For most of the human history of Australia, sea levels were much lower than they are today, and there was extra dry land where people lived.
Archaeologists could only speculate about how people used those now-submerged lands, and whether any traces remain today.
But in a study published today in PLOS ONE, we report the first submerged ancient Aboriginal archaeological sites found on the seabed, in waters off Western Australia.
The great flood
When people first arrived in Australia as early as 65,000 years ago, sea levels were around 80m lower than today.
Sea levels fluctuated but continued to fall as the global climate cooled. As the world plunged into the last ice age, which peaked around 20,000 years ago, sea levels dropped to 130m lower than they are now.
Between 18,000 and 8,000 years ago the world warmed up. Melting ice sheets caused sea levels to rise. Tasmania was cut off from the mainland around 11,000 years ago. New Guinea separated from Australia around 8,000 years ago.
The sea-level rise flooded 2.12 million square kilometres of land on the continental shelf surrounding Australia. Thousands of generations of people would have lived out their lives on these landscapes now under water.
Landscapes under water
For the past four years a team of archaeologists, rock art specialists, geomorphologists, geologists, specialist pilots and scientific divers on the Australian Research Council-funded Deep History of Sea Country Project have collaborated with the Murujuga Aboriginal Corporation to find and record submerged archaeological sites off the Pilbara coast in WA.
We studied navigation charts, geological maps and archaeological sites located on the land to narrow down prospective areas before surveying the seabed using laser scanners mounted on small planes and high-resolution sonar towed behind boats.