Bubbles preserved in 3.48-billion-year-old rocks provide the oldest evidence of life on land
The stunning fossil find, in the Pilbara region of Western Australia, indicates that life on actual earth existed up to about 580 million years earlier than previously thought.
And it could also have implications for the search for life on Mars, according to researchers.
Previously, the world's oldest evidence for microbial life on land came from 2.7 to 2.9 billion year old deposits in South Africa containing organic matter-rich ancient soils.
First author of the new study Tara Djokic, a PhD candidate at the University of New South Wales (UNSW), said: "Our exciting findings don't just extend back the record of life living in hot springs by three billion years, they indicate that life was inhabiting the land much earlier than previously thought, by up to about 580 million years
"This may have implications for an origin of life in freshwater hot springs on land, rather than the more widely discussed idea that life developed in the ocean and adapted to land later."
The fossils were found in the Pilbara region of Western Australia
Scientists are considering two theories regarding the origin of life. Either that it began in deep sea hydrothermal vents, or that it began on land in a version of Charles Darwin's "warm little pond."
This may have implications for an origin of life in freshwater hot springs on land
Ms Djokic said: "The discovery of potential biological signatures in these ancient hot springs in Western Australia provides a geological perspective that may lend weight to a land-based origin of life.
"Our research also has major implications for the search for life on Mars, because the red planet has ancient hot spring deposits of a similar age to the Dresser Formation in the Pilbara.
PhD candidate at the University of New South Wales Tara Djokic
"Of the top three potential landing sites for the Mars 2020 rover, Columbia Hills is indicated as a hot spring environment. If life can be preserved in hot springs so far back in Earth's history, then there is a good chance it could be preserved in Martian hot springs too."
The study, published in the journal Nature Communications, involved exceptionally well-preserved deposits which are about 3.5 billion year old in the ancient Dresser Formation in the Pilbara Craton of Western Australia.
They interpreted the deposits were formed on land, not in the ocean, by identifying the presence of geyserite – a mineral deposit formed from near boiling-temperature, silica-rich, fluids that is only found in a terrestrial hot spring environment.
The find could have implications for the search for life on Mars
Previously, the oldest known geyserite had been identified from rocks about 400 million years old.
Within the Pilbara hotspring deposits, the researchers also discovered stromatolites – layered rock structures created by communities of ancient microbes.
And there were other signs of early life in the deposits as well, including fossilised micro-stromatolites, microbial palisade texture and well preserved bubbles that are inferred to have been trapped in a sticky substance to preserve the bubble shape.
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Layered deposits in Uzboi Vallis
Professors Martin Van Kranendonk, of UNSW, said: "This shows a diverse variety of life existed in fresh water, on land, very early in Earth's history.
"The Pilbara deposits are the same age as much of the crust of Mars, which makes hot spring deposits on the red planet an exciting target for our quest to find fossilised life there."
Professor Malcolm Walter, founding director of the Australian Centre for Astrobiology, added: "The Pilbara provides us with a rich record of early life on Earth and is a key region for developing exploration strategies for Mars to try and answer one of the greatest enigmas in science and philosophy – did life arise more than once in the universe?
"That's why we are working to gain World Heritage listing for its main fossil sites."