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00:00And you can speak to David Hutt, the director of tonight's Equinox, after the program on our website at this address, chat.channel4.com.
00:30The steady evolution of life on Earth has been punctuated by dramatic periods of mass extinction.
00:4465 million years ago, two-thirds of all plant and animal species were wiped out in one of these catastrophes.
00:51The most famous victims were the dinosaurs.
00:54An extraordinary event coincided with the deaths of dinosaurs.
01:04A giant comet or meteorite struck the Earth.
01:08Some scientists promoted the view that the impact was so devastating to the world's environment that it triggered the mass extinction.
01:19But other scientists had never been satisfied with this explanation.
01:22They argue that there are forces deep within our planet which are responsible not only for the death of the dinosaurs, but for many other mass extinctions.
01:32Many people think that the debate on what caused mass extinction is over, and I believe this is far from true.
01:48There are basically two main models of what happened or what may have caused the mass extinction.
01:55Some people think there was nothing special, just something ingrown in the species that made them disappear in long length of time according to the normal ways of evolution.
02:07I believe these people are a minority.
02:08The other camp, if you want to use war-like terms, has a catastrophe happening at the time of mass extinction.
02:17Again, what was a catastrophe divides people into two camps.
02:21Some believe that it's a meteorite or a comet coming from outside the Earth that hit and change climate, destroy species.
02:28Something that is actually from inside the Earth, enormous volcanism as seen in flood basalts that was the cause of it.
02:35At the same time as a mass extinction, the Earth was rocked by a cataclysmic series of volcanic eruptions.
02:46They're called flood basalts.
02:49Many scientists believe that there is an unequivocal link between these eruptions and the death of the dinosaurs.
02:56Other mass extinctions coincided with flood basalt eruptions.
03:06It may be that the way life has ebbed and flowed over millions of years has been determined by events that occur deep in the heart of our planet.
03:15This is Kilauea, on the big island of Hawaii.
03:28It's the most active volcano on Earth.
03:31Several times in the geological past, the Earth has witnessed huge episodes of flood basalt eruptions, far greater than Kilauea.
03:39Enormous volumes of toxic gases poured up into the atmosphere, changing the global environment, rapidly, dramatically and disastrously.
03:54It's this poison of the atmosphere in the oceans which may have triggered off mass extinctions.
03:59Flood basalt eruptions poured out lava on a scale many times greater than any modern volcano.
04:20Remnants of these lavas can still be found around the world.
04:23In the British Isles, these cliffs along the west coast of Scotland are made of flood basalt.
04:30The same lava flows can be seen in Greenland, the eastern United States, and on the giant causeway in Northern Ireland.
04:37Flood basalts came from much deeper in the Earth than most volcanoes.
04:54This deep origin links the internal development of our planet to the evolution of life on the surface.
05:00Well, the flood basalt is essentially a period in the Earth's history when enormous amounts of hot lava come out on the Earth's surface, far more than is currently coming out on the Earth at the moment.
05:17These are really huge lavas and individually they may be hundreds, thousands, even tens of thousands times larger than the individual lavas that erupt on Hawaii.
05:27The Earth is literally letting off steam as the heat trapped inside tries to escape to the subzero temperatures of space.
05:38The geological history of the Earth has been controlled by this process of losing heat.
05:43At the heart of our planet is a solid iron core.
05:54This is surrounded by an outer core of liquid iron and nickel.
05:58The whole core is nearly 4,000 kilometers thick.
06:03The core is surrounded by the mantle, a 3,000 kilometer layer of hot solid rock.
06:09And above the mantle is the lithosphere, the thin cold crust of the Earth that carries the continents and oceans.
06:15Flood basalt were created when enormous plumes of hotter, solid material rise slowly from the core through the mantle.
06:28Each plume takes many millions of years to make this journey, and the last one to reach the surface was 15 million years ago.
06:35They carry so much heat, they can split continents apart.
06:42The nearest modern equivalent to a flood basalt was this eruption on Iceland in 1973, when cracks and fissures almost a kilometer long opened up and spewed out fountains of lava.
06:58Millions of tons of poisonous gases poured into the atmosphere, but even this was tiny by comparison.
07:08Picture a crack in the Earth.
07:11Well, in Iceland, a few hundred meters long, tens of meters of fire fountains, and blow that up by factors of a hundred and in excess.
07:19Think of fissures that must have been 400 kilometers long, with fire fountains that may have reached maybe hundreds of meters, possibly more than a kilometer, injecting gases and ash all the way to the upper layers of the atmosphere and then circulating them around the Earth.
07:37This is really something that must have been a frightening sight.
07:40But what these flood basalts did not produce was volcanoes as we know them.
07:58These flows first had such large volumes and came out sufficiently rapidly that they spread really like a very fluid liquid and spread over a very large area indeed.
08:09And so they basically didn't form a volcanic structure in the conventional sense.
08:18Flood basalts leave their mark on the landscape.
08:21This 100 meter high cliff in Oregon, in the northwestern United States, is made of frozen basalt lava.
08:28It erupted as a single sheet of molten rock.
08:32It's ten times thicker than any lava flow from a modern volcano.
08:35That one lava sheet is just a tiny part of the Columbia River flood basalt province that erupted over Oregon and Washington State 15 million years ago.
08:54Each layer in these hills is a single lava flow.
08:59More than 200 flows poured out in less than one million years.
09:05In geological terms, this is an incredibly short time.
09:09If you tried to imagine what this was like during the eruption of the basalt flow, you'd probably have to think of the closest thing we can know to hell.
09:22It was a vast sheet of lava being erupted.
09:25Whether it was anywhere from a month to a year, it still was coming out fairly rapidly.
09:30It inundated everything in its path.
09:33As the basalt flows came out, they were tremendously hot.
09:39At least a thousand degrees, probably close to 1100 degrees centigrade.
09:42It's really hard for us to imagine how devastating this was to the area, but when you start looking at the entire Columbia Basin and the extent of these flows, it had to have been a very serious impact to the environment.
09:56Many of the flows in the Columbia River province are like these, almost 100 meters thick.
10:08In just a few months, each flow traveled hundreds of kilometers.
10:12And by the time the eruption ended, more than 160,000 cubic kilometers of basalt had poured out onto the surface of the Earth.
10:26There hasn't been a flood-bathalt eruption for 15 million years, but there are modern volcanoes, like Hawaii, which produce almost identical lava.
10:38The rivers of lava beneath this crust can be as hot as 1200 degrees Celsius and give off deadly sulfurous fumes.
10:57These volcanologists know the dangers of working here, and accept some water.
11:17They're here to collect fresh samples and take measurements.
11:20One false step could send them to a fiery death.
11:27A chemical composition of this lava shows that, like the flood basalts, it is a primitive rock, originating at very deep levels inside the Earth.
11:38Ah! Tough volcanoes are made up.
11:461032?
11:481032 degrees centigrade.
11:501052?
11:521052.
11:53These geologists use the latest technology to measure the temperature of flowing lava.
12:01They use a radar gun to measure the speed of the lava.
12:04Basalt has been erupting from this volcano continuously for the last 15 years.
12:1010.2 on the right. Got it.
12:11The Hawaiian Islands are situated in the middle of the Pacific Plate, which of course is covered by the Pacific Ocean.
12:20And here, slap bang in the middle, there's a chain of islands, volcanic islands, of the tips of huge volcanoes.
12:27In fact, two of them are together the largest edifice on Earth.
12:30Hawaii is known as a hot spot for 10 years.
12:35It was created from a stationary source of heat deep within the Earth's mantle.
12:41As magma rose up to the surface, it met the Pacific Ocean's floor, moving slowly northwest in the process of continental drift.
12:50A volcanic island formed, then died as it travelled away from the heat source.
12:57Another island built up, then another.
13:00So the present active volcano is on the youngest island of the chain.
13:03The heat source beneath Hawaii is believed to be the tail end of a flood basalt eruption, still active millions of years after the main event.
13:18If one could go back and wander around many million years ago when the flood basalt province was forming, I think you'd see a scene that is very similar to what we see today here on Kilauea.
13:31An active lava field, but one in which the red hot lava is not very obvious, because most of it is down in channel ways and pathways, flowing under a surface crust that was formed earlier during the eruption.
13:43The most common Hawaiian lava flow is called Pahoihoi, from the Polynesian word meaning ropey.
13:54The slow-moving sheet of lava forms a rope-like texture on its surface.
13:59The crust cools rapidly and insulates the lava inside.
14:05These rivers of basalt can stay molten for many years.
14:08Steve self believes that the way Pahoihoi lava moves is very similar to the way that flood basalt eruptions flowed out and built up into vast, flat sheets.
14:22This is a wonderful example of a Pahoihoi sheet flow advancing very quickly across this flat crater floor.
14:28You can see that the lava flow front has a thickness of about a metre or less, and it's just a coherent sheet of lava gradually oozing forward.
14:38You can see it thudding out to make little lobes.
14:41Flood basalt provinces, which are provinces of huge lava fields, just immense in extent and thickness, with individual flows about the size of England.
15:02When we stare out across the flat surface of the Hawaiian Pahoihoi fields that are forming today, it's very similar, I believe, to staring out across the flat surfaces of the flood basalts.
15:15Columbia River is one of ten flood basalt provinces that erupted around the world in the last 300 million years.
15:29It's also the smallest by far.
15:31In India, a single flood basalt covers a third of the subcontinent, over 2 million square kilometers.
15:49Even larger flood basalts cover huge areas of Brazil and Argentina.
15:54The significance of these extraordinary volcanic events is only now being appreciated.
16:05It's a curious thing that flood basalts have just eluded attention until the last, really, ten years or so.
16:12And why is that?
16:15Well, partly, the answer to that is that it hasn't been appreciated until very recently that flood basalts are episodic eruptions of huge magnitude.
16:26So, in other words, it really wasn't until we were able to date them and determine their ages very precisely that we could actually see that that vast amount of material was erupted in discrete episodes of short duration.
16:40Paul Rene runs a laboratory in California, which calculates the ages of rocks using the slow decay of radioactive elements like potassium and argon.
16:51For the last few years, his team has been trying to establish the age of one of the oldest of the flood basalts provinces, the Siberian Traps in northern Russia.
17:00This is also the largest of all the flood basalts.
17:07Much of it has been eroded away, but when it erupted, it was nearly 20 times bigger than Columbia River.
17:13When the team dated the Siberian Traps, they found that enormous amounts of lava were erupted within a very short period of time.
17:26As soon as we began to realize that these are huge scale processes that were transferring a tremendous amount of heat and mass in the form of molten lava and gases to the surface of the Earth,
17:43we began to ask what sort of effects would this process have on the climate.
17:50The Siberian Traps erupted at precisely the same time as the greatest mass extinction of life on Earth, 250 million years ago.
17:5995% of all species of plants and animals were wiped out.
18:05Now, modern dating techniques have established correlations between other blood basalts and other mass extinctions.
18:13There are 10. We've found them, we've spotted them, they're well identified, they're well dated, and there is a remarkable correlation.
18:20With the best dating tools which we presently have, which include paleontology, paleomagnetism, and most powerfully, geochronology, using the argon-argon or potassium-argon dating methods,
18:34we have found, many labs around the world have found, that every single flood basalt, out of 10, but one or two, correlates with a mass extinction.
18:43There is no doubt that the mass extinction which killed the dinosaurs did coincide with a flood basalt eruption.
18:53Yet, despite this link, some scientists still prefer the idea that they were already.
19:02The extinction of the dinosaurs marks the divide between two major geological epochs, the Cretaceous and the Tertiary.
19:13At the Natural History Museum in London, Norman MacLeod has spent years looking for the causes of this and other extinctions.
19:22The Cretaceous-Tertiary boundary represents a mass extinction event.
19:25There have been several mass extinction events in Earth history, none of them are very well understood.
19:31We're interested in the study of extinction for a variety of reasons.
19:35From an evolutionary point of view, extinctions serve as a filter that constrain the nature of the evolutionary process.
19:43The cause of the mass extinction at the Cretaceous-Tertiary boundary has been the subject of intense scientific debate.
19:53For the last 20 years, the most popular theory has centered on a global catastrophe created by a meteorite impact.
19:59Large meteorites and comets have regularly struck the Earth.
20:08There are over 150 crater sites scattered all over the world, and there must have been many more impacts where the craters are no longer preserved.
20:16What sparked the dinosaur debate was a discovery that exactly 65 million years ago, a huge meteorite, at least 10 kilometers across, smashed into the Yucatan Peninsula of Mexico.
20:35The impact sent a cloud of dust into the atmosphere.
20:45It created havoc on the planet.
20:48Months of darkness, global wildfires, poisoned air and water, freezing temperatures.
20:54The effects on life would have been disastrous.
21:02The center of that impact was here, at a site that now spans the coastline of the Yucatan Peninsula.
21:08The crater it generated was at least 200 kilometers across.
21:19This group of researchers believes that such an impact could have released the energy of a billion Hiroshima bombs,
21:25and that it changed the history of the world.
21:28The evidence for that impact can be found in the most unlikely places.
21:41One of the best sites is in the banks of a muddy river in Texas.
21:46Meteorites contain significant amounts of iridium, a rare element not found in the Earth's crust.
21:52When the dust from the impact cloud settled on the surface, it formed a layer with a high concentration of iridium.
22:00And that layer has been found in sediments all over the world.
22:04The evidence for a global catastrophe is still preserved 65 million years later as a thin layer of brown sand.
22:13These are the deposits that were laying down at the very end of the Cretaceous.
22:17At the time of the impact at Yucatan, the Chicxulub structure in Yucatan.
22:23And this is the Cretaceous-Tertiary boundary right here.
22:26And this is defined by the presence of iridium, high iridium concentrations,
22:30and by the change in microfossils from a Cretaceous suite to a tertiary suite.
22:34It goes along right here and forms this little line marked by iron oxide stain in sand.
22:42However, there is strong fossil evidence that the mass extinction was not an instant event.
22:49The most insidious aspects of the catastrophic model is that it defers the explanation.
22:57The catastrophic model essentially comes down to a claim that a rock fell out of the sky,
23:05a large rock fell out of the sky, changed the environment, and everything died.
23:10Except those things that didn't die.
23:13And more and more paleontologists are becoming aware that this isn't very satisfying as an explanation.
23:19Even though the meteorite impact did coincide with mass extinction,
23:25the idea that it was the sole cause ignores crucial evidence from the fossil record.
23:30And the record is clear.
23:32Apart from the dinosaurs, many other species had already become extinct long before the impact.
23:38It appears that the impact happened right at the end of a long episode of extinctions.
23:46Probably driven by climate change, but it was happening to many groups and pretty much globally.
23:55And the impact was coincident with that.
23:58I do not myself believe that the impact caused the extinctions.
24:02The impact was not the only event which coincided with the death of the dinosaurs.
24:18At precisely the same time, 65 million years ago,
24:23one of the greatest of all flood basalts erupted on the landmass that is now India.
24:28These are the Deccan traps.
24:32They cover more than one third of the Indian subcontinent.
24:41Here, at Allura, the lavas are so massive,
24:44that stonemasons were able to carve these extraordinary temples out of the fine-grained solid basalt.
24:50None of this stone has been brought in or moved.
25:01It is all in exactly the same position as when it was erupted 65 million years ago.
25:07The hillside is composed of two distinct lava flows, lying one on top of the other.
25:22There may have been many hundreds of years between the eruption of the flows,
25:26and the join between them is much weaker than the rest of the rock.
25:39The thin white line marks the top of one of the lavas.
25:43Over the centuries, the elephants' trunks all broke off at the junction between the two flows.
25:49In the end, sculpture was defeated by geology.
26:00Sometimes, the gap between eruptive cycles was long enough for sediments to be deposited.
26:05In one of these sediments lies the proof that the flood basalt was erupting long before the Mexico meteorites struck the earth.
26:13We have been able to show in sediments, sandwiched between two layers of the Deccan traps,
26:19that the iridium anomaly that shows the time of the impact is located between the flows.
26:25So, volcanism started, went on for hundreds of thousands of years.
26:30Then there was an impact. Then there was more volcanism.
26:33And the real question is not anymore, was there one or the other?
26:36I believe we have ample field evidence the two happened.
26:40The big question is, how much did each one contribute to whatever happened?
26:45I would tell the top of my head if I make a bet.
26:48Well, volcanism was probably responsible for something like two-thirds of the extinction.
26:53They were already going on.
26:55The additional stress put on the environment by the impact may have pushed overboard another third of them.
27:01But how did flood basalts cause so much damage to the global environment that the majority of life on earth could not survive?
27:20Volcanic eruptions can seriously affect the climate.
27:23In 1991, the ash cloud from the explosive eruption of Mount Pinatubo in the Philippines was hurled high into the stratosphere.
27:32Within a few days, it would circle the earth.
27:35Sunlight round the world was reduced, and global temperatures fell for two years.
27:40If the eruption had continued, it could have affected the world's climate for decades.
27:52If the eruption had continued, it could have affected the world's climate for decades.
28:09Predicting this type of eruption is a major challenge.
28:14Propocatapetl is just 50 kilometers from Mexico City.
28:19It not only spews out huge amounts of ash, but also life-threatening gases, which endanger 20 million local inhabitants.
28:28These volcanologists are using a device called CoSpec.
28:37It measures the amount of sulfur dioxide in the volcano's smoke plume.
28:42They can measure the effects up to 50 kilometers away from the volcano.
28:47Sulfur dioxide reduces the amount of sunlight passing through the plume, and the instrument uses this to measure the volcano's activity.
28:58The plume can be highly dispersed.
29:00They may have to drive 200 kilometers or more to complete the survey.
29:06At the end of the run, they analyze the results.
29:16On this one day, together with all its ash, the volcano put out an incredible 17,000 tons of sulfur dioxide.
29:24Six months later, it was erupting 100,000 tons a day.
29:33When this amount of gas pours into the atmosphere, it can circle the globe.
29:41Basalt eruptions produce much less ash than explosive volcanoes, but they do erupt enormous amounts of gas.
29:50So could this be the key to the mass extinctions?
29:54There are some clues that can be taken from things like the eruption in 1783 and 84 of Laki in Iceland.
30:04We know that in that case, a flow which had about 12 cubic kilometers of volume induced cooling in the northern hemisphere by about 1 degree centigrade over the period of about a year,
30:18which doesn't sound like very much 1 degree centigrade.
30:21A big deal.
30:22But in fact, that's a big difference.
30:25These craters at Laki in Iceland are all that remain of the greatest basalt eruption in recorded history.
30:35This was a fissure eruption, the nearest modern equivalent to a flood basalt.
30:40It lasted only a few months, but its effect on the climate in the northern hemisphere was devastating.
30:47For the next three years, there were crop failures, famine and disease all over Europe and North America.
30:59A quarter of Iceland's population died.
31:02Compared to any flood basalt eruption, this was a tiny event, but the cause of the environmental stress was the same.
31:10The highly toxic gases emitted during volcanic eruptions.
31:14The main gases which cause problems are sulfur dioxide and carbon dioxide.
31:20And they are in fact buried, if you like, within the earth in different minerals which hold those gases.
31:29When the gas gets to the earth's surface, it expands dramatically, probably by several thousand fold.
31:35And all that gas then dissipates into the atmosphere.
31:441,200 metres above sea level is Kilauea's central crater.
31:50There has been any lava eruption actually in the crater for many years.
31:54But there is a constant emission of gases into the atmosphere from these funerals.
31:58Every day, a member of the Hawaiian Volcano Observatory team braves the huge volumes of sulfur dioxide and other toxic fumes to take samples.
32:14Without the gas mask, he would risk suffocation in minutes.
32:24And if it rains, the drops would absorb the sulfur dioxide, turning them into sulfuric acid.
32:30This work is important because changes in the concentration in the gases give clues about the state of the volcano.
32:40Fresh magma contains more gas.
32:44So if the concentration increases, it may show that the volcano is filling up with magma.
32:49The gases that basaltic eruptions emit are water and carbon dioxide, which are very common gases in the atmosphere.
33:04And also much more interesting for environmental impact, gases like sulfur dioxide, chlorine and fluorine, which can be released in the gaseous state.
33:13All of these can combine with water in the atmosphere to form various acids.
33:19The sulfuric acid stays in the atmosphere to form little round droplets or aerosols.
33:24And these droplets are what interfere with the incoming radiation from the sun.
33:29They both absorb it and backscatter it.
33:31So if there's a lot of aerosols in the atmosphere after an eruption, then less of the sun's radiation reaches the Earth's surface.
33:39And you generally have a cooling of the Earth's surface and thus change climate and alter weather patterns.
33:45Kilauea is releasing about a thousand tons of sulfur dioxide gas every day.
33:52When flood basalts were erupting, they may have discharged as much as three million tons of the gas a day.
33:59And this went on relentlessly for hundreds, if not thousands of years.
34:04The global cooling caused by these vast amounts of sulfuric acid was just the start of a lethal cycle.
34:17It was then followed by catastrophic global warming.
34:22We also get carbon dioxide, and as I think everyone knows, carbon dioxide is a greenhouse gas.
34:28And so if you put huge amounts of carbon dioxide suddenly into the atmosphere over a few years, then again, you might have warming effects.
34:36So you can get both cooling and warming depending on exactly where the gas goes in the Earth's atmosphere.
34:44We may well be seeing both of those effects, and they're not necessarily competing
34:49because they're producing climatic extremes in succession.
34:53And that's likely to be the most stressful kind of situation of all.
34:57In terms of effects on life.
34:59Because if you don't get it with one phenomena, you get it with the other.
35:04And it's really the one-two punch, if you like.
35:09This rapid fluctuation of warming and cooling would have changed environments all over the world,
35:15and even affected animals and plants that live far from the eruptions.
35:20So through this cycle, in years, decades, centuries, following one eruption, you would completely alter climate and harm the environment.
35:30Destroy the plants.
35:32Generate fires.
35:34Generate winter.
35:35Global winter.
35:36And then feeders.
35:37Animals who feed on plants would die.
35:40And then animals that feed on animals would die.
35:43So you break up the entire chain, and then think that you get another one, and another one, and another one.
35:49The flows of the flood basal hit and hit and hit again over hundreds of thousands of years.
35:55So you can imagine that by adding up these effects, you can in some cases reach a critical stage in which you really generate not a small harmful event, but a mass extinction.
36:09Flood basalt eruptions would have had an enormous influence on the way that life on Earth evolved.
36:15Their effects would not just have been local, but global.
36:18But there are questions which need to be resolved.
36:21If this primitive magma does originate from deep within the Earth, how does it reach the surface in such huge volumes?
36:28When will it happen again and trigger the next mass extinction?
36:39The heat source for most volcanoes comes from fairly shallow depths, just a few tens of kilometers beneath the surface of the Earth.
37:01Flood basalts are different.
37:06They tap a source of heat deep within the mantle.
37:10But the mantle is solid rock, almost 3,000 kilometers thick under the lithosphere.
37:16So how could such huge volumes of this material melt to form flood basalt larvas?
37:23The flood basalts are believed to originate deep within the Earth with what's technically called a mantle plume or a hotspot.
37:33There's a lot of debate about how these plumes might originate, but they're very likely to be a consequence of the Earth cooling.
37:43And to be a consequence of the way the Earth cools is that the interior of the Earth actually convects, it moves around.
37:51And these flood basalts seem to be triggered by the rise of large amounts of unusually hot material from the interior of the Earth.
38:01The Earth's rocky material at high temperatures and pressures moves around pretty much like toothpaste, but of course with much higher viscosities and much slower motion.
38:14We know that motion from plate tectonics.
38:17This is the big discovery of the last 30 years that the Earth's surface, the plates are moving apart at velocities typically between 1 and 10 centimeters per year.
38:26More or less, I think, the speed at which your nail grows or something like that.
38:31Well, this is just the top of a convection current.
38:34You must imagine that the kettle is full of liquid, which is sort of turning over at those typical speeds.
38:41And that is rock material.
38:43That is actual rock, not much less harder than the rock you see, but given the length of geological time, given millions of years, given proper temperatures,
38:54material can slowly displace and creep and will creep at that 1 centimeter per year velocity.
39:01And this is plate tectonic.
39:03This is global motion.
39:04At some point, this is not enough.
39:07And we have these plumes, these instabilities coming in.
39:10They are bigger, they are hotter, they are less viscous.
39:13It's possible that they move even faster.
39:15If you make a region of the Earth a little bit hotter, it becomes light and the forces of gravity make that material flow up to the Earth's surface.
39:29A bit like what people call a lava lamp you can buy in shops where you have two oils in the lamp and you heat one oil up at the bottom and it gets a little bit lighter and it forms a blob which rises through the other oil.
39:43And that seems to be what happens with the flood basalts.
39:52Bill Moore at UCLA is part of a team that develops computer models of mantle plumes.
39:58These show that in order to produce the volume of flood basalt that erupts on the surface, the head of the mushroom shaped plume may be over a thousand kilometers across.
40:08But how does this solid material turn into molten lava?
40:12The plume material is rising because it's hot.
40:16It's hot enough, it's hot enough that it would love to melt.
40:19Deep in the mantle the pressures are so great that they keep the melt from forming.
40:23They're confining the material into its solid phase.
40:27When the plume head finally arrives at the base of the lithosphere, the pressure has been dropping the whole time.
40:32And it starts to spread underneath the lithosphere.
40:35And finally it has gotten to a pressure low enough that it will allow this melt to form.
40:42Liquid, when it forms in the mantle initially, forms actually between the solid grains.
40:48And as soon as you get a little film of liquid in between solid grains, that liquid wants to get out of there.
40:53It is lower density and it's also under a lot of pressure.
40:56And it's much lower viscosity.
40:58So if you're squeezing this liquid, it's just like squeezing a sponge.
41:01The water wants to get out of there as fast as it can.
41:04And as soon as you form enough liquid to interconnect and make a network that can go from the source of the liquid up and out through a crack or some sort of vent to the surface, it goes.
41:17It goes, it goes quickly.
41:27How deep mantle plumes originate is still a matter of conjecture.
41:31Some ideas point towards a region about 700 kilometers below the surface.
41:36At this depth, there is a transition zone between the upper and lower mantle.
41:43Another intriguing idea is that they could come from even deeper.
41:47They could come from the boundary between the Earth's core, which is basically iron, liquid iron there,
41:53and the Earth's lowermost mantle, which is mostly rock, like the rock we know except higher temperature and higher pressure.
42:00At that boundary, a lot of heat is brought by the convecting fluid, the iron, which is just gurgling in the Earth's core, generating the Earth's magnetic field.
42:11That heat piles up and is unable to escape through the more viscous rock of the lower mantle.
42:18So a thermal boundary layer form thickens.
42:21You could imagine that eventually it becomes unstable and breaks in plumes that would then rise through the entire Earth.
42:28There's another series of models that suggest that, indeed, the activity begins at the core mantle boundary, but stops at the transition zone and triggers a second-order plume, which in turn will come to the surface.
42:41So the details vary, the depth, the size, but clearly major events deep into the Earth's mantle are responsible for what emerges eventually as a plume head or a flood bazaar.
42:53The time scale for this movement of rock inside the Earth is incredibly long.
43:02It can take a plume a hundred million years to rise up through the mantle and erupt as molten lava.
43:08But even with this slow progress, there are usually signs on the surface that a plume is on its way up.
43:15The surface actually feels the plume a long time before the plume gets there.
43:20That's because in the mantle, in order for anything to move, something has to get out of the way.
43:25And rock is viscous and it's slow.
43:28And even when a hot plume says, get out of my way, the rock is going to do it kind of slowly.
43:33And in fact, it's going to do it so slowly that it would rather push the surface up than get out of the way.
43:38So the first thing you see is whenever a plume is going to come up, you're actually going to get doming of the surface.
43:43This is a dynamic kind of topography. It's literally being pushed up by the plume.
43:50This doming effect is clearly present in the hot spot volcano of Hawaii.
43:55Data from deep ocean mapping reveals that over a large area around the Hawaiian islands, the ocean floor has been raised up by several hundred meters.
44:04The most likely cause is the plume which started its journey from the mantle, perhaps a hundred million years ago.
44:14Once the plume has reached the surface, its tail then provides a continuous supply of hot material.
44:20So Hawaii and other hot spot volcanoes represent the final stages of a huge transfer of heat from the Earth's deep interior.
44:37The Earth is a global object which is trying to cool down.
44:41It's trying to get rid of its heat. It will go to perpetual cooling, but it doesn't do it in a simple way because it's made of layers.
44:48And these layers have very different properties, so they're coupled.
44:53And things that happen in one will have an influence on the other.
44:57Magnetic changes in the Earth's field in the core.
45:00Plumes at the core-mental boundary.
45:03Instabilities in the lower mantle. Changes in the transition zone.
45:07Transformation of the lithosphere. Cracking up. Continental drift. Breakup of ocean basins.
45:12Flood basalts coming on the surface. Changes in the atmosphere.
45:17Hence changes in the biosphere.
45:19Are all, in a way, events that are coupled one to the other in a complex, non-linear causal way.
45:25The mantle plume under Hawaii may never have been large enough to erupt as a flood basalt.
45:34But other hot spot volcanoes are definitely linked to flood basalt eruptions.
45:38The island of Reunion, off Madagascar, is the hot spot that once fueled the Deccan traps of India.
45:49In the 65 million years since the flood basalts erupted, India has moved 6,000 kilometers away to the north.
45:56The flood basalts of the Deccan are cold and dead.
46:02But the remnants of the plume that once connected them to the hot interior of the Earth.
46:06Keep this volcano alive.
46:26The volcanic geysers of Yellowstone Park in Washington State, USA, are known to lie over the hot spot
46:36that created the Columbia River basalts, now 500 kilometers away.
46:41The slow, complex process of our planet's cooling may seem remote from our own history.
47:02But what happens inside the Earth has controlled our atmosphere, our environment, and consequently the evolution of life.
47:11It's interesting that the geologist is apparently bringing some really new lights to the biologists about evolution.
47:19The view which we have inherited from the 19th and first half of the 20th century, the neo-Darwinian view,
47:25sees evolution as a complex, interesting model of interaction between species and environment,
47:32leading to survival of the fittest, the well-known centers.
47:35Well, it seems to me that Darwin is right most of the time, and wrong at some key times in the Earth's history.
47:43Most of the time, evolution proceeds in the normal Darwinian way.
47:48But the times of those short catastrophes, when either an asteroid hits or a flood basalt is in place,
47:54are changing conditions so much that you cannot say that animals were not adapted.
47:59They could not be adapted to something that almost never happened.
48:03So at those times, which completely reorient the course of evolution,
48:07you should rather speak of the survival of the luckiest.
48:13Darwin's theory of the origin of species did not predict mass extinctions or flood basalts.
48:18But it may have benefited from them.
48:23It may well be that the way life has evolved on Earth has involved extinctions due to these,
48:32if you like, global environmental catastrophes.
48:35But those extinctions in themselves pave the way for the flourishing of life
48:40and rapid evolution after a mass extinction.
48:42So it could be that maybe we wouldn't be sitting here talking to each other
48:49unless there had been flood basalt eruptions in the past
48:52and other global catastrophes which had accelerated and triggered evolution of life.
49:05There is no reason to believe that the Earth will ever be completely stable.
49:09One day, a new giant plume will rise up from the bowels of the Earth
49:16and pour flood basalts out onto the surface.
49:19It may not happen for millions of years, but it will happen.
49:24When it does, whatever life forms are living on our planet
49:29will face the prospect of mass extinction.
49:31For them, too, it may be a case of survival of the luckiest.
49:37Or, too, no one will face possible.
49:40Then the side of the Muhammeden remains as nothingков über the sight Mountain.
49:45He has been alive, too.
49:47Theatic city are quite the only way to landfall.
49:49The struggle of the luckiest.
49:51It is not an accident or that the Romans is almosturn треб to adapt it.
49:56The traces of the Across the Earth
49:58Jesus temple in the country that we need to collect into distress
50:01at all during a nation after a new age.
50:02Take the library and the empty temple.
50:06Science Line has experts available now
50:18to answer any questions you might have about volcanoes.
50:21Call 0345 600 444.
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50:27and every weekday between 1pm and 7pm.
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50:32That's 0345 600 444.
50:37They created a monster.
50:39Half plane, half boat.
50:41A Soviet secret discovered accidentally by Western intelligence.
50:45A technical gamble that the experts said would not work.
50:48They were wrong.
50:49So wrong that this secret may well lead to a transport revolution.
50:53Ride the Caspian Sea Monster next Tuesday at 9 on 4.
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