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January 1, 2013

Fossils may date from 3.5 billion years ago

Scientists analyzing Australian rocks have discovered traces of bacteria that lived a record-breaking 3.49 billion years ago, a mere billion years after Earth formed.

If the find withstands the scrutiny that inevitably faces claims of fossils this old, it could move scientists one step closer to understanding the first chapters of life on Earth. The discovery could also spur the search for ancient life on other planets.

These traces of bacteria "are the oldest fossils ever described. Those are our oldest ancestors," said Nora Noffke, a biogeochemist at Old Dominion University in Norfolk who was part of the group that made the find and presented it last month at a meeting of the Geological Society of America.

Unlike dinosaur bones, the newly identified fossils are not petrified body parts. They're textures on the surfaces of sandstone thought to be sculpted by once-living organisms. Today, similar patterns decorate parts of Tunisia's coast, created by thick mats of bacteria that trap and glue together sand particles. Sand that is stuck to the land beneath the mats and thus protected from erosion can over time turn into rock that can long outlast the living organisms above it.

Finding the earliest remnants of this process required a long, hard look at some of the planet's oldest rocks, located in Western Australia's Pilbara region. This ancient landscape was once shoreline. Rocks made from sediment piled up billions of years ago are now exposed and available for examination. Relatively pristine in condition, such outcrops, along with others in South Africa, have long been a popular place to look for traces of life from the Archean eon, which ended 2.5 billion years ago.

There are older rocks on Earth, said Maud Walsh, a biogeologist at Louisiana State University in Baton Rouge. "But these are the best-preserved sedimentary rocks we know of, the ones most likely to preserve the really tiny structures and chemicals that provide evidence for life." Last year, another team of researchers published the discovery of microscopic fossils in Pilbara's Strelley Pool Formation, about 3.4 billion years old.

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