New Evidence Strengthens Claims of Ancient Life on Mars
Study of Martian Meteorite Reveals Magentic Fossils
February 26, 2001
Johnson Space Center
Researchers have found magnetic material in a 4.5
billion-year-old Martian meteorite that could only have been
produced by bacteria. This new data strongly supports the
primitive life on Mars hypothesis of David McKay and co-authors
"There are no known reports of any organic process that could
produce such magnetites," said Kathie Thomas-Keprta, an
astrobiologist at NASA's Johnson Space Center and the lead
researcher on the study. The Martian magnetites are identical to
those found in a bacteria strain on Earth called MV-1. "This
group of magnetite deeply embedded in the Mars meteorite is so
similar to the ones produced by the Earth bacteria that they
cannot be told apart by any known measurement," said David
McKay, a geologist at JSC and a co-author on the paper. "We
considered that perhaps earth bacteria or earth magnetite had
gotten into the Mars meteorite," McKay continued, "but extensive
examination and testing by both our team and many other
investigators eliminated that possibility."
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
3.9-billion-year-old carbonates within ALH84001. Previous work
by co-author Chris Romanek, of the Savannah River Ecology
Laboratory has shown that these carbonates formed on Mars; thus
the magnetite crystals must also have formed on Mars.
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.
"These crystals are so tiny, ranging from 10 to 200 nanometers,
that nearly a billion of them would fit on the head of a pin,"
The authors found that about a quarter of the Martian magnetites
from ALH84001 are identical to magnetites produced on Earth by
the magnetotactic bacteria strain MV-1, which has been
extensively studied by co-author Dennis Bazylinski, a
geobiologist and microbiologist at Iowa State University who has
developed many ways of culturing these difficult to grow
microorganisms. No one has found terrestrial inorganic
magnetites, produced either naturally or in the laboratory, that
mimic all the properties displayed by biogenic magnetites.
"There is currently no known inorganic chemical means of
producing these magnetite crystals with their unique
morphologies," he said.
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. These
characteristics make the magnetite crystals very efficient
compasses, which are essential to the survival behavior of the
bacteria by helping them locate sources of food and energy.
"Mars is smaller than Earth and it developed faster," co-author
Simon Clemett of Lockheed-Martin at JSC noted. "Consequently,
bacteria able to produce tiny magnets could have evolved much
earlier on Mars."
"The process of evolution has driven these bacteria to make
perfect little bar magnets, which differ strikingly from
anything found outside of biology," added, Joe Kirschvink, a
geobiologist at Caltech and a co-author of the paper. "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."
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. Also, 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. Surface features also suggest that
early Mars had large oceans and lakes. These attributes, coupled
with a CO2-rich atmosphere, provided the necessary environment
for the evolution of microbes similar to the fossils found in
A team of 10 researchers collaborated on the four-year study,
which was published Feb. 27 in a special Astrobiology issue of
the Proceedings of the National Academy of Science. The team,
led by Thomas-Keprta of Lockheed Martin at Johnson Space Center,
was funded by the NASA Astrobiology Institute. Co- authors of
the study are Simon Clemett and Susan Wentworth of Lockheed
Martin at the JSC; Dennis Bazylinski of Iowa State University
(funded by the National Science Foundation); Joseph Kirschvink
of the California Institute of Technology; David McKay, Everett
Gibson and Mary Fae McKay of JSC; and Christopher Romanek of the
Savannah River Ecology Laboratory.
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