Cracking open a 66-million-year-old cold case: drilling for clues in the Chicxulub impact crater

UAlberta scientists part of team to investigate impact site left from asteroid linked to mass extinction event that killed dinosaurs


Formed around 66 million years ago when a large asteroid hit the Earth, the Chicxulub impact structure is infamous for its link to the end-Cretaceous mass extinction—believed to have played a major role in the demise of the dinosaurs. Located underneath the Yucatán Peninsula, it is the best-preserved large impact crater on Earth.

Physics professor and Canada Research Chair in Rock Physics Doug Schmitt is currently stationed at the Chicxulub impact crater. We caught up with him to ask a few questions about the study and his involvement.

Hi Doug! Where are you right now?

We’re on standby and staying in a house in Mérida, Yucatán, which actually lies within the huge structure. There’s not very much room on the lift-boat platform ‘Myrtle’ that supports the drilling rig so they don’t really want people staying out there. It’s about an hour's boat ride out to the platform from the port of Progreso.

How long have you been there?

I left Edmonton on April 6, but I didn’t arrive here in Mexico until April 9 because I had to go for marine personal survival training in Louisiana that included getting out of a simulated helicopter crash into the ocean. We have already had two sets of seismic measurements on the rig: the first set on April 10 and 11 and the second set just this last Monday [May 2]. We are very excited about the data so far, as the quality is excellent. Now we’re just waiting to go out again once the drilling reaches the next break point.  

Who is “we?”

The seismic team consists of research professional Randy Kofman, graduate student Chris Nixon, and myself from the U of Alberta. We are also working closely with colleagues Sean Gulick and Steffen Saustrup from the U of Texas, Austin and Joanna Morgan from Imperial College, London. Sean and Jo are the ‘chief scientists’ for the project.


Who else is down there, and what specifically are you looking for?

Well it’s a pretty big project. There are two major organizations involved: IODP (International Ocean Discovery Program) and the ICDP (International Continental Scientific Drilling Program). The project is managed through ECORD (European Consortium for Ocean Research Drilling). They’re sponsoring this in part, with a lot of funds coming from other places as well.

We’re here for a lot of reasons, but the main thrust is actually to drill into a part of the impact structure of the Chixculub crater called the “peak ring.”

What’s a peak ring, and why is it so scientifically important?

If you’ve seen pictures of very large craters on the moon, (one example is the Schrödinger crater) you may have seen that they have a ring of mountains surrounding the centre. We actually do not know how those mountains are formed or what they consist of. There are many computer models that try to predict this but no one knows for sure. So, if we can find out what is in the peak ring it can give us some hard data on how these large craters (or impact basins) form. We are very interested in seeing what kinds of rocks are in the peak ring. Are they limestones from near the surface or hard metamorphic rocks from deep in the earth’s crust?

Another main motivation is to look at what happens right after the impact. You are going to have a lot of heat remaining after the impact, so it will be interesting to see if the biologists and geologists on the team can say something about how long it takes life to come back and, when it does, what kind of life recolonizes the structure. Hot water likes to move and so it will be important to put some constraints on the hydrology of the system. Part of that is even studying the rocks above the impact, because that will tell us a lot about the earth’s climate in the period following the impact.

“A major part of this is basic science—trying to understand what happened at the time as the impact structure formed.”

‘Pieces’ from the impact can be found all over the Earth at the Cretaceous-Paleogene boundary that is associated with mass extinctions of many kinds of life forms, but most popularly the dinosaurs. You can actually see this boundary in Alberta—there are places near Drumheller, for example, where Cretaceous-Paleogene boundary outcrops in the valley of the Red Deer River. The signature of the impact appears in sediments all around the world. This project, however, is right at the impact—and can tell us something about what happened there.

You mentioned this is really the only place on Earth we can study a peak ring. Why is that? Were there others that just eroded over time?

Yeah, that’s basically it. In some sense, this crater is fairly young, and it’s been buried by ocean sediments, so it’s relatively well preserved. There have been other big impacts, like the Sudbury Basin, but it’s been eroded away and metamorphically changed. This is the only place that we know of where there is a crater big enough on the Earth to have a peak ring. The others we know of—well, we can see them out on the moon or the planets, but unfortunately, we can’t go drill there yet.

It sounds like the fact that the crater is underwater played a factor in preserving it.

Yes, I think being in the ocean helped. People knew about this Cretaceous-Paleogene layer (still called the Cretaceous-Tertiary or K-T boundary) long before anyone knew where the source crater might be. Most people thought that if the impactor came down in the oceans the odds are it would be gone now—disappeared because of plate tectonics. But it turned out that it came down in a very stable part of the Earth’s crust, with nice sedimentation settling on top of it in that intervening period up until the present day—so basically it’s been nicely buried.

So does that mean it would have been underwater at the time of impact, as well?

We know that it was probably underwater because if you go out to many locations around the Gulf of Mexico and the Caribbean you can see what are called tsunami deposits, actually quite massive ones. These show that the Chicxulub impact created this massive wave—a massive tsunami. That shows that it had to have come down in the ocean at the time in a situation likely similar to what it is today.

Why is this trip such a big deal?

This has a long time in development—10 to 15 years. There has been a lot of geophysical work, and a lot of seismic work in particular, done to try to outline the structure. For a number of reasons it is much easier and better to collect seismic data out in the water. As a result, we have a much better picture of what the structure looks like there than would be possible on land. So although this isn’t the first drilling that’s been done here, it’s probably the one that’s the most justified scientifically in terms of where the actual drilling should be placed.

Certainly it looks like it has been the one most in the public eye, before your crew has really even got started. Why do you think has this has captured so much international attention?

I think it’s because everyone’s heard about the impact that killed the dinosaurs. That catches everyone’s imagination. We’ve all seen those pictures of a big object coming in, with the dinosaurs looking up. (It probably wasn’t anything like that. The actual impactor was probably about 10 kilometres in diameter and as such was larger than the thicker parts of the atmosphere, so there wouldn’t have been a fireball coming in).

But that, I think, really captures the public interest—and actually kind of overrides the science. A lot of other things happened as a result of this impact, not just the dinosaur extinction. There were many other extinctions, and things that happened to the Earth’s environment that we don’t understand.

For example, part of the reason for the drilling—a more subsidiary reason—is maybe we can find out how much CO2 and how much nasty sulfate was put into the atmosphere by looking at the rocks. These are things we haven’t been able to examine before; people have been making guesses as to how severe this might have been because there were no solid constraints on how much material went into the atmosphere.

Regarding the U of A’s involvement, what is your team specifically looking for and how did you get involved in the project?

Well, my team has probably actually been involved with as many scientific drilling projects as anyone on the planet, so we have a lot of expertise in that area. We are able to bring a component that’s kind of rare in academia.

We are carrying out borehole seismic measurements at Chicxulub. Already a great deal of surface seismic data has been collected that has been used to image the structure. However, the only way to calibrate such images is to measure directly in a borehole the time it takes a seismic wave to travel to depth. Another reason to do this is that we get a very good idea of how fast the seismic waves travel, and this can tell us a lot about the structure of the rock itself. The measurements consist of placing seismic receivers at different depths along the borehole and using them to record the seismic waves produced at the surface. We can then help calibrate that data and we can look at the physical properties of the rocks with that.

It’s a big team. We’re working really closely with people at the University of Texas at Austin—they provide the seismic source and we provide the borehole seismic equipment. We also work closely with the geophysical logging group from France. The two PIs are from U of Texas and from Imperial College, so really it’s a team effort. It’s not just us.

It sounds like you are working with some heavy hitters. What is it about the U of A that makes us such a strong partner for this kind of collaboration?

I think it’s just that we’ve built up the unique set of expertise, and because of this we are asked to participate in many scientific drilling projects around the world. This year was very busy with projects in Sudbury, Estevan, New Zealand and here in Chicxulub.

In geophysics, the number of groups that actually go out to collect data in the field is diminishing, and we’re one of the few groups left standing in academic circles who can carry out borehole measurements. We have great support in the physics department in terms of the shops and the technical support. Without out that it would not have been possible to build up this experience.

What do you expect will be the biggest takeaway from this for the broader public?

One, it may help us understand what happens after a big environmental disruption to the whole planet. The impact even may provide something of an analogy because it essentially dumped a lot of material, including carbon, into the Earth’s atmosphere—so studying Chicxulub may provide for us some insight and constraints into what might be happening down the road for us.

“A major part of this is basic science—trying to understand what happened at the time as the impact structure formed.”

There are some practical things, too. In Alberta and other places, there are impact structures that are actually good oil reservoirs because the rock is highly fractured and faulted. The Sudbury mining industry, too, owes its existence to that large impact as hot mineral saturated waters that circulated after the impact formed the massive mineral deposits there. The Chicxulub impact may be able to provide us more insights into how such deposits formed. So those are some of the more resource-based questions.

And then, of course, people love dinosaurs.

How long will you be down there?

Well, we have two limits. One is money and the other is hurricane season. The reason we’re here right now—perhaps not the nicest time of the year, because it’s very hot—is that we’re trying to catch this window where the weather is quite good before the hurricanes come.

The original plan was that we would here basically for two months, most of it on standby waiting for the call to go out. As before, we have been out now twice and now we’ll probably wait until the very end of the current round—the end of May or the first week of June—to do the final measurements, and then we’re done. The hard thing is that we have to be on call. It’s not easy to get here from Edmonton on short notice, so I will be staying here in Merida instead of flying back and forth from Edmonton.

The drilling happens in stages. Right now, there are predicted dates for when a certain stage will finish, but those are just predictions. Scientific drilling is by its very nature highly exploratory and unpredictable. Those who drilled in Alberta in the 1940s and '50’s when little was known about the geology under our feet probably experienced the same excitement.

Scientific drilling isn’t for the faint-hearted. There are many risks, and there’s a lot of things that could go wrong—you just have to roll with the punches. But this is balanced by the rewards of obtaining completely new and often unexpected scientific results, and of being involved in a highly collaborative and supportive community of researchers.

On May 12, ask the scientists drilling at the Chicxulub anything you like about the expedition on Reddit. Link to Reddit AMA (May 12).