It's life, but not as we know it. The oldest fossil ever discovered on Earth shows that organisms were thriving 4.2 billion years ago, hundreds of millions of years earlier than previously thought. The microscopic bacteria, which were smaller than the width of a human hair, were found in rock formations in Quebec, Canada, but would have lived in hot vents in the 140F (60C) oceans which covered the early planet. The discovery is the strongest evidence yet that similar organisms could also have evolved on Mars, which at the time still had oceans and an atmosphere, and was being bombarded by comets which probably brought the building blocks of life to Earth. The team who made the finding at University College London believe that looking for similar fossils on the Red Planet is the best chance of finding evidence of alien life. "Early Mars and early Earth are very similar places, so we may expect to find life on both planets at this time," said doctoral student Matthew Dodd, the lead