The Americas Rise of the Continents

New York City.

Gateway to the New World.

But also a gateway back into the distant past,

not just of New York, but of both North and South America.

I'm heading to the top of the tallest building in the city,

in fact in the whole of the Americas,

but because it's still going up, I have to have this.

Rising 104 floors, right beside where the twin towers once stood,

this is World Trade Center 1.

Few people realise it, but this building and the ones around it

have a direct connection to a mysterious past.

There's a secret hidden in this iconic skyline.

And deciphering it will reveal a long-lost world.

I'm going to reach back in time to explore this lost world.

The evidence that unlocks that ancient past is hidden all around us

in rocks, landscapes and even animals.

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

Those clues reveal a defining moment in the story of the Americas...

..and show how these turning points have transformed evolution...

It's moving.

..created incredible economic riches...

That feels really close.

..and changed the human history of these two great continents.

If you really want to understand the modern Americas,

you have to understand the remarkable story

of how they were born, from the wreckage of a lost world.

You can find a clue to the origin of both American continents

here at the top of World Trade Center 1.

It's the way that Manhattan skyscrapers are concentrated

in just two places -

Downtown, where I am, and a couple of miles further north.

And there you can see the Empire State Building -

that patch is Midtown.

New York skyscrapers are concentrated

in Midtown and Downtown for a very good reason.

One that's buried beneath each one of them

and that puts New York at the heart of an ancient world.

To find evidence for this ancient world, I need to explore

the foundations of the city's skyscrapers.

It's a bit rickety, this thing, isn't it?

Before any building goes up high, you've got to dig down deep.

And that takes some hard-core tools.

Now, that is the kind of geology hammer I have always wanted to have.

I'm looking for a particular type of rock.

One that dates back at least 300 million years.

Inside it, there's evidence of what this place was like

in the long-distant past.

A past that helps explain the mystery of New York's skyline.

Crystal.

High pressures.

This rock face, it's the foundation stone on which,

for me, modern America was built.

If you look at it, you can see there's a whole series of lines.

It's like bands coming through. And that's because of the crystals -

look, you can see them glittering away here.

They're all stacked on top of each other in a series of layers.

You can see that when you look at it closely.

When you zoom into this rock...

what you see is a mosaic of crystals...

..that are flattened in this direction

and are elongated, strung out in this direction here.

And that transformation, that rearrangement,

has been done under really high temperatures, maybe 700 degrees,

but also really high pressures.

You get an idea of just how much pressure

from a mineral that you actually find in here.

It's a mineral that gives this rock a blue tinge.

And it's a mineral called kyanite.

Now, kyanite is a really interesting mineral.

It's formed by pressures of four kilobars or more.

Four kilobars doesn't seem very much,

but if you were squeezed by four kilobars

you'd be squeezed by a block of rock a metre by a metre

that extends upward for 13 kilometres.

This dense bedrock is known as Manhattan schist.

The only way that you can generate the heat and pressure

that you need to form the dense strength of a rock like this

is if you produce it under an enormous weight.

The kind of weight that's far in excess

of anything you find around here today.

300 million years ago,

New York was at the foothills of a huge mountain range.

And this rock - this rock - was buried

13 kilometres beneath those soaring peaks.

Imagine that!

These mountains were the height of the Himalayas.

But they weren't just high.

They went on for thousands of kilometres.

And they played a critical role in this story of the Americas

because their formation is what brought

North and South America together.

430 million years ago,

North and South America were separated

by thousands of kilometres of ocean,

but they were on a collision course.

A slow-motion crash that raised giant mountains

all along the impact zone.

At the same time, it brought all the world's landmasses together

in one giant supercontinent - Pangaea.

The two American continents were at the heart of Pangaea,

on either side of a massive mountain range.

And New York was, in geological terms,

at the centre of this lost world.

It's funny. New Yorkers like to think of their city

as the centre of the world.

300 million years ago, it really was.

Now, all that's left here

of the enormous supercontinent of Pangaea

is the rock beneath the city.

You know, it's staggering to think

that in the last few hundred million years,

mountains of Himalayan stature have been eroded down

to leave us with a dense bedrock beneath our feet.

And that's left its legacy in this iconic skyline.

Where the bedrock is closest to the surface

in Downtown and Midtown

it makes strong foundations for skyscrapers.

Where it's been eroded away between the two,

the foundations are weaker and the buildings are smaller.

This icon of the modern world, the skyline of this great city

is underpinned by the long-lost world of Pangaea

and it's shaped much more than that.

Pangaea's had a huge influence on the modern-day Americas,

from their natural resources to their history.

But Pangaea also left its mark on the whole planet.

It played a critical role

in one of the most important evolutionary developments

in the story of life on Earth.

Nothing less than the invention of sex.

That rather significant development can only be understood

if we journey back to the early days of Pangaea,

before it was fully formed.

And there's one place in North America that can take us there.

The Grand Canyon.

This is a portal through time,

where you can see the history of the planet laid out before you.

You have a strange double vision as a geologist when you come here

because on the one hand you have this spectacular, jaw-dropping view,

and it's absolutely beautiful.

But as a geologist you see past that as well.

You see...a kind of deeper significance of what it means.

In this case, it means a huge, huge expanse of time.

The Earth's history being unravelled by the sun

as it exposes the deeper and deeper layers.

The rocks down there are 1.7 billion years old -

extraordinary number.

The only life on the planet was single-celled algae - it was slime.

And then, just a little bit higher,

the rocks are 500, 550 million years old.

That's where complex life starts growing.

That's a time when there was great ice sheets across the planet.

So there's 1.5 billion years of time just condensed into that view there.

Absolutely spectacular!

One set of layers that's important for our story of Pangaea

is this group of rocks over here. It's called the Supai Group.

They date from the earliest days of Pangaea,

before it was fully formed.

The layers are red because the rocks are packed full of iron.

Sediments are made of silts and sands

that have been washed off the land into coastal swamps and deltas.

The rocks show that this early Pangaea was a watery place

and fossils reveal the kind of life that was around at this time.

Amphibians.

Today amphibians, like frogs and salamanders, are relatively rare.

But before Pangaea formed,

amphibians were the dominant animals on the planet.

And if you imagine frogs and salamanders,

you realise how important water is for them,

particularly in that early spawning stage

and the development of the young, like tadpoles.

And that's something that amphibians have in common,

past and present, really, is that fundamental attachment to water.

And that wet world of early Pangaea would have been absolutely perfect

for these critters to flourish in.

Before Pangaea formed, the world had lots of coastal swamps

and wetlands for the amphibians to breed.

But then the world changed.

The evidence is just a short trek down from the canyon rim.

A layer of yellow rock, called the Coconino,

that was formed when the Americas were part

of the great supercontinent of Pangaea.

It reveals a landscape that would change the course of life on Earth.

Wind.

Sand dunes.

These are lovely rock surfaces. They're so smooth.

If you look at the sand grains...

what you see is lots and lots

of tiny, rounded grains.

The other thing is that they're all roughly about the same size.

What that's telling you is that the process that formed this was wind

because wind can pick up

only the finest sand grains and move it around.

Actually, what's interesting about them is that they're not horizontal,

they're actually inclined.

And sometimes that means that they've been started off horizontal

and then they've been tilted up, but not in this case.

We're looking at a surface that was always at this angle.

And this angle - it's about 33, 34 degrees - and the reason for that

is if you take fine, fine sand and just pour it out in a heap,

the angle that it falls at is about 33, 34 degrees.

And that's the angle that the sand grains hold themselves together at.

So what this is really telling us

is that the surface that I'm standing on

is that of an ancient desert sand dune.

In fact, in its time if we looked around,

it would have been just a sand sea for miles upon miles of huge dunes.

To imagine what it would've been like, you've got to think of

something like the Namib Desert in south-western Africa

where you've got dunes that are maybe 100 metres or so,

several hundred feet high. I mean, it's an extraordinary landscape.

And you just get the hint of it here.

We know from the Coconino layer

that the Grand Canyon had become the western edge of a giant desert...

..that spread across almost all of what is today the Americas,

Africa and Europe.

This gigantic desert was a direct result of Pangaea's formation.

One huge landmass meant that most of the land was distant from the sea

so rain-carrying winds couldn't reach the centre.

250 million years ago, Earth had become a desert planet.

Not good news for the amphibians.

But in the heart of this arid world, one type of animal did flourish.

Although this environment was extreme desert, it wasn't lifeless.

The evidence is right here on the rock face.

You can see these really odd markings.

And what they are are footprints, a track way of an animal

that was walking up here,

pushing down, kind of displacing the sand.

What is was was a reptile.

A reptile with a tail, because you can see

this sinuous track of this reptile that's dragged its tail up.

To adapt to these super-arid environments

required an evolutionary innovation that would be inherited

by all the reptiles - by birds, by mammals...

by you and I.

250 million years ago, America was at the centre not only of Pangaea,

but of a massive evolutionary change.

I've come to see what it was

in an ancient animal with a fearsome reputation.

The alligator.

It's mating season at the Colorado Reptile Park...

..and these feisty fellas scrap for the right to breed.

So keeper Jay Young has to tend their wounds.

Helping him treat his injured means I can get up close and personal

to an animal whose ancestors roamed the Americas

when they were part of Pangaea.

You let me know when you need this thing.

-I'm gonna give you the stick.

-Don't you need that?

ALLIGATOR GROWLS

Look at this. He's going to grab the tail.

Oh, my goodness!

Whoa! Whoa! Hissing everywhere.

-So what do I do?

-Move it...

Agh!

Where should I be? Your left or right as you come out?

Either way. Ready?

OK, now we yank and jump.

Make sure both the hands are near her neck

-at the same time.

-No, you jump.

I'll just stay at this end.

ALLIGATOR HISSING

-Yeah?

-OK, come up here.

-Are you sure?

-Yeah.

Jump on her back. That's it - all your weight.

Put your hands right here on her neck. OK, you got her?

-Yeah, I think so. We'll soon find out.

-OK.

-Hey there, honey.

-We'll soon find out. Anariki, is it?

-Yeah.

-Hi, Anariki. Pleased to meet you.

-I'm gonna get lunch.

I'll be back in a few! HE LAUGHS

I hope that's a joke. It's moving!

Ooh!

-OK, keep your hands on her neck.

-I haven't got it.

Just letting you get a sense of her power.

-Is she strong?

-It's incredible, yes, very strong.

She heard that Scots taste like chicken.

But very weak chicken!

This is the closest I'm ever going to get

to a creature from Pangaean times

because alligators share an anatomical connection

with the ancient reptilian fossils.

It's this - what we call the ankle joint, it's the crural-tarsal joint,

and it's a really distinctive adaptation.

You can get this thing underneath your body, you can push yourself

more upright and you can have this really fast gait.

That looks sore, doesn't it?

'Anariki's ancestors were hugely successful in Pangaea.

'The way they moved was part of it.'

-Back on her.

-I think that's it.

'But the biggest breakthrough was something

'that perfectly equipped them for Pangaea's desert world...

'The way they have sex.'

Alligator sex is pretty much like human sex,

certainly in the style of copulation.

The key is internal fertilisation.

Delivering the sperm inside the female and directly to the ova.

And that process involved the invention of sex.

Sex is the most efficient and direct way of achieving fertilisation.

It's how modern reptiles, birds and mammals impregnate.

Up until this innovation,

fertilisation could only occur externally, in water.

Amphibians were the first vertebrates to emerge onto land.

But because they fertilised externally,

they had to return to water to breed.

The newly evolved reptiles did things differently.

They fertilised and developed their eggs inside their females,

so by the time the eggs were laid, they had hard, impermeable shells.

These eggs didn't need water to survive.

This is chicken egg,

but surprisingly it's about the same size as an alligator egg.

But what's important is what's inside.

Because what's inside is the amniotic fluid.

That transparent liquid,

that's the stuff that contains the energy

and the life-sustaining waters

that amphibians would have found in the rivers and seas.

This object, the egg, was the revolution.

Mammals have taken those life-supporting fluids

inside themselves and supplied nutrition through a placenta.

But we're still children of that first amniotic reptile.

The Pangaean deserts were essentially

an impenetrable barrier to the amphibians.

But for the reptiles it was a different story.

The development of internal fertilisation and the amniotic egg

allowed them to spread into and thrive

in those arid environments.

It's a wonderful example of how environmental change

can be a catalyst for evolutionary advances

and those advances would lead eventually to the evolution of us.

It's interesting to think that the way that we have sex

and the way that we rear our young

have been shaped by these deserts of the distant past.

North and South America spent almost 100 million years

nestled together in the heart of Pangaea.

But by 200 million years ago, there were signs

that this gigantic landmass was about to break up.

This break-up would have a massive influence

on the modern-day Americas.

It would end up creating fortunes, destroying lives

and transforming the landscape.

The evidence for this cataclysmic event is right under the nose

of unsuspecting commuters, driving in and out of New York every day.

Connecting Manhattan to New Jersey is the George Washington Bridge.

Anchored on one side by an imposing cliff face, the Hudson Palisades.

I've come here to find evidence

of probably the single most important event

in the history of the two American continents.

The moment when they split from Pangaea.

There's a telltale sign here

that really shows how these rocks came into being.

Hexagon.

Vertical fracture.

You can see it in the shape of these blocks.

They've got these regular sides to them.

And this block as well - you can see it beautifully there.

And there's six sides -

one, two, three, four, five, six.

These hexagons are the flat-top surfaces

of columns that go straight the way down.

You can see it as vertical fractures in the cliffs

all the way along here.

What they are telling you

is that this rock started off as a liquid mush.

'A molten fluid that must have cooled rapidly.'

And as it cools, it congealed, it contracted in

and the most efficient way of doing that is to pull in from all sides

and create these wonderful hexagons.

So this rock, which is a kind of basalt, started off as hot magma.

The magma that erupted out is thought to have been brought up

by a current of hot rocks known as a mantle plume.

It's not clear why they form,

but rising mantle plumes push the land up

like a heat blister until it cracks and fractures,

triggering immense volcanic eruptions.

These cool and become layers of basalt.

Geologists have found evidence of this humungous volcanic outpouring

in places thousands of miles apart

If we just look at it on a modern map,

we find that the equivalent layer of this basalt

that we get here in eastern America

has also been found in eastern Canada,

it's been found in southern Britain, in Portugal

in West Africa and in parts of Brazil.

Now, viewed from the perspective of Pangaea 200 million years ago,

it makes perfect sense.

If you wind back time, all these places were joined together.

Part of a single, huge volcanic event

that spread across Pangaea's heart.

A fiery inferno covering 10 million square kilometres.

Across this huge area,

great sheets and rivers of lava burned for thousands of years.

Volcanic ash and gas played havoc with the planet's climate.

Large numbers of reptiles and half of all plant species were wiped out.

But these were also the death throes of the supercontinent itself.

The eruptions created chasms and rifts

that would eventually fill with water.

Pangaea split apart

and out of it emerged a brand-new continent...

North America

and the beginnings of a brand-new ocean...

..the Atlantic.

The mantle plume kick-started a process that is still going on today

with major consequences for the Americas.

3,000 kilometres from land

and 2,500 metres under the ocean,

you find strange volcanic vents

spewing superheated water.

Home to deep-sea shrimps

that feed on minerals erupting out of the Earth.

These vents are just one tiny part

of a huge underwater chain of volcanoes

called the mid-ocean ridge...

..that spreads down the middle of the Atlantic Ocean...

along which magma is constantly emerging,

cooling and turning into fresh rock.

The Mid-Atlantic Ridge marks where Pangaea fractured,

to create two new tectonic plates.

The North American plate on one side,

Eurasia and Africa on the other.

And as lava continues to erupt at the ridge,

these continental landmasses move gradually further apart.

It's odd to think that each year,

New York and the Americas get 2cm further west from Europe and Africa.

The New World driven inexorably away from the old.

It's this separation

with newly formed plates pushing away from each other on one side

and jostling for position with their neighbours on the other

that's shaped the New World.

By 130 million years ago,

North America had fully separated from Pangaea.

Then the action shifted south.

Around 85 million years ago,

the remains of Pangaea split again to form another plate.

Moving away west, separate from both Africa and North America,

was the newly formed continent of South America.

It's journey was to be anything but smooth.

Today, South America has

some of the most spectacular landscapes on Earth.

They're the product of a violent geological past

that shaped an equally turbulent human history.

This relationship between geology and history

is revealed in the Bolivian town of Potosi.

Once part of the Spanish Empire,

what the conquistadors plundered here

bankrolled their empire for three centuries.

But at a price.

Agh! Hey!

-Pedro, how are you?

-Good morning.

-Thanks for doing this.

-I'll give you a hand.

Local miner, Pedro Montes Coria,

is going to take me inside the deadliest mountain in human history.

Cerro Rico.

We're going to see what the conquistadors discovered here.

But this mine also reveals why South America's movement

has been such a violent process.

Before entering the depths,

miners fortify themselves

with intoxicating coca leaves.

-You have to chew the coca like this, one by one.

-Oh, OK.

I feel a kind of buzz on my tongue, actually.

Just on here...zzzz.

With coca, we are not very thirsty, hungry,

you want maybe to sleep.

We feel that we are stronger with the coca leaf.

So what age do you start eating coca leaves?

-When we come to the mine. We are ten years old.

-Ten years old?

-Yeah.

-Switch on the light.

-Oh, yeah.

Not only are many of the miners school age,

but they're entering a world where tunnels regularly give way

and explosives are unregulated

so the miners' first stop before the depths is to ask for protection.

-This way.

-OK.

-First to visit El Tio.

-Is that El Tio?

-This is the devil in the mountain?

-He is our God.

Of course he is like a devil, but not the same devil that we have outside

because everything here belongs to him.

We are going to do the ritual.

Take some coca and put in his hands,

on his willy, his head.

El Tio, lot of safety in the mine.

Yes. Do you know this alcohol?

I don't, no. It says, "Alcohol potable" so drinkable alcohol.

It says, "96" - oh, cha!

-"Industrial Bolivia."

-Cheers to you.

-That's...

-Very nice.

-And then good luck to me.

-Yeah.

HE COUGHS

-That is strong.

-Yeah.

Oh, gosh!

Oh! Whoo!

OK.

If anything, the rituals left me feeling even more nervous.

-Watch with the hole.

-The hole? It's deep!

-Yeah.

How far does that go down, do you think?

It's like 80 metres down, more or less.

This tunnel is connecting to another mine.

OK, so the mines are all interconnected.

All the mines - it's like Swiss cheese, full of holes.

Every step needs to be taken very carefully.

The miners work by digging and blasting through the rock.

Collapses and fatalities are a fact of life

and you never know what the other miners are doing.

What's happening?

-BLAST

-Oh, that was close.

-That's happening!

-That was it, was it?

Yeah.

-BLAST

-Oh!

BLASTS

-BLAST

-Shhh...!

That feels really close.

-I can smell the dynamite.

-Yeah.

-Really strong.

Down here is what three centuries of miners have been looking for.

So here we are.

OK, I see it. You see this band coming all the way down here?

Just in amongst it all is a rather dull grey mineral, and that...

Well, that's the silver.

That's what miners like Pedro are after.

And, for me, the way this precious silver is laid out

reveals a fundamental process that's shaped South America

and its often bloody history.

Hot fluids.

It's actually concentrated on these really narrow bands.

These are called veins

and you can actually see them all the way up across there.

Those metals would have been laid down by hot fluids.

And the reason the fluids were hot

was because deep beneath my feet at the time was molten magma,

magma that had risen up from the mantle,

carrying with it metal elements like zinc and gold and silver.

And as that magma rose higher and higher, it heated up

water that was circulating through the crust

and those waters, at several hundred degrees Celsius,

started to pick up those metal elements,

to carry them higher and higher

until they just ditched their cargo, stuffing them into veins like this.

But what's surprising is the source of that water.

Analysing the steam that emerges from volcanic vents nearby

reveals something unexpected.

The steam's chemical signature is similar

to that of water found 400 kilometres to the west.

The waters of the Pacific Ocean.

So the most obvious conclusion is that some of the hot waters

that have been percolating through these rocks in this region

started out in the Pacific.

And that is telling us about a process

that's going on deep beneath my feet now

and is really at the heart of those moving continents,

and that process is subduction.

Subduction is the key to understanding

how South America was changed as it moved west.

As the South American plate moved apart from Africa,

it collided with the Pacific Ocean plate

and the collision is going on right underneath Cerro Rico.

The ocean floor of the Pacific plate is sinking down,

dragging a part of the Pacific Ocean deep underneath South America.

This is subduction.

The sinking rock heats up

and minerals and water from the old ocean floor

escape into the continental rocks above.

It's this process that has given South America

its incredible mineral wealth.

From tin, copper and zinc to gold and silver.

Hey! Fresh air!

-Hey!

-Good, my friend.

-Thank you very much.

-Yes.

That's good then.

In the 17th century, the town of Potosi was as big as London.

The mines resources not only resulted in fabulous riches -

40,000 tonnes of silver came out of this mine -

but a terrible history of exploitation.

During the Spanish colonial centuries, it's been estimated that

as many as eight million indigenous people and slaves died

working the mines of Cerro Rico.

So the fruits of subduction

have shaped the recent human history of this region.

But over tens of millions of years,

it's also created the defining feature of the continent.

As the ocean plate pushes underneath the leading edge of South America,

it kind of gets snagged and jarred.

Pressure builds up and you generate these huge earthquakes

and also open up pathways

for magma to rise up to the surface and produce volcanoes.

And what you get over 60 million years

is the gradual uplift and crumpling of this whole region.

The result, almost a by-product of subduction,

is the longest mountain range on any continent...

The Andes.

The Andes stretch for more than 6,000 kilometres

along almost the entire western coast of the continent.

It's a long, narrow range

because the mountains follow the boundary between the two plates

where subduction is taking place.

And in a strange twist of fate,

their formation may give Bolivia the chance to gain

some measure of compensation for the traumas of the past.

As they have grown, the mountains have lifted one Bolivian lake

from its original position near sea level

to a height of nearly 4,000 metres.

This is the Salar de Uyuni, the biggest salt flat on Earth.

Hidden in this landscape

is a resource worth tens of billions of dollars.

It could have the global impact of the silver of Potosi,

but without its tarnished history.

FOOTSTEPS CRUNCHING

The key to understanding this new source of wealth

is inside something we nearly all carry in our pockets.

Open up any mobile phone, whether it's a fancy new touch-screen

or one of these old-style handsets

and you'll find the battery.

And what all these batteries have got in common is one key element.

The active components inside here are made of lithium carbonate.

As well as being in a mobile phone,

lithium's in laptops and all electronic devices.

It's used because of one quality above all.

And that is lithium is the lightest of all the metals

so it gives more power for its mass.

Now here's a thing.

Bolivia has as much as 50% of the world's lithium reserves.

Most of it in this extraordinary landscape.

Lithium isn't just for mobile technologies.

It also offers a potential clean green future for cars.

Until now, electric cars have been hampered

by the weight of their batteries.

But lithium makes it easier and cheaper

to produce lightweight batteries for the cars of tomorrow.

It's thought there's enough lithium here

to make batteries for more than four billion electric vehicles.

Enough to make Bolivia a Saudi Arabia of the 21st century.

In places, the lithium is only just below the surface.

Where the crust is thin, you can see the brine underneath.

And if you really hammer away at it,

then you can actually see the structure of the salt.

Look at that. It's beautiful.

All these symmetrical crystals.

The white ones are sodium chloride - that's just ordinary table salt

but this pink one here - that's potassium

and this one, the brown-coloured one, that - that's lithium.

So today the lithium's here at the surface in the salt

but it started off way down deep.

Subduction produced magma

that rose up and erupted out of volcanoes like that over there.

In fact, there's a whole series of them all the way around.

So these mountains are rich in lithium.

From the slopes of the Andes, run-off erosion

washes the metal-rich sediments down to the lake.

Since it's been uplifted, the lake has become surrounded by mountains

so no river can find a way out to drain the Salar.

The result is that the only way water leaves the lake

is through evaporation.

Over time, that concentrates minerals, including lithium,

in the lake bed.

There's now a plan to build

a full-scale lithium extraction plant in the Salar.

Huge multinationals want in,

but the Bolivian government says it wants to avoid

the foreign exploitation that marked colonial silver mining.

Subduction and the rise of the Andes

has given South America extraordinary mineral wealth

and all that a consequence of that gradual drift

of the New World away from the old.

That process has shaped the destiny of South America in another way.

I mean, here it's given us a landscape of jaw-dropping beauty,

but completely lifeless.

But elsewhere it's created some of the richest

and most unique habitats on the planet.

One ecosystem above all others owes its existence to the Andes,

because as the Andes grew,

the rivers of South America went through a series of massive changes.

Before the Andes, it's thought the main rivers flowed

in the opposite direction to today, into the Pacific.

When the Andes started to rise, they diverted rivers to the north,

where they flowed out into the Caribbean,

creating a huge area of wetlands close to the growing mountains.

But then further uplift blocked the route north

and forced the rivers to converge towards the Atlantic,

forming an enormous drainage basin.

And that led to the creation of the Amazon rainforest.

Meanwhile, on its western flanks,

the Andes created a rain shadow.

The result is the driest place on the planet...

the Atacama Desert.

By ten million years ago,

both South and North America looked similar to today,

but there was one critical difference.

They were still separate continents.

The stage was set for the final act in the story of the Americas.

It didn't lead to a dramatic change in the landscape.

But it did transform their wildlife.

Few animals are better suited to the mountainous terrain of the Andes

than the llama.

Hello!

These animals are just magnificently adapted for life at altitude.

There's obvious things for the low oxygen -

they've got big hearts and enlarged lungs, but there's something else.

Can you catch one for me, Clemente?

Just to see... There's something I want to show you.

-HERDER WHOOSHES

-OK.

Just any one. There we go.

OK. OK, this is nice.

So I just want to show you the feet because unlike other hoofed animals,

the llama's feet are split into two, they've got two toes.

And underneath the two toes - can I just lift it up a little bit?

It's got this thick leathery sole.

What that means is that it's perfect for sure-footedness

on really rough rocks.

Just perfect for up this mountain terrain.

And the other thing's inside - it's the blood

because the haemoglobin,

the red blood cells that carry oxygen through the body,

llamas have got more haemoglobin per unit volume

than any other mammal - it's extraordinary.

So there's a whole series of really clever adaptations.

They're just wonderful beasts.

Thanks for that. Let him go.

Since Inca times, llamas have been at the heart of Andean life.

The animals' wool is used for making clothing.

Its meat is a staple of local diets.

Even the animals' blood is sacred. It's sprinkled around doorways

to bring blessings to those who enter.

There's something unexpected

about this particular South American animal.

Llamas that seem so at home in the high mountains

aren't from this continent at all.

They evolved in the low-lying plains of North America.

They're living evidence of the final instalment

in the tale of the two continental Americas -

their joining up.

The llamas' ancestors first appear in North America

about 40 million years ago.

But they don't appear in South America

until three million years ago.

The two continents had been edging closer together.

Then, starting around 30 million years ago,

volcanic islands began to combine,

slowly building a land bridge between the two.

By three million years ago,

two continents that had been separate since the days of Pangaea

were finally joined again.

The New World was born.

Across this narrow link has come a great intermingling of species.

Northern mammals in particular invaded the south.

Deer, foxes and dogs all crossed over,

and cats that quickly became the prime predators.

The result was to increase South America's biodiversity.

Among the most successful arrivals, the llama,

ironically now long extinct in the north.

For me, the llama is the perfect symbol of the New World.

Originating in the northern continents

and flourishing in the southern.

It represents both the isolation and the coming together of the Americas.

Since that momentous joining,

the story of the Americas has been of a single land.

When the first humans arrived in North America,

they quickly moved into the south.

And when Europeans arrived,

both Americas were seen as a single New World.

Today, continental movement means

the Americas continue their westward drift from the Old World.

But on a cultural and economic level,

you can argue the opposite is the case.

Walk through any market place,

even one like this in the relatively inaccessible Andes,

and you find evidence for a connected world, old and new.

Here, you can find electronics, designed in America,

made in the Far East.

English football shirts.

And food.

Beef and pork that came here with the Europeans,

while potatoes and tomatoes and chocolate

were all South American in origin, now worldwide in consumption.

So, although the single continuous landmass of Pangaea

no longer exists,

our modern-day continents are linked in a different way.

Today, our great global economy binds all the continents together.

In essence, we've created a new Pangaea.

A Pangaea of our own making.

And in this Pangaea, just like the one 300 million years ago,

the Americas are right at the heart.

Subtitles by Red Bee Media Ltd