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Study Reasserts That Asteroid Blast Wiped Out the Dinosaurs

About 65 million years ago, a huge asteroid traveling 20 times faster than a bullet crashed into Mexico’s Yucatan peninsula, sending up projectile debris with such force that the debris rained back down as far away as New Zealand. The impact caused massive earthquakes, tidal waves, fires and a months-long global blackout — and eventually killed off the dinosaurs, along with half the other species on the planet.

That dramatic story was first advanced 30 years ago and got a boost in 1991, when researchers discovered the 10-kilometer Chicxulub crater in Mexico that looked as if it might be the asteroid’s landing site. It has slowly gained recognition among geologists to become the most generally accepted reason for dinosaurs’ demise.

But it’s remained controversial, with some scientists continuing to offer other explanations for the global die-off, including massive volcanoes in an area of India called the Deccan Traps, or a series of smaller asteroid impacts.

Now the single-impact theory has a new endorsement. A study to be published Friday in the journal Science, which was co-authored by 41 geologists, paleontologists and other scientists — what one co-author called a research “dream team” — reviewed 20 years of studies from sites around the world and concluded that the Chicxulub explanation fits the evidence best.

The researchers say that a layer of debris from the asteroid impact can be found at sites around the world, exactly at the boundary in the fossil record at which the dinosaurs and many other species disappeared. They can identify the debris because it contains a lot of Iridium, an element that’s rare on Earth but common in asteroids. The debris layer is thicker and more churned up closer to the impact site — deposits up to 80 meters thick have been found in parts of nearby Central America. Thousands of miles away, the layer is only a few centimeters thick.

“It’s quite a complicated story, but the answer’s quite simple and that is that the Chicxulub crater really is the culprit. We have very good evidence that fingerprints that debris right back to the Chicxulub crater,” co-author Kirk Johnson of the Denver Museum of Nature and Science told reporters.

But not all scientists are convinced.

The new study is “a rather selective summary of data and interpretations over the past 10 years […] There is no new information here whatsoever,” Princeton geologist Gerta Keller, a longtime proponent of the theory that the Deccan Traps volcanoes caused the extinction, told media organizations.

But the researchers in the new study contend that although the volcanoes were active for about 1.5 million years around the time of the extinction, there were only minor changes in the fossil record for about 500,000 years of that time, and then an abrupt change at the time of the asteroid impact.

Editor’s Note: An image posted with an earlier version of this article displayed a Woolly Mammoth skeleton, which does not apply to this study. The image has since been replaced.

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