Australian scientists have unearthed traces of the oldest life form ever found in 3.5 billion-year-old rocks in Western Australia.
In a major advance in the field, the University of New South Wales team says its discovery of microbial remains hidden in the famous Dresser Formation stromatolites offers clues for how life on Earth started, and where to look for signs of life on Mars.
Ever since they were discovered in the East Pilbara region in the 1980s, scientists have believed the stromatolites were created in areas of hydrothermal activity from layers of living organisms such as cyanobacteria, a single-cell microbe.
However, that theory has been unproven for nearly four decades, because time and weathering of the rocks has altered their mineralogy and prevented the identification of organic matter – until now.
To get a clearer picture of how these ancient rocks came into being, lead researcher Raphael Baumgartner and colleagues needed to study parts of the stromatolites that had not been affected by weathering.
They obtained samples extracted by diamond drilling from deep within the stromatolites, below the exposed area.
The team analysed the samples with cutting-edge micro-analytical tools and techniques including high-powered electron microscopy, spectroscopy, ion mapping and isotope analysis. The works, in other words.
Late one night they found what they were looking for: organic matter. It was there in the pyrite – a mineral also known as “fool’s gold” – from which the stromatolites are composed.
For Baumgartner, it was a “Eureka moment”.
“The organic matter that we found preserved within pyrite of the stromatolites is exciting – we’re looking at exceptionally preserved coherent filaments and strands that are typically remains of microbial biofilms.
“This is an exciting discovery – for the first time, we’re able to show the world that these stromatolites are definitive evidence for the earliest life on Earth.”
The scientists say their findings, combined with earlier work on the Pilbara stromatolites that suggested life may have begun on land rather than in the ocean, are helping us answer a central question: where did we come from?
“Understanding where life could have emerged is really important in order to understand our ancestry. And from there, it could help us understand where else life could have occurred – for example, where it was kick-started on other planets,” Baumgartner says.
As it happens, last month NASA and European Space Agency (ESA) scientists, including the heads of the Mars 2020 missions, spent a week in the Pilbara with UNSW team leader Martin Van Kranendonk for specialist training in identifying signs of life in these same ancient rocks.
“It is deeply satisfying that Australia’s ancient rocks and our scientific know-how is making such a significant contribution to our search for extra-terrestrial life,” says Van Kranendonk.
“This represents a major advance in our knowledge of these rocks, in the science of early life investigations generally, and – more specifically – in the search for life on Mars. We now have a new target and new methodology to search for ancient life traces.”
The team’s findings are published in the journal Geology.