NSF PR 00-96 - December 15, 2000
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New Report Links Meteorite to Possibility that Microscopic
Life Existed on Mars
New scientific evidence reveals that primitive life
in the form of bacteria could have existed on Mars.
Scientists supported by the National Science Foundation
(NSF) have reported that nanometer-sized crystals
in a Martian meteorite share several characteristics
with those produced by aquatic bacteria on Earth.
An NSF-funded team found the potato-sized meteorite
ALH84001 in Antarctica in 1984, and scientists determined
it was of Martian origin. In subsequent studies, some
of which became controversial, researchers claimed
that the 4.5- billion-year-old rock contained signs
of ancient life. Since then, scientists have been
searching for additional "biomarkers"--indications
of life--present in the meteorite.
Now, a team of scientists reports it has isolated crystals
of magnetite, an iron oxide, from the meteorite and
examined the crystals with electron microscopy. Among
the crystals are some ranging in size from 10 to 200
nanometers across that have an unusual shape. The
scientists determined that these magnetite crystals
from the meteorite resemble magnetite crystals produced
on Earth by biological processes.
"The geometry, chemistry and other characteristics
of these crystals suggested to us that they were produced
by a biological process," said Dennis Bazylinski of
Iowa State University, an NSF grantee who participated
in the research. "Finding them in material from another
planet is an amazing and important finding. There
is currently no known method of synthesizing these
types of particles, and therefore, they may prove
to be an excellent biomarker."
Magnetite is produced both biologically and inorganically
on Earth. Magnetotactic bacteria, which are common
in aquatic environments, produce the crystals within
their cells. The cells behave like miniature compass
needles, using the crystals and the Earth's magnetic
field to find conditions that promote their growth
and survival in water and sediment.
The magnetite crystals produced by magnetotactic bacteria
are chemically pure and distinct in size and shape
from crystals of nonbiological origin. The crystals
from the Mars sample share the same characteristics
of size, shape and chemical composition as those produced
by the bacteria.
Kathie Thomas-Keprta of Lockheed Martin Johnson Space
Center led the research team, which received funding
from NASA and NSF. The results will be published in
the December issue of Geochimica et Cosmochimica
Acta, the journal of the international Geochemical
Society and Meteoritical Society.
Scientists generally agree that ALH84001 is one of
16 meteorites found on Earth that originated on Mars.
It lay in Antarctic ice for more than 13,000 years,
but previous research by Chris Romanek of the Savannah
River Ecology Laboratory, South Carolina, produced
convincing evidence that the magnetite crystals contained
in the sample originated on Mars.