Friday, August 10, 2007

Deep history

As I write, my daughter and my two grandsons are touring the invasion beaches and battlefields of Normandy. The boys recently watched Tom Hanks' and Steven Spielberg's epic film Band of Brothers, and now they will see the places where the momentous events took place. Including, of course, the acres and acres of white markers in the military cemeteries.

And while they are at it, they will see a famous record of another cross-channel invasion: the Bayeux Tapestry.

According to a recent paper in Nature (July 19), England and France have not always been separated by water, even at times when sea level was as high as today. Apparently, the two landmasses were once connected by a rocky ridge between Dover and Calais. Then, sometime during successive advances and retreats of the last Ice Ages, a huge meltwater lake collected in what is now the North Sea basin, hemmed at the north by glacier and dammed at the south by the Dover-Calais ridge. To the west of the ridge, what is now the English Channel was a dry valley sloping down to the Atlantic shore; with so much ice on the continents, sea level was considerably lower than today.

As the North Sea basin filled, a trickle of cold meltwater overtopped the ridge, eroding a thin outflow channel in the sedimentary rock. The trickle became a gush, and the ridge gave way in a colossal washout. The North Sea meltwater lake emptied into the Atlantic in a surging flood the likes of which the world has seldom seen. Seldom, but not never. Geologists have long recognized that something similar happened in eastern Washington State about 15,000 years ago, creating the distinctive landscape features known as the Scablands. British geologists have now mapped identical landforms on the floor of the English Channel, indicating a flood from east to west.

My daughter is a geologist, and reads Nature every week. As she stands with my grandsons on the German pillbox at Pointe du Hoc, looking out into the Channel from which appeared the Allied armada of 1944, I hope she tells them the story of the Great Channel Megaflood. Human history is almost invariably influenced by geography. How sad it is that (according to polls) almost half of my grandsons' fellow Americans reject the glorious ongoing human quest to discover the planet-shaping history of deep time.