Most of the time the surface of our World gives no hint
of What lies beloW
but there are a feW places on earth
Where We can get a glimpse
of What's happening inside the planet.
That is just one fantastic sight.
You can really see hoW much of this cone has fallen in
These taller slopes are all very recent.
Like all the loose boulders We see doWn here
have fallen off the crater Walls since March.
This is Mount Kilauea on the island of HaWaii.
Scientists from the US Geological Survey
regularly fly up here to take the pulse of the volcano.
They need to get as close to the active crater as possible.
lt's not a place Where you Want to hang around
if you don't have to.
lt's the pond of lava at the bottom of the crater
Which they need to keep an eye on.
Any change in level could be Warning of an imminent eruption.
We're standing on the crater rim of Pu'u'O'o cone.
This is the active vent
on the eastern slope of Kilauea volcano.
Potential hazard here is the, When the pond is so loW
there's not much supporting the inside of the crater
so We'll have large chunks of the crater rim
that fall and if that happens pond level
Would then rise and fall, rise and fall
and you'll also get spatter and,
and of course you don't Want to be standing on a chunk
of rim that might actually go doWn in.
Mount Kilauea is the World's most active volcano.
Geologists suspect that all this vulcanism reflects
some remarkable phenomenon deep Within the planet.
But the problem scientists face
is that the Earth's interior is totally inaccessible.
Yet in a sense scientists have managed
to descend to the very centre of the Earth.
ln a remarkable series of experiments
they've probed our planet to its core.
They've shoWn hoW the same process
that created this volcano
also keeps the entire surface of our planet
in constant motion.
There's no better place to see that motion than lceland.
The island sits astride
an extraordinary break in the crust,
a rift that marks the boundary betWeen tWo of the vast plates
that make up the planet's outer skin.
Up close this rift appears
as a series of deep and narroW cracks
in the surface.
Here geologists like Bob White
can study at first hand the Way the plates move.
This fissure here is one of the, the many sWarm of fissures
across about a 50 kilometre-Wide zone
Where the motion betWeen the American plate on that side
is moving aWay from the Eurasian plate on that side
at a rate of about 20 millimetres a year,
on average, about that much per year.
The movement that's so visible in lceland
is in fact happening all over the World.
By the late 60s
scientistshad Worked out that beneath the crust
the entire surface of the planet is divided up
into a small number of pieces - plates.
These plates are all sloWly moving
carrying the continents With them.
The theory that described this motion
Was called plate tectonics.
lt Was the biggest step forward scientists
had ever made in understanding the Earth.
But there Was something missing.
They kneW the plates Were moving,
but scientists had no idea
Why they Were moving.
Nobody Was more Worried about this problem
than one of the architects of the theory;
Dan McKenzie.
By the beginning of the 70s
We had some understanding of
What Was going on the surface
'cos We'd been able to map the motions of the plates
really in quite some detail all over the, the World,
but What We really didn't have at that stage
Was any decent understanding
of hoW these motions Were maintained,
and the obvious place to look is,
is underneath the plates in the mantle
'cos it clearly, they clearly Weren't being driven
by the Winds from the outside, right.
lt had to be an internal process.
The first hint of What lies inside our planet
came from scientists like Bryndis Brandsdottir,
Who spends much of her time monitoring
the many earthquakes Which shake lceland.
We use different kind of sensors
to monitor different things Within the Earth.
For instance you can see earthquakes
Which occurred in the region late last night
and early this morning.
But With the right equipment
scientists can do far more
than locate and record local earth tremors.
With better senses We can record earthquakes
from all over the globe
and if they're big enough to send Waves through the earth
those Waves can give us information
about various places Within the Earth
By putting together information
from thousands of earthquakes,
scientists built up their first complete picture
of the Earth's interior.
At its centre lies the core,
an immense ball of liquid iron,
the size of the planet Mars.
Beyond the core is the vast bulk of the planet,
the mantle, Which is composed of solid rock.
The plates are simply the upper layer of the mantle
With the crust just a thin veneer on top.
But this picture gave no hint of any movement in the mantle
that could be driving the motion of plates.
To make progress
scientists needed a different approach.
Here in Lovgrun,
SWedish island in the Baltic,
scientists have long been intrigued
by a mysterious phenomenon.
Canadian geophysicist Dick Peltier
has made the journey from Toronto
to meet Martin Eckman
and see things for himself.
The sea has alWays been important here.
People notice When it changes.
ln 1940 Lisa Nygren Was a young Woman.
Lisa tell us that she is about 35 years old here
and you can see that in front of the boathouse here
there is a lot of Water.
NoWadays there is no Water here in the long ridge.
lt's completely dry, just gravel and grass.
lt seemed to the people here
that the sea Was sloWly ebbing aWay.
She tells me that When she Was young
there Was Water here,
it Was filled With Water,
a small inlet from the bay.
You mean you could bring boats
right up into What are noW fields.
Yes, roWing boats.
Peltier and Eckman are not the first scientists
to study the phenomenon.
TWo and a half centuries ago
the famous SWedish physicist Anders Celsius
noticed the same thing.
This is the famous rock of Lovgrun
and here is the sea-level mark made by Celsius
in 1 731 ,
so 250 years ago sea-level Was here.
Today it's doWn there.
Thanks to Celsius' foresight, Peltier and Eckman
can calculate the rate of apparent sea-level drop here -
over one centimetre each year.
The problem is there's absolutely no evidence of
any significant change to global sea-levels for 10,000 years,
since levels rose at the end of the lce Age.
Perhaps it's not the sea that is falling,
but Scandinavia Which is rising.
On the SWedish mainland Peltier and Eckman
have found evidence that this is indeed What's happening.
lt's astonishing.
Believe it or not, this is a beach.
We are noW 200 metres up a mountain
and 30 kilometres from the sea.
9,000 years ago this Was at sea-level
and this Was the seashore.
You can see the stones here
have been reWorked by the sea Waves.
Over the years this has been lifted up nearly 200 metres
and this is the result.
All the evidence suggests that
since the ice melted 10,000 years ago
Scandinavia has sloWly but steadily been rising out of the sea.
lt may seem completely bizarre
but When you think about it
there's a very simple and Wonderful explanation
that has to do With the Earth's mantle
and With lce Ages.
20,000 years ago
the Earth Was in the midst of an lce Age.
At that time all of Scandinavia Was covered by ice.
Over central SWeden the ice Was about 3 kilometres,
almost 2 miles deep.
The great Weight of the ice load forced Scandinavia to sink.
Just like loading a boat in the sea,
the greater the Weight of the load put in the boat
the deeper it sinks into the sea.
But by 9,000 years ago the ice had melted.
As time passes the land begins to rise
rebounding back to its original outline,
just as a boat bobs upWards
When load is removed.
So What Celsius first measured 21/2 centuries ago
Was not the sea ebbing aWay
but the land bobbing up
as the great Weight of the ice disappeared.
HoWever, this explanation, neat as it is,
requires that beneath Scandinavia
the earth's solid mantle is acting very strangely.
Like the Water beneath a boat
it must be floWing.
What sort of stuff is rock solid yet floWs?
Understanding that Would turn out to be the key
to the mystery of Why the plates move,
but to get that key
scientists Would have to perform
an ingenious series of experiments
Which Would take them deep into the planet's interior.
The first step Was to get hold of some rock from the mantle.
lt's rare stuff
but just occasionally olcanic eruptions
bring to the surface
small unmelted fragments of the mantle.
lt's a green crystalline material called olivine,
but to tell hoW this stuff behaves in the mantle
scientists need to simulate the enormous
temperatures and pressures of the Earth's interior
in the lab
so a tiny sample of olivine is squeezed
betWeen the jaWs of a specialised vice
called a diamond anvil.
To understand hoW pressure affects the sample,
Eckhard Salje needs to look
deep to the structure of the crystal.
The Way We are doing that
is to bounce off the sample here X-rays,
so radiation is coming in here,
it's bounced off here into a detector
and that Will tell us
What the actual atoms are doing.
As Eckhard uses these techniques to descend
ever deeper into the Earth,
he's revealing hoW the behaviour of our planet
is governed by What happens at the atomic level
inside the mantle.
Although the sample alWays remains solid
the intense pressures
can disrupt the structure of the crystals
and that means the solid material
can sloWly floW.
Suppose this is a piece of the Earth's mantle.
Seismologists tell us,
based on earthquake observations,
that this material is solid.
lt's elastic, it's resilient.
What could be more elastic or more resilient.
HoWever on a longer timescale
its behaviour is completely different.
So the mantle of the Earth is both a solid and a fluid.
lt's all a question of timescale.
So over long periods of time
the solid mantle is floWing,
but What does this floW have to do
With the motion of the plates?
Scientists Would find the ansWer to that
When they voyaged even deeper,
doWn to the iron core.
We have here a piece of iron
in Which We're going to re-create ignitions
at the centre of the earth.
And We have to do that by generating very high pressures
and We have to melt it
under those very high pressures.
Then We're going to stick it in this -
the hydrogen gas gun.
NoW Keith is loading the gun noW
With about 7lbs of gunpoWder.
When the gun is fired
it pushes this heavy piston
doWn this hydrogen-filled tube
Which starts out at 10 times atmospheric pressure,
but the time We arrive here
it's about 2,000 times atmospheric pressure.
Takes this disc, bursts it,
hydrogen comes out of here
and pushes on this projectile
accelerating it doWn this tube
up at, at about 10,000 Gs
up to a velocity of about 8 kilometres a second
Which is Why We call it the fastest gun in the West.
Once it gets here it impacts on the target
generating very high pressures,
melting the, melting the iron target
and has about 50 billionths of a second
to measure that temperature.
l'll zero the counters.
Neil Holmes is going to all this trouble
because he Wants to ansWer
a very basic question about the Earth's core.
HoW hot is it?
Yeah, everything looks good over here...
Since scientists are pretty sure
that the core contains molten iron,
the thinking is that its temperature must be close
to the melting point of iron.
Calibrate target chamber...
But not the melting point at the surface.
Bringing up X-rays...
The melting point under the stupendous pressures
at the centre of the planet.
Whenever you're ready. Ready to fire.
Let's go ahead, Yeah.
Well, there's not much left in here.
That used to be a part of some of it.
l don't knoW What.
So the Whole target, everything We started With,
is destroyed,
but When the projectile hit the iron,
the iron made a brief flash of light.
The colour of that light tells us What the temperature Was.
What it tells us is that melting temperature
is 6,200 Centigrade
This is over 1 ,000 degrees
hotter than the surface of the Sun.
What this means is the core of the Earth
is a gloWing ball of hot iron,
3,000 miles in diameter
and sloWly over the aeons that,
that heat is gradually moving out
to the surface of the Earth.
So at the Earth's centre beneath the mantle
there's a heat source hotter than the surface of the Sun.
Of course, as anyone Who's ever placed
a pan of Water on a stove Will knoW,
When you heat a fluid from beloW it starts moving.
A little bit of dye shoWs What happens.
Hot material comes up from the bottom,
rises to the surface Where it cools
and sinks back again.
This is the process knoWn as convection.
Could this be happening in the Earth's mantle?
To ansWer this question
scientists have had to put together
everything they've learnt about the Earth's interior;
the temperature of the core
size of the mantle
the properties of mantle rock
and the rate at Which they can floW.
Adding all this together
scientists came to an amazing conclusion.
Like Water in a gigantic saucepan,
the planet's interior is ceaselessly churning aWay
as it convects heat from the core
toWards the surface.
So the situation noW
is really very much more interesting
because We have this mobile Earth
Which is mobile because it's transporting heat
from the interior toWards the surface
both upWards by hot material rising
and doWnWards by cold material sinking
and the thing acts really just like a, an engine.
lt's converting heat, right,
the heat Which it's transporting,
into some sort of Work
and it's this Work Which is driving
the plates round on the surface.
lt's not difficult to see hoW the motion of the plates
relates to convection in the mantle.
At the mid-ocean ridges hot mantle is floWing up
and as it cools it forms neW plate
Which moves aWay from the ridge.
Eventually it's cold and dense enough
to sink back doWn again into the planet's interior.
So the complex motion of the plates
is actually part of a simple process
by Which the Earth is sloWly losing
its massive store of heat.
But What about the vulcanism in places like HaWaii?
HoW did that fit into mantle convection?
The ansWer to that started to become clear
When Dan McKenzie began experimenting With convection.
His idea Was to simulate the behaviour
of the Earth's interior in the laboratory.
The heat source, the core,
Was represented by a Waster bath.
For the mantle above McKenzie
chose a rather surprising material;
a layer of golden syrup.
What We Wanted Was to look at convection in something
Which had a very large range of viscosity
like the Earth does because We, We kneW that,
that plates on the Earth's surface
are really very viscousb and strong
because they move as units over huge areas,
but underneath that We knoW
from the Way in Which Scandinavia recovers
after the ice melted that,
that the viscosity underneath
there is very much loWer than the surface plates,
so What We Wanted Was a material
Which had a huge range of viscosity
and Lyle's golden syrup is ideal.
But When McKenzie ran the experiment
the result Was a tremendous surprise.
lnstead of large plates he found
that the convection organised itself
into an interlocking pattern of small cells
each centred around a rising plume of hot material
surrounded by sheets of cold sinking treacle.
We could heat it in different Ways,
right, We could do all kinds of different things.
We could alter the top temperature
and alter the viscosity contrast.
Really doesn't make much difference, right.
You alWays get this pattern,
lots of little cells,
not really at all like What We Wanted for plates,
but this then gave us the idea that,
that maybe on Earth
the same thing Was going on
and that underneath these big plates
there Were perhaps lots of little cells
like this Which Were convecting.
Could one of Dan McKenzie's
convecting cells lie beneath HaWaii?
lf so, then all this lava
is coming from a plume of mantle rock
that has risen from deep Within the planet.
Why don't you stand about here and give me enough coil...
Lava floWs in underground channels
doWn from the main vent.
That gives Carl Thornber and Dave Bercovici
a chance to go fishing for a sample.
Perfect, absolutely perfect shot.
OK, noW We are ready to go ahead With this sample?
OK, take care to hang on to the end of that.
OK, looks good.
We're at the top of that lava fall
and it's in.
Oh Jesus, that's moving.
OK, l'm trying to get a good sample.
Man it's hot.
Come on baby.
OK, We're coming up.
We've got a big one.
OK We're ready to pull and clinch.
OK, here We go.
1 , 2, 3. Let's go.
That Was a good sample.
Yeah.
Anyone for tea?
Routine analysis of fresh lava samples
alloWs us to predict What the volcano might do next,
but perhaps more significantly -
some of these are still hot -
more significantly in terms of,
of Where all these basalts come from
this stuff contains an extraordinary proportion of helium 3
Which is relatively rare in volcanic rocks.
NoW one might Wonder Where this helium 3 comes from.
One source Where helium 3 is,
is still present Within the Earth today
is at the core mantle boundary
and if that's the case then one might expect that this stuff
came from Way doWn there.
The composition of the lava indicates
that it's come from mantle rock
that has risen rapidly from deep doWn in the Earth,
and there's another line of evidence
that HaWaii sits above a plume.
This evidence comes not from the erupting lava,
but from the shape of the HaWaiian archipelago.
One of the major clues that We are standing above a mantle plume
is that the HaWaiian islands themselves
form an almost perfectly linear chain
that goes off to the north-West.
The plume is sitting under the Pacific plate
Which has been moving across it for 100 million years,
so the volcanic islands the plume created in the past
have been carried aWay by the moving plate.
ln time an entire line of volcanic islands
Was effectively burnt into the Pacific plate.
ln fact this island and Kilauea volcano
are moving off the centre of the plume
and giving Way to a neW volcano Loihi
Which is forming under Water
about 15 miles to the south-east of this island
and in about 200,000 years Loihi Will breech sea-level
and become the next HaWaiian island.
Once scientists realised
that mantle plumes really do exist,
they began to see them everywhere.
Where the plumes are coming up
they push up the surface a little bit
and so What We've been able to do,
quite recently actually,
is to, to map the Whole of the,
the convective circulation underneath the plates
and you can see that very clearly here in the Pacific.
Here's South America & North America & Australia
and Japan and HaWaii in the middle
and you can see these red patches
Where plumes are coming up
and the biggest of these is HaWaii
and What you're looking at here
essentially the fact that the sea floor's
all being pushed up, right,
by the plume coming up.
So HaWaii oWes its existence to the fact
that the plume beneath the island
pushes up the overlying plates into a large dome
and Where this happens on land,
the effects can be unexpected and far-reaching.
These patterns make sort of dimples
and even though they're very small
they control the, the, the floW of the,
of the largest rivers on Earth
and probably one of the best examples is, is the Nile
Where it floWs out from Lake Victoria here,
it floWs out through the depression, the dimple
betWeen these tWo plumes here
and then goes northWards
and it goes again through exactly betWeen these tWo
and then goes off into the Mediterranean,
so the convective circulation from the plumes
is actually much more important
in terms of hoW rivers floW than We thought before
and We can see this pattern of, of, of rising plumes
all over the Earth's surface everywhere We look.
So beneath the crust, beneath the plates
the rocks of the mantle move to their oWn rhythm.
Rising from deep Within the planet's interior
plumes of hot rock push up toWards the surface.
Less than 20 years ago plumes
Were no more than a theoretical possibility.
Today they are recognised as major features
of the planet Which can remain stable for tens,
perhaps hundreds of millions of years,
and it's becoming clear
that over Earth history they've played a major role
in shaping the surface of the planet.
These are the Kanheri Caves in Western lndia,
a large temple complex carved by Bhuddist monks
out of a single vast lava floW.
This floW is the result of a volcanic eruption
far bigger than anything humanity
has ever Witnessed.
Yet this is just one of dozens of such floWs
Which blanket much of Western lndia.
Piled one on top of the other,
they form this extraordinary mountain range,
the so-called Deccan Traps.
Here is evidence of vulcanism on a truly gigantic scale.
Most geologists assumed that the eruptions
Which produced this landscape
must have continued for tens of millions of years,
but in 1985
the French geophysicist Vincent Courtillot
came to the Deccan.
He Was interested in the Way the Earth's magnetic field
has changed over time.
When We first came here our purpose
Was to measure the magnetisation
of the lava in the Deccan.
When a lava floW cools beloW a certain critical temperature
it Will lock in the direction of the Earth's magnetic field.
lt has a memory of What the Earth's field
Was like at the time of cooling
and We knoW the Earth's field has been reversing,
flipping many times,
approximately once every million years.
So frozen into the lava layers
should be a history of these magnetic reversals.
Courtillot Was expecting to find dozens of them
recorded in the Deccan lava floWs.
What he actually found astonished him.
When We came here the estimates
for ages of the Deccan lava
ranged over as Wide as 50 million years,
so We expected to have recorded
maybe 50/60 reversals of the field.
When We had completed the sampling
and the Work in our laboratory
much to our surprise We found
that only 2 reversals had been frozen
in the lava.
That only 2 reversals had been recorded
Was proof that the Whole vulcanism
could not have lasted much more than say a million years.
This Was an enormous out rate indeed.
l could only have been caused by the massive eruption
at the Earth's surface of a mantle plume head.
Enough lava Was erupted here
to cover the United States
to a depth of nearly one kilometre.
Vincent Courtillot believes such a stupendous event
can only have been the result of a poWerful neW plume
splitting the crust
and breaking through to the surface.
When a mantle plume
comes to the surface of the Earth
the plume head Will bulge, deform the crust
and then burst out as a lava floW
With enormous volumes.
These plumes Which are born inside the mantle
and erupt to th surface of the Earth
Will modif the Whole landscape of a continent
in a very durable fashion.
And it hasn't happened only in lndia.
lceland too shoWs the unmistakable fingerprints of a plume,
but here the plume has done more than change the landscape.
There's evidence that
it's changed the motion of the plates,
reshaping an entire region of the globe.
lceland occupies a unique position on the Earth.
The fissure that runs across the island
is in fact, part of the vast mid-ocean ridge,
the great rift that runs up the centre
of the Atlantic
Where the ocean basin is sloWly opening up.
lceland is above Water
only because it is buoyed up by a mantle plume.
The influence of that plume is felt right across the island
in all sorts of Ways.
The Whole of lceland oWes its existence
to the mantle plume.
lt's elevating the Whole area something like 500 metres
above sea-level Where We're standing noW,
but the very hottest part of the plume
is right behind me underneath Vatna Jokull,
a huge glacier.
NoW the glacier's there
because that's the very highest point of lceland.
lt's the highest point of lceland
because the hottest material is underneath.
The mantle plume itself
is hotter than the rest of the mantle round it
so it's a little bit more buoyant and that buoyancy,
because it's less dense,
pushes up that region
and makes the very highest region,
the region Where the glacier forms.
NoW that particular glacier is the,
the largest glacier outside the Arctic or the Antarctic,
so it's a big feature
and it's another 1 ,000 metres above us,
so it's something like 4,000 metres
above its normal level.
lt's sort of ironic that the coldest part of the lceland
is sitting right above the hottest part of the mantle.
The hot mantle plume also creates volcanoes,
a dangerous combination of fire and ice.
ln fact there's 5 major volcanic systems
underneath Vatna Jokull
and it's those volcanic systems
that have been responsible
for some of the biggest eruptions
in lceland over the past centuries.
ln fact the, the biggest historic eruption
in the World occurred from a volcano underneath Vatna Jokull
in 1 783
and that particular eruption
didn't actually kill anybody
from the lava that floWed out from it
but such a lot of dust and ash
and other toxic gases Were erupted at the same time
that the majority of the livestock
on lceland Was, Was killed
and the next Winter in 1 783 and 1 784
25% of the population of lceland died
as a direct result of that eruption.
ln 1996
the volcanoes under Vatna Jokull spoke once again.
This time fortunately the ash fall
Was mainly confined to the ice cap itself,
but as the heat from the eruption melted the ice above,
a tremendous deluge of melt Water floWed out
from under the glacier sWeeping all before it.
As roads and bridges Were sWept aWay
lcelanders Were once more reminded
that the plume that has created their homeland
also harbours aWesome destructive energy.
lt's the poWer of mantle plumes
to drive enormous changes to
continents and oceans that intrigues geologists.
The material erupted from its volcanoes
has built up the crust of lceland,
but scientists noW suspect
that the plume may have shaped the environment here
in a far more profound Way.
They've started to ask themselves
Whether it's merely coincidence
that here a mantle plumesits right
underneath the great mid-ocean ridge.
Could the lceland plume have caused he rift
in the first place and triggered the opening
of the Atlantic 58 million years ago?
Clues to What happened then can still be found,
not in lceland but on the West coast of Scotland.
Here geologists have found that the Western lsles
are largely composed of volcanic rock.
Above the Atlantic surf rise great cliffs of basalt
With its characteristic hexagonal columns.
All these formations have been dated
to a relatively brief period,
58 million years ago.
Volcanic activity on this scale is evidence
for an event similar to that
Which caused the Deccan Traps,
a neW mantle plume head Which split the crust
and 2,000 kilometres aWay to the West,
Greenland too has similar huge basalt formations.
So the rocks on both sides of the Atlantic
bear Witness to the impact of a plume
from deep Within the mantle.
As the plume pushed up against the crust it split,
rifting Greenland off from Europe.
Once split,
Europe and Greenland continued to move apart
creating a neW ocean basin in the North Atlantic.
Ever since then the plume has been sitting
under the rift producing lceland,
the largest volcanic island on the planet.
The plume under lceland has produced some enormous changes
in the 60 million years or so since it started to rise
through the Earth's mantle.
Without that event in the planet's interior
the Whole of the northern hemisphere
Would look totally different
and North America Would still be joined to Europe,
but plumes may have even more significant effects
than the shaping of the planet's surface.
Some scientists are beginning to suspect
that they may change the course of evolution.
The vast Deccan lava floWs Were all erupted in,
geologically speaking, a blink of an eye, but When?
Usually they may extend up to 100 metres
you knoW and if We look very carefully...
Palaeontologist Ashok Sahni
has helped Vincent Courtillot pin doWn exactly
When the plume head hit the surface.
Could this event have had global consequences for living things?
These here are the teeth of mammals.
These mammalian teeth Were recovered in sediments
lying in-betWeen the Deccan floWs.
They belong to very primitive mammals
Which are related to the present-day shreWs.
These mammals evolved at a fairly fast rate
and it's possible to tell
from these teeth exactly Where We are in time.
They give us a date
for the initiation of the Deccan volcanics
and this date happens to be 65 million years.
They belong to an era that is What
We call the Cretaceous period
and surprisingly it is this Cretaceous period,
the end of this Cretaceous period
Which also saW the extinction of the dinosaurs.
lf you ask someone What killed the dinosaurs
he or she is likely to tell you Well,
it Was the impact of an asteroid
and they might Well be right.
But that cannot explain all of the extinctions.
Palaeontologists tell us that
Well before the impact hit the earth
species had begun sloWly disappearing.
When l mean sloWly
l mean in the course of tens of thousands
or hundreds of thousands of years.
This is precisely the timescale of the Deccan eruptions.
This is What makes me prefer that explanation.
As the large plume head came from inside the Earth
it started erupting lava floW after lava floW.
You should imagine these lava floWs
pumping into the atmosphere vast amounts of gases
sulphur dioxide, carbon dioxide,
chlorine and also large amounts
of dust obscuring the skies. Obscurity Would cause cold,
possibly freezing and then acid rains Would folloW.
Real hell everywhere.
And When the Deccan had finished erupting
60% of the species had disappeared
from the surface of the Earth.
Among the survivors Were those tiny shreW-like mammals,
our oWn ancestors,
Who Were to flourish in a World freed
from the grip of the large reptiles.
lf Vincent Courtillot is right,
then in a sense We human beings oWe our existence
to events deep Within the Earth.
The link betWeen the Earth's activity
and the course of evolution
is something We'll be exploring later in the series.
The scientists Who've explored the Earth's interior
have made a profound discovery.
Beneath all the complex changes
We see at the surface
there is an underlying simplicity -
the vast churning heat engine of the Earth's mantle,
an engine Which drives the dance of plate tectonics
and reforms our World
in a myriad different Ways.
Here in lceland scientists can Witness
the Workings of that engine at first-hand.
As the Earth cools by convection
so the continents shift over its surface and rift apart,
but plate tectonics means that continents don't just separate,
they must also collide
and it's What happens When tWo continents collide
that's the subject of our next programme.