Mars Meteorite: Proof of Life?

Mars Meteorite: Proof of Life?

Mars Meteorite: Proof of Life?

WASHINGTON – A controversial finding that a meteorite from Mars might contain evidence of life has been boosted by the discovery of a magnetic crystal that researchers say could have been made only by a microbe.

In a study appearing Tuesday in the Proceedings of the National Academy of Sciences, researchers at the Johnson Space Center in Houston say a crystallized magnetic mineral called magnetite, found in a Martian meteorite, is similar to crystals formed on Earth by bacteria.

"I am convinced that this is supporting evidence for the presence of ancient life on Mars," said Kathie Thomas-Keprta, an astrobiologist at the space center and the first author of the study.

Thomas-Keprta said there is no report of such magnetites being formed by any but biologic means.

The magnetite crystal was found in a Mars meteorite called Allen Hills 84001, or ALH84001. Researchers at the Johnson Space Center in 1996 announced that the space rock contained microscopic evidence of life, but their claim has been dismissed by most other researchers.

Thomas-Keprta said the new study strongly supports the original claim and may even suggest that there is still microscopic life on Mars.

"If it existed there at one time, we would expect it to exist today," she said.

The new finding is supported by a second paper in Proceedings.

E. Imre Friedmann, a biologist at NASA's Ames Research Center in Moffett Field, California, said an electron microscope examination of ALH84001 had found evidence of magnetite crystals formed in chains.

Friedmann said that on Earth the bacteria that make magnetite forms the material in chains and that these chains are surrounded by a membrane. Under the electron microscope, fossilized images of both the chains and the membrane can be seen, he said.

"We see chains that could have been formed only biologically," said Friedmann. "There is no way you could come up with a non-biological explanation."

On Earth, some bacteria that live on the bottom of lakes produce magnetite as a navigation aide. The magnetic crystals act as a sort of compass to allow the bacteria to orient themselves as they move along the lake bottom.

Friedmann said the bacteria require an environment that is low in oxygen. The built-in compass "helps them navigate in the proper oxygen levels," he said.

Thomas-Keprta said the magnetite is "a bacteria fossil, sort of like dinosaur bones."

She said magnetite could not come from Earth organisms because it was encased inside the meteorite in a carbonate mineral that has been age-dated at 3.9 billion years old.

Because of this age, said Thomas-Keprta, "this is evidence of the oldest life form ever found."

Mars now has neither standing water nor a magnetic field, which would prompt bacteria to make magnetite. But experts believe that the planet once had oceans, an atmosphere and a magnetic field. Thomas-Keprta said it was during this period, billions of years ago, that the bacteria lived and made the magnetite found in ALH84001.

Some researchers who rejected the 1996 study by the Johnson Space Center scientists said they are not convinced by the new evidence.

Ralph P. Harvey, a geologist who has studied ALH84001, said the new conclusions are "hasty" and should not be accepted without further study.

"I don't think this report should be considered as proof" that life ever existed on Mars, said Harvey, but he did not totally reject the Thomas-Keprta interpretation.

"The door is still open until further evidence is rolled out," said Harvey.

He said he is troubled that Thomas-Keprta and her co-authors found many crystals of magnetite in the meteorite, but are reporting only on those crystals that they believe could have come from bacteria.

"All of the rest of the magnetites say 'No' to life," said Harvey. "They are focusing only a minority of magnetites in this rock."

Also, said Harvey, the researchers are concluding that the selected crystals could be formed only by a life process when there is little research to support this.

"Their support for these magnetite crystals is that they have never been found in a non-biological setting," he said. "It is in my mind hasty to rule out another origin."

At 4.6 billion years, ALH84001 is the oldest of 16 meteorites found on Earth and identified chemically as originating from Mars. Scientists believe that an asteroid smashed into Mars 13 million to 16 million years ago and catapulted the Martian chunk into orbit. It wandered in space for millions of years and finally fell to Earth about 13,000 years ago. It was found on the Allen Hills ice field in Antarctica in 1984 and has been intensely studied since.