Scientists Link Diamonds To Earth's Quick Cooling

Scientists say they have evidence the Earth was bombarded by meteors about 13,000 years ago, triggering a 1,000-year cold spell. Researchers write in the journal Science that they have found a layer of microscopic diamonds scattered across North America. An abrupt cooling may have caused many large mammals to become extinct.

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Scientists say they've found evidence that the Earth was bombarded by meteors about 13,000 years ago, and they say that triggered a 1,000-year cold spell. Their evidence is a layer of microscopic diamonds. At that time, a sudden fallen in temperature wiped out many large mammals in North America and may have led to the rise of agriculture in the suddenly chillier Middle East. NPR's Richard Harris has the story.

RICHARD HARRIS: Thirteen thousand years ago, the Earth was gradually emerging from the last Ice Age, when all of a sudden, like, in a decade, much of the globe was suddenly plunged back to a deep freeze.

Dr. JAMES KENNETT (Emeritus, Earth Sciences, University of California, Santa Barbara): For 30 years, I've been working on this enigmatic abrupt cooling.

HARRIS: That's James Kennett, now Emeritus at UC Santa Barbara.

Dr. KENNETT: It always bothered me. What triggered this major cooling at a time when the Earth should have been warming?

HARRIS: For many years, Kennett focused on the leading hypothesis, that is, a huge ice dam in North America broke as the Earth warmed and all that fresh water rushed into the Atlantic Ocean. That, in turn, interrupted a set of currents known as the conveyor belt, which usually brings warm water and warm air up from the tropics into Europe and North America. There's a good deal of geological evidence for that explanation, but now Kennett is part of a team that has a much more exotic idea.

Dr. KENNETT: What we've discovered - and this is what was just published in Science Magazine - is a layer of nanodiamonds, which is totally remarkable.

HARRIS: That's right, nanodiamonds, billions of them, all in a layer that formed about 12,900 years ago. And where did these diamonds come from?

Dr. KENNETT: There's no other way, in my imagination, my knowledge - and anybody else's, as far as I know - that you can produce a layer of diamonds without having an extraterrestrial impact.

HARRIS: He argues diamonds require lots of heat and pressure. So, he says something big hit the Earth or maybe a fusillade of smaller objects did. But how could that have triggered a cold spell? And a cold spell that lasted more than 1,000 years? It's a matter of conjecture. One idea Kennett is toying with is that a meteor bombardment could have triggered the events that geologists have already discovered to explain the cold spell.

Dr. KENNETT: What we suggest is that the impact broke the dams at the edge of the ice sheet.

HARRIS: As a result, fresh water flowed into the Atlantic, changing ocean circulation and cooling the planet. Now, if all of this is starting to sound a little farfetched to you, you are by no means alone.

Dr. BEVAN FRENCH (Adjunct Scientist, Paleobiology, Smithsonian National Museum of National History): Uh, I'm skeptical.

HARRIS: That's Bevan French at the Smithsonian's Museum of National History. He, like many other scientists, isn't even convinced that the nanodiamonds are proof of an impact.

Dr. FRENCH: The fact that they've reported them here is, I think, a very exciting development, but I think you might be dealing with some kind of a combustion process rather than with an impact event itself.

HARRIS: So, there are a lot of questions Kennett and his colleagues have to answer before scientists will be convinced that there really was an impact 12,900 years ago and that it really was responsible for a big change in the Earth's history. Richard Harris, NPR News.

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