In the works of Plato, a Greek philosopher who lived around 2,400 years ago, the island of Atlantis was said to have been drowned in the Atlantic Ocean after the hubris of its people angered the Gods.
Although Atlantis was fictional, the idea that entire civilisations can disappear beneath the waves has intrigued us for millennia.
Now, innovative technologies are revealing real sites around the world that our ancestors were forced to abandon before they were swallowed by the oceans.
One such ‘Atlantis’ lies to the north of Australia.
At the height of the last Ice Age, around 21,000 years ago, the continent of Australia was around 20-per-cent larger than it is today. With more water locked up in ice sheets and glaciers, sea levels were around 120m (394ft) lower.
This exposed an additional 2,000,000km2 (around 772,000 sq miles) of land that connected Australia to New Guinea in the north and Tasmania in the south, creating a supercontinent known as Sahul.
Sahul’s Northwest Shelf was a vast landmass that covered 400,000km 2 (154,000 sq miles) – just over 1.5 times the size of the UK – and joined onto the modern-day Kimberley region in northern Western Australia, and the Arnhem Land region in Australia's Northern Territory.
Many archaeologists have argued that these ancient landscapes were unproductive environments and weren’t used much by the early Aboriginal people. But new research is challenging this long-held assumption.
The now-submerged region may also hold the secrets to one of the biggest puzzles in anthropology. Lying next to some of the oldest known archaeological sites in Australia, Sahul’s Northwest Shelf has long been recognised as a likely point of entry for the first people who made their way to the continent, some 65,000 years ago.
Now, the race is on to uncover the hidden treasures of this Atlantis-like land, before they’re destroyed forever.
Revealing lost landscapes
About 27,000 years ago, as the planet descended into the last Ice Age, the polar ice caps grew and the sea level dropped, exposing the low-lying landscapes of Sahul’s Northwest Shelf for the first time in 100,000 years.
“Archaeologists have only been able to speculate about the nature of the drowned landscapes people roamed before the end of the last Ice Age, and the size of their populations,” says Dr Kasih Norman, a researcher at the Max Planck Institute of Geoanthropology.
Norman led a recent study that combined sonar data with computer modelling to examine the Northwest Shelf in unprecedented detail.
The team overlaid estimates of past sea levels on existing high-resolution maps of the ocean floor to visualise what the region would have been like tens of thousands of years ago.
Their analysis revealed a rich and varied landscape of rivers, lakes, valleys and gorges. “Seeing those drowned landscapes and imagining the people that roamed across them during the last Ice Age really fired my imagination,” Norman says.
The region also boasted a large inland sea, called the Malita Sea, which covered an area of more than 18,000km2 (7,000 sq miles).
These new data “provide the texture necessary to begin to build a picture of the way these now-submerged landscapes were used and given meaning by societies over tens of millennia,” says Prof Sean Ulm from the Australian Research Council’s Centre of Excellence for Indigenous and Environmental Histories and Futures at James Cook University, who specialises in coastal and underwater archaeology.
Tracing a drowned civilisation
Norman and her colleagues used computer modelling to estimate how productive these landscapes would have been and how many people could have lived there, between 71,000 and 15,000 years ago.
They found that at the height of the last Ice Age, when the entire Northwest Shelf was dry land, the region had the capacity to support a population of more than 500,000 people.
On several islands that remain, dotted along what was once the coast of Sahul, archaeological evidence supports the theory that the Northwest Shelf was used regularly by Aboriginal societies.
The team’s population estimates are also in line with a recent study of genetic data from Indigenous people living on the Tiwi Islands, which lie to the east of Sahul’s Northwest Shelf. That study found evidence of a large population on the islands 20,000 years ago, followed by a population decline at the end of the last Ice Age.
What were the lives of the people who lived in this now-submerged landscape like? “This is really the fundamental question,” Ulm says.
“There’s extraordinary social, cultural and technological diversity among contemporary and recent Aboriginal societies. We have to assume that was also the case in the past,” he says.
“What we do know is that these societies that lived on the emerged continental shelves [of Australia] travelled long distances to and from the coast, and were connected with other distant inland societies through trade networks,” he explains.
Norman and her colleagues say that similarities in stone axe technology, rock art styles and languages suggest that the modern-day regions of the Kimberley, Arnhem Land and the now-flooded Northwest Shelf of Sahul together formed one huge interconnected cultural region during the height of the last Ice Age.
Read more:
- The 7 biggest ocean mysteries scientists can't explain
- Ancient Greek underwater 'city' formed naturally
- How underwater cities could solve Earth's overpopulation problem
Recovering ancient treasures
Part of the reason we know so little about the culture and lifestyle of the people of the Northwest Shelf is because the relics from their ancient societies are now hidden below the water.
“Hundreds of generations of people lived out their lives on lands that are now submerged by the sea,” says Ulm.
Archaeologists now have more tools available to locate ancient underwater sites and learn more about the lives of the people whose homes were lost to the ocean thousands of years ago.
“Most submerged cultural places around the world examined by archaeologists were first found by others by accident,” Ulm says. “[But] in the past few decades, more structured approaches have emerged, using many lines of evidence to develop predictive models of where sites and landscapes might be preserved underwater.”
Ulm was part of a team of archaeologists, rock art specialists, geomorphologists, geologists, specialist pilots and scientific divers that collaborated with the Murujuga Aboriginal Corporation – which brings together members from five traditional Aboriginal groups – to explore submerged archaeological sites off the coast of the Pilbara region of Western Australia.
The team used navigation charts, geological maps and known archaeological sites on land to identify potential sites on the seabed to explore.
At these sites, they used laser scanners and sonar to gather high-resolution maps of the ocean floor that further narrowed down their search. Scientific divers then conducted underwater archaeological surveys at the most promising sites.
All this hard work paid off, and in 2020 they reported the discovery of the first submerged ancient Aboriginal archaeological sites, where they recovered nearly 300 stone artefacts. These included tools for cutting and grinding, which had lain on the seabed for at least 7,000 years before their discovery.
Unfortunately, many other artefacts like these may be destroyed before we have a chance to find and recover them.
Submerged archaeological sites around Australia are under threat from coastal and offshore developments, including oil and gas exploration, renewable energy infrastructure and industrialised fishing.
“In the last couple of years, Aboriginal and Torres Strait Islander communities have worked with archaeologists to mitigate the impacts of development on their submerged cultural heritage,” Ulm says.
Indigenous groups and archaeologists are calling for stronger protections for these sites, which generally fall outside existing legislation in Australia that was designed to protect historic sites (such as those containing shipwrecks and sunken aircraft) from the modern era.
Ancient maritime explorers
How and when the first people arrived in Australia is one of the biggest unanswered questions in anthropology, and the Northwest Shelf is a key piece of this puzzle.
We now know that humans first arrived on the continent at least 65,000 years ago, and the most likely routes took them from southeast Asia to Sahul via modern-day Indonesia.
At this time, lower sea levels had exposed a long chain of more than 100 habitable islands on the Northwest Shelf between Indonesia and Sahul, which “may have enabled staged human dispersal from Indonesia to Australia, with people possibly using the archipelago as stepping stones,” Norman says.
These islands would have been visible from high ground on the islands of Timor and Roti, offering a clear target for the explorers to aim for.
However, this still required a sea crossing of nearly 90km (56 miles), which is two or three times longer than the voyages needed to reach Timor or Roti, and would have taken several days.
This suggests that the first Australians were skilled seafarers, capable of constructing maritime vessels as well as planning and navigating multi-day journeys.
Although we’ll likely never know exactly where people first arrived in Australia, the site where these intrepid explorers made landfall is likely to be at least 60m (197ft) underwater today.
Experts say that a group of more than 1,000 settlers must have made the journey, otherwise they would have been unlikely to survive long-term.
This initial founding population adapted to and thrived in Australia’s landscapes, spreading out across the newly discovered continent and flourishing into an estimated population of about 2.5 million people by the time European colonists arrived in the late 1700s.
A study published in 2024 used computer modelling to investigate the most likely routes taken by people as they dispersed across Sahul. It pointed to waves of dispersal radiating out across the continent, following river corridors and coastlines.
Advancing oceans
As the last Ice Age came to an end, around 18,000 years ago, melting ice sheets and glaciers released millions of cubic litres of water into the world’s oceans. This caused sea level rise on a scale unparalleled in human history.
Over a period of around 10,000 years, coastal areas were progressively submerged and the continent of Sahul was split into what’s become New Guinea and Australia.
Between 18,000 and 8,000 years ago, over 2,000,000km2 (around 772,000 sq miles) of Australia was flooded.
Coastlines around the continent retreated by over 100km (62 miles) in many places. Indigenous histories from around the coast of Australia tell of the drowning of vast coastal landscapes, which researchers believe are a record of these events.
This makes them the world’s longest-known continuous oral histories, which have been passed down from generation to generation for over 10,000 years.
But the climate warming and the sea level rise it caused wasn’t a smooth, continuous process – it came in pulses.
The first pulse began around 14,000 years ago and lasted about 400 years.
In that relatively short time, 100,000km2 (around 38,600 sq miles) of the Northwest Shelf flooded – an area roughly the size of Ireland. A second, more gradual period of melting between 12,000 and 9,000 years ago flooded a further 100,000km2 of the Northwest Shelf.
At times, people would have witnessed the ocean advancing by more than 20m (66ft) a year. “Such rapid and catastrophic marine inundation would have had profound effects in the space of a single human lifetime,” Norman says.
“Rising seas would have caused the coastline to migrate rapidly, compelling people to fall back as marine waters submerged once-productive landscapes.” Retreating coastal populations would have been forced together into a much smaller land area.
Based on the land area lost and population size estimates for the whole continent, a 2018 analysis estimated that population densities across Australia more than doubled in the 10,000 years after the end of the last Ice Age.
Several inland archaeological sites have been dated to this time, suggesting that many Aboriginal populations abandoned their coastal homes and moved inland.
The archaeological record shows hints of the significant cultural impact of this rapid influx of people.
For example, in the neighbouring regions of the Kimberley and Arnhem Land, archaeologists have documented sudden increases in the number of artefacts left behind, and new styles of rock art appearing, that coincide with the two great pulses of sea level rise.
Looking to the future
With global sea levels predicted to rise by more than 1m (3ft) by 2100, humanity is once again facing the prospect of losing large amounts of coastal land. Studies like these remind us that although climate change presents enormous challenges, human populations have survived rapid environmental change in the past.
Around the world, many ancient cultural sites have been discovered below the ocean’s surface – lost to sea level rise just like Sahul’s Northwest Shelf. “There’s plenty of archaeological evidence that humans once lived in areas that are now submerged all around the world,” says Norman.
Archaeological finds demonstrate that during the last Ice Age, humans made use of new landscapes exposed by the retreating ocean, including Doggerland in the North Sea, the Baltic Sea in northern Europe, and sites along the coasts of the Mediterranean, North and South America and South Africa. And then the rising waters forced them to retreat inland – sometimes at a pace that seems inconceivable today.
Modern populations are much larger, however, and many of our urban centres are on the coast, which will make adaptation even more difficult. The archaeological record also shows us that rapid climate change had a profound impact on the people who lived through it.
If we can learn from past societies, we may be better equipped for the future. Indigenous knowledge can offer unique and valuable insights that’ll help us cope with the environmental changes to come.
“The complex dynamics of First Nations people responding to rapidly changing climates lends growing weight to the call for more Indigenous-led environmental management,” says Norman.
“As we face an uncertain future together, deep-time Indigenous knowledge and experience will be essential for successful adaptation.”
About our experts
Dr Kasih Norman is a researcher at the Max Planck Institute of Geoanthropology. Her work has been published in various journals, including Scientific Reports, Nature Communications and Quaternary Science Reviews.
Prof Sean Ulm is a coastal and underwater archaeology specialist from the Australian Research Council’s Centre of Excellence for Indigenous and Environmental Histories and Futures at James Cook University, Australia. He has been published in the likes of Australasian Journal of Environmental Management, Journal of Anthropological Archaeology and Historic Environment.
Read more:
