[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Life's 'Signature' Not Found In Martian Meteorite According To New Research

University of California-San Diego
Media Contact: Warren R. Froelich, (619) 534-8564, wfroelic@ucsd.edu

June 5, 1998

LIFE'S "SIGNATURE" NOT FOUND IN MARTIAN METEORITE ACCORDING TO NEW RESEARCH
BY CHEMISTS AT UCSD

Grains of carbonate minerals believed to signal previous life on a Martian
meteorite are most likely non-biologic in origin, according to new studies
by chemists at the University of California, San Diego.

In a study reported in the current issue of the journal Science, the UCSD
scientists report that the carbonates laced through the potato-sized rock
are the product of reactions with atmospheric carbon dioxide.

"This data suggests that the carbonates were made by the interaction with
the atmosphere rather than with the water on the surface, as would be
required for a biologic process," said Mark Thiemens, professor of chemistry
and biochemistry at UCSD and principal investigator of the study. Other co-
authors of the study were UCSD chemists James Farquhar and Teresa Jackson.

The new results are based on the first multi-oxygen isotopic examination of
carbonate globules in the meteorite, named Allan Hills 84001 (ALH84001).
Isotopes are atomic elements that have the same chemical properties, but
different weights and slightly different physical properties.

In August 1996, research teams at NASA's Johnson Space Center and Stanford
University announced their belief that at least parts of the brown-colored
carbonates found in ALH84001 bore a striking resemblance to the earliest
microfossils on earth, suggesting past life on Mars.

To see if the origin of the carbonates could be determined, the UCSD
chemists measured the proportions of oxygen 16, oxygen 17 and oxygen 18
found in the sample, seeking clues in the form of clear isotopic
"signatures." An isotopic signature to achemist is what a fingerprint is to
a detective. For the carbonates, the UCSD scientists wanted to find out if
the fingerprints matched oxygen from the atmosphere or oxygen from the
hydrosphere.

If the signature pointed toward a water origin, that would support that
case for life, since on this planet and elsewhere, the genesis for all life
is water. If the signature matched the oxygen isotopes from the Martian
atmosphere, that would suggest a non-biologic origin.

"So if these things were biogenic, they should have equilibrated with
water," said Thiemens. "They didn't. They equilibrated with the atmosphere.

"What it looks like is that the Martian oxygen isotopes came from the
Martian carbon dioxide atmosphere. So what we're seeing looks like a garden
variety precipitate of carbonates, rather than life."

To continue his search for life's signature, Thiemens and other scientists
look forward to the next mission to Mars in 2005 when samples of the
atmosphere and rock are expected to be retrieved and returned to earth.

"In the meantime, there's a suite of Martian meteorites that we'll look
through and we'll do the same analyses," Thiemens said.

Funding for the UCSD study was provided by NASA.