How did the English Channel come into being?

W: Tom, do you know why Britain is separated from the continent?
M: No. But I guess millions of years ago Britain was also a part of the Continent.
W: You are right. Nearly 10,000 years ago, at the end of the Ice Age, a great flood washed over a wide, low plain, and created the English Channel. From then on, the island of Britain was isolated from the rest of Europe.
M: I know there have been many people who have wanted to swim across the Channel, and some of them have succeeded.
W: What’s more, quite a lot of people have thought of building a channel tunnel since the 18th century, but no one thought this dream would come true. Now, however, the channel tunnel, the longest underwater passage on the earth, has been built.
M: When was it built?
W: A British team started to drill southeast from Dover and a French team started to drill northwest from Sangatte in 1987. The two teams met under the channel in December 1990, and they celebrated the completion of the 23-mile shaft.
M: Was it opened to the public immediately?
W: No. The tunnel was opened to the public in 1993 and now it is able to carry up to 30 million passengers a year.