Original subtitles

MUSLIM CALL TO PRAYER

Istanbul.

For more than 2,000 years it stood at the crossroads between East and West.

The point where Europe ends

and Asia begins.

The two continents divided by the Bosphorus Straits.

This is one of the great journeys.

Stepping off the continent, leaving Europe behind.

But crossing the Bosphorus isn't all that it seems.

This notion that Europe and Asia are separate is a bit of a nonsense.

From a geological perspective, they're both part of the same vast landmass.

Eurasia stretches from the Atlantic coast of Portugal

all the way through to Russia's Pacific coast,

making it the biggest continent on the planet.

To reveal how this mighty continent formed, I want to reach back in time.

Because, if you know where to look, there are clues to its ancient past

written into the world around us.

Its landscapes...

..wildlife...

Hey! Is that karimeen?

..and the very rock from which it's built.

The tiniest detail can reveal the history of a vast continent.

Evidence that shows how Eurasia was assembled

in a series of monumental collisions...

This just kicked off just as we got here.

..catastrophic impacts

that created the conditions for civilisations to rise,

changed the course of life on Earth...

..and left an indelible mark on the landscape...

Just a wall of rock and ice.

..a mountain range spanning the entire continent.

The story of how that formed was the story of how Eurasia formed.

A continent forged in a series of collisions that continue to this day.

And because the process that built Eurasia is still active...

Whoo-ho-ho!

..the largest continent on the planet

is merely the start of something far bigger.

The first clue to uncovering Eurasia's past can be found here in Istanbul.

For centuries, the city's strategic location at the heart of the continent

has made it a major centre for trade.

Turkish delight. Lovely!

With honey and pistachios. Pistachios?

Yes, honey and pistachios. It's lovely.

Just as it does to this day.

We have a present for your mother-in-law.

There's a joke there, I'm sure.

That's the thing about these bazaars -

they still sell the traditional things

that they've been selling since this city was in its infancy.

Look at this. Exotic foods there, spices.

Metals, spice men...jewellery, precious stones like this, ceramics.

If you want it, it's here.

Now smell, please.

Wow!

But there's one product that's shaped Istanbul's history like no other.

In a way, this city is here because of this stuff - silk.

Look at it, it's just gorgeous.

If you go back to the sixth century,

this is one of the most expensive, most sought-after commodities,

partly because it comes all the way from China

and also because how it was made was this closely guarded secret.

The story goes that a delegation of monks would smuggle back

a couple of silkworm inside a bamboo cane, brought it back here

and then this place, Istanbul, just took off as a hub of silk production.

And the fabric gave its name to the Silk Road,

the network of ancient trade routes that runs across the entire continent,

connecting China through Istanbul and onto Europe.

And the Silk Road is crucial to the story of Eurasia today

because beneath it lies evidence

that reveals the origin of the continent itself.

Evidence that can be found 500 kilometres southeast of Istanbul,

where the Taurus Mountains reach the shores of the Mediterranean...

..in a place that's been both a staging post on the Silk Road

and a site of pilgrimage since the days of Ancient Greece.

This whole landscape is steeped in myth.

Just over the back is Mount Olympus, the home of the Greek gods.

Actually, it's one of about 20 Mount Olympuses

that are scattered across the ancient world.

But the mountain that I'm climbing now is unique - Mount Chimera.

It's named after this mythological creature that's got the tail of a snake,

the body of a goat and a lion's head.

Oh, yeah - and it breathes fire.

These are the eternal flames.

In Turkish they're called Yanartas, which is just "flaming rock".

Look at them. Today they're maybe half a metre high

but in ancient times they were much higher,

so that if you were out at sea, you could see this place as a lighthouse.

But my favourite story, though, is, because we're so close to Olympus,

this could be the source of the first Olympic flame.

It's such a surreal scene.

But what fuels these flames is far more ancient.

And analysing it takes you back tens of millions of years

to the time Eurasia formed.

Fossilised sea creatures.

Plankton.

Three to four kilometres into the Earth.

Do you see this black residue here?

It's soot - essentially carbon.

That tells us that these flames are burning an organic compound.

In this case, natural gas or methane.

A geochemical analysis of these flames indicates

that that gas is coming from carbon-rich rocks deep underground.

Much of it from fossilised sea creatures, plankton.

To transform plankton into gas,

you have to take the long-chain hydrocarbons that make up the cells

and you have to break them into smaller and lighter bits.

This process happens spontaneously at around 140 degrees...

..temperatures that can be generated by burying the rock

three to four kilometres down into the Earth.

The best way to do that

is to pile layer upon layer upon layer of sediment on top of it.

And the place where that process happens all the time

is the bottom of the deep ocean.

The gas here shows that millions of years ago

this region of Turkey was underwater.

But the evidence of a lost ocean doesn't stop there.

It can be found all along the ancient Silk Road.

This is Eurasia as we know it today

and here we are down here in southern Turkey.

Some of the biggest oil and gas fields on the planet occur east of Turkey

in a belt through Central Asia to Afghanistan.

But east and west of that too there's evidence of a former ocean.

There's precious stones that started off as rocks on the ocean floor.

Things like jade which occur in Pakistan, in Burma and in China.

And then marble occurs in Greece, Italy and other parts of Europe.

You also get metals that are formed on the bottom of the ocean,

metals like copper that you get found in Cyprus.

But the final evidence, the best evidence

is fragments of the rock that I'm sitting on.

These are fragments of ophiolite.

Ancient ocean crusts

which you find formed in a kind of belt all the way across this region.

What all these lines of evidence add up to

is the fact that there was once a vast ocean

that stretched the entire length of this continent.

The continent of Eurasia as we know it today

didn't exist 200 million years ago.

Where the south of the continent, Italy, Arabia and India, are today

there was a 90 million square kilometre ocean.

The Tethys.

Western Europe was lost beneath its waves...

..and Britain was a collection of tropical islands

off its northwestern shores.

Wrapped around its long arcing coastline,

all the Earth's landmasses were joined together

into one vast supercontinent.

Called Pangaea, it was a land dominated by the dinosaurs...

..just as fearsome marine reptiles ruled the Tethys.

Today, all those creatures are now extinct.

And the Tethys Ocean itself has long since disappeared.

But what destroyed the Tethys

and led to the extinction of many of the creatures that lived in it

is the same geological process that led to the formation of Eurasia.

Because the story of Eurasia

is essentially the story of how the Tethys died.

The mystery of how Eurasia formed from the death of the Tethys

involves one of the greatest mass extinctions in Earth's history,

the rise of its ancient civilisations

and will reveal the continent's ultimate fate.

And clues to how that happened

can be found in the southernmost tip of India.

These are the gentle backwaters of Kerala in southern India.

A place famed for its spices, especially black pepper.

One of the key staging posts

on another of those ancient trading routes that crisscross Eurasia.

For centuries, Kerala's lakes and waterways

supported a traditional way of life,

a floating existence that still survives to this day.

I'm here to find something truly ancient,

something that's lived in waters like these

for over 100 million years.

A creature that provides a direct link

back to the most important event in the formation of Eurasia...

..and is, for the local fishermen, these waters' most prized catch.

A fish known here as karimeen.

Hello!

How're you doing? Hi there.

The karimeen is tasty. Very, very tasty.

Is there a lot? Is it all over?

All over.

So how do you catch it?

Do you jump in?

Catch it.

You make it sound so easy.

First, two of the fishermen use a line

to scare the fish into the mud at the bottom of the lake.

Then the others swim behind, making a noise to startle the fish...

..before plucking them from the mud with their bare hands.

Hey! Is that karimeen? Yay!

Fantastic! Number one.

That's fast.

Very nice.

Put it in there.

This is it. This is what all the action was for. A karimeen.

Latin name Etroplus suratensis.

A fish whose anatomy reveals the evolution of entire continents.

IAIN'S VOICE ECHOES: ..the anal fin...

..shape of the skull...

It's a type of fish called a cichlid.

They're marked out by a couple of anatomical quirks

that make them distinctive.

One of them is right at the back.

It's at his rear end, basically, the anal fin.

Now, in most cichlids, the anal fin's got three or four spines

but this species has many more.

The other characteristic is at the front end.

It's in the distinctive shape of the skull

which relates to the swim bladder,

that sac that controls the buoyancy of the fish.

There's only one other group of fish

that share these distinctive characteristics.

The closely related Paretroplus cichlids.

And they live over 4,000 kilometres away...

..in Madagascar.

Now, Etroplus can tolerate slightly salty conditions

but they're essentially a freshwater fish,

so one thing's for sure is they didn't swim here.

Instead the answer is that it's not the fish that moved.

It was India.

This is a reconstruction of how the Earth's landmasses looked like

120 million years ago,

just before the emergence of the first cichlid fishes.

You can see up here, China and Siberia fused together.

And you can see the area here that's going to become Britain

and this in here in blue is the Tethys Ocean.

Then down here past the equator into the southern hemisphere,

tucked snugly in beside Madagascar, is India.

If I press "play" here I can simulate how the landmasses then move.

What you find is that in 90 million years,

India and Madagascar split.

Then suddenly, 25 million years after they separated,

India more than doubled its speed.

That's dramatic stuff.

That's a mini-continent, something like 3,000 kilometres across,

just speeding across the globe, crashing into Eurasia.

Fantastic! I never tire of watching this. It's great.

India's journey north was a key moment in the formation of Eurasia

because, as it moved, it closed the ocean in front of it,

spelling the beginning of the end for the Tethys.

But the big question is what caused it to speed up,

because that led to one of

the most catastrophic events in Earth's history.

You can see evidence of that cataclysm in the hills outside Mumbai,

a place known as the Deccan Traps.

The Deccan.

It's one of those words for a geologist that conjures up these images.

This iconic landscape. Stepped plateaus and things.

And yet this kind of gentle landscape holds in it

one of the cataclysmic geological events in the planet's past.

There's telltale signs in that cliff face there.

You see, it looks like a set of bands. They're layers of lava.

Molten rock that came out, solidified

and then built up layer upon layer upon layer

over tens, hundreds of thousands of years to form these hills.

68 million years ago, this landscape was very different.

Eruption after eruption poured 1.3 million cubic kilometres of lava

across southern India.

Enough to cover the UK in a layer of rock five kilometres thick.

All over these hills, there's gems like these just carved into the lava.

But there is no volcanic activity in India today,

so the question is where's the source of these eruptions?

And how did it speed India up?

This whole cave is carved out of a type of lava called basalt.

IAIN'S VOICE ECHOES: Ilmenite... magnetite...

latitude.

It's got really fine crystals.

About 10% are minerals called iron oxides - rust.

It gives us this reddy browny tint.

Minerals like ilmenite and magnetite.

And that's the clue, because these iron oxides are magnetic.

Just after the lava solidifies,

its temperature drops below 585 degrees

and the magnetic fields of the iron oxide crystals

align themselves with the planet's own field.

The thing about the Earth's magnetic field is that it changes

depending on your position on the planet,

where you are between the South Pole and the North Pole.

In other words, your latitude.

It's a property known as its inclination

and it means that the basalt contains a record of its position

at the precise moment it solidified,

which allows you to pinpoint exactly where it formed.

Today, this temple is at a latitude of 18.7 degrees north.

But the thing is, the magnetic inclination of the rock itself

tells us that it formed at a latitude of about 20 degrees south.

In other words, this lava formed in the southern hemisphere.

So the thing is that the source of this volcanism isn't to be found

deep beneath my feet here.

Instead it's several thousand kilometres in that direction.

If you trace India's journey back to the point it crossed 20 degrees south,

you arrive directly over a mantle plume.

A huge column of superheated rock

that rises up from near the Earth's core.

As India moved over the plume, it triggered the Deccan eruptions.

But deep underground it had another impact...

..something that can explain India's dramatic acceleration.

Continents flow around the mantle like vast ships.

Just as a hull of a ship lies below the water line,

so the bulk of a continent, maybe 80% of it, extends deep into the Earth.

Today, the Indian continent

is half the thickness of the other great landmasses.

It's thought that that's because

as the Indian Plate moved across that mantle plume

it melted away the base of the continental plate.

According to that idea, that huge loss of mass,

combined with the lubricating effect of that molten rock,

and also maybe an extra push from the mantle plume,

caused India to double its speed, propelling it towards Eurasia.

It was a geological cataclysm.

But the implications for life are even more dramatic,

because the Deccan eruptions contributed

to one of the greatest turning points in the history of life on Earth.

As the plume burnt its way up through the continent,

it pumped billions of tonnes of ash and toxic gas

directly into the atmosphere.

Over hundreds of thousands of years,

this slowly choked the planet and poisoned the oceans,

wiping out 50% of all life.

And for the dinosaurs it led to a drawn-out decline

until it's thought an asteroid finally finished them off.

But the end of the dinosaurs turned out to be our gain,

because, as one group of animals died out,

so another rose to take their place.

The mammals.

In a way, the extinction was curiously selective.

I mean, you and I would never have survived.

In fact, no land vertebrate larger than 25 kilograms made it through.

But back then our distant ancestors

had just the right mix of characteristics to survive.

And there's one modern mammal

that's thought to have similar adaptations today.

Because what's worked in the past

also works on the mean streets of Mumbai.

The city has such a large rat problem,

it employs a small army of rat-catchers, like Rakesh Daji Mittal.

So we think of humans as being the most successful mammal,

but I reckon we're looking at the ultimate one here - rats.

They've certainly got all the essential traits for survival.

They're small enough - they can get into nooks and crannies

and just keep themselves tucked away from harm.

And, in food, they're voracious eaters. They eat anything.

And that not having to rely on a single source of food is really useful.

It's...

And I guess the main thing is sex. These things breed like...

rats, really,

which is why the rat-catchers of Mumbai are struggling to keep up.

If it's a question of who's going to survive the next apocalypse,

my money's on them.

It's curious to think

that it might have been characteristics possessed by the humble rat

that enabled our distant ancestors to survive

where the dinosaurs had perished.

And that it was the movement of India that ultimately paved the way

for us to inherit the Earth.

As it continued north, India left the mantle plume behind.

But, now travelling twice as fast, it crashed into the rest of Eurasia...

..changing the face of the continent

and sealing the fate of the Tethys Ocean.

and sealing the fate of the Tethys Ocean.

But the demise of the Tethys

would have another major impact on human history...

..shaping the rise of Eurasia's civilisations.

Morning, Max. Hello, sir.

Hey! Welcome aboard.

It's small, isn't it?

To see how that lost ocean influenced our past and still affects us today,

you need to take a closer look at the most obvious result of the collision.

FAINT MUSIC Where's the music coming from?

Where's your tape deck? Your CDs?

Ah!

I love the music. I just can't get over the music.

Giorgio Moroder - lovely!

Ha-ha!

What a place you have here.

Ah! Ah-ah-ah!

It's a long way down.

It is a very, very long way down.

These are the Himalayas, the greatest mountain range on Earth.

Ah! Now we see the mountains. Here they are.

The Dhaulagiri's over there,

Manaslu's over here and Annapurna's ahead of us.

All three of those are over 8,000 metres.

26,500 feet. That's three of the top ten mountains in the world.

The mountains look solid and immovable.

Ah! That's majestic.

Just a wall of rock and ice.

But that is just an illusion.

These peaks are in fact a slow-motion car crash

playing out over millions of years.

Ah!

And still we climb.

Whoo-hoo!

It's absolutely stunningly beautiful,

but when you look at the mountains, as a geologist you see so much more.

It's almost like you see through the obvious snow and rock

to the inner workings.

You can see the process of mountain building almost in action.

I can see some folds.

So, Max, that's those folds up there.

See the rocks kind of wrapped around this enormous fold structure.

You can see that it comes across, swings down like a big Z shape.

It's not just the shape of them that's spectacular - it's the sheer size.

You see these Zs up there? Z.

We call them Z-shape folds.

It's very technical, geology.

These folds, some the size of entire mountains,

were created as India ploughed into the rest of the continent,

the immense power of the collision twisting and contorting solid rock,

as if it were Plasticine.

Ah, yeah.

I love it! Love it!

You might think these contorted rocks are pieces of the land

scrunched upwards as the two continents ploughed into each other.

But the reality is far more surprising.

This is one of the great rivers of Eurasia, the Kali Gandaki.

It starts up there in the north in Tibet

and flows down through the wilds of Mustang Province of northern Nepal,

down through here to India in the south.

For millions of years, it's been carving its way down through the Himalayas

to produce what down there is one of the deepest gorges in the world.

And it's in rivers like these that you can find clues

to the origin of the rock from which these mountains are formed.

Curious stones, called saligrams by the locals,

who worship them as manifestations of the Hindu god Vishnu.

What I'm looking for is hard, black nodules,

kind of black lumps of shale

that's fallen out of the cliff and then been washed around

and I'm hoping that at the heart of one of these nodules

we're going to find a saligram, because often they enclose them.

Need to break them open and reveal them.

What's lovely is that when you reveal them, if you get it,

you're exposing something that last lived in the Jurassic,

100-odd million years ago, sort of exposed back to the world.

And the other thing that's lovely, if you find one,

is you're the first person in the world to ever find that.

Cos it's been hidden away for 100 million years or so

and then you break it open.

It's your fossil.

So, if you see any, tell me.

You're looking for a natural weakness and once you get that...

This'll be the one.

This'll be the one.

This geology lark's harder than it looks.

The funny thing about it is, all the way up that road

there's guys selling these things.

They get them from the rock and sell them to all the tourists

and I thought no, no, I'm going to find them for real.

How much for this?

350. 350 rupees, OK. One...

This is going to be a bargain. There's 300... OK?

OK. OK.

Now this... This is a saligram.

Look at that. Absolutely beautiful.

Geologists know it better as an ammonite.

It's the fossilised remains

of an extinct member of the squid family.

The modern-day version would be the nautilus.

The body would be in here and the head

and tentacles would sit out here.

The thing is, just like the modern-day nautilus,

these creatures didn't live in the mountains - they lived in the ocean.

That's the thing about geology.

It's not really the rocks themselves that are important -

this is a rather boring black mud - but it's the stories they tell.

I mean, these ammonites were swimming around in Jurassic seas

when dinosaurs roamed the land,

when Eurasia was really coming together.

That's what the story of the rocks tell.

The walls of this valley, 2,700 metres above sea level,

are brimming with the remains of ancient sea creatures.

Marine fossils have been found right across the Himalaya,

including right at the top of Mount Everest.

It's astonishing to think that rocks that started out

at the bottom of the Tethys Ocean are now the roof of the world.

When India collided with Eurasia,

the ocean floor at the margins of the Tethys was thrust upwards...

..forming an immense barrier across the continent.

And it's by creating that barrier

that the Tethys has had a profound effect on the course of human history,

and still does to this day.

Because mountains this high can't help but interfere with the climate.

THUNDER RUMBLES

That is one angry sky up there, isn't it?

That's the thing about mountains - they create their own weather,

and the bigger they are, the bigger the weather they create.

Somewhere round that cloud and mist

there's the Himalayas, the biggest on the planet,

so it's no real surprise, then, that it produces

one of the most important weather systems on the planet - the monsoon.

THUNDER ROLLS

WIND AND RAIN

The winds that bring the moist air rise up along these slopes

and just dump rain and snow on those hills

and you get these brutal downpours like these,

running up to the wet season,

that dump water in the gorges and rivers up there,

create mudslides and landslides that just chuck it down, chuck material.

If you can just see, there's a river down there that's flooded,

that's full of mud and dirt that's been taken out of that mountain range.

This is one of the most dynamic active environments in the world.

But also one of the wettest.

THUNDER RUMBLES

THUNDER STILL RUMBLES

These sediment-laden waters flow down from the mountains

and out onto the plains of India, Pakistan and China...

..and, combined with the monsoon rains,

water and nutrient-rich soils from the Himalayas support three billion people.

Nearly half the world's population.

But the formation of Eurasia has had a much wider impact on civilisation.

Because India's collision was only the beginning of the end for the Tethys.

Arabia also moved north, creating the Zagros and Taurus Mountains

that run through Iran and Turkey.

Italy and Greece collided with northern Europe, building the Alps...

..and completing a mountain chain that spans the entire length of Eurasia...

..and marks the final resting place of the once-great Tethys Ocean.

And, just as the Himalayas support Asia's population today,

so this immense chain of mountains created the conditions

for the first civilisations to rise across the continent.

Oh, wow! Look at this.

Isn't that magnificent?

Many of the great Eurasian civilisations sprung up

in the shadow of the mountain chains that spanned the continent.

They occupied fertile river valleys that grew up

on the back of sediment the water washed down from mountains.

Following the line of the mountains and connected by trade routes,

a chain of empires developed across the continent.

But the mountains themselves also provided a sanctuary

for numerous city states, like the Pisidian city of Termessos

in the Taurus Mountains of southern Turkey.

If you were a society that lived in the mountains

then you had to work with the geological cards you'd been dealt.

This is a fragmented landscape.

Cities like this are physically hemmed in and isolated from the neighbours.

But isolation also means independence

and cities like this could become crucibles of invention and innovation.

Empires like the Greeks and the Romans

that had mountains at their heart became successful,

because they were able to harness that ingenuity.

So, in a way, Eurasia's long history of civilisation

goes back not thousands, but millions of years

to the formation of the mountains at the heart of the continent.

Eurasia as we know it was complete around 20 million years ago.

The landmasses that formed it had moved into their current positions.

And with the closing of the Tethys,

western Europe, including Britain, emerged from beneath the waves.

But the formation of Eurasia is really just the beginning of this story,

because the process that built it is still active today.

And by understanding that process

it's possible to chart the astonishing future that awaits the continent.

This is the Mediterranean Sea, instantly recognisable on a map.

In the west, it connects to the Atlantic Ocean

through the narrow Straits of Gibraltar

and then in the east it's the shores of Turkey and the Middle East that end it.

But, just like the Tethys before it, the Med too is closing,

as the vast African Plate moves north.

And where it collides with Eurasia beneath the southern tip of Italy

it's created a cluster of volcanoes that rise up from the ocean floor.

This is Strombolicchio.

It's actually the solidified throat of an ancient volcano.

200,000 years ago that rock was molten, rising up to spew

and explode out of a volcano that would have risen above our heads.

And then, around that time, that volcanic activity switched to the south

and this thing just crumbled and collapsed back down into the sea,

so all that's left is a solid volcanic neck.

The innards, the guts of an ancient volcano.

Today, the tiny island of Strombolicchio

lies two kilometres north of Stromboli...

..Italy's most continually active volcano...

Grazie.

..in a place you can see Eurasia's destiny taking shape.

The thing about volcanoes is that they're windows into the inner Earth.

This particular one is a window into the most important process

driving the movement of the continent.

The only trouble is that to understand it,

I have to get right up there.

The summit towers some 900 metres above sea level...

..casting a long shadow over the island

and the villages that cling to its shores.

Ha!

Look at it steaming away.

Oh, that's perfect!

This just kicked off just as we got here.

They call it "puffing" here - a big puff, and you can see all the boulders

just rolling down the hill and the smoke there.

We've arrived.

BLAST Hey! Hey!

Look at that.

That's Stromboli for you.

Isn't that magnificent?!

This volcano's been doing this, exploding like this,

every ten, twenty minutes really for the last 2,000 years.

Whoa!

That's a good 'un.

That's a cracker!

It's so hard to get an idea of the intensity of that,

but those orange balls that are getting kicked out there

are actually metre-sized boulders.

And the temperature of that must be 500, 600 degrees.

Extraordinary! You really don't want to be much closer than this.

Well, I do, but...

What makes Stromboli special is it doesn't really produce that much lava.

Unlike volcanoes like Hawaii and Etna that spew out these huge lava flows,

this volcano's eruptions are almost exclusively explosive.

And at night, when the sun goes down and the fireworks really start,

you really understand why it's called the Lighthouse of the Mediterranean.

Stromboli's regular explosive eruptions

create one of the planet's most astonishing spectacles.

But more than that, they're a clue to understanding the process

shaping the fate of the continent.

Whoo-ho-ho-ho!

IAIN'S VOICE ECHOES: ..viscous and sticky...

..trapped gases...

..so explosive...

..the Tethys destroying itself...

This crater rim is just littered with blocks

that have been thrown out of that vent down there.

Stuff like that.

This material is actually made of a rock called andesite.

Andesite is quite a light grey rock and that's cos it's got a lot of silica in it.

Because it's got a fair amount of silica in it,

it tends to make the magma quite sticky and viscous

and that means it traps gases.

It's just lots and lots of bubbles in this rock.

And it turns out that it's those bubbles

that's the reason why those eruptions are so explosive.

As the magma rises to the surface, the gas trapped inside expands

until the bubbles burst and the rock explodes.

But the gas responsible

isn't one you'd immediately associate with a volcano.

It's water vapour,

or steam.

This rock actually explains where the water comes from

to drive those steam eruptions.

You might think the steam comes from sea water

sinking into the volcano,

but actually the water's already in the rock.

Look at this. This is an andesite without all those bubbles

so that you can see all the beautiful crystals, called pyroxene.

Pyroxene crystals form at depths of five to ten kilometres.

And as they grow they encase tiny quantities of magma,

locking it away and carrying it up to the surface.

Now, if you could look into those tiny specks

of the original magma that formed this rock,

you'd find that there was water in them.

In other words, the water was actually in the magma

deep down in the mantle.

The only way water could be found so deep in the inner Earth

was if something carried it there.

In this case,

it was dragged down in the rock that forms the ocean floor itself.

Because Stromboli is a volcano

powered by a process called subduction.

Subduction generally happens when ocean crust meets continental crust.

The ocean crust rocks are denser so they sit lower in the mantle

and when they collide,

the ocean crust gets pushed under the lighter continental crust

descending down into the mantle. BANG

So that eruption up there actually started off

about 100 kilometres beneath our feet.

Down there, water gets forced out of those ocean rocks

and causes the rocks around them to melt,

which rise up and eventually burst out as volcanoes.

Subduction is the ultimate fate of all ocean crust.

But it isn't a consequence of the continents moving.

Subduction is the engine that drives the movement in the first place.

As the ocean crust descends beneath the continental crust,

it doesn't break off - it's still attached to all that ocean floor.

And it's that vast slab of rock heading down into the mantle

that pulls the ocean crust and in turn hauls the landmasses behind it,

dragging the continents across the face of the Earth.

Maybe it's because we live in the land that it's tempting to think

that it's the landmasses moving around that closed the oceans.

That it was the northward movement of India that destroyed the Tethys.

But actually it's the exact opposite.

It was the Tethys that pulled the continents together,

destroying itself in the process.

It was subduction that built Eurasia.

And it's subduction that's shaping its ultimate destiny.

For 300 million years subduction has been gradually,

inexorably closing the Tethys, creating Eurasia.

And as time goes on it'll close the Med too.

Africa will continue northwards, this whole area will emerge as land

and these islands will be the peaks of the Mediterranean mountains.

A great mountain chain at the heart of a new supercontinent.

As Africa ploughs northwards,

France and Germany become ever more mountainous.

And those peaks would look out over a vast desert

covering the whole of central Europe and Asia.

It's thought that 250 million years in the future

all of those continents will once again be joined together as one,

with Eurasia right at the heart of it.

Australia joins up with southern China.

The Americas crash into the shores of Africa.

And Britain is swept up towards the North Pole.

The formation of this vast new land, the planet's grand cycle,

that epic break-up

and movement of the continents across the face of the Earth

will begin once again.

Subtitles by Red Bee Media Ltd