Life on Earth '300 million years earlier than previously thought'
Living organisms may have existed on Earth as long as 4.1 billion years ago - 300 million years earlier than was previously thought, new research has shown.
If confirmed, the discovery means life emerged a remarkably short time after the Earth was formed from a primordial disc of dust and gas surrounding the sun 4.6 billion years ago.
The evidence was found in specks of graphite trapped within immensely old zircon crystals from Jack Hills, Western Australia.
Atoms in the graphite, a crystalline form of carbon, bore the hallmark of biological origin. They were enriched with C12, a "light" carbon isotope, or atomic strain, normally associated with living things.
It suggests that a terrestrial biosphere had emerged on Earth as early as 4.1 billion years ago, said the scientists writing in the journal Proceedings of the National Academy of Sciences.
The US scientists, led by Dr Mark Harrison, from the University of California at Los Angeles, said the graphite was completely encased in zircon that was crack-free and could not have been contaminated despite the passing of aeons.
They wrote: "This study extends the terrestrial carbon isotope record around 300 million years beyond the previously oldest-measured samples from south-west Greenland."
Some non-biological processes could also produce the light form of carbon, notably meteorite impacts, said the researchers.
But the amount of extra-terrestrial carbon needed to account for the findings made meteorites an unlikely source.
"A biogenic origin seems at least as plausible," the scientists added.
Confirming the connection with early life would represent "a potentially transformational scientific advance" they said.