How Britain became an island

Salon IFA 169 reports:'
According to Jenny Collier, of Imperial College, London, and her colleague, Sanjeev Gupta, the English Channel was formed some time between 450,000 and 200,000 years ago, when a natural land dam at the Strait of Dover failed. The results of their research are published in this month’s Nature, and are based on a new high-resolution sonar survey of the Channel floor, which shows the deep gouges and scour marks in the bedrock at the bottom of the Channel caused by the inundation, which occurred when a lake fed by meltwater from the British and Scandinavian ice sheets and by the Thames and Rhine river systems broke through the chalk ridge that once ran continuously from the Weald into the Artois region of northern France and Belgium.

The Imperial College team has yet to explain what triggered the event. According to Jenny Collier: ‘It is possible that it was the pressure of rising water and that it would have happened anyway, but there are little earthquakes in that area — there was one recently in Kent — and it is a tantalising possibility that one triggered the flood.’

‘This would have been a torrent of water carving out a huge valley through this wild landscape,’ said Dr Gupta. ‘There would be powerful eddies, with huge boulders and chunks of chalk … thrown around in the surge.’ The team estimates the surge released between 200,000 and 1 million cubic metres of water a second, equivalent to one hundred times the discharge of the Mississippi river.

One result was to cut Britain off from the European mainland even during periods of heavy glaciation when sea levels were low, making it much harder for early humans to settle what was previously a peninsula. This, in turn, seems to have contributed to a population crash and may explain why early human occupation of Britain came to an abrupt halt for almost 120,000 years. Professor Chris Stringer, of the Natural History Museum, who heads the Ancient Human Occupation of Britain Project, said: ‘We know of ancient humans 700,000 years ago at Pakefield, 500,000 years ago at Boxgrove, 400,000 years ago at Swanscombe and 220,000 years ago at Pontnewydd, but there is no evidence beyond 180,000 years ago until around 60,000 years ago.’'


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