Australia fossil find oldest ever
Relics of the dawn of life 3.4 billion years ago have been unearthed in Australia.
The microscopic fossils are the oldest ever discovered and date back to a time when the earliest forms of bacteria survived in an oxygen-free world, said the research in the journal Nature Geoscience.
"At last we have good solid evidence for life over 3.4 billion years ago," said Professor Martin Brasier, from the department of earth sciences at Oxford University. "It confirms there were bacteria at this time, living without oxygen."
When the bugs were alive, the world was still a hot, violent place shaken by volcanic activity. Thick clouds filled the sky, producing a "greenhouse effect" that made the oceans as warm as a hot bath. Any land masses that existed were small, around the size of Caribbean islands.
During this time, before the photosynthesising action of green plants and algae, there was hardly any oxygen on Earth.
The new fossil evidence, found at a remote site in Western Australia called Strelley Pool preserved in grains of quartz sand on the oldest shoreline known on Earth, points to early life living off compounds containing sulphur rather than oxygen.
"Such bacteria are still common today," said Prof Brasier, who was part of the Anglo-Australian team that made the discovery. "Sulphur bacteria are found in smelly ditches, soil, hot springs, hydrothermal vents - anywhere where there's little free oxygen and they can live off organic matter."
Scientists are convinced the tiny cell-like objects are biological and not mineral in origin. The fossils are clearly preserved and show precise cell-like structures, all of a similar size. The way they were clustered together in appropriate habitats also suggests biological behaviour.
In addition, the chemical make-up of the structures is right for biological organisms and crystals of pyrite associated with the cells could be by-products of sulphur metabolism.
The research may have implications for searching for signs of life on other planets. Life on Mars or the moons of Jupiter and Saturn is likely to follow similar lines. Any microfossils found on these worlds should pass the same evidence tests, according to the scientists. Prof Brasier said: "Could these sorts of things exist on Mars? It's just about conceivable."