By Brian Shicoff

The day was August 7, 1996. The place, NASA's Johnson Space Center. Scientists, after two years of painstaking detective work, announce fossilized life inside a 4.5 billion-year- old meteorite. Questions immediately arise. How could the scientists be sure that this meteorite that touched down on an Antarctic ice field in 1984 actually came from Mars? Well, since 1982, scientists have identified 11 other meteorites from Mars. This meteorite, ALH84001, contains a similar chemical signature to those already identified. Over the last ten years, planetary scientists have performed conclusive studies on these rocks, and their conclusions lead them to believe that ALH84001 is a Mars meteorite.

Maybe this meteorite did come from Mars. Still, how can they be sure life actually existed on Mars? Where is the hard, indisputable evidence? Well, inside the meteorite are small cavities containing tiny orange-brown globules of calcium carbonate, rare in meteorites, but very common in terrestrial limestone. The formation of limestone inside these meteorites requires water. However, there is no water presently visible on the surface of Mars. Nevertheless, scientists believe that these limestone deposits formed during a time where the Martian climate was once much warmer and wetter. They assert that these limestone deposits demonstrate an environment which could allow life to exist on Mars.

Surrounding each globule are specks of iron and sulfur compounds, whose structures resemble those produced by biologic activity. Near these compounds, scientists have detected polycyclic aromatic hydrocarbons, or PAHs. On Earth, PAHs can come from any kind of decay which releases carbon, but these PAHs inside ALH 84001 resemble those produced by the decay of simple organic matter.

Separately, any of these findings could be explained by other events, but together this meteorite and what is inside suggest that life on Mars once existed....or does it?

In fact, could an object that knocked into the Martian surface transfer microbes or life into the meteor? A little far-fetched, perhaps. But is this as far-fetched as the long string of explanations used to confirm these globules as containing life? Well, perhaps life was not carried to ALH 84001 by whatever hit the Martian surface. Perhaps, the life that came into contact with ALH 84001 came from our very own atmosphere. This could potentially explain both the globules, and the small organic matter.

With these alternate explanations in mind, the explanation offered by NASA scientists is to date, still inconclusive. Questions still remain, answers are few, and speculation great. Did life once exist on Mars? We may not soon know for sure.

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