How the Earth Was Made (2009) s02e12 Episode Script

212 - America's Ice Age

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.
" America's Ice Age 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 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 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, 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 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 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 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 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 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.
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.
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 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 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 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 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.