WASHINGTON (Aug. 6, 1996) -- Researchers testing a meteorite from Mars claim to have found evidence that primitive life once lived on the red planet. Other scientists, however, scoffed Tuesday and said stronger evidence is needed.
Scientists from NASA and three universities report in a paper to be published next week that chemical and microscopic tests of a rock from Mars detected organic compounds deposited in such a way that they could have come only from biological activity.
They also report seeing shapes that "resemble some forms of fossilized filamentous bacteria," although much smaller.
When studying these factors, the researchers report, "we conclude that they are evidence for primitive life on early Mars."
Carl Sagan, a leading authority on the search for extraterrestrial life, called the findings "evocative and very exciting." But he said the chemical compounds reported in the paper "are not evidence of life."
Other scientists said that the organic compounds found by the researchers could have been formed without life and one stated flatly: "I don't believe it."
The study is to be published next week in the journal Science. Draft copies were released by the journal Tuesday after the contents were leaked.
Co-authors of the study David S. McKay and Everett K. Gibson Jr. of the Johnson Space Center in Houston; Kathie L. Thomas-Keprta of Lockheed Martin, a NASA contractor in Houston; Hojatollah Vali of McGill University in Montreal, Canada; Christopher S. Romanek of the University of Georgia laboratory in Aiken, S. C., and Simon J. Clemett, Xavier D. F. Chillier, Claude R. Maechlin, and Richard N. Zare of Stanford University in California.
Past or present existence of life on Mars has been considered a possibility ever since studies by spacecraft landers showed that water was once present on the planet surface.
None of the Martian landers, however, found evidence that life now exists on Mars, nor did the robot craft find chemical markers for life in limited soil samples that have been analyzed.
The researchers say in the paper that a rock from space recovered in Antarctica contains organic compounds that could only have been deposited by biological activity.
The new findings center on a meteorite called Allan Hills 84001, the oldest of 12 pieces of rock that earlier studies confirmed as originating from Mars. It is thought the rocks were jolted away from Mars by some massive collision in ancient times and then drifted in space until they fell to Earth.
Studies show that Allan Hills 84001 was crystallized from melted rock about 4.5 billion years ago, a time when the solar system was forming.
The rock is thought to have been knocked from the Martian surface about 15 million years ago and then landed on the Antarctic ice sheet about 13,000 years ago. It was discovered in 1984 and scientists later identified it as originating from Mars.
Thin slices of the rock, say the researchers, revealed organic molecules called polycyclic aromatic hydrocarbons, or PAHs.
They said PAHs can be formed only in two ways -- by biological action, such as by microorganisms, or in the process that forms planets.
The researchers determined that the PAHs in the rock were deposited in cracks that occurred after the meteorite was formed, suggesting the molecules were deposited by later biological activity.
Also, the researchers said that within the PAHs, they found particles of magnetite and iron sulfide, both chemicals that can be related to bacterial action.
Sagan said that if the researchers did, in fact, find microfossils within the Mars rock, then that would represent the strongest evidence yet of life beyond the Earth.
But he said if the researchers' claim is based on the presence of organic chemicals, then the proof is lacking. That means, said Sagan, that "life, while possible, is not proven on Mars."
Referring to the organic compounds, Jack D. Farmer said, "If that's the evidence, I don't believe it."
Farmer, a geologist and paleobiologist of the Exobiology Branch of NASA's Ames Research Center in Mountain View, Calif., said the "vast bulk" of magnetite is inorganically formed and that "PAHs have no direct relationship to biology. They are not an indicator."
"The conclusion is at best premature and more probably wrong. The PAHs are just not a reliable biomarker," said John F. Kerridge, a planetary scientists at the University of California, San Diego. "You should not go public with evidence that's less than 100 percent sure. This is much less than 100 percent sure."
Original file name: CNI - AP.Study Hints Mars Life
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