05-24-2002, 10:37 AM
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Oh Crap!
-=Administrator=-
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Join Date: May 22 2001
Location: Newnan, GA - ATL
Age: 34
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Evidence of Earliest Life Disputed
wonder what else was in err
Quote:
Evidence of Earliest Life Disputed
Fri May 24, 4:57 AM ET
By PAUL RECER, AP Science Writer
WASHINGTON (AP) - A conclusion that a 3.85-billion-year-old rock contains evidence of life may be in error, according to a study that suggests the rock formed at temperatures too torrid to make life possible.
A study published in 1996 concluded a band of rocks on the Greenland offshore island of Akilia contained a high ratio of the isotope carbon-12, which was interpreted as evidence for the presence of microscopic life billions of years ago.
But the new study, by Christopher M. Fedo, a George Washington University geologist, and Martin J. Whitehouse of the Swedish Museum of Natural History, concludes the Akilia deposit was formed from superheated melted rock and that the enriched levels of carbon-12 could have been caused by chemical action, not by some life form.
"Our conclusion is that the rock came from a source that was molten, like a volcanic fountain," said Fedo, first author of the study released Friday in the journal Science. "The temperatures of molten rock would be far in excess of anything living. Therefore, any carbon in there got there by some other process."
The original study suggested that the rocks were sedimentary and therefore formed at temperatures cool enough to permit life. The interpretation that the rocks contained evidence of life was based on the ratio between carbon-12 and carbon-13. Living things, such as microbes, extract carbon from the environment and tend to concentrate carbon-12 instead of the heavier carbon-13. As a result, deposits that once contained life may be enriched with carbon-12.
But Fedo said geologists are now recognizing non-biological actions can enrich rocks with carbon-12, which means that, by itself, the isotope cannot be absolute proof for the evidence of life.
"These non-biological processes are consistent with the kinds of rocks exposed on this island," said Fedo. "The rocks are not sedimentary and were formed from a molten state. Any carbon trapped in there would have come from a later process. Also, we know that carbon-12 occurs in this type of rock."
Fedo said that if his interpretation is accepted, it will mean that a sedimentary rock formation on the mainland of Greenland may contain the oldest known evidence of life on Earth.
That formation, located at Isua, has been dated at 3.7 to 3.8 billion years old, only slightly younger than the formation on the island.
"The sedimentary origin (of the rocks at Isua) is important because that is consistent with the temperature range of liquid water, and liquid water and life are closely linked," said Fedo.
Gustaf Arrhenius of the Scripps Institution of Oceanography at University of California, San Diego, a co-author of the 1996 study, said his team is doing a new examination of the Akilia rock formation and "believe there is much basis for a careful reconsideration."
"If it is true, as Fedo interpreted it, then it is a mystery still how the isotopic ratio was achieved," said Arrhenius. He conceded, however: "It is not impossible that there are non-biologic mechanisms."
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