A Chip off the Doomsday Rock

What killed the dinosaurs? Scientists have been debating that one for a long time. They know that 65 million years ago, a large object, five or six miles across, blasted a 120-mile-wide crater at the tip of what today is Mexico's Yucatan peninsula. They also know that the impact, or more accurately, the worldwide, sunlight-blocking shroud of dust it kicked up, wiped out some 70% of the earth's plant and animal species--including the dinosaurs. But what, precisely, was the object that sealed their fate?

UCLA geochemist Frank Kyte thinks he may have found not just the answer but also a piece...

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