All language subtitles for Grand Canyon National Geographic Naked Science Grand Canyon 2008

The Grand Canyon-

a colossal labyrinth of towering buttes
and deep sided canyons.

For over a century,

scientists have puzzled
over how one small river

could cut such a deep slice
through the earth.

The Grand Canyon formed
through processes deep within the earth

invisible to the eye.

Today new discoveries point towards
new answers-

Scientists are on the brink
of understanding the geological forces

that created one of the natural wonders
of the world- the Grand Canyon.

It's a landmark so immense
that you can see it from space.

277 miles long, up to 18 miles wide
and one mile deep-

The Grand Canyon
is one of the deepest chasms on Earth.

Its walls plunge sheer
into the Earth's crust.

The Colorado River sliced through
2 billion years of our planet's history
in less than 5 million years,

exposing layer after layer
of geological time.

The first humans walked here
thousands of years ago.

Since then the canyon has inspired awe.

How did it come to be here

and what secrets lie hidden in its walls?

To many Native Americans
this land is sacred.

They have revered the canyon
for centuries.

The canyon is a very spiritual
and powerful place.

Our legends say that we actually
came from the bottom of the canyon.

Scientists like senior geologist
John Spencer

consider the Canyon
a treasure- and a mystery.

It's a bit startling,
because all around it it's very flat

and you can be 100 feet
from the edge of the canyon

and think this is a rather boring landscape

And then you walk over
and look into the canyon

and all of a sudden
there's this monster canyon in front of you

The layers of rock in the canyon walls
formed over thousands of millions of years

The deeper you go,
the further back in time you travel.

At the top the newest rocks,
at the bottom the oldest.

The Grand Canyon appears
to be upside down.

On top, fossils from an ancient sea.

At the bottom,
remains of an old mountain range.

Karl Karlstrom, geology professor
at the University of New Mexico

is an expert on the oldest rocks
of the canyon- one mile down.

They reveal what the Southwestern US
looked like two billion years ago.

We were interested in what's the oldest
chapter of Grand Canyon history.

And these rocks
are so spectacularly exposed

that we have the opportunity
to study the earliest history
in the Grand Canyon.

What's strange about these rocks
at the bottom

is that they are part
of an ancient mountain range-

now buried under thousands
of feet of rock.

They are the remains
of a range called the Vishnu Schist,

a layer of metamorphosed rock that
dates from around 1.7 billion years ago.

The human eye sees a line of rock.

Karlstrom's instruments
see evidence of a mountain range
that once towered six miles above.

His techniques bring the past back to life

His clue is the minerals in the rocks
that change chemical composition
under pressure.

More rock on top means
more pressure on the rock below.

This forces a mineral in the rock, garnet,
to take up more calcium.

The higher the calcium concentration
within the garnet

the brighter it looks
under a microscope.

This tells scientists
how deep a rock was buried.

We have learned that these rocks
were buried to great depth

and the amount of pressure
that they experienced

was equivalent
to about six miles of rock above them.

Karlstrom's findings
have helped other geologists

visualise how this area
may have looked 1.7 billion years ago.

Ron Blakey is a professor of geology
at Northern Arizona University in Flagstaff.

He studies ancient continents

and discovered that California
wasn't always America's West coast.

It's very likely that
the coastline of North America

at this period of time
was just south of Wyoming,

perhaps along the Wyoming/Colorado border

and extended up into the Lake Superior
region and then up into Canada.

So I would say that perhaps only
half to two thirds of North America

had been built at that period of time.

The Vishnu mountains stretched across
a very different landscape-

the south of North America
did not exist as we know it today.

The mountains towered up
out of an ocean along the ancient coast.

They eventually became part
of the North American continent

and formed the basement rocks
of the Grand Canyon.

I imagine
it looked like a bit of a train wreck

where each of these island chains
was perched offshore.

A series of island chains
that had substantial mountains

but fairly high peaks like in the Aleutians

Six miles beneath the summits
of these mountainous islands,

the rocks were developing
that distinctive calcium signature.

The mountains above didn't last long.

In around 500 million years,

erosion ground them down

until all that was left
was this at the bottom-

the Grand Canyon's most ancient layer.

As we rise up the side of the canyon,

we travel forward in time.

Each foot takes us closer
to the present day-

and each period
has its own history.

Over hundreds of millions of years
the landmasses continually change shape.

Forces deep inside the earth
cause continents to break apart,

drift away and form new ones.

Deep trenches open up beneath the ocean

Sea levels change
and flood low-lying areas.

At least eight separate seas
have flooded this area

since erosion cut down
the Vishnu Mountains.

They covered the land,
stayed for a few million years

and retreated again.

The evidence is here-

nearly two and a half thousand feet
above the modern Colorado River

and five and a half thousand feet
above present-day sea level...

These are the remains of oyster beds

that flourished here
nearly 100 million years ago.

The Cretaceous sea stretched from Kansas
in the east to Nevada in the west,

from Mexico in the south
to the Arctic in the north.

It was a shallow seaway
that covered much of the continent.

Sea creatures sank
to the bottom of the ocean

and fossilized in a thick,
grey layer of mud.

Scientists call it the Tropic Shale.

Wayne Ranney is fascinated
by this region, rich in fossils.

It gives him a clear idea
of this area's history.

This oyster bed, which contains
millions of oysters

is from a sea that
was a shallow sea that covered
the interior of North America

between about 80 and 90 million years ago

Oysters weren't the only creatures
living in this ancient sea.

Life was abundant.

Sharks, turtles and ammonites
also inhabited the waters.

Today, as erosion slowly wears away
the layers of rock,

new fossils appear.

And in 2005,

just 70 miles away
from the edge of the canyon,

palaeontologists found the well-preserved
skeleton of a plesiosaur...

a dinosaur-like, fish-eating reptile.

For David Gillette
it was a dream come true.

He is a curator of palaeontology
at the Museum of Northern Arizona
in Flagstaff.

For a vertebrate palaeontologist,
like myself,

finding plesiosaur skeletons
like we're finding in the Tropic Shale,

is almost a once in a lifetime experience

The one in front of me was a plesiosaur
that was about half-complete,

we found the front half of the body

and that's more exciting
almost than anything I can imagine.

Plesiosaurs were sea-going reptiles.

They were last seen
about 65 million years ago

when a catastrophic mass extinction
hit the earth.

Gillette's Plesiosaur
dates back much earlier.

It lived around 90 million years ago.

Clear proof that this area
was under the sea at that time.

The seas left deposits of mud, sand
and the remains of living creatures.

Sea currents moved this material
which then settled.

And over time the deposits
turned into layers of sedimentary rock.

Ron Blakey explains.

What I am going to show you now
is a form of sedimentation.

I have here a glass cylinder
that's filled with water and sediment,
mostly sand

and what I'm gonna do
is shake this up,

and the shaking up
provides energy

that allows the sand grains
to move around this cylinder of water,

and then when I set it down
that energy is removed

and the grains
will immediately settle out.

Let's see what happens...

As you can see the coarsest grains
have already settled out

and finer grains
and finer grains are settling,

and now most of the sand is out,

the water is still cloudy

because there is some fine material
still in suspension within this cylinder.

But all the energy of the system
has been removed

and so now even the finest grains over time
will settle out to form a layer of sediment

This process demonstrates how
sedimentary layers built the Grand Canyon

Over the course of time,
the glass cylinder turned many times.

And when the seas come and go
this is all that remains.

Millions upon millions
of years of sediment

compressed over time
to form layers of rock-

the building blocks of the Canyon.

But powerful forces
were building deep underground.

Forces that would thrust
these rocks a mile into the sky.

We are on a journey to discover
the geological processes
that created the Grand Canyon

We are in the cretaceous period-

where plesiosaurs
hunted in the shallow seas

that covered the area near to
where the Grand Canyon is now.

Seas flooded and retreated
over this area for millions of years,

overlaying the ancient Vishnu Mountains
with two miles of sedimentary rock.

Half of that has since eroded away,

to leave today's canyon, one mile deep.

The next major transformation will
push the land several thousand feet
into the air.

Deep beneath the earth
a monumental force builds up.

It is one of the greatest forces on earth-

the gigantic power
of colliding tectonic plates.

Over millions of years
the planet's surface changes.

Scientists explain the process
using the theory of plate tectonics.

The surface of the earth
is made up of a series of large plates.

They float on the soft, plastic part
of the earth's mantle.

The inner core of the earth
may reach over 12,000 degrees.

Heat escaping from the core
creates convection currents
in the next layer-

the lower mantle-

pushing the plates
slowly across the surface.

Scientists call it continental drift.

Over time, whole plates move apart
and crash back into each other,

shaping and reshaping our world.

Scientists believe that
these colliding tectonic plates

were instrumental in creating
the Grand Canyon.

Around 130 million years ago

the oceanic plate began to collide
into the western edge
of the North American plate.

Oceanic plates are 30-60 miles thick
and lie beneath the sea.

They consist of dense basalt
and get pushed down.

Continenal Plates
are mostly granite and lighter.

Oceanic plates subduct underneath them
when they collide.

So when the oceanic plate
hit the lighter north American plate,

the oceanic plate moved
under the west coast of America.

Over tens of millions of years the
continental crust compressed and thickened

As the oceanic plate thrust downwards,

the whole of the west of America
lifted slowly upward.

As the land rose, the sea retreated,

creating the landmass we see today.

The collision dragged down
portions of the leading edge
of the continental crust.

Beneath the surface it melted

and liquid rock pushed up
through the crust.

The Rocky Mountains formed in the north

In the south a range of ancient mountains
the Mogollan Highlands grew higher.

The area that today
is the Colorado Plateau

rose about one mile,

lifting the ancient sea floor
to where it is today-

seven thousand feet
above our present sea level.

So what do we see when we
look in the Grand Canyon?

When we have marine rocks now
exposed at seven thousand feet
above sea level

there is a big question here,

did the sea fall that far
or was the land uplifted that far?

Well clearly after the marine rocks
were deposited in the sea

that formed the rim of the Grand Canyon,

the area had to be uplifted.

The region of the Grand Canyon
was now high above sea level.

But at this point
it was an unbroken plain.

There was no canyon.

Making the canyon took another force
of nature- erosion.

Even as the land rose up,

a river flowed across the plain,
and began to cut down through the rock

Here we have a colourful layer cake,

which represents the rock formations
on the Colorado Plateau
in the Grand Canyon region

and the river itself
is represented by this knife.

Now as the Colorado Plateau
is uplifted

the river chisels its way down through
and actually makes a cut,

which is... I made a canyon.

70 million years ago

water and snowmelt flowed
from the Mogollan highlands

onto the surface
of the future Colorado Plateau.

They began slowly cutting
into the plateau area.

Ron Blakey demonstrates
how flowing water

can cut through the layers
of sedimentary rock to make a canyon.

When I cut a hole
in the side of the tub

we are going to see the sediment
is going to be eroded.

Let's see if this works.

There you can see
the erosion taking place.

As I lower the base level

by cutting a part of the plastic tub

you can see the water coming down
through the sediment and exposing it.

So if erosion cut through the rock

the next part of the puzzle
is to find the ancient river
that created the canyon.

Some of the old riverbeds
are still visible.

But they pose more questions
than the answer.

Richard Young Professor of geology at
the State University of New York at Geneseo

has been trying to solve the riddle
of the old river beds
since he was a grad student.

Young pieces together
the history of rivers

by looking at the shape and composition
of rocks found on river beds.

The modern Colorado River flows
from the Rocky Mountains in the East

to the Gulf of California
in the Southwest.

But as Young investigated
the ancient canyons

he found that something
just didn't add up.

It was a shock for a student
who just is getting started

and you want to believe
what your professors are telling you,

but everything you see
out in the field says that something
very different is happening.

To us, these look like big pebbles.

To geologists they're a missing link.

We see two things,
we see how round they are,

which indicates how far they have come

and secondly the rock types
are completely foreign to this area

and they come from at least
a hundred miles away from here.

The old stream pebbles are not native
to the region where Young found them.

They came from around 100 miles
southwest of the plateau.

The old river
must have transported the pebbles

from central Arizona
north and west to the Plateau region.

The orientation of the pebbles
in the river bed

shows the direction of the water flow.

Rivers cause pebbles to tumble
in the river channels.

They move until they reach this position
with the current flowing this way.

That's a stable position,
just like the shingles on a roof.

And that tells us that the river
was flowing in that direction.

As the ancient pebbles settled
on top of each other-

they left a lasting record
of how the river flowed.

This was strong evidence that
the rivers had to have flowed northeast-

the opposite direction to today.

But not only did the water
flow in the opposite direction,

it also in a different canyon
4 miles south of western Grand Canyon.

The old channel is now empty.

What happened?

Deep within the earth's core,

powerful forces
were about to shatter the surface

of what will become the Grand Canyon.

About 20 million years ago

the Oceanic Plate began moving north
relative to the North American Plate.

Heat built up under the Mogollan
Highlands south west of the Canyon.

The earth's crust began stretching.

Over millions of years,
vast areas of land deformed and cracked,

sheared upward or snapped down.

The Mogollan Highlands
fell thousands of feet.

Huge basins appeared on low-lying land.

Today geologists call it
the Basin and Range Province.

Wayne Ranney uses dominoes to explain.

Once faulting begins
we tilt all the fault blocks
down on individual faults

and you can see the surface tilting back
in the Colorado Plateau edge.

Rock layers that were once horizontal
are now almost vertical.

The region tilted- and then collapsed.

Ancient history is written
in the orientation of every outcrop.

The collapse re-drew the topography
of the region.

Before, the highlands to the south

towered several thousand feet
over the Colorado Plateau.

After the collapse

the Basin and Range area
was almost half a mile lower.

It was a major piece
in the scientific puzzle.

The rivers may have changed direction
because the whole landscape changed

When the basin and Range
faulting occurred it dropped that area,

it made it actually lower
than the Colorado Plateau.

And that's the reason that the rivers
were able to change direction

and flow in the opposite direction
towards California.

Scientists think they have solved
the mystery of how the rivers reversed

But the river was still four miles away
from where the canyon is today.

These ancient rivers did carve canyons-

but not where today's canyon is,
and on nothing like the same scale.

Sometime after the collapse
a new river formed-

the Colorado River-

and it took a new course.

But when- and why?

The challenge was to find
the earliest sign of this river.

Surprisingly, a clue came
from outside the Grand Canyon.

In the Lower Colorado river

about 100 miles before the river
enters the Gulf of California

scientists discovered a tiny fossil.

Kristin McDougall, research geologist
with the US Geological Survey

has studied these fossils.

They are called Foraminifers.

Foraminifers are like specks of dust.

It's a microscopic seashell.

The Cretaceous
planktic foraminifers that we find

look like three golf balls
hooked together.

Foraminifers are tiny-

a hundred of them
could fit on a grain of salt-

but they could show when the river
began cutting the canyon.

The Foraminifers are not native
in the Lower Colorado River.

Their home was much further north.

The only way their fossil remains
could have been deposited in sediments
in the lower Colorado River

is when the river transported them down

They were originally deposited
in the Cretaceous shales

on the Colorado Plateau
north of the Grand Canyon.

And they were eroded

and brought down along
the modern course of the Colorado River

and re-deposited.

Dating the sediments where
the fossils were re-deposited
helps to solve the mystery.

The sediments seem to have formed
when the river took its present course-

and geologically speaking,

it happened just an eye-blink ago.

These Cretaceous fossils
indicate that the Colorado River
became a through-flowing river

by at least
four and a half million years ago.

That's a very exciting find.

Evidence indicates that
4.5 million years ago

the river flowed along its present course
from the northeast to the southwest.

Scientists think they solved the mystery
of the age of the river.

But the solution raised a new question.

They knew when the river had formed

but they were still not certain how.

Most rivers begin energetically
at their source.

They rip through the terrain downwards

eroding anything in their path.

Downstream, things seem calmer.

The water moves slower,
and the channel is wider.

But back near the source,

the river lengthens its channel upstream
as the rushing waters erode more rock.

They cut their channel headward.

One theory is that the Colorado River
got started this way.

This headward erosion usually
happens where the steepness
of a riverbed rises.

It gives the river more energy
to cut deeper into the rocks.

The steeper the gradient
the more rainwater channels into the river

and the faster it pulls down the slope

The river eats into soil and rock
at the top

and may also lengthens
its channel headward.

Could headward erosion
have been the mechanism

that made the Colorado River
head out across the plateau?

We know that the Colorado plateau
rose about a mile above sea level
70 million years ago

creating a steep slope towards
the present-day Gulf of California.

It's a neat explanation
but it's controversial.

The modern Colorado River
is only around 4 1/2 million years old.

And the plateau rose 65
and half million years earlier.

Perhaps there was another
more recent uplift

that would explain how the river
crossed the plateau.

Searching for clues

scientists discovered
a layer of rocks downstream
in the lower part of the region

called the Bouse formation.

These rocks are around
six million years old,

and some parts are nearly
2,000 feet above sea level.

When scientists took a closer look
and discovered marine fossils in the rock

they knew they were onto
something extraordinary.

There are three key fossils
that we find in the Bouse Formation,

the first is a planktic foraminifer

which is one of the ones that
floats on the surface of the water

and then there is a specimen
called ammonia

and it's a very shallow water foram.

And then there's a third kind
that lives much deeper in the ocean.

The fossils meant the rock layer
is likely to have formed in seawater.

For Dr. Ivo Lucchitta,

the fossils led to a new theory
of what had happened here.

He believes that when the Gulf
of California first opened up,

it extended about 100 miles
further north than it does today.

Dead marine organisms
sank to the sea bed

and became entombed
in the white sedimentary deposit-

the Bouse Formation.

Yet today, the fossils
are hundreds of feet above sea level.

That was the clue that
he had been searching for.

One day by looking at
the present distribution elevation
of remnants of the Bouse

it occurred to me that
the Bouse and the land with it

had been uplifted
as much as perhaps 1700 feet
in the last 5 million years.

He believes that this area was uplifted
to its current elevation

after the fossils were deposited
around 6 million years ago.

And this second uplift
created an ideal scenario
for headward erosion.

By uplifting the plateau

you basically steepen
the gradient of the river
as it emptied into the Gulf

and therefore allowed them
to erode more rapidly.

The trouble is, not everyone agrees.

The apparent existence of marine
fossils in the Bouse Formation

1000 feet above sea level

is not irrefutable evidence
that the area was uplifted.

Senior geologist John Spencer
from the Arizona Geological Survey

is not convinced
about the second uplift theory.

I just was uneasy with the idea
that the Earth would just go
up and down like that,

I call it trampoline tectonics.

I didn't believe in trampoline tectonics

Spencer and his team
examine the Bouse rocks in the lab.

They are especially interested
in the levels of strontium isotopes.

Strontium isotopes found in these rocks

are irregular atoms undetectable
to conventional microscopes.

They come in heavier and lighter forms.

The relative concentration
of heavy and light forms varies.

It depends on the origin of the water.

River water usually has
a different strontium isotope
concentration than ocean water.

Depending on the concentration

scientists can often determine,

if sediment was formed
in freshwater or in the sea.

Spencer's graph of the isotope
concentration of the Bouse formation
confirms his suspicions.

The green dots represent
isotopic concentrations of sea water,

the blue dots represent
ratios typical for river water.

The red dots are his readings
from the Bouse formation.

They indicate freshwater.

When we got our first results
it was immediately clear that

we were seeing no marine signature
in any of the Bouse samples.

We were a little surprised.

We didn't expect that
every number would come out
looking like river water.

These results question
the validity of the second,
more recent uplift theory.

If the Bouse Formation
was never under the sea,

the uplift theory couldn't apply-

and headward erosion
along the lower Colorado
could not have happened.

Scientists had to look for another model

explaining how the river
cut across the plateau.

About 250 miles west
of Grand Canyon village

there is a canyon system
called the Lake Manix Basin.

Norman Meek Professor of Geography
at Cal State San Bernardino

believes this area may offer a clue
of how its bigger cousin got started.

The Lake Manix Basin has sometimes
been called the Grand Canyon
of the Mojave River,

because of the spectacular landscape
that's portrayed here,

a miniature version
of the Grand Canyon.

The site of Lake Manix Basin
is connected to Silver Soda Lake
via a canyon.

Meek wondered if
the formation of this canyon

could throw light on the formation
of the Grand Canyon.

First he examined
the site of Lake Manix.

Lake Manix is an extinct desert lake.

It used to stretch over an area
of more than 90 square miles.

Yet, many thousands of years ago
the lake disappeared.

Meek wanted to find out
when and why the lake drained.

At the edge of lake Manix

he found sediments
of ancient shorelines from the old lake

In the deposits
he found freshwater shells.

He took them to a radiocarbon dating lab
to find out their age.

Radio Carbon is an isotope
that occurs in all living creatures.

Its half life is almost 6000 years,

which means after around 6000 years
half of the original amount is gone.

By measuring how much radio carbon
is left in the shells

scientists can determine their age.

Meek found that the shellfish
in the Manix basin

were alive 19,000 years ago.

But after that they died.

At that point Lake Manix emptied.

When he looked at Silver Soda Lake

he found that it existed
from around the time
when Lake Manix emptied.

Could these two lakes be connected?

Meek suggested the canyon here
was cut by a mechanism called spill over

He theorized that 19,000 years ago

heavy rainfall or snowmelts
filled up the lake

until finally the water
spilled over the rim.

The lake drained dramatically.

Over a few thousand years

it cut down through the rocks
carved a canyon

and then created Silver Soda Lake.

It's just like a reservoir breaking,

there is a lot of energy,

that energy rips away
the sediments and the bedrock
that make up the canyon

and you get a through-flowing river

Scientists speculated

that if spill over explained how
a canyon formed in the Mojave desert,

it could also explain
how the Grand Canyon formed
just 250 miles to the east.

Now they just had to find the lake.

Today there is no lake-

but there are 200 feet
of green layered deposits-

remnants of an ancient lake
called Lake Bidahochi.

And so this green layer
right here reflects the idea

that Lake Bidahochi was in existence
east of the Grand Canyon
between 16 and 6 million years ago.

Over 10 million years

a lake deposited fine-grained sediments
like silt, clay and sand
mixed with grey volcanic ash.

The deposits indicate
the existence of a lake-

but they don't show how the lake
overspilled and carved the Canyon.

Jon Douglass, Geography professor
at Paradise Valley Community College in Arizona,

wanted an effective way to test the theory

He built a small scale model
of the Grand Canyon

to demonstrate
how the lake could have overflowed.

6 million years ago,
the canyon wasn't yet carved-

but Lake Bidahochi
was full to the point of overflow.

And then as the lake came in,
the lake filled.

It filled and filled,

higher and higher and higher
until it eventually spilled
across the lowest point;

across the Kaibab plateau.

And then water poured down
the other side;

those waterfalls
continued to retreat back

and the whole time
you're cutting Great Canyon.

Douglass suggests that Lake Bidahochi
drained and formed a stream.

The steep gradient of the riverbed caused
the stream to cut deep into the rock.

Over time the size
of the stream increased

and more and more water
poured out of the lake

which in turn cut deeper and deeper
into the rock.

But not all geologists agree.

They say there is no evidence of
there ever being a lake large enough
to carve the Grand Canyon.

So at present there is still
no definitive answer

as to how the river came into existence

What we do know

is that when it began flowing
around 4.5 million years ago,

it cut a one mile deep scar
in the surface.

To cut that whole canyon
in 5 million years is a considerable feat

How did the Colorado river
manage to cut the canyon.

There are bigger rivers
in the United States,

which haven't cut deep.

The biggest and longest river
in North America

is not the Colorado river
but the Mississippi.

It flows nearly 2500 miles
from its source in Minnesota

to its mouth at the Gulf of Mexico.

It carries 10 times more water
than the Colorado.

Yet, the Mississippi
did not carve a Grand Canyon.

Evidently, volume of water
is not the only factor.

Something else gave the Colorado River
its enormous cutting power.

The Colorado River begins
in the Rocky Mountains-

9000 feet above sea level.

On its course it drops ten feet
for every mile it flows.

The Mississippi on the other hand
begins its journey in Minnesota-

almost 1500 feet above sea level

dropping less than a foot per mile.

Although the Mississippi
has 10 times more water

it is a less erosive river,

because it has a lower gradient.

All rivers want to run downhill

It is the golden rule of gravity.

Two rivers can have
the same amount of water,

but for every one degree
of extra gradient,

the steeper river
gets a one percent increase in power.

My observations have been that
this river and even some of
its little tributary streams

have enough power that they cut though
any kind of rock like butter.

The speed and depth of cutting also
depends on the rock it is carving into.

Hard rock like granite is much tougher

so the river cuts a narrow gorge.

Soft rock like shale
is easy for water to cut through-

so the river carves a broad canyon.

With soft rock, as the sides erode away

the canyon widens.

Joel Pederson geomorphologist
at Utah State University

is on a quest to discover
how the river cut away the canyon walls

The information that we collect
from this what we are doing,

we're relating it
to the history of the river

and so what the river
is doing in the past,

as it's eroding
it is also stopping sometimes
and depositing sediment.

Pederson is interested in finding out
how fast the canyon erodes.

He uses a technique
called luminescence dating.

This uses light
to measure the age of a rock.

It works on sediments containing
minerals such as quartz or feldspar

that have been buried in the dark.

As sediment builds up
it is gradually sealed away from the sun

Pederson measures the amount of
luminescence a sample gives off
when exposed to light.

This method can date sediments

between a few hundred
to several hundred thousand years old.

We're collecting sediment
that hasn't yet seen light,

and the metal tube
prevents it from seeing light.

And we pull the tube out
and take it back to the laboratory.

In the laboratory

scientists expose the samples
of ancient river sediments

to specific wavelengths of light.

This energy excites
the electrons in the sediment-

some respond by releasing
their own energy, in the form of light-

and this minute signal is measured.

The greater the response from the
particles the longer they spent buried

So it's telling us that moment in time,
how many years ago it was,

that the river actually
deposited that sediment

and then buried it under more sediment
so it couldn't see light any more.

When Pederson measured the incision rates
along the whole length of the river

he found something unexpected.

179 miles downstream
the canyon appeared less deep.

Something changed and
lessened the river's cutting power.

Could it be that the river
lost its power due to changes
beneath the land itself?

It was an intriguing puzzle
scientists were desperate to solve.

3 and a half million years ago

the Colorado plateau ruptured and
created a deep chasm across the canyon

It's called the Toroweap fault.

Tectonic activity along the fault
slowly lowered the land
of the plateau to the west.

And as the land fell away,

it weakened the cutting power
of the river flowing over it.

Karl Karlstrom explains
with a loaf of bread.

We'll imagine this loaf of bread
as a stack of rocks

that is going to be incised
by the river to be the Grand Canyon.

And we'll imagine this knife
as the Colorado River itself,

which over time can erode through even
the hardest rocks to form a canyon.

But many times there's a break
in the crust called fault.

And so if I incise the river
at the same time

that I am moving one block down,

and I think you can see this
if I turn it up like this,

and you can see that
on one side the canyon is quite deep

and on the other much less deep.

Scientists had their answer.

The river stayed the same

but the land
west of the Toroweap Fault sank lower

and so escaped
the full cutting force of the water.

The Colorado river
has cut a masterpiece of a canyon.

But water doesn't only destroy rock-

amazingly it can also create it.

Scientists are intrigued
by new rocks within the canyon
that are still growing.

The Colorado river
has been a great destroyer.

In the last 4.5 million years

it has excavated
over 800 cubic miles of rock.

It created a gorge so big

that all of the river water in the world

would fill the canyon
to just over a third.

But the river can also create rocks.

At certain points in the canyon

scientists have discovered
new rocks forming today.

Laura Crossey, Professor
at the University of New Mexico

is an expert on these rocks...
the youngest in the canyon.

The big story of Grand Canyon
is the carving of this beautiful place,

there are other processes such as
travertine that cause changes to occur

and the younger rocks
to form inside that very canyon.

These travertines are special

because they are created from water
saturated in carbon dioxide

and they are actually formed
at the bottom of the canyon itself.

The carbon dioxide
comes from deep inside the earth.

It leaks out to the surface.

Here, it dissolves in water,

acidifying it and giving it the power
to dissolve limestone.

The carbon dioxide
escapes from the water,

forming bubbles like fizzy soda.

As the gas escapes,
it leaves behind calcium carbonate,

which coats objects in its path.

In some places
it forms stone waterfalls.

In others it covers sticks and twigs.

So these are just small examples
of the coatings of travertine

that form on every stick and twig and
cobble that comes down the stream-bed

It accumulates into
vast piles of sediment

which are instantly formed into rock,
the youngest rocks in the Grand Canyon.

Every drop in the river has in some ways
shaped the landscape here.

But water does far more than
destroying rocks and building them.

Without the river-

the current plant and animal life
would struggle to survive.

And it was the river
which attracted early settlers here.

When the ancestors of the Hualapai
arrived in the Grand Canyon
about seven hundred years ago

they celebrated the Colorado River
as an important source for life.

And it remains that today.

The river's all source of life out here.

The canyon to me personally
is something that our ancestors,
they fought hard to retain.

Because they knew the importance of it.

Our wish is to maintain it
in its natural state or its beauty.

Modern visitors of the canyon
are mesmerized

as the first Native Americans would
have been several hundred years ago.

It's one of the natural wonders
of the world.

A monument to the age-old,
colossal forces that created it.

1.7 billion years ago it began.

Layers of flat-lying,
stratified sediments

build up high canyon walls.

Uplift elevates the plateau
and rivers cut deep into the rocks.

And the climate today is arid.

Nothing is lost.

Everything is visible.

It is difficult to find a canyon
as impressive as this one:

Possibly in South-eastern Tibet,

home of the biggest, longest
and deepest canyon.

The Yarlung Tsangpo Great Canyon.

The climate is different and the area
is covered with dense vegetation.

The Euphrates is a very large river
running through arid Iraq,

a climate not dissimilar to Arizona.

But this area never uplifted
and formed a canyon.

The Grand Canyon might not be
the biggest and longest canyon on earth

But the powerful forces
that created it and made it unique

are still hard at work.

Nobody can predict
how much uplift there will be.

But if the river stays on course

then the future
of the Grand Canyon looks good.

And if you think this is grand-
you ain't seen nothing, yet.

Stick around for another
million years or two

and the canyon
might be even deeper with walls
just as sheer as they are today.

The Grand Canyon
is just getting grander.

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