By ELIZABETH PENNISI - SCIENCE AAAS
Added: Sun, 28 Aug 2011 14:49:19 UTC

Old stomping grounds. This landscape in Western Australia is home to these very ancient fossil cells (inset).
Credit: David Wacey/University of Western Australia

When Martin Brasier discovered what looked like fossil cells in between the cemented sand grains of an ancient beach in Western Australia, he knew he had his work cut out for him. One of the biggest challenges for geologists is deciding when a fossil is really a fossil, particularly when it comes to early life. There are no bones to go by, and the mineralized spheres representing simple cells and sometimes filaments could easily be crystals or other irregularities in the sediment itself. What's more, Brasier, a geologist at the University of Oxford in the United Kingdom, has been one of the most vocal critics of many of the most ancient fossils other researchers have found.

But now Brasier and David Wacey, a geologist at the University of Western Australia in Crawley, say they have discovered 3.4-billion-year-old cells, possibly the oldest fossils ever found. Other microorganisms as old or older have been reported, including an extensive set of photosynthesizing bacteria 20 kilometers away from Brasier and Wacey's find, but Brasier and others have questioned the validity of those fossils. The two scientists say their chemical analyses of the minerals near the cells suggest the microorganisms depended on sulfur for fuel. Such a beach might have been life's first breeding ground, Brasier says.

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TAGGED: PALEONTOLOGY