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Dr. David Morrison, Senior Scientist, NASA Astrobiology Institute

Dr. Morrison: Yes, certainly. I question your statement that there’s been much debate recently within the scientific community. There has been publicity given by journalists to a tiny minority – a fringe group basically – who seem to be holding out against this, and that’s to be expected. In science it’s rare that everybody gets on board when there is a real revolution in our perspective. But there is not a serious debate within the scientific community about the impact origin of the end-Cretaceous mass extinction

NTB: Can you elaborate on the evidence that exists that it was an asteroid that killed off the dinosaurs?

Dr. Morrison: The evidence is overwhelming that an impact was the cause, but we don’t know if it was a comet or an asteroid.

First, there was a mass extinction, indicating a sudden, catastrophic change in the climate of the earth. The paleontological evidence shows that it was quicker than one can resolve by looking at the geological data. Whether that means the extinction took place in a hundred-thousand years, ten-thousand years, or an afternoon is not clear, but it certainly took place in much less than a million years.

Second, we know there was a very large impact at that time because we have the crater – the Chixulub Crater in the Yucatan – which is well-documented. And more to the point, we have the ejecta that was dug out by that crater and distributed over the whole world. It’s a layer that is global in extent, and which contains the key chemical signatures of extraterrestrial material, as well as minerals generated by the shock of a violent explosion. That’s how we know it was something coming from the outside and not something volcanic, for instance.

NTB: I understand you have an asteroid named in your honor. How did that come about?

Dr. Morrison: Lots of scientists have asteroids named in their honor, believe it or not, because we’ve discovered so many asteroids. Unlike most discoveries in astronomy, the discoverer gets to name the asteroid. So some people who have made lots of discoveries have had an opportunity to name some of these for their scientific colleagues.

NTB: There was a 1-in-75 chance this year that a 164-foot long asteroid called 2007WD5, traveling at 30,000 miles per hour, could have plowed into the planet Mars. Had that actually occurred, what would’ve happened?

Dr. Morrison: That impact probability, at one point, was as high as 4 percent. 1-in-25. The probability, of course, is an expression of our uncertainty about the orbit. It’s not as though the orbit itself is flopping around; it’s just the degree to which we understand it. It’s only in Hollywood that asteroids capriciously change orbit.