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Britain's political separation from the European Union officially began last week. But the island's original split from mainland Europe actually happened hundreds of thousands of years ago.

Researchers have Watch Japanese black stockings female doctor gives oral sex service to patients Onlinea new theory for how this prehistoric "Brexit" likely went down: first with an overflowing glacial lake, and later with a catastrophic flood.

If it wasn't for this set of geological circumstances, Britain may have remained connected to mainland Europe, jutting out into the North Sea like Denmark does today, according to a study published Wednesday in Nature Communications.

"Without this dramatic breaching, Britain would still be a part of Europe," Sanjeev Gupta, a co-author of the study and Earth sciences professor at Imperial College London, said in a news release.

"This is Brexit 1.0 -- the Brexit nobody voted for," he said.

Gupta and his colleagues used high-resolution seafloor data and 3-D modeling to explore how the land bridge once linking Britain and Europe likely collapsed.

Previous research suggested that a glacial lake spilled over and formed the Dover Strait, which is now the narrowest part of the English Channel. But this new study suggests the split happened in two distinct stages.

The first separation event likely occurred some 450,000 years ago, when Britain and continental Europe were still connected via a chalk ridge that stretched from southeast England to northwest France. At that time, vast swaths of ice blanketed the North Sea from Britain to Scandinavia, and the entire English Channel was an expansive, frozen tundra, criss-crossed by small rivers.

At some point, a glacial lake likely spilled over and caused the initial erosion. Waterfalls cut through the land bridge and caused a rock dam to fall, releasing a fire-hose of lake water into the English Channel, the scientists found in their analysis.

"It would have been a cold world, dotted with waterfalls plunging over the iconic white chalk escarpment that we see today in the White Cliffs of Dover," Jenny Collier, a study co-author from Imperial College London, said in the press release.

Hundreds of thousands of years after that initial event -- probably around 160,000 years ago -- the chalk ridge likely experienced a "catastrophic failure," triggering a mega-flood that completed the split between Britain and mainland Europe, the scientists found, based largely on coastal sediment records.

Collier said it's still not clear why the glacial lake initially spilled over, or why the chalk bridge was finally breached, though the latter might be due to an earthquake. The team also hasn't yet developed an exact timeline for these events.

Still, Gupta said the geological split between present-day Dover, England, and Calais, France, was "undeniably one of the most important events in British history."

"When the ice age ended and sea levels rose, flooding the valley floor for good, Britain lost its physical connection to the mainland," he said, noting that the split has helped "to shape our island nation's identity even today."

In other words, without the first, geological Brexit, the current one may never have happened.