Remarkably preserved microfossils from a remote region of Western Australia that are at least 3.4 billion years old are providing insights into what type of life first existed on Earth and when it existed. They also highlight a potential target in the search for life on Mars.
The new research, published last week in Nature Geoscience, provides solid fossil evidence to date key branching points in the Earth's evolutionary clock.
Scientists based in The University of Western Australia's Centre for Microscopy, Characterisation and Analysis in collaboration with Oxford University have unearthed arguably the best-preserved pre-three billion year-old microfossils on Earth. These consist of remarkably preserved carbonaceous cells along with the protective tubes (sheaths) that housed some of these cells.
Leading author UWA Postdoctoral Research Fellow Dr David Wacey said direct evidence for early life in the form of microfossils was exceedingly rare and evidence for what type of life came first had until now proved elusive.
"Our research helps to answer the question: How did these microbes survive?" he said.
"On the early Earth, where free oxygen was rare or absent, evolving life had to employ other means to survive. Using a combination of electron microscopy and ion probe analysis, we were able to show that these particular microbes had a metabolism that was based on the use of sulfur. This ability to essentially ‘breathe' sulfur compounds has long been thought to be one of the earliest stages in the transition from a non-biological to biological world.
"By showing the intimate association of these 3.4 billion-year-old microfossils with the mineral pyrite (FeS2), we have now provided the earliest direct evidence of microorganisms employing a sulfur-based metabolism."
The microfossils come from Strelley Pool, a remote region of the Pilbara about 60 km west of Marble Bar. They are the oldest microfossils ever to be found in sandstones, extending the record of life on Earth in such rocks by about 300 million-years.