9000 years ago, Britain was a peninsula of Europe, but as the earth warmed and the seas rose, at some point roughly 8500 years ago, the North sea connected to what is now the English Channel. It may have been a gradual process: solid lowlands becoming marshlands and the marshlands expanding and eventually being an uninhabitable breach.
However, there were still significant islands in the North Sea. Doggerland, as it is now sometimes called, was not submerged until perhaps 6000 years ago into the beginning of the Neolithic. This area is now the Dogger Banks, with depths between 15 metres and 40 metres, and has been the subject of a certain amount of archeological study. Stone tools corresponding to those used in Britain in the mesolithic era have been recovered from the area. It is considered to have been grasslands.
I find this interesting to contemplate. At some point the remaining inhabitants would have just had to make the decision that they couldn’t make a go of it any more.
