Earth's oldest fossils have been found in Australia by a team from the University of Western Australia and Oxford University. The microscopic fossils show convincing evidence for cells and bacteria living in an oxygen-free world over 3.4 billion years ago.
http://www.sciencedaily.com/releases/2011/08/110821205241.htm
http://www.sciencedaily.com/releases/2011/08/110821205241.htm