NEW REPORT OFFERS EVIDENCE OF PRIMITIVE LIFE ON MARS
December 13, 2000
John Ira Petty
Johnson Space Center, TX
(281) 483-5111
Release: J00-84
New Report Offers Evidence of Primitive
Life on Mars
A new scientific report offers compelling evidence that primitive life
existed on Mars. Tiny magnetite crystals, identical to those used by
aqueous bacteria on Earth as compasses to find food and energy, have
been found in the Martian meteorite ALH84001. The report on the
finding is in the December issue of Geochimica et Cosmochimica Acta.
Written by a group of scientists led by Kathie Thomas-Keprta of
Lockheed Martin at Johnson Space Center and funded by the NASA
Astrobiology Institute, the report strongly supports the primitive
life on Mars hypothesis of David McKay and coauthors in 1996.
Coauthors of the new report on a four-year investigation are Dennis
Bazylinski of Iowa State University, Joseph Kirschvink of the
California Institute of Technology, Simon Clemett and Susan Wentworth
of Lockheed Martin at the Johnson Space Center, David McKay and
Everett Gibson of NASA’s Johnson Space Center, H. Vali of
McGill University in Montreal, and Christopher Romanek of the
Savannah River Ecology Laboratory.
Magnetite (Fe3O4) is produced inorganically on Earth. But the
magnetite crystals produced by magnetotactic bacteria are different
– they are chemically pure and defect-free. Their size and
shape is distinct. Magnetotactic bacteria arrange these magnetite
crystals in chains within their cells.
Their characteristics make the magnetite crystals very efficient
compasses, which are essential to the survival behavior of the
bacteria. No one has found terrestrial inorganic magnetites, produced
either naturally or in the laboratory, that mimic all the properties
displayed by biogenic magnetites.
“The process of evolution has driven magnetotactic bacteria to
make perfect little bar magnets, which differ strikingly from
anything found outside biology,” said coauthor Kirschvink, a
geobiologist. “In fact, an entire industry devoted to making
small magnetic particles for magnetic tapes and computer disk drives
has tried and failed for the past 50 years to find a way to make
similar particles. A good fossil is something that is difficult to
make inorganically, and these magnetosomes are very good
fossils.”
Scientists generally agree that ALH84001 is a member of the group of
16 meteorites found on Earth that originated on Mars. The
potato-sized igneous rock is the oldest of them – about 4.5
billion years. It lay in Antarctic ice for more than 13,000 years.
But the biogenic-type magnetite crystals are embedded in carbonates
within ALH84001. Previous work by coauthor Chris Romanek has shown
that these carbonates formed on Mars. Thus the magnetite crystals
must also have formed on Mars.
“These crystals are so tiny, ranging from 10 to 200 nm, that
nearly a billion of them would fit on the head of a pin,” said
Thomas-Keprta. Using electron microscopy, team members examined the
Martian magnetites still embedded in the carbonate and also removed
about 600 crystals and examined the individual particles to determine
their chemical composition and crystal geometry.
The authors found that about a quarter of the Martian magnetites from
ALH84001 are identical to magnetites produced on Earth by
magnetotactic bacteria strain MV-1, which has been extensively
studied by coauthor Bazylinski, a geobiologist and microbiologist who
has developed many ways of culturing these difficult to grow
microorganisms. “There is currently no known chemical means of
producing these magnetite crystals with their unique
morphologies,” he said.
Coauthor Clemett noted that “Mars is smaller than Earth and it
developed faster. Consequently, bacteria able to produce tiny magnets
could have evolved much earlier on Mars.”
When the team asserted in 1996 that Martian meteorite ALH84001 showed
signs of life existing on Mars, that planet was not known to have
ever had a strong magnetic field. But since then, the Mars Global
Surveyor has observed magnetized stripes in the crust of Mars that
show a strong magnetic field existed early in the planet’s
history, about the same time as the carbonate containing the unique
magnetites was formed.
"ALH 84001 has been of great heuristic value in the field of
astrobiology,” said Baruch Blumberg, director of the NASA
Astrobiology Institute. “Independent of its support or
rejection, it has raised stimulating hypotheses that will help to
focus our definition of how life, or variants of it, can be
recognized."
Vic Baker at the University of Arizona and Jim Head of Brown
University have inferred abundant water on early Mars from the
morphology of canyons prevalent on Mars. In a recent issue of
Science, Michael Malin and Ken Edgett present evidence of widespread
sediment layers on Mars that they interpret as produced by numerous
lakes. Adrian Brearly of the University of New Mexico has found
traces of ancient water, in the form of clay minerals, in ALH84001.
Mars has long been understood to provide sources of light energy and
chemical energy sufficient to support life. Early Mars, the authors
note, may have had even more chemical energy produced by active
volcanism and hydrothermal activity.
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