Deep Earth How Earth Made Us

Our planet is full of incredible natural wonders.

Look at that!

Whoo!

It has immense power...

..and yet, that's rarely mentioned in our history books.

I'm here to change that.

I'm looking at four ways the power of the planet

has shaped our history.

The power of fire...

Oh...

..that fuelled great technological breakthroughs.

Wind...

HE CHUCKLES

..that has influenced the rise and fall of empires.

Water...

Our struggle to control it has directed human progress.

But I'm going to start by looking inside the Earth itself.

It's an unknown world, hot and extreme.

HE CHUCKLES

It's provided the raw materials for our conquest of the planet,

but at a price.

This is the great untold story of human history.

Hidden unseen within the Earth,

extraordinary geological forces are at work.

Hi. Gracias.

Forces that have shaped our history.

To really understand and appreciate them,

I've got to go deep into the Earth itself.

This is the Naica mine in northern Mexico -

the starting point for a journey to one of the most

spectacular and extreme places on or in the planet.

I'm really starting to feel it now.

I'm getting hotter and hotter, the deeper in I go.

This heat is just a taste of what lies ahead.

Finally, I arrive at what they call "Base Camp".

You know, where I'm heading is just so extreme, so oppressive

that I'm going to need all of these people, all of these control systems

and all of this kit over here just to get there.

It's going to be like visiting another planet.

Beyond here is a chamber that reveals the power of the inner Earth

to influence human affairs.

But to get there,

they've had to develop some pretty esoteric equipment.

Get this.

It's like a chain mail of ice cubes.

It's heavy, isn't it?

The special refrigerated suit will keep me cool.

What a palaver!

-This brings down my core temperature?

-Yes.

Oh, feels very cold suddenly.

That's very odd!

But it's not the heat alone that's potentially lethal.

This is what? This is the oxygen?

Yes, it's fresh air.

-It's fresh air.

-Yes. You'll need it.

The heat is combined with nearly 100% humidity.

If I breathed that combination,

moisture would begin to condense inside my lungs.

After about ten minutes, I'd start to suffocate.

-You're ready.

-I'm ready? I don't feel ready.

OK.

Without this suit, I could die.

It seems a lot of effort,

but inside there is one of the geological wonders of the world.

HE BREATHES HEAVILY

WONDROUS MUSIC

That is unbelievable.

This is just mad!

Absolutely gorgeous, isn't it?

This is la Cueva de los Cristales -

for my money, the most spectacular cave of crystals

discovered anywhere in the world.

HE CHUCKLES

You know, I've travelled around the world

to see some of the most amazing geology,

but this place - this place just tops it all.

Look at it.

It really looks perfect.

You can see through them, they're so translucent.

And there's different types.

You can see these ones that are like roses building up

and then these columns, these pillars - absolutely magnificent.

Until recently, no-one knew this chamber existed.

It was uncovered when miners broke through by chance.

You know, these extraordinary crystals

are made up almost entirely of a pretty ordinary mineral - gypsum -

but it's the sheer scale of them that astounds you.

This strange world is shaped by forces

that have had a profound impact on human civilisation.

HE PANTS

Oh, this heat... This heat's just too much.

It's unbearable.

But, oh, hey, the heat - that's what it's all about.

That's the whole point.

It's this cauldron that's the reason that these crystals are here.

It's so hot because only about 5km below the cavern...

..is an area of the Earth's crust that is super-heated molten rock.

This heats water, which dissolves minerals from the surrounding rock.

Phenomenal pressure forces this mineral-rich water

up through cracks in the rock and filled this giant cavern.

Here, the conditions were perfect

for the minerals to slowly crystallise back out of the water.

The cave lay undisturbed for over half a million years,

so the gypsum crystals just kept growing

until the miners broke through and the cave was drained.

But the hot inner Earth has done far more than create these crystals.

This incredible hot world hidden just beneath the surface

is a driving force for powerful geological events

that have shaped the fate of peoples throughout history.

This is the Timna Valley in Israel's Negev Desert.

Today it's pretty well deserted.

But over 6,000 years ago,

this place witnessed

one of the world's first great scientific breakthroughs.

Up until this point,

humans had made all their tools from stuff just lying around -

stone, wood, bone,

anything, really, that they could get their hands on.

But then, between 6,000-7,000 years ago,

our ancestors made an extraordinary imaginative leap.

They realised that the rock here contained a secret.

These green bands are called malachite.

And it was these malachite seams

that around 6,500 years ago

were at the centre of that incredible leap of human ingenuity.

Like the gypsum inside the crystal cave,

these bands of malachite

formed when hot fluids rose from deep inside the planet

and leaked into these rocks.

But unlike gypsum,

when malachite is heated up...

..it does something special.

It releases a metal.

Copper.

You know, in its day,

this copper axe head would have been the pinnacle of technology.

For a start, it's weighty.

If you hit something or someone with this, it would leave a dent.

For another thing, it's hard enough to take an edge.

And if it gets blunt, you just sharpen it up.

You can still see evidence of the ancient smelting pits at Timna.

But the copperworkers left behind a more striking memorial to their work.

A network of hundreds of tunnels, all carved by hand.

This was the first large-scale mining anywhere on the planet.

Those early copper miners

would have squeezed through these narrow shafts on all fours,

smashing their way through the rock

and hauling their pails of copper-laced ore back to the surface.

You know, the copper revolution

changed our relationship with the planet

in a really profound way.

For the first time,

we were transforming what the Earth offered us

and in the process creating entirely new resources.

And copper was just the start of things to come.

About 5,000 years ago, tin was added to copper

to form a new, more durable metal alloy - bronze.

By 3,000 years ago, refinements to the smelting process

meant iron could be smelted out of rock.

Metal tools became the foundation for human civilisation.

So it's clear we owe a huge debt to those first copper miners at Timna.

But we also owe a debt to the deep Earth.

The key to Timna's role in early history is its location.

The Earth's crust is divided into huge pieces called plates.

Where they meet are cracks known as fault lines.

Timna is next to the Dead Sea fault,

which separates Africa from Arabia.

This fault also connects Timna to the deep, hot interior of the Earth.

It's this hot interior

that is ultimately the source

of all the metals that have so radically changed our history.

Fault lines allow them to rise to the surface...

..just as they did at the crystal cave in Mexico.

But fault lines began affecting human history

even before the discovery of metals.

In fact, we've been strangely drawn to these boundary zones

ever since the dawn of civilisation.

And you can see why

in the barren wilderness of the Lut Desert in Iran.

The landscape is covered in hundreds of holes arranged in rows.

These holes in the desert

can help explain our ancient attraction to fault lines.

But that involves me going down one -

something the locals seem a little bemused by.

Hi.

So this is it?

HE SPEAKS LOCAL LANGUAGE

That's tiny!

I don't think I'll really fit.

How deep is it?

ROCK THUDS

God! Apparently it's 50 metres.

That's over 150 feet.

OK, I guess we do it, huh?

So we go down?

And if this deep, dark hole wasn't scary enough,

the method for going down is unconventional at best.

So we take this, like a pulley?

And this goes over the top, I guess.

So do I go on this?

You can't buy those, I bet you!

I've never gone on a rope with a tripod pulled by a tractor before.

So...

TRACTOR ENGINE REVS

Well, I think we should just do this before I change my mind.

OK. What could possibly go wrong now?

Blooming heck. It really is deep.

Oh, this isn't natural.

I'm getting lowered down into the bowels of the Earth here.

I wasn't sure if I was claustrophobic

but now I realise I think I am.

It's so far up!

Look at that.

Oh, dear. I don't want to do this too many times.

HE EXHALES

METAL TAPS

For over 2,000 years,

local people have been digging shafts like this - by hand.

And I get the sense I'm about to find out why.

HE SIGHS

All right, here we go.

Hey hey!

Ooh! Oof!

WATER SPLASHES

I misjudged it.

Look at this!

This is the answer.

The essential ingredient of every civilisation on Earth.

Cold, fresh drinking water.

This is what made this remote corner of the Lut Desert

one of the few places in the region that could sustain towns and cities.

And I'll tell you...

..after a trip like that, this is so nice to have.

HE SIGHS

Right. I'm off to explore a bit.

I want to find where the water's coming from.

This tunnel leading off the shaft is called a qanat.

It's one of many in this region,

hacked out of solid rock

to capture ground water that's stored deep below the desert.

I feel as if I'm in an underground rain shower.

I've travelled about, I don't know, a couple of hundred metres now

and it seems to be getting smaller and smaller.

HE GROANS

It's a bit narrow here.

Well, this is it.

This is the source of all this water.

It's just pouring in from here.

Underground water exists beneath most deserts.

But it's usually so far down,

there's no practical way of getting at it.

The difference is, here there's a fault line.

The fault is full of thick clay

produced by the grinding of the surrounding rocks

as they rub along the fault line.

This forms a clay dam, which water can't penetrate.

Water flowing down from the mountains

pools against the dam,

creating an underground reservoir

through which a qanat is dug to channel the water.

Gravity does the rest.

So originally the water would've been banked up against this fault line,

unable to penetrate through the clay-rich barrier.

But what the locals did was to cut a qanat across the fault line,

breaching the barrier and releasing the water.

It was a simple but brilliant piece of engineering.

OK.

Qanats were an ingenious early example of a mains water supply.

The shaft is simply a way

to get access to the tunnel carrying the water, so it can be repaired.

Today, the qanats still carry water from underneath the Lut Desert

into the nearby city of Bam,

as well as irrigating date orchards for which this area is famous.

Oh! Oh, it's so good to see blue sky.

Oh!

Yeah, thank you.

But this place isn't a one-off.

In fact, if you look back at the ancient world,

you see a strong link between fault lines,

water and the growth of some of the first cities.

More than 2,000 years ago, Petra in Jordan

was the most important trade hub in the Middle East.

It was built along a branch of the Dead Sea fault

and was entirely dependent on natural springs,

which rose along the fault and fed its irrigation system.

Nearby is Jericho, said to be the oldest city in the world.

It was first settled 10,000 years ago

because deep ground water rose along fault lines

to create fertile pastures in the desert.

More unusual is the ancient Roman city of Hierapolis.

It was built next to these terraces of white rock.

Here, it wasn't just water that was important -

minerals carried in the water were thought to have revitalising powers.

So Hierapolis became an important healing centre

in the Roman Empire.

Whether it was minerals, metals or water,

ancient civilisations were repeatedly drawn to the resources

that fault lines brought up from the deep Earth.

It's a connection which led 11 of the 13 most important civilisations

of the ancient world

unknowingly to build their cities close to a plate boundary.

As the earliest civilisations developed,

so the relationship between fault lines and human history

became more sophisticated.

They even played a role

in the establishment of the most advanced early civilisation of all.

4,000 years ago, in the Bronze Age,

the island of Crete was home to the Minoans.

Their showpiece was the palace of Knossos.

You can see by the sheer scale and sophistication of Knossos

that the Minoans weren't just another early civilisation.

This, in a way, was the beginning of modern society.

Certainly, this was a place

that you and I would have felt reasonably at home.

There was running water, a sewage system

and large stores of food and wine.

It all allowed the Minoans to create a new kind of society.

For me, all this is a moment in history

that is much under appreciated.

What the Minoans represent is a great pivotal point

when life switched from being dictated

by the grim realities of survival

into something that we could actually enjoy.

What the Minoans invented was the day off.

And the Minoans took their pioneering responsibilities

in this area very seriously.

Now, this may look like a car park,

but, really, this is where the paraphernalia

of the Minoan leisure society really took off

because this is one of world's first sports stadiums.

In its day, 500 spectators would cram in here

to watch boxing, wrestling,

and the Minoans' most peculiar sport, bull-leaping.

The basic idea was that you wait for a massive bull to run at you,

then at the crucial moment,

you grab hold of the horns and flip yourself over the top.

How do you practise that?

No-one knows why the Minoans leapt over bulls,

but this bizarre sport was a forerunner to bull-fighting.

But the real legacy of the Minoans was how they made their wealth.

This was the Bronze Age.

To make bronze, you need two metals - copper and tin.

The problem was finding them.

For the Minoans, copper was relatively near at hand in Cyprus,

thanks to the fault line beneath it.

Tin was trickier.

Inside the Earth's crust, only two parts per million are tin,

so it's much rarer.

The hunts for tin led to distant lands

that were at the edge of the then-known world.

One such place was so full of tin

that it was called the Cassiterides - "the tin islands".

Today...

..we know it as Britain.

But the centres of Bronze-Age civilisation

were in the Mediterranean, 3,000km away.

Tin was also found in other far-flung locations

like Spain, Central Europe and even Iran...

..which meant tin had to be traded,

and for this, Crete was perfectly positioned.

The Minoans exploited their position

at the crossroads of many different trading routes...

..to become the world's first maritime superpower.

It may not seem like it today,

but in Bronze Age times, this island was at the centre of the known world,

with the mineral-rich heartlands

of Europe, the Middle East and North Africa all around.

For the Minoans, it wasn't so much about owning the raw materials

as knowing what to do with them, how to put them together.

They built an empire because they'd worked out how to exploit the geology

that their neighbours had on their doorsteps.

By the time of the Minoans,

fault lines had been a crucial factor

in the success of many early civilisations.

But the Earth extracted a price for these riches.

It was a price paid in full by the Minoans.

At the heart of the story was a small archipelago

100km north of Crete.

Today that island chain is known as Santorini,

famous for its pretty white houses and rugged coastline.

But at the time of the Minoans this was a busy port,

the key to their trading empire.

If Crete was the heart of the Minoan culture,

then this place was its backbone,

a centre of industry that helped fuel what was at the time

the most advanced civilisation on the planet.

But Santorini held a deadly secret.

Unknown to the Minoans,

it sat above one of the Earth's major plate boundaries.

Santorini formed when the African plate

started sliding below the European plate.

As the African plate melted inside the deep Earth,

molten rock rose back to the surface

to create what is actually a volcano.

OMINOUS RUMBLING

Around 3,500 years ago,

this volcano did what volcanoes tend to do -

it blew up.

Unluckily for the Minoans,

it was the biggest eruption of the last 10,000 years.

Today you can still trace why the eruption was so devastating

in the cliffs around Santorini.

This cliff is made entirely of ash and rock spat out by the volcano.

It's got distinct layers to it,

each of which are from different stages of the eruption.

In other words, this rock face is a timeline of events.

Climbing this cliff helps understand the disaster

that was unlike anything anyone had ever seen before.

This level here was the start of the eruption.

I'm kind of standing on the Minoan land surface.

And in the next five hours,

the eruptions threw out an enormous mushroom cloud of debris.

It just rained down ash after ash after ash.

This stuff is just like a silica glass.

It gets into your lungs and it just lacerates your lungs.

You just choke on it.

This innocent-looking gravel

was from the second and most lethal stage of the eruption.

Sea water invaded the volcano

and that mix of water with molten lava

produced a series of incredibly violent eruptions

that punched a jet of superheated gas and debris

high into the atmosphere.

As these clouds of hot gas and lava fell back to Earth,

they engulfed the outer edges of the island.

Ay!

But, incredibly, the worst was still to come.

Once the volcano had spewed out everything that was in its guts,

the weight of it collapsed into the void below,

producing the most enormous blast.

And in the death throes of that final blast,

there was one last catastrophic flourish.

The centre of the volcano crashed into the sea.

That sudden collapse created a gigantic tsunami...

..which quickly spread out across the Aegean towards Crete.

WAVE CRASHES

For a civilisation whose strength was in their navy,

the tsunami would have been devastating.

It's thought that as the tsunami swept through the Aegean,

it engulfed the Minoan harbours,

and any boats in them would have been smashed into matchsticks.

So perhaps it's not that surprising that not a single boat

from the vast Minoan fleet

has ever been found.

This was a catastrophe from which the Minoans would never recover.

A long chalk-and-ash cloud and a giant tsunami

meant that this maritime power was on its knees.

With the fleet gone,

and their most strategic trading post obliterated,

the Minoans went downhill fast.

Within a century or so of the eruption,

this once-great civilisation was finished.

The eruption of Santorini

was an extreme event.

But ancient history is littered with

tales of cities destroyed along plate boundaries.

And it's not just volcanoes that do the damage.

Fault lines are also home to another deadly force of nature.

Earthquakes.

Recent events in Haiti are a reminder of just how devastating earthquakes can be.

The appalling disaster is a terrible example of how the destructive power of the deep Earth

can be concentrated along fault lines.

Over the past 10,000 years,

many cities first established to take advantage of fault lines

have been flattened.

Hierapolis, with its famous health spa,

was destroyed by a giant earthquake in AD 60.

Jericho, the oldest city in the world,

has been hit over 15 times by large earthquakes.

Some believe it was this

that famously brought its walls "tumbling down".

Likewise, Petra was abandoned

after an earthquake demolished its irrigation system in AD 360.

And it continues to this day.

In 2003, the city of Bam, famous for its qanats,

was devastated by a massive earthquake

which killed over 30,000 people.

It makes you realise that, in effect, much of human history

has centred on a bargain between us and the inner Earth.

Plate boundaries provide access

to resources from deep inside the planet.

But live near one, and you also live with the risk of a sudden catastrophic disaster.

But even the most advanced of our ancestors

had no way of explaining this strange coincidence.

In fact, it's only in the last 50 years

that scientists have finally understood

the bargain that was inadvertently struck all those years ago.

You can see the theory in action in the middle of the Pacific Ocean.

This is Kilauea on Hawaii's Big Island.

It's one of the most active volcanoes on the planet

because it's fed by a chamber of magma deep inside the Earth

called a hot spot.

The hot spot has effectively punched a hole in the Pacific plate -

the piece of the Earth's crust on which Hawaii sits.

But remove the ocean around Hawaii and something strange is revealed -

a chain of mountains stretching along the sea bed

for over 5,000km.

This line of extinct volcanoes is explained

when you realise that the Pacific plate is continually on the move.

As the plate drifts over this stationary hot spot,

a volcano forms,

but after about a million years,

the moving plate pulls the volcano away from the hot spot.

Meanwhile, another eruption begins, forming a new island.

Today, Kilauea is still growing, but it hasn't got long to go.

In a few thousand years, it will drift away from the hot spot

and eventually disappear beneath the waves.

The Hawaiian islands chain is a beautiful demonstration

of a big idea

that explains why plate boundaries

bring us extraordinary benefits and terrible hazards in equal measure.

It's called plate tectonics.

The key is that all the plates, which divide the Earth's surface

are continually on the move.

Where they collide, they crumple the land

to form great mountain ranges, like the Himalayas.

Where they pull apart,

oceans form in the gap.

The friction of this continual movement

means that plate boundaries become melting zones

where minerals are concentrated

and are able to rise towards the surface.

But the flip side is that huge amounts of energy

are concentrated along the plate boundaries.

When one plate slides underneath another, volcanoes form.

When two plates lock together and then suddenly break free,

the jolt causes devastating earthquakes.

So we now know that plate boundaries are so rich in resources

for exactly the reasons they're so dangerous.

Yet the strange thing is this groundbreaking discovery

has made little difference to where we live.

If you look at the plate boundaries,

it's clear that many cities are located close by.

In fact, 10 of the 20 largest cities in the world

are next to dangerous fault lines.

So why are we still building next to these danger zones?

In the rugged hills of central California

is part of the answer.

And to see it, I'm heading into the skies.

At least, I hope I am.

This is the dinkiest helicopter I've ever been in.

It'll be nice when it's finished.

MOTOR STARTS

I'm going to see

perhaps the most famous geological feature on the planet.

And this is the best way to find it.

Yeah, yeah, yeah, this is it. This looks fantastic.

It's this beautiful funnel cut right through these hills here.

That's amazing.

This line of hills with a trench cut through the middle

is the San Andreas Fault.

This fault is a boundary between the North American Plate to the east

and the Pacific Plate to the west.

For 25 million years, they've been grinding past each other

to create the largest earthquake fault in North America.

The San Andreas Fault starts up there in northern California,

then slices down through 700 miles through here

down to the border with Mexico.

As it goes, it cuts through cities and towns

and passes across a path of roads, bridges,

aqueducts and fibre-optic cables.

If ever there was a fault line

that cut through the very fabric of a modern society,

then it's this one.

But a good reason why over 20 million people

carry on living so close to this danger zone

is that this plate boundary has made California rich.

It began with the Californian gold rush.

These nuggets of gold might have been found in streams,

but the gold originally rose in hot mineral-rich fluids

forced up between the plates.

In fact, almost everything that makes California wealthy

is at least partly related to the San Andreas Fault.

Take, for example, the scenery.

It was the colliding plates

that forced up mountains along the Californian coast.

And this dramatic landscape attracts thousands of tourists every year,

who spend an estimated 2 billion on sightseeing alone.

Then there's the wine.

That's partly down to the San Andreas too.

California is mostly desert

but when moist air rolls in off the ocean and hits the mountains,

it rises to form rain that irrigates this otherwise arid landscape.

It's a microclimate that has made this

one of the most productive farming regions in America.

But the ultimate gift of the San Andreas is this.

HISSING

Oil.

Black gold.

This is an oil seep,

which is when oil leaks to the surface, like a natural spring.

HISSING

Except this is black and gooey.

Look at that.

150 years ago, when the first people were looking for oil,

even the most witless prospector

realised that places like this were a good place to drill.

And drill they did.

Over the years, around 200,000 wells have been sunk here.

Most people probably think of Texas as America's oil state

but California was and still is one of the world's biggest oil producers,

drawing more than 700,000 barrels of crude oil

out of the ground every day.

The oil formed millions of years ago, deep inside the Earth.

But it was the San Andreas Fault which split the rock

and brought it close enough to the surface to be exploited.

So it seems that the San Andreas Fault

has brought California some serious economic benefits.

Its shaping of the land has created the conditions for oil,

for agriculture, for wine and even for tourism.

But how much is that really worth?

The money men have done the sums.

They reckon this state earns around 100 billion every year

because of the San Andreas Fault.

California's geology is a licence to print money.

Earthquake geologists like me

know that California gets struck by a big seismic shake

every 100 to 150 years.

And those major quakes are hugely destructive.

That doesn't seem to dampen the spirits

of the number-crunchers that are in these skyscrapers.

It's worked out that in a city like LA,

a major earthquake will cause up to 250 billion worth of damage.

Now, that is a huge sum.

But averaged out over a century, you're still in profit.

You've got 100 billion a year coming in,

versus a one-off hit of 250 billion.

That's a gain of 40 to 1.

Any economist will tell you that's a pretty decent return.

10,000 years

after our ancestors first settled along plate boundaries,

the benefits of living along a fault line are as potent as ever.

The point is that in pure economic terms,

we're still financially better off living along a fault line than not,

even when it's one of the most active in the world.

But the problem that I have with that equation

is that life's not just about money.

Istanbul, the only city in the world to straddle Asia and Europe.

This location at the crossroads of two continents

has made it a trading hub for centuries.

That's why I find it so exciting.

It's a vibrant, bustling, cosmopolitan place.

But Istanbul's location also brings with it great danger.

Nearby lies the North Anatolian Fault,

one of the most seismically active plate boundaries on the planet.

Scientists reckon a major earthquake is due here any time.

There's little doubt that in the very near future,

Istanbul will be struck by a big earthquake.

It's a strange feeling

that this city that I love could be destroyed in my lifetime.

But it doesn't have to be.

Here, they're starting to rewrite the terms

of our ancient bargain with fault lines.

The aim is to enjoy the benefits of living along this plate boundary

without having to pay a price in human life.

Below the waters of the Bosphorus,

the channel that separates Europe from Asia,

is a clue to the solution.

You know, this is such an eerie feeling.

I'm 35m below the level of the Bosphorus

and I'm walking parallel

to one of the most active earthquake zones in the world.

So not the kind of place you expect to find a major engineering project,

and yet that's exactly where

the Turkish authorities decided to build an underground train line.

This tunnel, which will one day link Asia to Europe,

is the deepest tunnel of its kind on Earth

and yet it runs alongside

one of the most dangerous earthquake faults in the world.

These engineers are confident they've got the risks covered.

Through some technical wizardry,

the whole tunnel's designed to absorb the vibrations

of even the largest of earthquakes.

What these guys are doing, effectively,

is confronting the earthquake threat head-on.

This technology won't allow us to stop earthquakes,

but it shows

that if we really want to protect against their consequences, we can.

Unfortunately, in Istanbul, this tunnel is only half the story.

You know, high-tech underground train tunnels are all very well,

but the reality is that most people who'll die in the next earthquake

will die because the buildings that they live and work in collapse.

And in that sense, Istanbul is completely unprepared.

It's reckoned that when the next earthquake comes,

it might bring down a quarter of the city.

And the thing is, it doesn't have to be like that,

because we have the technical know-how to keep buildings standing.

The irony is Istanbul already has a building

that has survived earthquakes for centuries.

This magnificent building is the Hagia Sophia.

It's got to be my favourite place in the city.

For the tourists that come here,

this is a fitting symbol of Istanbul's reputation

as a crossroads of different civilisations.

In its 1,500-year history, it's been a church and a mosque

and now a museum.

The Hagia Sophia has stood through more than a dozen earthquakes,

without the benefit of modern technology.

It was built on such a massive, monumental scale

that even the biggest earthquakes never managed to knock it down.

You know, it's no accident that when the earthquake does strike,

the two things that'll probably survive

are one of the oldest buildings in the city and one of the newest.

And that's because they're both structures

that we've decided are worthy of looking after.

Today, we have the technology to protect every building -

whether it's flats, factories or offices...

..if we choose to.

For 10,000 years,

we've lived with the benefits and the dangers of fault lines.

You know, it's clear that people

are going to continue to live along fault lines -

probably for the next 10,000 years.

But now we have two clear options -

stick with the old regime and take our chances

or embrace the new and take some kind of control.

The trouble is, protection doesn't come cheap.

Reinforcing every building in an earthquake zone would be massively expensive.

So even with all our knowledge,

the deep Earth is going to continue to confront us with some tough choices

for years to come.

Next time - the magic of water.

It's constantly transforming itself,

shifting between guises and from place to place.

Our struggle to control it has shaped the destiny of some of the greatest civilisations in history.

Subtitles by Red Bee Media Ltd

E-mail [email protected]