Fossil find offers glimpse at early life

Scientists have found Earth's oldest fossils in Australia and say their microscopic discovery is convincing evidence that cells and bacteria were able to thrive in an oxygen-free world more than 3.4 billion years ago.

The finding suggests that early life was sulphur-based, living off and metabolizing sulfur rather than oxygen for energy, and supports the idea that similar life-forms could exist on other planets where oxygen levels are low or nonexistent.

"Could these sorts of things exist on Mars? It's just about conceivable. This evidence is certainly encouraging and lack of oxygen on Mars is not a problem," said Martin Brasier of Oxford University, who worked on the team that made the discovery.

The microfossils, which the researchers say are very clearly preserved and show precise cell-like structures, were found in a remote part of western Australia called Strelley Pool.

In their study, published Sunday in the journal Nature Geoscience, Brasier's team said the tiny fossils were preserved between the quartz sand grains of the oldest shoreline known on Earth in some of the oldest sedimentary rocks ever discovered.

By analyzing the fossils and the surrounding environment, the scientists built a picture of Earth at that time as a hot, murky, violent place. Most significantly, there was very little oxygen, Brasier said.

"It's a rather hellish picture," he said. "Not a great place for the likes of us. But for bacteria, all of this was wonderful. In fact, if you were to invent a place where you wanted life to emerge, the early Earth is exactly right."