By Sid Perkins
Hundreds of thousands of years ago, as an ice age was ending, the spillover from an immense glacial lake in northern Europe sliced through a broad ridge that for millions of years had connected what is now England to the continent. The flood that resulted, one of the largest that scientists have ever identified, quickly created a breach that makes Britain the island that it is today.
The narrowest part of the English Channel is the 33-kilometer-wide Strait of Dover. The cliffs on both sides of this waterway were once part of a broad chalk ridge that connected England to France, says Sanjeev Gupta, a geologist at Imperial College London. The lowest spot on this ridge probably sat about 30 meters above today’s sea level, he notes.