Vast submerged area near Australia may once have hosted 500,000 people

An area of land north of modern Australia that was submerged by rising seas at the end of the last glacial period could have once been home to as many as 500,000 people.

Kasih Norman at Griffith University in Brisbane, Australia, and her colleagues have reconstructed the topography of around 400,000 square kilometres of land that is now covered by the Indian Ocean, known as the Northwest Shelf. Far from being uninhabitable, as was previously thought, the team says it was home to thriving populations of people for tens of thousands of years.

The study reveals features including an inland sea, similar in size to Turkey’s Sea of Marmara, as well as a vast freshwater lake along with gorges, rivers and escarpments like those that now exist in Kakadu National Park in the Northern Territory of Australia.

Norman says this flooded land has long been known about because of oil and gas exploration, but Geoscience Australia has recently released detailed sonar data, with each pixel representing an area of just 30 by 30 metres. “This is a high enough resolution to be able to talk about landscape features that were important to people,” she says.

The inland sea existed in a stable form between 27,000 and 17,000 years ago, the study found. A 2000-square-kilometre freshwater lake nearby was stable from 30,000 to 14,000 years ago. The lake would have been a vital refuge for people escaping the arid conditions of the Australian continent to the south.

By modelling these geographic features, the team estimates that the region could have supported a population of between 50,000 and 500,000 people.

“This massive landscape that is not there now would have been unlike anything that we have in Australia today,” says Norman. “To have a freshwater lake of that size next to an inland sea is just incredible and people would have been living across it. This is a lost landscape that people were using.”

But at the end of the last glacial period, sea levels began to rise dramatically. At first, the sea rose by around a metre every 100 years, but from 14,500 to 14,100 years ago, it rose 4 to 5 metres every 100 years, says Norman.

At that rate, people would have been able to watch the sea levels rise and would have been forced to move inland to escape inundation.

The modelling of how many people this region might have supported has never been done before, says Peter Veth at the University of Western Australia, and was made possible because of the new fine-grained palaeogeographic data available to the team.