Mary Kathleen Moore, age 7, of Leon, Iowa, for her question:
Was the whole earth covered with the Ice Age glaciers?
There have been several Ice Ages curing the long history of the earth. Each time a large area of the world was buried under massive glaciers. The glaciers of one such Ice Age covered an area of 12 million square miles. This is about one seventeenth of the earth's surface, or over a quarter of the land area. No Ice Age, it seems, was severe enough to cover all the earth with glaciers.
Ice Age glaciers were two to three miles thick. This mass of ice pressed down the level of the continents. Fingers of glassy ice clawed the rocks, tore loose boulders and soil, scraped the tops of peaked mountains and gouged great valleys in the ground. These are the records that tell us the stories of past Ice Ages. The massive glaciers changed the face of the earth wherever they touched.
The earliest records tell of an Ice Age that happened some 500 million years ago. Some 200 million years ago, the tropics were in the grip of an Ice Age. The icy glaciers left their tell‑tale marks in India, Africa, Australia and South America. The last Ice Age happened within the past million years. It came and went in four phases. We now live in a warm period following the last of these phases.
The glaciers of the last Ice Age covered all of Canada. They crept south across what is now the United States border and dipped far south in the region of the Great Lakes. They covered Greenland, northern Europe and Siberia. In America, the glaciers of the first phase reached Nebraska. In the second phase they reached down as far as Kansas. The third phase reached Illinois and the fourth phase reached Wisconsin. Each time the glaciers advanced and retreated, There was a warmer period between each icy period.
Let's imagine what North America was like when the Ice Age was at its worst. Canada, the northern edge of the United States and a vast area around the Great Lakes was under massive sheets of solid ice. Nothing grew or lived there. Animals and men had moved south as the glaciers advanced. Plant life was crushed and frozen.
The edge of the glacier was a high wall, a steep cliff of solid ice. Ahead of the glacier, the trees had perished with cold. The ground bore mosses, lichens and a few scrubby bushes. Snow could be expected any day of the year, For summer was never warm enough to melt ice and snow.
Yet, in this dismal world, mankind managed to live and look after his family. He hunted game right up to the very brink of the glaciers. We know, because we have found his arrowheads buried in the bones of Ice Age animals. Nor did this brave ancestor of ours settle for small game. He hunted the giant mammoth ‑ and left his arrowheads behind to prove it.
As the ice retreated during a warm period, plants sprang up in the marshy ground. The game returned northwards, and so did mankind. Somehow our distant ancestors survived through the longs bitter Ice Ages. Had the ice covered the whole earth at one time, all plant and animal life would have perished along with mankind.