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Researchers Point To The Demise of the Dinosaurs


This is SCIENCE FRIDAY. I'm Joe Palca.

You know the theory that a big collision, a comet or an asteroid, something like that, helped kill off the dinosaurs? The idea has been around for a while. But this week, new research published in the journal Science provides more accurate dates for the giant impact and the dino demise.

And, oh, by the way, if you're thinking about this, it's not going to be a problem. But next week, Ira is going to be talking about another asteroid. This is the 2012 DA14 that's making a close approach to Earth. So you don't have to worry. It's not going to kill us all off, but you want to listen next so you'll hear Ira and learn how we found this comet.

But there was another one that did hit Earth 66 million years ago, and the results show - so the question has been, did that - or how did that affect the dinosaurs' disappearing? And now there's a paper in Science that shows that these events, the asteroid or a comet hitting the Earth and the demise of the dinosaurs, were within 32,000 years of each other, which is just a blink of an eye when you're looking back at events 66 millions years ago.

Joining me now to talk about it is Paul Renne. He's a professor in the Department of Earth and Planetary Science at UC Berkeley and director of the Berkeley Geochronology Center. Welcome to the program.

PAUL RENNE: Thank you, Joe.

PALCA: So I want to be clear here. Are you saying - I mean, does this paper say now we know what killed off the dinosaurs?

RENNE: Well, yes and no.


PALCA: No, no, no. No fair. This isn't a congressional hearing. You have to...

RENNE: It's a really nuanced issue. And the question is, was there a single cause or were there a pattern of events that collectively did the job? And what our results show - and this, of course, is really just building on a theory that's existed for more than 30 years now. What our results strongly support is the idea that the impact of a large body, whose crater is found in the Yucatan Peninsula of Mexico, that that impact coincided to a very, very close proximity in time with the extinction. There were no dinosaurs that survived after that impact occurred. And many, many other creatures that are less photogenic and famous than dinosaurs went out as well. And so clearly, in our view, that was the final straw.

But there is evidence - and this has been overlooked by many people who have been interpreted our paper in various ways, surprisingly - that a lot of stressful conditions were occurring on Earth for something like a million or perhaps even two million years before this impact occurred. There is evidence that there were very rapid and very severe climate swings, temperature changes of up to, say, eight degrees centigrade over a very, very brief time intervals. That's a big change, changes in sea level and extinctions of dinosaurs and other animals, most notably on land, so mammals and dinosaurs both.

So these things were going on. And the extent to which these reflected global conditions or maybe only reflect local conditions in the areas where the fossil record is most complete, that's debated. But we think that there is sufficient evidence that climate deterioration or climate change was underway and that this really was just the final tipping point, if you like.

PALCA: If you have a question that you want to ask Paul Renne about this contemporaneous event 66 million years ago, give us a call. Our number is 800-989-8255, 1-800-989-TALK. So what is the need to refine this? Is there really - I mean is there still such a big debate about the relationship between the Chicxulub crater that this asteroid or comet caused and the dinosaur demise? I mean, what drew you to this topic?

RENNE: Well, I came at this topic for fairly esoteric reasons that have to do with calibrating our ability to date things in the geologic record.

And in so doing, I began to appreciate that - the existing data for this particular event, which is a nice sort of benchmark in the geologic record. We're inadequate really. And, in fact, the existing data, up until now, actually indicate that the impact and the extinctions were not synchronous. They're distinct within analytical uncertainties. They would appear to be separated by about 180,000 years. That is the extinctions appear, based on the existing radioisotope data, to have occurred 180,000 years before the impact.

Then on the other hand, there is a fairly small minority, I think, but still a fairly vocal one, of scientists that believe that the impact occurred 300,000 years before the extinctions. So with that level of discord in the community, it seemed appropriate to try and do a better job of dating both of these events, both the impact and the extinction and really lay those questions to rest.

PALCA: But to be clear, your data shows - which one does your data show came first?

RENNE: Well, I mean, the numbers are indistinguishable. So I would put absolutely no credence on our ability to tell which happened first. But let me see - and because they're so synchronous, I don't even really think of it that way.

PALCA: I see.


RENNE: I have to retrieve some distant memory cells here.

PALCA: That's OK. I didn't mean to put you on the spot. The point being here, that you're saying it's impossible, with available technology, to say whether it was before or after, and certainly not in so many hundreds of thousands of years.

RENNE: Right. We just can't tell them apart.

PALCA: All right. Well, let's see what our callers have to say about all this. And if I've done it properly, let's go to Daniel in Morristown, New Jersey. Daniel, are you snowed in yet?

DANIEL: Almost.

PALCA: OK. Well, I'm glad your phone is still working. What's your question?

DANIEL: Yeah. Well, I know - I was recently reading about the extinction of the mammoth species and that several, you know, subspecies survived far longer than we previously thought - you know, many tens of thousands of years longer in isolated regions. And I was wondering if there's - the same thing occurred with - during the dinosaur extinction, if there were any regions or isolated species that managed to survive longer, or vastly longer, than the general population of dinosaurs.

RENNE: Hi, Daniel. That's a really good question. And it sort of depends on how closely you look at the problem. Just to start off my answer, though, I would say that there is no credible evidence for any dinosaurs having survived past the level at which we can say, OK, here's where the record of the impact occurred. So it's a little layer of sediment that occurs all around the world, in the oceans and in many stratigraphic sequences on land, particularly in Montana where we've done our work. So you can really - you can put your finger on this layer, and that layer is characterized by high concentration of iridium and things like shocked quartz and other features that are really symptomatic of an impact. And nobody has ever found a dinosaur that was clearly alive after that time or above that level.

There have been some claims of dinosaur bones having been found above this level. And in every case that I'm aware of, those bones were what we would call reworked from lower levels. So they've been eroded from somewhere else and transported by streams and such, and end up appearing to be above the layer and hence, younger. But in all cases I'm aware of, you can show pretty easily that that's what happened.

But, you know, it's a really intriguing question. Did - how synchronous was the extinction of dinosaurs? Can we ever hope - and we certainly can't do this right now - but can we ever hope to be able to pin it down to a matter of, say, months? And this would - this would be a huge breakthrough because the ability of various animals at different trophic levels to find refuge or to survive certain types of effects is quite amazing. And it would be surprising to me if in one afternoon, an entire group of animals was wiped out. But we don't really have the clarity of tools to be able to answer that question.

PALCA: Daniel, thanks very much for that question.

DANIEL: Thank you. It was very interesting.

PALCA: OK. You know, that actually makes me wonder, though, Paul Renne, can you imagine those tools becoming available? Because, you know, it seems to me, 30 years ago, people would've said, we'll never be able to see a planet going around a distant star. That's way too far off. And now they can do that or they can infer their existence anyway. So what do you think?

RENNE: Yeah. No. And we always have this tendency to think that, you know, technology is not going to advance much beyond where we are today. I'm an optimist. I'd like to think that we could do that at some point. I think that it will require methods that are fundamentally different than what we have available today. In other words, it won't be using the same kinds of equipment that we have been using but just slightly better and more improved versions of those. It's going to require something completely different. And I can't conceive of what it's going to be. If I could, I'd be...


PALCA: Yes, I know exactly. It's like predicting the stock market. If you did that, you wouldn't be talking to me.

RENNE: Oh, sure, I would.

PALCA: Well, thank you very much for that. Let's take another call now and go to Barney, Barney in Kenner, Louisiana. Welcome to SCIENCE FRIDAY. You're on the air.

BARNEY: OK, thanks. I have a simple question. It's sort of like the last one. I'm just curious how come some creatures did survive, like turtles and alligators and things like that, and the dinosaurs got wipe out. But those creatures seemed to manage and they're still around today?

RENNE: Hi, Barney. That's a good question. I'm going to have to start off by pleading the fact that I am not paleontologist, and the specific resistance that different types of animals have to various environmental stresses is not really something I'm an expert in. I'm a geologist. And from what I understand from my colleagues who more knowledgeable than I, there was a huge variation in sort of survivability. And as - obviously know something about this. It seems to have something to do with - as far as I know, with which animals were adapted to living in relatively wet environments. So turtles and other aquatic vertebrates seemed to do better. And why that it is, I really - I don't know. I have to just tell you honestly.

PALCA: OK. Barney, you stumped our guest. Thank you for doing that. Appreciate it. We're talking with Paul Renne about the dating of the extinction of the dinosaurs. I'm Joe Palca and this is SCIENCE FRIDAY from NPR.

So the tools that you do have, have - you've now gotten this, I think, I read 32,000 years plus or minus. I mean, first of all, can you - you can't really squeeze anything more out of that. But are there are other timing issues that your techniques could be applied to that would be useful to know the answers for?

RENNE: Oh, sure. Yeah. The - and actually, just to go back, we can actually squeeze more out of this particular scenario. And it would be useful to that, I think, at some point. It takes incrementally more and more work, more time, more analysis to do a little bit better. So at this point, we don't really have a lot of pressure to push the precision too much on this topic, but we could, if we really wanted to. So there are other extinctions in the geologic record and, for example, at the end of the Paleozoic Era, the so-called Permo-Triassic boundary, which was actually the largest, most profound extinction that we know of in the history of life. That happened about 252 million years ago.

And it is associated with a very large - what we call flood basalt problems, of huge outpouring of magma that happened in Siberia, at, as far as we know, exactly the time, same time. So when I say as far as we know, what do I mean by that? Well, right now, you know, we're talking about a level of synchrony that set about the 100,000-year or maybe 50,000-year level. And it would be nice to be able to refine that a little bit. So one of the things you want to know is if, in fact, volcanism - and we think this is a factor at the end Cretaceous as well. We think volcanism is very likely to have been a factor in the earlier pre-impact environmental stresses.

So it would be nice to how long it takes for volcanism to generate gases that modify climate that actually start to have effects on the environment. And that's - those are the kinds of questions that we could be in a better position to address, if we can date things more precisely.

PALCA: Is there anyway from your data, to tell when the climate in this particular event began to stabilize or is that something that's different data set all together?

RENNE: No. Our exact, same type of data can address that, and that's really where we're headed now. We would hope to start to be able to sequence events that are manifesting in the deep ocean records, for example, with what we see on land. And there are some indirect ways bring those two records together on a uniform timescale. It requires calibrating when magnetic reversals occurred and calibrating the record of climate changes that are forced by Earth's orbital rhythms. And if we can bring all those things together and get them to be reading the same scale, we do have the possibility of really understanding these climate changes and their possible driving forces in much more detail.

PALCA: That's great. Well, we'll look forward to the next set of results and thank you very much for joining us today, Paul Renne.

RENNE: It's been my pleasure, Joe.

PALCA: Paul Renne is a professor in the Department of Earth and Planetary Science at UC Berkeley and director of the Berkeley Geochronology Center. Transcript provided by NPR, Copyright NPR.