Ancient Bacteria on Mars?
A dull grey chunk of rock collected in 1984 in Antarctica has recently excited science with the possibility that it contains evidence of life on Mars. Analysis of gases trapped within small pockets of the rock indicate that it is a meteorite from Mars. It is in fact the oldest rock known to science -- fully 4.5 billion years old. Back then, when this rock formed on Mars, that cold, arid planet was much warmer, flowed with water, and had a carbon dioxide atmosphere -- conditions not so different from those that spawned life on earth.

Intrigued by the parallel, a group of NASA scientists set out to investigate the meteorite for biological activity. The search did not yield conclusive results, but many aspects of the meteorite seem to point in the direction of bacterial life!

Three aspects of the Mars meteorite suggested ancient bacteria. First, the meteorite contains combinations of minerals similar to those produced by bacteria on earth. Second, polycyclic aromatic hydrocarbons (PAHs) are found in the interior of the meteorite, where they could not be the result of contamination. These PAHs, unlike others which have been reported in other meteorites, look surprisingly like the sort into which bacteria dissolve when subjected to rock-forming processes.

Lastly, when examined with powerful electron microscopes, carbonate patches within the meteorite exhibit tiny putative microfossils, some 20-100 nanometers in length . At 100 times smaller than any known bacteria, it is not clear that these structures actually are fossils, but the resemblance to bacteria is striking. While carbonate spheres tend to grow on rocks brought out of the Antarctic cold, the spheres within this meteorite must have been created before the meteorite arrived on earth, because some of them are cracked by whatever shock blasted the rock from the Martian surface.

Previous instances where meteorites were claimed to harbor evidence of life have, after much publicity, proven to be the result of contamination. So this claim has been treated with considerable skepticism by other researchers. Indeed, contamination does not seem to be a problem in this case. The PAHs, common in the interior of the meteorite, are absent from the outer rind, where the meteorite melted during atmospheric entry. Clearly more painstaking research remains to be done before the discovery can claim a scientific consensus.

Source: "Signs of Primitive Life on Mars Are Found in Ancient Meteorite" by John Noble Wilford, New York Times, August 7, 1996