Original subtitles

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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