Scientists raise new questions about life in Mars rock
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WASHINGTON (AP) - A chemical study casts fresh doubt on claims by NASA scientists that a rock from Mars contains evidence of life.
A California research team says a mineral structure inside the meteorite were made by nonbiologic processes, and not by ancient bacteria as proposed by some researchers at the National Aeronautics and Space Administration.
A space agency scientist says the research is flawed and does not prove that microbes never lived inside the rock known as Allen Hills 84001.
The study is to be published Friday in the journal Science.
Mark Thiemens, a professor of chemistry at the University of California, San Diego, said his team analyzed the chemical characteristics of oxygen found inside the rock and concluded that it was deposited there from the carbon dioxide and ozone of the Martian atmosphere.
Thiemens said that if the oxygen in the mineral structure had been deposited by a microbe or other life form, the chemical signature of the minerals would have matched that of oxygen in water, not oxygen in the atmosphere. Life, as it is now understood, depends on water and would leave behind a chemical residue of oxygen that was once in water.
"If these things were biogenic, they should have equilibrated (chemically matched) with water," said Thiemens. "They didn't. They equilibrated with the atmosphere."
He said the finding does not give final proof that the rock never contained life, but "it is a significant" argument against the NASA theory.
Everett Gibson, a NASA researcher at the Johnson Space Center in Houston and co-author of the theory that Mars once held life, said that Thiemens and his team may not have tested the precise structures in the rock that the NASA scientists believe were formed by life.
Traces of life found in the rock are visible only with powerful microscopes and not easily measured, said Gibson.
He said the Thiemens group used a crushed sample from the Mars rock that may have included other minute bits of minerals that distorted the chemical findings.
Thiemens said that a new study is under way in which an even smaller specimen will be analyzed and the results of that, he said, "will give definitive evidence that is pretty close" to a final answer.
The rock called Allen Hills 84001 has been identified as originating on Mars. It is believed that the rock was smashed into space when the Red Planet collided with an asteroid. The Mars rock is thought to have spent millions of years in orbit before falling to Earth several thousand years ago. It was found in an ice field, called Allen Hills, in Antarctica.
Gibson and his colleagues analyzed the rock at the moon rock laboratory in Houston and concluded that some mineral structures, called carbonates, were evidence that the microbes lived in the rock before it was blasted away from Mars.
Their finding has been controversial since it was first proposed in August 1996. Several other research teams have reported findings that tended to question the life theory. But Gibson said nothing has been found to conclusively disprove their interpretation of the biological origin of the carbonates.