Doug Noltemeies, age 10, of Rockford, Illinois, for his question:
How much ground did the Ice Age cover?
The earth scientists of 150 years ago knew nothing at all about the stupendous Ice Ages of the past. Modern researchers still are investigating the full extent of the monstrous glaciers. Many of the details remain hidden in the ground and also in the muddy seabeds.
The diary of the earth dates back some four billion years and cruel Ice Ages have been appearing now and then for a long time. The largest one seems to have been the most recent, known to earth scientists as the Wisconsin Ice Age. This monster began to relax its icy grip only about 11,000 years ago, which is a very short spell in geological history. Recent investigations suggest that it lasted about 115,000 years. It began as a medium sized Ice Age and then came a warmer change in the climate. The cruel glaciers shrank a little. But the climate changed again for the worse and the medium Ice Age grew into the frostiest giant of the earth's history.
Most of the earth's land areas are north of the equator and Ice Age glaciers wreak their worst havoc on the continents of the Northern Hemisphere. But the cooler climate of the Wisconsin Ice Age seems to have been world wide. Glaciers formed among the high mountains of South America, in Australia and even on the mountains of tropical Africa. The main ice sheets spread over North America, Europe and northern Asia.
Some geologists estimate that the total ice fields covered an area of almost 11 million square miles. This is nearly one fifth of the earth's entire land area and nearly twice the area of the present cap of Antarctica. The icy Wisconsin invasion reached its peak and declined suddenly. The world climate made an abrupt change and became 10 to 15 degrees warmer. The glaciers melted and quickly retreated. A few hard, icy cores still cling to the mountains of Greenland and a few other areas. But after some 115,000 years of ice bound captivity, flourishing springtime returned to much of the land. Ice Age glaciers tend to center themselves in certain regions and spread out through the edges to conquer surrounding territory. The Tisconsin Laurentide ice sheets covered nearly five million square miles. It spread eastward to the Atlantic coast and westward to meet another monstrous ice field. Its southern boundary ad¬vanced with a wall of ice 10,000 feet high and it reached as far as the Ohio and Missouri Rivers. Greenland, Iceland and all of Canada were buried in icy graves. Other glaciers of this Ice Age covered England, Scandinavia, the Alps and Siberia.
Ice Age glaciers engulf valleys and mountains and shift uncountable tons of earth in their paths. As they march, their icy claws scrape and gouge the hardest rocks. As they melt, they dump dirt and gravel and even boulders toted from afar. These piles of debris and the icy claw marks tell part of the glacial story. Debris from melting glaciers also washes into the sea. Researchers are tracing Ice Age events from cores of oozy mud taken from offshore ocean beds.