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>> Earth--a unique planet,

restless and dynamic.

Continents shift and clash.

Volcanoes erupt.

Glaciers grow and recede,

titanic forces that are

constantly at work, leaving a

trail of geological mysteries

behind.

This episode journeys back

through time to explore how ice

has shaped modern North America.

Geologists discover how

America's temperatures plunged

to an average of 26 degrees

Fahrenheit all year round, how a

wall of ice 8 times the height

of the Empire State building

covered much of North America,

and how ice created some of the

country's most stunning

geological wonders.

A deep-frozen episode in the

continuing drama of...

"How the Earth Was Made." S02x12 Americas Ice Age Original Air Date on February 16, 2010

-- Sync, corrected by elderman -- -- for www.MY-SUBS.com --

One awesome physical force has

had more impact than any other

on the shaping of modern North

America--

the dynamic, unstoppable power

of ice.

Over millions of years, ice

sheets a mile or more thick have

decapitated the continent's

mountains and dammed and

diverted its rivers.

But the full extent of how ice

has carved and sculpted the

landscape of the U.S. is only

now becoming clear as scientists

investigate the overwhelming

geological impact of America's

Ice Age.

U.S. for centuries, America's early

geologists were puzzled by

mysterious marks etched into the

bedrock of much of North America

and by lonely mounds of rock

randomly scattered across the

land.

[thunder]

Many believed such features were

evidence of a massive flood in

the long-distant past, but then

in 1847, a newly appointed

Harvard university professor

came up with a radical new idea.

Geologist Louis Agassiz compared

North America's landscape and

rocks with the geology of

mountain glaciers in his native

Switzerland, and he built on

theories he had developed in the

Swiss Alps a decade earlier to

declare that North America had

once been buried deep under ice.

Agassiz's work at Harvard made

him world-famous in his day, but

the final proof of his Ice Age

theory had to wait until the

1950s, when new evidence

came from the seabed of the

Atlantic Ocean.

That evidence is still stored to

this day in this refrigerated

laboratory at Miami University.

These thousands of plastic tubes

offer scientists a unique window

to look back at what the weather

was like on the ancient Earth.

>> These records which you see

in this room here basically are

the primary information we have

now about the climate changes we

have had over the last two

million years, so these really

were the starting points that

opened people's eyes about

changes which occurred during

glacial periods.

>> The mud cores were collected

by oceanographer Cesare

Emiliani.

The deeper he drilled, the

further back in time he went and

the older the sample he pulled

to the surface.

>> These are cores of deep-sea

mud, and within the mud are

small organisms which record the

temperature and the salinity and

the other conditions which were

prevalent when that organism

lived.

>> Those tiny undersea creatures

are called foraminifera.

Their chemical makeup varies

depending on the temperature of

the water in which they grow, so

the sea bugs in different layers

of mud act as tiny thermometers

recording how hot or cold the

Earth was at different times in

its past.

They reveal that just over two

million years ago, the average

annual temperature across the

lower 48 states was around 56

degrees Fahrenheit, about 3

degrees warmer than it is today.

Then the temperature regularly

started crashing below zero and

stayed there for month after

month.

Huge changes happened with what

in geological terms was

astonishing speed.

Within 10,000 years, the

year-round average temperature

bottomed out at just 26 degrees

Fahrenheit, the same as the

average winter temperature

in Chicago.

[car horns honk]

Even today, scientists are

uncertain what caused the

temperature to drop so quickly.

Variations in the Earth's orbit,

a change in the tilt of its

axis, and even the creation of

the Himalayan Mountain range are

all prime suspects, but one

thing is certain.

With subzero temperatures all

year round, snow never melted.

A major storm can drop more than

40 million tons of snow.

The ever-increasing weight

compacted down into thick layers

of solid ice.

America's Ice Age had begun.

An important clue to what

happened next lays in a rock

quarry just outside the town of

Champaign, Illinois.

In quarries like this, rocks

normally hidden deep underground

are exposed by commercial

blasting.

That gives geologists the chance

to examine rocks they could

never normally see.

>> This rock in the sandy,

cobbly bank is a very important

and significant piece of

evidence for the history of

North America during the last

several hundred thousand years.

It's what we call an erratic.

It's a rock that doesn't belong

here.

This rock traveled several

hundred miles to get to this

place.

>> In fact, this is a type of

granite usually found in Canada.

Somehow, it has traveled to

Illinois, but it's not unique.

All over the northern states,

rocks of all shapes and sizes

have been dumped in places they

don't belong.

This one, the size of an

elevator, is in Central Park,

New York. It was originally from

New Jersey. And this one, the

size of an automobile and

weighing just as much, comes

from 500 miles north of Ontario.

Scientists have figured out just

how such huge rocks must have

been transported over such long

distances.

The ice sheets which built up

two million years ago began to

move, flowing as huge glaciers

across the northern U.S.

>> Some of the very large rocks

can be literally frozen on and

plucked off from the rock where

they came from and transported

right in the glacier and moved

that distance of hundreds of

miles in the glacier like a

conveyor belt out to where we

finally find it on the landscape

or in an outcrop like this.

>> The investigators' next

challenge is finding out just

how far the ice flowed, and for

that task, they are taking to

the air.

In the early-morning light,

Brown spots a mysterious, small

hill standing out from the flat

Illinois plain.

Stripped of its camouflage layer

of trees, the shape of the hill

tells Brown the secrets of its

creation.

>> This gently rolling landscape

extends for about 400 miles.

We look at the landforms and how

they're shaped, and so we can

use that to unravel the history

of the Ice Age.

>> The landform Brown is

studying is a mound of rubble

that geologists call a moraine.

It is an accumulation of debris

that a glacier has plucked up

from the Earth, dragged along,

and dumped at the front edge.

This hill marks the spot where

the glacier finally stopped

flowing southward.

Geologists all over the U.S.

have recorded the positions of

other moraine hills, helping

them map out precisely how far

North America's ice sheets

spread.

Nearly 2/3 of the North American

continent was buried under ice.

So far, scientists studying

America's Ice Age have

discovered...

Tiny, temperature-recording sea

bugs in ocean sediment showing

the U.S. chilled down 27 degrees

at the start of the Ice Age, and

moraine hills of rock and debris

mapping out where the ice sheets

halted.

But the frozen chaos did not

stop there. The challenge now

facing geologists is figuring

out how ice created some of

modern North America's most

famous features.

>> Two million years ago,

temperatures fell, and massive

ice sheets spread out as

glaciers across much of North

America.

Geologists set out to discover

what the moving ice did to the

underlying land.

Everywhere the ice had flowed,

investigators discovered the

same puzzling feature--lines of

stones all laid out in the same

particular way.

>> This is a really good example

of a pavement of stones.

This concentration of small

rocks and cobbles that are

collected here in a line is just

one stone or two stones thick.

>> Scientists realized that the

stone pavements must have been

laid down at the base of a

glacier, and even the toughest

rocks had scratches and grooves

carved into their surface.

>> A glacier carries along other

fragments of rock, and as it's

doing so, it scratches,

polishes, and creates grooves in

the rock called striations.

>> Those scratches offered vital

clues to help uncover the

history of how the Ice Age

changed America.

>> We can measure their

orientation, and they can tell

us something about the direction

of ice flow. So I'm aligning my

compass parallel to the

striations on this rock.

The compass tells me that the

ice is flowing from about the

northeast, from this direction

to this direction.

>> But other scratches on rocks

found all over the northern

parts of the U.S. run in

puzzlingly different directions.

These ice-scraped rocks in New

York's Central Park show

scratches made by a glacier that

arrived from the northwest.

There's only one explanation for

the different ways in which the

ice appears to have moved.

The scratches were not all made

by a single ice sheet, as first

thought, but by many different

ones.

>> This phenomenon of advance

and retreat and changing of that

landscape happened many times,

Not just once, but many times.

>> Everywhere the ice flowed, it

marked the underlying rocks.

That's given investigators

plenty of clues to help

establish a pattern of ice

movements, but understanding the

full picture involves a lot of

geological detective work.

>> This cycle of glaciation, of

advance and retreat, leaves an

incredibly complicated record

for us to solve.

We only see fragments of this

puzzle in any place we look at,

like in a quarry, and so it's a

great challenge for us to figure

out how each of these fragments

fit together.

The ice changed the existing

conditions on the landscape.

Those changes include erosion of

glacial debris in a way that

changes the whole way these

areas look.

>> Grinding over the landscape

at speeds of around two feet per

day, the massive glaciers

diverted the course of ancient

rivers. Even the mighty

Mississippi was no match for the

ice.

>> It moved the position of the

Mississippi River.

The Mississippi River used to

flow through the middle of

Illinois.

>> A glacier advanced across the

state and created an ice dam

across the course of the old

river.

A huge lake grew at the edge of

the ice, eventually overspilled,

and cut a new river channel 80

miles to the west.

The same course that it follows

to this day. And when the ice

sheets melted away, their impact

on North America was almost as

great.

They produced immense floods of

water which all had to drain

away somewhere.

>> It formed a completely new

landscape with new river

valleys, new channels, new

places where rivers flow,

completely rearranging the

character of the existing

landscape.

>> Where rocks were soft or

weakened by faults, the glaciers

had carved out huge basins in

the landscape.

When the floods came, these

depressions rapidly filled up

with water.

>> Every natural lake here in

Indiana, illinois, wisconsin

were all created by glaciers.

>> The biggest ice-scoured

basins became what we now call

the Great Lakes.

These water-filled craters in

the North American landscape are

nearly 5,500 cubic miles

in size.

The water they hold could drown

the whole of New York state to a

depth of more than 600 feet.

But even that is just a tiny

fraction of the total flood

unleashed as the retreating ice

poured out nearly 39,000 cubic

miles of water.

That's over 100 times as much

water as is found today in every

single river on Earth.

The flood rushed down the

Niagara escarpment at the rate

of 42 million gallons a minute,

1 1/2 olympic-sized swimming

pools every second.

And that cut a gorge 7 miles

long and 180 feet deep through

solid rock.

The Ice Age had created one of

the modern wonders of the

world--Niagara Falls.

The investigators' next

challenge was figuring out why

the ice advanced and retreated

so often.

It wasn't until the mid 1960s

that the first real clues were

discovered.

The U.S. Military was building

bases in some of the Earth's

most remote locations.

>> This is an ideal Arctic

laboratory, permanently frozen

under a polar ice cap which

covers all but a few coastal

areas of the island.

>> Geologists realized that the

cores of ice being extracted by

hollow drills held a unique

historical record.

Those cores and many others

extracted since are housed in a

laboratory in Denver, Colorado.

>> We're in the Fort Knox of

Paleo climate.

What you see in these tubes is

golden in terms of what we know

about climate and what we've

learned about climate over the

last 50 years.

>> These tubes contain

3-foot-long plugs of ice, each

dug out from layer after layer

of compacted snow, but it is

what is trapped inside the ice

that most fascinates the

scientists.

As each year's snow falls onto

the last, it builds up in

loose-packed layers that trap

air between the snowflakes.

>> Ice cores are the only

archive we have, really good

archive we have, of past

atmosphere.

In an ice core, you can see tiny

bubbles, and those bubbles are

air, unadulterated air from as

much as 100,000 to a million

years ago.

>> The deeper the bubble, the

older the air.

>> It contains not only a

temperature signal, but it

contains dust signals that tell

us about atmospheric

circulation.

It contains a record of the

atmosphere, specifically the

greenhouse gases.

>> Each ice layer corresponds

with a precise time in Earth's

history when its snow first

fell, so by analyzing the

bubbles from any one layer,

scientists can figure out what

Earth's atmosphere was like at

any point in the past.

>> Imagine you're writing a book

and every year, you add a page

to that book and that page

stacks up and stacks up and

stacks up.

The climate scientists come

along later and read that page

by page by page as we go down

through an ice sheet.

>> Reading this frozen record of

Earth's climate has revealed

that the growth and retreat of

America's ice followed a

distinct pattern.

>> Over the last million years

or so, we see fairly regular

pacing of major, major

glaciations, roughly one every

100,000 years.

>> Some theories suggest those

colder spells coincide with

variations in Earth's orbit

around the sun, but that's not

the only thing the ice cores

revealed.

The cores that White has been

studying suggest that the longer

the Ice Age went on, the worse

it became.

>> Somewhere around 400,000

years ago, we went from a period

that had, eh, lesser

glaciations, if you will, to

ones that were very, very big.

>> So far, the geology

detectives he uncovered

evidence of how America's

ever-worsening Ice Age created

some of the continent's most

significant features.

Scratched rocks show how the

glaciers ground their way across

North America, and ice cores

record a 100,000-year cycle of

freeze and thaw and temperatures

that grew ever-colder as the ice

Age continued.

But new clues suggest that the

awesome impact of America's Ice

Age didn't stop there.

The investigation next explores

how ice distorted the shape of

the Earth and transformed the

coastal outline of the entire

North American continent.

>> Two million years ago, the

average annual temperature fell

dramatically.

Moving glaciers spread sheets of

solid ice as far south as

Illinois.

Investigators set out to

discover how thick those ice

sheets were and what the weight

of all that ice did to North

America.

Their first clue came in New

York state on Bear Mountain.

>> No one knows for sure how

thick the ice sheet was that

came from the northwest, but

right now, we're standing on the

top of Bear Mountain, about

1,280 feet above sea level.

What we're looking at here are a

series of chatter marks.

These are features of glacial

erosion.

They're produced by large blocks

of solid rock embedded in the

base of a very thick glacier.

Those boulders impinged on this

bedrock surface, plucking pieces

of rock off as the glacial ice

moved over Bear Mountain.

>> Charles Merguerian's

mountaintop discovery shows how

thick the advancing ice must

have been.

>> The glacial ice sheet could

care less about this large

mountain.

There's no question that the

glacial ice sheet traveled over

Bear Mountain as if it weren't

even there, and most people

think that this glacial ice

sheet was about a mile thick

or more.

>> The marks are clear evidence

that the New York ice sheet must

have towered about 4 times

higher than the Empire State

Building.

Figures like this have enabled

Merguerian to estimate the total

amount of ice that buried North

America.

It's a staggering 17 million

cubic miles of ice.

>> Imagine this block of ice--

It's about 6 inches thick--

being the ice sheet

that covered North America

during the last glaciation.

You'd need several billion of

these, maybe 100 billion.

It's a number almost too big to

imagine.

>> This block of ice weighs 27

pounds and is just half a cubic

foot in size, but there were 17

million cubic miles of ice

covering America.

When scientists calculated the

total weight of the ice, it was

an almost incomprehensibly large

figure--68,000 trillion tons.

Unsurprisingly, such a vast

weight of ice did not just

affect America.

It distorted the shape of

the planet.

>> I've got a beach ball here

that has a depiction of the

whole Earth and every continent

on it, and right here is the

outline of North America. And

during the Ice Age, snow started

to accumulate in Canada, and as

that ice thickened, it started

to flow from the centers of snow

accumulation southward into

North America, reaching its

maximum extent right here in

Illinois. And when it did that,

this mass of ice depressed the

continent.

>> Earth's solid crust sits on

top of a layer that scientists

call the mantle, semimolten rock

which behaves a little like hot,

sticky plastic.

The weight of the vast plains of

ice pushed down inland areas and

simultaneously made parts of the

coastline bulge up from the sea.

But investigators have also

found evidence of other ways

that the ice altered the outline

of America's coasts, the borders

with the sea that define the

continent we see today.

A vital clue came in downtown

Miami in the unlikely setting of

a municipal courthouse.

>> We're here in front of this

impressive building built in the

early 1900s because of the

materials used to face its

surface.

These stones are constructed of

fossilized coral reefs, and if

you know what you're looking at,

it can actually tell you quite a

bit about Florida's past and

maybe its future.

>> The coral stone is made from

the hard calcium carbonate

skeletons of tiny sea creatures,

animals that only grow in very

shallow water.

But this courthouse stone was

quarried out of an ancient coral

reef that now lies a mile from

the present-day ocean and way

above sea level.

>> I'm standing here about 5 or

6 feet above sea level and

walking alongside this rock

face, which is about 6 feet

tall.

The interesting thing about this

rock face is, it's actually

composed of fossilized corals,

and the fact that we're standing

here today amongst these fossil

corals tells us that in the

past, we would've been under 10

or 15 feet of water right now.

>> The coral stones have been

dated to around 130,000 years

ago, which means the sea level

around Miami must then have been

far higher than today.

As experts try to figure out why

the sea level was so high then,

new evidence emerged about

Florida's coral reefs, and the

mystery deepened even further.

Divers off the coast of Miami

found a coral reef now submerged

450 feet under the water.

These corals grew just 25,000

years ago, and because a reef

like this only forms in shallow

water, the scientists realized

that the sea level back then

must have been far lower than it

is today. And that means the

coastline would have been in a

completely different location.

>> Right now, we're about two

miles offshore, Fort Lauderdale,

on the edge of the gulf stream,

But 20,000 to 25,000 years ago

at the time of sea level low

extent, we would be sitting

right next to a beach here.

We'd be looking where we see

today the ocean and the

high-rises in the back.

We'd be looking towards a sandy

beach in front of a gently

rolling hillside.

>> Investigators studying the

coral records figured out that

the up-and-down sea levels would

repeatedly have altered the

entire shape of America.

>> If you look at the outline of

North America, the outline that

I learned to draw in elementary

school, if we were living years

ago, I would draw Florida

differently.

>> 25,000 years ago when sea

levels were low, Florida was

triple the size it is today

because more land was out of

the water.

Geologists realized that the

changes in sea level around the

Coast were directly related to

the different levels of ice

on land.

That discovery was the key to

understanding what the Ice Age

had done.

Water evaporated from the oceans

and condensed in the atmosphere

to form snow, but in the colder

times, that snow built up as ice

sheets on the land.

And with so much of the world's

total water supply locked up as

ice, the oceans simply ran short

water, and the sea levels

fell.

>> When the Earth is cold,

there's more ice on the land,

and sea level is lower because

of that.

When the Earth is warm, there's

less ice on the land, and sea

level is higher, and that makes

sense because that ice, when it

melts off the land, has got to

go in the ocean.

>> The story of how ice sculpted

modern North America is drawing

closer to the present day.

Chatter marks in upstate New

York reveal that ice sheets grew

a mile or more thick, and

ancient reefs off the coast of

Florida prove that water levels

in the ocean changed again and

again.

Ice had shaped the continent.

Now scientists discovered that

it had also uncovered a bridge

to other lands and shaped the

future of mankind.

>> North America's Ice Age began

Two million years ago.

As the Earth moved around the

Sun, America's temperatures

fluctuated.

130,000 years ago, it enjoyed a

warm, tropical climate.

Then 25,000 years ago, it grew

colder than ever.

Glaciers covered 2/3 of North

America with ice up to a mile

deep.

Now the investigation examines

how these freezing temperatures

altered the course of human

history in North America.

At Paisley Caves in Oregon,

scientists are unearthing vital

clues that humans left behind.

>> Here's your coprolite.

>> Oh, beautiful specimen.

>> The evidence is coprolite,

fossilized human excrement.

>> This site is the location of

the find of the oldest human

remains that have been directly

dated here in the United States

with DNA in them that indicates

people from probably Siberia

came here at least 14,300 years

ago.

>> Today North America is

separated from Siberia by open

water, but the presence of men

from Siberia on American soil is

Compelling evidence that around

14,000 years ago, a land bridge

Must have linked the two

continents.

Geologists know that the amount

of water locked up as ice on

land meant that there was less

water in the oceans.

More importantly for the future

of the U.S., the retreating

Pacific and Arctic Oceans left

the sea bed between America and

Siberia high and dry.

But a doubt still remains.

The men who lived in Paisley

Caves 14,000 years ago could

conceivably have reached America

by sea.

But that theory is diminished by

the discovery of this artifact.

This is a tool that has been

carved out of a bone belonging

to a Camelops, more commonly

called the western camel.

>> [bellows]

>> You can see the curvature of

the bone here.

This is the outside of the bone.

It would have continued on in

quite a large arch all the way

around.

What they have done is to saw

this piece out, and then they

have sawn in teeth right here

running all the way across.

>> The animal that died here was

the ancient ancestor to the

two-humped camel now found in

Asia.

Few people know it evolved in

the U.S.

>> Camels have been here for

about 40 million years, so what

has been surprising to me is the

fact that people didn't know

that camels were here.

>> In fact, the earliest camel

fossils ever found were

discovered in South dakota and

predate finds elsewhere in the

world by millions of years.

The finds are clear evidence

that camels evolved in America

and once lived nowhere else on

the planet.

>> [bellows]

>> So camels, which couldn't

have migrated by sea, could only

have crossed into asia via a

land bridge.

But a mystery remains.

Fossil records show that camels

disappeared from North America

12,000 years ago.

Scientists want to know why.

>> There is no doubt that the

end of the last Ice Age, we saw

a substantial reduction in the

number of species here in the

Western hemisphere, so what

causes those things?

It's possible that weather

changed so dramatically so

quickly that they could not

adapt.

>> Back in Denver in the ice

Core lab, jim White is examining

the piece of evidence which

could confirm that the Ice Age

killed off the camels.

>> This is a really fascinating

piece of ice and one of the most

important pieces of ice that we

have in the collection.

This is the aha moment of

climate change.

>> The evidence is an ice core,

a frozen time capsule recording

the temperature of North America

12,000 years ago.

It shows that the U.S. suddenly

got even colder.

>> We've opened our book of

climate, and if we read the book

from today going back in time,

that's page 12,000. And imagine,

if you will, from this moment

back in time, we had 1,000 years

of cold.

>> It's evidence of the last

gasp of the Ice Age, another

rapid freezing of America.

>> These abrupt climate changes

can be a 10-degree-celsius

change in temperature in 50

years or less, temperature

changes of a degree celsius per

year sustained over several

years.

>> That is a 16-degree-farenheit

fall in temperature.

>> You're looking at going from

a Miami-to-Montreal kind of

change in climate.

>> The big chill occurred

quickly, from mild to freezing

cold in less than a century, but

it lasted nearly 1,600 years.

It was a deep freeze so great

that it proved too much for

North America's camels,

mammoths, and other large

animals.

>> We're on a roller coaster of

climate change that must have

been extremely stressful for the

plants and animals that were

living during that time.

>> This final deadly big chill

of the Ice Age ended 10,000

years ago.

It was the last time ice

advanced across the continent.

Scientists investigating the

legacy of the advance of

America's ice sheets have

discovered coprolite--strong

evidence that glaciers caused

the sea level to drop, exposing

a land bridge that linked

Siberia to North America--

And this ice core which records

the final deadly deep freeze of

the Ice Age.

Next, scientists investigate how

the end of the big chill marks

the beginning of the warm period

America enjoys today and how

that may spell disaster for some

of her greatest cities.

>> Deep freezes over two million

years have seen giant ice sheets

rampaging across North America.

That ice crushed, scarred, and

flooded the land to create some

of America's most recognizable

geological features.

The Great Lakes, the mighty

Mississippi, and Niagara Falls

were all created by the action

of advancing and then

retreating ice.

For the last 10,000 years, the

Earth has experienced warmer and

warmer temperatures, and the

passing of its ice has impacted

the North American continent in

other equally significant ways.

>> The ice changed the existing

conditions on the landscape.

It's changed the way we live in

this environment.

We get our drinking water from

these materials.

Our rich agricultural soils are

a part of that legacy.

The most productive farmland in

the world is right here in North

America.

From an economic standpoint

alone, the billions of dollars

worth of productivity of

agriculture are a direct result

of the Ice Age.

>> During its Ice Age, vast

areas of North America were

covered by glaciers.

Today they cover just 29,000

square miles.

America's dwindling ice is a

precious resource.

Each summer in Washington state

alone, melting glaciers provide

470 billion gallons of drinking

water, but it comes at a price.

The melting ice has pushed up

sea levels by a foot each

century, and that rate is

increasing.

And the scientists who study

life in the oceans are seeing

firsthand the impact it is

having.

>> The coral animal itself

builds his city very much like

we humans do.

The coral had to move as sea

level changed.

As sea level went down, it had

to follow that sea level down.

As sea level came up, it had to

follow that sea level up.

The question we have to ask

ourselves as humans--as sea

level changes, will our cities

have to adapt just like the

coral reef?

>> Currently, about 10% of the

world's total land surface,

approximately 6 million square

miles, is covered by ice sheets,

but this ice is melting fast.

If present warming trends

continue, all the glaciers in

Montana's Glacier National Park

will be gone by 2030.

Today North America's longest

glacier is the Bering Glacier in

Alaska.

It is 130 miles long and 10

miles wide with solid ice up to

half a mile deep.

But over the past 20 years, that

ice has become thinner, as much

as 600 feet thinner at the point

where the glacier reaches the

sea.

So much ice is now melting that

every year, it pours out at

least 7 cubic miles of

floodwater, twice as much water

as there is in the entire length

of the Colorado River.

Over the same time, Arctic Sea

Ice has shrunk by 250 million

acres, an area the size of

Texas and New Mexico combined.

If Earth's ice continues to melt

at this rate, it will once again

redraw the map of America's

coastlines.

This is what Florida looked like

in 1995.

Here is what it could look like

in 100 years, a loss of more

than 4 million acres where 1.5

million people lived in 2010.

And at the ocean's present rate

of rise, this is the coast of

Florida as it might look at the

end of the next century, in the

year 2200.

This is Miami, or what's left

of it.

By then, the city's Ocean Drive

might be a drive under the

Ocean, a return to the sea

levels of 130,000 years ago.

The geologists investigating

America's Ice Age have found

evidence that the power of ice

has been crucial in helping to

create modern North America.

Bugs in sea mud acted as tiny

thermometers, recording the

start of America's Ice Age.

Moraine hills proved that moving

glaciers flowed far enough to

cover 2/3 of the continent

under ice.

Crescent-shaped marks on a

mountaintop in upstate New York

showed that the ice sheets grew

to be more than a mile thick,

and ancient coral reefs were

evidence that sea levels

repeatedly changed throughout

America's two-million-year-long

Ice Age.

The investigation has uncovered

the full picture of how ice

sculpted the geology of the

U.S., but that process is not

yet finished.

As North America's ice melts

back, it uncovers a landscape

that's been buried for

thousands, sometimes millions,

of years.

Living proof that the Earth is

is never at rest.

-- Sync, corrected by elderman -- -- for www.MY-SUBS.com --