Ancient red rocks in Western Australia’s Pilbara contain traces of a hot spring that hosted the earliest-known life on land 3.5 billion years ago.
A team of researchers discovered evidence of fossil stromatolites — structures formed by layers of cyanobacteria — in what appears to be an ancient freshwater hot spring.
They said the discovery, reported today in the journal Nature Communications, supports the emerging theory life may have evolved in land-based hot springs rather than in deep sea hydrothermal vents, and provides a new target in the search for ancient life on Mars.
“To actually find hot spring deposits is like a smoking gun for the story of a terrestrial hot spring setting for early life on the planet,” said author and PhD candidate Tara Djokic, from the Australian Centre for Astrobiology at the University of New South Wales.
The researchers said their finding makes the area, known as the Dresser formation, the oldest-known remains of a land-based hot spring on Earth — a whopping 3 billion years older than any previously discovered.
It also pushes back the earliest evidence of exposed land by 130 million years, and the fossil record of life on land by 580 million years.
The Pilbara is already well known for its stromatolite fossils, but until recently, the area was believed to have been a shallow marine environment.
Study co-author Professor Martin Van Kranendonk said one of the key findings was clear evidence of hot spring activity; in particular, the existence of distinctive mineral deposits, known as geyserite formed by hot mineral-rich water splashing onto land.
“We have this incredibly delicate texture preserved, with all these shapes and fabrics, and some of those include overlaps of layers that are characteristic of what we see in modern hot springs where there’s a pool and a rim that accretes out over the pool,” said Professor Van Kranendonk, also from the Australian Centre for Astrobiology.
Professor Van Kranendonk said the evidence for the stromatolites is equally convincing, including fossilised remains of gas bubbles which could only have been produced by bubble-rich mats of microbial material.
While stromatolites are commonly thought of as being found in warm, shallow marine environments, such as Shark Bay in Western Australia, they are also found in many freshwater hot springs around the world.
“There are amazing places you can go to in New Zealand where you have a hot spring that flows down the side of a hill, and the entire channel of that hot spring is lined with orange and green goo that’s all microbial mat that’s making stromatolite,” Professor Van Kranendonk said.
Searching for life on Mars
Commenting on the finding, Simon George, professor of organic geochemistry at Macquarie University, said the paper was very significant because it was the first time convincing evidence had been found for hot spring deposits from such an early period.
Professor George said while this find is not the earliest evidence of life, it strengthens the biological and geological evidence for life emerging around a land-based hot spring, and could encourage the search for even older hot spring deposits and fossils.
It could also influence the search for evidence of life on Mars, Ms Djokic said.
“What’s really exciting is that the Mars 2020 mission is in the process of choosing the next landing site for the rover and one of the top sites is a hot spring setting,” she said, pointing out that this particular site is around the same age as the Dresser hot spring site on Earth.
“We basically use the Earth as an analogue for everything in terms of what we know about life, so that becomes a huge driver of how we search for life elsewhere.”