NG_Amazing Planet_2of3_Ocean Realm
Transcript
00:00For a land-loving species like ourselves, the seas are lovely, dark, and deep, unplumbed
00:22and often better left that way.
00:27But take a giant step back, and it's clear the oceans define our planet.
00:32Land masses become afterthoughts, commas and parentheses, in a much greater story.
00:39And the seas have a way of reminding us now and again who's really in charge.
00:46They inundate.
00:48They tower and smash.
00:50They shrug mightily and create tsunamis.
00:54They exhale and spin off super hurricanes.
01:01And beneath the bounding main, they hide wonders.
01:06Phantasmagorical seascapes smoking and growing.
01:11Islands in the making.
01:15Creatures beautiful and utterly strange.
01:21Plunge into the ocean depths and examine their hidden riches.
01:27Step back in time to find out how it all began and how we got to today.
01:34And come to understand what this relentless force of nature can do at its most violent
01:41and most beautiful on our amazing planet.
01:50NASA Jet Propulsion Laboratory, California Institute of Technology
02:05Water.
02:07A single drop of it is a miracle.
02:11Colorless, tasteless, odorless.
02:15It is part of every living thing on the planet.
02:20And it has been here since almost the beginning of the Earth.
02:24It has been belched out of volcanoes as vapor, risen to great heights, fallen back to Earth
02:31as rain, fed life, returned to the soil, to rivers, and to the sea.
02:37Perhaps to be sucked down into the molten Earth again.
02:43A journey that each molecule in this drop may have taken thousands of times over millions of years.
02:51In it, life teems.
02:55And that's just a drop in the bucket.
02:58And what a bucket.
03:01No other planet in our solar system can lay claim to this strange blue liquid
03:06that made life possible and can also destroy it.
03:14More than 70% of the surface of the planet is covered with water.
03:20And that's just the surface.
03:23In volume, water fills up 320 million cubic miles.
03:29Some 95% of the livable habitats on Earth are in the oceans.
03:36If we were to divvy the oceans up,
03:40each person on the planet would have more than 50 billion gallons of water apiece.
03:47Five different oceans dominate the globe.
03:51The Arctic, Atlantic, the Indian, Antarctic, and the stupendous Pacific.
04:00Mother of all oceans.
04:03All of these bodies of water are so profoundly connected to each other
04:08that most oceanographers refer to the world ocean.
04:12A single marvelously complex entity.
04:16It is tossed by winds, tugged by the moon,
04:20driven by an invisible conveyor belt,
04:24tugged by the moon,
04:26driven by an invisible conveyor belt,
04:29and warmed by the sun.
04:31It can never rest.
04:38It is made of a substance so amorphous,
04:41it can take the form of a solid, liquid, or gas.
04:46To make matters more dizzyingly complex,
04:49the ocean's influence reaches high into the atmosphere.
04:53Each day, they absorb enough of the sun's energy
04:57to feed the world's oil demands three times over,
05:01the equivalent of 250 billion barrels of oil.
05:07Each day, a trillion tons of water evaporate,
05:11taking millions of megawatts of potential energy into the atmosphere.
05:16The results are titanic.
05:19The ocean atmosphere dynamic is the hydrosphere,
05:24the water world.
05:27It was long assumed that the ocean floors were as blank and featureless
05:31as the ocean surface itself.
05:34But their topography is even more complex and varied than that on dry land,
05:39with mountain ranges longer and taller than the Himalayas,
05:43and trenches deeper than the Grand Canyon.
05:49Our tour begins with the continental shelves,
05:53just beyond where you stick your toes in,
05:56submerged, gently sloping parts of the continents themselves.
06:03In the tropics, starting just yards offshore,
06:07we find the unequaled splendor of the coral reefs,
06:12a brilliant intermarriage of geology and biology.
06:17There are over 125,000 square miles of coral reefs
06:22across the globe, mostly in the tropics.
06:28The corals themselves are living things,
06:31but live on and among the limestone skeletons of their dead predecessors.
06:36They are architects of some of the largest skeletal formations in the world,
06:41providing natural breakwaters that protect shorelines.
06:46The largest of these is the Great Barrier Reef off the coast of Australia.
06:51The Great Barrier Reef started forming over 3 million years ago,
06:56when sea levels were far lower than today.
07:04As sea levels gradually rose,
07:07the corals kept pace, growing upward toward the sunlight.
07:12They now reach nearly 200 feet high,
07:17and their structure slows down the powerful wave energy of the open ocean,
07:24providing a stable environment for marine life to thrive over millennia.
07:32The coral reefs are home to an astounding number of interdependent species.
07:37It's a teeming Eden, a fantastically gaudy tranquility,
07:43punctuated by violence.
07:52In such a crowded coral reef community, symbiosis is a way of life.
07:58This fish, the parrotfish, does the reef an interesting favor.
08:03With powerful jaws and beaks that crush hard coral to extract the algae within,
08:09they grind the coral's skeleton, and they defecate the crushed sediment over the reefs.
08:16Thus, the parrotfish manufacture much of the sand in the coral reef community,
08:22sand that filters sediment from the waters,
08:25and protects coral from coastal erosion.
08:30The web of life on the ocean's reef is bustling, dense, and complex.
08:40Some attach themselves to the coral itself.
08:45Others cling to it, and with chameleon-like skill,
08:48hide in plain sight from predator and prey.
08:53Still others seek safe refuge in its crevices,
08:57and venture out at night to hunt and feed.
09:01But not all these fish live in the reef.
09:04Many merely swim by for take-out.
09:08Part-time visitors to the reef, sharks, skates, rays, and countless others.
09:17Beyond the reef, further along the continental shelf,
09:21we drop deeper and deeper into the ocean.
09:27The continental shelf continues to slant gently away to a depth of about 650 feet.
09:35Next we reach the continental slope,
09:38which can plunge down over 5,000 feet to the deepest parts of the ocean.
09:44Beyond the continental slope is deep ocean floor, the abyssal plain.
09:50For long stretches, it is as flat and featureless as we once thought the seafloor would be.
09:57But in places it is punctuated by some of the most fantastic canyons,
10:02mountain ranges, trenches, and volcanoes on Earth.
10:07And nothing is quite as spectacular as the Mid-Ocean Ridge,
10:11the largest geological feature on the planet.
10:15It runs 40,000 miles across the world oceans.
10:21These are the seams where the world is tearing itself apart and creating itself anew,
10:27spewing lava and heating up the crust.
10:33Along the ridge are hydrothermal vents, chimneys, and black smokers.
10:38This is where water and gases, heated by the inner Earth, force their way out.
10:44Ocean waters are sucked into the crust and spit back out with a different chemical composition.
10:51It's a fine-tuned machine, albeit a slow one.
10:56It may take millions of years for all the water on the planet to cycle through these vents.
11:03They act as filters do in a fish tank, cleaning out and rejuvenating the ocean's waters.
11:10The water from these vents is heated by molten magma beneath the Earth's crust.
11:15The crust, after all, is merely a thin film surrounding an enormous ball of molten energy.
11:22The magma-heated water is constantly escaping where it can,
11:26creating these fantastic chimneys and smokers.
11:33And they create one of the most extreme environments in the world.
11:39Far beyond the reach of sunlight, at depths of 7,000 feet,
11:45with extreme pressures and temperatures beyond 700 degrees Fahrenheit,
11:50it's the last place you'd expect to find living things.
11:56Or is it?
11:58Oddly, a resilient community of surreal organisms calls this place home.
12:05And they manage to survive completely cut off from what happens on the surface of the planet.
12:14Without any sunlight, they live off chemical compounds from within the Earth that we humans find toxic.
12:24Here, where the Earth is giving birth to itself,
12:29we find a clue as to how life itself may have been born under the brutal conditions of the primordial oceans.
12:40But that begs a question.
12:44Where on Earth did the oceans come from in the first place?
12:59In the beginning, Earth gave no clue that it would one day become that big blue marble in the sky.
13:15When it began to coalesce some 4.6 billion years ago,
13:19the planet was no longer just an ocean.
13:23When it began to coalesce some 4.6 billion years ago,
13:27the planet was a super-hot, molten sphere,
13:32racked by super-collisions as its gravity reeled in
13:36and the primordial planet reeled from, a bombardment of asteroids and comets.
13:43Sometime in the first 200 million years,
13:46the bombardment slowed and cooling took hold long enough to give the Earth a thin black skin.
13:53But the Earth was still so hot,
13:55the skin kept swallowing and recycling itself back into the molten mantle.
14:00Nothing like a continent could form yet.
14:05Giant cannonballs of lighter magma were shooting to the Earth's surface from deep within its mantle.
14:12Eventually, the cooled, hardened magma reached the surface and refused to be subsumed again.
14:20Finally, the first continents could begin to form.
14:24The Earth was about to undergo a sea change.
14:29All along, the Earth had been belching out gases from its molten magma.
14:34Water vapor began saturating the atmosphere.
14:38When the saturated atmosphere could hold it no longer,
14:42water vapor droplets formed and the skies opened.
14:47Eventually, the hot Earth found itself deluged by a torrential downpour,
14:52lasting perhaps millions of years.
14:57Nascent oceans formed,
14:59but it seems continuing asteroid and comet bombardments may have evaporated them.
15:06Rocking the Earth and starting the process all over again.
15:17Finally, 3.8 billion years ago, the Earth emerged as an ocean planet.
15:25But these were not like the oceans we have today.
15:28The early oceans were acidic, dense, shallow and corrosive.
15:36The skies above glowed red from particles in the atmosphere.
15:42And somehow, there was life.
15:45These are fossils of extremely primitive bacteria,
15:49almost 4 billion years old,
15:52that may have lived in ancient steaming mud pools,
15:55much as heat-loving organisms have been found thriving
15:59in the harsh, wet heat of geysers and hot springs today.
16:06Where life may first have taken hold around the underwater volcanic vents,
16:11like those found on the Mid-Atlantic Ridge.
16:14By about 3.5 billion years ago,
16:17despite hot lava still spilling forth above and below the oceans,
16:23strange domes and pillows of a new kind of life
16:26had taken shape in shallow water.
16:29Their descendants to this day can be found in places
16:32like Shark Bay, Australia.
16:35These are stromatolites, colonies of bacteria.
16:42A kind of bacteria that can turn sunlight into food
16:46and burp out oxygen as a by-product.
16:49The first photosynthetic creatures.
16:53As their numbers increased,
16:55they pumped more and more oxygen into the world.
17:00At first, the new oxygen stayed on the surface,
17:04absorbed by iron-laden rocks and water.
17:08But eventually, the concentrations reached the point
17:12where the oxygen had nowhere to go but up,
17:15into the atmosphere.
17:19At the time, oxygen was poisonous to just about everything alive,
17:24and it displaced the methane that kept the skies above warm.
17:29Thanks to the billions of tiny exhalations of the cyanobacteria
17:33over millions of years,
17:35the sky took on, for the first time, its blue tint.
17:40Ultimately, the stage was set
17:42for oxygen-dependent life to really take off.
17:46But something went terribly wrong.
17:53Apparently, the Earth turned into a cosmic snowball.
17:58Now, this is currently only a theory,
18:00but there's evidence from around the world
18:03that ice may have existed at the equator
18:06as well as the poles some 2.2 billion years ago.
18:11This is what some scientists think happened.
18:16All that oxygen destabilized the world climate
18:19by destroying the greenhouse gas, methane.
18:24And because oxygen isn't nearly as efficient at trapping heat as methane is,
18:32the world cooled dramatically.
18:38As snow and ice began to cover more and more of the cooling planet,
18:43it reflected more and more of the sun's energy back into space,
18:48leading to further cooling,
18:51leading to further ice,
18:53further reflection,
18:55and an even colder Earth.
18:58This chilly feedback loop is called runaway albedo.
19:03And believe me,
19:05you don't want to be around the next time it happens.
19:11Over millions of years,
19:13sea ice slowly groaned and cracked its way toward the Earth's equator.
19:18When it reached the tropics,
19:20it rapidly engulfed the tropical seas,
19:23and soon the entire globe was covered in ice.
19:30The frozen planet must have looked like something out of a science fiction movie
19:34or perhaps a bit like Europa, Jupiter's frozen moon.
19:39When the process was complete,
19:41the surface of the planet was one big shimmering snowball
19:45or something, a slush ball.
19:48Some scientists theorize that the entire Earth's oceans
19:52were frozen to a depth of half a mile below sea level.
19:56This begs two giant questions.
20:00What on Earth could survive such an event?
20:03And what else on Earth could have stopped the snowballing snowball?
20:09The answer may well be one and the same.
20:13Magma.
20:15Bless its hot red heart.
20:19It continued to spew out not only heat from the Earth's core,
20:24but greenhouse gases that could trap the heat from the sun.
20:28And it may well have provided warmer oases
20:31where life could hibernate long enough to survive the big chill.
20:37While the snowball theory continues to raise questions
20:40about the extent of Earth's deep freeze,
20:44few debate that it was Earth's inner engine of heat and lava
20:48that snapped it out of its cold spell.
20:51And by that point in Earth's history,
20:54that engine had already begun to do something remarkable
20:57to the planet's surface.
21:03Continents wholly unrecognizable today
21:06had surfaced and started to move,
21:09tearing apart, banging into each other,
21:12grinding by one another.
21:14The remarkable story of plate tectonics had begun.
21:19And in the oceans, life would never be the same.
21:29Jostled by the bumper car antics of restless continents,
21:34the story of Earth's oceans was about to get dramatically more dynamic.
21:42By two billion years ago,
21:45our Earth had begun to look vaguely familiar.
21:50There were continents,
21:52clearing skies,
21:55and endless oceans,
21:58chock full of bacteria.
22:04Perhaps one billion years ago,
22:07multicellular life emerged,
22:10colonies of algae and later seaweed.
22:15At about the same time,
22:18the first supercontinent, Rodinia, appeared
22:22and broke apart again.
22:27What followed is a global billiard game
22:30of continents banging into one another,
22:32sticking together, breaking apart.
22:41By about 600 million years ago,
22:43the supercontinent, Penosia,
22:45came together and broke up.
22:51In the ocean world around it,
22:53sponges, jellyfish, and flatworms prowled the seas.
23:01At about this time,
23:03another cataclysmic snowball
23:05apparently swept over the planet,
23:07jump-starting evolution once again.
23:16By 540 million years ago,
23:18the continents were flooded by shallow seas,
23:23and the amazing monsters of what's called the Cambrian Explosion
23:27appeared in the oceans.
23:29Here, the arms race of predator and prey really took off.
23:33Creatures developed hard shells
23:35and used pinchers as weapons.
23:43500 million years ago,
23:45the continents surrounded the ancient Iapetus Sea,
23:52and an extensive inland sea
23:54inundated most of the ancestral North American continent.
24:00The first vertebrates soon appeared,
24:04jawless fish resembling today's lampreys.
24:14Around 450 million years ago,
24:17the Panthalassa Ocean covered much of the Northern Hemisphere
24:21as the Iapetus Sea closed.
24:24And finally came the kings of the oceans, sharks.
24:32It would take them 80 million years
24:34to perfect their killing ways.
24:37Then came their first golden age
24:39and millions of years of domination.
24:55By 400 million years ago,
24:57the continents had again crumpled together
24:59into a supercontinent, Pangaea,
25:02surrounded by the superocean, Panthalassa,
25:06and the much smaller Tethys Ocean.
25:11Sea levels fell substantially
25:13as ice covered much of the Southern Hemisphere
25:16and swamps formed along the equator.
25:20These waters eventually became
25:23the hunting grounds of ichthyosaurs and plesiosaurs,
25:27reptilian sea monster equivalents
25:30of the dinosaurs evolving on dry land.
25:41By about 225 million years ago,
25:45Pangaea began to break up
25:47and slowly our recognizable Earth began to take shape.
25:52The infant Atlantic Ocean began to grow.
25:58What on Earth could have been driving
26:00this bumper car game of crashing continents?
26:09The Earth actually is not solid.
26:12It's broken up into a dozen or so major plates
26:16These float along the top of the molten mantle.
26:20Some move apart, some crash together,
26:23some grate by each other.
26:25As the plates shift, they change the shape of our oceans.
26:34At the mid-Atlantic ridge,
26:36two plates, the American and the Eurasian,
26:39pull away from each other at a rate of about an inch per year.
26:46Lightning speed in geological terms.
26:49Their movement is triggered by molten magma
26:52beneath the oceanic crust.
26:56On this ridge, the ocean floor is literally
26:59bursting apart at the seams.
27:04Superheated lava gurgles up,
27:07creating new ocean floor.
27:12But the magma doesn't need to seep through the crust
27:15to create beauty.
27:17Not far away, marine scientists
27:20have discovered something amazing.
27:24Fantastic geological sculptures.
27:27Spiral towers formed not by magma itself,
27:30but by the way it heats up the ocean floor.
27:34They call it the Lost City.
27:38Here we find mystical formations standing precipitously
27:42nearly 20 stories off the ocean floor,
27:45like a wonderland of cathedral spires.
27:49Fueled by magma churning far below it,
27:52the crust has uplifted and split,
27:55exposing mantle rock.
27:57The spires tower from there.
28:00It has taken some 1.5 million years
28:03for this hot young crust to reach here
28:06from the mid-ocean ridge nine miles away.
28:09But unlike the smokers at the ridge itself,
28:12these spires are not directly venting volcanic activity.
28:17Instead, they are built by a chemical reaction
28:20between seawater and rock,
28:22a reaction cranked up by the heat of the mantle rock.
28:28The pH here is like that of liquid Drano.
28:32But the temperatures hover around a balmy 170 degrees Fahrenheit.
28:42So what does the ever-widening Atlantic mean for the Pacific Ocean?
28:50It's shrinking at roughly the same rate.
28:54On the other side of the planet,
28:56just off the coast of the Marianas Islands,
28:59lies a volatile trench.
29:05At a depth of over 35,000 feet,
29:08the Mariana Trench boasts the deepest point on the planet.
29:13There's enough room here to fit 28 Empire State Buildings.
29:18It's nearly seven miles down.
29:22But how did it get so low?
29:25The Mariana Trench is a subduction zone,
29:28the spot where the Pacific Plate and the Philippine Plate collide,
29:33where the Earth swallows the Pacific Plate into its belly.
29:38The subduction zones not only form deep trenches,
29:42they also trigger volcanic forces,
29:45and they wreak havoc on the ocean floor.
29:48The volcanic rim of the Mariana Trench yields more surprises.
29:55This is where the Earth pops the bubbling,
29:57at the deep ocean's Champagne Vent.
30:02Bubbles of carbon dioxide released from the crust
30:05percolate through the ocean to the surface,
30:08eventually reaching the atmosphere.
30:11How this CO2 affects our oceans is still anyone's guess.
30:16Around the corner and over the hill,
30:18we see sulfide chimneys standing 30 feet tall,
30:22where smoky hot gases are vented through the sea.
30:29Temperatures here are a cool 460 degrees Fahrenheit.
30:34Despite the boiling, toxic nature of the environment here,
30:38life has learned to live with it.
30:40Life that survives on energy from within the planet
30:44rubs shoulders with life that gets its energy from the sun,
30:48baffling scientists.
30:51Down the ridge, things get more violent.
30:55The Mariana Trench is a subduction zone,
30:58the spot where the Pacific Plate and the Philippine Plate collide.
31:02Down the ridge, things get more violent.
31:06As the Earth heaves, the surface of the undulating crust cracks,
31:11giving way to molten lava.
31:15Violent eruptions spit fire and sulfur into the ocean.
31:20Primordial gases from within the Earth's mantle
31:23burst through the crust and are released perhaps
31:26for the first time in billions of years.
31:30And now that we've seen the marvelous engines
31:33that create such wonders,
31:35we look back to see how it has changed the planet
31:38as we know it today.
31:48Five million years ago,
31:50a nanosecond in the scheme of things,
31:52and the Earth looks just as it does today.
31:55Right? Not quite.
31:58Look closely. There.
32:01North and South America aren't joined.
32:05A tiny little lost piece of the Earth's great big jigsaw puzzle
32:09is about to slide into place
32:12and change the world's oceans entirely.
32:18Not to mention the history of humanity.
32:26Nor the new pattern of violence
32:29about to appear in the skies above.
32:38It seems unimaginable that such a tiny change
32:41in our jigsaw Earth
32:43would utterly alter the course of the water world.
32:48Both the oceans blow in the skies above.
32:52But it did.
32:56It did.
33:01Twelve million years ago, the ocean was in constant motion.
33:05Currents circulated, shifting, twisting,
33:08squeezing around the continents.
33:10North and South America were unconnected.
33:14Water moved unhindered between the Atlantic and Pacific
33:18along something called the Central American Seaway.
33:22And to the north, there was no Arctic ice.
33:26All of this was about to change.
33:29Farther south in the tropics,
33:31the Cocos Plate slid violently under the Caribbean Plate,
33:35and volcanic peaks broke the surface.
33:42Over time, sediments plugged up the gaps around the islands.
33:47And voila!
33:49The isthmus of Panama was born.
33:52The isthmus cut off the free exchange
33:55between the Atlantic and Pacific.
33:58The direct line between the oceans was sealed.
34:04Nothing would ever be the same.
34:08With its passage to the Pacific blocked,
34:11any current running from the Atlantic
34:14had to do an about-face.
34:17Joining in turbocharging the early Gulf Stream,
34:20the currents turned up the heat in Europe.
34:24But perhaps the most profound change was in the far north.
34:30Some scientists think that the warm waters of the Gulf Stream
34:33carried more heat to the North Atlantic,
34:36causing more water to evaporate into the cold northern air.
34:41The evaporated water fell back into the Arctic Sea as rain and snow,
34:46diluting its salt levels.
34:49Fresher water, of course, freezes more easily.
34:53And by three million years ago, we had an Arctic ice cap.
35:00The white ice shield reflected the sun's heat back into space,
35:04ensuring its continued existence.
35:07Temperatures dropped further.
35:12And the ice cap became a key part of the powerful engine
35:16that drives the entire world ocean system,
35:20even today.
35:27It's called the Thermohaline Ocean Conveyor Belt.
35:31And it, more than anything, shows why the world's great seas
35:35are actually one great ocean.
35:39Here's how it works.
35:43When Arctic temperatures freeze the seawater,
35:46salt is locked out of the ice.
35:49The denser, saltier water pushes downward into the ocean
35:53and heads south.
35:55Currents on the conveyor belt
35:57take a global trip as they flow around the Horn of Africa,
36:01through the Indian Ocean,
36:03and eventually weave their way to the Pacific.
36:06The system curves around and repeats itself.
36:10The Gulf Stream in the Atlantic is so powerful,
36:13it transports about 40 million cubic yards of water every second.
36:21More importantly, this leg of the conveyor belt
36:24makes temperatures in the British Isles and northern Europe
36:27much milder than they would be otherwise.
36:32That's why it's warm enough for palm trees to grow on the coast of England.
36:38Because sea and air are so closely tied,
36:42the ocean conveyor affects weather profoundly.
36:46In some cases, with help from the rotation of the Earth,
36:50the ocean atmosphere dynamo works itself into a dangerous frenzy.
36:57The hot sun heats the sea surface,
37:00evaporating one trillion tons of water into the sky each day.
37:11The rotation of the Earth sends winds and ocean currents
37:14swirling in and out of the ocean.
37:17The rotation of the Earth sends winds and ocean currents
37:20swirling over the globe.
37:22It's called the Coriolis effect.
37:26The momentum of the Earth's rotation deflects currents
37:29away from the equator toward the poles.
37:32They form a clockwise gyre in the northern hemisphere
37:36and a counterclockwise one in the southern hemisphere.
37:43Cold air currents clash with warm currents,
37:46creating storms.
37:51When ocean temperatures rise and storm winds pick up speed,
37:55vast amounts of water evaporate from the ocean's surface.
37:59Warm, moist air climbs rapidly upward
38:02and then condenses as it cools,
38:05releasing even more energy.
38:08Heavy rains fall and winds accelerate.
38:11Bands of thunderstorms begin to radiate outward
38:14for hundreds of miles.
38:18The winds crank up the storms
38:21as the oceans feed the rage.
38:26The force of the Earth's rotation, the Coriolis effect,
38:29causes the bands of storms to rotate into spirals,
38:33forming hurricanes in the Atlantic Ocean
38:36and typhoons in the Pacific Ocean.
38:40Hurricanes can stir up more than a million cubic miles
38:44of the Earth's atmosphere every second.
38:49With the onset of global warming,
38:52the seas have become the great repository of the extra heat.
38:58And it's beginning to look as though hotter oceans
39:01are feeding more and more monstrous hurricanes.
39:05Year after year, storms reach havoc and destruction.
39:09And it seems in recent years,
39:12we have entered a period of heightened storm activity.
39:18As the sea temperatures continue to rise globally,
39:22so does the ferocity of the storms.
39:29But the water world may well have
39:32more frightening things up its sleeve than hurricanes.
39:44As the continents have gone sliding and banging
39:47around the planet through the ages,
39:50congregating and then heading off in their own directions repeatedly,
39:57they have massively reshaped the oceans.
40:01But it's far more than shape that's at stake.
40:06All life is dependent on the water world,
40:09the way our oceans are yoked to our skies.
40:16Our oceans, despite their profound interconnectedness,
40:20have very different chemical make-ups,
40:25their own personalities, as it were.
40:29The Atlantic is saltier than the Pacific.
40:33The North Atlantic has the highest concentration of carbon dioxide,
40:38while the Antarctic has the lowest.
40:42The chemical composition of the oceans has changed drastically
40:47and abruptly throughout their history.
40:51Given that something as small as the isthmus of Panama
40:55forever changed the way the water world functions,
40:58it seems clear that plate tectonics,
41:01creating new oceans here and slamming others shut there,
41:07has had a profound effect on the Earth as a whole.
41:13So what does the future hold?
41:16Thanks to plate tectonics, we can take a peek
41:19at what the planet might have in store for us.
41:25DENAKEL DESERT
41:29Could it be that in the middle of this hot, dry desert,
41:32an ocean is being born?
41:36The fault lines here in the Denakel Desert in Ethiopia
41:40are growing at a startling rate.
41:45With the Red Sea just over the ridgeline to the east,
41:48it is ripe for a deluge.
41:52A slight breach could send in the waters of the Red Sea,
41:56filling the basin of the East African Rift,
42:01creating a new sea.
42:04The momentum of the plates eventually slides Somalia
42:07and Madagascar out into the Indian Ocean,
42:13and Arabia pushes northward, eliminating the Persian Sea.
42:18All over the world, the movement of the plates
42:21begins to make our globe less recognizable.
42:26California seems intent on becoming an island,
42:29sliding north toward Alaska.
42:32Australia heads north, gobbling up islands along the way
42:36and becoming attached to Asia.
42:39Africa's huge mass drives northward toward Europe
42:43and eventually does away with the Mediterranean.
42:48The collision slowly thrusts the Alps
42:51up to the heady heights of the Himalaya and beyond.
42:57How will all these continental antics
43:00millions of years from now affect the oceans?
43:03Well, it may not be pretty.
43:06We have grim evidence that the obliteration of the sea,
43:10like the Mediterranean, can have a huge impact on Earth.
43:18On the floor of the Mediterranean Sea
43:21lies a signpost of disaster.
43:24A geological feature tells the story
43:27of a different sea at a different time,
43:30dating back some six million years.
43:33It shows a small shoreline far below the waters of the current sea.
43:41Pointing to a cataclysmic event
43:44that may have changed the course of human evolution.
43:53It was the Miocene Epoch.
43:58Ancient mammals roamed the land.
44:04But around six million years ago,
44:07the collision crushed together the opening to the Mediterranean,
44:11choking it off from the Atlantic Ocean.
44:17With virtually no refreshment from the ocean
44:20and inadequate rains,
44:23over thousands of years the entire Mediterranean Sea evaporated,
44:28creating vast expanses of scorched earth.
44:33Elsewhere on Earth, even bigger changes were underway.
44:41For several million years, the Antarctic ice cap had been growing,
44:45turning more and more ocean into ice.
44:52The increased ice reflected more of the sun's energy back into space.
44:58An ice age resulted.
45:03The world's sea level dropped 165 feet,
45:07further cutting off the Mediterranean Sea from the Atlantic.
45:12Around the Mediterranean, entire species were wiped out
45:16and life decimated.
45:19Others fled.
45:22It was a cataclysm in the making.
45:25But then, the cavalry arrived.
45:28A very wet cavalry.
45:39Several hundred thousand years after the Mediterranean evaporated,
45:43something caused the Atlantic to breach the Strait of Gibraltar.
45:47Nobody really knows what.
45:50The possible result was a giant 3,000-foot wave
45:55The possible result was a giant 3,200-foot waterfall
46:00with a force thousands of times greater than Niagara Falls
46:04that shot through Gibraltar to fill almost a million square miles
46:08of the Mediterranean basin.
46:11If the ocean hadn't charged through the Strait,
46:14we might have faced living on a frigid planet,
46:17if we survived at all.
46:20The Earth's climatic path could have changed
46:23and history might be very different,
46:26or perhaps even non-existent.
46:29One theory says the Mediterranean crisis
46:32transformed woodland landscapes in Africa
46:35to open savannas,
46:38encouraging our early ancestors to descend from the trees
46:42and take a chance walking on two feet.
46:48We are here, it seems, by extraordinary chance.
46:52Who knows how many crises the Earth underwent
46:55during our evolution that could have changed us one way or another.
47:00And who's to say severe climate change won't happen again?
47:05Could a snowball deep freeze sweep across the world as we know it?
47:14Or could rising temperatures instead cause rising sea levels,
47:18creating a true water world?
47:22Let's look as far into future possibilities
47:25as our plate tectonics time machine will allow.
47:29We can see amazing changes,
47:32but not yet the force that almost certainly will drive
47:35all the continents back together,
47:39as it has done time and time again
47:42throughout the history of the Earth.
47:45In the next 50 million years, the Atlantic continues to grow,
47:49but its North American plate could begin to shrink.
47:56150 million years in the future,
47:59the mid-Atlantic ridge may slide under North America,
48:03pushing the eastern coast of America high atop a mountain range,
48:08and the mighty Atlantic begins to disappear.
48:12By 250 million years into the future,
48:15the Pacific Ocean widens to encompass most of the globe.
48:19The continents compress into the future supercontinent,
48:23Pangaea Ultima.
48:26Imagine humanity on one continent.
48:31Will we still be here?
48:34Or will we have left already,
48:37taking with us the history of our blue planet
48:40as a story to be told again and again
48:43to different planets in different solar systems?
48:48One thing seems certain.
48:51Earth as home seems a place hard to forget.
49:01And we owe its perfection, its place as our home,
49:07to its oceans.
49:10For the time being, our oceans take care of us,
49:16and the engine that drives our planet's climate
49:19maintains a comfortable range of temperate zones and seasons across the globe.
49:25Our restless oceans are always changing,
49:29constantly morphing.
49:34Will we end up in a snowball Earth,
49:38or one that's too hot to handle?
49:44And what is most likely to survive?
49:53Only time will tell.
49:56And either way, the oceans hold the key.
50:07NASA Jet Propulsion Laboratory, California Institute of Technology