New report links meteorite to possibility that microscopic life existed on Mars

December 14, 2000

New scientific evidence reveals that primitive life in the form of bacteria could have existed on Mars. Scientists supported by the National Science Foundation (NSF) have reported that nanometer-sized crystals in a Martian meteorite share several characteristics with those produced by aquatic bacteria on Earth.

An NSF-funded team found the potato-sized meteorite ALH84001 in Antarctica in 1984, and scientists determined it was of Martian origin. In subsequent studies, some of which became controversial, researchers claimed that the 4.5-billion-year-old rock contained signs of ancient life. Since then, scientists have been searching for additional "biomarkers"--indications of life--present in the meteorite.

Now, a team of scientists reports it has isolated crystals of magnetite, an iron oxide, from the meteorite and examined the crystals with electron microscopy. Among the crystals are some ranging in size from 10 to 200 nanometers across that have an unusual shape. The scientists determined that these magnetite crystals from the meteorite resemble magnetite crystals produced on Earth by biological processes.

"The geometry, chemistry and other characteristics of these crystals suggested to us that they were produced by a biological process," said Dennis Bazylinski of Iowa State University, an NSF grantee who participated in the research. "Finding them in material from another planet is an amazing and important finding. There is currently no known method of synthesizing these types of particles, and therefore, they may prove to be an excellent biomarker."

Magnetite is produced both biologically and inorganically on Earth. Magnetotactic bacteria, which are common in aquatic environments, produce the crystals within their cells. The cells behave like miniature compass needles, using the crystals and the Earth's magnetic field to find conditions that promote their growth and survival in water and sediment.

The magnetite crystals produced by magnetotactic bacteria are chemically pure and distinct in size and shape from crystals of nonbiological origin. The crystals from the Mars sample share the same characteristics of size, shape and chemical composition as those produced by the bacteria.

Kathie Thomas-Keprta of Lockheed Martin Johnson Space Center led the research team, which received funding from NASA and NSF. The results will be published in the December issue of Geochimica et Cosmochimica Acta, the journal of the international Geochemical Society and Meteoritical Society.

Scientists generally agree that ALH84001 is one of 16 meteorites found on Earth that originated on Mars. It lay in Antarctic ice for more than 13,000 years, but previous research by Chris Romanek of the Savannah River Ecology Laboratory, South Carolina, produced convincing evidence that the magnetite crystals contained in the sample originated on Mars.

National Science Foundation

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