Science: How the Ice Age Began

About 2 million years ago, the earth's climate began to undergo drastic changes. The polar icecaps increased dramatically in size. Glaciers spread as far south as present-day New York City. Seeking to escape the chilly weather sweeping the face of the earth, many animals—including man—sought refuge in more southerly latitudes. Less adaptable or mobile creatures were destroyed by the advancing freeze.

Though this scenario for the beginning of the ice age has been well documented by fossil records, scientists have long been uncertain about what caused the cooling. Now, after studying cylindrical-core samples...

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