The latest fossils were found in the Dresser formation Kathy Campbell, University of New South Wales

It’s the age-old question: where do we come from? New fossil evidence suggests the first spark of life may have occurred in a hot spring on land rather than a hydrothermal vent in the deep sea.

Charles Darwin proposed in 1871 that life originated in a “warm little pond”. But the dominant theory nowadays is that primitive microorganisms first assembled in hot, chemical-rich water at hydrothermal vents at the bottom of the ocean.

One reason for favouring this marine model is that fossil evidence of early land-based microbial life has been lacking. Until recently, the oldest evidence of life on land was only 2.8 billion years old, whereas the oldest evidence from the sea was 3.7 billion years old.


The rocks here are 3.5 billion years old Kathy Campbell, University of New South Wales

Now, a team led by Tara Djokic at the University of New South Wales in Australia has discovered fossils of land-based microorganisms. They were found in 3.5-billion-year-old rocks in an extinct volcano in the Dresser Formation in the hot, dry, remote Pilbara region of Western Australia.

The fossils include stromatolites – layered rock structures created by microorganisms – and circular holes left in the rock by gas bubbles that look like they were once trapped by sticky microbial substances. Both types of structures are preserved in geyserite, a type of rock that is only found in and around freshwater hot springs in volcanic areas on land.

Land-based launch pad?

The findings suggest that microbes were present on land and in the ocean around the same time, says Djokic. The question is – which came first?

“There are now a number of converging lines of evidence that point to terrestrial hot springs over hydrothermal vents for the origin of life,” says Djokic.

Small bodies of water like hot springs may have been more conducive to the formation of life because they can evaporate and concentrate the building blocks of life, says Djokic. “In hot springs, you’ve also got a nutritious concoction of elements because hot fluids circulate through the underlying rocks and bring up different minerals,” she says.

Recent research suggests that the element mix in ancient hot springs would have been more likely to give rise to life than that of deep sea vents.

Primitive microorganisms formed in the springs could have then spread to the sea, where they could have adapted and continued to evolve, Djokic says.

The findings are compelling, says Gregory Webb at the University of Queensland in Australia. “There are lots of microbes that live in terrestrial hot springs today, so it’s not a stretch to believe that an ancient hot spring could have accommodated life,” he says.

Then again, making assertions about life on early Earth is tricky, says Webb. “Microbial life isn’t easy to see, even today, so rocks that preserve evidence of ancient bacteria are hard to find and hard to study.” He is not ruling out the deep sea model of the origin of life.

Ancient life on Mars

Djokic and her colleagues believe the research could have implications for the search for ancient life on Mars. Earth and Mars both formed around 4.5 billion years ago and had volcanoes and hot springs dotted across their surfaces.

“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,” says Djokic.

One of the three potential landing sites for NASA’s Mars 2020 rover mission is Columbia Hills, a rocky formation that is thought to have once been a hot spring environment.

Journal reference: Nature Communications, DOI: 10.1038/ncomms15263

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