A group of rock formations in Western Australia have been identified as some of the earliest evidence of life on Earth, scientists said on Wednesday.
The findings were published in the latest edition of the journal Nature.
Doubts about whether the formations known as stromatolites were signs of ancient life have persisted since they were described almost three decades ago.
Some scientists believed these stromatolites were formed by micro-organisms that lived on Earth more than 3 billion years ago. Others argued that they were formed chemically from hydrothermal vents in the deep ocean.
A study led by Abigail Allwood, of Macquarie University in Sydney, has now offered the strongest evidence yet that they were formed by interactions between microbial life and the sediments in which they had been preserved.
Allwood and her colleagues analyzed different stromatolites in rocks covering more than 10 kilometers.
The stromatolites varied in shape and each had their own environmental niche. Their complexity makes them highly unlikely to be of chemical origin, the scientists said.
The most convincing explanation is of a complex ecosystem in which different kinds of organism played distinct roles.
"We believe that many different types of organisms may have coexisted at this time, so that we have not just the oldest evidence of life, but we also have the oldest evidence of biodiversity," she said in a statement.