What killed the dinosaurs?

Geological findings indicate that 66 million years ago, an asteroid hit the earth in an impact so strong that it lead to the extinction of the dinosaurs. Now, researchers are studying the asteroid’s landing site off the coast of  Mexico, in search of clues about how life recovered after the impact.


Geological findings indicate that 66 millions years ago, an asteroid hit the Earth in an impact so strong that it led to the extinction of the dinosaurs.

Now researchers are studying the asteroid's landing site off the coast of Mexico in search of clues of how life recovered after.

Reporter Andrea Vasquez has the interview via Google Hangout.

Sean Gulick, thanks for joining us.

My pleasure.

Can you explain what would have happened during the event when the asteroid hit the Earth, and how that created what you're looking at today?


So, 66 million years ago, a 14-kilometer-wide -- at least that's what we think -- asteroid, a rocky asteroid, struck the Earth at about 20 kilometers per second -- so, incredibly high velocity -- creating a very large impact structure.

And we know something about how these structures are formed, but only primarily from models.

And so what we're interested in doing is collecting the rocks within the crater to actually calibrate those models, and tell us if this is in fact how they work.

And, specifically, when it hits, it's much like a rock hitting a pond.

So, if you throw a rock into a pond, it kind of opens up a hole, which then maybe splashes back upwards and collapses outwards as the sides collapse in, creating kid of a wide, flat crater from an initial kind of deep, narrow crater.

And so that's what we think happened beneath the Yucatán Peninsula.

And the peak ring is specifically important in your research, isn't it?

Can you explain what a peak ring is and why it's so important?


So, it turns out that impact craters have sort of a set of forms, if you will, land shapes that are common at certain size ranges.

So, when we hit the largest class of impact craters, we start to see features in the center of impacts like rings of mountains, which we call a topographic peak ring, that we think are the rocks that would have been brought up from the deepest levels within the target -- inside the Earth in this case.

Brought upwards above the Earth's surface and collapsed outwards to form this ring of mountains.

And if so, it would tell us that our idea that targets being hit by impacts temporarily behave like a fluid, with this incredible amount of material coming from deep and being resurfaced onto the planet's surface, is the correct way to think about the problem.

And so the peak ring is the best place to test that idea.

Does this crash site at Chicxulub resemble the landing site or crash site of other smaller craters and asteroids that have hit the Earth?

So, there's two ways to answer that question.

One is that -- are the target rocks different here?

And it turns out the target rocks in the Yucatán Peninsula are different in the fact that they're largely limestones, largely carbonates, but also a large amount of evaporated ocean sediments.

We call them evaporites.

It turns out that those rocks may be really important from the standpoint of the mass-extinction even that followed.

But in addition, it's actually basically a crustal location, so we're looking at deep rocks that are probably granites.

And so what we were hoping to test would be, if we drilled the peak ring, would we see uplifted deep rocks -- i.e., would we see granites -- or would we see something that came in very shallow -- i.e., would we see limestones -- within the peak ring?

But as far as the impact site in general, it has all of the normal crater shape and all of the normal landforms that we see not just on Earth, but on every large impact on the moon, on Mercury, on Mars.

It doesn't matter.

It appears that if you have a big enough impact, you create the same sort of features.

You create this basin with this ring of mountains in the center, and melt sheets inside that.

And, so, to test how impacts work across the solar system, we can do so by drilling in the Yucatán Peninsula.

And what are you looking to find out about the event that actually led to the extinction of the dinosaurs and what happened thereafter?

We have a lot of people who attempt to understand processes by getting the right physics into their computer models and then running these models until they match our observations.

And right now, our observations have been largely geometry.

What's the shape of the crater?

How deep is it?

Things like that.

But not specifically 'What are the rocks that make up key features within the crater, like the peak ring?'

And, so, to understand those processes, we kind of need to understand the amount of energy involved.

And if we can find that our models are correct, then we can say, 'This is in fact how much energy we think was released by this impact.'

I mean, our initial estimates are that it's an enormous amount of energy, something like 100 million atomic bombs worth of energy in a single event.


So, you know, much larger than any earthquake or any volcanic eruption that we're normally used to thinking about.

As far as why that's an extinction event, well, then we also need to use these models to understand how much of the volatiles, how much of the material that you can combine with the atmosphere or with the ocean are released.

And that again comes back to understanding the fundamental process of how impacts work.

So, if we have a lot of these evaporites -- ocean sediments, for instance -- or evaporated ocean -- there might be a lot of sulfur.

And, so, that, for instance, if it all gets vaporized and all put into the atmosphere, it combines with the atmosphere to become aerosols, which is a great way to help block the sun, along with the dust, for instance.

And that is ultimately what scientists think led to an ice age that led to the extinction of the dinosaurs?

The initial effects of everything raining back down to Earth might have created a heating phenomenon around the globe -- scattered wildfires and raising temperatures locally.

That could have actually caused a lot of extinctions.

But perhaps not enough to kill everything off, or to entirely take away even any one given species.

So, instead, we think the long-term effects are actually potentially more important, where all of the dust, the aerosols in the atmosphere, could have, as you said, caused a cooling event afterwards, but also potentially chemical changes.

So we could expect that a lot of the material getting into the oceans could have caused ocean acidification -- you know, a changing of the pH -- maybe even metal poisoning.

So, there's a lot of ideas, but we do think that if you add them all up and you make it global, it seems like something like 75% of life went extinct because of this event.

Well, we can't wait to see what else you find from this investigation.

Well, thank you.

Thanks for being with us.

Our pleasure.