Watch the Program

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The Big Die-Off

Around 13,000 years ago, right as North America's warm climate suddenly flipped back into ice-age conditions, most of the continent's biggest beasts went extinct. Nobody knows why.
running time 7:41

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Who or What Did It?

Did hunters kill off the mammoths and other "megafauna"? Or did the climate do it? Neither, says James Kennett of UC Santa Barbara and colleagues: It was a comet.
running time 9:24

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A Furious Debate

Critics say evidence for a comet isn't strong enough. Kennett and his colleagues counter that the same could be said for the leading contender among purported causes, the hunting "overkill" theory.
running time 8:20

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Jewels in the Earth

Evidence is also lacking, Kennett says, for "overchill," the climate theory. By contrast, he claims, the comet hypothesis has support from some rather striking evidence, in the form of millions of tiny diamonds.
running time 8:52

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Where's the Crater?

Skeptics point to two problems they see with the comet theory: No associated crater has been found, and sources other than a comet might have produced the mini-diamonds.
running time 6:57

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An Open Question

Climate scientist Paul Mayewski finds nanodiamonds in Greenlandic ice layers right at the time when the supposed comet struck. But the jury remains out on just what caused the great die-off.
running time 8:27