Australia: Life on Earth is even older than we thought, Australian scientists said on Thursday as they unveiled fossils dating back a staggering 3.7 billion years.
The tiny structures — called stromatolites — were found along the edge of Greenland's ice cap, and were 220 million years older than the previous record holders.
They prove that life emerged fairly shortly — in geological terms — after the Earth was formed some 4.5 billion years ago, said lead researcher Allen Nutman of the University of Wollongong.
And, he added, they offer hope that very basic life might at one point have existed on Mars.
"This discovery represents a new benchmark for the oldest preserved evidence of life on Earth," Professor Martin Julian Van Kranendonk, a geology expert at the University of New South Wales and one of the study's co-authors, said in a statement.
"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."
The one-to-four centimetre (0.4-1.6 inch) high Isua stromatolites — exposed after the melting of a snow patch in the Isua Greenstone Belt — matched other biological evidence on the evolution of the genetic code that placed the origins of life in a similar period, Nutman said.
Stromatolites are formed when microorganisms, such as certain kinds of bacteria, trap bits of sediment together in layers.
These layers build up over time to create solid rocks.
The rocks themselves were never alive, but their existence shows the very simple single-cell organisms that made them were present on Earth hundreds of millions of years earlier than previously thought.
Life on Mars?
Vickie Bennett from the Australian National University, who also worked on the study, said the research provided a new perspective on Earth's history and "turns the study of planetary habitability on its head".
"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," she said.
The discovery could help the hunt for life on Mars, considered the most likely location for microbial life-forms among other planets in the Solar System.
The Red Planet is believed to have once run with water and had an atmosphere, which together with warmth, could provide the right conditions for bacterial life.
"The significance for Mars is that 3,700 million years ago, Mars was probably still wet and probably still had oceans and so on, so if life develops so quickly on Earth to be able to form things like stromatolites — it might be more easy to detect signs of life on Mars," Nutman told AFP.
"Instead of looking at just the chemical signature, we might be able to see things like stromatolites in images (from Mars) sent back to Earth."
The earliest evidence of life on Earth ahead of the Greenland discovery was made in 2006 when Australian and Canadian researchers dated microfossils in rocks from Pilbara's Strelley Pool Chert formation at more than 3.4 billion years old.
Nutman, who has carried out research in remote Greenland where the stromatolites were discovered for more than three decades, said the site was known to be home to some of the world's oldest rocks.
"Importantly, they are locally well-enough preserved and they haven't been too deformed... so you can still see some of the original features," he said.
The findings are published in the journal Nature.