Mars rock could have carried life, study shows

By Maggie Fox, Health and Science Correspondent

WASHINGTON, Oct 26 (Reuters) - 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 on 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 sterilise 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 sterilised 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."

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