Rotorua's hot springs have featured in a study that has pushed back the oldest geological record of life on land by hundreds of millions of years.
A Kiwi co-author of the study, published today, says the landmark finding reopens one of the biggest debates in science - whether life began on land or in the sea - and also holds implications for hunts for life on Mars.
The study revealed how fossil evidence of early life has been discovered in 3.48 billion-year-old hot spring deposits in the Pilbara Craton of Western Australia - pushing back by three billion years the earliest known existence of inhabited terrestrial hot springs on Earth.
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 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 extended the geological record of life on land by more than 580 million years.
So far, the oldest accepted evidence of life on Earth 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 in Mesa, Arizona, last week.
"This work is also highly relevant to Mars exploration," said study co-author and University of Auckland astrobiologist Professor Kathy Campbell.
"One of the key aims for Nasa's 2020 Mars rover landing is the search for fossils in ancient 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.
They discovered the existence of a mineral deposit called geyserite, forming around the spring vents and pools from approximately 100C 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, published in the journal
, indicated that a diverse range of life existed in these hot springs 3.48 billion years ago.
Its first author, University of New South Wales researcher Tara Djokic, also noted the new insights may hold 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.
Scientists 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 these ancient hot springs in Western Australia provides a geological perspective that may lend weight to a land-based origin of life," Djokic said.
"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 in the Pilbara.
"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."