Original subtitles

male narrator: Planet Earth is unique,

an immense ball of rock 25,000 miles around.

lt is a refuge,

1/3 land, 2/3 water,

and with an atmosphere rich in oxygen,

it is the only known home in the universe

for living creatures.

But this blue-green oasis

has not always been so welcoming.

The planet bears the scars of a traumatic past,

a past of extreme environments

and extreme catastrophes.

Over the course of nearly 5 billion years,

it has been a changing world,

a world of fire,

a world of ice,

one of raging seas

and poisonous skies.

The life-forms that now cling to its surface

are the lucky survivors

of a succession of deadly mass extinctions.

Forjust over 200 years,

determined scientists have explored the planet

and unearthed its secrets.

Their remarkable discoveries have led them to tell

an incredible story,

the story of "How The Earth Was Made."

For thousands of years, humans had no knowledge

of the true age and origin of the world.

Butjust over 200 years ago, all this would change.

Scotland, the Edinburgh coast:

it was here, one day in 1 788,

that the discovery of a small rocky outcrop

would completely rewrite the history of the Earth.

Geologist Geoffrey Boulton

is on his way to the desolate Siccar Point,

where this discovery was made

by a maverick Scottish farmer, James Hutton.

Hutton was to become the father of modern geology.

- Hutton was a man who was enthusiastic

in the pursuit of truth, a very inquiring mind.

When he took over his father's farm,

he saw, underneath the soils, rocks

and wondered what these were.

narrator: Hutton spent years obsessed with understanding

how the rocks of the Earth were made.

His intrepid field expeditions took him all over Scotland,

and they led him to realize that extremely slow processes

could create the rocks he saw from layers of sediment.

- He rode miles and miles on his horse

to go places where he thought he could find

exciting geological experiences

even though he suffered terribly from saddle sores.

narrator: Hutton concluded that rocks could take

hundreds of thousands of years to form.

But his claims were speculative,

and his radical ideas flew in the face

of the accepted version of Earth history,

provided by the church.

For generations, the Christian church

had been the sole authority on all creation,

based on the book of Genesis.

And using the biblical genealogies,

church leaders were now confidently claiming

they knew the exact age of the Earth itself.

- Archbishop Ussher in the 1 7th century

had calculated that the Earth was 6,000 years old,

and indeed, he calculated that it was made

on October the 14th in the afternoon.

narrator: Hutton was convinced

that the Earth had to be much older.

And when his explorations led him to Siccar Point in 1 788,

he would finally find the proof he was looking for

in the unusual formation he discovered.

- These rocks are notjust any old rocks.

They're very special rocks, and the reason they're special

is because of the story Hutton was able to tell from them.

narrator: Here, two layered rock formations

stand at right angles to each other.

- He knew these rocks

had once been laid down horizontally on the seafloor.

They must then have been buried under great depth

to recrystallize.

They must then have been tilted on end by great Earth forces.

Then they were eroded away and truncated.

Then these rocks were deposited on top.

And he realized that that would not take hundreds of years

nor thousands of years but many millions of years.

narrator: Hutton's discovery was a turning point.

From that day forward, it was rock, not scripture,

that would become the trusted guide to the distant past.

And over the next two centuries,

the study of rocks around the globe

would lead to the awesome revelation

that this blue-green planet

has been on the most astounding journey...

Ajourney that began in a world of fire.

lt is now believed that the Earth

was formed from collisions among the countless meteors

that made up the early solar system.

Back then, the surface was an ocean of molten rock

miles deep.

Temperatures exceeded 8,000 degrees Fahrenheit,

similar to the surface of the sun.

And huge meteorites rained down in a relentless bombardment.

The man who first proposed this hellish origin for the planet

was the Victorian scientist Lord Kelvin.

A British expert in thermodynamics,

Kelvin believed that the Earth was slowly cooling down.

The fires of the planet's interior,

visible in volcanic eruptions,

suggested to him that the planet had once been completely molten.

Kelvin used thermodynamics

to calculate a new age for the Earth.

He reasoned that the molten planet

would need nearly 20 million years

to cool to its present temperatures.

Kelvin was correct about the Earth being molten

but not about its age.

His figure was a colossal underestimate.

Like all 1 9th-century scientists,

Kelvin was unaware of a key source of heat

inside the early Earth

that prevented the planet from cooling as he predicted:

radioactivity.

ln the early Earth, radioactive particles

of uranium, thorium, and potassium

were in huge abundance.

The heat produced from the decay of these particles

would keep the Earth extremely hot

for an extremely long time.

But although these particles

confounded Kelvin's calculations,

they would eventually prove the keys

to unlocking the true age of the Earth.

ln the 20th century,

rare particles of surviving radioactive uranium

were collected together

to create the first atomic weapons.

But scientists had earlier found a different application,

using the radioactive particles to accurately date the planet.

ln 1 91 1 , a gifted 21-year-old geology student, Arthur Holmes,

used radiation to revolutionize

our understanding of Earth history.

After Holmes,

geologists would talk in billions,

not millions, of years.

Radiometric dating was simple in principle.

lt was based on the discovery

that traces of the radioactive element uranium,

found throughout the rocks of the Earth,

decayed into another element, lead.

Like sand trickling through an hourglass

over hundreds of millions of years

and at a steady rate,

a sample of radioactive uranium will decay to lead.

By measuring the proportion of uranium to lead

in crystals trapped in ancient rocks,

Holmes could accurately calculate their ages.

Collecting data from samples from all over the world

would be a lifetime's work.

But as Holmes grew older, so did the Earth.

lts calculated age extended first to 1 billion,

then 3 billion,

then finally to 4.5 billion years.

Today 4.5 billion years

is still the accepted age for the Earth.

Time on this incredible scale

is known to those in the business

as deep time.

- lt's difficult to imagine how vast deep time is.

But think of it this way.

That's a grain of sand.

lf it represented a year, then the length of my finger

would be equivalent to the whole of my lifetime.

From the tip of my finger to my elbow

would take us back to the pilgrim fathers.

From here to the rocky island you see on the horizon

would take us back to the age of the dinosaurs.

And if we were to turn round and go to the equator,

then it would be equivalent to going back

to the beginning of the Earth 4 1/2 billion years ago.

narrator: The search for the age of the Earth was over,

and the results had opened a window on the past.

For the first time,

scientists could put rocks in the correct order,

look deep into the Earth's past, and tell its story.

They would discover evidence of an epic journey

with many twists and turns.

But the most significant step may well have been taken

within just a few hundred million years of its birth,

when the planet became a water world.

4.5 billion years ago, the Earth was formed

from the collisions of millions of meteors

in the young solar system.

Temperatures were so high

that the planet's surface was a molten ocean.

But even at that time, Earth was beginning to cool.

The radioactivity that provided much of the heat

was slowly declining, paving the way

for the planet's first radical change,

its transformation into a water world.

The Barberton Hills, South Africa:

this remote region is home

to some of the oldest rocks on Earth.

South African geologist Gary Stevens

is on the lookout for some

of these incredibly rare survivors

from the first billion years of Earth history

whose unique shape tells a story.

- This area of South African geology,

here on the eastern side of Mpumalanga, is critical

for our understanding of early Earth processes.

narrator: Gradual erosion along the trickling creek

can occasionally expose these primordial rocks.

- Here we have an interesting rock.

The rounded shape of this rock over here

is very different than the rounded shape

of the rest of the rocks in this river.

This is one of these

3.5-billion-year-old pillow lavas.

The rounded pillow shape in the rock

is a result of the lava

that formed underwater in an ocean

approximately 3 1/2 billion years ago.

narrator: Pillow lavas are created today

off the coast of Hawaii,

where volcanic vents erupt into the Pacific Ocean.

This unique pillow shape is only formed

when lava solidifies under deep water.

All rocks found from the period 3.5 billion years ago

have been pillow lavas.

By 1 billion years into the planet's existence,

water had taken over.

But geologists believe that it had already been around

a long, long time.

4.4 billion years ago,

the Earth was around 1 00 million years old.

Meteors still crashed into the planet,

but gradual cooling of the core had allowed most of the surface

to solidify into a crust of dark volcanic rock.

And even then, at this early stage,

water was forming on the surface.

No rocks now survive from this most early period,

but tiny crystals of zircon do.

Uranium-carrying zircon is one of the crystals

that helped date the Earth.

But these crystals can also retain

the chemical fingerprints of water molecules,

and these fingerprints

are all over the most ancient zircons.

But the origin of the majority of the planet's water

remains a mystery.

As the planet cooled, the surface rocks

began spewing out tons of carbon dioxide.

Some water vapor

would have been vented during this process,

but some believe it would not have been enough

to cover the surface.

- The rocks, the material that accreted

to form the Earth itself,

would have been too dry, too close to the really hot sun.

We have this problem of trying to understand

where our water world got all of its water.

narrator: lmpact expert Dan Durda supports the theory

that the source of most of the Earth's water

was extraterrestrial.

- The idea today is that the Earth's oceans

arrived from above.

They were brought in

in the water-rich asteroids and comets

which peppered the Earth during the tail-off

in its accretionary process.

What l have here is a piece of an actual meteorite.

This is the material

from which the Earth itself formed.

This primitive little meteorite

contains about 5% of water.

lt's that water, in objects like this,

that was delivered to the Earth to form the Earth's oceans.

narrator: Scientists are divided on this,

but wherever the water came from,

when it did arrive,

it changed the planet dramatically.

As it evaporated off the surface,

huge amounts of water vapor rose to join the carbon dioxide

in the young atmosphere, forming thick blanketing clouds.

This condensing water would trigger

the greatest downpour the Earth would ever see.

[thunder booming]

As thunderstorms rocked the skies,

the rain began to fall on the rocky surface below,

and it kept on falling.

[thunder booming]

lt would rain for millions and millions

and millions of years.

The result would be a water world.

4 billion years ago,

the Earth was now 1/2 billion years old.

Over 90% of its surface had become a vast ocean.

Small volcanic islands poked out from the waves.

The monstrous seas were iron-rich,

making them an olive green color.

Carbon dioxide filled the skies so thickly

that they appeared red.

The dense atmosphere produced enough pressure

to crush a human body flat.

And it was hot.

Temperatures exceeded 200 degrees Fahrenheit.

This toxic, hostile water world would remain

for another 1/2 billion years.

But dramatic transformations were on their way.

Renewed volcanic activity

would trigger the construction of the continents

by creating a totally new kind of rock.

Earth was about to become a granite planet.

3.4 billion years ago,

the Earth was just over a billion years old.

Huge green oceans dominated.

None of the crumbling volcanic islands

dotting the surface

survived the punishing seas for long.

But everything was about to change.

An upsurge in undersea volcanic activity

was about to create a tougher type of rock

and give birth to the continents.

ln remote areas of the globe,

the primeval cores of these first continents

have been exposed.

South Africa:

geologist Gary Stevens is climbing

on some of the oldest continental rock on Earth.

These rocks are special.

- We're standing here on an ancient granite.

This granite forms the nucleus

of one of the world's oldest continents.

And we can see it here

in the Barberton area in South Africa.

narrator: These eroded outcrops of rock

are the visible peaks

of what is known as the Kaapvaal craton,

a titanic mass of ancient granite

underlying southern Africa,

a remnant of the early Earth.

3.5 billion years ago,

granite was appearing everywhere.

An upsurge of volcanism had fractured

the crust of the Earth underneath the vast oceans,

allowing water to plunge into the cracks

alongside the molten lavas.

The mixture of superheated water and basaltic lava

produced the new rock, granite.

lt rose from the depths

to form the first true continental crust.

- This is why granite is special and important.

lt's light.

This rock, granitic rock, has a much lower density

than this rock, a basaltic rock.

The difference in density between these two rocks

is greater than the difference in density

between water and air.

This rock would be typical for oceanic crustal material.

This is typical of the continents.

Continents are light and buoyant,

oceanic crust denser and heavier.

lt literally floats on the mantle.

narrator: Granite crust was not only light.

lt was tough,

tough enough to withstand the erosive power of the oceans.

For the next couple of billion years,

slowly but surely,

the granitoid proto-continents grew larger.

On different parts of the globe, granite crust appeared

that would one day form the hearts

of the major land masses.

The dominance of the oceans was over.

The continents had arrived.

The slow expansion of the granite proto-continents

was to change more than just the appearance of the planet.

The shallow coastlines

would bring life to the sunlit surface

and help trigger the production of oxygen.

Almost since the arrival of the first oceans,

it is believed that primitive single-celled life-forms

had appeared deep beneath the waves,

living off the heat produced by the subsea volcanic fissures.

But now they were evolving and spreading upwards.

On the continental coasts, an organism was appearing

that was to transform the planet:

the stromatolite.

The stromatolite would live off sunlight,

and it would fill the atmosphere with oxygen.

This primeval organism can still be found today.

Western Australia:

Martin van Kranendonk is over 1 00 miles

from the nearest town,

heading across the outback to a remote beach.

- We're going down this track

to one of the most unique places in the world,

where you've got living stromatolites

on the shoreline here at Shark Bay.

narrator: On the narrow, sandy coast of Shark Bay,

a multitude of stromatolites fill the tidal shallows.

Each of these unusual rocky mounds

are up to one foot across and two feet high.

lt was only in the 1 950s

that the importance of Shark Bay was realized.

Following trips to this remote site,

Australian geologist Phillip Playford

was the first to discover how stromatolites formed.

Playford identified a rare bacterial algae

found in a slimy film coating their surface

as the creator of the mounds themselves.

- Stromatolites are made up

of very thin layers of microorganisms

that build up slowly, layer by layer,

year by year,

as they use light energy to gain their food,

and as a waste product, they precipitate rock.

narrator: Other geologists recognized the significance

of Playford's findings.

Patterns they had seen in rocks billions of years old

were in fact fossilized stromatolites.

Playford's discovery

had sparked off a fossil revolution.

- Once people knew that these kind of structures

were made by living organisms,

they went back into the rock record

and found that they found the same kinds of structures

and therefore could deduce that life occupied planet Earth

3 1/2 billion years ago.

These are really the ancestors of everything on Earth.

We're actually looking at our great-great-great-great-great-

great-great-great-great- grandmothers and grandfathers.

narrator: The rock record shows that by 2.5 billion years ago,

stromatolites were blossoming globally.

All beaches on Earth would've resembled Shark Bay.

And as stromatolites filled the shallows,

they began to fill the atmosphere with oxygen.

- Planet Earth in the solar system

is the only planet that has an atmosphere

composed of a large amount of oxygen.

Geoscientists think that that oxygen

came only from the reaction of stromatolites.

narrator: The algae turned sunlight into oxygen,

a process known as photosynthesis.

Over a period of 2 billion years,

countless generations of stromatolites

pumped out over 20 million billion tons of oxygen.

At first, the gas dissolved into the oceans,

where it rusted out billions of tons of iron.

But eventually, it would also fill the atmosphere

and transform the planet.

The planet's very appearance was dramatically altered.

As the iron left the oceans, they changed from green to blue.

When the oxygen moved on to the atmosphere,

it diluted the remaining thick carbon dioxide

and cleared the air.

After nearly 2 billion years of oxygenation,

the blue planet was born.

The Earth now had its blue oceans

and its blue sky.

Relics of this great transformative period

survive today in immense layers of iron-rich sediment

originally deposited

on the floors of the ancient oceans.

Scattered all throughout the globe,

the banded iron formations, as they are known,

are vital for today's economies.

They are the major source of all the iron mined today.

Following its oxygenation, the Earth was more recognizable.

But before it would become the planet we know,

a new cycle of cataclysmic events would take place.

Over the next billion years,

deep movements would wrench apart the crust,

and life, which had just begun to make its mark,

would face its toughest test yet.

1 .5 billion years ago,

planet Earth was almost 3 billion years old.

For the first time in its history,

it was beginning to resemble the planet we know.

Newly arrived oxygen had turned the oceans blue,

and the continents had grown

to cover nearly 1/4 of the surface.

But their expansion was not over,

and beneath the oceans, deep forces were at work,

rearranging their positions.

lmperceptibly, the continents were on the move.

Mark McMenamin is an expert in plate tectonics,

the study of continental movement.

Until the 1 960s, this was radical science.

- ln the 1 9th and early 20th century,

the consensus view was that the continents were fixed.

All geology was local,

and the continents stay in one place.

narrator: But problems for this view had been mounting.

One of the greatest mysteries

was the geographic position of certain fossils.

- Trilobites like the one on my left here

belong to the genus Paradoxides.

narrator: The Paradoxides really was a paradox.

lt was a freshwater creature with a curious distribution.

- This trilobite is found

in the eastern part of North America...

- And also in Britain,

on the other side of the Atlantic Ocean.

narrator: The freshwater Paradoxides

could not have swum the vast salty ocean.

And they were not the only fossils

showing bizarre intercontinental distribution.

Geologists struggled for an explanation.

ln 1 912, a radical new theory would emerge from Greenland

that would lay the foundations for plate tectonics

and shake Earth science to its foundations.

The new theory was put forward

by a German weather scientist, Alfred Wegener,

a man who had spent much of his career

conducting atmospheric research in Greenland's frozen wastes.

But Wegener had always been fascinated

by the geologist's fossil paradox,

and he boldly claimed that the answer

was staring them in the face.

- Ever since accurate world maps were available,

schoolchildren and others have pointed out the fit

between the east coast of South America

and the west coast of Africa.

And this was always dismissed in reputable scientific circles

as just a coincidence of no meaning.

And so many disappointed children

were turned away and told that their idea was wrong.

narrator: Wegener proposed that the continents

had indeed once been joined together

and had subsequently drifted apart.

His observations in Greenland convinced him

this continental drift was possible.

- l think that his inspiration was meteorological.

Perhaps he saw breakup of ice floes

and made what we would call an extrapolation

to the hard rock part of the planet.

narrator: But few geologists could accept

the radical theories of a mere meteorologist.

- There was complete rejection of what Wegener was saying.

This is a tall order, to take a gigantic continent

and shove it through the ocean floor

to get it halfway across the globe.

narrator: Throughout his life,

Wegener fought to gain evidence for his theory.

But his brave attempts eventually led to his demise.

ln 1 930, his last expedition to Greenland ended in tragedy

when he lost his way in a snowstorm.

- ln an icy situation on a glacier,

it's difficult to find your way.

Separated from both his base camp

and the other members of his expedition,

he basically got lost and died of exposure.

narrator: Wegener was dead,

but his theory of continental drift lived on.

The breakthrough came after the U.S. Navy

produced a global map of the ocean floor,

originally commissioned for submarine warfare

during World War ll.

[sonar pinging]

This detailed map revealed one of the Earth's greatest secrets:

the fractured network of submarine mountains,

volcanic rifts, and trenches

that split the oceans into enormous plates of crust.

These plates would be the building blocks

for the new science of plate tectonics.

The rifts and trenches would provide a solution

to how continents drift

by proving that the ocean floors are continuously being recycled.

- Plate tectonics is completely driven

by the destruction of the old and the creation of the new

narrator: Deep below the surface,

mobile mantle rock is in continuous circular motion,

following convection currents of heat

generated deep within the planet.

Where these currents rise, the rifts form,

and the plates are pushed apart,

with new ocean crust created in the gap.

Where the mantle currents sink back down into the Earth,

they drag old oceanic plate down with them

towards the interior.

As the ocean plate moves, so do the continents.

- That oceanic plate drags the continent along with it.

The process is like an escalator or a conveyor belt.

narrator: The process of ocean creation

is visible today on a rocky island

in the middle of the Atlantic:

lceland.

lceland lies on the Mid-Atlantic Ridge,

a 1 0,000-mile-long range of subsea volcanic mountains

that mark one of the deep rifts in the Earth's crust.

- lceland is really like a peak of this mountain chain.

lt's like huge volcano sitting on top of it.

narrator: Seismologist Páll Einarsson

studies the volcanism of this remote island,

volcanism that is helping to expand the Atlantic Ocean.

Occasionally, an unusual type of volcanic eruption on lceland

confirms the plate-tectonic process:

a fissure eruption.

A fissure eruption is a wall of fire.

They can be 25 miles long

and spew lava hundreds of feet into the air.

- People fear eruptions.

They respect the volcanoes.

narrator: The fissures mark the path

of the deep plate boundary that is creating the Atlantic.

All across the island,

running from northeast to southwest,

are the remains of these fissure eruptions,

scarring the rocky landscape with shallow canyons.

These canyons are very slowly widening lceland.

At their base, new crust is being created,

pushing Europe and America apart.

- So here we are located in the fissure

between the two continental plates,

the two crustal plates.

Here on my left, we have the North America plate,

and on the other side, we have Europe.

This fissure here is in a lava flow

that's only about 8,000 years old.

So in 8,000 years,

that's how much the two plates have moved.

- The rate of continental drift

averages about 2.5 centimeters per year,

the rate at which fingernails typically grow.

narrator: 2.5 centimeters, one inch per year,

means that in one human lifetime,

America and Europe will move just six feet further apart.

But over millions of years, this speed of movement

was enough to shift the continents

thousands of miles.

Using plate tectonics as their guide,

geologists such as Mark McMenamin

have reconstructed the epic story

of continental movement from the beginning.

From samples taken from present-day continental margins,

they've compared fossils and microfossils

and matched up distinctive types of ancient rocks

to reconstruct where the continents used to be.

- lt's a tricky task.

lt's kind of like Humpty Dumpty.

You've got all of these pieces.

You need to use whatever clues you can,

whatever fingerprints you can,

to put one continental margin against the other.

narrator: They are now confident

that they can trace the movement of the continents

back over a billion years

to a time of a mass continental collision.

As the oceans between them were swallowed up,

the large land masses drew together

in what was to become a supercontinent, Rodinia.

lt is believed that Canada and the U.S.A.

formed the supercontinent's heart,

with other continents bunched around them.

But Rodinia was unlike any continent seen today.

lt was a desolate, lifeless place.

- lt would've been very much like being in the desert.

lt would've been similar to parts of the Sahara,

Death Valley.

There would have been no plants, no forests,

no grasslands.

Rodinia would have been a barren continent.

narrator: Rodinia may have been lifeless,

but it was to have a profound effect

on life in the oceans.

ln the oxygenated waters,

primitive life-forms were blooming

alongside the stromatolites.

But the huge supercontinent was about to give them

a tremendous shock.

Rodinia was to trigger what is now known

as "snowball Earth,"

the biggest freeze the world has ever seen.

By around 700 million years ago, Rodinia's position

was blocking the currents that brought warm water

from the equator to the poles.

Without this heat, the polar regions froze.

The resulting ice reflected more of the sun's rays

away from the Earth,

and in a catastrophic snowballing effect,

temperatures dropped still further,

and the ice advanced to cover the Earth.

Surface temperatures fell below minus 40 degrees.

The oceans were covered in an ice sheet

almost a mile deep.

The only life on Earth, marine bacterias and algae,

were trapped beneath in the darkness.

The result was disaster.

All but a tiny fraction of organisms

were driven to extinction.

The whole planet was dying.

650 million years ago, climate changes triggered

by the formation of the supercontinent Rodinia

had left the surface of the Earth

covered with a sheet of ice one mile thick.

Temperatures hovered below minus 40 degrees Fahrenheit.

Marine organisms, the only life on the planet,

had almost been wiped out.

The future of life on Earth hung in the balance.

But beneath the ice,

the supercontinent was in turmoil.

Vast volcanic eruptions were splitting Rodinia apart.

- lt's thought that the accumulation of heat

at the base of the supercontinent

is what eventually leads to its undoing.

lt's like putting a blanket over the Earth.

The heat that's generated in the Earth's interior

will accumulate underneath that blanket.

narrator: The heat would spell the end of the snowball.

As Rodinia ruptured,

carbon dioxide released by the eruptions

created a temporary greenhouse effect.

The ice sheets drew back.

Rodinia had broken into giant fragments.

And the icy grip on life was broken.

As shallow seas opened up in Rodinia's wake

and oxygen levels increased,

the primitive organisms were free

to take their next great step forward.

They would become complex and a lot more dangerous.

The Canadian Rockies:

these remote mountains are home to a rare record

of this key event in the evolution of life,

the so-called Cambrian explosion.

- For the first time in the history of life on Earth,

we have some of the highest oxygen levels

that we've had since the Earth was actually formed.

Life bloomed.

We see animals unlike we've ever seen before.

narrator: Paleontologist Paul McNeil

is hiking up to a remote mountain quarry

known as the Burgess Shale.

The astonishing fossils in this quarry

are a window on the world as it existed

over 500 million years ago.

- lf you surveyed all the people

who study the history of life,

you get almost unanimous agreement

that this is one of the most important

fossil sites in the world.

narrator: The man who discovered the Burgess Shale

was an American, Charles Doolittle Walcott,

the president of the Smithsonian lnstitute.

This fanatical fossil hunter, who was born into poverty,

had lived the American dream.

Armed only with a high school diploma,

he had fought his way to the top

of the American scientific establishment.

But it was his tenacious fossil-hunting expeditions

in the most remote mountains of North America

that would lead to his most stunning achievement.

- This is the actual location

where Walcott first made his amazing discovery.

As the legend goes, it was August 31 , 1 909,

riding along this very trail with his wife in a snowstorm.

And as they were riding along, a large slab of rock came down,

blocked the trail, and they couldn't get by.

Now, being a gentleman, as all paleontologists are,

he immediately leapt off his horse,

flipped over the slab of rock,

and found an incredibly well-preserved fossil.

lt was down on the trail.

Where did it come from?

Nowhere but up there.

narrator: The source of the rockfall

was a section of the cliff no more than 1 00 feet across,

a small area that became

the celebrated Burgess Shale quarry.

Walcott, often aided by his own family,

eventually extracted over 60,000 fossils.

And since Walcott,

a further 1 00,000 have been excavated

from this uniquely rich cliff face.

- Quarrying the rocks out of the mountain

requires a tremendous amount of work,

a lot of backbreaking labor.

But it's also extremely exciting,

because every time you split open a rock,

you never know what you're gonna find.

Most of the time, you find nothing,

but every once in a while, you find a new animal,

one that's never been seen before,

one that's been revealed for the first time

in 1/2 billion years.

narrator: The thousands of fossils

found in the Burgess Shale

reveal that starting 500 million years ago,

life exploded with staggering diversity and complexity.

- The preservation of these fossils

is actually incredible

in that they're actually preserved in three dimensions.

You can excavate through the fossils themselves,

see the internal organs,

remove the organs, see the digestive tract.

This is fantastic preservation.

Oh, look, it's starting to crack,

and there goes a piece.

What we have here is an actual anomalocaris.

These guys were up to a meter in length.

That actually made them the T. rex of the Cambrian.

narrator: ln the Cambrian seas, the oxygen-rich shallow waters

were teeming with complex organisms.

And creatures were feeding not just on plants

but on each other.

- The Cambrian is actually one of the most special times

in the history of life.

We see more different types of animals

than we see in the rest of the entire history

of life on Earth.

narrator: From this time onwards,

with a biological arms race driving their evolution,

creatures would become increasingly complex,

with the development of hard shells, skeletons,

eyes, and teeth.

Modern animals had arrived on Earth.

The high level of oxygen that had triggered

this explosion of life in the seas

was also making a final modification

to the atmosphere.

Over the next 1 00 million years,

oxygen reached today's high levels,

a level dense enough to allow an ozone layer

to form in the upper atmosphere.

This layer was to free life-forms from the oceans.

Previously, powerful ultraviolet light

would destroy any organism not protected by the water.

Now the ozone layer would act as a UV shield.

400 million years ago,

the Earth is more than 4 billion years old.

Over the next 1 00 million years,

the continents would once again converge.

And this time, thanks to the ozone shield,

life was free to leave the oceans

and conquer the land.

Planet Earth had become a world of tropical swamps.

South Georgia, U.S.A., the Okefenokee Swamp.

- The Okefenokee is believed to be

what we would call an analogue,

a modern analogue, or an environment

that's very similar to the wetlands

that existed on Earth in the past.

narrator: Fred Rich is an expert on prehistoric swampland.

Geologists like him believe that this freshwater swamp

closely mimics the surface of the continents

300 million years ago

in a period known as the Carboniferous.

- The Carboniferous was an unusual time

because it was the first period in Earth history

when large plants occupied Earth's surface,

40, 50, 70 feet high, that grew in dense groves

and produced a vast forest canopy

and a steamy tropical jungle atmosphere

that was something entirely new on the face of the Earth.

narrator: This dense tropical swampland

would dominate the Earth for the next 60 million years.

The evidence is present

on all of today's continents in the form of coal.

The coal we use for fuel was formed

from millions of years' worth of accumulated plant matter,

most of which existed less than 300 million years ago.

And it formed because of the unique way

freshwater swamps decompose.

- Okefenokee is derived from a Native American word

that means "land of the trembling earth."

lt's not very easy to walk through the swamp,

because the subsurface is soggy plant remains.

narrator: The freshwater

prevents the vegetation from decaying,

allowing huge amounts to build up over time.

- Beneath me is not the regular sort of soil

that you would have in your backyard.

The soil that you see here is the plant material

that accumulated last year or perhaps five years ago.

lt's leaves, stems, twigs.

There's still a good bit of water in this.

But if we put this under a tremendous amount of pressure

and add some heat,

by covering over with layers of rock

and leaving it in the ground for millions of years,

eventually it will change to this.

This is a piece of bituminous coal,

and it's around the order of 200 million years old.

narrator: As the dead plants

were transformed to coal on land,

the shallow waters surrounding the continents

were preserving millions of generations

of dead marine organisms

that would become our other major fossil fuels,

oil and gas.

Every year, mankind mines almost 5,000 megatons of coal,

30 billion barrels of oil,

and 3,000 billion cubic meters of gas.

This fertile period of Earth history

has given us much of the energy we use today.

Without it, the lndustrial Revolution

may never have happened.

Plants were not alone in making a new life on the land

300 million years ago.

As time went on, first enormous insects...

Then ambitious amphibians

and finally early reptilians left the seas

to take their first steps on the muddy shorelines.

The U.S. east coast back then would have teemed with monsters:

three-foot millipedes on land,

two-foot dragonflies in the air,

and proto-alligators patrolling the nearby waters.

The world was over 4 1/4 billion years old,

and for the first time,

the surface was host to a complete modern biosphere.

But the all-conquering life-forms

were about to experience a hell on Earth.

Forces deep within

were about to give life on the surface

its sternest test ever.

Enormous volcanic eruptions

would herald the biggest mass extinction

in the planet's entire history.

250 million years ago:

for hundreds of millions of years,

life on the surface

had faced numerous challenges to its survival

but nothing on the scale of what was about to happen.

ln what would one day become Siberia,

the Earth's crust became a volcanic morass.

The cause was a rare mantle plume eruption.

No one knows for sure why they occur,

but occasionally, huge masses of hot mantle

from deep within the Earth surge upwards,

melting and smashing the crust above.

The eruptions continued for over 1 million years.

They spewed out over 1 million cubic miles of molten rock,

enough to bury the modern U.S.A. in a layer over 1 ,000 feet deep.

Clouds of poisonous gases spread out

and shrouded the entire globe.

lt was too much for most species of life.

Over 95% were driven to extinction.

lt was the most cataclysmic event

the planet has ever witnessed.

The planet that emerged from the chaos was much changed.

A new supercontinent, the great Pangaea,

now dominated.

And the climate was altering dramatically.

Over the next 200 million years,

oxygen and carbon dioxide would rise to new peaks.

And under these conditions,

the animals that had survived the extinction

were to evolve into the most infamous creatures

ever to walk the Earth...

[screeching roar]

The dinosaurs.

Utah, U.S.A.

Paleontologist Reese Barrick is on the hunt for dinosaurs.

ln this dusty corner of the western U.S.A.,

the rocks are packed with their bones.

- Almost 1/3 of the history of life on this planet

was dominated by dinosaurs.

lt really, truly is a dinosaur planet.

We have, from the bottom of this slope,

sediments that are 1 50 million years.

And as you go up the slope, you actually end up

in the Cretaceous at 125 million years.

How we doin', Barb?

- Doin' great. - Find anything fun?

- A small rib and some interesting fragments.

- Well, that's a start for the day.

narrator: Compared to modern creatures,

dinosaurs were enormous.

The average mammal today is smaller than a dog.

The average dinosaur was larger than a grizzly bear.

[dinosaur roaring]

- Marvin, excellent. Look at that.

That is a spectacular therizinosaur claw.

This animal's gonna have to be 300 kilograms,

so it's about the size

of a National Football League lineman.

[chuckles]

These are absolutely fantastic

because they're very well-preserved bone.

A perfect claw.

Absolutely brilliant, Marvin. Nice job.

narrator: The first recorded dinosaur fossil find

was a bone discovered by young Mary Ann Mantell

in England in 1 822.

Her husband, Dr. Gideon Mantell, was intrigued

and set about determining

what type of creature it belonged to.

The fossil was unlike anything he'd ever seen.

After much research,

he decided it was in fact a tooth

from an enormous lizard.

He named the beast lguanodon,

after the iguana lizard he thought it resembled.

Over the next few decades, across Europe and the U.S.A.,

more and more huge bones were unearthed,

and given their similarity to modern lizards,

the name dinosaur, meaning "terrible lizard,"

was coined.

[dinosaur roaring]

But many paleontologists today

believe one of the reasons dinosaurs grew so large

was that they weren't cold-blooded

like today's lizards.

They were lukewarm-blooded.

This gave them the advantages

of both cold-blooded lizards and warm-blooded mammals.

- Dinosaurs were able to be active

and collect food all year long,

and yet they could put a greater amount

of the food that they ate towards growing

as opposed to just heat generation.

narrator: But another reason for their size

may have been the sweltering oxygen-rich environment

that came to dominate the dinosaur era,

an environment triggered by volcanism.

Starting around 1 80 million years ago,

a new upsurge in volcanic activity

split apart the supercontinent.

The continental fragments began their long journeys

into the positions they occupy today.

North America, South America, Africa, and Europe

all went their separate ways.

The Pangaean supercontinent was no more.

Each of the new continents still carried dinosaurs,

and the steamy volcanic climate seemed to suit them.

lt was global warming gone wild.

CO2 levels increased over 500%, and temperatures soared.

ln the greenhouse conditions this created,

huge tropical forests spread across many of the continents.

- The increasing amount of tropics

meant that there was a lot more lush vegetation,

which means there's a lot more food for dinosaurs,

which allowed them not only to specialize

and evolve to specialize

on different types of plant materials

but allowed them to get extremely large.

narrator: Many scientists believe

that evolving for millions of years

in this warm oxygen-rich world

allowed the lukewarm-blooded dinosaurs

to reach their enormous sizes.

Huge dinosaurs may have been a biological response

to a volcanically overactive planet.

But size would not save the dinosaurs

from what was to come.

Their time on Earth would end

in sudden, unstoppable devastation.

1 00 million years ago,

planet Earth was ruled by dinosaurs.

[dinosaur screeching]

Huge beasts filled the land, the sea, and the air.

They lived in a sweltering world defined by overactive volcanism,

and before it was finished,

this volcanism would bring to the surface

some of the planet's most wondrous riches:

diamonds.

Kimberley, South Africa:

Jock Robey is chief geologist at De Beers,

the largest diamond company in the world.

- Diamond is simply the high-pressure form

of the element carbon.

This is a typical eight-sided crystal called an octahedron.

Uncut, it is worth $2,000 a carat.

As a cut stone, it would probably sell for $80,000.

narrator: For thousands of years,

diamonds had been found worldwide

washed up in sandy riverbanks,

but their source had remained a total mystery.

lt was not until 1 869

when huge unique diamond discoveries

were made in South Africa

that their remarkable origin was revealed.

- What is special about the diamonds

found in the Kimberley area

was, here, for the first time ever,

they found the source rock of diamonds.

This is a piece of rock mined from the kimberlite,

and as we turn it, it contains a diamond.

narrator: The diamond-bearing rock was extracted

from strange vertical formations.

- As the miners were digging, they found that the diamonds

were contained in a body of rock

that had a shape of an ice cream cone:

slightly broader at the surface, yellow in color,

tapering down to a narrower point.

narrator: Henry Carvill Lewis,

a visiting American mineralogist,

put together the pieces.

He realized these diamond mines

were actually the mouths of ancient volcanoes.

The miners were digging down into their roots,

through the diamond-bearing magma that remained.

But these were clearly not normal volcanoes.

They were over three times deeper,

extending nearly 1 00 miles

beneath the surface of the continent.

Uniquely intense pressures and temperatures at this depth

make it the only place that diamonds can form,

and the diamonds could only be brought up

by uniquely intense eruptions.

The diamond-bearing magma exploded out of the Earth

at over 300 miles an hour.

- lmagine the force and the power of this volcano

to cut those sheer vertical walls

and blow this up another thousand meters.

This is the power of these volcanoes.

narrator: When the Pangaean supercontinent split apart

over 1 00 million years ago,

scientists believe the enormous upheaval

triggered these supereruptions.

Because supercontinental breakups are rare,

so are the diamonds they bring to the surface.

The diamonds that erupted into the dinosaur world

would survive unblemished until the present day.

But the dinosaurs would not be so lucky.

65 million years ago,

the planet was lush.

Vegetation was thick on the surface.

Living things were prospering like never before.

But the dominant dinosaurs

were about to be wiped from the face of the planet.

[dinosaur roaring]

- Dinosaur bones are found continuously

throughout the sedimentary record

from 230 million years ago

right up to 65 million years ago,

and then, instantaneously, they vanish.

narrator: Not only dinosaurs

but over 70% of species on Earth disappeared.

From plant life upward, something terrible had happened

to the entire ecosystem of the planet.

This mass extinction remained a mystery

for generations of paleontologists.

But it is a mystery no longer.

Colorado, U.S.A.:

Dan Durda is taking samples

from an exposed layer of rock exactly 65 million years old.

Scientists now believe that it holds the answer.

For Dan Durda, this powdery rock

is an indication that the dinosaurs perished

in a sudden astronomical catastrophe.

- Dinosaurs and 75% of all the other plants and animals

that lived with them, this layer is their tombstone.

This thin layer of clay is the important evidence

of a violent event in the history

of life on the planet.

narrator: The evidence held in the tombstone layer

is a huge amount

of an exceptionally rare element, iridium.

The remarkable concentration of iridium

was discovered accidentally in 1 980

by a father-and-son team of scientists,

Luis and Walter Alvarez.

On the planet's surface,

iridium is usually found in very small concentrations.

Most of this rare element originates from space rock

deposited from the multitude of small meteors

vaporizing in the upper atmosphere every day.

The Alvarezes were looking for variations

in the strength of these tiny meteor showers,

but when they realized this huge concentration

was held in the infamous tombstone layer,

they proposed a radical new theory for the extinction:

death from above.

The dinosaur planet had been hit by an enormous meteor.

Their theory remained controversial for over ten years

until the final piece of the puzzle

was discovered in Mexico:

a hidden crater over 1 00 miles across.

- ln 1 990, the Chicxulub impact crater was discovered,

and its age, when finally dated,

turned out to be precisely 65 million years old.

lt turned out to be,

it was the smoking gun for the Alvarez theory.

narrator: Worldwide, the tombstone layer

contains an estimated 200,000 tons of iridium.

This translates to a meteor over six miles in diameter.

lts impact on the planet would have been devastating.

- You've got to imagine Mount Everest

flying at you across the sky at 20 kilometers per second.

Several thousand cubic kilometers

and launched around the entire planet,

slowly raining back down through the atmosphere

to settle across the surface of the Earth

as a thin layer of dust and debris.

narrator: But the meteor was not alone

in wreaking destruction.

Today in lndia, ancient lava flows exist

that are so thick,

whole temples have been carved into their layers.

The lavas were the result of a massive eruption

that was occurring simultaneously

with the meteor strike.

Although not as extensive

as the earlier Siberian eruptions,

these lava flows in western lndia

could have buried the U.S.A. to a depth of over 600 feet.

The huge clouds of toxic dust they produced

would have rivaled those of the meteor.

65 million years ago,

the meteor impact and the eruptions

would have been a deadly double blow.

Whichever had the stronger effect,

the combination of these events

sounded the death knell for the dinosaurs.

[dinosaur roaring]

A dust cloud lingering high in the upper atmosphere

and blocking the sun devastated the life below.

The huge dinosaurs,

along with most other major species,

were extinct.

The new world that was to follow

would be the world of the mammals

and the world of man.

50 million years ago,

life was slowly recovering after the cataclysmic extinction

that obliterated the dinosaurs.

The Earth had been around for over 4.4 billion years,

but only now were the first mammals,

our ancestors, beginning to flourish.

Long before humans arrived,

the continents continued to move and crash into one another.

Slowly but surely, the surface started to look familiar

as plate tectonics and erosion

created the dramatic landscapes we see today.

The Swiss Alps:

some mountain chains can be explained

by volcanic eruption of rock from the depths of the Earth.

But the greatest, including the Alps,

contain no volcanoes.

They appear to have risen as if by magic

up from the plains beneath.

This famous range runs through the heart of Europe

and reaches over three miles above sea level.

How was such a huge mass of rock pushed up so high?

Adrian Pfiffner is an expert

on the structure of the Alpine chain,

and he knows the answer.

- The scene we see in front of us

is the result of a collision between two continents,

the African continent and the European continent.

narrator: A close study of the Alpine rocks

can provide clear evidence

of how the mountains were formed.

The secret is revealed in quartz crystals

that are extremely small.

- These slices are about 25 thousandths of a millimeter.

At that thickness,

you see through one single grain.

narrator: The tiny crystals in the rock

reveal massive deformation.

- The quartz grains have been really stretched,

elongated and flattened.

You need large stresses in order to deform these rocks.

One process that is doing this

is actually the collision of two continental plates.

narrator: For the last 45 million years,

as the continents have continued to move,

the African plate and subplates have been grinding into Europe.

The continental crust along the collision point

experiences extreme pressure,

and the solid rock itself is warped and buckled.

- lf you assume that my hands are two plates

which are squeezing the rocks in between,

you can see that some of the material escapes upwards

and leads to the building of a mountain chain.

narrator: The twisted folds of the rock strata are exposed

as the mountains are slowly squeezed higher and higher.

One famous Alpine mountain

demonstrates clearly this collision

of the African and European continental plates:

the Matterhorn.

The Matterhorn is the child of two continents.

- What's amazing about the Matterhorn is,

the top pyramid of the Matterhorn

is a piece of Africa, and it lies on Europe.

narrator: ln the formation of this classic mountain,

the two continental plates have actually overlapped.

- You can think of a car crash.

lf two cars crash with each other,

maybe one car slides over the other one.

The two continents moved together,

and Africa moved on top of Europe.

narrator: Plate tectonics are responsible

for all the Earth's mountain ranges,

and over millions of years of growth,

the only thing that has stopped them

grinding inexorably skywards is erosion...

Erosion by snow, wind, and rain.

- This is the action of water that is eroding the mountains.

Now, this might seem to be something very small,

but actually, if you look at the entire Swiss Alps,

50 million tons is eroded every year,

and this corresponds to a small mountain

roughly 1 ,000 meters high, one every year.

narrator: The height of mountains around the world

are determined by these two opposing forces---

uplift and erosion---

changing them by fractions of an inch,

up or down, each year.

But plate movement and water erosion

can also create the opposite of a mountain.

Under the right conditions,

the surface itself can be cut away,

sometimes spectacularly.

The Grand Canyon:

over 1 mile deep,

1 0 miles wide,

277 miles long,

and still growing.

- One of the great stories of exploration

is when the first Europeans

saw the Grand Canyon in the year 1 541 ,

and a couple of those men came over to the rim,

they saw the river down below,

and they thought it was six feet wide.

The explorer sent a couple of his men down,

and they came back later and said,

"The canyon is deeper than it looks."

narrator: Wayne Ranney is an expert

on this geological phenomenon,

its unique scale the consequence of titanic forces of nature.

Over the course of the last 6 million years,

this spectacular canyon has been carved

by the slow, winding Colorado River

in combination with dramatic uplifting

of the Colorado Plateau.

Plate tectonic processes

have pushed the whole plateau upwards.

lt now lies over 8,000 feet above sea level.

- This uplift probably occurred

with the Pacific plate coming into the North American plate

and wrinkling the crust,

much like if you took a throw rug on a hardwood floor

and pushed it along the hardwood floor.

When the edge of that rug reaches the wall,

you'll see this big bow-up in the rug,

and that's exactly what's happened

to the western edge of North America.

narrator: The river looks too small

to cut a canyon so deep,

but its height above sea level

means that the force of gravity gives it great power.

- All you have to do is look at big rivers

like the Amazon or the Mississippi.

They have much more volume of water

than the Colorado River does,

and yet they don't cut large canyons,

because their landscape is not elevated.

So uplift brings the rocks into an elevation

where the river can then saw down

through all of those layers

and create the canyon landscape we see today.

narrator: Plate tectonics combined with erosion

have sculpted many of the features

on the surface of our planet,

and as a general rule, the mostjagged, tallest peaks

and the deepest canyons

are the youngest of these grand structures,

all formed within the last 50 million years.

But the final touches have been added

by yet another major force of nature.

2 million years ago in east Africa,

ancestors of modern humans

were taking their first steps on Earth.

At the same time, down from the North Pole,

enormous icy glaciers began to descend.

The Earth was about to enter the ice ages.

2 million years ago, ancestors of modern humans

had begun to spread out of Africa.

But the Earth around them was cooling down.

Before long, much of the planet

would be coated in huge glaciers.

The ice ages had arrived.

The grand freezings were triggered

when overflowing volcanoes in Panama

created the land bridge joining North to South America

and radically altered global ocean currents.

The polar seas cooled significantly.

The result was that pronounced dips in global temperature

could now tip the planet into ice ages

lasting tens of thousands of years.

lceland:

the Langjökull glacier.

ln the highest, coldest parts of the planet,

glaciers still reign supreme.

Few venture out in these hostile terrains,

but glacier climatologist Finnur Pálsson and his team

regularly battle the freezing elements.

- When you're doing glacier fieldwork,

conditions can be very bad.

narrator: Outside, it is below minus 20 degrees Fahrenheit.

- l like to work in harsh conditions.

Difficulty is something you need to tackle.

narrator: Finnur is keeping tabs on the growth of the glacier.

At present, it is over 350 square miles,

the size of New York City.

And although it may look static,

in fact, it is in constant motion.

Glaciers are formed initially by snowfall on high areas.

The compacted ice is then dragged down

by the force of gravity.

The glaciers move like slow-motion rivers.

- You can think of ice

as soft material like toothpaste.

lt flows.

lf you make a big blob of toothpaste on a plate,

it will slowly sink down and flow away to the edges.

narrator: Finnur and his team in lceland regularly check

on the incremental movement of the ice.

- This is a satellite positioning system.

We can calculate the position of this point

with an accuracy of about two centimeters

to calculate how fast the glacier moves.

narrator: Finnur's measurements tell him

that this glacier is moving at over 1 50 feet per year.

ln today's mild temperatures,

glacial advance is kept in check by glacial melting,

but if global temperatures were to drop

byjust a few degrees for a long period,

then the glaciers would grind slowly forward,

and the Earth would enter another ice age.

The existence of ice ages was first discovered

by 1 9th-century Swiss geologist Louis Agassiz.

As he explored the Swiss Alps in the 1 830s,

Agassiz couldn't help but notice

the immense boulders scattered over farmland

and the bizarre towers of gravel capped by stones

that stood guard over some of the mountain valleys.

To explain how the rocks arrived at these positions,

he speculated that they had been carried and deposited

by ancient glaciers that had once filled the Alpine valleys

and covered the Northern Hemisphere.

lnitially ridiculed by his peers,

Agassiz's ice age theory became accepted

as telltale signs that these huge glaciers

had indeed covered the continents

were found all over the globe.

The evidence is everywhere.

New York's Central Park:

this oasis of green in the middle of Manhattan

exposes part of the island's ancient bedrock.

Many large outcrops are visible,

and they contain the footprints of the glaciers.

Climate expert Joerg Schaefer

is looking for subtle traces of this frozen world.

- lt's actually something l bet

that most New Yorkers do not know.

You see the ice age is everywhere

if you open your eyes.

narrator: Look closely, and the superhard bedrock

is marked with scores of tiny parallel lines

fractions of an inch deep.

- So this point here is actually one of the most amazing spots

of evidence for an ice age in the middle of New York City.

narrator: The grooves were caused by small rocks

caught under the massive weight of a moving glacier.

- These little rocks basically cut like a knife

into this very hard bedrock.

This is clear proof that, once,

an enormous ice sheet was moving in this direction

in the middle of New York City.

narrator: The glaciers that hit New York were massive.

They rolled down from the Arctic

and buried Manhattan under a huge depth of ice.

- To give you an idea about the thickness

of the Laurentide ice sheet in the Manhattan area,

it was at least twice as thick

as the Empire State Building is high today.

narrator: Over the last 2 million years,

as the climate fluctuated,

the huge ice sheets waxed and waned.

With every pass, they gouged and crushed

and reshaped the land beneath them.

As the last glaciers retreated 1 0,000 years ago,

they left behind a bruised and battered landscape

and created features we still see today.

ln the U.S.A., Cape Cod and Long lsland

are built on immense piles of boulders

dropped from the retreating edge of the North American ice sheet.

And the great weight of the ice formed huge depressions

that now make up the Great Lakes.

ln the warmer climate

that followed the last glacial retreat,

early humans had free reign over the surface.

ln this brief period, a fraction of a fraction of 1%

of the history of the Earth,

the entire history of human civilization has taken place.

Human ingenuity has reshaped our planet.

From our perspective,

our achievements are breathtaking.

But will we continue to survive and prosper?

- Humans have, with technology,

dominated the planet more completely, perhaps,

than any other animal in the history of life,

but we've done it for such a short period of time

that we've got a long ways to go.

narrator: Over the past 4.5 billion years,

the Earth has been on the most incredible journey.

Over the eons of its existence, the planetary environment

has undergone immense transformations.

And since the arrival of life,

these transformations have in many ways

determined which organisms will survive

and which will be swept aside.

lf this turbulent past is any guide to the future,

life and humans in particular

will face further battles for survival

as the planet continues along its path of change.

- Life is highly dependent on the Earth.

What the Earth gives us is what we have to deal with.

- lt's hard to separate completely

the processes of geology and the processes of life.

Life in some ways drives geology,

and geology creates the environments

in which life thrives.

narrator: Our first major challenge will be the climate.

At the start of the 21st century,

we may worry about global warming,

but most scientists recognize

that we are in a gap between ice ages.

Our whole civilization has occurred

in a brief warm period, 1 0,000 years so far.

This warmth has proved crucial.

- lt's definitely not a coincidence

that civilizations developed over this period of time,

because the climate is so favorable to our species

to develop and flourish.

The period we live in the moment climate-wise

over the last, let's say, 1 0,000 years

is exceptionally stable.

lt's almost unbelievably stable

if you look into the geological record.

lt certainly will not stay forever like that.

narrator: Even if our industrial economies

effect a global warming

over the next couple of centuries,

they can do no more than delay the inevitable.

The continents' current positions

keeping the polar oceans cool

mean that in just 1 5,000 years, a new ice age may occur.

- The New York area is going to be completely changed

by the next cycle of glaciation,

and at some point, glaciers are going to move down

and grind New York into the North Atlantic Ocean.

narrator: But even if we survive the big freezes,

there will be greater challenges to come.

As plate tectonics move the continents

and end the ice ages,

coastal regions will be engulfed,

and whole countries will disappear.

200 million years from now,

a new supercontinent, Pangaea Ultima,

is due to take shape

as first the Mediterranean and then the Atlantic Ocean

are swallowed up.

- There will be continents eventually colliding

with the east coast of North America,

so New York, in the long run, will be destroyed

in a continent-to-continent collision

and will be completely crushed

and thrust upward as a new mountain range.

narrator: The Earth will once again

be thrown into deadly turmoil.

Oxygen levels and surface temperatures

could fluctuate wildly

and lead to new mass extinctions.

But even the trauma of supercontinental disruption

is nothing compared to what will follow.

Everything will grind to a halt

when the plate-tectonic engine finally stops.

- The maintenance of habitability on this planet

is involved with the plate-tectonic cycle.

lt's not an infinite cycle.

There is an end in sight.

lt's billions of years from now,

but we know, eventually, the system will wear out.

narrator: The fires in the depths

that have dominated activity on the surface

will one day use up their fuel,

and the story of planet Earth will be over.

Without its burning heart, the Earth will share

what many believe was the fate of Mars.

The atmosphere and oceans will be stripped away,

and the surface will become a bone-dry barren desert.

The planet will be dead.

But this is a picture of an incredibly distant future.

For at least the next billion years,

as the Earth continues its epicjourney,

some form of life should continue.

But the human species, which has walked the Earth

for over 2 million years

and mastered it only in the last 1 0,000,

may be in danger.

As the environment transforms,

Earth could well become unfit for humans.

lf that happens in the distant future,

rather than be forced to face extinction

like our predecessors,

technology may allow us to leave Earth

in search of new homes,

other blue-green planets on which to make a new start,