Life on Mars?

The Allan Hills meteorite from Mars is peppered with tiny magnetic crystals that on our planet are made only by bacteria.

The case for ancient life on Mars looks better than ever after scientists announced that they had discovered magnetic crystals inside a Martian meteorite -- crystals that, here on Earth, are produced only by microscopic life forms.

The magnetic compound, called magnetite or Fe₃O₄, is common enough on our planet. It is present, for example, in household video and audio tapes. But only certain types of terrestrial bacteria, which can assemble the crystals atom by atom, produce magnetite structures that are chemically pure and free from defects.

Scientists studying the Allan Hills meteorite, a 4-billion-year-old rock from Mars that landed in Antarctica about 13,000 years ago, found just such crystals deep inside the space rock.

"Finding this type of magnetic crystal in any material from another planet is an amazing and important finding," said Dr. Dennis Bazylinski, a geobiologist at Iowa State University. Bazylinski leads one of the few labs capable of culturing these magnet-producing bacteria, which are common in many freshwater and marine environments on Earth.

Bazylinski was one of nine researchers conducting the four-year investigation, which was funded by NASA's Astrobiology Institute. A report of their research is in the December 2000 issue of the journal Geochimica et Cosmochimica Acta.

"We're not claiming that this is proof of life on Mars," said Dr. Everett Gibson, an astrobiologist at NASA's Johnson Space Center in Houston, Texas, who also participated in the study.

"What we're claiming is that these magnetites (from the meteorite) are basically indistinguishable from certain biogenic (i.e., biologically-produced) magnetites on Earth. And furthermore, we know of no other mechanism to make them, either on Earth or Mars," Gibson said.

An electron microscope image of magnetite crystals from the meteorite.

The scientists believe that these crystals traveled from Mars in the meteorite, rather than being produced on Earth by bacteria that contaminated the meteorite after it arrived in Antarctica.

"That was a real concern -- whether (the magnetite crystals) could be terrestrial contamination," Gibson said. But several facts support a Martian origin, including the deep embedding of the crystals in the carbonate material of the meteorite and the preference of the magnetite-producing bacteria for low-oxygen environments, making it unlikely that such bacteria would live where the meteorite was found.