Wednesday, August 08, 2007

The English Channel Flood

Another one from New Scientist:

Britain was last connected by land to continental Europe around 500,000 years ago - by a chalk ridge across the English Channel. From Dover, of course.

What destroyed that last land connection? A megaflood, whose root cause was the retreat of an ice age - the third-to-last one. That retreating ice resulted in a large glacial lake in the south of the North Sea. Of course, sea levels were down with the ice age, and once the glacial lake had reached a critical level - the top of that connecting ridge - it breached. This happened some time between 200,000 and 450,000 years ago. The flooding lasted several months; Gupta and Collier of Imperial College London calculated that through those months, a million cubic metres per second poured through the breach. This gouged deep valleys in the English Channel - the evidence left behind.

This was also proposed back in 1985, based on a low resolution sonar survey. The latest finding used much higher resolution, and convinced past skeptics - one of whom said he was a convert, and ready for his sackcloth and ashes.

This timeline of glaciation lists the past ice ages. The most recent ones are:

- 12,ooo to 110,ooo years ago;

- 130,000 to 200,000 years ago;

- 340,000 (+/-) to 450,000 years ago

Of course, the ice ages simply meant that habitable areas were reduced to more equatorial regions. They didn't halt evolutionary or technological processes, but just reduced the ranges through which animals and hominis - Sapiens, Neanderthalensis, etc - could live and spread.

Which puts the African origins of Homo Sapiens into some perspective.

1 comment:

Anonymous said...

All that chalk removed by the flood must have caused large deposits to be left down stream. Have any core drilling tests been done down stream to look for evidence of chalk in the ocean bed.