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BEAUTIFUL corals, graceful sea turtles and 4-metre-long tiger sharks. It is easy to see why tourists flock to the Dampier Archipelago in north-west Australia to dive among the thrilling – if occasionally intimidating – marine life. But these seas contain something that isn’t advertised by tour guides. When Chelsea Wiseman and her colleagues went diving here in 2019, they found stone tools on the seabed. The artefacts were last touched by human hands at least 7000 years ago, before the sea rose, the land drowned and the sharks moved in.

“We were ecstatic, just blown away, to find the tools,” says Wiseman, an archaeologist at Flinders University in Adelaide, Australia. And with good reason. During the early millennia of human evolution, sea levels were mostly much lower than they are today, with huge areas of what is now submerged coastal shelf inhabited by our ancient relatives. What they were up to in these Stone Age coastal areas has long been a mystery because studying these underwater sites is so hard.

With the archaeology of our coastal waters largely unexplored, we are missing a huge piece of human history. Now, however, that is changing. Underwater archaeology like that carried out by Wiseman and her team is already showing us how people lived and thrived along Stone Age coasts. It even suggests that, as the seas rose, people took action to hold them back, in a poignant foreshadowing of today. And as the coasts were a crucial route for Stone Age travellers, studying them is changing our understanding of how and when humans began spreading around the world.

Underwater archaeology began in the 19th century. For decades, it mostly involved investigating shipwrecks, and we tended to learn about ancient maritime life. For instance, we found that civilisations that existed around the edges of the Mediterranean Sea 3500 years ago often shipped metals in the right ratios to be smelted into strong alloys like bronze. This focus on wrecks was understandable, says Jonathan Benjamin at Flinders University, who led the work at the Dampier Archipelago as part of a project called the . Shipwrecks are often easy to find. “I call them the castles of the sea,” he says.

He is part of a small band of underwater archaeologists who are raising their ambitions. To them, the seabed isn’t an inconsequential backdrop on which wrecks fester. It is a vast and complex drowned landscape, scattered with the remnants of ancient human lives. Since the ice sheets were at their peak about 20,000 years ago, rising seas have drowned at least 20 million square kilometres of coastal territory around the world – an area almost as large as the North American continent. Some even think of it as a lost, fragmented continent. They call .

“Some think of our drowned coasts as a lost, fragmented continent. They call it Aquaterra”

Surprisingly, the artefacts on this drowned terrain can be better preserved than those on dry land because the seabed has seen less of the industrial development that can damage archaeological sites. The trouble is that accessing those artefacts has long been seen as close to impossible. Looked at another way, the huge expanse of seabed isn’t thrilling, it is daunting. Where do you start? And how do you carry out the careful work of archaeology while wearing a cumbersome diving suit and flippers, in water that can be nearly opaque with clouds of silt? “The argument is that it’s too difficult to do underwater archaeology if what you’re looking for is small bone and stone tools,” says Benjamin. “But it’s not impossible.”

Take Doggerland. This once-fertile area of marshes and rivers now lies beneath the North Sea between Great Britain and continental Europe. Over the years, ancient stone artefacts have been recovered in dribs and drabs from the region, either by fishing vessels or amid the gravel routinely dredged up for use as aggregate.

Louise Tizzard at Wessex Archaeology, a research company in the UK, decided to follow up on one such isolated find consisting of 33 hand axes and some woolly mammoth and bison remains. Her team traced where the find had been dredged up to a site known as Area 240, some 11 kilometres off the east coast of England, where the water can be 35 metres deep. Scuba diving can be dangerous below about 30 metres, so the researchers scooped up more gravel using a dredger and then picked through it meticulously. In 2014, they revealed that they had found , all dated to around 200,000 years ago.

“It’s amazing to swim along an area and think: ‘millennia ago, this was dry land where people were living’”

This is expensive work. Hiring a boat can cost £40,000 a day on its own. Fortunately, companies that wish to develop in UK waters are required to undertake a full environmental assessment that includes consideration of underwater archaeology. With plenty of offshore wind turbines going up, more of this work is being done every year. “It’s opened up a lot more of the seabed than we’ve ever been able to look at before,” says Tizzard.

Even so, sites like Area 240 are rare. We are a long way from being able to read the sea floor deftly enough to easily identify probable sites of similar significance. “People talk about the difficulty of finding a needle in a haystack,” says Geoff Bailey at the University of York, UK, who has . “Finding a needle in a haystack is actually quite easy: you just need a metal detector. The problem is finding the haystacks.”

Hug the coast

For many archaeologists, the solution is to ignore the extraordinary deeper-water sites for now and instead hug the coast. Sites that are about 10 metres deep or less can be dived on by anyone with a little scuba training. Floating above these places is a powerful experience, says Wiseman. “It’s amazing to swim along an area and think: ‘several millennia ago, this was dry land where people would have been living.'”

The discoveries she helped make in Dampier Archipelago are already enriching the local archaeological record, which – judging by rock art on land nearby featuring what appear to be extinct animals like the wolf-like thylacine – may stretch back more than 20,000 years. Perhaps most interestingly, a statistical analysis shows that the drowned stone tools, which include hammerstones and blade-like “flakes” are, on average, larger than those found nearby on dry land. Given this distinction, it is possible that the underwater archaeologists have found evidence of a previously unknown tool-making tradition in the area that was practised before the sea level rose.

“We always knew of the sites and expected them to eventually be found,” says Peter Jeffries, CEO of the Murujuga Aboriginal Corporation, a non-profit made up of the traditional owners of the land that incorporates Dampier Archipelago. The discoveries “confirm the truth and value in our Dreamtime stories”, he says.

As Jeffries’s comments show, this kind of archaeology can mean a great deal to local communities. In the research community, however, both Bailey and Benjamin say there are those who think this sort of work simply costs too much. “They might say: you spend millions of dollars and ultimately you find a scatter of stone artefacts,” says Benjamin.

But attitudes are changing, not least because there is a growing appreciation of just how important the world’s coasts have been to human history. At coastal caves in South Africa, investigations over the past two decades have revealed that . Around the same time, these people began producing elaborate art and jewellery that hints they were cognitively similar to modern humans. Some researchers even link the two trends, says Manuel Will at the University of Tübingen, Germany. They point out that seafood contains more of the nutrients, including omega-3 fatty acids, that are believed to support brain growth and development. It isn’t a consensus view, but the argument is that humans began to behave in a modern way because they adopted a seafood diet – which would make coasts pivotal to our human story.

“Coasts are widely seen as important migration corridors that early humans used to spread”

Less contentiously, coasts are now widely seen as important migration corridors that ancient humans used to spread from our roots in Africa across the world over the past 100,000 years. Some of the earliest evidence of human occupation in the Americas comes from a 14,200-year-old site called Monte Verde in southern Chile. The site’s coastal location fits with the idea that early Americans arrived in Alaska and then rafted down the Pacific coast. Previously, archaeologists thought that, after marching across an ancient land bridge called Beringia between Siberia and Alaska, people then dispersed across the inland plains of North America. “But there has been a 180-degree shift – a sea change, if you will – to the idea that coasts were far more important,” says Jon Erlandson at the University of Oregon.

This means that the earliest evidence of humans spreading into new continents might lie underwater. Erlandson is in the process of identifying areas off the coast of California where items left by the first Americans might still be preserved. Likewise, as the Deep History of Sea Country project pushes further offshore, there is the potential to uncover evidence of the earliest archaeological remains anywhere in Australia.

Studying underwater sites can also help us understand how people reacted as the seas gradually swallowed their land. Ehud Galili at the University of Haifa, Israel, is a pioneer of drowned landscape archaeology and has been diving and studying ancient settlements off the coast of Israel for decades. In 2019, he and his colleagues published a paper describing what appears to be , at a 7000-year-old site called Tel Hreiz that lies about 4 metres below the waves, 90 metres offshore.

“I saw an elongated feature, 100 metres long, made of boulders, and I realised it was exceptional,” says Galili. This wall of boulders was on the seaward side of the settlement so seems to have been a barrier to protect against erosion. “We now know the history of coastal protection starts 7000 years ago,” he says.

Building the wall was a huge undertaking: some of the boulders probably weigh more than a tonne. But it ultimately failed, given that Tel Hreiz was inhabited for only a few generations. It does show, at least, that ancient people valued living next to the sea enough that they would strive to keep their settlements from being lost to the waves.

More evidence in this vein comes from the Isles of Scilly, an archipelago off the
south-westernmost tip of England that is unusually rich with ancient monuments, including hundreds of cairns, standing stones and chamber tombs. In 2020, a team led by Robert Barnett at the University of Exeter, UK, showed how sea-level rise between 5000 and 4000 years ago submerged 36 per cent of the islands’ land area. The team also reviewed the archaeological evidence from the islands and found that this loss didn’t lead to a drop in human activity. Instead, . The rising seas would have had a progressive and obvious impact on the ancient islanders’ home. “Some researchers have speculated that the unusual concentration of megalithic burial monuments was an attempt to establish continuity in the face of such an unpredictable world,” says Bailey. It is, of course, hard to know for sure.

“If you’re not studying ancient coastal societies, you’re missing out on a huge portion of human history”

Back in Australia, ancient minds may be slightly easier to read. “Our history and culture is handed down, generation to generation, through knowledge sharing between family and community members,” says Jeffries. His community and dozens of others all around the Australian coast still tell stories relating to the loss of land as the seas rose.

For several years, Patrick Nunn at the University of the Sunshine Coast, Australia, and his colleagues have been . Because so many of these coastal communities tell at least one story on the theme of land lost to the sea, Nunn suspects they all relate to a time when sea levels rose dramatically around Australia. This stopped happening about 7000 years ago after most of the ice sheets associated with the last glacial period had melted, which means the stories may be among the oldest still being told. Nunn thinks they hint at just how traumatic it was for ancient societies to deal with sea-level rise, while also offering a way for dozens of today’s communities to remember long-lost territories. Perhaps that explains why Jeffries wasn’t surprised when Wiseman dived into the sea and brought ancient drowned artefacts back to the surface.

With research like this, we are beginning to build a detailed picture of the value of coasts to past populations. But with so much of Aquaterra yet to be explored, far more can still be learned. Benjamin is keen to get back in the water and go diving for more drowned secrets. “If you’re not studying ancient coastal societies,” he says, “then you’re missing out on a huge portion of human history”.