SCIENTISTS FIND EVIDENCE OF ANCIENT MICROBIAL LIFE ON MARS
An international team of researchers has discovered compelling
evidence that the magnetite crystals in the martian meteorite
ALH84001 are of biological origin.
The researchers found that the magnetite crystals embedded in the
meteorite are arranged in long chains, which they say could have been
formed only by once-living organisms. Their results are reported in the
Feb. 27 Proceedings of the National Academy of Sciences.
"The chains we discovered are of biological origin," said
Dr. Imre Friedmann, an NRC senior research fellow at NASA's Ames
Research Center in California's Silicon Valley and leader of the research
team. "Such a chain of magnets outside an organism would
immediately collapse into a clump due to magnetic forces," he said.
The chains were formed inside organic material whose structure
held the crystals together. "The end result looks somewhat like
a string of pearls," Friedmann noted. Each magnetite crystal in
the chain is a tiny magnet, approximately one-millionth of an inch in
diameter. Magnetite is an iron oxide, similar to iron rust.
The chains may have served as 'compasses' for the host
magnetotactic bacteria, so named because they navigate with the
help of the magnetic crystal chains inside their bodies. The chains
were preserved in the meteorite long after the bacteria themselves
The researchers say the magnetite chains probably were flushed
into microscopic cracks inside the martian rock after it was shattered
by an asteroid impact approximately 3.9 billion years ago. This
cataclysmic event on Mars' surface also may have killed the
bacteria. The same, or a later, asteroid impact ejected the rock,
now a meteorite, into space.
Another NASA research group, led by Kathie Thomas-Keprta of
NASA's Johnson Space Center, report in the same issue of PNAS
that the magnetite crystals inside the meteorite are similar to those
formed by 'modern' magnetotactic bacteria now living on Earth.
The team studied only single crystals, however, not the elusive
Friedmann's team discovered the crystal chains using a
technique that enabled them to 'see' the tiny chains inside the
meteorite without destroying them. Besides the chain-like formation,
the team discovered that individual crystals are of similar size and
shape, do not touch each other and that the chains themselves are
flexible, further evidence of biological origin.
"Until now, studying life has been like trying to draw a curve
using only one data point -- life on Earth," said Friedmann. "Now
we have two data points to draw life's curve." The next step
is to find the remains of the bacteria themselves, he said.
The fact that a small (about 4-pound) meteorite from a planet
contains large numbers of bacteria suggests that such bacteria were
widespread on the surface of Mars, the researchers say. A stone of
similar size from Earth would contain many bacteria.
In addition, since magnetotactic bacteria require low levels of
oxygen, this finding indicates that photosynthetic organisms, the
source of oxygen in the atmosphere, must have been present and
active on Mars 3.9 billion years ago.
"Finding evidence of life on Mars is one of the central
problems in astrobiology research today," said Dr. Michael
Meyer, head of NASA's astrobiology program, which funded the research.
In addition to his fellowship at NASA Ames, Friedmann, who is best
known for discovering microorganisms living inside desert rocks, is
professor emeritus of biological science at Florida State University.
Members of the research team include Dr. Jacek Wierzchos
(University of Lleida, Spain), Dr. Carmen Ascaso (CSIC, Madrid, Spain),
and Dr. Michael Winkelhofer (University of Munich, Germany).
The meteorite ALH84001 was found in the Allen Hills region of
Antarctica in 1984 by researchers supported by the National Science
Foundation's Antarctic Search for Meteorites Program, a joint effort
by the NSF, the Smithsonian Instituttion and NASA. The Case
Western Reserve University in Cleveland manages the program.
Full text of the research paper is available at: http://www.pnas.org
Images of the magnetite chains inside the ALH84001 meteorite and,
for comparison, inside a modern magnetotactic bacterium are at:
Ames Research Center is NASA's lead center for astrobiology, the study
of the origin, evolution, dissemination and future of life in the universe.
NASA Ames is the location of the central offices of the NASA Astrobiology Institute,
an international research consortium.