The same NASA researchers who made headlines in 1996 by announcing they had found what looked like fossil bacteria in a 4-billion-year-old Martian meteorite have now discovered more evidence to back their controversial claim. David McKay and his colleagues at the Johnson Space Center in Houston recently examined samples of two other meteorites believed to have been blasted from Mars' surface. Both rocks appear to contain tiny fossils similar in size and shape to common bacteria.
One of the meteorites is only about 165 million years old, suggesting that life may have persisted on Mars for billions of years. If the rocks hold remnants of bacteria, McKay suspects similar microbes may still thrive on the Red Planet, perhaps in ice pockets.
He is careful to add that his finds are not conclusive. "We were beat up so much two years ago that I've become a lot more conservative about my interpretations," he says. Proof that bacteria once roamed Mars must wait for sophisticated analyses that will peek inside the meteorites, looking for biochemical markers unique to living organisms.
