By Richard Stenger
CNN.com Writer
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| Close-up view of a meteorite that has provided tantalizing
evidence of fossilized life on Mars |
The presence
of extraordinary magnetic fossils in a meteorite from Mars suggests
that the planet once hosted primitive life, scientists reported
this week.
The only known
sources of such microscopic magnetic crystals on Earth are certain
types of bacteria that produce them to seek food and energy.
Magnetite,
the mineral form of black iron oxide, is created through natural
forces on our planet. But magnetite crystals like those produced
exclusively by a class of aqueous bacteria are different. They
are chemically pure and free of defects.
"The
process of evolution has driven magnetotactic bacteria to make
perfect little bar magnets, which differ strikingly from anything
found outside biology," said Joseph Kirschvink, a geobiologist
who took part in the NASA-funded study.
"In fact,
an entire industry devoted to making small magnetic particles
for magnetic tapes and computer disks has tried and failed for
the past 50 years to make similar particles," he said in
a statement.
The microorganisms
arrange the magnet crystals in their cells as miniature compasses,
which direct them along naturally occurring magnetic fields towards
hospitable environments.
The magnetic
samples came from the oldest identified red planet meteorite,
a potato-sized igneous rock with an estimated age of 4.5 billion
years. Life could have thrived on the planet at the time, scientists
theorize.
"Mars
is smaller than Earth and it developed faster. Consequently, bacteria
able to produce tiny magnets could have evolved much earlier on
Mars," said Simon Clement, another scientist who investigated
the meteorite.
Kirschvink,
Clement and other planetary scientists published their findings
in the December issue of Geochimica et Cosmochimica Acta, the
journal of the Geochemical Society and the Meteoritical Society.
The meteorite
landed more than 13,000 years ago in Antarctica, according to
researchers, where it remained buried in ice until its discovery
in 1984.
NASA scientists
created a stir in 1996 when they announced they had discovered
microscopic fossils of life in the meteorite, known as ALH84001.
Critics have
countered that terrestrial life could have contaminated the rock
after it reached Earth. But later research demonstrated that the
samples came from an uncontaminated section of the meteorite,
the report authors said.
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