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Scientists extend record of earliest life on land

Scientists extend record of earliest life on land by millions of years

A study of hot spring deposits in New Zealand and Australia provides new evidence that life existed in these environments around 3.48 billion years ago, millions of years earlier than previously thought, according to an international research team including University of Auckland astrobiologist Professor Kathy Campbell.

A study of hot spring deposits in New Zealand and Australia provides new evidence that life existed in these environments around 3.48 billion years ago, millions of years earlier than previously thought, according to an international research team including University of Auckland astrobiologist Professor Kathy Campbell.

Evidence of life from thermal hot springs – a key site of discovery for scientists because we know they host a diverse range of microbial life living under extreme environmental conditions like those of early Earth – has previously only been dated to 400 million years ago.

The new study extends that by more than 3 billion years and is published today in Nature Communications.

“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?” says Professor Campbell from the University’s School of Environment.

“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.”

The research team examined and compared bio-signatures from hot spring deposits of only a few thousand years old in the Rotorua area to very similar rock textures newly found in the 3.48 billion-year-old Pilbara Craton of Western Australia, and discovered the existence of a mineral deposit called geyserite, forming around the spring vents and pools from approximately 100 C fluids and only found in terrestrial hot springs.

Previously, scientists studying the Pilbara Craton thought it was an ancient marine environment but the presence of geyserite indicates it was in fact a hydrothermally-formed volcanic crater so any bio-signature evidence found associated with very old geyserite is evidence of terrestrial – not marine – life.

The scientists discovered stromatolites, layered mounds of sediments that are produced when microbes are present. Along with other microbial bio-signatures, the study indicates that a diverse range of life existed in these hot springs 3.48 billion years ago.

The oldest accepted evidence of life on Earth so far was discovered in shallow marine rocks in Greenland which have been dated to about 3.7 billion years, and many scientists believe life must have begun in the oceans.

Others are holding out for an on-land origin, a topic of debate in scientific sessions at the Astrobiology Science Conference held in Mesa, Arizona, last week.

The oldest life on land previously recorded was in organic-rich ancient soils and ponds in Africa dated at between 2.7 billion to 2.9 billion years ago. The latest study therefore extends the geological record of life on land by more than 580 million years.

ends

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