Humans arrived in Australia 10,000 years earlier than was previously thought, casting doubt on the theory that they killed off the giant kangaroo and other unique animals, scientists believe.
New artefact evidence suggests that the continent was first occupied about 65,000 years ago, long after the ancient ancestors of modern humans emerged in Africa.
The discovery challenges the theory that people caused the extinction of Australian megafauna including giant kangaroos, wombats and tortoises which disappeared more than 45,000 years ago.
"Previously it was thought that humans arrived and hunted them out or disturbed their habits, leading to extinction, but these dates confirm that people arrived so far before that they wouldn't be the central cause of the death of megafauna," lead scientist Dr Ben Marwick, from the University of Washington, said.
"It shifts the idea of humans charging into the landscape and killing off the megafauna.
"It moves toward a vision of humans moving in and coexisting, which is quite a different view of human evolution."
Since 1973, digs at Madjedbebe, a rock shelter in Australia's Northern Territory, have unearthed more than 10,000 stone tools, ochres, plant remains and bones.
A dating technique called optical stimulated luminescence (OSL) was used to determine the age of the oldest buried artefacts.
The process can show the last time a sand grain was exposed to sunlight up to 100,000 or more years ago.
This and other tests built up a picture of the environment and showed that when the first humans arrived, northern Australia was wetter and colder than it is today.
The findings, published in the journal Nature, support the theory that our species Homo sapiens evolved in Africa before dispersing to other continents, Dr Marwick said.