Birth of an Island

Britons sometimes like to forget that their proud island was once a mere peninsula of the European continent--a condition that, as geologists figure it, ceased only a short time ago. Dr. Harold Godwin of Cambridge has now estimated within a few centuries the date when the friendly sea broke through to form the English Channel and give Britain its freedom. It was 5000 B.C., says Dr. Godwin.

Dr. Godwin is a specialist in phytogeography, which means that he studies remains of ancient plants with an eye to what they tell about ancient climate and geography. His favorite haunts are peat beds, where plant material is often preserved so well that the species can be identified easily after many thousand years. Pollen grains are especially useful. Birch pollen found at a certain level of an ancient peat bed is proof that the climate was cold when the peat was formed. If the peat is dated by its carbon 14 content, the actual age of the cold period can be determined.

Ten thousand years ago, says Dr. Godwin, the last remnants of the Pleistocene glacier held out in the higher mountains of northern Britain. Plant remains of this date show that the country was open, arctic tundra with scattered patches of silver birch. Sea level was much lower. Peat dredged from the bottom of the North Sea shows that the southern two-thirds of its basin was filled by a chilly swamp connecting Britain with the continent, from Denmark to France.

After 8000 B.C.. the climate grew steadily warmer, melting the remnants of ice. Warmth-demanding plants (e.g., oak, elm and alder) invaded the Britannic Peninsula. New animals and new tribes of men trooped across the marshes. The climate was probably almost as warm as today. "A bit chillier," hazards Dr. Godwin. "A bit, but not a lot."

As the climate grew still warmer, it melted much bigger masses of ice in Siberia and North America. The water released raised the sea level, and the Atlantic Ocean ate its way southward over the "Doggerland" in the basin of the North Sea. By examining peat from the sea bottom, Dr. Godwin can tell the date when the salt water flowed over each bed.

The process of making Britain an island took several thousand years, but by 5000 B.C. (about the time of man's first agriculture, in the Middle East) the English Channel had connected with the North Sea. From then on, no intruder--:plant, animal or human--invaded England by dry land.

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