All language subtitles for BBC How Earth Made Us EP01 Water (2010) English

Of all our planet's forces,

perhaps none has greater power
over us than water.

For me, water's the most
magical force on Earth.

The presence of water shapes,
renews and nourishes our planet.

Oh, my gosh!
You're getting all wet there!

It's our planet's lifeblood.

It pumps through it continuously,

delivering vital ingredients for life.

Ah, it's glorious.

Water makes Earth alive.

Yet water is just one of the ways

that the power of the planet
has shaped our lives.

The Earth has immense power...

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

I'm here to change that.

In this series, I'm exploring
four great planetary forces

that have influenced our history.

The power of the deep Earth...

...that fuelled technological innovation.

Wind.

It has shaped the fate
of entire continents.

And fire...

...which gave us the power
to conquer the planet.

But I'm going to start with water.

The magic of water is that
it's constantly transforming itself,

shifting between guises
and from place to place.

Our struggle to control it
has been behind the rise and fall

of some of
the greatest civilisations on Earth.

The centre of the Sahara Desert
in North Africa.

One of the driest places on Earth.

I'm over six hours' drive
from civilisation.

Temperatures here regularly reach
40 degrees Celsius,

and there's less than a centimetre
of rainfall each year.

Ah....

The whole thing's moving.

It's like walking on water.

Yet hidden amongst these dry dunes
are clues

that point to the dramatic influence
the planet has had on human lives.

I've come here because although
you'd never know it,

the story of this place
is all about water.

The clues are etched
into that rock face there.

Prehistoric rock art
dating back 6,000 years,

and depicting the most unlikely
cast of characters you've ever seen.

Wow, what is that?

It's a giraffe...

It's a giraffe, look at it,
there's the neck.

There's its ears, that's an eye,

and its mouth.

T hat's really natural, isn't it?

And this looks like the giraffe
dipping its head down,

drinking some water -
we've got a herd of giraffes here!

There's two cats.

They're fighting.

This... What is this?

It looks like the figure of a man,
but he's wearing a bikini.

And this is clearly a crocodile,
which is especially odd here.

This is an aquatic animal,
it doesn't just paddle around.

It needs a lot of water to live in.
In fact,

all the creatures that are depicted
on these rocks are not desert animals -

they need wet conditions.

In such a parched wilderness,
how can this be?

The only explanation is that
6,000 years ago, this place was wet.

Once you know what to look for,
the evidence is all around.

Up there is a river valley
that's been carved out into the rock,

and it's been carved by running water

which has flowed down here,
smoothing off this rock bed,

and then cascaded down into the valley
and off there.

6,000 years ago,
that was a big river.

Satellite images reveal
that the river bed I'm standing in

is just one of a network
of past river valleys

that crisscross the Sahara Desert.

10,000 years ago, this dry, empty place
was entirely different.

Little is known about the early Saharans
who lived here then,

but we do know that they depended
entirely on water.

Water formed the lakes
in which they swam.

Water nourished the plants
which fed the animals they hunted.

Water filled the clay pots
from which they drank.

But then the climate changed.

About 5, 500 years ago,
the Sahara began to dry.

The rains failed, the rivers shrank,
and the lakes dried out.

For the early Saharan people
there was only one option -

to follow the rains
and abandon the desert.

The fortunes
of the early Saharan people

reveal a universal, timeless truth -

our fate is inextricably linked to water.

The problem is,
water never stands still.

It's always on the move
across the planet.

We think of this as a blue planet.

But while water is abundant,
most of it is no use.

More than 97% of the Earth's water
is salty ocean, which we can't drink

or use to grow crops.

Less than 3% is fresh water,
on which all human life hangs.

What's more, that tiny fraction
is often hard to pin down,

because fresh water
has a life cycle all of its own.

I'm about to explore that cycle,
in all its elusive glory.

You know, water seems so familiar,
doesn't it?

But to see its remarkable qualities

you have to go
to some extreme lengths.

Here we go...

Ho-ho! Feel that!

Here we go!

Oh... Hey-hey! Oh, we're off!

Oh, my God!

It's a bit bouncy!

I shouldn't have had
that bacon and eggs this morning.

O-o-o-h!

The fresh water that we depend on
begins its life in the oceans.

As the sun's rays beat down
on the surface of the sea,

they heat the water molecules
until some evaporate.

It's the start
of an extraordinary journey.

You know, when water evaporates,

it feels as if it vanishes into thin air.

But although we barely notice it,

water molecules are suspended
around us all the time.

It's just that we're only aware of it
when they clump together

as cloud.

At any one time, less than a thousandth
of the world's fresh water is up here

in the atmosphere.

It may not seem much, but this is what
spreads water from the seas to the land.

A water molecule doesn't hang around
up here for very long.

In fact, it spends less time
up here in the atmosphere

than at any other time on its journey -

a mere nine days

until the typical water molecule
crashes to Earth as rain.

For most of us, rain is perhaps

the most familiar stage
of the water cycle,

but notoriously the least reliable.

As the water falls as rain,
it joins a bigger system,

cascading and carving its way across
the land surface as streams and rivers.

Look at that!

Water absolutely everywhere!

Rivers and rain are the part
of the water cycle that we depend on.

Whoo-hoo!

And yet they're only a tiny proportion
of the world's fresh water...

...a measly 2%
of all fresh water on the planet.

The rest of the Earth's fresh water

is locked away down there,
on the ground.

Oh...

Oh!

What a landing!

The vast majority of it is stored as ice.

Most of the rest
seeps deep into the Earth,

where it's known as groundwater.

Hidden away down here

is the planet's second-largest store
of fresh water.

But in the end,
all water arrives back in the oceans,

and the cycle begins again.

What that circulation
means for us humans

is that water is a moving target.

We constantly have to seek it out
on its endless cycle and intercept it

wherever and whenever we can.

This quest to...

to pin down water has played
a defining role in human history.

You can trace the impact
of our quest for water

right back to the dawn of civilisation,

about 12,000 years ago.

It all began with a big block of ice.

12,000 years ago,

much of the northern hemisphere
was covered in a single, huge ice sheet.

And even today
you can see its legacy...

...here in Iceland.

This glacier is a tiny remnant
of that once enormous expanse of ice.

Ice is like a storage cupboard in the
circulation of water around the planet,

a store into which water
can be deposited or withdrawn.

And it was a shift in the amount
of water locked up here

that was to drive one of the greatest ever
transformations of human society.

Today, the ice sheet here
is melting and retreating,

and releasing
this great armada of icebergs.

But if you go back 12,500 years ago,

it's a very different story.

Then the ice was expanding,

sucking moisture out of the atmosphere
in vast quantities

and locking it away in the ice.

And the effects of that
were felt right across the planet.

Thousands of kilometres
away in the Middle East...

...it led to a drought
which lasted for centuries.

It had its most profound impact
in what would become known

as the Fertile Crescent, an area famed
for its exceptionally rich soil.

This drought would trigger the start
of the defining characteristic

of human civilisation.

Back then, every human on the planet
was a hunter-gatherer.

Those living in the Fertile Crescent,
the Natufians, thrived on rich pickings

of fruit and berries,
with plenty of deer and ibex to hunt.

But as the drought took hold,
to survive they would have to adapt.

They came up
with two distinct strategies.

One group developed this,
the Harif point,

a new, state-of-the-art arrowhead

that allowed them to tackle a drought
by hunting more efficiently.

But a second group came up
with something a little bit more subtle.

Although you wouldn't know it,
this is a sickle,

and it offered a completely new approach
to gathering food.

This small, stone blade represented

a decision not to chase food,
but to stay put and grow it.

The Harif point did a good job
for the hunters.

But it was the sickle
that really changed history.

In a drought,
it's safer to stay close to water,

but that decision to remain in one place
meant planting crops was essential.

If you go foraging in the forest,

you can only collect so much food
with your bare hands,

but if you've got one of these,
you can harvest fast and furious,

and for the same amount of effort,
you can collect far more food.

With this simple tool,

these people had begun
the agricultural revolution.

And the rest, as they say,
is history.

A lack of water
and a simple but ingenious response

led to the birth of civilisation.

But once farming took hold,
it had a profound impact

on our relationship with water.

No longer
could we simply follow the rains.

Now people needed
regular, reliable sources of water

to make sure their crops grew.

So the need for water
began to define

where the first civilisations
could flourish.

That led people to the one stage
of the water cycle

that offers reliable fresh water -

rivers.

Across the planet,

rivers cover a tiny proportion
of the Earth's surface,

but for the first farmers,
they became magnets.

But rivers did more than supply
a steady source of water.

They changed the very character
of the civilisations

that grew up along them,

influencing everything
from politics to social organisation.

The power of rivers to shape history
is graphically illustrated

by perhaps the greatest
of all early civilisations...

...Ancient Egypt.

You might think you know the story -

a mighty civilisation
that built the pyramids

under the autocratic rule
of ruthless Pharaohs.

But if you want to understand
what really made Egypt great,

you have to leave the pyramids
and the temples behind...

...and come here, to a small place
that hardly anyone visits.

You know, at first glance
these look like your average, everyday,

2,000-year-old steps.

But this staircase
is what made Ancient Egypt tick.

You get an idea of its true purpose
by the markings on the side wall -

these grooves were carefully carved
into the marble -

because this was
a beautifully simple measuring device.

And to see what it was measuring,
you have to pop round the corner.

Oh!

It's all wet!

And this is it -

the Nile river.

That set of steps and markings
is a Nilometer.

It measured the changing level
of the river.

Each year when it flooded, the maximum
height that the waters came to

would directly predict
the yield of the crops

and, with that,
the profits that the farmers made.

It worked
because the water of the river

carried something special within it -

an almost invisible treasure

that was the secret
of Egypt's economic might.

What made Egypt great is this stuff -

silt.

It's a rich soup of minerals, which...

It's like an espresso.

Tiny flecks of rock and minerals
that the river picked up

over its wandering course
and swept along with the flow.

All rivers carry some silt,

but the Nile has the benefit
of starting in Ethiopia,

where the rock is young and volcanic.

This forms the richest of silts.

140 million tonnes of the stuff
are carried by the Nile down river

to Egypt each year.

Every year, the seasonal flood
covered the fields

and left behind nutrient-rich silt
that fertilised the crops.

The more silt,
the more food was produced.

It was the size of the flood -

and with it the bounty of silt -
that the Nilometer was used to predict.

So, simply by measuring the height
of the Nile, the Egyptians were able

to forecast food production
and, with it, the profits of the farmers.

Each year, they used this information
to set tax levels.

So the wealth and the might
and the splendour of Ancient Egypt

is all down to a simple twist
of geographical fate.

In fact, Ethiopia itself gets
almost no benefit

from that fertile soil
washed from its highlands.

It's even said that
its greatest export is the silt

that it sends down the Nile,
silt that made the Pharaohs rich.

But the ebb and flow of the Nile

had more far-reaching implications
for the Egyptian people than mere taxes.

Intriguingly, it may be that
where access to water is limited,

that actually determines

the way a society is organised
and even its use of slavery.

Where water is in short supply -

or from a single source,
as it is in Egypt -

then you need a highly structured
society to get the best out of it.

For large-scale irrigation,
you need bureaucrats to decide

where to dig the water channels.

You need teams of working men -
slaves, really -

to do the actual hard work of digging.

And once the channels are in place,
you need farmers with money enough

to buy the water it's delivered.

So right away you've got
three tiers of society,

and I haven't even mentioned
the Pharaohs.

So the rigid, hierarchical structure
of Egyptian society

wasn't just dictated by the Pharaohs.

It also emerged because the Egyptians
had only one water source -

the Nile.

5,000 years ago,

it wasn't just the Ancient Egyptians
who noticed the value of rivers.

Other great civilisations were also
forming along the banks of rivers.

In Mesopotamia,

the Sumerian civilisation flourished
between the Tigris and the Euphrates.

Further east, the Harappan civilisation
formed by the Indus.

And early Chinese civilisations
were emerging along the Yellow River.

But not all early farmers were content
to settle by rivers.

Others learned
to exploit new sources of water,

in the unlikeliest places.

Like the Sahara Desert, in Libya.

These are the remains
of the ancient city of Garama,

which about 2, 500 years ago
was the centre of a powerful empire.

Today, it's a bit of a maze,
but from up here

you can see the shapes of the buildings,
the way the streets interconnect.

You get a real sense of how this place
must have worked in its prime.

This was the home
of the Garamantians...

...which, for me,
are a rather forgotten people.

They've been eclipsed in the history books
by their showy contemporaries,

the Greeks and the Romans.

The Garamantians dominated
the Sahara Desert for almost 2,000 years.

They were the society that first brought
civilisation to the desert.

Far from just scraping by
in this harsh landscape,

the Garamantes were flourishing.

They grew crops
such as cereals and grapes.

They kept horses and pigs.

Clearly, they needed
large amounts of water.

So where did they find it,
here in the middle of the desert?

Now, this is the key to the Garamantians'
incredible success.

It's vertical holes
that are sunk deep into the ground...

...40 to 50 metres -
that's about 150 feet.

And the purpose of them
was pretty simple -

it was to bring water up
from below ground.

In this environment, it must have
seemed like it was almost magic.

In fact, the Garamantians
had discovered groundwater.

Beneath the surface of the Sahara
is a surprising part

of the great water cycle -

a massive store of groundwater.

This is water
that has seeped into the ground

and has collected
in porous layers of rock.

The water came from the period

thousands of years before,
when the Sahara was lush and wet.

Some of that water percolated
into the rocks below and remained there,

despite the dramatic drying above...

...until the Garamantes found it.

You kind of dig them down
until you hit the water table

and then you just keep doing
the same thing.

There's one after another, after another,
all in a whole line.

But these holes aren't wells -
they're maintenance shafts.

They reach down to tunnels
which carried the water.

The point is, right up there at the end
is where the water source is,

so the water flows naturally from
the escarpment up there, underground,

down to the kind of oasis over there.

Now, that's where
the Garamantians' city was.

What they could have done is
they could have dug wells down

and lifted the water out, but that's
a lot of work for very little return.

Much better to use gravity
to channel the water

in an underground tunnel
straight to where they need it.

That was the Garamantians'
real ingenuity.

The Garamantes had managed
to tap the same water

that the early Saharans had enjoyed
thousands of years earlier.

By mining groundwater,
the Garamantians managed

to turn the clock back on the Sahara -
they made the desert bloom again.

But the human struggle
to pin down water

is forever balanced on a knife edge.

Get that balance wrong
and you pay the price.

For all their ingenuity, the Garamantes
over-exploited their groundwater.

Eventually it ran out,
and so did their civilisation.

Now all that remains are the bats.

Today, modern Libyans have tapped
into this same groundwater supply,

by using pumps to reach deeper
than the Garamantes could.

But just like their ancient predecessors,
they're exploiting a finite resource.

At most,
it will last only another 50 years.

But water in this most inaccessible stage
of the water cycle

is found in many other places.

It's at its most spectacular
in Tallahassee, in Florida.

Here, divers are just beginning
to explore a mysterious series of caves

called a karst system, carved out
by groundwater over millions of years.

This is one of the planet's
least known frontiers.

When they began,
these divers had no idea

of the extent of the cave network.

To explore these caves,
they've made the longest dives in history,

travelling more than ten kilometres
from the cave entrance.

They're sometimes underwater
for 24 hours at a time.

Their efforts have revealed

one of the world's largest
underwater cave systems.

It's part of a huge store of groundwater,
of varying depths,

that underlies all of Florida
and reaches into neighbouring states.

And it's not just the USA.

There's groundwater
in the most unexpected places.

More than 30% of all the fresh water
on Earth is under our feet.

Looked at this way, our apparently
solid planet is more like a sponge.

In our early history,

the need for reliable supplies of water
led us to rivers and groundwater.

But as humans spread across the planet,
they learned to exploit

the vagaries of the water cycle
in many different ways.

The key was adaptation.

Take rain.

A familiar occurrence
in many parts of the world.

But this is rain
at its most extreme -

the monsoon.

The significance of the monsoon
isn't the human discomfort

but how the people here
have learned to live with it.

I'm travelling to the very epicentre
of the monsoon,

a place called Cherrapunjee,

which holds the world record
for the highest rainfall in a single year.

I thought I knew rain.

If you're from the west of Scotland,
you've met rain before,

but this is different,
it's different rain.

It's hard to explain.
It's the sheer intensity of it -

it just comes barrelling down.

But also, the raindrops are massive.

You feel as if you could fill an egg cup
with them, which means that,

within minutes, you're just soaked.

It's pointless with a hood
and all the rest of it - I'm soaked.

What I really need is a brolly,
like this chap.

Very wet!

Wet.

Just watch it, it's very slidy.

Back in west Scotland, where I'm from,
the average annual rainfall

is nearly a metre,
and that might horrify a Californian,

but here in Cherrapunjee,
the annual average rainfall

is more than ten times that -
between 11 and 12 metres.

That's nearly the height
of a four-storey building.

Streams turn to rivers,
and rivers turn to torrents.

When you live with so much water,
you have to adapt...

just to get around.

And that's exactly what
the local Khasi people have done.

Look at this!

Isn't this fantastic? Look at it!

It's a living bridge - look, you can see
all these roots coming down.

The texture of them is beautiful.

I mean, this entire structure
is built of growing rubber tree.

It's just mad when you follow it!

You can see that this is the perfect union
of the tree and the villagers.

The locals have kind of trained
the roots,

kind of guided them through,
knitted them together.

What they've done here is
they've grabbed some rootlets like this

and taken it round.
And look, here it is...

this set of rootlets here.
That's incredibly strong.

It's an anchor for the bridge.

Ordinary bridges would rot under
the relentless drenching of the monsoon.

What's clever about these root bridges
is they get stronger as they get older.

So wide! I mean, a whole village
could get through here.

Surprisingly, the intensity
of the monsoon rain is all down

to a basic property of water.

Compared to other substances,
water takes a lot of energy to heat up.

So the land and the ocean
react very differently

to the rising temperatures
of early summer.

During these months,
India's land surface heats up much more

than the surrounding Indian Ocean.

The high temperature
reduces the density of the air,

creating low pressure.

That sucks moist ocean air
onto the land,

which brings rain.

It's because the whole system
is driven by the sun's heat

that the rains come in the summer.

But it also means that the monsoon

only lasts
for three months of the year.

For the rest of the time,
there's virtually no rain.

The people of India have adapted,

as much as they can,
to these extremes of the monsoon.

I think it's this way.

It's great,
you have to use your elbows in here.

But outsiders are not always
so sensitive to its rhythms.

Here in India, the changing strength
of the monsoon year on year

had really tremendous impacts
on the country's political fortunes.

That's especially true
of its recent colonial past,

the story of which was played out

against a backdrop
of water abundance and scarcity.

Clearly there are lots of reasons
to explain the fate

of British colonial rule in India,

but one of the least explored
and most intriguing is water.

In the 19th century,
the failure of the British

to manage India's water supply
had significant consequences...

for them and for the Indian people.

Perhaps it was naivety, perhaps
it was because they were outsiders,

perhaps it was their inability
to cope with extreme weather,

but the British never really
got to grips with the monsoon.

For thousands of years,
people here have been developing ways

to deal with the monsoon.

And this was one of the most important -
it's a huge open well

that was dug down deep enough
to reach groundwater.

When the rains came, the water was
filtered through the surrounding ground

and held in the well
like a gigantic bucket.

But these stepwells,
as they were known,

were more than water collectors.

The genius of this design was
it turned the mundane need for water

into a social ritual.

People didn't just come here
to dip for water - they gossiped,

they bathed, they even worshipped.

Over 3,000 stepwells were built,
up until the 19th century.

For millions,
they were the main source of water.

Despite the fact that structures
like this helped the Indian people

survive droughts,
the British didn't like it.

They were concerned that people bathing
in the same water they drank from

was bad news.

So on health grounds,
they shut them down.

I mean, they may have had a point,

and they solved that issue
by bringing in piped water,

but at the same time,
they imported another problem

that was much, much worse.

It's a little-known fact,

but the British built canals
on a colossal scale across India,

more than 57,000 kilometres
of them -

perhaps their biggest
engineering achievement anywhere.

Yet the British didn't realise that,
even more than stepwells,

these huge bodies of standing water
were a health hazard -

the perfect environment
for malaria to breed and spread.

Given the lack of sensitivity
the British showed to the Indian climate,

it's perhaps ironic that the monsoon
played a significant role

in undermining British rule in India.

At the end of the 19th century,
the monsoon rains failed.

For a decade,
there were repeated droughts.

Crops were ruined,
and there were terrible famines.

But the British failed
to respond effectively -

in fact, they even continued
to export rice.

This indifference to the rhythms
of the monsoon fuelled popular anger

against colonial rule, and the
independence movement grew rapidly.

Today,
the stepwells are being repaired.

Pumps accessing groundwater
are used to protect

against the unreliable monsoon.

And that's made India the largest user
of groundwater in the world.

Adapting to the water cycle has meant
the difference between success

and failure for many civilisations.

But there was another strategy
that also brought success...

...and that was to take control
of the water cycle.

There was one early civilisation
above all others that took control

of the planet's most dramatically
changing source of water.

They mastered the monsoon.

They were the Khmers,

and from the 9th century,
they dominated the area

we now know as Cambodia.

And this was
their greatest achievement...

the legendary temple complex
of Angkor.

You get a real sense
of the age of this place here,

cos this was built
over 1, 200 years ago.

In a few places, like here,
you can see it's showing the age.

Look, the faces have all gone,

but, look at this, that looks as if
it could have been carved just yesterday.

Angkor was built
to honour the Hindu gods

and it symbolised the extraordinary
success of the Khmers.

In a way, this place is a monument
to something else -

the Khmers' ability to harness
the power of the monsoon.

The Khmers were first drawn to this region

by the Tonlé Sap lake
and the river that feeds it.

Today, it's home to a floating,
permanent community,

replete with all the necessary amenities.

All life here is lived on the river -

the whole village, houses, shops,
churches, schools, everything.

A hardware store!

Everybody's watching telly.
They're all watching soap operas,

or just chilling out.

People settle here today
for the same reason

the Khmers did over 1,000 years ago -

the unusual behaviour of the lake
around monsoon time.

Each year when the monsoon rains fall,
the land around here

just can't drain fast enough, and this
lake, Tonlé Sap, swells enormously.

It more than trebles in size,
becoming, for just a few months,

the largest freshwater lake
in Southeast Asia.

And every year, the water brings with it
a spectacular bounty.

Fish! Loads of them, nibbling away
at your toes in this murky water.

So many,
that when it floods, the Tonlé Sap lake

becomes the richest source
of freshwater fish in the world.

Back in the 9th century,
the Khmers realised

that this annual influx of fish and water
offered a glittering opportunity.

They set about building a fishing industry
here, and with the profits,

they built the temples of Angkor.

But as it grew, the Khmer kingdom
faced a stumbling block.

When the monsoon finished each year,
the fish and water would vanish.

So each year, the inhabitants
were plunged into drought and hunger.

The Khmer rose
to the challenge magnificently.

They decided that rather than be
at the whim of the monsoon,

they would make it work for them.

This is part of a vast network

of irrigation tunnels
that crisscross the whole of Angkor.

When the Khmer started digging these
in the 9th century,

people had seen nothing like them.

This was plumbing on a grand scale.

From the air, it's still visible today.

Over 1,000 years ago,
the Khmers managed to divert a river

by 80 kilometres.

They built canals

that extended over an area
of 1,000 square kilometres

and dug reservoirs

that could hold up to 600 million
cubic metres of monsoon water.

With this system, the Khmers seized
control of the planet's water cycle.

They turned the seasonal rainfall
of the monsoon into a reliable,

all-year-round water supply.

It was an enormous achievement,
enabling Angkor at its peak

to support a population
in excess of one million.

Thanks to their control of water,

the Khmers had built the largest
pre-industrial city in the world.

The Khmer hung on
until the 15th century,

which was when the kingdom of Angkor
finally went to the wall.

They were victims
of their own success.

Their population went through the roof,

and they simply outstripped
their resources, including -

despite all that
incredible engineering -

including the water supply.

I guess that there are limits

to what even
the mighty monsoon can sustain.

Today, we control water
on a massive scale.

The world's reservoirs now hold
over 10,000 cubic kilometres of water.

That's five times as much water
as in all the rivers on Earth.

And because most of it is pooled in the
more populated northern hemisphere,

away from the equator, the extra weight
has slightly changed how the Earth

spins on its axis.

It's caused the Earth's rotation
to speed up,

shortening the day by 8 millionths
of a second in the last 40 years.

Today, we take our control
of water for granted.

Modern civilisation
couldn't exist without it.

But there's still only a finite amount
of water to go around.

In many parts of the world,

scarcity has led to a bitter struggle
for control over the available supply.

And that's true
in even the wealthiest countries.

Today, Los Angeles is a city
with every luxury and convenience.

Yet not so long ago,
at the turn of the last century,

Los Angeles was struggling.

LA's problem was its location,
hemmed in on three sides by desert

and on the fourth by ocean.

So it lacked the most basic
requirement for city life -

a reliable water supply.

So it came up with a plan
to get the water it so needed.

400 kilometres to the north
of the growing city,

nestled within the Sierra Nevada
mountain range,

was a place called Owens Valley.

It was a verdant place, where people
were settling and building farms.

At the heart of it was plentiful water -

a wide river feeding a huge lake.

This valley must have seemed like
the answer to Los Angeles' prayers.

There was enough water here
to easily supply

over one million people.

There was only one problem...

it didn't belong to them.

It belonged to the farmers
of Owens Valley.

It would have to be taken by stealth.

It wasn't long before men appeared
in the valley,

masquerading as investors.

They offered to buy up farmland
at seemingly irresistible prices,

just to get the water rights
that went with it.

It wasn't technically illegal,
but it was certainly shady.

And it worked.

In 1913,
after six years of construction,

an aqueduct was opened.

And this is it.

In a way,
this aqueduct was a triumph,

certainly as far
as Los Angeles was concerned.

It allowed millions of people
200 miles down there

to live in a growing and vibrant city.

But that's not how people here saw it.

The Owens Valley farmers
didn't give up without a struggle.

A kind of loose resistance movement
started,

and they would take over places like this
and open the sluice gates,

allowing the water to pour back
down into Owens Valley.

And regularly
they'd dynamite the aqueduct.

But the city rebuilt it,

and a game
of cat and mouse continued

for three more dynamite-filled years.

Eventually, the police clamped down
with a "shoot to kill" policy,

and the rebellion fizzled out.

The city had won.

Today, the Los Angeles Aqueduct
is just part of a giant network

of pipes and aqueducts all serving
one of the world's great cities.

But, back in Owens Valley,
the lake has all but vanished,

and the river is barely a trickle.

The story of Owens Valley
is not an isolated case.

Today, there are conflicts over water
taking place all around the world.

Israel, the Palestinians,
Syria and Jordan

dispute access to the River Jordan.

Egypt, Sudan and Ethiopia
quarrel over the waters of the Nile.

On the Indus river,

India and Pakistan are in conflict over
dams built on the river's tributaries.

And these are only some
of the more well-known examples.

10,000 years ago,
we lived at the whim

of the unpredictable water cycle.

Since then, we have harnessed
the power of rivers

to advance our civilisations.

We have extracted groundwater
from the depths

of the most unlikely places.

And we have learned to redirect
and store water on a massive scale.

Today, we have unprecedented power
over the planet's water.

But one thing hasn't changed -

there's still only a finite amount
of water on Earth.

It seems to me

that water is the Achilles heel
of our modern civilisation.

It's the one resource,

more than any other,

with the potential to limit our ambitions.

The fundamental limits
of the water cycle are still there.

But the lesson of history is that
the most successful civilisations

learn to adapt to those limits.

So the problem is more with us.

Now, that prospect may find you gloomy
or, like me, more optimistic.

But either way,
at least the future's in our hands.

Next time, the contradictory role
of the deep Earth.

It drove great
technological breakthroughs,

but its gifts...

came at a price.