NatGeo_Birth of America
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00:00North America.
00:09Towering mountains crown a landscape of astonishing diversity, home to over 500 million people.
00:18Its great cities are as individual as the landscape around them.
00:23But how was North America made?
00:26What forces created its features?
00:29What gave it its distinctive shape?
00:32This is the extraordinary story of the forging of Earth's oldest continent, the birth of
00:39North America.
00:58The Earth from space.
01:01A unique perspective.
01:03It helps us understand the forces that continue to shape our world.
01:10Earth has seven continents.
01:14This is the story of one of them.
01:17North America takes up 16% of our planet's total landmass, more than Europe and the Middle
01:24East combined.
01:29It is home to Yellowstone National Park, the Grand Canyon, Mount St. Helens, and the
01:36largest group of freshwater lakes on the planet, the Great Lakes.
01:42It's also home to the world's oldest rocks.
01:49Rocks that have helped to reveal our planet's dramatic history and unravel the secrets of
01:54the birth of America.
01:59The cool thing about this planet is that with the eyeballs of somebody who's thinking about
02:03rocks, you can look at a layer of rock and say, hey, that's not a layer of rock.
02:07That's an ancient swamp, or that's an ancient sand dune.
02:14To decipher North America's past, geologists must first find its origin.
02:22In Canada's Northwest Territories, some 200 miles from the nearest city, this rock outcrop
02:29near the Acasta River is the first chapter in the story of the birth of a continent.
02:38Dr. Wouter Bleeker is working here to pinpoint just how old America really is.
02:46Here at Acasta, we find the oldest continental crust, actual rocks you can stand on.
02:52So we basically see the initiation of continental growth here.
02:57This is where it starts.
03:00The birth of America is set in motion 4.6 billion years ago, as our sun explodes into
03:07life.
03:09Mass and debris hurtle around it, and eventually eight planets emerge from the vortex.
03:20At more than 12,000 degrees Fahrenheit, one of these newly formed planets appears nothing
03:26more than a ball of boiling lava.
03:30Earth is a primeval hell.
03:36The heaviest elements, like nickel and iron, sink down toward the center of the Earth and
03:41form its core.
03:44The lighter elements, including oxygen and silicon, rise toward the surface and form
03:51oceans of molten rock.
03:56Slowly the Earth's surface cools.
03:59The lava solidifies and forms patches of crust.
04:05As this crust grows, it gets heavy and sinks back down into the mantle.
04:13Deep below the surface, it remelts, and the lighter elements rise up again, eventually
04:19forming granitic lava.
04:23Granite is less dense than other rocks in the mantle.
04:26It floats on the surface.
04:28As it solidifies, it forms rafts of land.
04:36Think of it as the scum on a pot of soup.
04:39If you boil that soup long enough, that scum will nicely separate and float on top of the
04:47soup.
04:49And that is what continental crust is.
04:51It's basically the scum of the Earth.
04:56Here at Acasta, this scum is actually a granitic rock called tonalite.
05:03Tonalites are important because they are the first materials that actually make stable
05:09continental crust.
05:13All continents contain chunks of tonalites that date back over 500 million years.
05:20These form rafts of continental crust called cratons.
05:28North America is made up of at least six of them.
05:33For researchers to date the birth of North America, they must find the earliest craton.
05:40And to do that, they have to date tonalite from all over the continent.
05:50It's a complex process.
05:54They look for microscopic evidence created as the rock was formed.
05:59Telltale mineral crystals, tough enough to survive over eons.
06:04One of the toughest minerals of them all is zircon.
06:10Zircon contains uranium-238, an unstable radioactive isotope.
06:17Scientists know that this isotope decays, gradually turning into lead.
06:22Importantly, they also know exactly how long this process takes.
06:29Imagine that the top half of this hourglass is uranium-238 and the bottom is lead.
06:35Over 4.46 billion years, half of the sand representing uranium will drop into the compartment
06:42representing lead.
06:44This uranium-238's rate of decay, it's half-life.
06:50By measuring the amount of lead and uranium isotopes in the zircons from the Acasta tonalite,
06:57scientists can pinpoint the rock's age and figure out how old this part of North America
07:02is.
07:05The tonalite found near the Acasta River in Canada's Northwest Territory is 4.03 billion
07:12years old.
07:14This is the oldest rock in the North American continent at this point in time, right here
07:20at Acasta, within the core of the Slave Craton.
07:24These tonalites predate most other rocks by billions of years.
07:29They are the oldest rocks ever discovered.
07:33The core of the Slave Craton in North America contains the oldest surviving landmass on
07:38Earth.
07:41The next challenge is to figure out what embryonic North America might have looked like.
07:50Professor Ron Blakey is an expert in continental mapping at the University of Northern Arizona.
07:58When the early continents formed, some four billion years ago, they were probably scattered
08:03about the surface of the Earth.
08:05But this far back, we would just be completely speculating on what the position of the continents
08:10would be.
08:15This is our planet today.
08:17Seven distinct continents, all surrounded by water.
08:23But take away the oceans, and we see that a hard outer shell, or crust, covers the Earth's
08:29surface.
08:32The oldest and thickest crusts form our continents.
08:36That's around 40% of Earth's skin.
08:39The rest is underwater, oceanic crust.
08:46Oceanic crust forms a thin layer at the top of the Earth's mantle, an 1,800 mile thick
08:51layer of superheated molten rock, magma.
08:57Heat escaping from the center of the Earth creates convection currents in the mantle.
09:03It's believed that this slow boiling motion breaks the crust up into pieces, called tectonic
09:09plates.
09:12In some places, magma from the mantle escapes through the gaps between plates.
09:19As it rises and solidifies, it forms new oceanic crust, and forces the plates apart.
09:27In other places, the mantle drags oceanic crust down, consuming it.
09:35As a result, the Earth's crust is constantly moving, traveling about 30 miles every million
09:41years.
09:45Ohio University professor Damien Nance specializes in plate tectonics.
09:52We create, if you like, a conveyor belt, and continents are carried by these conveyor belts,
09:58much like suitcases on an airport conveyor belt.
10:03Starting some 4 billion years ago, Earth's churning interior and a cooling of its surface
10:09creates and moves these rafts of land.
10:13Cratons collide and form continents.
10:16Some of these merge, forming supercontinents, Valbara, Rodinia, Laurusia, and Gondwana.
10:333.5 billion years after the oldest surviving continental crust forms, Gondwana moves slowly
10:39north from the South Pole, breaking up into smaller pieces.
10:43Eventually, these pieces recombine with others, forming a landmass of incredible size.
10:50From this, North America will eventually emerge.
10:58Over billions of years, the dynamic movement of Earth's crust has shaped and moved entire
11:04continents.
11:06When these landmasses collide, they produce mountains.
11:11These are the Appalachians, the oldest surviving mountain range on the continent.
11:17Today, they stretch nearly 2,000 miles southwest from Newfoundland to central Alabama.
11:27But when they first appeared over 270 million years ago, North America still did not exist.
11:36These mountains crowned a supercontinent called Pangaea.
11:42When they were at their maximum height, they would have been perhaps the most profound
11:48mountain range existing on the planet.
11:51In a road cut in the Appalachian foothills, Ohio University professor of geological sciences,
11:58Damien Nance, examines the geology exposed in the Appalachians today.
12:04What may look a rather unimpressive wall of rock to the casual eye, has proven to be
12:10a geologic Rosetta Stone in this part of the Appalachian.
12:14And it records the very first collisional event in the building of the Appalachians.
12:22These belts of folded rocks are the surviving record of three titanic collisions that created
12:28the mountains.
12:33Thousands of years after the creation of the Acastatonalite, two ancient continents begin
12:38to collide.
12:41As these two continents close in on each other, the ocean floor is pushed down underneath
12:47what will become Africa.
12:50Gradually, the ocean is consumed.
12:54Huge sections of the seafloor are dumped on the edge of the continent, creating ridges
12:59and valleys.
13:03As the continents continue their inexorable journey, island landmasses are compressed
13:09between the two.
13:12The debris accumulates, now on dry land.
13:19The continental collision forces the debris further upward, driving the Appalachian mountains
13:26higher.
13:33It's the geological equivalent of a car crash.
13:42If you imagine a wreck between a truck and a much smaller car, the first thing that happens
13:48when the two hit each other is a collision between the front of the two vehicles.
13:54You can think of that as the first collisional episode in the Appalachians.
13:58The next thing that happens is the truck heats a windshield, and that, if you like, is the
14:03second collisional event in the Appalachians.
14:07And finally, the car disappears under the truck, and that, if you like, is the climactic
14:13collision, the one that produced the final Appalachian, and brought the whole process
14:17then to a close.
14:24Back at the road cut, there is evidence of the three phases of uplift, and by dating
14:29the rocks, scientists can tell when each happened.
14:36Building the Appalachians took nearly 200 million years.
14:41The movement of these continental masses is typically in the orders of centimeters
14:47per year, which is a very slow rate. It's about the rate your fingernails grow.
14:55This mountain-building process involves hundreds of thousands of cubic miles of rock.
15:02It's thought the Appalachians originally rose higher than the present-day Himalayas.
15:09Today, they are a shadow of their former selves, cut down to size by another powerful geological
15:18process, erosion.
15:22The mighty Appalachians were tamed by another powerful enemy, water.
15:29When water freezes, it expands in volume by as much as 8%.
15:37Here a bottle of water rapidly freezes, the ice expands, and the bottle cracks.
15:46This same action applies to rocks. Water freezing in cracks breaks them apart.
15:54When temperatures rise, the ice melts and washes away the debris.
16:01Wind and rain add to the process, and over eons, they have the power to utterly transform
16:08the landscape.
16:11Erosion can do incredible damage to a mountain range, and we can see that in the modern Appalachians.
16:18The modern Appalachians are simply the remnants of this once vast and very high mountain range.
16:25Today, Pangaea's eroded mountains are in North America.
16:34How they came to be here is the next step in the story of the continent.
16:42Continents trap heat.
16:44Continents act a little bit like a book on an electric blanket.
16:48If you put a book on an electric blanket, it gets hot.
16:54The book acts as an insulator, trapping heat underneath it.
17:01Continents do the same thing with heat generated in the Earth's interior, and so if you put
17:06a very large continental mass together, like Pangaea, heat builds up beneath it.
17:14Pangaea is big. It's nearly as big as all of our seven continents put together.
17:21The temperature builds up underneath the continent and heats it up.
17:28As the rock absorbs heat, it arches.
17:32Then at its weakest points, it cracks, including along the line of the Appalachian Range.
17:40It's a process called rifting.
17:45As Pangaea cracks, it creates long, thin valleys.
17:52These elongated depressions fill with sediment washed down from surrounding highlands.
18:01Today we call one of these the Newark Basin of Pennsylvania, New York, and New Jersey.
18:09This sediment, now solidified, has been quarried.
18:14Today you can see it on the streets of New York City every time you look at a brownstone.
18:23Two hundred and thirty million years ago, the rifting between North America and Africa
18:29creates a new ocean, the Atlantic.
18:34As the two landmasses continue to pull apart, water floods the widening gap.
18:42The continental landmass we call North America is created, nearly four billion years after
18:48the first land formed.
18:52Its shape and features look different from the continent we know today.
18:58Other geological processes will change them.
19:03America is constructed by plate movement, but it is shaped by fire, ice, and water.
19:12Millions of years after Pangaea splits, a shallow sea stretches across the interior
19:21of the North American continent.
19:24It's called the Western Interior Seaway. It bisects North America from the Arctic Ocean
19:30to the Gulf of Mexico.
19:34It is the hunting ground of mighty carnivorous reptiles, mosasaurs, and plesiosaurs.
19:42You think, wow, that's amazing, a sea was on this continent. But it's not that amazing.
19:48A continent like North America is quite large.
19:50You see, at the highest point in North America is Mount McKinley, which is a mere four or
19:54five miles tall.
19:55So you have a continent that's four thousand miles wide, and the highest point is four
20:00miles.
20:01The continent's effectively flat as a board. Of course, it's wrapped onto the earth.
20:07So if the continent flexes a little bit, flexes down, the sea can come onto the continent.
20:13Flexes up, the sea goes off the continent.
20:16It's a process called uplift.
20:19Seventy million years ago, a giant uplift forces the inland seas outward, emptying the
20:25continent.
20:27The retreating seas leave a rich mix of layered sediments in their wake.
20:32In time, this seabed will become America's Great Plains, an immense sweep of country
20:39reaching from Mexico, across Texas, up to Montana, and into Canada.
20:45Denver Museum of Science and Nature's curator, Kirk Johnson, specializes in the region.
20:51For twenty million years, this area wasn't a mile high. It was six hundred feet below
20:56the surface of the Salty Sea.
20:58Just go dig a hole in the pier shale and you'll find the teeth of fifty foot long marine reptiles,
21:03and giant fossil fish, and ammonites, and meter long clams, a whole host of things that
21:07really show you that there was a sea right here.
21:14Uplift drains the sea away from the interior plains. Further west, the same uplift triggers
21:21a different effect.
21:23The results are still visible today.
21:27The entire western interior of North America was flat as a board. Then, about sixty nine
21:32million years ago, the Rocky Mountains pushed up.
21:40Most mountain belts are created on the margin of colliding plates. But the Colorado Rockies
21:46formed more than six hundred miles away from the edge of the Pacific Plate.
21:52Some other force must have pushed them up.
21:57The subducting plate off the west coast of North America, instead of going in and diving
22:01down and creating volcanoes right along the margin of North America, went in shallow.
22:10Like a spatula under a pizza.
22:16Cracks in the crust allow granitic magma to escape the mantle. It rises to the surface
22:23and creates volcanoes.
22:26Today there are two hundred and sixty two volcanic fields in North America. The majority
22:32of them have had little impact on the surface of the continent.
22:40There is one exception. It's called a supervolcano.
22:50Supervolcanoes leave enormous scars on the landscape, scars that are visible today.
22:57This is a satellite view of the Snake River Plain. It's four hundred miles long, a broad
23:04flat depression that covers one quarter of the state of Idaho.
23:09It's best known for its fertile agricultural land, home of the famous Idaho potatoes.
23:18The land here contains a record of the North American plate's gradual movement over a stationary
23:25hotspot in the Earth's mantle.
23:28This hotspot produces a place on the Earth's surface that experiences active volcanism
23:34for long periods. Below the crust, abnormally hot mantle material wells upward.
23:41As North America drifts across this hotspot, it leaves unmistakable evidence of each eruption
23:48on the surface of the Earth.
23:50Today, the hotspot is directly under Yellowstone National Park.
23:58Eventually, the park's boundaries will pass over it. But for now, Yellowstone is the largest
24:05volcanic system in North America.
24:11Hank Hessler is the Yellowstone National Park geologist.
24:17Trying to imagine what the catastrophic eruptions look like is a challenge. No human has ever
24:25witnessed these type of eruptions.
24:30But humans have recorded devastating eruptions in the past.
24:34May 18, 1980, Washington State. Mount St. Helens erupts with a total force of 24 megatons.
24:44That's almost 1600 times as powerful as the bomb that destroyed Hiroshima.
24:50Compared to an eruption at Yellowstone 2 million years ago, Mount St. Helens is small change.
24:58Today, the caldera of the last eruption of this supervolcano forms the heart of Yellowstone
25:06National Park.
25:12Calderas appear when the magma chamber beneath the volcano empties after a large eruption.
25:19Fractures form around the edge of the chamber. They serve as vents, and as the magma chamber
25:25empties, the center of the volcano collapses.
25:30Yellowstone scientists have calculated that the eruption 2 million years ago ejected 588
25:37cubic miles of volcanic material into the stratosphere.
25:43To put this in comparison, this is about 6,000 times larger than Mount St. Helens.
25:50What does 6,000 times larger than something mean? Well, many of us have spent $1,000 in
25:57our lives. 6,000 times larger than $1,000 is $6 million. And not many of us have spent
26:05$6 million in our life.
26:10A supervolcano belches millions of tons of sulfurous gases and ash particles into the
26:16atmosphere.
26:20This volcanic debris reflects the sun's rays, decreasing the amount of sunlight reaching
26:26the surface of the Earth, often triggering what's called a volcanic winter.
26:33Volcanic winters can drop global temperature by up to 9 degrees.
26:42Plummeting temperatures have also shaped modern North America.
26:50During much of the last billion years, the Earth has had no permanent ice. But cooling
26:56temperatures have occasionally helped cover much of the globe with immense ice sheets.
27:04These are ice ages.
27:07200,000 years after an eruption at Yellowstone, the Earth enters an ice age.
27:18Boulder-studded glaciers advance and retreat over much of North America, carving and sculpting
27:24the landscape.
27:33Hofstra University professor of geology, Charles McGarrion, is an expert on glaciation.
27:39These boulders act like tools and actually gouge the Earth's surface and produce gouges
27:45and grooves on the orders of feet.
27:49It's like repeatedly dragging a cheese grater over cheese. Boulders embedded in glaciers
27:56gouge out grooves on the surface of the continent, over and over again.
28:02But it's the final polish of the Earth's surface and the position of streams and creeks and
28:07valleys that was the product of glaciation.
28:12But the glaciers have another important effect.
28:19At the peak of the last ice age, so much water is trapped as ice on land that sea levels
28:25drop by as much as 450 feet. Huge new tracts of land are exposed.
28:33Today, you can stroll to the shoreline from New York's boardwalk in just a few minutes.
28:40During the last ice age, it would take days.
28:47During glacial periods, when sea level was down 50 to 100 meters, the walk was about
28:53200 miles to get to the shoreline because the entire continental shelf of eastern North
28:58America was exposed during the last glacial episode.
29:05The ice age exposes so much land that America's coastline looks very different than it does
29:11today. Florida is around twice as wide as it is now.
29:19Three hundred thousand years ago, the outline of North America as we know it today is trapped
29:26in ice. It's only when the glaciers finally melt that the true shape of the continent
29:33will emerge.
29:37Three hundred thousand years ago, glaciers from the last great ice age are sculpting
29:44North America. Giant boulder-studded ice sheets gouge large chunks out of the earth.
29:53They create depressions in the landscape. When the ice melts, it pools.
30:02The most obvious effects of glacial meltback are the Great Lakes of the upper part of the
30:07United States, where enormous tracts of terrain that have been sculpted by glacial ice were
30:12later filled in by the meltback of glacial ice sheets.
30:16North America's Great Lakes cover more than 94,000 square miles. They hold enough water
30:23to submerge the contiguous 48 states under nine and a half feet of water.
30:29They are the largest group of freshwater lakes on earth, so big they are often described
30:35as inland seas.
30:38They emerge toward the end of the last ice age, when ice sheets many times the size of
30:44Texas recede.
30:47As ice sheets melt, water fills depressions in the landscape, creating millions of lakes.
30:55This is the most unique. It is Utah's Great Salt Lake. It's actually just a small remnant
31:08of a much larger ancient one.
31:11Lake Bonneville covered almost 20,000 square miles. Salt Lake City is built on its bed.
31:19The ancient lake existed from about 30 to 14,000 years ago.
31:26Professor Marjorie Chan of the University of Utah stands above Salt Lake City on the
31:32ancient shoreline of the Bonneville Lake. She's been studying it for six years.
31:37We're on the ancient shoreline of Lake Bonneville, and about 15,000 years ago, at this elevation
31:43of 5,100 feet, the whole area and valley behind me would have been covered by a deep
31:50lake. Antelope Island and Stansbury Island would have been surrounded by fresh water,
31:55maybe with even fish, and perhaps even my toes would be in the water at the shores of
31:59Lake Bonneville.
32:02Fed by meltwater from retreating glaciers, the level of Lake Bonneville gradually rose.
32:0915,500 years ago, the water reaches an elevation of about 5,000 feet, the lowest natural outlet
32:20for the basin. At Idaho's Red Rock Pass, the lake begins to spill over. The outflow
32:31of water begins to cut down into the rocks. Red Rock Pass weakens.
32:39Then collapses, unplugging the lake and causing a catastrophic flood. 15 million cubic feet
32:49of water gush out of the lake every second, about 150 times greater than the flow at Niagara
32:57Falls.
33:00The amount of water that was rushing out would be the equivalent to, you know, I mean more
33:06than that goes through the Amazon River, just huge amounts of water. And this is what
33:11we call the Great Flood.
33:14In about a year, the lake's level drops by almost 400 feet, releasing 380 cubic miles
33:21of water onto the Snake River Plain.
33:27The lake only stops emptying when the water level drops below the outlet at Red Rock Pass.
33:33The remaining water slowly begins to evaporate, leaving behind salt crystals.
33:41Over thousands of years, almost all of the lake disappears. Large salt flats mark its
33:48boundaries.
33:49Today, the Great Salt Lake is all that remains.
33:56The Great Salt Lake is really kind of a unique body of water. It's about three to five times
34:02saltier than ocean water even.
34:05There are nearly five billion tons of salt in the lake, and about two and a half million
34:10are added each year from surface and groundwater flow.
34:15The Great Salt Lake is very different from normal freshwater lakes. Here's a cup of freshwater,
34:20and you can see that we would use an egg to represent the human body with the large mass
34:23of water, and when the egg goes in, it sinks. But in Great Salt Lake water, we have a much
34:29higher density of salts concentrated through evaporation, and when we put the egg in, it
34:36floats just like a body would in the Great Salt Lake.
34:40Because of its unusually high salt concentration, it's easy to float in the lake, particularly
34:47in the saltier north arm, Gunnison Bay.
34:51Called America's Dead Sea, Utah's Great Salt Lake is anything but dead. It provides a habitat
34:59for millions of shorebirds and waterfowl, all feeding off the lake's abundant brine
35:05shrimp.
35:08The retreating glaciers of the last Great Ice Age leave their mark all over North America.
35:15There's evidence in the most unexpected places.
35:21New York, America's famous city. Most of us associate it with skyscrapers, not glaciers
35:29but New York's frozen geological past has shaped the city.
35:38Just 20,000 years ago, Manhattan and the Bronx were scoured by great plates of ice.
35:47Look past the joggers and workers enjoying their lunch break, and you can find plenty
35:52of evidence of glacial movement, even in Central Park.
35:57Dr. Charles McGarrion can spot the signs a mile away.
36:05Picture a thick ice sheet, an ice sheet that is perhaps a mile thick. Think about the mass
36:11at the base of a mile thick sheet of ice, enormous pressures. And these enormous pressures
36:16literally pulverize rock.
36:19The rock formations in Central Park bear the scars of this pummeling.
36:24We're standing here right in the center of the large exposure of rock, much of which
36:31has been removed by a glacier.
36:3420,000 years ago, New York is covered by a sheet of ice 5,000 feet thick.
36:43And you can picture how a one mile thick sheet of ice, with huge boulders embedded in the
36:49base of the ice, would have created this groove.
36:55The abrasive cycle of glacial advance and retreat even affects the city's design.
37:01It's amazing, but even the skyline of New York is dictated by geology.
37:08Turns out that tall buildings, which are the hallmark of New York City, must be rooted
37:12in solid rock.
37:14If you look at Manhattan, you recognize that the building heights actually oscillate from
37:19high buildings to low buildings back to high buildings again. Why? Because in that area
37:25there's a very deep valley that's been sculpted by glacial ice and then backfilled with glacial
37:31sediment. Well, you just simply cannot build tall buildings in soft sediment. So the building
37:37height change in New York City is actually showing what the underlying geology is.
37:46North America's glacial period finally ends about 8,000 years ago. It has shaped the coastline
37:54of the continent and applied the finishing touches to the landscape. Glaciation has molded
38:01our cities and left behind great lakes, plains, and mountains. The continent we know today
38:12has finally arrived.
38:20This is continental North America. The continent we see from space today is the product of
38:28an eons-long cycle of cataclysm and creation. Over billions of years, North America's features
38:38have changed dramatically, just as our own features change with time.
38:45The geologic history of North America has shaped it just like an individual's history
38:52has shaped their face. Injuries that they may have had, a baseball in the nose, a fist
38:59in the jaw, all this is reflected in a person's face, just like a continent reflects its past.
39:10Collisions between tectonic plates have deformed North America's face, building the immense
39:16Appalachians and the Rockies. Its valleys and canyons are open wounds, a testament to
39:24the erosive power of water. And immense inland seas, now long gone, left the mineral-rich
39:32landscape of the Great Plains. Ice applied the final touches, exfoliating the continent's
39:40features, filling in depressions, creating shorelines.
39:48North America, like all of Earth's continents, is a product of our planet's dynamic nature,
39:56a story that continues to evolve. In the future, plate movement will rip the continent apart,
40:04just as it has time and again throughout its long past.
40:12It's happening today, right under our feet. This is the San Andreas Fault. It runs roughly
40:24800 miles through California. It's the main boundary between the Pacific and North American
40:32tectonic plates. These two plates are moving in opposite directions to each other. The
40:43Pacific plate is moving northwest relative to the North American plate. California is
40:51being ripped apart two inches a year. At this rate, a million years from now, California
40:58will separate from North America and become an island state like Hawaii. But that's not
41:09all. If we plot the projected movement of the Earth's plates over the next tens of
41:16millions of years, the face of the whole continent becomes unrecognizable.
41:24Fifty million years from now, the Atlantic Ocean has widened. It has pushed New York
41:34away from Africa, moving the continent across Yellowstone's hotspot. Minnesota now sits
41:43on top of the supervolcano. One hundred million years from now, California's Napa Valley and
41:51San Francisco Bay Area have become Alaskan Mountains. The Atlantic Ocean continues to
42:01widen. A subduction zone forms along its western shoreline. This zone will consume the Atlantic
42:10Ocean and set North America on a collision course with Europe and Africa. Two hundred
42:20million years from now, America's eastern seaboard no longer exists. North America and
42:27Europe collide to create a new supercontinent. Today's New York is now in the middle of a
42:37mountain range, once again at the center of a huge landmass, just as it was five hundred
42:45million years ago. This may be our continent's future, but on a time scale that far outstrips
42:57our lifetimes. There are other changes, however, that mankind will witness. In the coming centuries,
43:06the North American continent may be a very different place. Much of Florida is now a
43:15subcontinent. The Big Apple is a modern-day Atlantis. It's an apocalyptic vision of North
43:24America's future, but it's us that's making it happen. For the first time in Earth's long
43:31history, the natural processes that forged the planet's continents are being influenced
43:37by man. Humans are very, very powerful geologic agents. Look at the fossil fuel industry.
43:44Farm fields that stretch over hundreds of thousands and millions of acres. Look at the
43:51expansion of cities over many tens of square miles that have completely changed the landscape.
44:01By the end of this century, the population of the United States alone is set to double.
44:08To accommodate our ever-growing population, we're building new cities. Industrialization,
44:15our use of fossil fuels, and our continuing love affair with the automobile has sent carbon
44:21dioxide levels in the atmosphere soaring. Carbon dioxide traps heat inside Earth's atmosphere,
44:30increasing the greenhouse effect. The ice caps are melting, and sea levels are beginning
44:37to rise. Jeremy Weiss is a global warming expert at the University of Arizona. He paints
44:49a gloomy picture of the future of North America. With global warming, there are certainly going
44:54to be winners and losers. The losers, however, are going to be far outnumbering the winners.
45:02In 2005, more than a hundred cubic miles of ice from Greenland and Antarctica melted into
45:10the sea. If Greenland's ice melts completely, it will release enough water to raise all
45:17the world's oceans by 23 feet. Certainly, as the glaciers melt, the shape of North America
45:24will change. This is the bathtub effect. You fill up the bathtub, the shape of the water
45:31changes. So as glaciers melt, sea level will rise. In fact, virtually all coastal cities
45:41would be completely devastated. Sea level rise associated with global warming will literally
45:48shrink North America. The shape of North America could change significantly, especially along
45:55the Gulf Coast and Atlantic Coast of the United States. For example, the states of Louisiana,
46:01Florida, and North Carolina will see the greatest effects as far as loss of land to sea level
46:08rise. Minimizing or reversing these trends is the
46:13way forward. Minimizing or reversing these trends requires urgent action. In the short
46:22term, the next hundred or so years, the shape and character of continental North America
46:29will change. How dramatically is up to us. In the long term, we make no difference to
46:37nature's billion-year-old processes of growth and destruction. These are impossible to control.
46:46The awesome forces that created North America are still at work.
46:57We won't be around to see the results of these changes, but perhaps other generations will
47:04map their new continent and reveal evidence of our time, just as we have unearthed the
47:10story of North America so far.