The earliest known human settlements in Australia, now submerged by the sea, have been discovered.

The unprecedented find of bones and artefacts were discovered in a cave at the coast of Barrow Island, which lies about 50 kilometres from mainland Western Australia. These are remains from some of the first human inhabitation of Australia 50,000 years ago, according to a study published in Quaternary Science Reviews.

Much of the land inhabited by the first Aboriginal people of Australia is now deep underwater. A rare site that survived, known as Boodie Cave on Barrow Island, was abandoned about 7,000 years ago when sea levels rose to their present levels.

"The cave was used predominately as a hunting shelter between about 50,000 and 30,000 years ago before becoming a residential base for family groups after 10,000 years ago," said study author Peter Veth of the University of Western Australia in a statement.

Boodie Cave was filled with human artefacts, such as charcoal and stone tools, as well as the remains of the animals that they ate. The thrown away animal bones reveal important information about how the people lived 50,000 years ago, and also about the environment they were living in.

During this time sea levels fluctuated hugely. At times when the coast retreated, there were fewer bones of fish and other marine creatures the people would have eaten. When the sea levels were higher and the coast was close, there were many more fish bones left in the cave.

"The large cave on Barrow Island provided rich records of ancient artefacts, gathering and hunting of marine and arid animals, and environmental signatures which show the use of a now-drowned coastal desert landscape – if you like an Atlantis of the South," Veth said.

"We know about old desert sites from the northern hemisphere but few have these extraordinary dietary records."

Boodie Cave
Excavation of Boodie Cave, Barrow Island, off the coast of north-west Australia. Peter Veth / University of Western Australia

The find shows the adaptability of the first people of Australia, hunting and eating entirely different land-based animals when the sea receded.

"Remarkably, the early colonists of the now-submerged North West Shelf did not turn their back on the sea or remain coastally tethered but rapidly adapted to the new marsupial animals and arid zone plants of the extensive maritime deserts of north-west Australia."

Boodie Cave
Artefacts found at Boodie Cave Peter Veth / University of Western Australia
Boodie Cave
The excavation of Boodie Cave took more than three years Peter Veth / University of Western Australia