If true, these so-called thermophiles may have been either the first creatures on Earth or simply the sole survivors of the planet's fiery childhood. Resurrecting findings from a 1989 report, British researchers announced last week that primitive life may have existed on Mars as recently as 600,000 years ago. The reseachers base their finding on the high concentration and the carbon composition of organic compounds they detected in a young Martian meteorite. The meteorite, discovered in Antarctica in 1979 and known as EETA79001, formed 180 million years ago and was ejected from Mars 600,000 years ago. The researchers argue that the organic matter in the meteorite was incorporated before the rock left Mars.
Critics maintain that the organic compounds are terrestrial contaminants.
The studies suggest that if life got a foothold on ancient Mars, it may have survived at least until very recently. That's the same signature the team had found in terrestrial rocks that date from 2.8 billion years ago and contain fossil evidence of bacteria. Some scientists question whether Martian organisms could have increased carbon-12 by this amount. That is roughly the same isotopic ratio found in organic material on Earth today. That's just the point, says Jeffrey L. Bada of the Scripps Institution of Oceanography in La Jolla, Calif., who contends that the material is a contaminant.