Prehistoric Men

by Robert J. Braidwood

In earlier times the earth looked very different. Geologists call the last great geological period the Pleistocene. It began somewhere between a half million and a million years ago, and was a time of great changes. Sometimes we call it the Ice Age, for in the Pleistocene there were at least three or four times when large areas of earth were covered with glaciers. The reason for my uncertainty is that while there seem to have been four major mountain or alpine phases of glaciation, there may only have been three general continental phases in the Old World.[2]

[2] This is a complicated affair and I do not want to bother you with its details. Both the alpine and the continental ice sheets seem to have had minor fluctuations during their main phases, and the advances of the later phases destroyed many of the traces of the earlier phases. The general textbooks have tended to follow the names and numbers established for the Alps early in this century by two German geologists. I will not bother you with the names, but there were four major phases. It is the second of these alpine phases which seems to fit the traces of the earliest of the great continental glaciations. In this book, I will use the four-part system, since it is the most familiar, but will add the word alpine so you may remember to make the transition to the continental system if you wish to do so.

Glaciers are great sheets of ice, sometimes over a thousand feet thick, which are now known only in Greenland and Antarctica and in high mountains. During several of the glacial periods in the Ice Age, the glaciers covered most of Canada and the northern United States and reached down to southern England and France in Europe. Smaller ice sheets sat like caps on the Rockies, the Alps, and the Himalayas. The continental glaciation only happened north of the equator, however, so remember that “Ice Age” is only half true.

As you know, the amount of water on and about the earth does not vary. These large glaciers contained millions of tons of water frozen into ice. Because so much water was frozen and contained in the glaciers, the water level of lakes and oceans was lowered. Flooded areas were drained and appeared as dry land. There were times in the Ice Age when there was no English Channel, so that England was not an island, and a land bridge at the Dardanelles probably divided the Mediterranean from the Black Sea.

A very important thing for people living during the time of a glaciation was the region adjacent to the glacier. They could not, of course, live on the ice itself. The questions would be how close could they live to it, and how would they have had to change their way of life to do so.

GLACIERS CHANGE THE WEATHER

Great sheets of ice change the weather. When the front of a glacier stood at Milwaukee, the weather must have been bitterly cold in Chicago. The climate of the whole world would have been different, and you can see how animals and men would have been forced to move from one place to another in search of food and warmth.

On the other hand, it looks as if only a minor proportion of the whole Ice Age was really taken up by times of glaciation. In between came the interglacial periods. During these times the climate around Chicago was as warm as it is now, and sometimes even warmer. It may interest you to know that the last great glacier melted away less than 10,000 years ago. Professor Ernst Antevs thinks we may be living in an interglacial period and that the Ice Age may not be over yet. So if you want to make a killing in real estate for your several hundred times great-grandchildren, you might buy some land in the Arizona desert or the Sahara.

We do not yet know just why the glaciers appeared and disappeared, as they did. It surely had something to do with an increase in rainfall and a fall in temperature. It probably also had to do with a general tendency for the land to rise at the beginning of the Pleistocene. We know there was some mountain-building at that time. Hence, rain-bearing winds nourished the rising and cooler uplands with snow. An increase in all three of these factors—if they came together—would only have needed to be slight. But exactly why this happened we do not know.

The reason I tell you about the glaciers is simply to remind you of the changing world in which prehistoric men lived. Their surroundings—the animals and plants they used for food, and the weather they had to protect themselves from—were always changing. On the other hand, this change happened over so long a period of time and was so slow that individual people could not have noticed it. Glaciers, about which they probably knew nothing, moved in hundreds of miles to the north of them. The people must simply have wandered ever more southward in search of the plants and animals on which they lived. Or some men may have stayed where they were and learned to hunt different animals and eat different foods. Prehistoric men had to keep adapting themselves to new environments and those who were most adaptive were most successful.