♪♪ -It's one of the planet's best known landscapes.

A breathtaking natural monument.

♪♪ 280 miles long, 19 miles at its widest.

Average depth -- 4,265 feet.

The Grand Canyon.

♪♪ For decades, geologists Karl Karlstrom and Laurie Crossey have been exploring and questioning it.

Because the Grand Canyon's full of stories and mysteries.

Its age and formation have been debated for 150 years.

We sometimes forget it tells the story of 2 billion years of the Earth's history.

-Each layer like a chapter of a book, as we go back in time.

As we go down the river, we go down deeper into Earth history.

And that's going to be part of our adventure is looking through this great library of geology exposed here in Grand Canyon.

-The 280 miles of the Colorado River that cuts through the Grand Canyon must be traveled to get there.

Crossing a hundred rapids.

-Whoo!

-Karl and Laurie are the experts.

They've led hundreds of expeditions.

In the Grand Canyon, they're researching the explosion of life.

♪♪ They study fascinating periods in Earth's history.

They delve into the formation of the American continent.

-Time aspect of this trip is difficult.

It's still difficult for geologists to put your mind through all the time that our planet has gone through to get to here we are today.

Mother Earth has provided us with places where the secrets are told a little more clearly, and Grand Canyon is one of them.

-For eight days, Karl and Laurie take us on a journey to discover the Grand Canyon and the stories it tells.

♪♪ ♪♪ ♪♪ -This journey begins at Lees Ferry, the only access to the Colorado River by boat for more than 200 miles, the starting point for any descent into the Grand Canyon.

♪♪ Glade Zarn's been a river runner for 15 years.

He's in charge of navigating the boat and the smooth running of the trip.

He's a friend of Karl and Laurie, a lover of the Grand Canyon.

♪♪ Karl and Laurie are already at the launch site.

Jeff Carpenter, a.k.a.

Carp, is with them.

Carp is a close friend of theirs.

He's a naturalist and is accompanying them on this trip.

He's been down the Grand Canyon 50 times, often on the trail of reptiles.

-That's maps.

Maps and books.

-This is almost nothing compared to the hundreds of trips made by the two geologists.

-So, once we launch, we are on this river and we're in this canyon.

It's getting deeper and deeper above us, and we're self-sufficient.

Everything we need we hope we have, and whatever we -- whatever we didn't bring, we don't need.

-I'm guessing we have more than we need.

-I hope so.

But it's a marvelous trip, and it's -- it's adventurous.

We'll see a lot of white water and a lot of flat water.

And then, so for tomorrow night -- So we're here at river mile zero.

Where's zero?

There it is.

-Lees Ferry is the entry point to the Grand Canyon.

The exit is 280 miles further on.

There's no escape, except at Diamond Creek, 224 miles away.

The Grand Canyon is strikingly gigantic, 19 miles at its widest point, an average depth of 4,265 feet in the heart of the Colorado Plateau.

-Hey!

-Hey, dude.

It's been a long time.

-How you doing?

-It takes a few hours to launch the boat, set it up, load it for eight days of navigation and camping.

Five of them set off for the Grand Canyon, Carp, Karl, and Laurie, Glade, but also Amy.

She's a river runner like him and will assist him.

Each trip to the Grand Canyon is an experience in itself.

-Every trip is like your first time.

-Every trip is like your first time.

Every trip is a unique trip.

But it's all one trip.

-Yeah, part of the journey.

-Every single trip is so exciting.

You can do it a hundred times like I have, and then this trip will be its own trip.

Everything's different.

New things you discover, new people you go down the river with, new science, new ideas come along.

♪♪ ♪♪ -At Lees Ferry, there's no telling the extent of the challenge ahead.

♪♪ But only a third of a mile after the start, the Grand Canyon takes shape.

-Good morning, Grand Canyon!

-The Colorado rapidly cuts into the plateau, and the weight of the cliffs can already be felt.

♪♪ At the fifth mile, the Navajo Bridge represents the last contact with human construction for a long time to come.

♪♪ The bridge is anchored in the upper geological layer of the Grand Canyon -- its summit, in a way.

-The beauty of this river trip is, as we go down the river, the river is cutting deeper into older and older layers, and they present themselves, they introduce themselves to the geologists, to everyone.

Each layer has its own name, its own story, its own history that we wanted -- the geologists, the detective has to figure out.

This particular first layer, it's called the Kaibab, the Kaibab Limestone.

And it becomes -- it's right here right beside us.

It becomes the rim of the Grand Canyon, way up above us once we get into the depths of Grand Canyon.

-This layer is the first of more than 20 that make the Grand Canyon the world's largest geological laboratory.

The river progressively reveals the layers during the trip.

They succeed each other according to a sacred rule.

The most recent cover the oldest, from 270 million to 1,800,000,000 years ago.

The journey takes the crew back in time and follows in the footsteps of Karl and Laurie's studies.

The mysterious explosion of life 500 million years ago.

The astonishing Snowball Earth, a period when the Earth was entirely covered in ice.

The formation of continents when they arrive in the depths of time revealed by the Grand Canyon.

♪♪ ♪♪ Karl and Laurie see past environments in the rocks of the Grand Canyon.

The Earth's extraordinary dynamism -- vanished seas, rivers, deserts.

-Feel like you're in the Sahara Desert or one of those big dune seas, they're called, sand seas.

-The rocks tell us stories.

-So, see how that's a set right there that's pinching?

That set represents the migration of a single dune.

And then this would be another dune and another dune.

So when you have interfering sand dunes, it leaves this beautiful record, like footprints of a sand dune.

-Even for Karl and Laurie, reading the Grand Canyon isn't easy.

Ancient times mingle with more recent ones.

-There's old stories embedded in the rocks, and there's young stories about the river carving.

You flip a little switch and you go from millions to thousands to billions and back.

We're so lucky.

-Well, in Grand Canyon, you have to do all of it.

-You do.

-Because there's geologic time all around you at all different scales.

-Yeah, that's right.

-The first mile sets the pace of the navigation.

The Colorado flows at a speed of nearly 4 miles per hour, descending at an average of 1.64 feet per half mile.

You'd expect a to tempestuous river, but the Colorado is peaceful.

Until the House Rock Rapid appears.

-House Rock.

-House Rock.

-The first big boy.

-First big one.

Well... -For the river runners, the Grand Canyon begins with House Rock.

-Looks like a fun level.

-Oh, I love this rapid.

-Oh, man.

-That is so beautiful.

-It really is.

-But a rapid isn't simply adrenaline on a boat.

A rapid is a landscape in the making, a landscape in action.

And proof that the Grand Canyon keeps getting bigger.

-You know, we say that the Earth is dynamic, and the forces of erosion, the climate of all these things, play a role in shaping the landscape.

In Grand Canyon, the rapids are always forming where side canyons come into the main stem.

[ Thunder crashes ] When a rainstorm comes to this region, the water floods off the edge and is able to carry big, large boulders down into the arroyos, which then wash into the Colorado River.

So it's the side streams that help widen the canyon and the storms and the seasons.

Millions and thousands of seasons working through long geologic time.

-These millions of storms and millions of seasons that knead the lateral canyons shape this spectacular landscape day after day.

-And Rider Canyon right here drains a big area up on the plateau.

Funnels that water, carving this narrow slot canyon and bringing that debris during storm events out, forming a fan.

We see a beautiful debris fan in front of us.

What that fan building out does is, it pushes the river over, against this sheer cliff on the left side.

And so we form this beautiful, sinuous rapid.

-House Rock is the first major rapid in the Grand Canyon.

Glade likes to see what he's getting himself into.

-Okay.

So, what's your -- what's your line?

What's your plan to get down through there?

-Well, I think I'm gonna just kind of ride this tongue out there.

Not too far left because right kind of in the middle of the rapid, there's a big old ledge that can take a motor off.

So kind of go down straight, start to turn, and then get the motor back out into the deep water, and then try to just kind of nose in to each one of those waves.

The rapids are really dependent on water level, you know, and down here, the water fluctuates on a day-by-day basis.

It's, uh -- like, this month, for the rest of the month, they're doing 9,000 cubic feet per second all the way up to 17,000.

So if you're on the low water, you know, you have half the river that you would on the high water.

And it kind of just depends on the topography of the rapid and the landscape around it.

Sometimes the high water makes the rapids really big.

In other rapids, the high water will make them kind of go away.

But this one, it's kind of big no matter what.

♪♪ ♪♪ ♪♪ ♪♪ ♪♪ ♪♪ -[ Laughing ] -Thank you.

That was refreshing.

I like that.

-Great ride!

-That was fun, huh?

-That's refreshing.

Being on the edge.

I like it.

Hey, did you look down in the hole?

-I did.

-You see the bottom?

-No.

[ Laughter ] -Man, that one wave came over.

Pwoo!

♪♪ -Sometime around this time of day, we'll start looking for a camp.

And, you know, some are really big and wide open.

Some are a little more cozy and bushier and stuff, but they're all good.

And at the end of the day, you're freaking camping in Grand Canyon, so hard to complain.

-Being a river runner means mastering the art of navigation on the river and in the rapids.

But the role involves much more -- overseeing safety, camps, meals, the atmosphere.

♪♪ Above all, river runners are among the Grand Canyon's greatest connoisseurs.

Local knowledge.

Sensory knowledge.

♪♪ -It's like a dance between your angle and momentum and the power that you might have versus the power of the river.

What got me is it's that dance that you are -- you know, this boat is a tool of your idea of how everything is working down there.

-When Glade maneuvers in a rapid, he puts everything he knows about the area into action.

It's a feeling shared by the river runner community.

♪♪ It's a culture, even, the heart of which is located around Flagstaff.

-Almost to the boat shop, top of Grand Canyon Avenue here, home of Brad Dimock.

I met him a few years ago and started building boats with him.

He's been a pretty big pillar in the boatman community.

He's been guiding for 50 years.

Here we are.

♪♪ -Being a river runner is a seasonal activity.

And in winter, Glade works with Brad Dimock, a friend of Karl's, a significant figure in the Grand Canyon culture, of which he is the historian and memory.

-Everything in his workshop recalls the spirit of this community.

Brad Dimock builds wooden boats here, some of them original models, others copies of famous boats.

♪♪ The most famous of these is that of John Wesley Powell, the first man to descend the Grand Canyon and record it on a map.

♪♪ -Powell boat is is a pretty cool boat.

They look like this.

And they've got that beautiful round belly and a keel along the bottom.

So they go straight really well, but they don't turn very good, which has turned out to be a problem in Grand Canyon.

But Powell was going with the best thing he could come up with.

But he wasn't really that interested in a boat trip.

It was just the only way he could get through this wild, great unknown, as they called it, part of the American continent that had no maps.

Nobody really knew what was out there.

-In 1869, John Wesley Powell set off into the Grand Canyon.

He was no adventurer.

He was a scientist and a pioneer of geology in America.

At the time, the Grand Canyon was the last unexplored land in the United States.

He didn't know what he'd find as he meandered down the river.

He risked his life and those of his men, but discovered a staggering place, the importance of which he immediately understood.

-Landscape that was very new to everyone, really, not just the American public.

And it was considered horrible, ugly, dangerous.

Why would you ever go there?

And it was Powell that began to describe it and describe its beauty and its geologic significance.

That really changed the American perception of Grand Canyon.

And the Grand Canyon itself is first described from the bottom up.

But he brought the canyon country and Grand Canyon in particular into the awareness of the American public and the world.

-The shadow of John Wesley Powell still hangs over the Grand Canyon.

Reports of his expeditions are read by every river runner.

The names of the places still carry his imagination.

♪♪ Like Marble Canyon.

Where the crew made progress during their second day on the Colorado.

-Yeah.

When John Wesley Powell came through here, he called this Marble Canyon.

And it was because of this rock reminded him of marble, and in a way, it's like marble.

Of course, it's the limestone, which if you metamorphose limestone, you'd get marble.

So it's kind of a similar -- similar look.

But he knew it wasn't a metamorphic rock.

♪♪ -The evocative name Marble Canyon comes from a layer that appears at the 22nd mile.

The Redwall layer.

♪♪ The crew enters a world of cracks, cavities, and caves.

This red wall layer houses the Grand Canyon's vast water reservoir.

It is very difficult to trace.

Karl and Laurie try to understand where it is stored and how it moves.

-Wow.

-This place is so cool!

-Look at the ceiling.

-Ooh.

-Watch your head on the ceiling.

-Yeah.

-But you can see how the limestone has been dissolved away.

-Isn't that crazy?

-Oh, man, look at the textures.

-Beautiful.

-Ooh!

-Glade is the only person of the group to have been in this cave before.

He begins by showing them some crystals embedded in the rock.

-A little later in the rock history.

-There's another... -Look at that.

-I got one other cool thing to show you guys.

You just hang here.

I'll be right back.

-But it's the journey of the water he wants to live again.

-So, we have vertical passageways for the water to move down into the aquifer.

-Wow.

-These are the superhighways of groundwater hydrology.

Well, water follows the gravity, so it will -- it'll come down and form pools in the -- in this large, world-class aquifer.

-We call it an aquifer.

Well, I don't see any water here, but the evidence of the water carving the caves is all around us.

And you can imagine this network is just all interconnected passageways, and some big rooms like we're in here.

And when the aquifer's wet times in Earth history, the aquifer fills with water, and there would be a great deal of water stored in these bigger areas.

And then, when the canyon cuts down, the river cuts down, the water is following the base level, and these aquifers can drain into this part.

♪♪ -Hi.

-Wow.

-That was amazing.

What a view.

-You float up there like water in an aquifer.

-[ Laughs ] [ Thunder crashes ] -When rain or snow falls on the Colorado Plateau, the water doesn't accumulate.

It erodes the landscape, penetrating directly into the soil.

It moves along a complex network to reach the aquifer of this Redwall layer, which feeds all the Grand Canyon's seeps, waterfalls, and springs.

♪♪ A mile or so downstream from the cave, Laurie studies a particular spring.

Fence Spring.

-Okay, beauty, the water is boiling up in, the lower world water coming into the river.

-Laurie has been collecting data here for over 10 years.

Each time they descend into the Grand Canyon, they retrieve the probe they installed in Fence Spring.

-To help you?

-I can't get it open?

-Here's the second set of channel locks.

-Let's try it with two.

-Huh?

Yeah, I can do it with two.

-Okay.

Be very careful with this one.

They mean a lot to me.

-It's what?

-That one -- this pair means a lot to me, so don't drop that one.

-Okay.

-Whatever you do.

-No pressure.

Those are your dad's?

-No, that's -- it's got my name engraved with the date of my first trip on it.

-Aww.

-Somebody gave it to me when I got a boat.

Yeah, but you got to be real careful with it.

-I know.

-Okay.

-Whoo!

-There she blows.

-So we'll -- we'll replace it.

-Yep.

-Coming out.

-Coming out.

-Giving us information.

-Fantastic.

-All right.

It's artesian.

It's called artesian pressure.

It's coming up with great pressure from deep, deeper in the earth.

But this water, if we look at its chemistry, we find out that its isotopes tell us it came from that side of the river, rain and snow that fell thousands of years ago.

-Laurie wonders how long this water has been flowing.

She tries to reconstruct its history, as the implications are fundamental in a desert region.

-There it is.

It turns out that that's a more complicated question than you might think.

This water actually is a mixture of different fluids.

And those fluids have different lengths of time that they reside in the earth.

Some of the water is traveling very fast, and some of the water has been in the earth for thousands of years.

So what we have here at the spring is a mixture.

When we look at the springs in Grand Canyon, there are literally hundreds of springs throughout the canyon.

Of all of those hundreds of springs, they're all important for local ecosystems.

♪♪ -In the Grand Canyon, life surges from the springs.

And a mile or so after Fence Springs, Vasey's Paradise is the finest example of this.

♪♪ -Wow!

-It's so beautiful.

And you can smell it.

♪♪ ♪♪ ♪♪ -When John Wesley Powell got here and saw this lush vegetation, he thought it looked like a Paradise, and as a consolation to his friend Vasey, who couldn't make the trip, he named it Vasey's Paradise.

They'd had a rough time till here.

This is -- This looks like a paradise compared to a lot of places they had to go through.

-These springs are an oasis in the desert.

They make up only 0.01% of the Grand Canyon's landscape but contain 500 times more species than the surrounding area.

They are rare and delicate ecosystems.

-Those springs are a source of narrow endemism where you have -- they're so isolated that the organisms live there gradually changed genetically over time, and become differentiated from other populations at other springs, so that if they did come back together, they probably couldn't interbreed.

And so that isolation is an important source of evolution and narrow endemics.

-In the heart of the luxurious Vasey's Paradise, naturalist Jeffrey Carpenter is searching for the species that symbolizes this endemism.

It's very small, hard to spot among the watercress.

It's a species you wouldn't expect to see on a trip to the Grand Canyon.

-This is a Kanab ambersnail.

It's an endemic.

It only lives here.

This is a really unique environment in the Grand Canyon.

♪♪ So, this is its only patch of habitat here about, so we called it a narrow endemic.

Beautiful little snail.

We'll see a little bit of an amber shimmer when the light hits it right.

-The tiny Kanab ambersnail is the emblematic animal of Vasey's Paradise.

In the Grand Canyon, each spring is unique and home to its own assembly of species.

♪♪ Vasey's Paradise is particularly rich.

But Vasey's Paradise could have disappeared, drowned, been submerged.

6 miles downstream, the traces of an aborted dam project still mark the rock.

-These holes all around here, are kind of all over, sprinkled throughout this little section, they're all test adits.

They're testing the integrity of the rock to see if it was suitable to build a dam site, to build a dam right here.

We call it the Marble Canyon dam site.

And this was back in probably early, mid '60s when all this stuff was going on.

They, uh -- they had a pretty grand plan.

-Remind us what could have happened.

-Totally.

Yeah.

It is a good reminder.

-It's so visual, too, to imagine a concrete wall here that's immensely thick, to hold back a huge amount of water, and that water would have gone into all these old cracks in the aquifer, refilled the aquifer.

-Yeah.

Could you imagine?

-Just the unintended consequences of the dams were not really thought through, for Glen Canyon, even.

-Yeah.

-You know, Lake Mead.

These things were not thought through.

What's going to happen in geologic time or even decades?

-Yeah, even a lifetime.

-Yeah.

-We still haven't learned to think about the long-term consequences of what we're doing on the planet Earth.

-Yeah.

I think that is kind of the human folly.

♪♪ -Humans now have a stranglehold on life in the Grand Canyon.

♪♪ That's why each end of the Grand Canyon is marked by the presence of a gigantic dam.

Hoover Dam downstream, the largest in the United States.

And Glen Canyon Dam upstream, the second largest in the country.

It has greatly altered the ecology and functioning of the Grand Canyon.

♪♪ ♪♪ -Glen Canyon Dam is 200 meters tall.

It was completed in 1963, and it provides water and hydroelectric power for 40 million people.

The dam tremendously changed the river ecosystem.

It separated the river from climate in a way that's really dramatic.

The river downstream is still very wild, but it's changed.

♪♪ -Larry Stevens is a friend of Karl, Laurie, and Carp.

A river runner and ecologist, he has extensive knowledge of the flora and fauna of the Grand Canyon.

He studies the impact of the dam, notably.

They appear at the foot of the concrete structure in the algae that Larry collects.

-Before the dam, a muddy river here didn't allow any sunlight to reach the floor of the river.

With sediment being trapped in Lake Powell and not passing through the dam, we have a clear water river.

And the river, the sunlight reaching the floor of the river allows algae to grow.

The algae is the base of the food chain here.

Invertebrates eat it, the fish eat the invertebrates, birds eat the fish, and we have things like peregrine falcons and bald eagles and osprey now in the river system, all related to the presence of algae.

♪♪ -Larry constantly monitors the parameters of the river water.

It is clearer now, cooler.

Its temperature is much more constant.

Before the dam, it could freeze in winter and rise to 29 degrees Celsius in summer.

As a result, half of the native fish species has disappeared.

And the humpback chub, a fish adapted to Grand Canyon conditions before the dam, has become an endangered species to be saved at all costs.

-Half a billion dollars has been spent to ensure the longevity and the persistence of humpback chub.

Humpback chub are a very odd-shaped fish.

They have a big dorsal hump on their backs that many thought were to help stabilize them in very turbulent flow that the pre-dam river had here.

The fish has been evolved here over the last 2 million years, so it's a long history of the fish being in the -- in the river with very high variation in flows, turbulence, and whatnot.

-The humpback chub has evolved slowly in an environment that was altered overnight.

♪♪ Below the dam, the Colorado no longer roars like it used to.

It was tempestuous.

Fiery.

It flowed freely.

♪♪ Thousands of years of flooding have left their mark on the riverbanks.

Back then, the Colorado was a free-flowing river that scored everything in its path.

-The scouring floods that came through in pre-dam time removed vegetation every year from the shoreline.

Oddly, the dam has actually increased biodiversity here because it's a much more stabilized ecosystem.

We've actually modified the ecosystem, dampened down the flooding, the scouring that used to happen here turned it into a very predictable river, but that's increased the productivity and also the biodiversity of life in the river.

♪♪ -The tamarisk is a prime example of this paradoxical development.

This invasive plant has thrived since the dam.

It's late flowering makes it an essential resource for hundreds of species of pollinators.

Which, in turn, attract birds.

Who nest there by the dozens.

♪♪ The dam has stabilized the environment, increasing its richness.

But it keeps on evolving, and Larry's always discovering species that before didn't live in the Grand Canyon.

-I collect what I don't recognize.

This is perhaps a legume.

I have to take it to a botanist to really get it identified.

Big strange plants.

This is actually a desert willow.

So I know this is genus Chilopsis, but it's a new non-native species in the river corridor.

So this is the first record of it.

And this will be pressed and provided, given to a museum.

Nature is moving along at its own pace.

No matter what we do, nature will still proceed.

Glen Canyon Dam has a life expectancy of 640 years before it totally fills with sediment and water pours over it and, then, very quickly, the cliffs will erode around it, and the river will return to its course.

Because of my geological training, that gives me a little bit of solace.

♪♪ We have an impact here.

It might be several centuries, but, eventually, the river will find its way back and make its way to the sea.

♪♪ ♪♪ -♪ Well, she's walking down underneath the ground ♪ -The third day begins peacefully with music in the camp.

-♪ Up and down ♪ ♪♪ ♪ It's all right, baby, it's all right ♪ ♪ Take anything you want from me ♪ ♪♪ ♪ Anything ♪ ♪♪ -The crew is making progress in Marble Canyon, where humans lived long before the dams were built.

The oldest evidence of our presence in the Grand Canyon is 12,000 years old.

But the most spectacular evidence of human life is more recent.

-So, if you guys look at the base of this cliff on the right here, you see these three little alcoves.

And on that far right alcove, you'll see these four little square dots.

Those are the doorways to the Nankoweap Granaries.

They're open now, but when they were in use, they would be sealed up with another piece of stone.

-The Pueblo Indians lived here around 1,000 years ago and stored in Nankoweap's granaries the beans, squash, and corn they grew in some of the Grand Canyon's deltas.

♪♪ In those days, the climate was wetter than today.

Then a great drought hit the American Southwest.

And the Pueblo Indians gradually left the Grand Canyon.

♪♪ But it remained sacred ground for at least a dozen tribes today, especially where the Colorado and Little Colorado meet.

♪♪ ♪♪ -So, it's a very special environment for the ecosystem.

And for the people who have lived in this area, this is an even more sacred place.

This is a place where the waters are meeting, the joining of the two waters.

Sort of the heart and the lungs and the backbone of the region are the water that sustains all life.

So they're saying is, "Water is life."

-The birthing place of the Sipapu or Sipapuni was a few miles up here, and according to their legends, that's where all life comes from.

-Well, it's a very sacred place to the tribes who -- -A lot of tribes.

-Yeah.

♪♪ -At the 61st mile of the descent, the Little Colorado flows into the Colorado.

It's much more than just an affluent.

♪♪ For many tribes, it is also the place of their emergence into the world from the depths of the earth.

♪♪ As with the Hopi Indians.

♪♪ ♪♪ -My name is Lyle Balenquah.

I am a member of the Third Mesa Greasewood clan from the village of Paaqavi, and my lineage is of the Hopi people.

And my people are the ones who built this ancestral place here.

Within Hopi oral tradition, we talk about this being the fourth world of the Hopi.

Hopis believe that we occupied three previous worlds before this fourth world.

The emergence point for this fourth world is down in the Grand Canyon, from the confluence where the Little Colorado River and the Colorado River meet.

When those clans emerged out of the Grand Canyon, and that's really a metaphor, talking about the ancestral people moving out of the Grand Canyon to start exploring different parts of the southwest.

And out of that emergence point come many Hopi clans that are still around today.

♪♪ -Lyle Balenquah lives on the mesas that make up Hopi territory.

The final site of the Great Migration that took place some 800 years ago.

It was a necessity in the face of an increasingly dry climate.

The Hopi emerged from the Grand Canyon and became a farming people, able to grow corn in very arid lands.

♪♪ -So when we emerged into this new fourth world, we were given three sets of technology that we would use to sustain ourselves in this new landscape.

We were given a gourd of water, a bag of corn seed, and a planting stick.

And so that was the gift given to us, which we were then used to sustain ourselves as we migrated across the landscape.

And so for us, corn is the foundation of who we are.

So there's a connection between the seed and Grand Canyon and the seed that we now grow at Hopi.

♪♪ -This unbreakable tie with the Grand Canyon runs through every aspect of Hopi culture -- the corn kernels, their oral history, their symbolism.

On the reservation, an exceptional assembly of rock signs and engravings suggest that Lyle's ancestors inscribed a map in stone to show the way to the Grand Canyon.

-But we know that that image on the far left there references the Grand Canyon.

And you see it kind of traverses this trail system, maybe, that kind of connects to this spiral here.

So the spiral itself could be indicating this spot that we're at right now.

And it's a general metaphor for how you would traverse different landscapes to get from here 70 miles west to the Grand Canyon.

And so we remember that history, not just through the telling of this image here, but also by continuing to visit the Grand Canyon in the present day.

♪♪ -The Hopi often commemorate their origins in their sacred places at the confluence of the Little Colorado and Colorado.

♪♪ This confluence is a key place in the Grand Canyon, as the Colorado permanently loses its clearness due to the dam.

-And, hello, Colorado.

-Yeah.

-I know, I always like it muddy, actually.

-Natural.

Natural.

-You do?

-The Little Colorado provides sediment for the main river.

Here, the Colorado rediscovers the red color that gave it its name.

♪♪ -And they've been a very narrow, close-walled canyon, and now we're going to start to see farther.

We're going to see bigger vistas.

We're going to see new strata as we go yet further back in time on the Colorado River.

♪♪ -Karl and Laurie arrive at their field of study.

In these landscapes, they observe the creation of continents... the evolution of life... and the Snowball Earth.

They think about the formation of the Grand Canyon.

They're about to travel into the depths of geological time, where the rapids become furious and give rise to the valley of adrenaline.

The start of a new journey.

♪♪ ♪♪