New Report Offers Evidence of Primitive Life on Mars
John Ira Petty
Johnson Space Center, TX
(281) 483-5111
Release: J00-84
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
NASAís 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 ñ 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 ñ 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 planetís 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.
