Science Interviews

Interview

Mon, 15th Dec 2014

The mass-extinction before the dinosaurs

Professor Paul Wignall, Leeds University

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An asteroid was at least partly to blame for the dinosaursí demise, but are giant rocks from space the only things that have threatened to wipe life off the face of the Earth? Before the dinosaurs ever existed, there was a time when the planet was teeming with strange creatures in both the sea and on land, until disaster struck and all life nearly died.Permian life at Sea

Paul Wignall from University of Leeds here with us live to tell us about the biggest mass-extinction in the history of life on Earth...

Ginny -   So, an asteroid was at least partly to blame for the dinosaurís demise, but are giant rocks from space the only things that have threatened to wipe life off the face of the Earth?  Before the dinosaurs even existed, there was a time when the planet was teaming with strange creatures in both the sea and on land until disaster struck and nearly, all of life died.  Paul Wignall from the University of Leeds joins us to tell us about the biggest mass extinction in the history of life on Earth.  So Paul, how big are we talking here?

Paul -   The biggest of all time as you said.  So, weíre looking in full time when there was about 90% of all species, animals and plants disappeared.

Ginny -   That's a huge proportion but do we have any idea of exactly how many creatures that would be?

Paul -   Itís difficult to say, but weíre probably of the order of millions and numbers of species would be millions as well.

Ginny -   When exactly did this happen?

Paul -   I had what we call the end of the Permian period and that's 252 million years ago.  So, a long time ago.

Ginny -   That's quite early in the sort of history of life.  I imagine, the world wouldíve looked very different back then.  What kind of creatures were there around?

Paul -   Yes, it was indeed a long time ago.  The animals on land would look rather sort primitive to us today.  So, rather sort of lumbering, sort of creatures, sort of premature reptiles and a group known as the therapsids which have gone on to give rise to the mammals.  But back in those days, there were rather sort of sprawling sort of posture.

Ginny -   What about plants?  Would the plants have been very different?

Paul -   Not quite as different.  There were no sort of familiar flowering plants that we now, but then there were conifers, fur trees, and ferns and things like that were present then.

Ginny -   And in the sea, were things similar, where there are weird creatures there as well?

Paul -   Again in the sea, there are some groups which have now long gone like the trilobites which were familiar with fossils but they are no longer with us.  Although groups like fish and molluscs and things like the brachiopods which are a group of little shell fish and so on, they were present and common in the sea then.  So, some of them, we still have with us and others disappeared.  Some of them disappear at this mass extinction.

Ginny -   And trilobites, those ones that look like kind of giant wood lice arenít they?

Paul -   That's right, yeah, like little sea wood lice.

Ginny -   So, it wouldíve looked quite different in some ways, but quite similar in others?

Paul -   That's right.  Some of the modern looking fish werenít around at that time and there are clams as well, modern clams hadnít arisen.  But in other ways, it wouldn't be as quite as strange as life on land wouldíve looked.

Ginny -   So, what happened to all these amazing creatures?  Why did they die out?

Paul -   They died out, we think, because of this huge volcanic area in Siberia which we know erupted at exactly the time of the extinction.  So, that looks like the culprit if you like, the large smoking gun for this catastrophe.

Ginny -   And how do you know that, firstly, that that happened and secondly, that that was what wiped out life?

Paul -   We know what's left of this province.  At that time, there were millions of cubic metres of lava erupted and itís a timing really as in a lot of things started in the past.  We know from dating, it was exactly the time of the extinction.

Ginny -   How do you go about dating things?

Paul -   You can do it sort of directly because Ė if you go to Siberia and you look at these lavas, they had layers of sediment in-between the lavas and you can collect fossils from those layers of sediment.  And so, you can look at the lavas and fossils, and look at the timing of everything.  And you can give a natural sort precise age of the lavas by dating which a geologist use a technique called geochronology.  Itís where you use radioactive elements and the rate at which they decay tell you how old rocks are.

Ginny -   Now, I can see how a volcano erupting in Siberia would kill off a lot of animals in Siberia, but how did that affect the rest of the world?

Paul -   The actual lava was only dangerous in Siberia, but the main problem with large scale volcanism and a lot of giant eruptions and other gases that come out.  The gas is actually rather familiar to us today as well as carbon dioxide which is a greenhouse gas of course.  And then we have all the gases like sulphur dioxide and some acetic halogen gases as well which will come out in huge amounts from giant scale volcanic eruptions like this.

Ginny -   Would those gases have been directly poisoning animals?

Paul -   Not directly.  The carbon dioxide, its main effect is to cause warming and we know that things were extremely warm at the time of this extinction.  For the other gases, we think, actually one of the main effects of some of these other gases is that they do damage to our ozone shield.  As a result of that, it allows a lot of UV radiation to sort of bathe the planet which is obviously not good.

Ginny -   So, what is it that would actually be killing off the animals?

Paul -   Well, UV radiation would cause the effects of cancer if you like, but the cell damage, it causes plants to die and the animal that eat plants will therefore struggle.  In the oceans, itís actually a little different.  I think itís the warming effects of oceans that's really harmful thing.  That causes increases in temperature but you also start to lose the oxygen content of the oceans as well.  So, itís sort of this warm, lack of oxygen is bad in the oceans.

Ginny -   How warm are we actually talking?  How big a difference from before the volcano to after it?

Paul -   Itís huge.  Itís one of the biggest warming events weíve yet discovered.  Temperature is rising about 15, approaching 20 degrees C.  Certainly, for the ocean surface water approaching temperatures of the high 30s Ė 30 degrees, 37 degrees, that sort of temperature which is the sort of temperature that you take a shower at, but this is sort of year round and because itís pretty, pretty harsh.

Ginny -   That's a huge difference. How quickly did that happen?

Paul -   Itís a good question.  We say between tens to hundreds of thousands of years.  So, as a geologist, I think that's quick but obviously, not on a human scale, itís relatively slow.

Ginny -   But too fast for most animals to evolve to survive it?

Paul -   That's right.  Once you start getting temperatures above sort of 35 degrees C, a lot of things can't survive at those temperatures.  You just run into all sorts of problems.  Photosynthesis for most plants is very difficult to that temperature as well.  So, you start to run out of plant matter and stuff, run out of things to eat.

Ginny -   But there were a few things that survived.  What made them special?

Paul -   Yes, there's a few survivors fortunately so they carry on populating the planet.  In the oceans, I think we looked at groups particularly some molluscs groups, are good at tolerating low oxygen and high temperature and they do quite well at that time.  They do survive the extinction.  On land, I think itís an interesting selection of animals that survive including a group which give rise to mammals later on.  I think for some of those animal groups on land, I think the ability to adapt wouldíve been good.  That's sort of the hot temperature equivalent of hibernating.  So, when it gets really hot then itís a good idea to just sort of sleep it out for several months and just wake up when things get a little bit better for short periods of time.

Ginny -   So, was this all just chance that these volcanoes erupted?  Could it happen again?

Paul -   It could happen again.  There's been events like this as well.  This is just the worse one of its kind.  I think weíll know if it happens because the magma rises up from deep within the Earth.  In effect, geophysicists and people who study the structure of the Earth would see it coming.

Ginny -   But even if we could see it coming, would there be anything we could do?

Paul -   No.

Ginny -   Fairly worrying, but I guess we just have to keep our fingers crossed that it doesnít happen again in our lifetimes at least.

Paul -   I think so, yes.

Ginny -   Thanks so much for your time.  that was Paul Wignall from the University of Leeds.

 

 

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