Scientists Find Evidence of Ancient Microbial Life on Mars
The researchers found that the magnetite crystals embedded in the meteorite are arranged in long chains, which they say could have been formed only by once-living organisms. Their results are reported in the February 27 Proceedings of the National Academy of Sciences.
The chains were formed inside organic material whose structure held the crystals together. "The end result looks somewhat like a string of pearls," Friedmann noted. Each magnetite crystal in the chain is a tiny magnet, approximately one-millionth of an inch in diameter. Magnetite is an iron oxide, similar to iron rust.
The chains may have served as 'compasses' for the host magnetotactic bacteria, so named because they navigate with the help of the magnetic crystal chains inside their bodies. The chains were preserved in the meteorite long after the bacteria themselves decayed.
Another NASA research group, led by Kathie Thomas-Keprta of NASA's Johnson Space Center, report in the same issue of PNAS that the magnetite crystals inside the meteorite are similar to those formed by 'modern' magnetotactic bacteria now living on Earth. The team studied only single crystals, however, not the elusive chain-like structures.
Friedmann's team discovered the crystal chains using a technique that enabled them to 'see' the tiny chains inside the meteorite without destroying them. Besides the chain-like formation, the team discovered that individual crystals are of similar size and shape, do not touch each other and that the chains themselves are flexible, further evidence of biological origin.
The fact that a small (about 4-pound) meteorite from a planet contains large numbers of bacteria suggests that such bacteria were widespread on the surface of Mars, the researchers say. A stone of similar size from Earth would contain many bacteria.
"Finding evidence of life on Mars is one of the central problems in astrobiology research today," said Dr. Michael Meyer, head of NASA's astrobiology program, which funded the research.
The meteorite ALH84001 was found in the Allen Hills region of Antarctica in 1984 by researchers supported by the National Science Foundation's Antarctic Search for Meteorites Program, a joint effort by the NSF, the Smithsonian Institution and NASA. Case Western Reserve University in Cleveland manages the program.