What Killed the Dinosaurs ?

Listen to the argument between two scientists: Monica Grady and Mike Widdowson. They are discussing what killed the dinosaurs.

Transcript

Interviewer: Later in the programme we’ll be asking whether the Dow Jones Index is falling because of internal economic factors in America or because of conflict in the Middle East.

Now today’s weather. Well, it’s warmer than it was 20 000 years ago when we were in the middle of an ice age but colder than it was in the Jurassic Period when there wasn’t even any ice on the poles.

Top Topics

Yes, you’re listening to Top Topics here on 21st Century Radio. Our guests in the studio today are Dr Monica Grady of the Natural History Museum (now at the OU) and Dr Mike Widdowson of the Open University.

Dr Grady, simple question for today’s Top Topic – what killed the dinosaurs?

Monica Grady: A very large asteroid coming in very very fast.

Interviewer: How do you know that?

Monica Grady: How do we know that? We know because the asteroid made an enormous great big hole in the ground, it left sediment all over the Earth’s surface, it left its fingerprint that we can interpret.

Interviewer: And when did that happen?

Monica Grady: About 65 million years ago, plus or minus a Tuesday.

Interviewer: Well, there it is. Dr Widdowson, that’s very clear. An asteroid killed the dinosaurs. How can you argue with that?

Mike Widdowson: Because of 11 major extinctions in the last 300 million years. Seven of those coincide with some of the most massive eruptions you can possibly imagine.

Interviewer: So you think it was volcanoes?

Mike Widdowson: I think it was volcanoes.

Interviewer: Why do you think it wasn’t an asteroid?

Mike Widdowson: Because we only have evidence for one asteroid at one particular time coinciding with one mass extinction. There are seven others which coincide with these volcanic episodes. So I think the evidence is conclusive.

Interviewer: Dr Grady, conclusive evidence that it was volcanoes that killed the dinosaurs.

Monica Grady: No, it wasn’t. It was an asteroid. This asteroid left an enormous hole in the ground. As material was excavated from this hole it was thrown into the atmosphere. The atmosphere became dark and cold. But, before it became dark and cold, it had been very very hot. The energy from the asteroid was transferred into the atmosphere and it grilled the dinosaurs to death.

Interviewer: Well that’s very conclusive isn’t it, DrWiddowson? How did your volcanoes kill the dinosaurs then? Explain that.

Mike Widdowson: The size of the volcanoes that we’re talking about is absolutely colossal. They produced lava fields and these lava fields would take you about two hours in a fast jet to fly over. They are up to two kilometres thick and in that two kilometres you probably have hundreds and hundreds of flows. Each of those flows is capable of creating a major environmental disaster.

Interviewer: How?

Mike Widdowson: The way it operates is through the release of gas and of ash. The worst gas is sulfur dioxide which, when injected into the atmosphere, combines with water to produce acid. This falls as acid rain and imagine acid rain around the globe for year upon year upon year. Imagine what that would do to the ecosystems and to the animals which fed and survived on those ecosystems.

Interviewer: There you are Dr Grady, that must be conclusive. Acid rain poisoned these animals, not just when the dinosaurs were killed but in other extinction episodes.

Monica Grady: Yes, that’s quite right. Acid rain was very important. It was very important when the asteroid slammed into the Earth as well, because by an amazing coincidence the asteroid plummeted into sulfur-rich sediments. That sulfur was thrown into the air and, as Dr Widdowson said, combines with oxygen and rains out as sulfuric acid. But along with that, during the asteroid impact, the energy fused nitrogen and oxygen in the atmosphere which rains out as nitric acid so you get this extremely poisonous acid rain, a mixture of nitric and sulfuric acids, raining down over the planet along with the heat which ignited bush fires and wildfires so there were global wildfires going on as well.

Interviewer: So the asteroid impact was worse
in environmental terms than the volcano,
Dr Widdowson.

Mike Widdowson: Well, if this were a game of poker I would say we’re going to raise you one because, whilst the impact is an instantaneous event and the global wildfires and the spreading of the sediments and the impact waves, the effects of those may last a few years or decades. With a volcanic eruption such as we’re talking about, those eruptions are going to occur over periods of hundreds, thousands, possibly even millions of years so we’re getting a relentless input of gas and ash into the atmosphere time and time again which eventually drives any ecosystem or the survivors of any ecosystem virtually to extinction.

Interviewer: And you say this has happened not just to kill the dinosaurs but in other extinction events on the planet.

Mike Widdowson: The other very famous one is one which erupted on what we call the PT boundary with the Permian Triassic boundary about 250 million years ago and that produced the mother of all extinctions. Virtually everything on the planet was wiped out. Very few things survived that. There’s no evidence for a meteorite impact at that particular point in time but there is evidence for an absolutely colossal basalt eruption.

Interviewer: Is it possible that these could both be causes of extinction at different times? Could you both be right? Could these both be mechanisms for extinction?

Monica Grady: Yes, I think they could. There is no doubt whatsoever that there was an asteroid impact at the end of the Cretaceous. There seems to be no doubt that there wasn’t an asteroid impact at other times associated with other impacts. These things don’t have to be either/or. An extinction could be caused by one mechanism at one time and by another mechanism at another time.

Interviewer: Dr Widdowson?

Mike Widdowson: In the Deccan we have evidence for Monica’s impact actually preserved in between the lava flows so what we do know is that the volcanism began and was under way when this huge meteorite slammed into the Gulf of Mexico and that the volcanism continued after that event. So, if you like we may have a double whammy effect on opposite sides of the globe, almost unique and extremely potent in the way it might affect life on Earth.

Interviewer: Thank you very much Dr Widdowson and Dr Grady.

You’re listening to 21st Century Radio Top Topics where it’s time for our hot holiday hotspots. Looking today at the Bay of Naples and Yellowstone Park. What makes them such attractive holiday destinations . . .