Archeologists using sophisticated dating techniques on artifacts found in a rock shelter near Kakadu National Park show that humans were there about 65,000 years ago - as much as 18,000 years earlier than previously thought.

And the study published in the journal Nature might push that date back even earlier because some of the artifacts were potentially as old as 80,000 years.

"People got here much earlier than we thought, which means of course they must also have left Africa much earlier to have traveled on their long journey through Asia and south-east Asia to Australia," said lead author Associate Prof Chris Clarkson of the University of Queensland, as quoted by The Guardian.  "It also means the time of overlap with the megafauna, for instance, is much longer than originally thought - maybe as much as 20,000 or 25,000 years."

This changes the timeline of human migration in the "Out of Africa" theory that non-African people can trace their origins to a group of early hominids who left the mother continent 60,000 years ago.  Also, "It puts to rest the idea that Aboriginal people wiped out the megafauna very quickly," added Professor Clarkson.

These artifacts number about 11,000 and include the world's oldest ax heads as well as ochre likely used for art.  The archeologists found them buried under two and a half meters of sand at a rock shelter called Madjedbebe on the traditional lands of the Mirarr people.