Deposits preserved in 3.48 billion-year-old rocks formed in ancient hot springs in Western Australia provide evidence that microbial life on land originated 580 million years earlier than thought.
The finding could help solve one of the most important debates in evolution—whether life on Earth arose in small, terrestrial ponds, or deep in the ocean, researchers said.
Previously, the world’s oldest evidence for microbial life on land came from 2.7-2.9 billion-year-old deposits in South Africa containing organic matter-rich ancient soils.
Scientists at the University of New South Wales (UNSW) have now discovered fossils in 3.48 billion year old hot spring deposits in the Pilbara region of western Australia that have pushed back by 580 million years the earliest known existence of microbial life on land.
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 English biologist Charles Darwin’s “warm little pond”.
The finding 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, researchers said.
Researchers, including professor Kathleen Campbell of the University of Auckland, studied exceptionally well-preserved deposits which are about 3.5 billion years old in the ancient Dresser Formation.
They interpreted the deposits were formed on land, not in the ocean, by identifying the presence of geyserite—a mineral deposit formed from near boiling-temperature, silica- rich, fluids that is only found in a terrestrial hot spring environment.
Previously, the oldest known geyserite had been identified from rocks about 400 million years old.
Within the Pilbara hotspring deposits, the researchers also discovered stromatolites—layered rock structures created by communities of ancient microbes.
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.