When did life begin? According to geologist Abigail Allwood of Macquarie University in Australia, the answer is more than 3.4 billion years ago, nearly a billion years earlier than any other estimate. Allwood bases her claim on fossil formations, called stromatolites, in northwestern Australia.
Scientists have been arguing for decades over whether such structures are remnants of early microbial life, but the Australian formations are the best evidence yet. Although Allwood recovered only a few ancient organic scrapings, not enough to prove life's presence conclusively, she says the diversity of shapes suggests that several types of living organisms were at work. Other geologists suggest Allwood's weird formations could just be the result of strong ocean currents or oozing minerals. Allwood disagrees, noting that the strange rock patterns are too uniform to have been caused by random chemical activity.
The rocks are more than curious relics. If there is life on Mars, stromatolites could help astrobiologists find it. "We know that similar conditions existed on Mars for at least a short period of time," Allwood says. "So if we're looking for evidence of life there, these fossils help us figure out what to look for and where to look for it."