Impact! Tracking Near-Earth Asteroids

AMNH Scientist Interview: Denton Ebel

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A 3-D geophysical map of the now-buried Chicxulub Crater. The white line is the shoreline between the Yucatan Peninsula and the Gulf of Mexico.

V.L. Sharpton, LPI

But the bigger dinosaurs were toast.

Nothing that big survived as far as we know. Some people say nothing bigger than a killer whale survived. Others say nothing bigger than a breadbox! We see evidence of the heat pulse in the sediment layers—soot particles and burned pollen mixed with the spherules.

Literally dinosaur toast. So where does your research come in?

What we did was calculate, for the first time, what the identity and composition of the material condensing from the plume theoretically should have been. And the evidence we have on Earth [the spherules] happens to match our calculations. Also, other scientists thought since spherules were dispersed globally 65 million years ago, their origin must have been many meteorites entering Earth’s atmosphere around the same time. We said, no, you don’t have to invent these hypothetical meteorites, you can get all the global spherules from just one impact instead, one plume which was carried around the world through the stratosphere. And we have the crater to prove it.

What about competing dinosaur extinction theories?

Well, some people think that intense volcanism in India 66 million years ago may have caused global climate change that contributed to the dinosaurs’ extinction. Those eruptions were very slowly oozing out of fissures in the ground and spreading out over large areas. But nothing was shooting high into the air, let alone into the stratosphere. Such oozing volcanoes can cause greenhouse warming in the lower atmosphere, which can raise global temperature over a long period of time. But there's no evidence that that would cause a mass extinction. My research only adds details to the impact that were not there before.

What’s the likelihood of another asteroid as big as Chicxulub happening again?

Every hundred million years is tossed around. The problem with big impacts is that we don’t really know, because these are unique events of which we have very little record. Most asteroid-impact craters get erased over time by erosion, deposition, and/or plate tectonics. Still, the probability is extremely low. And scientists have identified most of the dangerous ones. Put it this way: the probability of someone throwing a meteorite at you is greater than the possibility of you getting hit by one from space.