How to Understand the Ice Age

In its four-billion-year history, the earth has endured plenty of ice ages, most of which would have been frigid enough to freeze a woolly mammoth solid. However, the capital-lettered “Ice Age” refers to the cold snap that had much of the northern hemisphere in its grip about 20,000 years ago. Here’s how the Ice Age unfolded, and what it meant for our primitive human forebears.

Instructions

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1. The Ice Age wasn’t only cold. One of the strange things about earth’s climate is that unusually cold conditions in one place have a way of being balanced by unusually hot conditions elsewhere. Besides these extremes of hot and cold in widely separated locations, the Ice Age also saw huge swings in precipitation, which often resulted in debilitating droughts--which themselves prompted migrations by animals and people.
2. Much of the northern hemisphere was covered by glaciers. These huge, thick sheets of ice, which covered large portions of Europe, Asia and North America, rendered vast areas uninhabitable by humans, and were also responsible for lowering sea levels by hundreds of feet. Over the course of the Ice Age, these glaciers advanced and retreated numerous times, leaving geological scars that can still be seen today.
3. Conditions prompted humans to perfect the art of fire. Although there is evidence that humans have been using fire for hundreds of thousands of years, the Ice Age put a premium on pyrotechnic skills--since, during a cold night on the tundra, a roaring fire might mean the difference between life and death. In fact, it’s likely that the Ice Age unleashed a new wave of human inventiveness--such as the long spears used to hunt woolly mammoths--as tribes were forced to adapt to the perilous climate.
4. Land bridges allowed people and animals to migrate between continents. Because water levels had been depleted so dramatically by spreading glaciers, the Ice Age saw the appearance of land bridges, such as the one connecting eastern Asia and Alaska. As water levels returned to normal, these bridges later disappeared.
5. The end of the Ice Age marked the beginning of agriculture. As the world slowly began to warm up, conditions became ripe in certain places for herding animals and planting food crops. The art of agriculture also benefited from the fact that primitive humans had hunted large animals like mammoths to extinction—and needed to find another reliable food source.

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