Monday February 26 7:23 PM ET

Scientists See Evidence of Life on Mars Meteorite

WASHINGTON (Reuters) - Scientists have found compelling new evidence of possible ancient microscopic life on Mars, derived from magnetic crystals in a meteorite that fell to Earth from the red planet, NASA (news - web sites) announced on Monday.

An international team of researchers working with a Martian meteorite found in Antarctica discovered magnetite crystals arranged in long chains within the potato-sized space rock. Those chains could only have been formed by once-living organisms, the U.S. space agency said in a statement.

``The chains we discovered are of biological origin,'' Imre Friedmann of NASA's Ames Research Center in California said in the statement. ``Such a chain of magnets outside an organism would immediately collapse into a clump due to magnetic forces.''

Each magnetite crystal in the chain is a microscopic magnet, and they are strung together like pearls in a necklace, according to the researchers. Magnetite is an iron oxide, something like iron rust.

The meteorite under study, known to scientists as ALH84001, was discovered in the Antarctic in 1984 but caused a furor in 1996 when NASA researchers first raised the possibility that the rock might contain evidence of ancient microbial life.

Since then, the rock's significance has been disputed by astrobiologists around the world. The current findings, reported in Tuesday's editions of the Proceedings of the National Academy of Sciences (news - web sites), appear certain to feed the controversy.

Friedmann's research team said the magnetite crystals formed inside organic material whose structure held the crystals together. The crystal chains may have acted as compasses for the bacteria that held them -- such bacteria are called magnetotactic bacteria because they navigate by the magnetic crystal chains they contain.

The bacteria decayed but the crystals remained, the researchers reported. Most likely, the crystals were flushed into tiny cracks in the Martian rock when an asteroid slammed into the planet some 3.9 billion years ago; a later impact ejected the rock -- making it a meteorite -- and sent it toward Earth, the researchers said.

Another NASA research team, led by Kathie Thomas-Keprta at Johnson Space Center in Houston, reported in the same publication that the magnetite crystals in the Martian meteorite are similar to those formed by magnetotactic bacteria living on Earth.

The long chains of crystals indicate a large number of bacteria were present on the Martian meteorite, the researcher said, which suggests that such bacteria were widespread on Mars.

Because magnetotactic bacteria require low levels of oxygen, it could mean that photosynthetic organisms, the source of oxygen in the atmosphere, might have been present on Mars 3.9 billion years ago, the researchers said.

Images of the Martian crystal chains and their possible earthly counterparts can be seen online at http:/amesnews.arc.nasa.gov/releases/2001/01images/magneticbacteria/bacteria.html