The team, which includes UNSW Professor Martin Van Kranendonk, discovered the 3.7 billion-year-old fossil stromatolites – formations created by communities of ancient microbes – in the world’s oldest rocks in the Isua Greenstone Belt along the edge of Greenland’s Ice Cap.
The stromatolites, which were exposed by the recent melting of a perennial snow patch, are 220 million years older than stromatolites from the Pilbara region of Western Australia which were previously regarded as the world’s oldest.
The research team, led by Professor Allen Nutman of the University of Wollongong, says the discovery not only provides greater insight into the early diversity of life on Earth; it could also have implications for our understanding of life on Mars.
The findings are published today in the journal Nature.
“This discovery represents a new benchmark for the oldest preserved evidence of life on Earth,” says Professor Van Kranendonk, Director of the Australian Centre for Astrobiology in the UNSW School of Biological, Earth and Environmental Sciences.
“The structures and geochemistry from the newly exposed outcrops in Greenland display all of the features used in younger rocks to argue for a biological origin.
“It points to a rapid emergence of life on Earth and supports the search for life in similarly ancient rocks on Mars, which was a damp environment 3.7 billion years ago,” he says.
For much of Earth’s history, life was just single cells. Stromatolite fossils are layered mounds of carbonate constructed by these communities of microbes as they grow.
The 1 to 4-centimetre high Isua stromatolites were laid down in a shallow sea, providing the first evidence of an environment in which early life thrived. Their discovery pushes back the fossil record to near the start of the Earth’s geological record.
“The significance of stromatolites is that not only do they provide obvious evidence of ancient life that is visible with the naked eye, but that they are complex ecosystems,” says Professor Nutman, who is also an Associate Member of the Australian Centre for Astrobiology at UNSW.
“This indicates that as long as 3.7 billion years ago microbial life was already diverse. This diversity shows that life emerged within the first few hundred millions years of Earth’s existence, which is in keeping with biologists’ calculations showing the great antiquity of life’s genetic code,” he says.
“This discovery turns the study of planetary habitability on its head,” she says. “Rather than speculating about potential early environments, for the first time we have rocks that we know record the conditions and environments that sustained early life. Our research will provide new insights into chemical cycles and rock-water-microbe interactions on a young planet.”
Professor Martin Van Kranendonk adds: “UNSW research into early life on Earth continues through the Australian Centre for Astrobiology, which integrates knowledge from early Earth with modern microbial systems to better understand where to explore for life on Mars, in the rest of the Solar System, and beyond.”
Several lines of evidence, such as details of the chemistry, sedimentary structures and minerals in the rocks, together indicate that the stromatolites were formed by live organisms. Previous genetic molecular clock studies suggest life originated on Earth more than 4 billion years ago.
The investigation, conducted by the Australian science team in collaboration with a UK partner, was funded by a grant from the Australian Research Council. The team also includes Professor Allan Chivas from the University of Wollongong.