What wiped out the dinosaurs?

07 November 2017

Interview with

Professor Joanna Morgan, Imperial College London

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66 million years ago, a meteor collided with Earth and the aftermath was catastrophic: for a start, it wiped out the dinosaurs. Now, thanks to a new model of the event, scientists have a much clearer idea of how the climate conditions changed afterwards. Izzie Clarke heard what happened from the author of the study, Joanna Morgan…

Joanna - When it hit the Earth’s surface it pushed it down about 30 kilometres, making this enormous hole that was 100 kilometres wide and 30 kilometres deep, and that took only about a minute. And then it took about another nine minutes to collapse into it’s current crater; that’s 200 kilometres wide and a kilometre deep. It hit in Mexico; it hit what’s currently the Yucatan Peninsula. It was a particularly bad place; at that location there were sediments that were full of carbon and sulphur and those were ejected into our Earth’s atmosphere and that’s what caused some of the rapid climate change immediately after impact.

Izzie - What effect did that have at the time?

Joanna - Sulphur is quite bad for us. Sulphur forms an aerosol and that reflects sunlight  so what we can when we use what we call global climate models, is that sulphur injection into the atmosphere led to global cooling of more than 25 degrees centigrade for about a year. Actually, we had sub-freezing temperatures for 3 to 16 years after this impact.

Izzie - This happened 66 million years ago, so how on earth are you able to work all of this out?

Joanna - In terms of the climatic gases, we can run numerical simulations. When the asteroid hits we can simulate that, and the passage of a shock wave travelling through the rocks leads to this degassing, so that’s how we make our calculations of the sulphur. Then, what happens immediately afterwards, we can look at what’s called the fossil record, so the sediments that filled the crater after impact. We can look at the little tiny fossils and the chemistry of those layers to tell us about things like temperatures post-impact, and how life came back to the impact site.

Izzie - What effect did this have on the animals and plants on the planet?

Joanna - We had both global cooling and global blackout of light for at least three years. That seems to very dramatically affect the photosynthesising plants, both in the ocean and the marine world. We had something like 90% of the photosynthetic plankton at the top of the oceans going extinct so that had an affect on everything. So everything that feeds off that would have been affected by the loss of these primary producers.

Izzie - Is that what led to the extinction of the dinosaurs?

Joanna - We think so. This was the most dramatic effect that could have been global; that’s correct. Closer to the impact site you can see that there would have been more wildfires and there would have been a large pulse of radiation from the expanding plume, a little bit like a nuclear explosion. So, closer to the impact site, other things could have caused the death.

Izzier - Gosh! That doesn’t sound like a pleasant environment to be in. How sure are we that this is what wiped out the dinosaurs, because some have argued that volcanoes also played a large role?

Joanna - That’s true. We can see the extinction of the small things like the plankton I was just talking about, that happened exactly coincident with the impact. So you get the impact ejector in a layer all around the globe and that’s when the extinction of those small things occurred.

For dinosaurs it’s more difficult because the bones are bigger and there’s less fossils. But you have to say that, given it caused the catastrophe of the primary producers, it seems very likely that it also caused the death of the dinosaurs. Having said that, there were volcanic eruptions going on for quite a long time and they may have made things more ready for extinction, as in things might have been quite stressed already.

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