Exploring the oceans' greatest catastrophe
Helen - There have been 5 so-called Mass extinctions in the history of the planet earth when large swathes of life on land and in the sea disappeared. Most famous of these events was the one 65 million years ago that saw the end of the dinosaurs, probably thanks to a massive meteor crashing into the earth.
But the most devastating extinction took place in the oceans long before dinosaurs evolved, back at the end of the Permian era, around 250 million years ago.
Paul Wignall from Leeds University, here in the UK, is a geologist who researches the Permian extinction and I chatted to him about just want went on back then.
Paul - In a nutshell every died basically. To a first order you're seeing the extinction of just about everything. About 95% of species on the level seafloor disappeared. Most fish groups disappeared as well. So, it was pretty devastating.
It's so big is this extinction that we almost take the world back to the pre-Cambrian, the time before complex life evolved. So we have in the seas of the earliest Triassic, after the extinction, were in a sense almost dead seas, there's not much around. We just have a lot of microbial life which is very much like the pre-Cambrian world.
Helen - And what were the groups that we just don't see any more? Which ones were snapped out and wiped out completely?
Paul - The end of the Permian, the groups that we loose completely, there's 2 major groups of corals, and they disappear. And although we have corals today they're not actually very closely related to these Permian corals. The trilobites, famous fossils, die out at this event. And things called sea scorpions, they go out at this time as well.
Helen - They were really big weren't they?
Paul - They were. They'd managed to colonise rivers and freshwater environments by the late Permian as well. They don't cross the boundary, so we don't see those ever again.
The main shelly group at this time was a group known as the brachiopods, which we do actually have today, I think you can find them around the shores of New Zealand in particular, but in the Permian they were the most common fossil around. So they were almost entirely wiped out.
Helen - And in terms of large vertebrate life in the oceans, was there much going on at the time in the Permian.
Paul - Various fish groups, particularly some armoured fish, with heavy armoured scales, they disappear. A lot of the famous marine reptiles like ichthyosaurs and plesiosaurs, they actually come along after the extinction. So following the extinction event we actually see a lot of reptile groups return to the oceans and you get all sorts of swimming reptiles in the Triassic, so in a way they benefit from the extinction because they radiate afterwards.
Helen - Life on land also took an enormous knock didn't it? What was going on there at the time as well?
Paul - The end Permian extinction was utterly catastrophic on land. We see the loss of all forests at this time, all major trees and things die off. It's also the real extinction event for insects, because insects as we know are a very successful group which are generally diversifying all the time, but that wasn't the case at the end of the Permian, so we loose a lot of insect groups. Something severe happened on land and in the sea around the same time. We're looking at a whole global ecosystem breakdown.
Helen - So, the Permian extinction really did shake up life on earth like never before, and the big question is - why did it happen? What was it that made so many species go extinct?
Over the years, various theories have been drawn up - some say it could have been another meteorite impact like the one that wiped out the dinosaurs, although there isn't too much evidence for that.
But as Paul explained, there was something rather spectacular going on at the time that could ultimately be to blame.
Paul - We've got the culprit. There's a huge amount of volcanism going on at that time in Siberia so that seems to be the giant smoking gun, so we're trying to link that volcanism in to that extinction in the oceans.
Helen - And this was enormous volcanism wasn't it? We can't actually picture in our minds compared to the kind of volcanic activity we see today. It was enormous wasn't it?
Paul - Yes it was. It's a style of volcanism which fortunately we don't see today but it's known as flood basalt volcanism and basically it involves enormous eruptions involving thousands of cubic kms of lava. Most volcanic eruptions today involve less than a cubic km of lava. So we're talking about enormous individual flows covering large areas of Siberia.
But with those flows a lot of volcanic gas would come out as well.
Helen - And it was that potent cocktail of volcanic gases that's thought to have triggered the crisis in the Permian oceans.
One of the gases spewed out by the Siberian traps, those gigantic volcanoes, was sulphur dioxide - which has various effects in the atmosphere including forming acid rain.
And there was also an awful lot of carbon dioxide released, which as we know from what us humans have been getting up to in recent times is a powerful greenhouse gas, and there's evidence that back in the Permian the earth warmed up and its thought this led to the oceans becoming very low in oxygen, making them distinctly inhospitable for most forms of life:
Paul - If you look at the oceans today they're extremely well ventilated - there's oxygen available everywhere in the world's oceans and that's because they circulate very effectively. The circulation is essentially driven by the temperature difference between the poles and low latitudes, the equator, so you generate cold, dense water at the poles, which sinks and then warms surface waters travels to the poles, like the Gulf Stream for example.
Back in the Permian presumably a similar sort of circulation was going on but then if you turn that off that ocean conveyor as it's know, they you'd cease to supply so much oxygen to the ocean waters.
It's a bit like on a giant scale if you stick a goldfish bowl on a window on a sunny day that goldfish bowl will warm up and the oxygen in the water will decline and your goldfish will probably die.
Sarah - Ok, so Helen we've got carbon dioxide billowing out of these enormous volcanoes and that would have heated up the planet and turned the oceans stagnant - which already makes conditions pretty unbearable- but what about the other affects of CO2? Did the oceans become more acidic as well, back then as they seem to be doing now?
Helen - Well, it's interesting because the idea of ocean acidification has only really been on our radar for less than a decade, and it's the scientists studying our present-day oceans and atmosphere who came up with the theory, and found that over the past 200 years the oceans have become around 30% more acidic, a consequence, we think, of more and more carbon dioxide dissolving into the oceans from the atmosphere - because as well as being a greenhouse gas, carbon dioxide is acidic.
But it was this discovery of recent ocean acidification - and concerns about what could happen in the future - that gave geologists studying the past, the idea that maybe this was what happened then too.
Paul - It's actually very hard thing to test for back in the rock record because acidification essentially dissolves things of course, it dissolves shells and it dissolves limestones and things. So in effect by removing something it leaves no evidence behind.
You can do more indirect ways of looking for it, for example you can look to see if the extinction was selective. Was it particularly hard on organisms whose shells dissolve easily? And that sort of work is really only just being done so we don't yet know the answer to that.
Helen - There was one study out earlier this year that provides some evidence of acidification in Permian seas, from a team who looked at Calcium isotopes in limestone deposits in China. But as Paul said, we're still a way off knowing if that's really what happened and what impact it had.
Sarah - So, we had this massive extinction, 250 million years ago, that virtually wiped out life in the oceans - but can this tell us anything about changes taking place with oceanlife today and the prospects for the future?
Helen - Well, it's often said that we are entering the 6th mass extinction, and this one hasn't got anything to do with asteroids or volcanoes but it's us humans who are to blame for churning out pollutants and greenhouse gases, and for wiping out habitats and species around the world.
The Permian extinction was far more catastrophic than even the gloomiest predictions for the impacts of humans on the planet, and it happened over a much longer time frame - tens of thousands of years - compared to the impacts we're having over a matter of decades.
But even so, there are some aspects of the Permian extinction that may help us understand what's going on today, and what might lie in store.
Acidification studies are one area that will surely benefit from understanding what happened in the past and how different animals responded to it, and as Paul said, that's ongoing research.
And studies of what happened following the Permian extinction tell us is how quickly surviving species were able to diversity and restore global biodiversity to its former glory. And that shows us how different groups of animals evolve into new species at different rates:
Paul - Things like bivalves are like evolutionary carthorses, they just plod along, they'll take a long time to recover. Other groups like for example fish, they evolve quickly, so we can predict that they'll start diversifying again very quickly if we drive them to extinction.
But I'm talking as a geologist here, so when I say something evolves quickly I'll say fish probably will have recovered in a million/1.5million years, bivalves might take 15-20 millions years. We're talking about long time scales. But it's quite easy to predict what will bounce back quicker than say other groups.
Helen - But I suppose that's a geologist's point of view on the planet and we may or may not be around to see this?
Paul - As a measure of just how long it takes, the end Permian extinction took about 80-100 million years later you've finally got back to the pre-extinction diversity levels, so it is a long time. Life gets there eventually, but anything as big as the end Permian extinction takes a long time to recover from.
Helen - It was thought that reefs took 5 million years to recover after the Permian extinction, but a new study just out in the journal Nature Geoscience shows that in fact it only took 1.5 million years for reefs to reform with multicellular life like sponges and serpulid worms, showing that as soon as environmental conditions returned to normal, reefs started growing again.
But as Paul said, it takes a very long time for life to recover from a mass extinction, and while, in the grand scheme of life on earth, things will go probably on, from our human perspective we can't simply expect to sit by and watch life recover from the damage we are inflicting on the oceans today- so efforts to protect life in the ocean are really very important indeed.
Find out more:
Paul Wignall, Leeds University
The Permo-Triassic Extinction - information from the Palaeobiology and Biodiversity Research Group at the University of Bristol