Controversy has surrounded the Martian meteorite ALH84001 since 1996, when scientists first proclaimed that it bore traces of primitive life. What they had found were minuscule mineralized structures, which they took for fossilized, bacteria-like organisms. This theory was soon challenged, though, by scientists who argued that the structurescrystals, essentiallycould have grown through purely physical processes. Now two separate studies, published in yesterdays Proceedings of the National Academy of Sciences, make a strong case for the fossilized life theory and may just put the controversy to rest.
Imre Friedmann and his team of researchers from the NASA Ames Research Center point out that the magnetite crystals inside ALH84001 form chains with gaps between them, resembling a string of pearls. These crystal chains are difficult to explain without the presence of life: "Such a chain of magnets outside an organism would immediately collapse into a clump due to magnetic forces," Friedmann explains. The other researchers, led by Kathie Thomas-Keprta of the NASA Johnson Space Center, offer supporting evidence: they note that the magnetite crystals inside the meteorite are both physically and chemically identical to those found in terrestrial magnetotactic bacteriaorganisms that use a string of magnetic crystals inside their bodies to navigate, much like an internal compass. If these crystals are in fact remains of magnetotactic bacteria, they are not only definite proof of past life on Mars but evidence of the oldest life ever found.
