美国国家公共电台 NPR Asteroid Impact That Wiped Out The Dinosaurs Also Caused Abrupt Global Warming

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ARI SHAPIRO, HOST:

A giant asteroid¹ slammed into Earth about 65 million years ago. That impact killed off the dinosaurs². And now scientists say it had another major effect on the planet, one that's a cautionary tale. Here's NPR's Nell Greenfieldboyce.

NELL GREENFIELDBOYCE, BYLINE³: The so-called Chicxulub asteroid was more than 5 miles wide. When it crashed into our planet, there was chaos⁴.

PAGE QUINTON: You had a huge asteroid hitting the ocean at high speed. That's going to cause tsunamis⁵.

GREENFIELDBOYCE: Page Quinton is a geologist⁶ at the State University of New York in Potsdam. She says the impact also set off massive wildfires and created a global cloud of dust and debris⁷ that blocked the sun for months or decades.

QUINTON: So on the short term, there's a variety of very, like, quick, scary stuff going down. And the dinosaurs of course, you know, feel that impact.

GREENFIELDBOYCE: What she and some colleagues wanted to know was the long-term impact from carbon dioxide. Carbon dioxide, as we all know, is a greenhouse gas, and a lot of it was released by those fires and vaporized rock. Ken⁸ MacLeod is a paleontologist at the University of Missouri. He turned to an unusual place to find a record of past temperatures - tiny bits of fossilized fish so tiny they can look like sand or crud.

KEN MACLEOD: But under the microscope, they are unequivocally fish fossils. So there are these millimeter-, half-millimeter-long little teeth, and under the microscope, they're gorgeous. There are little scales or bits of bone.

GREENFIELDBOYCE: It turns out that their chemistry is different depending on the temperatures when they lived. He and Quinton analyzed⁹ fossils from before and after the asteroid impact, and what they found is striking. After the impact, global temperatures rose by about 5 degrees Celsius¹⁰.

MACLEOD: And then it stays at that level for an interval¹¹ that spans a hundred thousand years.

GREENFIELDBOYCE: He sees a lesson here that's relevant for today.

MACLEOD: The carbon dioxide that was put into the atmosphere after the impact was probably introduced on the time scale of years to decades, which is pretty comparable to the timescale on which we're introducing CO2.

GREENFIELDBOYCE: By burning fossil fuels. He's not the only one to make this connection. Brian Huber is a paleontologist at the Smithsonian's National Museum of Natural History.

BRIAN HUBER: We are basically replaying that instantaneous event.

GREENFIELDBOYCE: He says how long the warming persisted was stunning¹², and that's why he found these results in the journal Science a little bit frightening. Nell Greenfieldboyce, NPR News.