NEW YORK (CNN) -- Independent tests have cast doubt over earlier studies that detected possible signs of past life on a Martian meteorite, according to an article in Sunday's New York Times.
Results of one study appeared to invalidate three of four lines of evidence scientists said in August were signs of microorganisms, and another study raised doubts about the fourth line of evidence.
Dr. David McKay and Dr. Everett Gibson Jr. of the Johnson Space Center in Houston reported on studies they led that concluded a meteorite, found in Antarctica and believed to come from Mars, contained evidence of nanobacteria.
Their studies, they said, found evidence of carbonate globules that may indicate water, deposits of minerals that have in some cases been produced by bacteria, structures that resemble bacterial fossils on Earth, and rock compounds that often have biological origins.
Scientists who worked on the latest studies were almost apologetic about their findings, and stressed that their findings did not conclusively rule out the possibility of life on Mars.
The new studies indicated that some of the signs taken to indicate possible life could have come from contaminates on the Antarctic ice.
"There is nothing else in this rock that looks like nanofossils, and the things that look like nanofossils aren't," said Dr. Harry McSween Jr. of the University of Tennessee at Knoxville.
McKay said that his team disagreed with the new interpretation.
"We're basically not worried by all this," he said. "For one reason, we don't think they're looking at the same places in the meteorite."
McKay added that his team was preparing reports on further examination of the rock and would be presenting the findings in two to three months.
When the findings were originally reported, the scientists stressed that none of the four lines of evidence proved the existence of past life, but that all four taken together make a compelling case for microbial life on Mars.
The report of the new studies -- by McSween, Dr. Ralph Harvey of Case Western Reserve University in Cleveland and Dr. John Bradley, a geochemist and executive director of MVA Inc., a company in Norcross, Georgia, that specializes in the microscopic analysis of materials -- appeared in Geochimica et Cosmochimica Acta, an international journal of geochemistry.
Original file name: CNI - Mars Evidence Questioned
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