Fossil evidence of early microbial life has been found in ancient hot spring deposits in the Dresser Formation in the Pilbara Craton, Western Australia, that date back approximately 3.48 billion years. A paper reporting this discovery is published in the journal Nature Communications.
Paleontologists are considering two hypotheses regarding the origin of life. Either that it began in deep sea hydrothermal vents, or alternatively that it began on land in a version of Charles Darwin’s ‘warm little pond.’
“The discovery of potential biological signatures in ancient hot springs in Western Australia provides a geological perspective that may lend weight to a land-based origin of life,” said lead author Tara Djokic, a Ph.D. candidate at the University of New South Wales.
“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.”
Previously, the world’s oldest evidence for microbial life on land came from 2.7- 2.9 billion-year-old deposits in South Africa containing organic matter-rich ancient soils.
“Our exciting findings don’t just extend back the record of life living in hot springs by 3 billion years, they indicate that life was inhabiting the land much earlier than previously thought, by up to about 580 million years,” Djokic said.
Djokic and her colleagues from the Universities of Auckland and New South Wales studied exceptionally well-preserved deposits which are 3.48 billion years old in the Dresser Formation.
They interpreted the deposits were formed on land, not in the ocean, by identifying the presence of geyserite.
“This mineral only forms around the edges of terrestrial hot spring pools and geysers. These are found actively forming today in New Zealand, Yellowstone National Park and Iceland to name a few,” the researchers said.
Previously, the oldest known geyserite had been identified from 400-million-year-old rocks.
Within the Pilbara hotspring deposits, Djokic and co-authors 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 fossilized 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.
“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 fossilized life there,” said co-author Professor Van Kranendonk, from the University of New South Wales, who was part of a research team that recently found some of the oldest evidence of life on Earth — 3.7 billion-year-old fossil stromatolites in Greenland.
“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?’,” said co-author Professor Malcolm Walter, also from the University of New South Wales.
“It’s a significant finding and one that re-opens one of the biggest debates in science and that is, did life begin on land or in the sea?” said co-author Professor Kathy Campbell, an astrobiologist at the University of Auckland.
“This work is also highly relevant to Mars exploration. One of the key aims for NASA’s 2020 Mars rover landing is the search for fossils in ancient (more than 3 billion year old) volcanic hot springs which we now know once existed on the Martian surface.”
Tara Djokic et al. 2017. Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits. Nature Communications 8, article number: 15263; doi: 10.1038/ncomms15263