New evidence for Martian life


New research announced Thursday in the Feb. 27th Proceedings of the National Academy of Sciences (PNAS) suggest that, indeed, early microbial life appeared at about the same time on Mars as it did on our planet [Friedemann Freund, Aaron Staple, and John Scoville. Special Feature: Organic protomolecule assembly in igneous minerals. Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 5, 2142-2147, February 27, 2001,].


An international team of researchers studying a four billion year old meteorite from Mars found microscopic magnetic crystals inside the ancient rock. The telltale crystals were arranged in long chains, which the scientists say could have been formed only by once-living organisms.

"The chains we discovered (in the martian meteorite ALH84001) are of biological origin," asserted Dr. Friedmann, an NRC senior research fellow at NASA's Ames Research Center and leader of the research team. "Such a chain of magnets outside an organism would immediately collapse into a clump due to magnetic forces."

Both the chain-like arrangement of the martian crystals and the traits of the crystals themselves bear a striking resemblance to similar crystals produced by bacteria on Earth.

The bacteria, which are mostly from the Magnetospirillum genus, grow the "magnetite" crystals (Fe3O4) atom by atom in small internal pouches, then line up several of these crystals to collectively act as a bar magnet. Following this internal "compass needle" allows the bacteria to search the body of water that it lives in for suitable oxygen concentrations in a more efficient, straight-line path.

Friedmann's team says the magnetite chains in the meteorite probably were flushed into microscopic cracks inside the martian rock after it was shattered by an asteroid impact on Mars' surface approximately 3.9 billion years ago. This cataclysmic event also may have killed the bacteria. The same, or a later, asteroid impact ejected the rock, now a meteorite, into space. 

The magnetite crystals probably formed about 3.9 billion years ago, when the rock was ejected from Mars. For comparison, the earliest well-documented life on Earth dates back 3.6 to 3.7 billion years. Both planets formed about 4.5 billion years ago.

"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.

Communicated by Jérôme and Didier - March 2001

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