"Without this dramatic breaching Britain would still be a part of Europe," says Sanjeev Gupta—and no, he's not talking about Brexit. In what he dubs "Brexit 1.0—the Brexit nobody voted for," the Imperial College London researcher reveals two massive floods were responsible for physically separating Britain from Europe about 150,000 years ago. Researchers say a chalk land bridge, perhaps 20 miles long and 330 feet high, connected England and France 450,000 years ago, per a release. It also acted as a dam, keeping a massive lake on the edge of an ice sheet stretching across the North Sea from spilling into what is now the English Channel—at the time, a dry, frozen tundra. Then the lake overflowed, researchers say, sending water crashing over the land bridge in a series of waterfalls.
Researchers say the flow—perhaps caused by a chunk of the ice sheet falling into the lake—left its mark in a series of deep holes in the bedrock of the Channel, including some a few miles wide, which were spotted by engineers surveying for the Channel Tunnel decades ago. The water also weakened the land bridge substantially so that a second flood about 150,000 years ago caused it to fail completely. Researchers say the resulting "megaflood" likely carved a valley in the bedrock as it breached the land bridge, per the Guardian. Rising sea levels at the end of the Ice Age made Britain's separation complete. "This was really one of the defining events for northwest Europe—and certainly the defining event in Britain's history," Gupta tells the BBC. (Researchers have found evidence of another "catastrophic collapse.")