Oldest fossils called into question

Ars Technica : Until recently the oldest fossils on Earth were thought to be contained in the 3.46-billion-year-old Apex chert in Western Australia. But now researchers claim that the microscopic structures found in the rock are not actually fossils of single-celled organisms, as had been previously proposed. In an earlier study, Martin Brasier of Oxford University and his colleagues had argued that the shapes are actually microscopic hydrothermal vents. Now they have used transmission electron microscopy to examine 0.1-µm-thick slices of the chert. If the structures were fossils, they would be surrounded by a wall of carbon-rich material left from the hydrocarbons created by the microorganisms. Instead, Brasier’s team found that the structures are filled with mica and that carbon material is distributed throughout. However, the researchers also examined rocks just 20 million years younger than the Apex chert, and the images revealed the expected structure of fossils. So the oldest fossils are still very, very old.