An international team of researchers has discovered compelling evidence that the magnetite crystals in the martian meteorite ALH84001 are of biological origin. 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 Feb. 27 Proceedings of the National Academy of Sciences. The chains were formed inside organic material whose structure held the crystals together. 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. The researchers say the magnetite chains probably were flushed into microscopic cracks inside the martian rock after it was shattered by an asteroid impact approximately 3.9 billion years ago. This cataclysmic event on Mars' surface also may have killed the bacteria. The same, or a later, asteroid impact ejected the rock, now a meteorite, into space.