Science Interviews


Sun, 24th Jun 2007

How Dinos Died - Meteorites, Flood Lava and Supervolcanoes

Dr Janet Sumner, the Open University.

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Janet Sumner is interested in the subject of Mega-eruptions and meteorites, things which are devastating for life on Earth.

Arenal VolcanoJanet -   I work on natural hazards and theyíre much larger things than Joelís Curtain hazards [see Joel Veitch interview], in fact these are pretty big natural hazards.

Chris -   This would be a giga-giga-giga Curtain?

Janet -   It would be a super-giga-Curtain, yes.  Itís the kinds of thing that really results in a global mass extinction.  Thatís a total eradication of entire groups of species Ė weíre talking the death of the dinosaurs, basically.

Chris -   So what do you think that actually triggered the death of the Dinosaurs?  Do you know what it was?  Was it a massive great eruption?  Weíre all used to the idea that some kind of meteorite slammed into the Earth, which do you think it is?

Janet -   Thatís true, actually.  It was, and it still is widely believed that the dinosaurs were wiped out by the impact of the Chicxulub meteorite into the Yucatan peninsula in Mexico about 65 million years ago.  But there have been five great mass extinctions in the past 450 million years.  The dinosaur one is the only one associated with a meteorite impact, all the other mass extinctions including the dinosaurs as well all correspond to the outpourings of huge flood lava eruptions.

Chris -   If we could look at both of those in turn then, the meteorite that slammed into the Gulf of Mexico, how big would have that needed to be to alter the planet so dramatically that nearly all life ceased?

Janet -   Well, it was many many tens of kilometres across, and basically the effects of a large meteorite impact like that are devastating.  But the fact is, because weíd had this really long running eruption going on for thousands of years, the dinosaurs were already on their way out and all the impact did was finish them off a bit quicker.

Chris -   Thatís interesting, I didnít realise that the dinosaurs were already waning, I thought they were at their peak at that time.

Janet -   No, theyíd already pretty much had it, because there had been one of these huge flood lava eruptions going on in India for many thousands of years.  What we now know happens with these flood larva eruptions is; when a volcano explodes it releases ash and sulphur, that gets up into the atmosphere and it produces a kind of blanket in the atmosphere and that prevents the sunís rays from getting through.  So it causes a global environmental change, and interestingly itís actually the opposite of whatís going on at the moment, because right now weíve got global warming, but when you get a big flood lava eruption like this you actually get global cooling, because this blanket stops the rays of the sun from getting through and keeping us warm.

Chris -   So what actually is this flood lava?  Where does it come from?  What provokes it and why is it so devastating?

Janet -   These massive eruptions are often associated with plate tectonic movements and rifting and big up wellings of hot material coming out of the mantle.  They can break through cracks in the surface.  They can go on for thousands of years and can produce piles of lava that are up to three kilometres thick.  The thing about the sulphur and the ash, youíve got to get it up into the atmosphere for it to do its work.  For a long time, scientists thought that flood lavas just kind of spew out onto the ground, really quietly and then just flow off.  The research Iíve been doing has now proved that thatís not the case, because Iíve found lots and lots of beds of ash within these flood lava successions.  Where youíve got ash, you have to have an explosive eruption.  So now it seems that these flood lavas are coming out so violently the molten rock is being ripped to bits and forming a huge curtain of fire, topped off by a massive ask plume.  So hey presto!  Now we can get our ash and sulphur up into the atmosphere and cause enough global cooling to cause mass extinctions.

Chris -   So when was the one which had done for the dinosaurs?

Janet -   The Chicxulub impact was 65 million years ago.

Chris -   But when was the big lava outpouring which had begun to see off the dinosaurs?

Janet -   It started just over 65 million years ago, so exactly the same period.  It just preceded the Chicxulub impact, which happened virtually at the end of it.

Chris -   And where was all that lava coming out?  Was it an unstable period of Earthís geology so it was coming out everywhere, or was it just one place on Earth?

Janet -   They tend to happen periodically in different parts of the Earth.  The one I was looking at was actually in India, as rifting was starting to happen in India.  Weíve got one closer to home [The Naked Scientists is based in the UK] in the North Atlantic igneous province just up to the North of us.  Thereís also one that happened in Africa so they happen all over the world at different periods.

Chris -   So how can people have missed this before, because I know everyoneís attention has been focussed on the fact that a meteorite arrived, it changed the Earthís weather so dramatically it wiped out the dinosaurs, how could they missed three kilometres thick of lava deposits?

Janet -   Well, we knew it was there, and we knew that large flood lava eruptions do cause mass extinctions because of this really strong correlation, we didnít know the mechanism for getting this ash and sulphur up into the atmosphere to actually cause the global cooling.  Everybody thought the lava just flooded out Ė hence the name, flood lavas.  But now we know that there is a mechanism for them to come out explosively and to actually put that ash up into the atmosphere where it can do itís damage.

Kat -   So is there any chance of one of these flood lava eruptions happening again, are we due one?

Janet -   That is always the question that everybody asks Ė ďare there going to be any more mass extinctions?Ē  And why?  Because weíre worried about us, arenít we?!

Kat -   Yeah!

Janet -   Well the answer is yes, there could be another mass extinction;  one, if we were hit by another meteorite and two, if there was another flood lava eruption.  But what is more likely to happen, a much bigger hazard to us is if we have a super-volcano go off.  Now super volcano eruptions happen every 50 thousand to every 100 thousand years, and there are a number of super volcanoes around the world.  One particular candidate is long overdue, and thatís Yellowstone volcano in the US.  That is overdue by some thousands of years, so if that was to blow, it probably wouldnít cause global mass extinction but it would certainly cause global famine.  That would probably mean the end of civilisation as we know it.

Chris -   Whatís the prospect that it will?  Whatís going on there? People say that the land is moving, how long has it been there?

Janet -   Oh gosh, Yellowstone has been there for hundreds of thousands of years, and I think itís had three major eruptions in its lifetime.  It is due for another one, and scientists have seen that the land is doming up.  But it could be another 50 thousand years, because itís been very hard to predict with these.

Chris -   Would it definitely go bang, or could it just go Ďphutí like a failed firework?

Janet -   I donít think itís going to go Ďphutí, I think the chances of a big bang are probably fairly high.  But I donít want to be too depressing here, doom and gloom.  What I actually wanted to say was, have you ever seen a meteorite?

Chris -   Well, I have, but only in a museum, Iíve never actually held one.

Janet -   If you want to hold something from outer space you can because Iíve got one in my pocket.

Chris -   Oh wow!

Kat -   I want it!

Janet -   Now thatís a stony iron meteoriteÖ

Chris -   This is incredibleÖ

Kat -   I want to see it!

Chris -   Iím holding a pebble in the palm of my hand, and Iím going to give it to Kat in a minute because sheís itching to look at it.  It just looks like any other lump of rock, but it looks a bit rusty.  Is there any iron in it?

Janet -   Itís a bit rusty on the outside, youíll see it has one polished cut surface on it and you can actually see the iron glinting in it.  Thatís a lump of rock and iron which makes it a stony iron meteorite.  Youíll notice the outside of it is quite smooth, thatís something called a fusion crust.  It happened as it heated up and started to melt as it came through our atmosphere, and ultimately landed on Earth.  This one is the size of a golf ball, but itís also quite heavy because of all the iron in it.  Now if you can imagine a much much larger scale meteorite and that hitting the Earth, it would probably make a bit of a mess.

Chris -   That would be about 4.5 billion years old presumably, the age of the solar system?

Janet -   Yes.

Chris -   So thatís pretty impressive, I donít think Iíve ever held anything quite that old.

Kat -   Thatís pretty cool.

Chris -   It wouldnít have been once!


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