All language subtitles for Making North America Series 1 NOVA 3of3 Human 1080p

KIRK JOHNSON:
North America,
the land that we love.

It looks pretty familiar,
don't you think?

Well, think again!

The ground we walk on
is full of surprises...

if you know where to look.

As a geologist,
the Grand Canyon is perhaps

the best place in the world.

Every single one of these layers
tells its own story

about what North America

was like when that layer
was deposited.

So are you ready
for a little time traveling?

I'm Kirk Johnson,
the director

of the Smithsonian National
Museum of Natural History.

And I'm taking off...

(exhales)

...on the field trip
of a lifetime.

Wow, look at that rock
right there-- that is crazy.

In this episode,
North America is locked

behind an enormous wall of ice.

How did the first humans
to ever set foot

on the continent
manage to get in?

This is not the easiest thing
in the world.

Once they got here,
the challenges were daunting.

(lowing)

But somehow, we turn the rocks
of our homeland...

Oh, man!

...into riches.

This thing is phenomenal.

But what challenges lie ahead?

Because our continent
may be hiding

some pretty dangerous secrets.

"Making North America: Human,"
right now, on "NOVA."

Major funding for "NOVA"
is provided by the following:

Major funding for "NOVA"
is provided by the following:

gleaming cities.

The incredible wealth
of our land,

supporting a population
of over half a billion.

But rewind the clock
just 15,000 years

and our continent
was truly a wild kingdom

filled with amazing
Ice Age creatures.

(roaring)

Still, there was one animal
found nearly everywhere

but here... us.

So how, in the blink
of a geologic eye,

did we turn
an unpopulated continent

into a rich and dynamic
civilization?

And what surprises does our
homeland still hold in store?

The story of humans in
North America begins with ice.

Alaska's Mendenhall Glacier,

a 13-mile-long expanse
thousands of feet thick.

This particular ice
has been here for centuries.

It may not be as old as rock,
but for a geologist,

it's no less intriguing...
if a bit risky.

Just a bad place to trip.

Yeah, I guess there's
that, isn't there?

Yeah.

Once you start fallingon this ice

you keep falling untilyou hit something flat.

JOHNSON:
15,000 years ago,

this is what much of
North America looked like.

By then, humans had migrated
from Africa to Europe,

Asia, and Australia.

Not yet to the Americas,
but that was about to change.

North America
was in the grip of an ice age.

So much of the world's water
was locked up in ice sheets

that sea levels dropped,

exposing a thousand-mile-wide
expanse of land

that connected Siberia toAlaska, the Bering Land Bridge.

In the summer, this would have
been a huge, open expanse,

allowing ancient
hunter-gatherers from Siberia

to migrate east
into North America.

But the open landscape
abruptly ended

at the edge of a vast ice sheet

in what is now
southeastern Alaska.

Would they have tried
to cross it?

Ready for this?

I think so.

All right,
here we go.

A little bit higher
and to your right

and you should be good.

That's it, yup.

This is not the easiest thing
in the world.

(breathless):
You know, it's hard to imagine
somebody crossing

even one ice field like this,
much less an entire ice sheet.

This is insane.

Glaciers are perilous,
ever-shifting

and often unstable.

Early explorers would have had
a tough time getting very far.

Imagine trying to cross
big ice sheets

100 miles wide,

couple thousand feet high,
into North America.

Based on this,
I'm pretty sure the people,

if they came into North America
at that time,

didn't go over the ice.

MAN:
Looking good, buddy!

JOHNSON:
So how did the first Americans
wind up on the other side

of this daunting barrier?

The traditional view is that
when climate began to warm

about 13,000 years ago,

melting along a seam between
two great inland ice sheets

opened a corridor.

But there's another
potential route

to the rich land beyond the ice,
first hinted at

by a discovery made over
1,000 miles to the south

off the coast of California.

25 miles from Santa Barbara

lie the remote and windswept
Channel Islands.

Here on Santa Rosa Island,
a little over 50 years ago,

a lone archaeologist
stumbled upon

some of the very earliest
human remains

ever found in North America.

Joining me is Joe Watkins,

a National Park Service
anthropologist

and a member of the
Native American Choctaw tribe.

He's taking me to a spot
that has tremendous meaning

to Native peoples
and scientists alike.

This is a very
important place;

it's what brings us
to Santa Rosa Island.

Well, that's a nicebluff right there.

Yeah.

JOHNSON:
Right here in an area calledArlington Springs back in 1959,

archaeologist Phil Orr spotted
a couple of distinctive bones

revealed in the weathered cliff.

Joe has a replica.

It's clearly a thighbone.

There's the knee jointand there should be

a ball on the...

Here it is.

That fits on...
that fits on right there.

So I've got a thighbone
of a human.

Exactly, and there were
two femurs that came out.

They come from a man about
five-foot-one-inches tall.

But it's the age
that has put

the prehistory
of North America on its ear.

JOHNSON:
Named Arlington Man,

these bones date
to around 13,000 years ago.

They're among the oldest human
remains ever to be discovered

in North America.

More than 13,000 years ago

puts these bones
during the last ice age.

Exactly.

And that's what makes them
significant.

JOHNSON:
Significant because not only
was Arlington Man

one of the earliest known
inhabitants of North America,

but he lived and died here

on an island
miles off the coast.

WATKINS:That means that Arlington Man--

or his ancestors--
probably got here by boat.

That's an amazing fact.

They didn't walk here,
they paddled here.

If boats were in use here,
then they were probably in use

all along the coastline,
from Alaska to South America.

They may have been similar
to traditional Inuit boats--

wooden frames
covered with walrus hides--

agile and rugged vessels.

This kind of technology
could have opened a way south

even before the ice sheets
melted.

WATKINS:
If you figure boats
into the equation,

it really opens up a wholedifferent set of possibilities.

You don't have to go
through the ice,

you can just paddle down
the coastline.

JOHNSON:
Using boats to probe the shore
could have opened the way

for seafaring hunters

to settle along the western edge
of the continent.

And as they made their way
into this unexplored land,

what untapped riches
would they have found?

Luckily for us,
there are a wealth of clues

in the unique geology
of Southern California...

...extracted over the years from
an iconic tourist attraction,

the La Brea Tar Pits.

This is one of the greatest
fossil sites in the world,

and it's right
in the middle of Los Angeles.

Shallow pools of natural sticky
asphalt have been bubbling up

from below the surface herefor tens of thousands of years,

creating a lethal trap
for unsuspecting animals

and a perfect graveyard
for their bones.

Hey, Carrie, how's it going?

Hi, Kirk, how are you?

JOHNSON:
Carrie Howard
is a paleontologist

working with an incredible trove
of animal fossils

all pulled from the pits.

What these bones tell us
is that this area

was once a great
hunting ground--

and not just for ancient people.

Wow, that's a nice skull.

Oh, yeah, this is
a saber tooth cat skull.

It sure is!

(laughs)

As you can tell.

It would have stabbed
or sliced its prey.

In one, in,boom you're done.

Wow, so think about that,just about the time that

people showed up in NorthAmerica for the first time,

these guys were waitingto greet them.

(laughing):
A bad day in California.

More than a million bones
have been found here

in the last century--the largest, from huge mammoths

that weighed
up to 12,000 pounds.

All told, something like 620
different species

of plants and animals
have been identified.

Bison scapulae.

Horse neck vertebrae.

More bison leg bones.

These are really great.

Wow, look at those things,
that's a huge animal.

Big camel vertebra.

Wow.

Toes of camels and more camels,
and more camels!

There are a lot
of camels here.

HOWARD:
Yeah, not many people know
camels originated

in North America.

JOHNSON:
It's so amazing to hear

there were camels
here in Los Angeles.

(trumpeting)

For ice age hunters,

the mammoth would have been
especially valued,

each one providing
thousands of pounds of meat--

if you could bring it down.

What kind of weapon
could have evened the odds?

To track down an answer,
I head to Boulder, Colorado.

A few years ago, Patrick Mahaffy
was having

some landscape work done
behind his house.

One day, when he checked in
with the work crew,

he got an unexpected report.

PATRICK MAHAFFY:
I got home from work.

It was a very busy day for them,

and I asked, you know,
like you do on a project,

"How did the day go?"and they went through this list

of all the things
that they'd done.

And then they said,"Oh, and there's one last thing.

We found something."

JOHNSON:
They found what seemed to be
an intentionally buried cache

of mysteriously shaped stones.

DOUG BAMFORTH:
That one's amazing.

That is amazing.

JOHNSON:
Archaeologist Doug Bamforth
was called in to take a look.

I regularly get phone calls
about people's discoveries.

But I don't get very excited,
because they usually

don't turn into
much of anything.

But then I went up the next day
and it was just breathtaking.

JOHNSON:An 83-piece stone age tool kit,

each piece
carved by ancient hands.

BAMFORTH:
There's a good sharp edge.

You could only hold it between
the tips of your fingers,

but you could do light cutting.

JOHNSON:
13,000 years ago,
these sharpened stones

would have been
the most advanced technology

on the continent.

BAMFORTH:
You have to imagine a world
with no metal in it.

All the things that we rely onto cut things and scrape things

and do almost all
of our physical work, right,

the fundamental material
that we use,

did not exist in the world.

JOHNSON:
Like other early human
societies,

North Americans relied on stone.

So Doug wanted to know
how old were the tools

in this collection?

To find out, Doug decided
to test for DNA residue

that might give him a clue
about the age.

Incredibly,
he found traces of blood

from several species of animals.

Two in particular surprised him.

He found DNA from the ancestors

of modern-day
horses and camels--

species that once lived
in North America

around the end of the Ice Age,

clear evidence that these tools
were once used

by some of
the earliest American hunters.

BAMFORTH:
Getting artifacts that have
blood residue on them

from camels and horses tells us

that these are among the oldest
tools we know about

in North America.

So evidence of some of the very
earliest people who were here.

JOHNSON:
The most lethal hunting weapon
they devised was a spear tip

known as a Clovis point,
named after the site

where it was first discovered
in New Mexico.

Clovis points all share
a common design:

a symmetrical, fluted shapewith sharp edges on both faces.

More than 4,000 Clovis points
have been found

all across North America,

a sign that the first Americans
traded weapons-grade rock

and the latest hunting
technology

over hundreds of miles.

Bob Patten has been crafting
Clovis point replicas

for over 40 years,
and he's offered to show me

just how tricky it can be
to coax a sharp-edged weapon

from a stone.

BOB PATTEN:
These are antler.

Oh, I see.

That catches the blow.

And I want you to reachforward a little bit.

There you go.

Wow, my first flake!

Awesome!

JOHNSON:We're using a rock called chert.

It's similar to flint and wasfavored by stone age toolmakers

because of a very special
property:

with a bit of persuasion,
the rock will break off

razor-sharp flakes.

PATTEN:
This is better
than an X-Acto knife.

Wow, you're cutting
leather with a rock.

You can cut with
great precision there, too.

I can see the spear point
in there,

I just can't quite get
to it yet.

JOHNSON:Bob's going to put the finishing
touches on my Clovis point.

He seems to have a knackfor finding just the right spot

to hit the stone.

It's a very subtle thing,

and you have to train yourself

in order to do this
consistently.

Now we've got a tool
we can go hunt a mammoth with.

Oh, you'd put it
on something fairly long

because a mammoth
is a big animal

that you don't want to get
too close to until he's dead.

JOHNSON:
It's hard to imagine
how a relatively small stone

could bring down an animal
the size of an elephant.

To test its killing power,

I'm going to use
a block of ballistics gel.

It's a material
used to test firearms,

because it has
the same consistency as flesh.

You've got the mammoth,
I've got the spear.

JOHNSON:
A piece of animal hide coversthe front of the ballistics gel,

so I'll be able to see how well

the spear point
penetrates skin, too.

All right,so the angle is here.

It's like shootinga pool cue.

And now.

The blade went in

like it was goinginto a block of butter,

and when it hit the actual shaftthat's when it stopped.

Well, I think we know

why that style of point
was so successful.

Yeah, that thingreally worked.

It does cut.

And we should be ready to go
and conquer the continent.

JOHNSON:
Clovis points have been found
embedded within the bones

of mammoths, demonstrating
just how successful

these weapons could be
in bringing down

even the biggest beasts.

These Clovis spearheads
are exquisite artifacts,

just beautiful things to behold.

But in reality they were
lethal killing machines.

By 12,000 years ago, mammoths,saber-toothed cats, dire wolves,

camels and many other largemammals had all but disappeared,

likely the victimsof an expanding human population

and a changing climate.

But others thrived
on a landscape that offered

more than a million square miles
of grass-covered prairie--

home to a North American icon.

WATKINS:
On the Great Plains,
these oceans of grasses

were the primary food
for millions of bison.

These bison were the supermarket
on the hoofs

for the nomadic Native American
tribes that hunted them.

The bison hides could be used
for housing.

They made them into teepees
that could be put up

and taken down
in a matter of minutes,

just so that the Native American
tribes could follow the herds

from one spot to the next.

For 10,000 years,
this was their staple food.

JOHNSON:
The geology of North America
created a landscape

ideally suited to support
abundant animal life,

sustaining a growing
human population.

But not all Native Americans
hunted for a living.

In Colorado's Mesa Verde
National Park,

I've come to see a genuine
wonder of the ancient world.

Tucked away in these
rocky hills

stands an 800-year-old
architectural masterpiece

called Cliff Palace.

(laughing):
Oh man, that
is so awesome.

Built from finely laid
sandstone slabs,

pine beams and mortar
beneath natural overhangs,

this 150-room complex was home
to the ancient Puebloans,

forbearers of today's
Puebloan peoples.

This is a massive set
of structures here.

So these were a people thatreally invested in real estate.

SCOTT TRAVIS (laughing):
Yeah.

JOHNSON:
Scott Travis is the park
archaeologist.

It's characteristicof cliff dwellings at Mesa Verde

to have this type of scale,but nothing approaches

the sheer sizeof this particular site.

JOHNSON:
And this original cavelikestructure is a natural formation

in the sandstone.

TRAVIS:
It's just a natural part
of the evolution

of these canyon systems.

JOHNSON:
These formations--
along with others like them--

provided shelter for thousands.

And for centuries,

the people here
worked the land as farmers,

even though conditions
were often tough.

TRAVIS:
Mesa Verde is a wonderful
example of how

the Ancestral Puebloans
took advantage

of their local situation.

Not only did they create
remarkable architecture

within the alcoves,
they were able to farm

in one of the harshestenvironments on this continent.

(thunder)

They did this with a combination
of expert geological knowledge

and the ability to control
scarce water resources

to farm in a situation
that is difficult even today.

JOHNSON:
And other farming cultures
did even better,

using their resource wealth
to build big cities

and giant places of worship.

Like the builders
of the mysterious mounds

at Cahokia, Illinois,

who raised corn
to support a city of 15,000.

Or the Maya of Central America,
who built canals

and irrigation networks that
sustained great stone cities.

Hundreds of thousands
lived in the Aztec capital

in Central Mexico at the end
of the 15th century.

But the story of human
interaction with the geology

of North America was about to be
turned on its head

by the arrival of outsiders.

Western European explorers
opened the way for conquerors,

colonists, and their slaves,
who would all ultimately

displace most of
the Native population.

What drew so many to voyage
so far into an unknown world?

To find out, I'm traveling
to North Carolina

to a research station
that studies a native plant

that enticed European settlers
with a promise of riches.

It's pretty cool.

I have never been in
a tobacco field before.

This is the plant that gotNorth America started

as a Btish colony.

Sort of the first
cash crop.

It was the one thateconomically could keep

the early colonistsin business

and in great part,because there was

a perfect stormof the right plant,

brought to the right place,
in the right climate,

at the right time,
with, importantly,

the right kind of soil
for growing it.

Huh.

JOHNSON:
Dave Montgomery studies

how the earth's thinnest and
most fragile geological layer

has shaped the destinies
of human societies--

including ours.

So what is soil?

So soil is sort of the frontier
between the worlds of geology

and the world of biology.

It's that interface,

and it's made dominantly
of rotten rocks.

JOHNSON:
But what kind of rotten rock?

Dave reveals the recipe
that makes life on land

and all agriculture possible.

The first ingredient is sand.

JOHNSON:
Sand is any mineral
ground down into tiny grains

by natural wear and tear.

This looks likea nice beach sand,

it's justlittle quartz grains.

Little clear grains of quartzis what I am seeing.

Yeah, quartz and feldspar.

It's not unlike
a California beach.

JOHNSON:
Silt is next.

Made of the same stuff as sand,
but ground much finer.

MONTGOMERY:
It's too small to really see,
but you can feel the grit.

If you put a little
on your teeth

you'll feel the grit
between your teeth.

Oh, yeah.

It's really gritty.

I don't really likeeating silt.
No.

JOHNSON:
The finest is clay,

made up of mineral crystals
so tiny,

they're visible
only with a microscope.

This is all geology still.

This is all geology,
this is the basis,

the backbone
of making a soil.

And the geological part,

some combination
of these three components

makes up about 40% to 50%
of the volume of most soils.

So what's the rest?

JOHNSON:
How about the rich black stuffwe associate with fertile soil?

The stuff of life--
or, actually, of death.

So it's nice and dark.

It looks like
coffee grounds.

So it's rotted
plant matter.

You've got pieces
of plants...

Oh, this smells nasty.

I guess it's
dead stuff though, right?

It's dead stuff.

That's why it smells
so good.

I'm going to put this
back in the jar.

So that's it,these four things?

Well, then there's also
living matter,

which in this case,

we have worms.

So you can think of themthe way that Charles Darwin did,

as God's plowmen.

They basically plow the fields.

Underground, they're likelittle underground miners.

JOHNSON:
There's one last ingredient,

a geologist's best friend.

We have timein a jar here?

We got time
in a bottle here.

We're not gonna open it.

How much time do you havein that bottle?

There's only one way
to find out.

Don't open that jar.

It can be a million years
in that jar.

It could be.

JOHNSON:The British colonists got lucky

when they chose
to plant tobacco here.

For tens of thousands of years,

nature had been preparing thesoil along the Southeast coast,

giving it all the right
ingredients,

especially
an extra helping of sand.

Perfect for growing
the original wacky weed.

But they soon paid a price.

It's not hard to seewhat growing millions of pounds

of tobacco to ship back home
did to the land.

Even today, comparing soil
from the forest

to soil from the tobacco field
tells the whole story.

So over here on this side,we've got the forest soil,

which is probablya lot more like

the native soil was like

when colonial agriculture
arrived in the New World.

Yeah, lots of organic
matter in it

and roots and twigs
and stuff like that.

You notice the dark colorrelative to the soil next to it,

which is from the conventionallyplowed tobacco field.

JOHNSON:
The sickly yellow color shows
the soil's exhaustion.

These fields are lush todaythanks to chemical fertilizers.

But the colonists
had no such tricks,

and growers soon hit a wall.

MONTGOMERY:
The erosive effects
of colonial agriculture

were so apparent
on the American landscape

that people at the highest
levels of American society

were very concerned
about what it meant

for the future of the country.

Washington even wrote
in a letter in the 1790s

to Alexander Hamilton
about his prediction

that American society would be
compelled to push inland,

to push westward,

due to the search
for fresh and fertile soils

after having worn out the soils
along the Eastern seaboard.

JOHNSON:
But the founding fathers
needn't have worried.

Because migrating farmers wouldsoon discover the Great Plains,

with some of the best soil
in the world.

MONTGOMERY:
Dirt is destiny
in that sense,

where degrading the soils
of the Eastern seaboard

and then opening up
the fresh fertile soils

in the American Midwest

served like a great magnet
pulling people westward

towards the source of fertility
and prosperity

in the heart of the country.

JOHNSON:
The great magnet
of North American soil exerted

an irresistible pull on those
with a pioneering spirit.

But the westward expansion also
got a major shot of adrenaline

with the discovery of a new gift

from the geology
of the continent: gold.

In 1848, Mexico ceded
to the U.S. a territory

that included what would become
the state of California.

At the time, San Francisco
was little more

than a military garrison
with a population under 1,000.

But that changed when James
Marshall found nuggets of gold

in a streambed at Sutter's Mill
in Coloma, California.

When word got out, California
became a hot destination.

In 1849, about 80,000 people,

called '49ers,
joined the gold rush.

Over the next six years,
about 200,000 more followed,

turning San Francisco

into one of the largest cities
on the continent.

By then, prospectors
had snatched up

pretty much all the gold
to be found just lying around,

and so the party
had to move underground.

Pretty sweet place here.

Yes, it's beautiful here.

So they started mining
around here in 1849...

JOHNSON:
Lisa White is a geologist
and a native San Franciscan.

Her passion for California's
amazing geological history

was bred in the bone.

Let's go have a look.

JOHNSON:
Who better to show methis historically preserved mine

in the Sierra Nevada mountains?

The miners must havebeen short guys.

Well, I fit
right in here!

Yeah, I guess you do!

Not me.

WHITE:This is such an incredible mine
for so many different reasons.

Unbelievably, they dug out

the earliest part
of this mine by hand.

Wow, look at that,
you can actually see

the pick marks wherethey carved this thing.

As Lisa leads me further
into the mountain,

we spot a change in the rock.

Ah, here we go.

JOHNSON:That's somethingdifferent.

WHITE:
It is, it is.

It's a quartz vein, and it's
important and distinctive

because when the miners would
locate these quartz veins,

they knew they were in the area
they wanted to be for gold.

So the gold is actually
in the quartz?

The gold is in the quartz,yes it is,

and so looking for these
was the way to the gold.

I've got a quartz sample
here in my pocket

with some gold flakes in it.

Wow, there's a lot of gold
in there actually, wow.

It's really beautiful.

Yeah, if you like gold!

But the gold
is in the quartz

and not in the rock
next to the quartz?

Exactly, so that's keyto understanding its formation.

JOHNSON:
When Earth was forming, mostheavy metals like iron and gold

sank to the molten core.

But as Earth cooled,

small amounts remained
in the rocky mantle.

Later, asteroids deposited
more of these metals.

But for gold to work its way
back up to the surface,

it had to hitch a ride on some
kind of geological shake-up,

like an earthquake.

WOMAN (on phone):
9-1-1.

MAN:
...Cypress section of
the freeway has come down.

JOHNSON:
Violent earthquakes like
this one in San Francisco

cause serious damage
above ground.

But they also wreak havoc
below the surface.

Most people know that California
is earthquake country,

but even in the past,
earthquakes were key

because earthquakes
would fracture the rocks.

And in many ways, the cracks,

they're like pathways for fluids
from deep within the earth.

JOHNSON:
Deep below, millions of years
of earthquakes

and pressure from molten rock

have created
a network of cracks.

These provide pathways

for superheated water
full of minerals,

like gold
from deep in the earth.

When that hot fluid rises up
through the fractured rock,

it cools down, and the minerals
carried within crystalize.

Over time, that builds up
a vein of quartz,

and trapped inside the quartz
are bits of gold.

Over millions of years,

they formed the seams
found all over California.

WHITE:
So every time you look
at a vein of quartz

you're really seeing an ancient
earthquake in many ways.

JOHNSON:
I've always thought
of earthquakes

as very destructive
kinds of things,

but looking at this,

if earthquakes are involved
in the formation of gold,

maybe there's a silver lining--
I guess a gold lining--

to earthquakes.

The California Gold Rush
didn't last very long.

But between 1848 and 1860,

it's estimated that more than
one million pounds of gold

were found in these hills.

Over the following years,
much of it made its way

right here to the Old Mint
in San Francisco,

affectionately called
The Granite Lady.

This building
once held the machinery

that turned California gold
into beautiful coins.

It's no longer in operation,
but there's a vault here

holding something
that these days is truly rare.

Oh, man.

This thing is phenomenal.

A massive nugget of gold,

the largest to be found
in California in decades.

Worth around $400,000!

It was probably buried
about 40 million years ago,

and it was dug up
a few months ago.

Gold is so dense that
it doesn't look that large,

but it feels really heavy.

It's like five pounds packed
into the palm of my hand.

You feel both the power
of the earth

and geology and chemistry,

but you also feel the weight
of human history.

Gold has driven
the behavior of humans

since it was first found.

I actually have
gold fever right now.

I want to take a bite
out of this thing.

It's an amazing thing.

Striking it rich
in gold or silver

was the dream of thousands
of prospectors.

But what other treasures

did the geology of the continent
have to offer?

Turns out the real moneywas about to be made back east,

in the iron and coal mines

poised to power the nation's
next great leap.

(whistling)

By the 1860s,

the industrialization
of the American economy

was going full steam,
literally.

Unbelievable.

Perhaps the one technology
that best symbolized

the massive transformation
underway was this:

the steam locomotive.

In 1863, the U.S. government
launched an ambitious effort:

to unite the coasts with
a transcontinental railroad.

Two railroad companies set out
to meet in the middle.

Progress from the east
was relatively rapid

thanks to the wide-open prairie

and a natural pass
through the Rockies.

But construction
of the western line

progressed much more slowly,

impeded by the Sierra
Nevada Mountains.

The only option:
cut a pass by hand.

From this logging train,

we can see just
what they were up against.

This is granite,
an incredibly hard rock,

and the people that had to build
the first railroad

across the Sierra Nevadas
cut through this rock

with hand tools, sledge hamms,
steel drills, and explosives.

Incredibly hard work.

(hammer ringing)

They relied heavily
on Chinese immigrant laborers.

In harsh conditions,
they carved 15 tunnels,

largely using hand tools
and dynamite.

(explosion)

The longest stretched
about a third of a mile

and took 15 months to complete.

Eventually, the two lines met
in Utah on May 10, 1869.

It had taken six years,

but America's new East-Westrailroad was open for business.

The building of the
transcontinental railroad

was an epic endeavor.

But once it was done,

it linked the United States
from coast to coast,

and within 50 years of that,

there was a quarter
of a million miles

of railroad tracks
spanning the continent.

And with the two coasts linked,
the economy roared,

fed by the continent's
abundant geological gifts

of coal, metals,
and other resources,

and eventually
by a powerful new fuel.

I've come to the great city
of Los Angeles.

It's an amazing
metropolitan area.

Something like 18 million people
live here.

That's a lot of people,and they use a lot of resources.

It's no secret that Los Angeles

has an insatiable thirst
for oil.

But what's less well known

is the area's history
as a major producer.

That story takes me back
to the La Brea tar pits.

The natural asphalt that trapped
so many ancient animals

is actually a form of oil.

Paleontologist Carrie Howard

takes me into one
of the fossil pits

to see LA's black gold up close.

I'm just dying
to get down in there

and scrape some of those bones
right now.

But if I did that,

I would actually probably be
stuck, right?

HOWARD:
Yeah, even if you just stepped
right there,

don't be fooled.

Even, like, an inch
could stick your shoe,

and then you'd definitely
need help.

JOHNSON:
This sticky oil was produced

by the slow accumulation
and burial of marine plankton

over millions of years.

Compressed
and heated underground

and turned into thick oil,

it's managed to seep upwards
to bubble up here.

It may not seem like much,

but there's a lot more
where this came from.

These tar pits
with their fantastic fossils

are just the tip of the iceberg,

because deep beneath the streets
is a tremendous amount of oil.

Once Californians
realized the scale

of this geological treasure,

they kinda went nuts
exploiting it.

What I've got here is a picture
from 1901 of this very spot,

and I can see a house down there
that's in this photograph.

But what's not here today

are the dozens of oil derricks
that were here in 1901.

This place was
an incredible oil field.

Oil is really the DNA
of Los Angeles.

It was discovered here first
in 1892,

and it kicked off
an amazing oil boom.

And even today,
Los Angeles is defined by oil.

In and around Los Angeles,

there are oil wells
almost everywhere.

Pretty amazing.

Right here in the middle
of a neighborhood

is full-on oil rigs.

There's a house
and there's a pump jack,

and a house and a pump jack.

Looking down, and it's a greatview of the city of Los Angeles.

There's oil rigs
all over the place down there.

Los Angeles County has more
than 3,000 active oil wells

tirelessly pumping more than
14 million barrels a year.

But that's just a tiny fraction

of the total
North American output.

From Mexico to the oil sands
of Alberta, Canada,

and the Arctic Coast,

we're pumping oil
and natural gas

out of the ground
at a record rate.

Which begs the question:
should we?

When we burn fossil fuels,
the release of carbon dioxide

causes Earth's atmosphere
and oceans to warm.

As a result,
glaciers are melting

and sea levels are rising

much faster than at the end
of the last ice age.

Our impact on the planet
is a huge concern,

but as a geologist, I also worry
about the nasty surprises

our continent has in store
for us.

In the Pacific Northwest,

there are chilling cluesabout a future natural disaster.

This is an old-growth
rainforest.

Some of these trees
are more than 500 years old,

and they've witnessed events
we can barely imagine.

And it's trees like these

not too far from here
that played a key role

in resving a mystery
of epic proportions.

Meet geologist Brian Atwater.

He and I are paddling up
the Copalis, a coastal river

that rises and falls
with Pacific Ocean tides.

We're here at low tide.

But at high tide,

the river can rise enough
to overflow its banks,

flooding the surrounding marshes
with salt water.

But it wasn't always that way.

Once, this was a lush
coastal rainforest.

Now, all that remains

are massive roots sticking out
of the eroded riverbank

and the trunks
of long-dead cedar trees--

a ghost forest.

Brian has brought me here
to show me evidence

of one of the worst earthquakes
to hit North America

since human beings arrived here.

He's found signs in a place

where geologists
feel right at home:

in the mud.

Slicing into the bank
reveals three layers.

They tell a story of change
over time.

The lowest once supported
a healthy rain forest.

BRIAN ATWATER:
So this is almost like
a garden soil, right?

But it's got tree roots in it.

It's a forest floor soil.

JOHNSON:
Just above is a layer of sand
entirely out of place.

Its sharp definition
tells Atwater

that whatever put it here
came fast and furious.

You don't see sign
of a gradual change from here

because there's such
a black and white difference

between this and this.

How do we do this combination?

How do we go from forest floor
to some kind of muddy flat

and have a sand layer brought in
first, right at that time?

JOHNSON:
The answer lies
about 80 miles away

at the bottom
of the Pacific Ocean.

It's called the Cascadia
subduction zone,

a 700-mile-long crack
in the crust of the planet.

It's where a Pacific Ocean plate

is trying to slideunder the North American plate.

(plates scraping)

But the plates are stuck.

So the story there, you know, is

with the down-going
oceanic plate

and the overriding continental
plate stuck together here,

they go closer and closer
like that,

and the overriding plate
gets shortened and bulges up.

JOHNSON:The old growth forest that once
stood around the Copalis River

sat on that bulge.

But then the plates broke free
along the fault,

causing a violent earthquake,

dropping 600 miles of coastline
as much as five feet

and into the tidal zone,
where it sits today.

The local landscape drops.

The ghost forest
goes for a swim.

That's it for them.

But the disaster wasn't over.

That same tectonic rupture

also drove the edgeof the continental plate upward

and triggered a series
of huge waves--

a tsunami.

The tsunami comes in.

That's the first thing
the forest gets to see.

JOHNSON:
What the forest sees is a rush
of salt water and sand

inundating the land,

the final blow
from a massive fault rupture

that turned an old-growth
rainforest...

...into this.

We now know that this
cataclysmic one-two punch

took place in the year 1700.

Today, everyone wants to know:
will it happen again?

Is the Pacific Northwest
living on borrowed time?

Tsunami is running.

JOHNSON:
At Oregon State University,

Chris Goldfinger studies
deep-sea earthquakes

that can cause
devastating tsunamis.

He's examined hundreds
of sediment cores

from the sea floor,

sampled all along the 700-mile
Cascadia subduction zone.

Analyzing each one,
he's assembled a history

of earthquakes
going back 10,000 years.

And the news is not good.

Chris estimates that
severe earthquakes strike

somewhere along the fault line
about every 240 years,

most often in Oregon
and Northern California.

We're now 315 years
into a 240-year average,

and so that drivesthe probability up quite a bit.

It's up around 37%
in the next 50 years.

(rumbling)

JOHNSON:
Today, seismologists warn
that the next big one

in the Northwest
could be even more destructive

than the earthquake and tsunami
that struck Japan in 2011.

Luckily, there is time
to prepare,

thanks to a warning
from an ancient disaster

written in the land.

Geology gives us many,
many examples

where what we've learned from
interrogating the earth's past

prepares us
for the earth's future.

The relentless forces
beneath the earth

will continue shaping our
continent far into the future,

as they have
from the very beginning,

since the first land formed
from molten rock

and the pieces of our homeland
slid into place.

As seas and mountains
rose and fell,

as creatures small and mighty
lived and died here,

geology has profoundly shaped
our destinies

ever since we set foot
upon these shores--

soil, oil, minerals.

The power of the rocks beneath
our feet cannot be ignored.

So what can we expect?

Not just in our lifetimes,but over the serious long haul?

Well, over the next
175 million years,

geologists predict
that North America

will slowly converge
with Europe and Africa

until eventually, the Atlantic
will completely close.

And once again, we'll be part
of one giant super continent:

Pangea Ultima.

North America today

is just the middle
of this continent's

long and interesting story,

and it will go on
for tens of millions

and hundreds of millions
of years into the future.

Because in geology,
one thing is for sure:

no landscape is permanent.

The investigation continues
online

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♪

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