Tuesday, July 25, 2006

Tearing continents apart

Three hundred miles to the northwest of here, a third of the way to Iceland, a speck of quano-covered rock juts from the stormy waters of the North Atlantic. It is called Rockall and may well be, as the sailors say, "the most isolated speck of rock in the world." Britain, Ireland, Iceland and Denmark all claim it, but since it is almost impossible to land on and is hardly bigger than your backyard is might seem improbable that anyone would want it. However, it stands in the middle of a relatively shallow submerged bank of considerable size (50x150 miles), and who knows what mineral riches might lie down there. Fishing rights, too, are at stake.

The Atlantic is full of islands, of course, but they are all volcanic. Rockall is granite -- continental rock -- and there may lie the answer to its riddle. Geologists believe the Rockall Bank is a fragment of the supercontinent of Pangea that broke off and sagged beneath the waves when the Atlantic Ocean was opening up 200 million years ago. Pangea was ripped apart from below, with lava oozing up to form new ocean floor. The definitive rupture corresponds to what is now the Mid-Atlantic Ridge, but apparently another rift separated the Rockall Bank from what is now Europe. Most of the floor of the Atlantic Ocean is new volcanic rock (basalt) less than 200 million years old, but down there under the waves near Rockall is a chunk of more ancient submerged continent, a true Atlantis, of which only a jagged tooth is visible.

On my New England college campus (out there across the Atlantic) I have found only one remnant of that time 200 million years ago when Pangea was being torn asunder, a six-inch-wide dike of basalt that oozed up through a crack in the stretched granite continent. When a large parking lot was planned for the spot, I managed to have the outcrop saved, and there it now sits, a sacrificed parking slot in the middle of a sea of asphalt, preserving a small clue to one of the great episodes in the planet's history.