Cold air flowing off the ice sheets caused such heavy precipitation when it encountered warm and humid air to the south that whole regions there filled with water, too. The basins of Nevada became lakes and the ranges among them were islands. Lake Bonneville filled a third of Utal1. Huge lakes grew in the Gobi Desert, in Australia’s Great Artesian Basin, in various lowlands across North Africa. There were forests in the Sahara, as fossil pollen shows, and networks of flowing streams. Their dry channels remain. In North America, where the ice started to go back about twenty thousand years ago, the first vegetation to spring up behind it was tundra. Carbon i4 can date the fossil tundra. The dates, particularly in the East, show a slow, and kantoor huren per uur rotterdam then accelerating, retreat.
After five thousand years, the front was still in Connecticut. In another twenty-five hundred years, it crossed the line to Canada. Human beings, living on the tundra near the ice, perforce were inventive and tough. Culture, in part, was a glacial effect. In response to the ice had come controlled fire, weapons, tools, and fur as clothing. Creativity is thought to have flourished in direct proportion to proximity to the glacier-an idea that must infuriate the equatorial mind. The ice drew back from Britain a geologic instant before the birth of Shakespeare. The fossils of Homo sapiens have never been found in sediments older than the Ice Age. In the way that scenes of vanished mountains can be inferred from their debris, the vision of continents covered with ice came straightforwardly to Agassiz as the product of reasoning carried backward from kantoor huren per uur amsterdam evidence through time. It is one thing to say that the ice was there, quite another to say how it got there. If the origin of mountains is sublimely moot, so is the origin of the ice. Characteristically, the prime mover is not well understood. The ice did not come over the world like a can of paint poured out on the North Pole. It formed in places well below the Arctic Circle, and moved out in every direction-including north-until cut off by the unsupportive sea. Geologists call these places spreading centers, the same term they use for the rifted boundaries where plates tectonically divide. To the question ‘Why did the ice form?” they can answer only with speculation.