Extraterrestrial Extinctions
A couple of recent studies make it sound like the universe was out to get the woolly mammoth.
One study says that mammoths in and around Alaska may have been killed when a comet or asteroid exploded in the atmosphere more than 30,000 years ago. Another suggests that the whole species was wiped out when an even bigger comet blasted Earth about 13,000 years ago.
There's no doubt that comets and asteroids slam into Earth from time to time, with deadly effects. When a small asteroid exploded above Siberia a century ago, for example, it flattened hundreds of square miles of forest. A much larger asteroid may have killed off the dinosaurs when it slammed into Earth 65 million years ago.
Whether they explode in the air or on contact with the ground, the effects are similar: massive shockwaves and fires, and clouds of debris that can blot out the Sun.
One team of researchers says that's what happened about 13,000 years ago. A large comet exploded above Canada, the team says, setting much of North America ablaze. The blast melted a glacial icepack, and hurled so much debris into the sky that the entire planet grew much cooler for a thousand years. The devastation killed much of the plant life in northern latitudes, depriving the mammoths of food.
Other researchers disagree with the conclusions. But few disagree that similar impacts have happened in the past -- or that they could happen again in the future. More about that tomorrow.
Script by Damond Benningfield, Copyright 2008
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