Another Chance for Life on Mars

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The NASA scientists who startled the world three years ago with the declaration that life exists on Mars are at it again. But this time, they have double evidence: two meteorites encrusted with what is thought to be fossilized bacteria. Samples have been taken from both a 1.3 billion-year-old meteorite that fell to Earth in Egypt in 1911 and a 165 million-year-old rock that landed in India in 1865. For the moment, however, caution is the name of the game. "We're not counting on getting many converts," Dr. David S. McCay, a Johnson Space Center geologist, said of the two rocks. "We have not proven they are fossilized bacteria, nor have we proven they are from Mars."

But if the rocks are inconclusive evidence, they at least are two more pieces of inconclusive evidence, notes TIME science correspondent Jeffrey Kluger. "If we're finding a number of rocks with these features, it at least teaches us something about the characteristics of these meteorites. Either they all have these false alarms embedded in them, or they all have lifelike features in them." One point in the Egyptian rock's favor: a glassy crust that formed around the meteorite as it plunged to Earth, making it less likely to have picked up contaminants that could replicate fossilized bacteria. Critics remain unconvinced, and wonder whether earthly geological processes might not have produced the same "counterfeit" effect, says Kluger. The agency's response? Just a request for the public to keep an open mind.