Thanks to Brilliant for supporting this episode of SciShow.

Go to Brilliant.org/SciShow to check out their Geometry Fundamentals course. [♪ INTRO]. We are fascinated by the idea of Atlantis - a whole civilization lost to sea.

And while many people have claimed they’ve found it, it… probably never existed. But the oceans have claimed land where humans once lived, especially in the aftermath of the most recent ice age. Meet Doggerland - a real-life Atlantis lost to the slow rise of the sea and two catastrophic disasters.

Thousands of years after it disappeared, we’re just beginning to piece together what life there was like. Earth’s most recent glacial period, what we sometimes call the Ice Age, bound up a lot of water in the form of glaciers. Because of this, the sea level was lower 12,000 years ago than it is today - by roughly 70 meters.

That was enough to connect Britain to mainland Europe with a land bridge. Archeologists call this area Doggerland, after the North Sea’s Dogger Bank.  It was half the size of Germany, and home to hunters and gatherers who roamed the plains. Today, fishing boats in the North Sea between England and the Netherlands are reminded of this when, alongside fish, they pull up tools, weapons, and even ancient human remains!

Archeologists have known about Doggerland for well over a century, but learning more has been a challenge because underwater archeology is tricky... and expensive.  The usual strategy of “go to place and start digging” isn’t really an option. But, with some clever scientific tricks, we can start to build a picture of this place, even though we’re separated from it by both time... and a lot of water. Much of what we know about the land itself comes from seismic surveys that look for oil and gas under the sea.

A boat sends out a sound wave that travels through the water and reflects off the seafloor, as well as the layers of sediment and rock beneath it.   They bounce back up to the surface and are detected by long lines of sensors towed behind the boat. This gives a 3D view of the entire area, and reveals that the ground that those ancient people roamed is now 30 to 50 meters below the seafloor.  This was a landscape of rolling hills, rivers, and marshlands. A 2007 study counted 1600 kilometers of long-lost rivers, 24 lakes and wetlands, and 10 estuaries where fresh water once met the sea.  We can learn what plants covered this landscape by looking for pieces of DNA in sediment cores and identifying individual grains of pollen buried beneath the seafloor.  Over the years, scientists have found birch, pine, oak and hazel were the main trees present.

And one expedition even found evidence of a fossilized forest. Then there’s Doggerland’s ancient inhabitants - both human and non-human animals. And we’ve been able to learn about them from what they’ve left behind.

Animal bones recovered from the sea and evidence from nearby archeological sites indicate Doggerland was home to horses, mammoths, and deer.  Occasionally, human remains wash ashore or get pulled up by boats. A 2016 study collected over 50 of these and used radiocarbon dating to figure out they’re up to 11,000 years old.  By looking closely at the carbon and nitrogen in these bones, the researchers were even able to infer what those people ate.  See, atoms of carbon and nitrogen can come in heavier and lighter versions, called isotopes.  The mix of isotopes in any particular food depends on the environment it’s from and how high up the food chain it was.  So a plant, land animal, or fish from a lake or ocean all have different mixtures, which are transferred to the bones of the humans eating them.  The researchers figured out the inhabitants of Doggerland relied on food from the land and freshwater rivers, but they didn’t eat much that came from the ocean.  We can also see that as sea levels rose and the climate changed, they gradually ate less from the land. This means they adapted to their surroundings instead of packing up and leaving.  But if you look out at the North Sea today, you can tell that a lot has changed.

As the last glacial period passed its peak, the ice began to melt. But if that was all that had happened, Doggerland would have flooded gradually. Instead, two ancient disasters helped bury it more quickly.

As the glaciers melted, a massive lake formed in the middle of what is now Manitoba. But 8400 years ago, the ice sheet that formed the northern shore of the lake suddenly collapsed, and the water rapidly spilled into the ocean.  Sea levels jumped half a meter in a single year.  As if that wasn’t enough, a few hundred years later, a catastrophic tsunami called the Storegga Event tore across the North Sea.  It originated from an undersea landslide off the coast of Norway, possibly triggered by an earthquake. By the time it hit Doggerland, the wave would have been around three meters high.

And for a place that was already suffering from sea level rise, it was likely catastrophic. By looking through those seismic surveys used to map Doggerland and taking sediment cores, scientists have been able to identify the deposits of sediment left by this massive wave. It probably wasn’t the final submergence of Doggerland, but it was only a matter of time afterwards until the rising seas swallowed it completely.  We can’t say for sure whether this catastrophic flood inspired the story of Atlantis.

But it’s a reminder of the ever-changing surface of our planet. Today, climate change means we’re facing rising sea levels again. The story of Doggerland illustrates how drastic the consequences can be.

But understanding the world around us can help us turn things around. And the courses over on Brilliant can help you learn. Like their newly revamped Geometry Fundamentals, which shows you how intuitive geometry can be with just a bit of common sense and simple reasoning.

Brilliant puzzles you, surprises you, and expands your understanding of the world we live in. Their courses and Daily Challenges are sure to keep your brain on its metaphorical toes. Right now, the first 200 people to sign up at Brilliant.org/SciShow will get 20% off an annual Premium subscription.

And by checking them out, you’re also supporting us - so thank you. [♪ OUTRO].