Paleobotanist discusses extinction of dinosaurs

Sunday, March 13, 2011

Paleobotanist Kirk Johnson is co-author of a recent study concluding that dinosaurs went extinct after an asteroid crashed into Mexico 65.5 million years ago, blowing debris around the world, knocking down forests and causing tsunamis and earthquakes.

It is a hypothesis that first emerged in 1980 and got some confirmation in 1990 when researchers discovered the 120-mile-wide Chicxulub crater in Mexico. But the new study, published in the journal Science in March, is much more definitive, put together by 41 scientists using past studies of Chicxulub, fossil records and analyses of debris embedded in a finger-thin rocky layer of the Earth to bolster the asteroid explanation.

Johnson isn't a dinosaur expert. His focus is plant fossils from the period before and after the asteroid impact, particularly those found in that finger-thin layer, known as the K-T boundary. He has dug up fossils all over the world, including in the American West, Mongolia, India, the Amazon, Alaska's Bering Sea and the rainforests of New Zealand.

In a recent interview, Johnson spoke by phone at the Denver Museum of Nature & Science, where he is chief curator and vice president of research and collections, about how one becomes an expert in 65.5-million-year-old plant life.

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