ASHINGTON
- It plunged through Earth's atmosphere in a brilliant fireball,
but the inside of a chunk of Mars rock that fell to Earth 13,000
years ago stayed cool enough to sustain life, scientists
reported Thursday.
The findings support theories that life might not have
originally arisen on Earth, but was seeded from space.
"What's exciting about this study is that it shows the
Martian meteorite made it from the surface of Mars to the
surface of Earth without ever getting hot enough to destroy
bacteria, or even plant seeds or fungi," Benjamin Weiss, a
graduate student at the California Institute of Technology who
led the study, said in a statement.
"Other studies have suggested that rocks can make it from
Mars to Earth in a year, and that some living organisms can live
in space for several years. So the transfer of life is quite
feasible."
Weiss and colleagues studied the magnetic field of ALH84001
-- a potato-sized meteorite found in Antarctica. It attracted
global attention in 1996 when NASA scientists said they had
found chemical traces that could have been left by tiny bacteria
that either hitched a ride on the meteorite, or had once lived
in it before it was knocked off Mars.
Scientists are still studying and debating the evidence found
in the rock, which is considered fairly pristine.
Heat can change the magnetic properties of rocks, so Weiss
and colleagues tested thin slices of the meteorite with a device
called the Ultra-High Resolution Scanning Superconducting
Quantum Interference Device Microscope (UHRSSM). It detects
microscopic differences in the orientation of magnetic lines in
rock samples.
"Heating the meteorite to 40 degrees C (104 degrees F)
reduces the intensity of some magnetic features, indicating that
the interior of the rock has not been above this temperature
since before its ejection from the surface of Mars," they wrote
in Friday's issue of the journal Science.
"Because this temperature cannot sterilize most bacteria or
eukarya, these data support the hypothesis that meteorites could
transfer life between planets in the solar system."
Eukarya are made of cells with a true nucleus, including all
plants and animals.
Bacteria Could Have Survived Trip From Mars
Scientists think ALH84001 was knocked off Mars about 16
million years ago by an asteroid. But if the tiny bacteria were
snugly inside, they just may have survived, although there is no
scientific evidence to suggest that the traces found in the
meteorite were from bacteria that lived after they left Mars.
Studies have shown bacteria can survive the conditions they
would encounter in space if a big meteorite knocked a chunk of
Mars off the planet and sent it spinning toward Earth.
And just two weeks ago scientists said they had revived 250
million-year-old bacteria from an underground cavern near
Carlsbad, New Mexico.
Mars has, or had at one time, all the necessary ingredients
for life -- sunshine, organic molecules and liquid water. Some
experts have even suggested that life originated on Mars. It is
widely accepted that Mars would have been warm and wet billions
of years ago before losing its protective atmosphere.
"In fact, we don't think that this particular meteorite
brought life here," Weiss said. "But computer simulations of
ejected Martian meteorites demonstrate that about one billion
tons of rocks have been brought to Earth from Mars since the two
planets formed."
The report, he says, answers one major objection to the
panspermia theory that life may have come from space. Critics of
the theory have argued that any life form reaching Earth by
meteorite would have been sterilized by the heat generatme from space. Critics of
the theory have argued that any life form reaching Earth by
meteorite would have been sterilized by the heat generated by
going through the atmosphere.
"ALH84001 has stimulated a remarkable amount of research to
test the hypothesis that life exists elsewhere than on Earth,"
biologist Baruch Blumberg, who directs NASA's Astrobiology
Institute, said in a statement.
"The present study indicates that the temperature inside the
meteorite could have allowed life to persist and possibly travel
to Earth from Mars."
