Researchers from the University of Western Australia and Oxford University have found the Earth’s oldest fossils. The microscopic fossils show convincing evidence for cells and bacteria living in an oxygen-free world over 3.4 billion years ago.
The team, led by Dr David Wacey of the University of Western Australia and Professor Martin Brasier of Oxford University discovered the microfossils in a remote part of Western Australia called Strelley Pool. They are very well-preserved between the quartz sand grains of the oldest beach or shoreline known on Earth, in some of the oldest sedimentary rocks that can be found anywhere. “At last we have good, solid evidence for life over 3.4 billion years ago,” said Prof. Brasier, of the Department of Earth Sciences at Oxford University, who co-authored the study.
Three and a half billion years ago, the world’s oceans were a steamy 104 to 122 deg. F. They churned with strong currents and covered most of the surface of the Earth, exposing very little land. Volcanic activity was violent and widespread, supplying large amounts of sulphur. Meanwhile, oxygen levels remained very low, largely due to the absence of plants and algae. It can be difficult to confirm that apparent microfossils are signs of life rather than regular patterns formed by chemical processes in the absence of biology. However, the cell-like formations combined with the metabolic waste products taken together provide “strong evidence” of an ancient sulphur-based bacterial ecosystem, the paper said. ‘Such bacteria are still common today, sulfur 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,’ explains Professor Brasier.
The researchers said they are now re-examining other rocks from a similar time period that have been proposed to contain evidence for life. They suggested that similar bacteria may also be found in other parts of the solar system such as Saturn’s moon Titan or Jupiter’s moon Europa. “Could these sorts of things exist on Mars? It’s just about conceivable,” said Prof. Brasier.