Cosmos: A Spacetime Odyssey (2014) s01e09 Episode Script
The Lost Worlds of Planet Earth
1 NEIL DEGRASSE TYSON: Yes, this is home.
This is Earth.
Having trouble finding a familiar continent? The past is another planet.
Actually, many.
I'm standing on the great expanse of time that has elapsed since the Big Bang.
In order to think about it, we've compressed it all into a single year.
It's the early morning of December 23 on this Cosmic Calendar of ours, or about 350 million years ago, when our world was a mere four billion years old.
Earth looks so different.
You might not even know the place.
The stars wouldn't help you.
Even the constellations would have been different back then.
The dinosaurs were still more than 100 million years in the future.
There were no birds, no flowers.
And the air was different, too.
The atmosphere had more oxygen than at any other time in Earth's history, before or since.
This allowed insects to grow much larger than they do today.
How? Insects don't have lungs.
Life-giving oxygen is taken in through openings in the outside of their bodies and transported through a network of tubes.
If an insect were too large, the outer reaches of these tubes would absorb all the oxygen before it could ever get to its internal organs.
But during the Carboniferous Period, the atmosphere had almost twice the oxygen as today.
Insects could then grow much bigger and still get enough oxygen in their bodies.
That's why the dragonflies here are as big as eagles and the millipedes the size of alligators.
So why was there so much oxygen back then? It was produced by a new kind of life.
DEGRASSE TYSON: What kind of life could've changed the Earth's atmosphere so dramatically? Plants that could reach for the sky-- trees.
In their competition for sunlight, trees evolved a way to defy gravity.
Before trees, the tallest vegetation was only about waist-high.
And then something wonderful happened.
A plant molecule evolved that was both strong and flexible, a material that could support a lot of weight, yet bend in the wind without breaking.
Lignin made trees possible.
Now life could build upward.
And this opened a whole new territory, a three-dimensional matrix for communities far above the ground.
Earth became the Planet of the Trees.
But lignin had a downside: it was hard to swallow.
When nature's demolition crew, the fungi and bacteria, tried to eat anything with lignin in it, they got a really bad case of indigestion.
And termites wouldn't evolve for at least another 100 million years.
What to do with all those dead trees? It took the fungi and bacteria millions of years to evolve the biochemical means to consume them.
Meanwhile, the trees just kept springing up, dying, falling over and getting buried by the mud that built up over eons.
Eventually, there were hundreds of billions of trees entombed in the Earth, buried forests all over the Earth.
What possible harm could come from that? (waves crashing in distance) This cliff in Nova Scotia is another kind of calendar.
It tells the story of that other world that once flourished right here.
And this is the death mask of that 300 million-year-old tree.
It was cast by minerals that replaced the original wood cell by cell-- in other words, a fossil.
The tree surrendered its organic molecules to the environment long ago, its carbon and water.
Only its shape remains.
When this tree was alive, it took in carbon dioxide and water and used sunlight to turn them into energy-rich organic matter.
The tree gave off oxygen as a waste product.
That's what trees and other plants still do.
When plants die, they decay, and this reverses the transaction.
Their organic matter combines with oxygen and decomposes, putting carbon dioxide back into the air.
This balances the books for the chemistry of Earth's atmosphere.
But if the trees are buried before they can decay, two things happen they take the carbon and stored solar energy with them and leave the oxygen behind to build up in the atmosphere.
That's what happened around 300 million years ago.
There was an oxygen surplus.
That's how the bugs got so big.
And what became of all that buried carbon? It lay there for eons before dealing life on Earth its most devastating blow of all time.
There are places on this planet where you can walk through time and read the history written in the rocks.
This beach in Nova Scotia is one of them.
Every layer is a page.
Each one tells the story of a flood, one after another, over millions of years.
The layer cake of flood deposits was slowly buried and turned into rock by heat and pressure.
The same forces that built mountains then tilted and uplifted them, along with the entombed fossil forest.
The newer layers were always deposited on top of the older ones.
All the pages are in the correct order, bearing witness to what happened here over millions of years.
Back that way lies the more distant past.
And with every step I take, I move about 1,000 years closer to the present and away from the world of 300 million years ago.
lies that way.
This was the beginning of the end of the Permian world, an event of unequalled carnage.
The Permian is the darkest corridor in this memorial to the broken branches on the Tree of Life-- the Halls of Extinction.
Death has never come so close to reigning supreme on this world in the quarter billion years since.
The eruptions, in what is now Siberia, lasted for hundreds of thousands of years.
The lava flooded and buried more than a million square miles.
This event dwarfs any volcanic eruption in historical times.
Huge quantities of carbon dioxide came pouring out of the volcanic fissures.
This greenhouse gas warmed the climate.
And this is where the long-buried forests of the earlier Carboniferous Period reenter the story.
During the intervening those trees had turned into immense deposits of coal, and as it happened, one of the world's largest accumulations of coal was buried right there in Siberia.
The heat from the lava baked the coal, driving methane and sulfur-rich gases out of the ground.
They were laden with toxic and radioactive ash particles-- coal smoke.
This witch's brew polluted the atmosphere and radically destabilized Earth's climate.
A sulfuric acid haze blocked incoming sunlight and darkened the planet.
Global temperatures plummeted to subfreezing.
During lulls in the eruptions, the acid haze fell back to the surface.
But the carbon dioxide remained and built up in the atmosphere to cause global warming.
Years of frigid cold alternating with millennia of stifling heat battered a dwindling population of plants and animals.
They had no chance to adapt to the drastic swings in climate.
As the global warming continued, the surface and the bottom waters slowly mixed, raising the temperature of the once-frigid depths of the sea floor.
Methane-rich ices that had been frozen in the sediments began to melt.
Newly liberated methane gas made its way to the surface and into the atmosphere.
Methane traps heat far more efficiently than carbon dioxide, so the climate got even hotter.
And the methane also destroyed the ozone layer in the stratosphere.
The natural sunscreen that protects life from deadly ultraviolet rays was eaten away.
The circulatory system of the world ocean shut down.
These stagnant waters became oxygen-starved, killing almost all the fish in the sea.
But one kind of life flourished in this brutal environment bacteria that produced deadly hydrogen sulfide gas as a waste product.
That was the last straw.
The poison gas killed almost all the remaining plants and animals on the land.
This was the Great Dying.
The closest life on Earth has ever come to annihilation.
Nine in ten of all species perished.
It took a long time for life to bounce back.
For a few million years, Earth could have been called the Planet of the Dead.
We are descended from one of the few species that managed to squeak by.
You are human and alive at this very moment because they managed to endure, conveying their DNA through one of the most treacherous periods in the history of life.
DEGRASSE TYSON: This mountain was made entirely by life.
The life that flourished back in the glory days of the Permian, before all hell broke loose.
This is part of the 400 mile-long Guadalupe Mountain chain that runs through Texas and New Mexico.
It's the world's largest fossil reef.
All this was once a great inland sea.
The reef flourished and grew for millions of years, and was home to multitudes of sponges, green algae, and animals too small to see.
When these creatures died, they sank to the bottom and were buried in the silt.
Over millions of years, their remains were converted into oil and gas.
Eventually, the basin silted in and the reef died.
This marine ghost town was then buried a mile beneath the surface.
Later, tectonic forces lifted the skeletal reef high above sea level, where it was eroded and sculpted over eons by wind and rain.
Just imagine what this place looked like 275 million years ago, when it was a vibrant, tropical inland sea, dotted with islands and brimming with life.
Until about New England and North Africa were next-door neighbors.
There was no such thing as the Atlantic Ocean.
Those thin blue fingers at the center-- they were lakes.
They were the first outward signs that the supercontinent was splitting apart and that life on Earth was due for another big shake-up.
A million years later, the lakes became a long bay, which would grow into the Atlantic Ocean.
These profound changes at the surface were merely symptoms of a drama that was unfolding far beneath, in the depths of the Earth.
By the time we got here, the telltale traces of global upheaval were buried at the bottom of the deep blue sea.
We were completely cut off from the great story of Earth's violent past-- a species of amnesiacs trying to find out who we were and what happened before we awakened.
In 1570, Abraham Ortelius created the first modern world atlas, reflecting on the discoveries of the previous 80 years-- the Golden Age of Exploration.
Before the ink was dry, Ortelius stepped back from his masterpiece and became the first of many to notice the striking puzzle-piece fit between the continents on either side of the Atlantic.
He later wrote that the Americas were torn away from Europe and Africa by earthquakes and floods.
But Ortelius's observation remained nothing more than a hunch for the next couple of centuries until an early 20th century German astronomer and meteorologist amassed the evidence to build the scientific case for it.
Alfred Wegener had been drafted during the First World War, but was wounded soon after.
As he recovered in a field hospital, he scoured scientific literature for clues to the Earth's past.
Years before, Wegener had happened upon an intriguing paper in the stacks of his university library.
It puzzled Wegener that fossils of the same species of a now-extinct fern were reported to be found on both sides of the Atlantic.
Even more curious were the discoveries of fossils of the same dinosaurs on both continents.
In the early 20th century, geologists explained how life crossed the oceans by imagining that land bridges had once existed between them.
It was thought that these land bridges gradually disintegrated and vanished beneath the waves long ago.
But there was one piece of evidence that convinced Wegener that the prevailing scientific view must be wrong the Earth itself.
Why would a mountain range cross the oceanic divide to continue on another continent? And why would you find the same unique pattern in the layers of rocks in both Brazil and South Africa? And another thing under what circumstances could tropical plants have flourished in the frozen wastes of the Arctic? Wegener concluded that there was only one logical solution to this puzzle There had once been a single supercontinent on Earth.
He named it Pangaea.
So Wegener becomes the toast of the scientific world, right? Not exactly.
Most geologists ridiculed Wegener's hypothesis of continental drift.
They preferred their imaginary natural land bridges to explain away Wegener's evidence.
How, they asked, could a continent plow through the solid rock of the ocean floor? Wegener had no convincing answer.
He became the laughingstock of the field; a pariah at scientific conferences.
(dogs barking) Despite this, Wegener continued to fight for his ideas, conducting daring research expeditions to gather evidence.
On one of these, he learned that colleagues were trapped on an ice cap without food.
On his way back from the mission, he became lost in a blizzard.
A day or two after his 50th birthday, he disappeared, never knowing that, in time, he would be vindicated and come to be viewed as one of the greatest geologists in history.
Scientists are human.
We have our blind spots and prejudices.
Science is a mechanism designed to ferret them out.
Problem is, we aren't always faithful to the core values of science.
Few people knew this better than Marie Tharp.
It's 1952, and Marie is patiently enduring the slights of her fellow members of the geology department.
Her degrees in geology and mathematics count for little with them.
Bruce Heezen, a graduate student from Iowa, has just returned from a lengthy expedition to map the ocean floor using sonar.
(Heezen grunts) Will you do something with these? Bruce, look.
It's-- it's all come together.
There's this giant rift valley that runs through the bottom of the Atlantic.
Aw, geez, Marie, come on.
This is just more girl talk.
You're not in enough trouble with everyone here already? This sounds too much like continental drift.
You want to end up like Wegener? DEGRASSE TYSON: But Marie would not be dissuaded.
Years later, when Marie and Bruce placed a map of oceanic earthquake epicenters on a light table over her seafloor map, the earthquakes fell right along the rift valley.
This was the smoking gun for Wegener's moving continents.
Heezen now knew that Marie had been right all along.
Together, they created the first true map of the Earth, including the ocean floor.
We were at last ready to read the autobiography of the Earth.
DEGRASSE TYSON: Let's take the Ship of the Imagination to a part of the world that has been off-limits to all but a few of us.
Two-thirds of the Earth lies beneath more than It's a vast and largely unexplored frontier.
Everybody knows the Alps and the Rockies, but some of the world's most amazing mountain ranges are hidden from view.
Below 1,000 meters, we enter a world where there is no sunlight.
Hidden in the darkness, a world of wonders.
This is the longest submarine mountain range in the world, the Atlantic Mid-Ocean Ridge.
It wraps around our globe like the seam on a baseball.
The past is another planet, but most of us don't really know this one.
We don't see the mountains for the water.
This is the world that Marie Tharp was the first to imagine.
The highest peaks of the ridge rise over four kilometers above the ocean floor.
There are sprawling mountain ranges and canyons, too.
We've now entered the Marianas Trench, the deepest canyon on Earth, more than ten kilometers deep.
It formed when tectonic forces pushed the seabed under the adjoining continental plate.
More people have walked on the Moon than have ever been down here.
The pressure here is a crushing eight tons per square inch.
Being this deep in the ocean is like having 50 jumbo jets stacked on top of you.
Yet even here, life has taken hold.
The fact that sunlight can't penetrate the deep ocean doesn't mean there isn't light down here.
Many underwater species glow in the dark, through a process called bioluminescence.
Our long history as land mammals, denizens of the sunlit world, hasn't prepared us for the amazing variety of life that evolution has crafted in the deep oceans.
Since there's no sunlight down here, there's no photosynthesis.
That means there are no plants to feed on, and yet, even here, in a world of permanent midnight, there's a thriving food chain.
It begins with a process called chemosynthesis.
These microscopic creatures have learned to eat what's pouring out of that vent a noxious compound called hydrogen sulfide.
That thick black smoke provides the chemical energy that makes life possible here.
Tiny crustaceans eat the bacteria, and the larger animals eat the crustaceans.
One day, on some future Earth, these mountains could very well end up above the water.
Tectonic forces continue to shape our planet.
The future is also another planet.
It was a volcano like this one that created the Hawaiian islands millions of years ago.
We live on the crust of a seething cauldron.
At the center of our planet, there's an iron core.
It's nested inside of a larger, liquid iron shell.
Wrapped over this is the part called the mantle.
It's rocky but hot and viscous.
Like a pot of soup cooking on a stove, the mantle is churning.
What keeps it moving? Two things the heat left over from Earth's formation, and the decay of radioactive elements in the core.
And this outer layer-- the crust, where you and me and everyone we know lives-- is only as thick as the skin on an apple.
The mantle drags the solid overlying crust along with it.
The crust resists because it's cool and rigid.
From time to time, it reaches the breaking point.
When that happens, the Earth quakes.
It's not because somebody misbehaved and is being punished.
It's due to random forces that are governed by the laws of nature.
Our sense of the stability of the Earth is an illusion due to the shortness of our lives.
If we could watch our planet on its own timescale, in which big changes take millions of years to play out, we would see it as the dynamic organism it really is.
(rumbling, crackling) This is the world of the late Triassic period about 200 million years ago.
That little guy? It's one of our distant ancestors.
He lived in Newark, New Jersey.
Wherever you walk on Earth lost worlds lie buried beneath your feet.
50 or 100 million years ago, even the most seemingly ordinary places have been the scene of epic change.
These Palisades are a monument to the breakup of the supercontinent Pangaea.
The sequence of volcanic eruptions that made these cliffs also led to the next mass extinction-- the one that ended the Triassic world.
But a catastrophic extinction event for one species is a golden opportunity for another.
The Triassic extinctions offered one group that had been around for a while the chance to take center stage.
The dinosaurs had a good, long run for 170 million years.
Back then, India was an island.
It crept northward at the pace of a few inches per year on its slow but inexorable rendezvous with Asia.
Then, once again, the molten rock beneath Earth's surface burst forth and flooded a huge area of western India.
The knockout punch literally came out of the blue.
(rumbling, whooshing) Few animals larger than a hundred pounds survived the catastrophes of the late Cretaceous.
The dust cloud brought night and cold to the surface for months.
The dinosaurs froze and starved to death.
But there were small creatures who took shelter in the Earth.
And when they emerged they found that the monsters who had hunted and terrorized them were gone.
The Earth was becoming the Planet of the Mammals.
And the Earth continued its ceaseless changing.
This was once a desert where nothing could grow.
It was a million square miles of sand and salt, far more hostile than any environment on Earth today.
Daytime temperatures were hot enough to bake bread.
And it was more than a mile below sea level, so the atmospheric pressure was about 50% higher than what we're used to.
It would be hard to think of a more unpromising environment on this planet.
Yet this was the basin of the Mediterranean five and a half million years ago, before it became a sea.
The Earth never stops moving for long.
The natural dam at the western end of the deep basin gave way, probably due to earthquakes.
And the deluge began.
The torrential waters rushed in at a rate 40,000 times greater than Niagara Falls, turning a vast desert into the Mediterranean Sea in less than a year.
There were as yet no humans to witness this enormous flood, nor to admire the beauty it created.
Meanwhile, half a world away, a broad channel separated North and South America allowing ocean currents to flow from the Atlantic into the Pacific Ocean.
Tectonic forces gradually brought these two continents together, closing the channel and creating the Isthmus of Panama.
This reorganized the worldwide pattern of ocean currents, which, in turn, affected the global climate.
In Africa, the lush green forest canopy gave way to a sparser landscape.
Some species that were highly specialized for life in the trees became extinct.
But the generalists, the ones that could find a way to make a living no matter what life threw at them, endured and evolved.
Our ancestors had once burrowed deep in the ground to avoid predators who stalked the surface.
But when the dinosaurs perished, they emerged into the daylight, and over the eons, made new lives in the branches of the trees.
They developed opposable thumbs and toes for swinging from branch to branch, across the broad canopy of treetops, where all their needs were fulfilled.
They could also walk upright, but only for short distances.
With so many trees around, they didn't have to go very far.
But then it got colder, and the trees thinned out, broad grasslands sprang up, and our ancestors were forced to traverse them in search of food.
You needed a totally different skill set to make it on the savanna.
In the old days, you could sit perched on your tree branch and watch the big cats from a safe distance.
Now you were playing on the same dangerous field.
(growling) The survivors were those who evolved the ability to walk great distances on their hind legs and to run when necessary.
(growling) This changed the way they looked at the world.
Hands and arms were no longer tied up with walking.
They were free to gather food and pick up sticks and bones.
These could be used as weapons and tools.
Think of it A change in the topography of a small piece of land half a world away reroutes ocean currents.
Africa grows colder and drier.
Most of the trees can't withstand the new climate.
The primates who lived in them have to seek other homes, and before you know it, they're using tools to remake the planet.
The Earth has shaped the course of human destiny, but so has the invisible pull of distant worlds.
DEGRASSE TYSON: The planets have influenced our lives, but not in the way you think.
The gravitational pull of Venus-- small but close-- and that of Jupiter-- distant but massive-- tilted the Earth's axis this way and that and ever so slightly tweaked the shape of its orbit.
This periodically altered the amount of sunlight falling on the edge of the northern ice cap.
Sometimes it made the summers there colder, and the glaciers advanced southward from one year to the next, grinding and scraping, and crushing everything in their path.
That's what we call an ice age.
At other times, changes in Earth's axis and orbit made the Arctic summers warmer.
And the melting glaciers began to retreat.
Imagine how resourceful our ancestors had to be in order to survive these radical changes in climate.
With each glacial period, the ice sheets grow at the expense of the oceans; the world sea level falls by more than 400 feet, uncovering wide areas of land along the edges of the continents.
15 to 25,000 years ago, there was a period when the ice receded, exposing a temporary land bridge.
The gateway to the other half of the planet swings open.
Bands of wanderers crossed the land bridge to North America and parts south.
About 10,000 years ago, the manic swings of the climate and sea levels came to a stop.
A new and gentler climate age began.
It's the one we live in now.
When the great ice sheets melted, the sea rose to its present height and the rivers carried silt from the highlands to build great delta plains where they met the sea.
On those fertile plains, we learned a new way of life how to grow things, to feed ourselves and more.
For most of us, this meant an end to a million years of wandering.
The way the planets tug at each other, the way the skin of the Earth moves, the way those motions affect climate and the evolution of life and intelligence-- they all combined to give us the means to turn the mud of those river deltas into the first civilizations.
There's nothing like an interglacial period, one of those balmy intermissions in an ice age.
And the great news is that this one is due to last for another 50,000 years.
What a break for our kind.
Just one problem.
We can't seem to stop burning up all those buried trees from way back in the Carboniferous Age, in the form of coal; and the remains of ancient plankton, in the form of oil and gas.
If we could, we'd be home free, climate-wise.
Instead, we're dumping carbon dioxide into the atmosphere at a rate the Earth hasn't seen since the great climate catastrophes of the past, the ones that led to mass extinctions.
We just can't seem to break our addiction to the kinds of fuel that'll bring back a climate last seen by the dinosaurs; a climate that will drown our coastal cities and wreak havoc on the environment and our ability to feed ourselves.
All the while, the glorious sun pours immaculate, free energy down upon us; more than we will ever need.
Why can't we summon the ingenuity and courage of the generations that came before us? The dinosaurs never saw that asteroid coming.
What's our excuse? There's a corridor in the Halls of Extinction that is, right now, empty and unmarked.
The autobiography of the Earth is still being written.
There's a chance that the end of our story lies in there.
DEGRASSE TYSON: Congratulations.
You're alive.
There's an unbroken thread that stretches across more than three billion years that connects us to the first life that ever touched this world.
Think of how tough, resourceful and lucky all of our countless ancestors must have been to survive long enough to pass on the message of life to the next and the next and the next generation, hundreds of millions of times before it came to us.
There were so many rivers to cross, so many hazards along the way.
Predators, starvation, disease, miscalculation, long winters, drought, flood and violence.
Not to mention the occasional upheavals that erupted from within our planet and the apocalyptic bolts that come from the blue.
No matter where we hail from or who our parents were, we are descended from the hearty survivors of unimaginable catastrophes.
Each of us is a runner in the longest and most dangerous relay race there ever was, and at this moment, we hold the baton in our hands.
The past is another planet.
And so is the future.
Some 250 million years from now, many geologists think that the lands of the Earth will be united once again.
All this beauty will have vanished and the Earth of our moment in time will take its place among the lost worlds.
The great internal engine of plate tectonics is indifferent to life, as are the small changes in the Earth's orbit and tilt and the occasional collisions with little worlds on rogue orbits.
These processes have no notion of what has been going on over billions of years on our planet's surface.
They do not care.
Each of us is a tiny being riding on the outermost skin of one of the smaller planets for a few dozen trips around the local star.
The things that live the longest on Earth endure for only about a millionth of the age of our planet.
So, of course, the individual organisms see nothing of the overall pattern.
Of changing continents climate evolution.
That we understand even a little of our origins is one of the great triumphs of human insight and courage.
Who we are and why we are here can only be glimpsed by piecing together something of the full picture, which must encompass eons of time millions of species and a multitude of worlds.
In this perspective, it's not surprising that we're a mystery to ourselves and that, despite our manifest pretension, we are far from being masters of our own little house.
This new corridor has no name above the entrance to designate its epoch, and we don't yet know which failed species will be memorialized within its walls.
What happens here, in countless ways, both large and small, is being written by us.
Right now.
This is Earth.
Having trouble finding a familiar continent? The past is another planet.
Actually, many.
I'm standing on the great expanse of time that has elapsed since the Big Bang.
In order to think about it, we've compressed it all into a single year.
It's the early morning of December 23 on this Cosmic Calendar of ours, or about 350 million years ago, when our world was a mere four billion years old.
Earth looks so different.
You might not even know the place.
The stars wouldn't help you.
Even the constellations would have been different back then.
The dinosaurs were still more than 100 million years in the future.
There were no birds, no flowers.
And the air was different, too.
The atmosphere had more oxygen than at any other time in Earth's history, before or since.
This allowed insects to grow much larger than they do today.
How? Insects don't have lungs.
Life-giving oxygen is taken in through openings in the outside of their bodies and transported through a network of tubes.
If an insect were too large, the outer reaches of these tubes would absorb all the oxygen before it could ever get to its internal organs.
But during the Carboniferous Period, the atmosphere had almost twice the oxygen as today.
Insects could then grow much bigger and still get enough oxygen in their bodies.
That's why the dragonflies here are as big as eagles and the millipedes the size of alligators.
So why was there so much oxygen back then? It was produced by a new kind of life.
DEGRASSE TYSON: What kind of life could've changed the Earth's atmosphere so dramatically? Plants that could reach for the sky-- trees.
In their competition for sunlight, trees evolved a way to defy gravity.
Before trees, the tallest vegetation was only about waist-high.
And then something wonderful happened.
A plant molecule evolved that was both strong and flexible, a material that could support a lot of weight, yet bend in the wind without breaking.
Lignin made trees possible.
Now life could build upward.
And this opened a whole new territory, a three-dimensional matrix for communities far above the ground.
Earth became the Planet of the Trees.
But lignin had a downside: it was hard to swallow.
When nature's demolition crew, the fungi and bacteria, tried to eat anything with lignin in it, they got a really bad case of indigestion.
And termites wouldn't evolve for at least another 100 million years.
What to do with all those dead trees? It took the fungi and bacteria millions of years to evolve the biochemical means to consume them.
Meanwhile, the trees just kept springing up, dying, falling over and getting buried by the mud that built up over eons.
Eventually, there were hundreds of billions of trees entombed in the Earth, buried forests all over the Earth.
What possible harm could come from that? (waves crashing in distance) This cliff in Nova Scotia is another kind of calendar.
It tells the story of that other world that once flourished right here.
And this is the death mask of that 300 million-year-old tree.
It was cast by minerals that replaced the original wood cell by cell-- in other words, a fossil.
The tree surrendered its organic molecules to the environment long ago, its carbon and water.
Only its shape remains.
When this tree was alive, it took in carbon dioxide and water and used sunlight to turn them into energy-rich organic matter.
The tree gave off oxygen as a waste product.
That's what trees and other plants still do.
When plants die, they decay, and this reverses the transaction.
Their organic matter combines with oxygen and decomposes, putting carbon dioxide back into the air.
This balances the books for the chemistry of Earth's atmosphere.
But if the trees are buried before they can decay, two things happen they take the carbon and stored solar energy with them and leave the oxygen behind to build up in the atmosphere.
That's what happened around 300 million years ago.
There was an oxygen surplus.
That's how the bugs got so big.
And what became of all that buried carbon? It lay there for eons before dealing life on Earth its most devastating blow of all time.
There are places on this planet where you can walk through time and read the history written in the rocks.
This beach in Nova Scotia is one of them.
Every layer is a page.
Each one tells the story of a flood, one after another, over millions of years.
The layer cake of flood deposits was slowly buried and turned into rock by heat and pressure.
The same forces that built mountains then tilted and uplifted them, along with the entombed fossil forest.
The newer layers were always deposited on top of the older ones.
All the pages are in the correct order, bearing witness to what happened here over millions of years.
Back that way lies the more distant past.
And with every step I take, I move about 1,000 years closer to the present and away from the world of 300 million years ago.
lies that way.
This was the beginning of the end of the Permian world, an event of unequalled carnage.
The Permian is the darkest corridor in this memorial to the broken branches on the Tree of Life-- the Halls of Extinction.
Death has never come so close to reigning supreme on this world in the quarter billion years since.
The eruptions, in what is now Siberia, lasted for hundreds of thousands of years.
The lava flooded and buried more than a million square miles.
This event dwarfs any volcanic eruption in historical times.
Huge quantities of carbon dioxide came pouring out of the volcanic fissures.
This greenhouse gas warmed the climate.
And this is where the long-buried forests of the earlier Carboniferous Period reenter the story.
During the intervening those trees had turned into immense deposits of coal, and as it happened, one of the world's largest accumulations of coal was buried right there in Siberia.
The heat from the lava baked the coal, driving methane and sulfur-rich gases out of the ground.
They were laden with toxic and radioactive ash particles-- coal smoke.
This witch's brew polluted the atmosphere and radically destabilized Earth's climate.
A sulfuric acid haze blocked incoming sunlight and darkened the planet.
Global temperatures plummeted to subfreezing.
During lulls in the eruptions, the acid haze fell back to the surface.
But the carbon dioxide remained and built up in the atmosphere to cause global warming.
Years of frigid cold alternating with millennia of stifling heat battered a dwindling population of plants and animals.
They had no chance to adapt to the drastic swings in climate.
As the global warming continued, the surface and the bottom waters slowly mixed, raising the temperature of the once-frigid depths of the sea floor.
Methane-rich ices that had been frozen in the sediments began to melt.
Newly liberated methane gas made its way to the surface and into the atmosphere.
Methane traps heat far more efficiently than carbon dioxide, so the climate got even hotter.
And the methane also destroyed the ozone layer in the stratosphere.
The natural sunscreen that protects life from deadly ultraviolet rays was eaten away.
The circulatory system of the world ocean shut down.
These stagnant waters became oxygen-starved, killing almost all the fish in the sea.
But one kind of life flourished in this brutal environment bacteria that produced deadly hydrogen sulfide gas as a waste product.
That was the last straw.
The poison gas killed almost all the remaining plants and animals on the land.
This was the Great Dying.
The closest life on Earth has ever come to annihilation.
Nine in ten of all species perished.
It took a long time for life to bounce back.
For a few million years, Earth could have been called the Planet of the Dead.
We are descended from one of the few species that managed to squeak by.
You are human and alive at this very moment because they managed to endure, conveying their DNA through one of the most treacherous periods in the history of life.
DEGRASSE TYSON: This mountain was made entirely by life.
The life that flourished back in the glory days of the Permian, before all hell broke loose.
This is part of the 400 mile-long Guadalupe Mountain chain that runs through Texas and New Mexico.
It's the world's largest fossil reef.
All this was once a great inland sea.
The reef flourished and grew for millions of years, and was home to multitudes of sponges, green algae, and animals too small to see.
When these creatures died, they sank to the bottom and were buried in the silt.
Over millions of years, their remains were converted into oil and gas.
Eventually, the basin silted in and the reef died.
This marine ghost town was then buried a mile beneath the surface.
Later, tectonic forces lifted the skeletal reef high above sea level, where it was eroded and sculpted over eons by wind and rain.
Just imagine what this place looked like 275 million years ago, when it was a vibrant, tropical inland sea, dotted with islands and brimming with life.
Until about New England and North Africa were next-door neighbors.
There was no such thing as the Atlantic Ocean.
Those thin blue fingers at the center-- they were lakes.
They were the first outward signs that the supercontinent was splitting apart and that life on Earth was due for another big shake-up.
A million years later, the lakes became a long bay, which would grow into the Atlantic Ocean.
These profound changes at the surface were merely symptoms of a drama that was unfolding far beneath, in the depths of the Earth.
By the time we got here, the telltale traces of global upheaval were buried at the bottom of the deep blue sea.
We were completely cut off from the great story of Earth's violent past-- a species of amnesiacs trying to find out who we were and what happened before we awakened.
In 1570, Abraham Ortelius created the first modern world atlas, reflecting on the discoveries of the previous 80 years-- the Golden Age of Exploration.
Before the ink was dry, Ortelius stepped back from his masterpiece and became the first of many to notice the striking puzzle-piece fit between the continents on either side of the Atlantic.
He later wrote that the Americas were torn away from Europe and Africa by earthquakes and floods.
But Ortelius's observation remained nothing more than a hunch for the next couple of centuries until an early 20th century German astronomer and meteorologist amassed the evidence to build the scientific case for it.
Alfred Wegener had been drafted during the First World War, but was wounded soon after.
As he recovered in a field hospital, he scoured scientific literature for clues to the Earth's past.
Years before, Wegener had happened upon an intriguing paper in the stacks of his university library.
It puzzled Wegener that fossils of the same species of a now-extinct fern were reported to be found on both sides of the Atlantic.
Even more curious were the discoveries of fossils of the same dinosaurs on both continents.
In the early 20th century, geologists explained how life crossed the oceans by imagining that land bridges had once existed between them.
It was thought that these land bridges gradually disintegrated and vanished beneath the waves long ago.
But there was one piece of evidence that convinced Wegener that the prevailing scientific view must be wrong the Earth itself.
Why would a mountain range cross the oceanic divide to continue on another continent? And why would you find the same unique pattern in the layers of rocks in both Brazil and South Africa? And another thing under what circumstances could tropical plants have flourished in the frozen wastes of the Arctic? Wegener concluded that there was only one logical solution to this puzzle There had once been a single supercontinent on Earth.
He named it Pangaea.
So Wegener becomes the toast of the scientific world, right? Not exactly.
Most geologists ridiculed Wegener's hypothesis of continental drift.
They preferred their imaginary natural land bridges to explain away Wegener's evidence.
How, they asked, could a continent plow through the solid rock of the ocean floor? Wegener had no convincing answer.
He became the laughingstock of the field; a pariah at scientific conferences.
(dogs barking) Despite this, Wegener continued to fight for his ideas, conducting daring research expeditions to gather evidence.
On one of these, he learned that colleagues were trapped on an ice cap without food.
On his way back from the mission, he became lost in a blizzard.
A day or two after his 50th birthday, he disappeared, never knowing that, in time, he would be vindicated and come to be viewed as one of the greatest geologists in history.
Scientists are human.
We have our blind spots and prejudices.
Science is a mechanism designed to ferret them out.
Problem is, we aren't always faithful to the core values of science.
Few people knew this better than Marie Tharp.
It's 1952, and Marie is patiently enduring the slights of her fellow members of the geology department.
Her degrees in geology and mathematics count for little with them.
Bruce Heezen, a graduate student from Iowa, has just returned from a lengthy expedition to map the ocean floor using sonar.
(Heezen grunts) Will you do something with these? Bruce, look.
It's-- it's all come together.
There's this giant rift valley that runs through the bottom of the Atlantic.
Aw, geez, Marie, come on.
This is just more girl talk.
You're not in enough trouble with everyone here already? This sounds too much like continental drift.
You want to end up like Wegener? DEGRASSE TYSON: But Marie would not be dissuaded.
Years later, when Marie and Bruce placed a map of oceanic earthquake epicenters on a light table over her seafloor map, the earthquakes fell right along the rift valley.
This was the smoking gun for Wegener's moving continents.
Heezen now knew that Marie had been right all along.
Together, they created the first true map of the Earth, including the ocean floor.
We were at last ready to read the autobiography of the Earth.
DEGRASSE TYSON: Let's take the Ship of the Imagination to a part of the world that has been off-limits to all but a few of us.
Two-thirds of the Earth lies beneath more than It's a vast and largely unexplored frontier.
Everybody knows the Alps and the Rockies, but some of the world's most amazing mountain ranges are hidden from view.
Below 1,000 meters, we enter a world where there is no sunlight.
Hidden in the darkness, a world of wonders.
This is the longest submarine mountain range in the world, the Atlantic Mid-Ocean Ridge.
It wraps around our globe like the seam on a baseball.
The past is another planet, but most of us don't really know this one.
We don't see the mountains for the water.
This is the world that Marie Tharp was the first to imagine.
The highest peaks of the ridge rise over four kilometers above the ocean floor.
There are sprawling mountain ranges and canyons, too.
We've now entered the Marianas Trench, the deepest canyon on Earth, more than ten kilometers deep.
It formed when tectonic forces pushed the seabed under the adjoining continental plate.
More people have walked on the Moon than have ever been down here.
The pressure here is a crushing eight tons per square inch.
Being this deep in the ocean is like having 50 jumbo jets stacked on top of you.
Yet even here, life has taken hold.
The fact that sunlight can't penetrate the deep ocean doesn't mean there isn't light down here.
Many underwater species glow in the dark, through a process called bioluminescence.
Our long history as land mammals, denizens of the sunlit world, hasn't prepared us for the amazing variety of life that evolution has crafted in the deep oceans.
Since there's no sunlight down here, there's no photosynthesis.
That means there are no plants to feed on, and yet, even here, in a world of permanent midnight, there's a thriving food chain.
It begins with a process called chemosynthesis.
These microscopic creatures have learned to eat what's pouring out of that vent a noxious compound called hydrogen sulfide.
That thick black smoke provides the chemical energy that makes life possible here.
Tiny crustaceans eat the bacteria, and the larger animals eat the crustaceans.
One day, on some future Earth, these mountains could very well end up above the water.
Tectonic forces continue to shape our planet.
The future is also another planet.
It was a volcano like this one that created the Hawaiian islands millions of years ago.
We live on the crust of a seething cauldron.
At the center of our planet, there's an iron core.
It's nested inside of a larger, liquid iron shell.
Wrapped over this is the part called the mantle.
It's rocky but hot and viscous.
Like a pot of soup cooking on a stove, the mantle is churning.
What keeps it moving? Two things the heat left over from Earth's formation, and the decay of radioactive elements in the core.
And this outer layer-- the crust, where you and me and everyone we know lives-- is only as thick as the skin on an apple.
The mantle drags the solid overlying crust along with it.
The crust resists because it's cool and rigid.
From time to time, it reaches the breaking point.
When that happens, the Earth quakes.
It's not because somebody misbehaved and is being punished.
It's due to random forces that are governed by the laws of nature.
Our sense of the stability of the Earth is an illusion due to the shortness of our lives.
If we could watch our planet on its own timescale, in which big changes take millions of years to play out, we would see it as the dynamic organism it really is.
(rumbling, crackling) This is the world of the late Triassic period about 200 million years ago.
That little guy? It's one of our distant ancestors.
He lived in Newark, New Jersey.
Wherever you walk on Earth lost worlds lie buried beneath your feet.
50 or 100 million years ago, even the most seemingly ordinary places have been the scene of epic change.
These Palisades are a monument to the breakup of the supercontinent Pangaea.
The sequence of volcanic eruptions that made these cliffs also led to the next mass extinction-- the one that ended the Triassic world.
But a catastrophic extinction event for one species is a golden opportunity for another.
The Triassic extinctions offered one group that had been around for a while the chance to take center stage.
The dinosaurs had a good, long run for 170 million years.
Back then, India was an island.
It crept northward at the pace of a few inches per year on its slow but inexorable rendezvous with Asia.
Then, once again, the molten rock beneath Earth's surface burst forth and flooded a huge area of western India.
The knockout punch literally came out of the blue.
(rumbling, whooshing) Few animals larger than a hundred pounds survived the catastrophes of the late Cretaceous.
The dust cloud brought night and cold to the surface for months.
The dinosaurs froze and starved to death.
But there were small creatures who took shelter in the Earth.
And when they emerged they found that the monsters who had hunted and terrorized them were gone.
The Earth was becoming the Planet of the Mammals.
And the Earth continued its ceaseless changing.
This was once a desert where nothing could grow.
It was a million square miles of sand and salt, far more hostile than any environment on Earth today.
Daytime temperatures were hot enough to bake bread.
And it was more than a mile below sea level, so the atmospheric pressure was about 50% higher than what we're used to.
It would be hard to think of a more unpromising environment on this planet.
Yet this was the basin of the Mediterranean five and a half million years ago, before it became a sea.
The Earth never stops moving for long.
The natural dam at the western end of the deep basin gave way, probably due to earthquakes.
And the deluge began.
The torrential waters rushed in at a rate 40,000 times greater than Niagara Falls, turning a vast desert into the Mediterranean Sea in less than a year.
There were as yet no humans to witness this enormous flood, nor to admire the beauty it created.
Meanwhile, half a world away, a broad channel separated North and South America allowing ocean currents to flow from the Atlantic into the Pacific Ocean.
Tectonic forces gradually brought these two continents together, closing the channel and creating the Isthmus of Panama.
This reorganized the worldwide pattern of ocean currents, which, in turn, affected the global climate.
In Africa, the lush green forest canopy gave way to a sparser landscape.
Some species that were highly specialized for life in the trees became extinct.
But the generalists, the ones that could find a way to make a living no matter what life threw at them, endured and evolved.
Our ancestors had once burrowed deep in the ground to avoid predators who stalked the surface.
But when the dinosaurs perished, they emerged into the daylight, and over the eons, made new lives in the branches of the trees.
They developed opposable thumbs and toes for swinging from branch to branch, across the broad canopy of treetops, where all their needs were fulfilled.
They could also walk upright, but only for short distances.
With so many trees around, they didn't have to go very far.
But then it got colder, and the trees thinned out, broad grasslands sprang up, and our ancestors were forced to traverse them in search of food.
You needed a totally different skill set to make it on the savanna.
In the old days, you could sit perched on your tree branch and watch the big cats from a safe distance.
Now you were playing on the same dangerous field.
(growling) The survivors were those who evolved the ability to walk great distances on their hind legs and to run when necessary.
(growling) This changed the way they looked at the world.
Hands and arms were no longer tied up with walking.
They were free to gather food and pick up sticks and bones.
These could be used as weapons and tools.
Think of it A change in the topography of a small piece of land half a world away reroutes ocean currents.
Africa grows colder and drier.
Most of the trees can't withstand the new climate.
The primates who lived in them have to seek other homes, and before you know it, they're using tools to remake the planet.
The Earth has shaped the course of human destiny, but so has the invisible pull of distant worlds.
DEGRASSE TYSON: The planets have influenced our lives, but not in the way you think.
The gravitational pull of Venus-- small but close-- and that of Jupiter-- distant but massive-- tilted the Earth's axis this way and that and ever so slightly tweaked the shape of its orbit.
This periodically altered the amount of sunlight falling on the edge of the northern ice cap.
Sometimes it made the summers there colder, and the glaciers advanced southward from one year to the next, grinding and scraping, and crushing everything in their path.
That's what we call an ice age.
At other times, changes in Earth's axis and orbit made the Arctic summers warmer.
And the melting glaciers began to retreat.
Imagine how resourceful our ancestors had to be in order to survive these radical changes in climate.
With each glacial period, the ice sheets grow at the expense of the oceans; the world sea level falls by more than 400 feet, uncovering wide areas of land along the edges of the continents.
15 to 25,000 years ago, there was a period when the ice receded, exposing a temporary land bridge.
The gateway to the other half of the planet swings open.
Bands of wanderers crossed the land bridge to North America and parts south.
About 10,000 years ago, the manic swings of the climate and sea levels came to a stop.
A new and gentler climate age began.
It's the one we live in now.
When the great ice sheets melted, the sea rose to its present height and the rivers carried silt from the highlands to build great delta plains where they met the sea.
On those fertile plains, we learned a new way of life how to grow things, to feed ourselves and more.
For most of us, this meant an end to a million years of wandering.
The way the planets tug at each other, the way the skin of the Earth moves, the way those motions affect climate and the evolution of life and intelligence-- they all combined to give us the means to turn the mud of those river deltas into the first civilizations.
There's nothing like an interglacial period, one of those balmy intermissions in an ice age.
And the great news is that this one is due to last for another 50,000 years.
What a break for our kind.
Just one problem.
We can't seem to stop burning up all those buried trees from way back in the Carboniferous Age, in the form of coal; and the remains of ancient plankton, in the form of oil and gas.
If we could, we'd be home free, climate-wise.
Instead, we're dumping carbon dioxide into the atmosphere at a rate the Earth hasn't seen since the great climate catastrophes of the past, the ones that led to mass extinctions.
We just can't seem to break our addiction to the kinds of fuel that'll bring back a climate last seen by the dinosaurs; a climate that will drown our coastal cities and wreak havoc on the environment and our ability to feed ourselves.
All the while, the glorious sun pours immaculate, free energy down upon us; more than we will ever need.
Why can't we summon the ingenuity and courage of the generations that came before us? The dinosaurs never saw that asteroid coming.
What's our excuse? There's a corridor in the Halls of Extinction that is, right now, empty and unmarked.
The autobiography of the Earth is still being written.
There's a chance that the end of our story lies in there.
DEGRASSE TYSON: Congratulations.
You're alive.
There's an unbroken thread that stretches across more than three billion years that connects us to the first life that ever touched this world.
Think of how tough, resourceful and lucky all of our countless ancestors must have been to survive long enough to pass on the message of life to the next and the next and the next generation, hundreds of millions of times before it came to us.
There were so many rivers to cross, so many hazards along the way.
Predators, starvation, disease, miscalculation, long winters, drought, flood and violence.
Not to mention the occasional upheavals that erupted from within our planet and the apocalyptic bolts that come from the blue.
No matter where we hail from or who our parents were, we are descended from the hearty survivors of unimaginable catastrophes.
Each of us is a runner in the longest and most dangerous relay race there ever was, and at this moment, we hold the baton in our hands.
The past is another planet.
And so is the future.
Some 250 million years from now, many geologists think that the lands of the Earth will be united once again.
All this beauty will have vanished and the Earth of our moment in time will take its place among the lost worlds.
The great internal engine of plate tectonics is indifferent to life, as are the small changes in the Earth's orbit and tilt and the occasional collisions with little worlds on rogue orbits.
These processes have no notion of what has been going on over billions of years on our planet's surface.
They do not care.
Each of us is a tiny being riding on the outermost skin of one of the smaller planets for a few dozen trips around the local star.
The things that live the longest on Earth endure for only about a millionth of the age of our planet.
So, of course, the individual organisms see nothing of the overall pattern.
Of changing continents climate evolution.
That we understand even a little of our origins is one of the great triumphs of human insight and courage.
Who we are and why we are here can only be glimpsed by piecing together something of the full picture, which must encompass eons of time millions of species and a multitude of worlds.
In this perspective, it's not surprising that we're a mystery to ourselves and that, despite our manifest pretension, we are far from being masters of our own little house.
This new corridor has no name above the entrance to designate its epoch, and we don't yet know which failed species will be memorialized within its walls.
What happens here, in countless ways, both large and small, is being written by us.
Right now.