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A Huge Clue to a Mass Extinction

In 1980 a giant crater,110 miles wide, was discovered in Mexico. Many scientists believe it was caused by a huge asteroid, or space rock, that struck Earth 65 million years ago, killing the dinosaurs.

Now scientists have found another crater, in Australia, that could explain an even earlier destruction of life on Earth. Tests on rocks from the 75-mile-wide crater show that it was formed 200 million to 280 million years ago--the same period when 90% of all animals, including early reptiles and sea creatures called trilobites, suddenly became extinct.

If an asteroid carved this crater, the impact would have thrown tons of dust into the air, blotting out the sun. Earth would have turned dark, cold and hostile to life. "It would have almost certainly caused a global environmental disaster," says earth scientist Michael Rampino.

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