Science News-- Geologists locate evidence of the first Brexit: Britain's escape from the mainland

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April 4 (UPI) -- New research suggests the original Brexit occurred roughly 450,000 years ago. The separation occurred in two stages, researchers determined.

Researchers combined new geophysical data with sear floor topography to better understand how and when the English Channel was flooded and Britain was separated from mainland Europe.

Scientists hypothesize that the English Channel was once a dry land bridge made of chalk, dissected by a series of streams. Roughly 450,000 years ago, spill over from a glacial lake began filling in the channel. Catastrophic flooding finished the job. Eventually, rising seas covered the channel immediately.

New images of the English Channel seafloor revealed the presence of a significant valley system, with holes and rivulets -- marks left by flooding. Researchers believe several holes in the chalky seafloor are evidence of an waterfalls.

The chalk bridge served as a dam against the proglacial lake, a lake at the base of a glacier. Markings in the ancient chalk suggests the bridge couldn't last, however. Waterfalls left indentations in the bedrock -- indentations than can be picked up by sonar.

"We still don't know for sure why the proglacial lake spilt over. Perhaps part of the ice sheet broke off, collapsing into the lake, causing a surge that carved a path for the water to cascade off the chalk ridge," Jenny Collier, study co-author Earth scientist at Imperial College London, said in a news release.

Researchers believe the initial spill-over -- likely trigged by broken fragments of the glacier -- was followed by long series of floods. Scientists published their findings in the journal Nature Communications.

"The breaching of this land bridge between Dover and Calais was undeniably one of the most important events in British history, helping to shape our island nation's identity even today. When the ice age ended and sea levels rose, flooding the valley floor for good, Britain lost its physical connection to the mainland. Without this dramatic breaching Britain would still be a part of Europe.