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The oldest signs of life on land yet

Fossils found in Australia – in ancient hot spring deposits – have pushed back the earliest known evidence for land-based microbial life to 3.48 billion years.

This is the Dresser Formation in the Pilbara of Western Australia. Its ripply texture might have been formed when long filaments of bacteria were entombed by the silica from the mineral-rich water from a hot spring, 3.48 billion year ago. Image via UNSW.

Scientists have found the oldest evidence yet for microbial life on Earth, in 3.48-billion-year-old hot spring deposits in the Pilbara region of Western Australia. They believe the region might once have been a volcanic crater on a small island, dotted with hot springs and ponds that teemed with life. The evidence comes in the form of fossils that push back by 580 million years the earliest known existence of microbial life on land. To these scientists, the discovery also suggests something startling about life’s origins. Tara Djokic, the University of New South Wales PhD candidate who led the research, said in a statement:

Our exciting findings … 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 work was published May 9, 2017 in the peer-reviewed journal Nature Communications.

Although the idea of life beginning in Earth’s oceans – in deep-sea hydrothermal vents – has entered popular culture, scientists still discuss another possibility. That is, life might have begun on land in a version of what the English naturalist, geologist and biologist Charles Darwin described as “warm little ponds.”

Djokic and her colleagues believe the rocks containing the fossils were formed on land, not in the ocean, because they identified the presence of geyserite – a mineral deposit formed from near boiling-temperature, silica-rich, fluids found only in a terrestrial hot spring environment.

UNSW PhD student Tara Djokic in the Dresser Formation in the Pilbara Craton of Western Australia. Image via Dale Anderson/ UNSW.

Within the Pilbara hotspring deposits, the researchers also discovered stromatolites, which are layered rock structures created by communities of ancient microbes. And according to their statement:

… 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 (microbial) to preserve the bubble shape.

Van Kranendonk, Director of the Australian Centre for Astrobiology and head of the UNSW school of Biological, Earth and Environmental Sciences, said:

This shows a diverse variety of life existed in fresh water, on land, very early in Earth’s history.

The work also has implications for the search for life on Mars, because Mars has ancient hot spring deposits of a similar age to the Dresser Formation in the Pilbara. Djokic said:

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.

Read more via UNSW

The ancient Dresser Formation in the Pilbara region of Western Australia. Image via Kathleen Campbell/ UNSW.

Bottom line: Scientists at the University of New South Wales have found fossils in ancient hot spring deposits that back the earliest known evidence for land-based microbial life to 3.48 billion years.

Deborah Byrd

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