 contained evidence of life, said that Buseck has not even looked at the Mars meteorite.
``How can he draw this conclusion without seeing the material?'' Gibson asked. He said that other researchers have found evidence that supports the NASA group.
In 1996, Gibson and some other NASA-supported researchers announced that they had found evidence in ALH84001 of life -- microscopic fossils that could have been bacteria, and carbon chemicals that are linked to life processes.
They suggested that the bacteria lived on the Red Planet billions of years ago, when Mars had water and warmer temperatures, and that microbes left evidence inside the Mars rock.
ALH84001 is thought to have formed on Mars about 4.6 billion years ago and is the oldest of 16 meteorites found on Earth that have been identified chemically as coming from Mars.
Scientists believe that an asteroid smashed into Mars 13 million to 16 million years ago and catapulted into orbit a chunk of Mars that contained ALH84001. The Mars rock wandered in space for millions of years and finally fell to Earth about 13,000 years ago. It was found on the Allen Hills ice field in Antarctica in 1984 and has been intensely studied since.
Gibson said that other scientists have found evidence that supports the findings of his NASA team.
``Our group feels more strongly about our hypothesis now than we did in 1996,'' he said.
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