Water How Earth Made Us


Water

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Of all our planet's forces,

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perhaps none has greater power over us than water.

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

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

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

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It's our planet's lifeblood.

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It pumps through it continuously,

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delivering vital ingredients for life. Ah, it's glorious.

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Water makes Earth alive.

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Yet water is just one of the ways

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that the power of the planet has shaped our lives.

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The Earth has immense power...

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

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I'm here to change that.

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

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that have influenced our history.

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The power of the deep Earth...

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..that fuelled technological innovation.

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Wind.

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It has shaped the fate of entire continents.

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And fire...

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

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But I'm going to start with water.

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

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shifting between guises and from place to place.

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

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of some of the greatest civilisations on Earth.

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The centre of the Sahara Desert in North Africa.

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One of the driest places on Earth.

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I'm over six hours' drive from civilisation.

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Temperatures here regularly reach 40 degrees Celsius,

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

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Ah...

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The whole thing's moving.

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(HE STRAINS)

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It's like walking on water.

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Yet hidden amongst these dry dunes are clues

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

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

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the story of this place is all about water.

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The clues are etched into that rock face there.

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Prehistoric rock art dating back 6,000 years,

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

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Wow, what is that?

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It's a giraffe...

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

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

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and its mouth.

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That's really natural, isn't it?

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And this looks like the giraffe dipping its head down,

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

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There's two cats.

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They're fighting.

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This... What is this?

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

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

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

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

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

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they need wet conditions.

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In such a parched wilderness, how can this be?

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

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

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

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and it's been carved by running water

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

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and then cascaded down into the valley and off there.

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

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

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is just one of a network of past river valleys

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that crisscross the Sahara Desert.

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

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

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but we do know that they depended entirely on water.

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Water formed the lakes in which they swam.

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Water nourished the plants which fed the animals they hunted.

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Water filled the clay pots from which they drank.

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But then the climate changed.

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

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

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For the early Saharan people there was only one option -

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to follow the rains and abandon the desert.

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The fortunes of the early Saharan people

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reveal a universal, timeless truth -

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our fate is inextricably linked to water.

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The problem is, water never stands still.

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It's always on the move across the planet.

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We think of this as a blue planet.

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

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

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or use to grow crops.

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

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

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

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

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

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But to see its remarkable qualities

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you have to go to some extreme lengths.

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(MOTOR CHUGS INTO LIFE)

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(REVVING)

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Here we go...

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Ho-ho! Feel that!

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# WAGNER: Ride Of The Valkyries

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Here we go!

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

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Oh, my God!

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It's a bit bouncy!

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

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O-o-o-h! (LAUGHS)

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

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

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they heat the water molecules until some evaporate.

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It's the start of an extraordinary journey.

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You know, when water evaporates,

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it feels as if it vanishes into thin air.

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But although we barely notice it,

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water molecules are suspended around us all the time.

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

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At any one time, less than 1,000th of the world's fresh water is up here

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in the atmosphere.

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

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

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

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than at any other time on its journey -

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a mere nine days

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until the typical water molecule crashes to Earth as rain.

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(THUNDER RUMBLES)

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(BIRD SQUAWKS)

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For most of us, rain is perhaps

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the most familiar stage of the water cycle,

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but notoriously the least reliable.

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

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

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Look at that!

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Water absolutely everywhere!

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

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Whoo-hoo!

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

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

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The rest of the Earth's fresh water

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is locked away down there, on the ground.

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Oh... (LAUGHING)

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Oh!

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What a landing!

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The vast majority of it is stored as ice.

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Most of the rest seeps deep into the Earth,

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where it's known as groundwater.

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Hidden away down here

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

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

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and the cycle begins again.

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What that circulation means for us humans

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is that water is a moving target.

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

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wherever and whenever we can.

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This quest to...

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

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You can trace the impact of our quest for water

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right back to the dawn of civilisation,

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about 12,000 years ago.

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It all began with a big block of ice.

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12,000 years ago,

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

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And even today you can see its legacy...

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..here in Iceland.

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

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

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a store into which water can be deposited or withdrawn.

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

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

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Today, the ice sheet here is melting and retreating,

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and releasing this great armada of icebergs.

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But if you go back 12,500 years ago,

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it's a very different story.

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Then the ice was expanding,

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sucking moisture out of the atmosphere in vast quantities

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and locking it away in the ice.

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

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Thousands of kilometres away in the Middle East...

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

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It had its most profound impact in what would become known

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

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This drought would trigger the start of the defining characteristic

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of human civilisation.

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

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

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

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

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They came up with two distinct strategies.

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One group developed this, the Harif point,

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a new, state-of-the-art arrowhead

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

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

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

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and it offered a completely new approach to gathering food.

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This small, stone blade represented

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

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The Harif point did a good job for the hunters.

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But it was the sickle that really changed history.

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

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

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If you go foraging in the forest,

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

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

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

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With this simple tool,

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these people had begun the agricultural revolution.

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And the rest, as they say, is history.

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A lack of water and a simple but ingenious response

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led to the birth of civilisation.

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But once farming took hold, it had a profound impact

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on our relationship with water.

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No longer could we simply follow the rains.

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Now people needed regular, reliable sources of water

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to make sure their crops grew.

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So the need for water began to define

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where the first civilisations could flourish.

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That led people to the one stage of the water cycle

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that offers reliable fresh water -

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rivers.

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Across the planet,

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

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but for the first farmers, they became magnets.

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

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They changed the very character of the civilisations

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that grew up along them,

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influencing everything from politics to social organisation.

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The power of rivers to shape history is graphically illustrated

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by perhaps the greatest of all early civilisations...

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..Ancient Egypt.

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You might think you know the story -

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a mighty civilisation that built the pyramids

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under the autocratic rule of ruthless Pharaohs.

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

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

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

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

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2,000-year-old steps.

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But this staircase is what made Ancient Egypt tick.

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

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these grooves were carefully carved into the marble -

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because this was a beautifully simple measuring device.

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

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Oh!

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It's all wet!

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And this is it -

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the Nile river.

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That set of steps and markings is a Nilometer.

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It measured the changing level of the river.

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

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would directly predict the yield of the crops

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

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It worked because the water of the river

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carried something special within it -

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an almost invisible treasure

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that was the secret of Egypt's economic might.

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What made Egypt great is this stuff -

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silt.

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

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It's like an espresso.

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Tiny flecks of rock and minerals that the river picked up

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over its wandering course and swept along with the flow.

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All rivers carry some silt,

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but the Nile has the benefit of starting in Ethiopia,

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where the rock is young and volcanic.

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This forms the richest of silts.

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

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to Egypt each year.

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Every year, the seasonal flood covered the fields

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

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The more silt, the more food was produced.

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It was the size of the flood -

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

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

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

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

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

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is all down to a simple twist of geographical fate.

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In fact, Ethiopia itself gets almost no benefit

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from that fertile soil washed from its highlands.

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

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

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But the ebb and flow of the Nile

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

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

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that actually determines

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

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Where water is in short supply -

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

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

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For large-scale irrigation, you need bureaucrats to decide

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where to dig the water channels.

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You need teams of working men - slaves, really -

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to do the actual hard work of digging.

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

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to buy the water it's delivered.

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

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and I haven't even mentioned the Pharaohs.

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So the rigid, hierarchical structure of Egyptian society

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wasn't just dictated by the Pharaohs.

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

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the Nile.

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5,000 years ago,

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

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

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In Mesopotamia,

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the Sumerian civilisation flourished between the Tigris and the Euphrates.

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Further east, the Harappan civilisation formed by the Indus.

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And early Chinese civilisations were emerging along the Yellow River.

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

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Others learned to exploit new sources of water,

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in the unlikeliest places.

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Like the Sahara Desert, in Libya.

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These are the remains of the ancient city of Garama,

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

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

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

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

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This was the home of the Garamantians...

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

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

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the Greeks and the Romans.

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

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

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Far from just scraping by in this harsh landscape,

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the Garamantes were flourishing.

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They grew crops such as cereals and grapes.

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They kept horses and pigs.

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Clearly, they needed large amounts of water.

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

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

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

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

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And the purpose of them was pretty simple -

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it was to bring water up from below ground.

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

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In fact, the Garamantians had discovered groundwater.

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Beneath the surface of the Sahara is a surprising part

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of the great water cycle -

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a massive store of groundwater.

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This is water that has seeped into the ground

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and has collected in porous layers of rock.

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The water came from the period

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

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

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despite the dramatic drying above...

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..until the Garamantes found it.

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

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and then you just keep doing the same thing.

0:28:180:28:20

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

0:28:200:28:25

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

0:28:260:28:30

They reach down to tunnels which carried the water.

0:28:300:28:34

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

0:28:340:28:38

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

0:28:380:28:42

down to the kind of oasis over there.

0:28:420:28:45

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

0:28:450:28:48

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

0:28:480:28:51

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

0:28:510:28:56

Much better to use gravity to channel the water

0:28:560:28:59

in an underground tunnel straight to where they need it.

0:28:590:29:02

That was the Garamantians' real ingenuity.

0:29:030:29:07

The Garamantes had managed to tap the same water

0:29:110:29:15

that the early Saharans had enjoyed thousands of years earlier.

0:29:150:29:20

By mining groundwater, the Garamantians managed

0:29:200:29:23

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

0:29:230:29:28

But the human struggle to pin down water

0:29:310:29:34

is forever balanced on a knife edge.

0:29:340:29:37

Get that balance wrong and you pay the price.

0:29:370:29:41

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

0:29:420:29:48

Eventually it ran out, and so did their civilisation.

0:29:480:29:54

Now all that remains are the bats.

0:29:550:29:58

(SQUEAKING AND FLUTTERING)

0:29:580:30:00

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

0:30:050:30:10

by using pumps to reach deeper than the Garamantes could.

0:30:100:30:15

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

0:30:150:30:20

At most, it will last only another 50 years.

0:30:200:30:24

But water in this most inaccessible stage of the water cycle

0:30:270:30:31

is found in many other places.

0:30:310:30:33

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

0:30:350:30:39

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

0:30:410:30:47

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

0:30:470:30:53

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

0:30:560:31:00

When they began, these divers had no idea

0:31:010:31:04

of the extent of the cave network.

0:31:040:31:06

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

0:31:090:31:14

travelling more than ten kilometres from the cave entrance.

0:31:140:31:17

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

0:31:200:31:25

Their efforts have revealed

0:31:300:31:32

one of the world's largest underwater cave systems.

0:31:320:31:36

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

0:31:370:31:42

that underlies all of Florida and reaches into neighbouring states.

0:31:420:31:47

And it's not just the USA.

0:31:470:31:50

There's groundwater in the most unexpected places.

0:31:500:31:55

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

0:31:550:31:59

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

0:32:020:32:08

In our early history,

0:32:160:32:18

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

0:32:180:32:23

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

0:32:260:32:31

the vagaries of the water cycle in many different ways.

0:32:310:32:35

The key was adaptation.

0:32:390:32:42

(THUNDER RUMBLES)

0:32:430:32:45

Take rain.

0:32:460:32:48

A familiar occurrence in many parts of the world.

0:32:530:32:57

But this is rain at its most extreme -

0:32:570:33:01

the monsoon.

0:33:010:33:03

The significance of the monsoon isn't the human discomfort

0:33:120:33:16

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

0:33:160:33:20

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

0:33:210:33:24

a place called Cherrapunjee,

0:33:240:33:27

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

0:33:270:33:32

(THUNDER RUMBLES)

0:33:410:33:44

I thought I knew rain.

0:33:440:33:47

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

0:33:470:33:50

but this is different, it's different rain.

0:33:500:33:52

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

0:33:520:33:55

it just comes barrelling down.

0:33:550:33:57

But also, the raindrops are massive.

0:33:570:34:00

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

0:34:000:34:03

within minutes, you're just soaked.

0:34:030:34:05

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

0:34:050:34:08

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

0:34:080:34:11

Very wet!

0:34:120:34:14

Wet.

0:34:150:34:16

Just watch it, it's very slidy.

0:34:160:34:18

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

0:34:220:34:26

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

0:34:260:34:30

but here in Cherrapunjee, the annual average rainfall

0:34:300:34:34

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

0:34:340:34:40

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

0:34:400:34:43

Streams turn to rivers, and rivers turn to torrents.

0:34:480:34:54

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

0:34:590:35:03

just to get around.

0:35:030:35:06

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

0:35:060:35:10

Look at this!

0:35:190:35:21

Isn't this fantastic? Look at it!

0:35:210:35:25

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

0:35:250:35:31

The texture of them is beautiful.

0:35:310:35:33

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

0:35:400:35:44

It's just mad when you follow it!

0:35:500:35:51

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

0:35:540:35:57

The locals have kind of trained the roots,

0:35:570:36:00

kind of guided them through, knitted them together.

0:36:000:36:03

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

0:36:060:36:09

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

0:36:090:36:12

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

0:36:120:36:15

It's an anchor for the bridge.

0:36:150:36:17

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

0:36:190:36:24

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

0:36:240:36:29

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

0:36:290:36:34

(THUNDER RUMBLES)

0:36:350:36:37

Surprisingly, the intensity of the monsoon rain is all down

0:36:440:36:48

to a basic property of water.

0:36:480:36:50

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

0:36:550:37:00

So the land and the ocean react very differently

0:37:040:37:07

to the rising temperatures of early summer.

0:37:070:37:10

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

0:37:130:37:17

than the surrounding Indian Ocean.

0:37:170:37:19

The high temperature reduces the density of the air,

0:37:210:37:25

creating low pressure.

0:37:250:37:28

That sucks moist ocean air onto the land,

0:37:280:37:32

which brings rain.

0:37:320:37:34

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

0:37:380:37:41

that the rains come in the summer.

0:37:410:37:43

But it also means that the monsoon

0:37:460:37:48

only lasts for three months of the year.

0:37:480:37:52

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

0:37:520:37:56

(TRAIN HOOTER BLARES)

0:37:580:38:00

The people of India have adapted,

0:38:040:38:07

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

0:38:070:38:10

I think it's this way.

0:38:110:38:13

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

0:38:130:38:16

But outsiders are not always so sensitive to its rhythms.

0:38:220:38:26

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

0:38:310:38:35

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

0:38:350:38:40

That's especially true of its recent colonial past,

0:38:400:38:44

the story of which was played out

0:38:440:38:45

against a backdrop of water abundance and scarcity.

0:38:450:38:49

Clearly there are lots of reasons to explain the fate

0:38:490:38:52

of British colonial rule in India,

0:38:520:38:54

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

0:38:540:38:59

In the 19th century, the failure of the British

0:39:020:39:05

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

0:39:050:39:10

for them and for the Indian people.

0:39:100:39:12

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

0:39:210:39:25

perhaps it was their inability to cope with extreme weather,

0:39:250:39:29

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

0:39:290:39:33

For thousands of years, people here have been developing ways

0:39:380:39:41

to deal with the monsoon.

0:39:410:39:43

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

0:39:430:39:47

that was dug down deep enough to reach groundwater.

0:39:470:39:51

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

0:39:510:39:56

and held in the well like a gigantic bucket.

0:39:560:40:00

But these stepwells, as they were known,

0:40:000:40:03

were more than water collectors.

0:40:030:40:05

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

0:40:050:40:09

into a social ritual.

0:40:090:40:11

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

0:40:110:40:16

they bathed, they even worshipped.

0:40:160:40:18

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

0:40:220:40:27

For millions, they were the main source of water.

0:40:280:40:31

Despite the fact that structures like this helped the Indian people

0:40:360:40:39

survive droughts, the British didn't like it.

0:40:390:40:42

They were concerned that people bathing in the same water they drank from was bad news.

0:40:420:40:47

So on health grounds, they shut them down.

0:40:470:40:50

I mean, they may have had a point,

0:40:500:40:52

and they solved that issue by bringing in piped water,

0:40:520:40:56

but at the same time, they imported another problem

0:40:560:40:58

that was much, much worse.

0:40:580:41:00

It's a little-known fact,

0:41:030:41:04

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

0:41:040:41:08

more than 57,000 kilometres of them -

0:41:080:41:11

perhaps their biggest engineering achievement anywhere.

0:41:110:41:15

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

0:41:180:41:22

these huge bodies of standing water were a health hazard -

0:41:220:41:26

the perfect environment for malaria to breed and spread.

0:41:260:41:31

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

0:41:360:41:40

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

0:41:400:41:45

in undermining British rule in India.

0:41:450:41:48

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

0:41:550:41:59

For a decade, there were repeated droughts.

0:42:040:42:08

Crops were ruined, and there were terrible famines.

0:42:080:42:11

But the British failed to respond effectively -

0:42:130:42:17

in fact, they even continued to export rice.

0:42:170:42:21

This indifference to the rhythms of the monsoon fuelled popular anger

0:42:210:42:26

against colonial rule, and the independence movement grew rapidly.

0:42:260:42:31

Today, the stepwells are being repaired.

0:42:400:42:42

Pumps accessing groundwater are used to protect

0:42:450:42:48

against the unreliable monsoon.

0:42:480:42:50

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

0:42:520:42:57

Adapting to the water cycle has meant the difference between success

0:43:060:43:10

and failure for many civilisations.

0:43:100:43:13

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

0:43:180:43:22

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

0:43:230:43:27

There was one early civilisation above all others that took control

0:43:330:43:37

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

0:43:370:43:41

They mastered the monsoon.

0:43:420:43:45

They were the Khmers,

0:43:500:43:52

and from the 9th century, they dominated the area

0:43:520:43:55

we now know as Cambodia.

0:43:550:43:58

And this was their greatest achievement...

0:43:580:44:01

the legendary temple complex of Angkor.

0:44:010:44:05

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

0:44:120:44:15

cos this was built over 1,200 years ago.

0:44:150:44:18

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

0:44:200:44:23

Look, the faces have all gone,

0:44:230:44:26

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

0:44:260:44:31

(THUNDER CRASHES)

0:44:350:44:37

Angkor was built to honour the Hindu gods

0:44:410:44:43

and it symbolised the extraordinary success of the Khmers.

0:44:430:44:47

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

0:44:520:44:55

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

0:44:550:45:00

The Khmers were first drawn to this region

0:45:100:45:13

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

0:45:130:45:17

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

0:45:200:45:25

replete with all the necessary amenities.

0:45:250:45:27

All life here is lived on the river -

0:45:350:45:37

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

0:45:370:45:43

A hardware store!

0:45:460:45:49

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

0:45:530:45:57

or just chilling out.

0:45:570:45:58

People settle here today for the same reason

0:46:000:46:03

the Khmers did over 1,000 years ago -

0:46:030:46:06

the unusual behaviour of the lake around monsoon time.

0:46:060:46:11

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

0:46:110:46:15

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

0:46:150:46:21

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

0:46:210:46:26

the largest freshwater lake in Southeast Asia.

0:46:260:46:30

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

0:46:370:46:42

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

0:46:470:46:52

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

0:46:560:46:59

becomes the richest source of freshwater fish in the world.

0:46:590:47:02

Back in the 9th century, the Khmers realised

0:47:060:47:09

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

0:47:090:47:14

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

0:47:180:47:22

they built the temples of Angkor.

0:47:220:47:25

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

0:47:280:47:32

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

0:47:340:47:39

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

0:47:390:47:44

The Khmer rose to the challenge magnificently.

0:47:440:47:47

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

0:47:470:47:52

they would make it work for them.

0:47:520:47:54

This is part of a vast network

0:48:100:48:12

of irrigation tunnels that crisscross the whole of Angkor.

0:48:120:48:15

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

0:48:150:48:19

people had seen nothing like them.

0:48:190:48:21

This was plumbing on a grand scale.

0:48:210:48:24

From the air, it's still visible today.

0:48:340:48:37

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

0:48:400:48:44

by 80 kilometres.

0:48:440:48:46

They built canals

0:48:480:48:50

that extended over an area of 1,000 square kilometres

0:48:500:48:55

and dug reservoirs

0:48:550:48:56

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

0:48:560:49:01

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

0:49:040:49:09

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

0:49:090:49:13

all-year-round water supply.

0:49:130:49:16

It was an enormous achievement, enabling Angkor at its peak

0:49:180:49:23

to support a population in excess of one million.

0:49:230:49:26

Thanks to their control of water,

0:49:310:49:34

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

0:49:340:49:39

The Khmer hung on until the 15th century,

0:49:500:49:53

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

0:49:530:49:57

They were victims of their own success.

0:49:570:49:59

Their population went through the roof,

0:49:590:50:02

and they simply outstripped their resources, including -

0:50:020:50:06

despite all that incredible engineering -

0:50:060:50:09

including the water supply.

0:50:090:50:11

I guess that there are limits

0:50:110:50:13

to what even the mighty monsoon can sustain.

0:50:130:50:16

Today, we control water on a massive scale.

0:50:250:50:28

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

0:50:320:50:39

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

0:50:390:50:44

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

0:50:460:50:51

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

0:50:510:50:55

spins on its axis.

0:50:550:50:56

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

0:50:560:50:59

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

0:50:590:51:05

Today, we take our control of water for granted.

0:51:130:51:17

Modern civilisation couldn't exist without it.

0:51:170:51:21

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

0:51:220:51:27

In many parts of the world,

0:51:270:51:30

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

0:51:300:51:35

And that's true in even the wealthiest countries.

0:51:350:51:39

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

0:51:400:51:45

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

0:51:510:51:54

Los Angeles was struggling.

0:51:540:51:57

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

0:51:580:52:03

and on the fourth by ocean.

0:52:030:52:06

So it lacked the most basic requirement for city life -

0:52:060:52:10

a reliable water supply.

0:52:100:52:12

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

0:52:150:52:19

400 kilometres to the north of the growing city,

0:52:260:52:29

nestled within the Sierra Nevada mountain range,

0:52:290:52:32

was a place called Owens Valley.

0:52:320:52:35

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

0:52:360:52:41

At the heart of it was plentiful water -

0:52:410:52:45

a wide river feeding a huge lake.

0:52:450:52:48

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

0:52:530:52:57

There was enough water here to easily supply

0:52:570:53:00

over one million people.

0:53:000:53:02

There was only one problem...

0:53:020:53:04

it didn't belong to them.

0:53:040:53:06

It belonged to the farmers of Owens Valley.

0:53:060:53:10

It would have to be taken by stealth.

0:53:100:53:12

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

0:53:230:53:25

masquerading as investors.

0:53:250:53:28

They offered to buy up farmland at seemingly irresistible prices,

0:53:290:53:34

just to get the water rights that went with it.

0:53:340:53:37

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

0:53:390:53:43

And it worked.

0:53:440:53:46

In 1913, after six years of construction,

0:53:460:53:50

an aqueduct was opened.

0:53:500:53:51

And this is it.

0:53:510:53:53

In a way, this aqueduct was a triumph,

0:54:060:54:09

certainly as far as Los Angeles was concerned.

0:54:090:54:12

It allowed millions of people 200 miles down there

0:54:120:54:15

to live in a growing and vibrant city.

0:54:150:54:18

But that's not how people here saw it.

0:54:180:54:21

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

0:54:220:54:26

A kind of loose resistance movement started,

0:54:290:54:31

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

0:54:310:54:35

allowing the water to pour back down into Owens Valley.

0:54:350:54:38

And regularly they'd dynamite the aqueduct.

0:54:380:54:42

But the city rebuilt it,

0:54:440:54:46

and a game of cat and mouse continued

0:54:460:54:49

for three more dynamite-filled years.

0:54:490:54:52

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

0:54:520:54:57

and the rebellion fizzled out.

0:54:570:54:59

The city had won.

0:54:590:55:02

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

0:55:060:55:11

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

0:55:110:55:16

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

0:55:350:55:38

and the river is barely a trickle.

0:55:380:55:41

The story of Owens Valley is not an isolated case.

0:55:430:55:48

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

0:55:480:55:52

Israel, the Palestinians, Syria and Jordan

0:55:570:56:00

dispute access to the River Jordan.

0:56:000:56:03

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

0:56:050:56:10

On the Indus river,

0:56:130:56:16

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

0:56:160:56:21

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

0:56:210:56:24

10,000 years ago, we lived at the whim

0:56:280:56:32

of the unpredictable water cycle.

0:56:320:56:35

Since then, we have harnessed the power of rivers

0:56:370:56:41

to advance our civilisations.

0:56:410:56:43

We have extracted groundwater from the depths

0:56:470:56:50

of the most unlikely places.

0:56:500:56:52

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

0:56:540:56:59

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

0:57:050:57:10

But one thing hasn't changed -

0:57:110:57:14

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

0:57:140:57:18

It seems to me

0:57:260:57:27

that water is the Achilles heel of our modern civilisation.

0:57:270:57:31

It's the one resource,

0:57:310:57:33

more than any other,

0:57:330:57:34

with the potential to limit our ambitions.

0:57:340:57:37

The fundamental limits of the water cycle are still there.

0:57:390:57:43

But the lesson of history is that the most successful civilisations

0:57:430:57:48

learn to adapt to those limits.

0:57:480:57:50

So the problem is more with us.

0:57:520:57:55

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

0:57:550:58:00

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

0:58:000:58:05

Next time, wind. For thousands of years,

0:58:080:58:10

the wind has shaped the destiny of people

0:58:100:58:13

across the planet.

0:58:130:58:16

It's made fortunes

0:58:160:58:18

and brought ruin.

0:58:180:58:20

Even today, we're still at its mercy.

0:58:200:58:25

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