Original subtitles

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

It looks pretty familiar, don't you think?

(explosion)

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 onthe field trip of a lifetime...

Wow, look at that rock right there.

That is crazy!

...to unlock the secrets of our continent's incredible past.

In this episode, we going to jump back millions of years

to a North America that's full

of all kinds of unusual creatures...

Yikes!

...turning up in the most unexpected places.

A 14-foot-long fish in Kansas?

MAN: That's what I'm telling you!

JOHNSON: It's a time when much of the Midwest was underwater.

I'm on the hunt for clues to the amazing connection

between our land and everything that's ever lived here.

From the rise of early life...

NOAH PLANAVSKY: What I'm holding in my hands

is a fossil that's two billion years old.

Wow.

JOHNSON: ...to the destruction of the biggest, baddest beasts

of all time.

(explosion)

It doesn't look like much, but this layer is Armageddon.

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

Major funding for NOVA is pwith gleaming cities,ing:ld

almost half a billion people,

and still, some spectacular wildlife.

But if we could rewind the clock

and travel back in time millions of years,

life on our continent gets a whole lot wilder.

Yikes!

That makes a grizzly bear look like nothing.

This land is filled with the bones

of some mind-blowing ancient creatures that once roamed

and swam across a continent

that was completely different from the familiar place

we call home today.

When you dig deep and follow the clues,

you uncover an incredible fact...

That powerful forces in the ground beneath our feet

and the rocks all around us have shaped every plant

and animal that's ever lived here.

You just have to look to follow the twists and turns,

the ups and the downs...

of North America's incredible life story.

In an empty corner of Utah lies a very special landscape.

I'm flying over a remote regioncalled the Kaiparowits Plateau.

I love this place because its rocks contain a record

of one of the most important chapters

in the history of life in North America.

My guide for the day is paleontologist Joe Sertich,

an old friend from the Denver Museum of Nature and Science.

SERTICH: Pretty good place to be a paleontologist, huh?

JOHNSON: Oh yeah, this is awesome.

JOHNSON: What makes the Kaiparowits so amazing for paleontologists

is that it's jam-packed full of dinosaur fossils.

They're sticking out everywhere.

Hey, look at that!

All sorts of chunks of little bone here, it looks like.

JOHNSON:This is a great place for using my favorite little trick

for testing fossils.

Uh-uh, it sticks on the end of the tongue.

It actually sticks really hard.

The little pores in the bone will try and pull the water

out of your tongue,

and a real piece of fossil bone

will stick really hard to the tip of your tongue.

But Joe hasn't brought me all the way out here

to suck on a few broken bones.

He's got something much cooler to show me,

the cast of a skull belonging to a new species of dinosaur

discovered right here that Joe helped identify.

SERTICH: I think you're going to like this.

Whoa, look at that.

Yeah.

This is the lower jaw.

Well, there's no doubt that guy's a meat-eater.

Look at that, little steak knives in his face.

Exactly.

Yikes.

That makes a grizzly bear look like nothing.

SERTICH: This is a dinosaur called Lythronax.

JOHNSON: Lythronax?

Lythronax isa pretty cool name.

It actually meansthe king of gore.

The king of gore?

Yeah.

JOHNSON: Who came up with that name?

I did. You did.

(both laughing)

That's one of the things about finding dinosaurs,

you get to name them.

You get to come upwith the name-- exactly.

JOHNSON: The really exciting thing about the King of Gore

is that when you put flesh on the bones that Joe found...

Lythronax looks a lot

like the much more famousand fearsome Tyrannosaurus rex.

But it's ten million years older.

Maybe he was T. rex's gr eat-great-great-granddaddy.

80 million years ago, all of North America,

not just the Kairparowits,

was home to creatures like Lythronax.

And for the next 14 million years,

our continent was like a dinosaur movie set

with a cast list featuring some of the biggest superstars,

like T. rex, the hadrosaurs,

and my favorite dinosaur, triceratops.

We know this because we find their fossils

all over the place.

In fact, of all the dinosaur species discovered worldwide,

fossils of more than a quarter of them have been found here

in North America.

So the big question for me is, why?

What was it about North America

that made it such a dinosaur factory?

What was the continent like back then that it could produce

such a diverse cast of dino characters?

Well, before we can unravel this mystery, we need to understand

the intimate connection between life and the land.

It's a process that's been going on since life first emerged

more than three-and-a-half billion years ago,

long before the dinosaurs roamed the land,

in a time before North America even existed

and the earth was covered almost entirely in ocean.

There's some intriguing evidence for this link

in an unexpected corner of the North American plate:

the Bahamas.

I've come here to see a rare living fossil,

one that helped change the earth itself.

Without it, life as we know it might not even exist.

My guides are marine scientistsNoah Planavsky and Pamela Reid.

So what did you think whenyou first saw these things?

You feel like you've stepped back in time

to early earth.

It's another world. You'll see.

I've been waiting my whole lifeto see these things.

JOHNSON:But to see anything, first we'vegot to dive down about 20 feet,

where we'll have a brief window of time

before powerful currents threaten to sweep us away.

We're looking for one of theoldest organisms on our planet,

but as we descend, there is not much sign of life.

Could it be hiding behind these strange rocks?

Actually these rocks are the very things I've come to see.

They're called stromatolites,

and believe it or not, they're alive.

You can't see them,

but just beneath the surface of these boulders

is a thin coating of bacteria.

Over thousands of years, these microbes accumulated

layer after layer of mud and sand

to build mounds up to eight feet tall.

Today, living, growing stromatolites like these

are extremely rare,

but these precious examples hold the key to the evolution

of virtually all complex life.

I could stay down here for hours,

but the current is getting stronger,

and we don't want to get pulled out to sea.

That was amazing down there.

The current really picked up.

It was rippingthrough there, too.

And that is actually why,

important reason for why we have these stromatolites.

What's special about this spotthat allows them to be here?

Well, you noticed a very strong current?

We were being hauled alongby that current.

REID: And you also noticed

there were sand waves that were going over the stromatolites.

That sand will actually bury the stromatolites

for months at a time

And then unbury them again.

And unbury them again,

and that burial is really important

to the existence of the stromatolites.

JOHNSON: When the sand is swept away,

the stromatolites are vulnerable to seaweed and corals

that block the sun.

The sand protects them.

REID: It keeps away the higher organisms,

the seaweeds, the corals.

In early earth, there were no corals and seaweeds

to compete, so they actually had

a much bigger territory, and they dominated the planet.

For about 80% of earth history,

stromatolites were kings.

JOHNSON: That's a long, long time to rule.

Stromatolites are the earliest fossilized form of life

we've ever found.

NOAH PLANAVSKY: What I'm holding in my hands is a fossil,

a stromatolite from North America.

It's two billion years old,

almost two billion years old.

Wow.

JOHNSON: So how old do these things actually get?

PLANAVSKY:The oldest examples we find are 3.5 billion years old.

JOHNSON:3.5 billion years-- I love that.

That's time, man.

3.5 is almost three quarters

of the entire history of the planet.

So these organisms have seen it all.

PLANAVSKY: They're a continuous recordof life thriving on our planet.

JOHNSON: So why were stromatolites so successful?

Three billion years ago,

our planet was almost unrecognizable.

Covered by enormous oceans, there were no continents,

just hundreds of small volcanic islands

belching out huge amounts of carbon dioxide...

and even toxic substanceslike sulfur dioxide and arsenic.

Most creatures today would suffocate in these conditions,

but the microbes that built stromatolites

used them to their advantage.

PLANAVSKY: The really clever thing about these organisms

is they developed a way to thrive

in the conditions back then,

in an atmosphere that would have been toxic to life

as we know it today.

JOHNSON: But how did they do it?

To find out, Noah and I wade into the slime

of this shallow lake.

This stuff is slippery, man.

JOHNSON: This place is teeming with bacteria,

similar to the ones that live on stromatolites.

Oh, look at that.

PLANAVSKY: The same type of organisms

that form the stromatolitesare forming these mats.

Looks like kind of a nasty black lasagna.

Smells bad too.

There's also some bubbles coming off in the water, seems like.

PLANAVSKY: Let's see what they are.

So I have a gas probe here.

Let's bury it in the microbialmat here and see what we get.

Very uppermost portion.

And it's what gas?

Oxygen.

Oxygen-- this is coming out of the mat?

Exactly.

The waste product thattransformed our planet

is oxygen.

JOHNSON: Oxygen a waste product?

That's what we breathe.

But these little microbes do the opposite:

they take in carbon dioxide and water and release oxygen.

It's called photosynthesis,

the chemical reaction at the heart

of every green plant alive on earth today.

This was the contribution of the stromatolite bacteria

to early Earth.

In a place filled with volcanoes and water,

over the courseof more than two billion years,

they pumped out so much oxygen

that the atmosphere changed from what would have been

a deadly poison for us

into something that made it possible

for life as we know it to exist.

So these things didn't onlyjust live in their environment,

they actually transformedthe environment

and made it livablefor other things.

Absolutely.

JOHNSON:It was a critical turning point.

Now a new kind of lifeform could finally join the party:

creatures that didn't produceoxygen, but instead consumed it.

About 640 million years ago, complex life took off,

with the evolution of primitive animals like sponges,

followed a little later

by a group of jellyfish-like creatures called Cnidaria,

the first animals to possess nerves and muscles.

Over millions of years, life grew ever more complex.

Fish got a skull and backbone 420 million years ago.

By this time, land had emerged, so it wasn't long

before the first amphibians hauled themselves

out of the water and onto the shore.

This led to the evolution of reptiles,

and then, more than 200 million years ago, to the dinosaurs.

Which brings us right back to where we started--

the big mystery.

What was it about this continent

that allowed so many kinds of dinosaurs to thrive?

You can find one clue rightsmack in the middle of the U.S.,

in the Great Plains of central North America.

For most people,

a drive across the Great Plains is an exercise in boredom.

For me it's just the opposite.

As a geologist I think about what's beneath the plains,

the stories that lie beneath the prairie.

Just outside the town of Oakley in western Kansas,

some strange but spectacular shapes burst up

out of the plains.

They're called Monument Rocks.

This place is so cool.

The story goes that early settlers crossing the plains

used these as landmarks to help them navigate.

One of the most amazing things about this place

is how much time it represents.

Just one inch of this chalk is 700 years.

That means that a foot of the chalk is 8,400 years,

or roughly the entire duration of human civilization.

There's about 40 feet of this stuff above me,

and there's another 300 feet below me.

There's literally millions of years represented

in this one place.

It's a snapshot of a time

when North America was going through some major changes.

This place is filled with fossils.

Hey, Chuck!

Long time no see.

Good seeing you.

Hey, Barb, how are you doing?

Good to see you.

JOHNSON: And nobody is better at finding them

than Chuck Bonner and rbara Shelton,

who've hunted for fossils in these rocks for over 40 years.

Let's go findsome fossils.

All right, sound good.

Well, come on.

JOHNSON: When I told them I was coming by, they offered to show me

their newest discovery.

That's pretty cool.

How did you find this thing, Chuck?

Well, I was searching alongthese slopes here

and found somebig bones sticking out.

That's cool.

What did you think when you first saw this, Barb?

Lot of digging, that's what I think.

Let's put a little water on here, huh?

Yeah, let's bring it to life.

JOHNSON: A little water reveals a skull with some major-league teeth,

no question a vicious predator.

But this was no dinosaur.

These jaws belong to an 80-million-year-old fish

called Xiphactinus.

This jaw is huge.

This must have been an immense fish.

Probably close to 14 feet long.

14-foot-long fish in Kansas.

Name me a living 14-foot-long fish.

Well, if you count the billon a marlin, maybe.

We're in Kansas, Chuck.

So a 14-foot-long fish in Kansas?

Yeah, sure.

JOHNSON: What is this ancient marine predator doing

750 miles from the nearest ocean?

Well, it turns out,

80 million years ago, the ocean was here,

right on top of Kansas.

It was teeming with mighty sea creatures

like Chuck and Barbara's 14-foot Xiphactinus.

But it wasn't just Kansas that was covered in water.

About 130 million years ago,

the ocean began to invade North America.

Water flooded in and formed a massive inland sea

up to a thousand miles wide.

It split the continent into two landmasses:

Laramidia in the west and Appalachia in the east.

The big inland sea would have huge consequences

for life on our continent,

especially North America's dinosaurs.

Back in the Kaiparowits in Utah,

where scientists have discovered

an amazing new collection of dinosaurs,

paleontologist Joe Sertich shows me his latest find

from this extraordinary dinosaur graveyard.

That's pretty clearlya horn.

SERTICH: Yep.

Here you can see where the eye would have been.

There's a large section of the horn coming off.

There's the tip of the horn there.

It's starting to look more and more like a brand new species.

This is so Jurassic Park.

It is.

JOHNSON: The new dinosaurs here are remarkably different

from other dinosaurs that livedfarther north at the same time.

So what is it with all this diversity?

From around a hundred million years ago,

our continent was split down the middle by the inland sea.

Over time, sea levels changed, shifting the coastline

back and forth all the time.

And keeping the dinosaurs of North America on their toes.

With their home turf constantly changing,

groups of dinosaurs evolved over time and adapted

to their local surroundings.

Joe and his colleagues have collected

an amazing variety of dinosaurs and fossil plants,

showing how different environments

drove dinosaur diversity.

So what you're saying

is that these differentenvironments along the coastline

create different landscapes

for dinosaurs to evolve in.

Exactly.

SERTICH: We suspect that these different ecosystems

are driving dinosaur diversification

as dinosaurs and other animalsadapt to their local conditions.

And that makes North Americaa dinosaur factory.

Exactly.

JOHNSON: As a paleontologist,

it's really exciting to think that 75 million years ago,

this land was full of dinosaurs of every description.

They all lived along this huge inland sea

that split America down themiddle and created a whole bunch

of different habitats.

But 70 million years ago, something dramatic happened.

The great North American seaway began to drain away.

So what happened to make this enormous body of water

totally vanish?

To solve that mystery,

I've got to head east from Utah to Colorado.

This place was also once covered by the vast inland sea.

With a big sky overhead, you can see for miles.

Ah, it's really great views up here.

Three sixty.

But I didn't climb this hill just for the view.

I'm on the hunt for some strange-looking objects

that I'm hoping to find right under my feet.

That's what I'm looking for, but it's not a very good one.

These hollowed-out rocks are clues that help explain

why North America's giant inland sea disappeared.

Here's a pretty good one.

After a rain, the water pools in them like this

and the birds come and bathe in these things,

and the locals call these things birdbaths,

but they're actually somethingmuch more interesting than that.

JOHNSON: These rocks once contained fossils of ancient shellfish

called ammonites.

You can pretty clearly see the shape of the shell

if you start in the center here,

and the spiral goes all the way out.

And in the middle, there wouldhave been a series of chambers.

The fleshy part of the animal would have stuck out

of the shell here and it would have looked

something like a squid or an octopus.

For more than 40 million years, North America's inland sea

was filled with giant ammonites like these.

But it's one thing to find marine fossils

in the flatlands of Kansas.

It's another to find them inthe mountains high above Denver.

The big question here is, what's going on?

But I've got an altimeter here and the altimeter says

that I'm 7,703 feet above sea level.

That means that something took marine creatures

and brought them to an elevation

that's more than a mile above sea level.

It's the same thing

that made North America's inland sea disappear.

And driving it all

is the constant motion of the ground itself.

Because the surface of ourplanet is broken up into pieces

that slowly slide along a conveyor belt of hot rock

miles beneath us at about two inches a year.

Around 70 million years ago,

a piece of crust under the Pacific Ocean was diving down

at the western edge of North America.

We think that it then began toslide right under the continent,

making it rise, forcing it up inch by inch

to create an icon of the North American landscape...

the Rocky Mountains.

The birth of this majestic mountain range

was the death of North America's great inland sea.

As the Rockies began to rise, the land under the Inland Sea

was forced up and all of its waters drained

into what is now the Arctic Ocean and the Gulf of Mexico.

This left the marine creatures living in the Inland Sea

literally high and dry.

It's mind-boggling to think that the bottom of the sea

could be found at the top of a mountain range,

but here are all these fossils that say that it's so.

The forces under the earth are so slow, but so relentless.

Over millions of years,

they completely altered theshape and form of the continent

and changed the fates of the millions of plants and animals

that were living there.

From the very beginning, rocksand life have been intertwined.

But this process doesn't always move slowly.

And change doesn't always come from below,

as our old friends the dinosaurs were about to find out.

So I pack my bags and head north...

to track down a 66-million- year-old smoking gun.

Thanks so much.

These are the North Dakota Badlands.

Thousands of square miles of arid gullies and buttes.

I'm driving deep into the badlands here,

on what is called the state highway, but it's actually

a gravel road.

And right around us here is what's called

the Hell Creek formation.

It's a 300-foot-thick layer of rock that stretches

over four states,

and it's a spot that I just keepcoming back to again and again.

And here's a cow I'm about to hit.

I just can'tet enough of this place,

because hidden in these hills is evidence of an earth-shaking,

life-changing event.

To find it, I'm going to have to do a little digging.

I've actually got a couple ofpieces of fossil charcoal here,

and that's pretty common in these layered rocks--

you find evidence of the ancient world,

whether it's the mud at a bottom of a lake,

the coal from a swamp,

or the charcoal from an ancient forest fire.

And every layer used to be

the surface of the earth at a certain point in time.

Now there's a stack of these layers,

and I'm looking for one layer in particular--

one very thin, one very special, one very scary layer.

After a few minutes of digging,

I find the 66-million-year-old layer I've been searching for.

There it is, right along here.

It's a little rusty orange layer.

It doesn't look like much, but this layer is Armageddon.

To show you why, I need to get in closer.

What I'll do is just set upmy handy-dandy field microscope.

I'm looking at this layer under the microscope

and what I'm seeing is that it's actually composed

of little round ballsabout a millimeter in diameter.

And these things are what used to be little glass beads.

So what you've got basically issome sort of geologic phenomenon

that's dropping beads of glass onto an ancient landscape.

So what could have happened here?

One way you get a layer of glass beads on a landscape

is to have a violent event

that melts rock and blasts it in the air.

As the molten rock flies through the air,

it cools into glass and rains down on the landscape

as glass beads.

If all we found in this layer were glass beads,

the most likely explanation might be

a massive volcanic eruption.

But there's something else hidden within this layer

that changes the story...

tiny crystals called shocked quartz.

Quartz is an extremely common mineral.

You can find it all over the planet.

But when it shows up with these parallel lines

as shocked quartz, that means it's been exposed

to huge amounts of energy...

Like you get at nuclear test sites.

But when this layer of earth was laid down,

there were no atomic bombs.

There was only one thing that could have made

a big enough bang to shock quartz.

About 66 million years ago,

an asteroid the size of Mount Everest was headed for Earth.

It entered the atmosphere

at over 20 times the speed of a rifle bullet

and exploded with more power than a billion atomic bombs,

sending a superheated plume of vaporized rock

shooting across North America

and over a hundred miles up into space.

This cloud of doom carried droplets of molten glass

and shocked quartz all the way to where I found them

in North Dakota and beyond,

bringing death and destruction to our planet.

But what effect did it have on the dinosaurs?

For the last 30 yearsit's been pretty widely thought

that one of the main groupsof animals that were the victims

of this event were the dinosaurs.

If this is the case,

it's useful to have some real scientific data.

30 miles down the road is a guy who can help me with this.

Tyler Lyson is a paleontologist

who's been digging up dinosaur fossils in these badlands

for more than 20 years.

It's been a long time,buddy.

Yeah, how's it going?

Always good in dinosaur land.

What have you got going?

Have a look at this.

Here we have a thescelosaur.

JOHNSON: Tyler and his crew have pulled dozens of dinosaur skeletons

from these rocks, among them big names

like triceratops and Tyrannosaurus rex.

All told, how many different kinds of dinosaurs

have you found in this area?

Two dozen.

We've found allthe major players here.

Just happens to be oneof the best places in the world

to find dinosaurs.

It's a rich, rich area.

JOHNSON: But where do we find these dinosaurs?

Are they below the impact layer or above?

Before the asteroid struck?

Or after?

So where is the asteroidimpact layer here?

It's right at the layer of that boulder right there.

So what do you get below that?

LYSON: Well, we have some really big dinosaurs.

We have the big plant-eating dinosaurs

like triceratops, edmontosaurus, thescelosaurus.

And then the thing that ate those dinosaurs, like T. rex.

JOHNSON: So above the asteroid impact layer,

what do you get?

LYSON: Well, we get a few turtles, we get crocodiles, some birds,

a few lizards and fish.

You find any dinosaursat all above there?

No dinosaurs above that black line right there.

JOHNSON: So below is dinosaurs and above is no dinosaurs.

Absolutely right.

JOHNSON:Nobody has ever found dinosaursabove the asteroid impact layer

in North America or anywhere else on the planet.

To me, that's pretty convincing evidence

that this catastrophic collision wiped out the dinosaurs.

And they weren't the only living things to suffer.

This amazing fossil leaf just popped out of this rock.

Tap a little bit more, expose it.

There's a leaf that hasn't seen the sun for 66 million years.

You can even see holes in the leaf

where cretaceous insects fed on the leaf

when it was growing in a forest that was full of dinosaurs.

And it's this world that was terminated

by the impact of the asteroid.

We lost more than half the species of plants

and more than half the species of insects.

It was truly an ecosystem-wide devastating event.

But even with all this globaldestruction, among the survivors

was one special group of animals that managed to hang on:

the mammals.

It was little mammals not unlike these chipmunks

that survived the asteroid impact, and they survived

because they had small body size, a large population size,

they could reproduce fast, they lived in burrows.

They were almost pre-adapted to survive an event

like the asteroid impact.

And once the dinosaurs were gone

they had the world to themselves.

In the millions of years that followed,

mammals evolved and changed, spread and diversified.

They filled every available niche on land, sea, and air

here in North America and all over the planet.

But it's the evolution of one particular group of mammals,

the primates, that's of special importance to us.

But there's a huge mystery.

Today, except for some monkeys in Central America,

the only primates native to ourcontinent are us: human beings.

If you want to see other primates,

like gorillas, baboons, and monkeys,

you have to visit a zoo.

Or come to a place like this:

the Duke University Lemur Center.

Whoa!

Look how high that thing is going.

It's an 80-acre site

dedicated to the study and preservation of lemurs,

a group of primates that evolved in Madagascar.

Here they come, there's a bunch coming at me right now.

That one's eating one peanut in each hand.

It's like he's eating ice cream cones.

Wow, this is awesome to be so close to these things.

Incredible how well they move through the forest

and to actually see them moving around the trees.

They'll go straight up a tree 40 feet

and then jump probably 25, 30 feet between the trees.

Seeing these little guys leap from tree to tree,

you quickly realize that almost everything about primates

is perfectly adapted to a tree-filled environment.

And that kind of makes you wonder.

We've got plenty of forests here in North America.

Why don't we have primates like these lemurs

jumping through our trees?

Well, the fact is, we did.

And paleontologist Doug Boyer can show us.

Ah, that's a nice one.

JOHNSON: One example is now

a jumble of bones encased in ablock of sandstone from Wyoming.

This particular accumulation of bones happens to be

about 48 million years old.

There's still a lot of rock on it though.

Well, instead of extracting every bone physically,

we can scan it.

JOHNSON: As the scanner gets to work, a faint image comes into view.

Now we can see somethingstarting to come through.

JOHNSON: Oh, wow, look at that.

There's the elbow coming into view.

It's so tantalizing.

You just see those...there's sort of shapes in there.

JOHNSON: From the scan data,

Doug builds upa full 3-D image of the fossil.

It reveals an amazing feature.

We have some of the hand here.

Here's some of the finger bones.

JOHNSON: How long those fingers are!

They're really long.

BOYER: This animal had incredibly long fingers.

If we were to scale this animal up to your size...

My fingers would be,like, that long.

Freakishly long fingers.

You'd have fingers that were about nine inches long.

Wow.

JOHNSON: Those long fingers, perfect for grasping,

are a tell-tale sign of a primate.

And thousands of early primate specimens have been found

all over America.

These little guys were about two feet long.

Like the lemurs, they were great tree-climbers

and probably lived on fruit.

When you watch these guys moving around the forest,

you realize what all these adaptations are for:

the long fingers, the long toes, the tail, the ability to jump.

When you look at the fossils,

it's the same features preserved in the bones.

It doesn't take an expert to realize

that those fossils belonged

to animals that were like these animals

and lived and moved in forests.

So, how did all these ancient primates get here?

Where did they come from?

56 million years ago, a huge, fiery rift opened up

in what's now the North Atlantic.

An event with dramatic consequences

for North America and our entire planet.

Volcanic eruptions poured huge amounts of lava

for thousands of years.

Releasing colossal amounts of greenhouse gases,

like carbon dioxide and methane.

Like a blanket in the atmosphere,

they kept in the heat, leading to an intense period

of global warming that changed the vegetation

across North America.

The cool forests covering the north

turned into dense subtropical rainforests

stretching all the way to Alaska.

These trees kept their leaves all year round,

providing food and shelter for primates

so they could make the leapfrom Asia across a land bridge,

a leafy highway to North America.

They hung around for more than 20 million years,

spreading all over our continent.

But then temperatures dropped sharply,

wiping out the subtropical forests

and their leaping inhabitants.

For millions of years,

nearly all of North America would remain primate-free.

Then, around 14,000 years ago,

almost a blink in geological time,

a certain two-legged primate made its entrance.

That primate, of course, was us,

and our arrival changed everything.

The first humans to arrive in America

found a land full of untold riches.

They'd really have a whole new world open in front of them.

They could move down the coast, which was full of resources:

fish, whales, seals, deer.

And the coastline is like an open pathway, a gateway

into a continent four billion years in the making...

providing us with an enormous geological bounty.

Gifts of the earth hidden in the landscape--

gold, iron, oil, and more--

harnessed to build the vast civilization

that surrounds us today.

For the first time

in the history of life in North America,

here was a species that wouldnot just adapt to the landscape,

but transform it.

The investigation continues online

MAN: Ready for this?

10,000 years ago, our continent was locked in ice.

So how did we get here?

JOHNSON: It's hard to imagine somebody crossing

even one ice field like this.

What challenges did we face?

And how do we turn the rocks of our homeland into riches?

Oh man, this thing is phenomenal.

Making North America, next time on

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