New Study Supports Crucial Low-Temperature Origin For Potential Microfossils In Mars Meteorite

March 13, 1997


ATHENS, Ga. -- A new study on a Mars meteorite supports a low-temperature origin for carbonate globules inside the rock, researchers said today. This new evidence is consistent with theories that microscopic depositions in the rock may be the fossilized remains of bacteria.

The research was published today in the journal Science.

"We felt confident that some parts of this study could be solved in a relatively short time frame, and this is one of those issues," said Dr. Christopher Romanek of the University of Georgia's Savannah River Ecology Laboratory in Aiken, S.C. "This work supports our earlier interpretation for a low-temperature origin of the globules."

In addition to Romanek, authors on the Science paper include Drs. J.W. Valley of the University of Wisconsin, J. M. Eiler and E.M. Stolper of the California Institute of Technology, C.M. Graham of the University of Edinburgh and E.K. Gibson of NASA. Romanek began his work on the Mars rock when he was a postdoctoral fellow at NASA.

Two years before the idea of Martian life ever crossed his mind, Romanek (and others) determined the Martian origin for mineral deposits or carbonate "globules" in the meteorite and determined the globules formed at a temperature capable of sustaining life. This information is crucial because extremely high formation temperatures rule out the possibility of life. Romanek has been convinced all along that the carbonate globules formed at low temperatures.

At center stage of the controversy is the Martian meteorite, known as Alan Hills 84001, which was found in Antarctica about 13 years ago. It formed on Mars 4.5 billion years ago and, according to the researchers' paper published in Science last August, came in contact with liquid water between 3.6 billion and 4 billion years ago. From the water sprouted mineral deposits that bear a striking resemblance to fossilized bacteria.The researchers believe that about 16 million years ago, a comet or asteroid struck the Martian surface and blasted pieces of the rock into space, where they drifted for millions of years. The meteorite, found in Antarctica in 1984, fell to Earth about 13,000 years ago.

Shortly after the press conference last August which announced to the world the finding of potential microfossils in a Martian meteorite, Valley contacted Romanek regarding new tests he could perform using a technique known as secondary ion mass spectrometry (SIMS). This technique offered a major advance over earlier analyses of the meteorite.

"In our previous measurements, we had to measure hundreds of globules at a time," said Romanek. "With this instrument carbonate globules can be studied individually."

Valley and co-worker John Eller carried out analyses on the globules at the SIMS facility at the University of Edinburg in Scotland. The SIMS analysis technically allows for in situ analyses of oxygen and carbon isotope ratios in extremely small samples of carbonate and silicate minerals. These measurements are then correlated with chemical, spatial and textural information.

While recent papers have suggested a high-temperature origin for the carbonate globules in ALH8401 of up to 650 degrees centigrade, the SIMS test suggests a potential formation temperature of less than 300 degrees C, and indeed Romanek believes it may have been cool enough for microscopic life to have flourished.

Romanek does not discount the possibility that future studies could provide a convincing alternative explanation for the formations found inside the meterorite, but for now, he believes the original conclusions of the study still offer the best explanations.


University of Georgia

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