Earth: The Inside Story (2014) - full transcript

male narrator:
EARTH...

THE ONLY PLANET ORBITING THE SUN

THAT HAS CONTINENTS,

OCEANS,

PLATE TECTONICS,

AND THE SOLE PLANET
WITH AN ATMOSPHERE

THAT HAS SUSTAINED LIFE
FOR BILLIONS OF YEARS.

HOW DID EARTH GET THIS WAY?

WHAT'S BEHIND THE POWER,
THE VIOLENCE

THAT CRACKS SOLID ROCK
IN AN INSTANT,

THAT SHATTERS BUILDINGS



AND SENDS TSUNAMIS
RACING FOR THE SHORE,

THAT ERUPTS SEAS OF LAVA
AND BILLOWING CLOUDS OF ASH?

EARTH HAS BEEN
MAKING HEADLINES LATELY.

- POWERFUL IMAGES OF DESTRUCTION
NEVER SEEN IN OUR LIFETIME.

narrator:
PEOPLE ARE ASKING,

"HAS EARTH ENTERED A PERIOD
OF INTENSE GEOLOGIC UPHEAVAL?"

SCIENTISTS HAVE NEW ANSWERS
TO QUESTIONS ABOUT OUR HOME,

THE THIRD PLANET FROM THE SUN.

IT'S A STORY THAT,
JUST A FEW DECADES AGO,

COULD NOT HAVE BEEN TOLD.

ABOUT 10 BILLION YEARS

AFTER THE BIG BANG
CREATED THE UNIVERSE,

OUR SOLAR SYSTEM BEGAN TO FORM.

SCIENTISTS CALCULATE
THAT THIS HAPPENED



4.567 BILLION YEARS AGO,

AND THAT WAS WHEN PLANET EARTH
WAS CREATED.

- A LONG TIME AGO,
ABOUT 4 1/2 BILLION YEARS AGO,

THE EARTH FORMED
FROM THIS NEBULA AROUND THE SUN.

THE SUN IN THE CENTER,
AND THE NEBULA SWIRLING AROUND,

AND THE BITS
OF THE NEBULA ACCRETING,

THAT IS, STICKING TOGETHER
AND COLLIDING WITH EACH OTHER,

AND IT WAS
A VERY TURBULENT TIME.

[explosion]

AND THE EARTH
GRADUALLY CAME TOGETHER,

AND AS IT BECAME MORE MASSIVE,

THE GRAVITATIONAL FORCE
BECAME LARGER,

AND IT COULD ATTRACT
MORE OF THE SMALL PIECES,

AND THE EARTH GREW AND GREW.

narrator:
IT TOOK ABOUT 100 MILLION YEARS

FOR EARTH TO REACH
ITS PRESENT SIZE,

BUT BEFORE IT DID,

OUR PLANET EXPERIENCED ITS
LARGEST, MOST DRAMATIC EVENT.

- SO AFTER
THE EARLY EARTH FORMED,

PROBABLY TENS OF MILLIONS
OF YEARS AFTERWARDS,

YOU HAD A MARS-SIZED OBJECT
THAT ACTUALLY HIT THE EARTH.

[explosion]

narrator: THE GIANT PLANETOID
IMPACTOR WAS CALLED THEIA.

- THE MARS-SIZED IMPACTOR
HIT THE EARTH,

AND IT SPEWED OFF A LOT
OF THE MATERIAL FROM THE EARTH,

AND PART OF THAT
FORMED THE SMALL--

THE MOON THAT WE NOW HAVE.

AND ALSO WE GENERATED A LOT
OF HEAT FROM THIS IMPACT,

AND SO IT MIGHT HAVE REMELTED
A LOT OF THE EARLY EARTH.

narrator:
SCIENTISTS ONLY RECENTLY LEARNED

OF THIS MASSIVE IMPACT

BY STUDYING ROCKS
COLLECTED ON THE MOON.

IT TURNED OUT THAT
THE MOON ROCKS WERE VERY SIMILAR

IN COMPOSITION TO EARTH ROCKS.

AFTER THE IMPACT,
THE MOON BECAME A SATELLITE,

WHILE THE EARTH WAS LEFT
A MOLTEN BALL OF FIRE.

- AND SO THE EARLY EARTH
WAS, LIKE, THIS MOLTEN MASS.

THAT MUST HAVE LOOKED
LIKED MAYBE ONE GIANT VOLCANO

OR LAVA LAKE.

IT SLOWLY SOLIDIFIED
AND FORMED THIS OUTER CRUST

THAT IS WHERE WE STAND TODAY.

narrator:
AS THE CRUST FORMED,

COLLISIONS AND BOMBARDMENTS
DIED DOWN,

BUT THE METEORITES
CONTINUE TO FALL TO THIS DAY.

- WE START WITH SOME
BREAKING NEWS THIS HOUR.

PEOPLE IN THE URALS IN RUSSIA

HAVE SEEN BURNING OBJECTS
RAINING DOWN FROM THE SKY

AFTER A METEORITE EXPLODED
ABOVE THE EARTH,

CAUSING A METEOR SHOWER.

EYEWITNESSES REPORTED
SEVERAL BLASTS.

[glass shattering]

narrator: DESPITE THE SHOCK
THAT A METEOR SHOWER CAN CAUSE,

METEORITES ARE
EXTREMELY VALUABLE TO SCIENTISTS

WHO STUDY WHEN THE EARTH
WAS CREATED.

THEY ARE COLLECTED
AND STUDIED WORLDWIDE.

BUT THE BEST PLACE
TO FIND THESE ROCKY ALIENS

IS ONE OF THE EARTH'S
MOST UNEARTHLY PLACES:

ANTARCTICA.

ON THE SLEEK, BLUE ICE EXPANSE

OF THE CENTRAL ANTARCTIC
ICE SHEET,

THE SURFACE IS SWEPT CLEAN
BY RELENTLESS WINDS.

A METEORITE SITS EXPOSED
FOR AN AVERAGE OF 20,000 YEARS,

SOMETIMES
FOR SEVERAL MILLION YEARS,

BEFORE SCIENTISTS MIGHT SPOT IT
AND COLLECT IT.

A TYPE OF METEORITE
CALLED A CHONDRITE

CONTAINS THE SAME BASIC ELEMENTS

THAT MAKE UP THE SUN
AND PLANETS,

SO THEY TELL US A GREAT DEAL

ABOUT WHERE
WE ORIGINALLY CAME FROM

AND WHEN.

TO FIGURE OUT HOW OLD
METEORITES AND THE EARTH

ACTUALLY ARE,

SCIENTISTS USE
HIGH-PRECISION INSTRUMENTS

TO MEASURE
THEIR RADIOACTIVE PROPERTIES.

BUT WHY MUST SCIENTISTS
RELY ON METEORITES

TO FIGURE OUT HOW OLD
THE EARTH REALLY IS?

WHY DON'T THEY SIMPLY STUDY
THE OLDEST ROCKS

THAT WERE FORMED
ON THE EARTH ITSELF?

- FROM THE EARTH'S FORMATION
AROUND 4.6 BILLION YEARS AGO

UP TO ABOUT
3.8 BILLION YEARS AGO,

IS AN ERA CALLED THE HADEAN,

WHEN THE EARTH WAS UNDERGOING
HEAVY BOMBARDMENT,

AND THERE'S
VIRTUALLY NO ROCK RECORD

FROM THAT PERIOD OF TIME AT ALL
ON THE EARTH REMAINING TODAY.

narrator:
THE HADEAN ERA,

GREEK FOR UNDERWORLD,
OR HELL.

NOTHING SURVIVED THIS INFERNO...

OR DID IT?

IT WAS A MISSING LINK HUNDREDS
OF MILLIONS OF YEARS LONG

BETWEEN EARTH'S CREATION
AND ITS OLDEST ROCKS,

LIKE THESE 3.6 BILLION-YEAR-OLD
ROCKS FOUND IN AUSTRALIA.

- BEAUTIFUL.

narrator: BUT BREAKTHROUGHS
IN ANALYZING THESE ROCKS

FINALLY OPENED A WINDOW
INTO THE HADEAN.

- INTERESTINGLY, WE DO HAVE
SOME MATERIALS FROM THAT TIME.

THEY ARE SMALL ZIRCON GRAINS,
4.4 BILLION OR SO OF AGE.

narrator: ZIRCONS ARE
THE OLDEST TERRESTRIAL MATERIAL

EVER FOUND ON EARTH.

BUT ROCKS CONTAINING ZIRCONS
THAT ARE BILLIONS OF YEARS OLD

HAVE ONLY BEEN DISCOVERED
IN A HANDFUL OF PLACES ON EARTH,

LIKE ANTARCTICA.

THE REST HAVE BEEN OBLITERATED.

STUDYING THOSE RARE VESTIGES
OF THE EARLY DAYS OF EARTH,

SCIENTISTS WERE ASTONISHED
TO FIND EVIDENCE

THAT VERY EARLY ON,
EARTH DEVELOPED A CHARACTERISTIC

THAT IT AND NO OTHER PLANET
IN THE SOLAR SYSTEM POSSESSES:

PLATE TECTONICS.

- PLATE TECTONICS
HAS BEEN AROUND ON EARTH

FROM THE EARLY DAYS,

AT LEAST 2 1/2,
3 BILLION YEARS AGO.

SO MORE THAN 3/4 OF THE LIFE
OF THE PLANET.

narrator: MARS NEARLY DEVELOPED
PLATE TECTONICS,

BUT FAILED.

- MARS IS SMALLER THAN EARTH.

IT COOLED FASTER.

IT MAY WELL HAVE HAD A STYLE
OF PLATE TECTONICS

EARLY IN ITS HISTORY,
BUT IT CLEARLY DOES NOT TODAY.

narrator: VENUS, CONSIDERED
EARTH'S SISTER PLANET,

IS ALSO MISSING EARTH'S TRAIT
OF PLATE TECTONICS.

- VENUS DOESN'T HAVE
PLATE TECTONICS

IN THE STYLE THAT WE RECOGNIZE

WITH VERY CLEAR, LINEAR
BOUNDARIES BETWEEN RIGID PLATES,

PERHAPS BECAUSE THERE'S NO WATER
ON THE SURFACE OF VENUS.

narrator:
LIQUID WATER:

IT IS THE STRIKING AND
DISTINGUISHING CHARACTERISTIC

OF EARTH'S SURFACE,

AND SCIENTISTS ARE FINDING
THAT THIS SUBSTANCE IS THE KEY

THAT STARTED EARTH'S EARLY CRUST

INTO CONSTANT,
EVER-CHANGING MOTION.

- ONE OF THE REASONS
WE HAVE PLATE TECTONICS,

WHICH WE DON'T SEE
ON ANY OTHER PLANETS,

IS THAT WE HAVE
A LOT OF WATER ON THE EARTH.

SO WE HAVE WATER
NOT ONLY IN THE OCEANS,

BUT THERE'S APPROXIMATELY
AN OCEAN'S WORTH OF WATER

LOCKED UP IN THE ROCKS IN, SAY,
THE UPPER 100 KILOMETERS

OF THE EARTH.

WHEN YOU PUT WATER INTO A ROCK,

IT MAKES THE ROCK WEAKER
BY MAYBE A FACTOR OF 100

THAN IT WOULD BE
WITHOUT THE WATER.

WEAKER ROCKS
MAKE FOR PLATE TECTONICS

BECAUSE YOU HAVE TO HAVE
PLATE BOUNDARIES

WHERE ROCKS EITHER SLIDE
BY EACH OTHER,

OR ONE GOES DOWN
UNDERNEATH THE OTHER.

AND SO UNLESS YOU HAVE ROCKS
THAT ARE WEAK ENOUGH

TO BE ABLE TO SLIDE
PAST EACH OTHER,

YOU'RE NOT GONNA HAVE
PLATE TECTONICS.

narrator: BUT WHERE
DID EARTH'S VAST AMOUNT

OF LIQUID WATER COME FROM?

- IN THE EARLY HISTORY
OF THE EARTH,

WHEN THERE WAS A LOT
OF VOLCANISM GOING ON,

VOLCANOES ACTUALLY
BROUGHT GASES UP

THAT CREATED
THE EARLY ATMOSPHERE.

AND MAGMA HAS WATER
IN THE FORM OF VAPOR

THAT IT CAN BRING UP.

[rumbling]

narrator:
ICY METEORITES AND COMETS

WERE THE OTHER LIKELY SOURCE

THAT INFUSED EARTH'S CRUST
WITH WATER

AND GOT IT MOVING.

AND ONCE PLATE TECTONICS
STARTED,

IT NEVER STOPPED.

IT HAS INFLUENCED EVERYTHING
THAT HAS HAPPENED ON THE SURFACE

INCLUDING LIFE.

- THE OXYGEN, THE MINERALS,
EVERYTHING THAT WE GET

COMES FROM THE INTERIOR
OF THE EARTH.

WE ALL HAVE INTERNALLY WITHIN US

A WHOLE SUITE OF MINERALS
AND THINGS THAT--

WE'RE FROM THE EARTH.

ESSENTIALLY, THAT'S WHERE WE--

OUR CHEMICAL MAKEUP
IS FROM THE EARTH.

AND IF YOU HAD NO WAY OF GETTING
THAT OUTSIDE OF THE EARTH,

THEN ESSENTIALLY YOU'D HAVE
A DEAD PLANET.

narrator: PLATE TECTONICS
BECAME RECOGNIZED

AS BEING A CRUCIAL INGREDIENT
FOR LIFE,

AS IS WATER.

THIS WAS AN IMPORTANT PIECE
OF KNOWLEDGE

FOR SCIENTISTS WHO WERE STUDYING
EARTH'S ANCIENT ROCKS.

IF THE CONDITIONS FOR LIFE
WERE PRESENT

WHEN EARTH'S ANCIENT ROCKS
FORMED BILLIONS OF YEARS AGO,

THEN WASN'T IT POSSIBLE
THAT LIFE ALSO TOOK HOLD

IN THE EARLY DAWN
OF EARTH'S FORMATION?

THE SEARCH WAS ON.

SOME SCIENTISTS ZEROED IN ON
THE 3.5 BILLION-YEAR-OLD ROCKS

IN THE OUTBACK
OF WESTERN AUSTRALIA.

- AMAZINGLY, IT TURNS OUT
THAT FAIRLY SOON AFTER,

PEOPLE STARTED DISCOVERING
SOME POTENTIAL SIGNS OF LIFE

IN THOSE ROCKS,

AND ONE OF THE MAJOR DISCOVERIES

WAS STRUCTURES
CALLED STROMATOLITES.

narrator: STROMATOLITES
ARE PECULIAR ROCKY STRUCTURES

BUILT BY COLONIES
OF CYANOBACTERIA,

OR BLUE-GREEN ALGAE.

THEY ARE EXTREMELY RARE
ON EARTH TODAY,

GROWING IN ONLY A FEW PLACES,

LIKE LAGUNA BACALAR IN MEXICO.

BUT THEY WERE THE FIRST
LIFE FORMS TO APPEAR ON EARTH,

AND THEY GAVE RISE
TO ALL OTHER FORMS OF LIFE,

INCLUDING PEOPLE.

IT TOOK AWHILE, THOUGH.

- STROMATOLITES DOMINATE
THE FIRST 3 BILLION YEARS

OF THE HISTORY OF LIFE ON EARTH.

SO FROM 3 1/2 BILLION YEARS AGO

TO UP TO ABOUT
1/2 A BILLION YEARS AGO,

THE FOSSIL RECORD CONSISTS

ALMOST ENTIRELY
OF STROMATOLITES.

narrator: STROMATOLITES LIVED
IN OCEANS AND LAKES.

FOR THAT PERIOD,
NO FOSSILS HAVE BEEN FOUND

OF CREATURES THAT LIVED ON LAND.

DOES THAT MEAN
THERE WERE NO CONTINENTS

FOR THE FIRST 3 BILLION YEARS
OF EARTH'S HISTORY?

ONCE AGAIN,

EARTH'S ANCIENT ROCKS
YIELDED CLUES TO THIS MYSTERY.

- WE DON'T KNOW FOR SURE
WHEN PLATE TECTONICS STARTED,

BUT WE DO KNOW FOR SURE
WHEN WE FIRST HAD CONTINENTS.

WE HAVE INTACT AREAS
THAT WE CAN GO AND MAP IN

THAT GO BACK AS FAR
AS 4 BILLION YEARS.

THAT'S NEARLY 90%
OF THE AGE OF THE EARTH,

SO WE'RE QUITE SURE
ABOUT THE FACT

THAT WE HAD CONTINENTS
BACK THAT FAR.

narrator: NO ONE KNOWS
WHAT THE CONTINENTS WERE LIKE

4 BILLION YEARS AGO

OR WHY WE ENDED UP
WITH SEVEN CONTINENTS

THAT RIDE AROUND
ON A DOZEN LARGE CRUSTAL PLATES

AND MANY MICROPLATES IN BETWEEN.

BUT THE QUESTION THAT PLAGUED
SCIENTISTS FOR YEARS WAS THIS:

WHAT WAS THE PRIME FORCE
THAT MADE THE PLATES MOVE?

THERE WERE
TWO CONTENDING FORCES.

THE FIRST WAS DISCOVERED ABOARD
SEAFARING RESEARCH VESSELS

MAPPING THE SEA FLOOR
DECADES AGO.

SCIENTISTS LEARNED
THAT THE SEA FLOOR

WAS SPREADING APART
IN THE MIDDLE OF THE OCEANS

AT SUBMARINE MOUNTAIN RANGES
CALLED MID-OCEAN RIDGES.

SUBMERSIBLES WERE SENT DOWN

AND CAME BACK WITH FOOTAGE
OF HOT GASES WELLING UP

IN THE RIFT ZONES.

MAGMA WAS RISING
FROM BELOW HERE,

AND IT WAS BELIEVED
THAT IT WAS PUSHING

THE OCEANIC PLATES APART.

THE KEY TO PLATE TECTONICS
WAS AT LAST DISCOVERED...

OR WAS IT?

SEISMIC EXPERIMENTS
OF EARTH'S DEEP CRUST AND MANTLE

CHANGED SCIENTISTS' THINKING.

A SECOND FORCE WAS DISCOVERED

WHERE PLATES
COLLIDED HEAD-ON,

AS THEY DO UNDER
THE ANDES MOUNTAINS OF ECUADOR.

ONE PLATE WAS IMAGED DIVING
UNDERNEATH THE OTHER.

THE WAS CALLED
A SUBDUCTION ZONE.

THE SINKING SLAB
APPEARED TO BE PULLING

THE REST OF THE PLATE BEHIND IT,

MAKING THE ENTIRE PLATE MOVE.

A GREAT DEBATE AROSE OVER
WHICH FORCE WAS MORE IMPORTANT

IN DRIVING PLATE TECTONICS:

PUSHING FROM THE RISING MAGMA
OR PULLING IN SUBDUCTION ZONES.

THERE NOW APPEARS
TO BE A WINNER.

- WHEN PEOPLE FIRST RECOGNIZED
MID-OCEAN RIDGE SPREADING

AS THE KEY TO UNDERSTANDING
PLATE TECTONICS,

THE VIEW WAS THAT THE MAGMA,
THE MANTLE,

ROSE UP IN THE CENTER
AND FORCED THE PLATES APART.

BUT THAT VIEW
HAS CHANGED OVER THE YEARS

AND HAS LARGELY BEEN REPLACED
BY THE VIEW THAT IT'S THE PULL

OF THE SUBDUCTION SLAB
THAT MATTERS MOST.

- BOB, CAN YOU PLEASE HAND ME
THE PVC PIPE, PLEASE?

- SURE.

narrator: SO SCIENTISTS
LOOKED HARDER AT SUBDUCTION,

AND AS THEY DID, MORE GEOLOGIC
WONDERS WERE UNCOVERED.

FOR ONE, SEISMIC STUDIES
OF SUBDUCTION ZONES

REVEALED THAT OCEANIC PLATES
ARE VERY THIN

COMPARED TO CONTINENTS.

THE SEA FLOOR
IS 3 TO 6 MILES THICK,

WHILE CONTINENTS AVERAGE
30 MILES THICK

AND SWELL UP TO 50 MILES
UNDER GREAT MOUNTAIN BELTS.

THIS HAS A MAJOR INFLUENCE

ON HOW THE PLATES
AFFECT EACH OTHER,

ESPECIALLY IN SUBDUCTION ZONES.

WHERE SUBDUCTING PLATES
MEET CONTINENTS,

EARTH'S TALLEST MOUNTAINS
ARE BUILT:

THE HIMALAYA OF ASIA,

THE ALPS OF EUROPE,

THE ANDES OF SOUTH AMERICA.

SUBDUCTION CREATED THEM ALL.

BUT SUBDUCTION CAN CREATE HAVOC
ON THE SURFACE.

AS SEISMIC NETWORKS
IMPROVED AROUND THE WORLD,

IT BECAME APPARENT
THAT SUBDUCTION WAS THE CULPRIT

BEHIND EARTH'S
MOST POWERFUL EARTHQUAKES.

- FIRST THE EARTHQUAKE ITSELF...

[people screaming]

A GROCERY STORE IN THE CAPITAL
AT THE MOMENT OF IMPACT.

narrator:
THE TOHOKU EARTHQUAKE OF 2011

WAS THE MOST POWERFUL
EVER KNOWN IN JAPAN

AT MAGNITUDE 9.

IT STRUCK
WHERE THE OCEANIC PACIFIC PLATE

SUBDUCTS UNDER A PIECE
OF THE NORTH AMERICAN PLATE.

- WHERE SUBDUCTION IS OCCURRING,

YOU SEE A VERY WELL-DEFINED ZONE
OF EARTHQUAKES,

ESSENTIALLY BETWEEN
THE DOWNGOING OCEANIC CRUST

AND THE CONTINENTAL CRUST,

AND IT FORMS A LINE
OF EARTHQUAKES

WHERE THESE TWO CRUSTS
ARE IN CONTACT WITH EACH OTHER

AND SLIPPING PAST EACH OTHER.

[siren wailing]

narrator: SUBDUCTION QUAKES
CAN ALSO GENERATE

DEVASTATING TSUNAMIS

BECAUSE OF THEIR PROXIMITY
TO COASTLINES.

- ONE OF THE WORST
EARTHQUAKES EVER...

- THE JAPANESE QUAKE AND
THE 2004 INDIAN OCEAN EARTHQUAKE

OFF SUMATRA
ARE STRIKING EXAMPLES.

EARTHQUAKES AND TSUNAMIS
ARE NOT THE ONLY ACTION

SPAWNED BY SUBDUCTION.

SUBDUCTION
ALSO CREATES VOLCANOES,

AND THEY, TOO,
CAN BE LARGE AND DANGEROUS.

- VOLCANOES IN THE SUBDUCTION
ZONES ARE FORMED

BY MAGMAS THAT ARE MORE SILICIC,
OR MORE VISCOUS,

AND THEY ARE
MUCH MORE EXPLOSIVE.

SO THOSE ARE THE VOLCANOES
THAT CAN REALLY BE DANGEROUS

AND REALLY CREATE TROUBLE.

narrator: SUBDUCTION VOLCANOES
ARE EARTH'S MOST NOTORIOUS:

MOUNT TUNGURAHUA IN ECUADOR,

MOUNT VESUVIUS IN ITALY,

MOUNT ASAMA IN JAPAN,

MOUNT SAINT HELENS
IN THE U.S.

ALL ARE KNOWN FOR EXPLOSIVE,
DESTRUCTIVE ERUPTIONS.

THEY ALSO GROW TO GREAT HEIGHTS.

THIS IS CHIMBORAZO,

RISING 20,700 FEET
ABOVE SEA LEVEL

IN THE ANDES MOUNTAINS
OF ECUADOR.

WHEN MEASURED FROM THE CENTER
OF THE EARTH'S CORE

TO THE VOLCANO'S SUMMIT,

CHIMBORAZO
IS EARTH'S TALLEST MOUNTAIN,

SOARING OVER 7,000 FEET CLOSER
TO THE SUN THAN MOUNT EVEREST.

THAT'S BECAUSE THE VOLCANO SITS
ON THE EQUATOR

WHERE THE EARTH BULGES OUTWARD
FROM THE FORCE OF ROTATION.

EARTH SCIENTISTS
HAVE GOTTEN A GOOD HANDLE

ON THE FORCES
DRIVING PLATE TECTONICS,

LIKE SUBDUCTION,

BUT QUESTIONS REMAIN.

ONE OF THE BIGGEST QUESTIONS
IS HOW PLATE TECTONICS IS LINKED

TO PROCESSES OPERATING
DEEP BELOW EARTH'S CRUST.

THE DEEPER WE LOOK,
THE LESS WE KNOW.

BUT NEW RESEARCH
IS TURNING UP BIG SURPRISES

LURKING IN THE CENTER
OF THE EARTH.

- TUMBLE INTO CASCADING
SALT BEDS,

ESCAPE FROM HISSING STEAM CAVES,

BEHOLD THE STAGGERING
UNDERGROUND OCEAN.

YOU WILL ENCOUNTER BREATHTAKING
DANGERS BEYOND BELIEF

HERE AT THE CENTER OF THE EARTH.

[thunder crashes]

narrator:
THE INSIDE OF EARTH,

AN OBJECT OF GREAT CURIOSITY,

WILD CONJECTURE.

AT THE CENTER OF IT ALL
IS THE EARTH'S CORE,

WHICH WAS DISCOVERED
ACCIDENTALLY ONLY 140 YEARS AGO.

- A HUGE EARTHQUAKE
IN THE 1880s WAS--

THE WAVES FROM THAT EARTHQUAKE,

TRAVELING THROUGH
THE EARTH'S CORE,

BOUNCING OFF THE EARTH'S CORE,

WERE RECOGNIZED AS ARRIVING
AT DIFFERENT TIMES

FROM THE SEISMIC WAVES

THAT TRAVELED THROUGH
THE OUTER LAYERS OF THE EARTH.

AND WITH THAT,
THE EARTH'S CORE WAS DISCOVERED.

IT TOOK UNTIL THE 1920s
TO RECOGNIZE

THAT THE EARTH
HAD A SOLID INNER CORE

INSIDE THE FLUID OUTER CORE.

narrator: AT HALF THE SIZE
OF THE PLANET,

THE EARTH'S CORE IS PECULIAR
IN THAT IT'S ALL MADE OF IRON.

BUT ITS INNER HALF IS SOLID,
AND ITS OUTER HALF IS LIQUID.

- THE EARTH'S OUTER CORE
IS MOLTEN

BECAUSE IT'S VERY HIGH
TEMPERATURE, AND IT'S--

THE TEMPERATURES ARE
ABOVE THE MELTING TEMPERATURE

OF THIS IRON-RICH MATERIAL,

BUT THE EARTH'S INNER CORE
IS ACTUALLY--CAN BE SOLID

BECAUSE WE HAVE
EVEN HIGHER PRESSURES,

SO GET TO OVER
3 MILLION ATMOSPHERES,

SO 3 MILLION TIMES THE PRESSURE
AT THE SURFACE OF THE PLANET.

AND AT THOSE HIGH PRESSURES,

THEY CAUSE THE MATERIAL
TO ACTUALLY SOLIDIFY.

narrator: FORTUNATELY FOR US
AND ALL LIVING THINGS,

THE EARTH'S OUTER CORE IS FLUID,

FOR IT GENERATES OUR PLANET'S
PROTECTIVE MAGNETIC FIELD.

- IF WE DIDN'T HAVE THE EARTH'S
MAGNETIC FIELD TODAY,

WE PROBABLY COULDN'T HAVE LIFE
ON THE SURFACE OF THE PLANET.

THE SUN'S ALWAYS THROWING ALL
THESE PARTICLES AT THE PLANET,

BUT THEN THE EARTH'S
MAGNETIC FIELD

PROTECTS THIS NICE,
PROTECTIVE COATING

THAT PROTECTS US
FROM THESE DAMAGING RAYS

AND PARTICLE--
HIGH-ENERGY PARTICLES.

narrator: THE EARTH IS UNIQUE
AMONG PLANETS

IN HAVING A MAGNETIC FIELD.

MARS HAD ONE EARLY ON,

BUT ITS SMALL CORE
COOLED QUICKLY,

AND IT WAS LOST AND, WITH IT,

THE CHANCE FOR LIFE
TO TAKE HOLD ON ITS SURFACE.

MEANWHILE, EARTH'S MAGNETIC
FIELD, FOR ALL ITS IMPORTANCE,

IS NOT WELL UNDERSTOOD.

WHAT IS GETTING CLEARER
IS WHAT IS ACTUALLY GOING ON

IN THE EARTH'S CORE ITSELF.

- OKAY.
LET'S PUT IT ON THERE.

narrator:
THAT IS BECAUSE

SCIENTISTS HAVE
FINALLY RE-CREATED

THE CORE'S EXTREME CONDITIONS
IN THE LAB.

3 MILLION ATMOSPHERES
AND 10,000 DEGREES FAHRENHEIT,

THE SAME TEMPERATURE
AS THE SURFACE OF THE SUN.

- SO YOU HAVE TO REACH
MILLIONS OF ATMOSPHERES,

AND YOU HAVE TO REACH
THOUSANDS OF DEGREES,

SO THAT'S A VERY CHALLENGING
TECHNOLOGICAL PROBLEM.

OKAY, GREAT.

LOOKS GOOD.

SO ONE WAY TO REACH
THE VERY HIGH PRESSURES

AND TEMPERATURES IN THE PLANET
IS TO COMPRESS MATERIALS

BETWEEN THE TIPS
OF TWO DIAMONDS,

AND SINCE DIAMOND IS THE HARDEST
MATERIAL ON THE PLANET,

WE CAN GENERATE
VERY HIGH PRESSURES.

AND THEN,
AT THE SAME TIME,

WE CAN USE LASERS
TO HEAT THE SAMPLE

AND TO REACH
THE SAME CONDITIONS

WE THINK ARE INSIDE THE PLANET.

narrator: THE CORE'S SUN-HOT
HEAT IS CRUCIAL TO UNDERSTAND.

IT AFFECTS EVERYTHING
AT THE SURFACE,

1,800 MILES ABOVE.

TO GET UP HERE,

IT TRAVELS THROUGH TWO LAYERS
OF SOLID ROCK.

THE FIRST IS THE MANTLE,
EARTH'S BIGGEST LAYER BY FAR.

AND THEN THE CRUST,

REALLY JUST A THIN VENEER
ON THE EARTH.

SCIENTISTS BELIEVE THAT
THE IMMENSE HEAT OF THE CORE

MAKES THE MANTLE SO HOT
THAT IT ACTS LIKE A FLUID

AND RISES
UNTIL IT HITS THE CRUST.

SOME OF THE HEAT THEN CIRCULATES
ALONG THE CRUST'S UNDERSIDE

UNTIL SUBDUCTING SLABS OF CRUST
TAKE IT DOWNWARD.

IT'S A GIANT RECYCLING TREADMILL
CALLED CONVECTION.

THROUGH EXPERIMENTS,

SCIENTISTS HAVE CALCULATED
THAT HEAT'S ROUND TRIP

FROM THE CORE TO THE CRUST
AND BACK TO THE CORE AGAIN

TAKES 300 MILLION YEARS.

THIS CIRCULATION OF HEAT
IS KEPT ALIVE

BY THE SINKING
OF COLD, HEAVY PLATES

INTO THE HOT MANTLE BELOW.

IN OTHER WORDS,

THOSE SLABS CAUSE
QUITE A STIR AS THEY DESCEND.

- WE CAN TRACK THOSE SLABS
WITH TOMOGRAPHY

DOWN AT LEAST
INTO THE MIDDLE MANTLE.

AND PROBABLY THOSE SLABS
REACH ALL THE WAY

TO THE CORE-MANTLE BOUNDARY,

AND THERE'S A SLAB GRAVEYARD
THAT SITS ABOVE THE CORE.

THAT SLAB GRAVEYARD
MAY IN TURN HELP DRIVE

THE CONVECTION CELLS
IN EARTH'S MANTLE

THAT IN TURN THEN REACH UP

AND DRIVE THE PATTERN
OF PLATE TECTONICS

AND THE SHIFTING PLATES
AT EARTH'S SURFACE.

narrator: THE SINKING SLABS NOT
ONLY DRIVE HEAT IN THE MANTLE;

THEY HAVE RADICALLY CHANGED
THE MAKEUP OF THE MANTLE

OVER THE COURSE
OF GEOLOGIC TIME.

- THE MANTLE IS A VERY
COMPLICATED MIXTURE OF THINGS

THAT HAVE BEEN STIRRED
INTERNALLY

AND THINGS THAT HAVE COME UP
TO THE SURFACE,

BEEN OCEAN FLOOR FOR A WHILE,
AND THEN TAKEN BACK DOWN.

IN THE 4.5 BILLION-YEAR HISTORY
OF THE EARTH,

THE ENTIRE MANTLE HAS BEEN
CIRCULATED ABOUT ONCE.

VIRTUALLY NOTHING
AT THE EARTH'S SURFACE

OR IN THE INTERIOR IS PERMANENT.

THINGS ARE CHANGING
ALL THE TIME.

narrator:
HEAT RISING UP FROM THE CORE

DOES NOT ALWAYS
RECYCLE BACK DOWN.

SOMETIMES IT ESCAPES
ITS EARTHLY CONFINES

AS VOLCANIC ERUPTIONS.

EARTH IS BY FAR

THE SOLAR SYSTEM'S MOST
VOLCANICALLY ACTIVE PLANET.

VOLCANOES ARE NATURE'S MOST
VIOLENT AND DESTRUCTIVE FORCE.

BUT IRONICALLY,

THIS FORCE EMANATING FROM
THE EARTH'S MANTLE DEEP BELOW

IS AT THE VERY ROOT
OF THE CREATION AND MAINTENANCE

OF LIFE ON EARTH'S SURFACE.

- VOLCANOES HAVE CERTAINLY
INFLUENCED LIFE ON EARTH.

AND THAT'S NOT JUST WHEN
THEY HAVE A BIG ERUPTION

AND PEOPLE DIE.

BUT THEY ALSO MAY HAVE CREATED
LIFE ON EARTH.

IN THE LAST FEW DECADES,

HYDROTHERMAL VENTS WERE
DISCOVERED DEEP IN THE OCEAN,

AND MINERALS ARE COMING OUT
THAT CAN ACTUALLY FEED LIFE

AROUND THOSE VENTS,

AND A VERY SURPRISING FIND
WAS THAT LIFE COULD EXIST

AT SUCH DEPTH IN THE OCEAN.

narrator: VOLCANOES WERE
THE ORIGINAL ARCHITECTS

OF OUR ATMOSPHERE,

UNLOCKING CO2 AND WATER
FROM THE MANTLE'S ROCKS

AND TAKING THEM TO THE SURFACE.

ONE OF THE LARGEST
CONCENTRATIONS

OF ACTIVE VOLCANOES
ON EARTH IS IN JAPAN--

MORE THAN 100.

MOUNT FUJI
IS JAPAN'S LARGEST VOLCANO,

RISING 12,400 FEET HIGH.

THIS GRACEFUL PEAK IS
A MASSIVE SUBDUCTION VOLCANO,

BUT THE LARGEST VOLCANOES
ON EARTH ARE 100 TIMES BIGGER.

THEY BELONG TO A RARE CLASS
OF VOLCANO

KNOWN AS A MANTLE PLUME VOLCANO,

AND THE LARGEST OF ALL
ARE ON HAWAII.

LAVA HAS BEEN ERUPTING
FROM THIS SPOT IN THE PACIFIC

FOR AT LEAST 75 MILLION YEARS.

IT BUILT MAUNA LOA, EARTH'S
LARGEST VOLCANO BY VOLUME.

BUT MAUNA LOA IS NOT THE BIGGEST
VOLCANO IN THE SOLAR SYSTEM.

- THE LARGEST VOLCANO
IN THE SOLAR SYSTEM

IS OLYMPUS MONS ON MARS.

IT'S ABOUT 26 KILOMETERS HIGH

AND AROUND
600 KILOMETERS ACROSS.

narrator:
COMPARED TO HAWAII,

OLYMPUS MONS IS VASTLY BIGGER
IN ALL RESPECTS.

WHY ARE EARTH'S VOLCANOES
SO MUCH SMALLER?

- ON MARS,
THERE'S NO PLATE TECTONICS,

SO THE SAME, LET'S SAY, HOT SPOT
CAN BUILD UP A VOLCANO

IN THE SAME LOCATION FOR VERY,
VERY LONG PERIODS OF TIME.

ON THE EARTH,
WE CAN'T HAVE THAT SITUATION

BECAUSE THE PLATES ARE MOVING,
SO YOU GET, FOR EXAMPLE,

HOT SPOT LIKE THE ONE THAT
FORMED THE HAWAIIAN VOLCANOES,

BUT THE PLATE IS MOVING OVER IT,
SO IT PUNCHES ONE VOLCANO,

BUT THEN THE PLATE MOVES,

AND THE VOLCANO MOVES
SOMEWHERE ELSE.

SO ON EARTH, WE DON'T REALLY
BUILD THOSE SIZES OF VOLCANOES.

[fire roaring and crackling]

narrator: THE SOURCE THAT FEEDS
EARTH'S GIANT VOLCANOES

IS THOUGHT TO BE
A NARROW CYLINDER OF HOT ROCK

THAT REACHES DEEP
INTO THE MANTLE.

HOW DEEP IS A MATTER OF DEBATE.

BUT RECENT SEISMIC STUDIES
OF THE HAWAIIAN CHAIN

IMAGED FOR THE FIRST TIME

A HOT PLUME REACHING HALFWAY
TO THE EARTH'S CORE.

CHEMICAL ANALYSIS OF LAVAS
RETRIEVED IN DRILL CORES

TRACES THE PLUME EVEN DEEPER,

ACTUALLY EXTENDING
TO THE EARTH'S CORE ITSELF.

THE DEEPEST REACHES
OF OUR PLANET, THEN,

ARE INTIMATELY CONNECTED

WITH GEOLOGICAL ACTION
AT THE SURFACE.

WITHOUT THESE
DEEP-SEATED FORCES,

LIFE WOULD HAVE NOT GAINED
A FOOTHOLD ON OUR PLANET,

AND IT WOULDN'T HAVE FLOURISHED

AND EVOLVED INTO COUNTLESS
WONDROUS FORMS

WITHOUT SOMETHING ELSE:

A REMARKABLY STABLE,
PRECISELY TUNED CLIMATE.

FOR MOST OF EARTH'S EXISTENCE,

THE TEMPERATURE AT THE SURFACE
HAS RARELY WAVERED.

WHY THIS IS
IS A GREAT MYSTERY.

THE GLOBAL MEAN TEMPERATURE
IS A COMFORTABLE 59 DEGREES.

INCREASE THAT
BY JUST 18 DEGREES,

AND ICE AT THE POLES WOULD MELT.

DECREASE IT BY 18 DEGREES,

AND THE ENTIRE WORLD
WOULD FREEZE OVER.

OTHER PLANETS
ARE FAR FROM HABITABLE.

VENUS,
WITH 200,000 TIMES MORE CO2

IN ITS ATMOSPHERE THAN EARTH,

IS RAVAGED BY TEMPERATURES
REACHING 900 DEGREES FAHRENHEIT.

MARS, LONG AGO STRIPPED OF ITS
ATMOSPHERE AND MAGNETIC SHIELD,

IS DEEPLY FROZEN TO AN AVERAGE
OF 70 DEGREES BELOW ZERO.

[lively music]

¶ ¶

EARTH'S CLIMATE IS KEPT MODERATE
BY A LITTLE UNDERSTOOD INTERPLAY

OF GEOLOGIC AND BIOLOGIC FORCES.

VOLCANIC ERUPTIONS SPEW CO2
INTO THE AIR.

PLATE TECTONICS BUILDS MOUNTAINS

AND RIFTS APART OCEAN BASINS.

THEN WEATHER ERODES THE LAND,

CAPTURING CO2

AND LOCKING IT AWAY
IN SEDIMENTS.

LIVING ORGANISMS ADD
THEIR ALTERATIONS INTO THE MIX.

ALL IS BUILT INTO A SYSTEM
OF GLOBAL CHECKS AND BALANCES.

THERE HAVE BEEN ONLY A FEW TIMES

WHEN EARTH'S CLIMATE TIPPED
WELL BEYOND ITS COMFORT ZONE.

EARTH'S COLDEST EXTREME HAPPENED
ABOUT 750 MILLION YEARS AGO

AND PROBABLY SEVERAL TIMES
BEFORE THAT.

IT WAS CALLED SNOWBALL EARTH.

- SNOWBALL EARTH REFERS
TO A TIME IN THE EARTH'S HISTORY

WHEN THE EARTH
WAS ENTIRELY COVERED WITH ICE.

THAT MEANS GLACIERS
ON THE CONTINENTS

AND SEA ICE COVERING
MOST OF THE OCEANS

ALL THE WAY DOWN TO THE EQUATOR.

narrator:
DURING SNOWBALL EARTH,

THE TEMPERATURE
AT THE EQUATOR PLUNGED

TO MINUS 4 DEGREES FAHRENHEIT.

LIFE, STILL IN
ITS PRIMITIVE BACTERIAL STAGE,

SURVIVED THE DEEP FREEZE
AS IT DOES TODAY:

BELOW ICE SHELVES
AND EVEN BELOW GLACIERS.

SCIENTISTS THINK THAT
THE TRIGGER FOR SNOWBALL EARTH

WAS THE BUNCHING
OF CONTINENTS AT THE EQUATOR.

THE GIANT LAND MASS
ATTRACTED MOISTURE,

AND GREAT STORMS ENSUED.

RAIN STRIPPED CO2
FROM THE ATMOSPHERE

AND LOCKED IT
IN ERODING SEDIMENTS.

AS CO2 LEVELS DROPPED,
SO DID THE TEMPERATURE.

VOLCANIC ERUPTIONS EVENTUALLY
OVERPOWERED SNOWBALL EARTH

BY INJECTING CO2
BACK INTO THE ATMOSPHERE.

AS THE CLIMATE RESTABILIZED,

THE SURVIVING BACTERIAL
LIFE FORMS MULTIPLIED,

PHOTOSYNTHESIZED,

AND FILLED THE AIR WITH OXYGEN,

A REQUIREMENT
FOR MORE COMPLEX LIFE.

FINALLY, 550 MILLION YEARS AGO,

LIFE BRANCHED OUT AND BEGAN
ITS EXTRAORDINARY JOURNEY

OF DIVERSIFICATION
AND EVOLUTION.

WHY THIS HAPPENED
IS STILL A MYSTERY,

BUT THE EXTREME HIT
THAT LIFE TOOK

DURING SNOWBALL EARTH

MAY HAVE ACTUALLY BEEN
PART OF THE REASON.

- ONCE LIFE WAS ESTABLISHED
ON THE EARTH,

IT CONTINUED TO SHOW EVIDENCE
THAT IT WAS EXTREMELY ADAPTABLE,

THAT WHATEVER HARSH CONDITIONS
WERE THROWN AT IT,

THAT IT WAS ABLE TO ADAPT
TO FIND A WAY TO SURVIVE.

SO EVEN THROUGH PERIODS
LIKE SNOWBALL EARTH,

LIFE WOULD ADAPT TO THOSE
CONDITIONS AND REEMERGE.

AND IN FACT, THOSE SORTS OF
CONDITIONS WERE MAJOR FACTORS

DRIVING THE EVOLUTION
OF LIFE ON EARTH.

narrator: THE NEXT TIME EARTH'S
CLIMATE WAS KNOCKED OFF BALANCE

WAS AT A TIME WHEN EARTH
EXPERIENCED ITS BIGGEST UPHEAVAL

SINCE THE EARLY DAYS
OF ITS FORMATION.

- ABOUT 250 MILLION YEARS AGO,

95% OF LIFE ON EARTH
DISAPPEARED.

WE THINK THAT'S BECAUSE
OF VERY LARGE ERUPTIONS

IN THE SIBERIAN TRAPS.

[clacking]

narrator: EARTH SCIENTISTS HAVE
MAPPED 800,000 SQUARE MILES

OF SIBERIA THAT WERE COVERED
BY LAVA FLOWS

UP TO 12,000 FEET THICK.

THEY CALL THIS PROVINCE
THE SIBERIAN TRAPS.

- THOSE ERUPTIONS
WOULD HAVE PUT A LOT OF DUST,

A LOT OF SULFUR
IN THE ATMOSPHERE,

COOLED THE TEMPERATURE.

SO THIS KILLED
A LOT OF LIFE ON EARTH.

narrator: THE CLIMATE RECOVERED
EVENTUALLY, AND SO DID LIFE.

BUT 90 MILLION YEARS AGO,

THE HOTTEST PERIOD EVER KNOWN
ENVELOPED THE EARTH.

DINOSAURS ROAMED
WHAT ARE NOW THE ICY REALMS

OF THE ARCTIC CIRCLE.

AROUND THEM WERE FELLOW
SWAMP-DWELLERS LIKE ALLIGATORS.

WHAT WERE THEY DOING
AT THE EARTH'S POLES?

SCIENTISTS FIGURED OUT THAT
PLATE TECTONICS WAS THE CULPRIT.

100 MILLION YEARS AGO,

THE CONTINENTS
HAD WRENCHED APART,

AND SEA LEVEL ROSE.

MOUNTAIN BUILDING SLOWED DOWN,

AND SO DID RAINFALL AND EROSION.

BUT CO2-SPEWING
VOLCANIC ERUPTIONS,

ESPECIALLY IN THE MID-OCEAN
RIFT ZONES, DID NOT.

- WHEN CONTINENTS
ARE SPLITTING APART

AND YOU HAVE MORE SEA FLOOR
SPREADING,

YOU'RE ADDING MORE CO2
TO THE ATMOSPHERE,

AND IT'S NOT BEING REMOVED
AS QUICKLY

BY WEATHERING OF THE CONTINENTS,

SO IT'S WARMER
DURING THOSE PERIODS.

[bird cawing]

narrator: TEMPERATURES ROSE
TO A BALMY 54 DEGREES

AT THE NORTH AND SOUTH POLES.

THE CLIMATE SO AGREED
WITH THE DINOSAURS

THAT THEY DOMINATED LIFE
ON EARTH FOR MILLIONS OF YEARS.

THEN,
65 MILLION YEARS AGO,

A MASSIVE METEORITE IMPACT
SUDDENLY ENDED THEIR REIGN.

[explosion]

THE METEORITE GOUGED OUT
A HUGE CRATER

OVER 100 MILES ACROSS

WITH THE TOWN OF CHICXULUB,
MEXICO, AT ITS CENTER.

THE CITY OF MERIDA
ALSO LIES WITHIN THE CRATER,

WHICH WAS BURIED BY SEDIMENT
MILLIONS OF YEARS AGO

AND ONLY DISCOVERED BY CHANCE
AS GEOLOGISTS EXPLORED FOR OIL

IN THE 1970s.

THE CRATER AND ITS SURROUNDINGS
ARE ALSO THE SITE

OF THE GREAT CITIES
BUILT BY THE ANCIENT MAYA.

BUT NONE OF THE HUMAN DRAMA
PLAYING OUT IN THIS REGION

WOULD HAVE BEEN POSSIBLE

IF IT WEREN'T
FOR THE KILLER METEORITE

THAT STRUCK HERE,

WIPING OUT THE DINOSAURS.

THEIR EXTINCTION OPENED
AN EVOLUTIONARY DOOR

FOR MAMMALS LIKE US TO EVOLVE.

BUT 65 MILLION YEARS AGO,

THE EARTHLY STAGE
WAS FAR FROM SET

FOR THE ENTRANCE OF PEOPLE.

CO2 LEVELS AND TEMPERATURES
WERE MUCH TOO HIGH.

LUCKILY FOR US, PLATE TECTONICS
BUILT THE MOST MASSIVE STRUCTURE

ON EARTH TO MAKE
THE CLIMATE HUMAN-FRIENDLY:

THE GREAT HIMALAYA RANGE.

ABOUT 60 MILLION YEARS AGO,
INDIA, ONCE A MASSIVE ISLAND,

RAMMED ASIA, AND THE BUILDING
OF THE HIMALAYA BEGAN.

AS THE HIMALAYAS GREW,

A GREAT BLOCK OF LAND
ROSE UP BEHIND THE RANGE.

IT FORMED THE TIBETAN PLATEAU

AND EVEN RAISED THE LAND
AS FAR TO THE NORTH AS MONGOLIA,

MORE THAN 1,000 MILES AWAY.

SINCE THEN, THE EARTH'S CLIMATE
HAS NEVER BEEN THE SAME.

- THERE'S A REAL BELIEF
AMONGST GEOLOGISTS

THAT THE GROWTH OF THE HIMALAYA
IN TIBET

OVER THE LAST 60 MILLION YEARS

HAS LED TO MAJOR CHANGES
IN THE GLOBAL CLIMATE.

THE INDIAN MONSOON IS CREATED

WHEN WARM AIR
FROM THE INDIAN OCEAN

MEETS THE MOUNTAINS
OF THE HIMALAYA

AND DUMPS THE RAIN
ON THAT MOUNTAIN FRONT.

PRIOR TO THE FORMATION
OF THE HIMALAYA IN TIBET,

THERE WAS NO MONSOON.

THERE WAS NO BARRIER
TO THE NORTHWARD PROGRESS

OF THE MOIST INDIAN OCEAN AIR.

narrator: THE NEW MONSOON
BEGAN DUMPING RAIN AND SNOW

ON THE GROWING MOUNTAINS
OF ASIA.

THIS ERODED THE ROCKS
AND CHANGED THE CHEMICAL BALANCE

IN THE ATMOSPHERE.

MASSIVE AMOUNTS OF CO2
WERE REMOVED FROM THE AIR,

SO MUCH THAT THE GLOBAL CLIMATE
BEGAN TO COOL.

IT WAS THE FIRST TIME IN
HUNDREDS OF MILLIONS OF YEARS

THAT THE EARTH'S CLIMATE
COOLED SO DEEPLY.

BUT BEFORE WE HUMANS
MADE OUR APPEARANCE,

PLATE TECTONICS HAD A FEW MORE
MODIFICATIONS TO MAKE.

- ALL RIGHT, HERE.
HERE WE GO.

narrator:
IN ANTARCTICA,

SCIENTISTS MADE
THE STARTLING DISCOVERY

THAT THIS LONELY CONTINENT
AT THE BOTTOM OF THE WORLD

WAS ONCE CONNECTED TO AUSTRALIA.

THEN 40 MILLION YEARS AGO,

THE LAND MASSES RIFTED APART,

COMPLETELY CHANGING
OCEAN CURRENTS IN THE REGION.

- OVER THE LAST
40 MILLION YEARS,

ANTARCTICA BECAME AN ISOLATED
CONTINENT DOWN THERE,

AND SO THE CIRCUM-ANTARCTIC
CURRENT FORMED,

WHICH ISOLATED THAT CONTINENT
SO IT COULD COOL

AND START TO GROW AN ICE SHEET.

narrator:
FOR THE FIRST TIME,

ANTARCTICA BECAME FROZEN
WITH ICE,

UP TO 15,000 FEET THICK,

DROPPING GLOBAL TEMPERATURES
EVEN MORE.

AND THEN,
3 MILLION YEARS AGO,

A NEW LAND BRIDGE WELDED SOUTH
AND NORTH AMERICA TOGETHER.

BEFORE THAT, THE TWO CONTINENTS
WERE SEPARATED

BY THE ANCIENT PANAMA SEAWAY.

AS PLATE TECTONICS
JOINED THEM TOGETHER,

OCEAN CURRENTS WERE RADICALLY
REROUTED ONCE AGAIN.

- THE GULF STREAM, INSTEAD OF
GOING INTO THE PACIFIC OCEAN,

IT ACTUALLY WAS THEN REDIRECTED
UPWARD IN THE ATLANTIC,

BRINGING MORE MOISTURE
UP INTO THE NORTH ATLANTIC,

AND THAT'S A SOURCE
OF MOISTURE FOR ICE

ON THE CONTINENTS UP THERE.

narrator:
BY 2 1/2 MILLION YEARS AGO,

TEMPERATURES PLUNGED SO MUCH
THAT THE PLEISTOCENE ICE AGES

WERE TRIGGERED,

AND IN THIS ICE AGE WORLD,

WHEN FREEZING GLACIAL PERIODS
ALTERNATED

WITH MUCH WARMER INTERGLACIALS,

THE STORY OF HUMAN EVOLUTION
UNFOLDED

IN THE EAST AFRICAN RIFT.

[women conversing]

HUMANS HAVE LIVED
THROUGH EIGHT MAJOR ICE AGES

OVER THE PAST MILLION YEARS.

THE LAST GLACIAL PERIOD
ENDED 10,000 YEARS AGO,

AND WE ARE NOW AT THE TAIL END
OF AN INTERGLACIAL.

THE CLIMATE HAS BEEN
WARM ON AVERAGE,

BUT WITH ENOUGH VARIATION
TO PROFOUNDLY AFFECT PEOPLE

AND EVEN CIVILIZATIONS.

- ONCE WE ENTERED
THE WARM PERIOD WE'RE IN NOW

THAT STARTED
ABOUT 10,000 YEARS AGO,

THE CHANGES IN CLIMATE
HAVE BEEN RELATIVELY SMALLER

THAN THE ICE AGES,

BUT THEY'VE BEEN BIG ENOUGH

THAT THERE WERE DROUGHTS
AND FLOODS AND COLD PERIODS

AND LITTLE MINI ICE AGES.

AND THAT PEOPLE
WERE STILL MIGRATING

AND STILL HAVING TO ADAPT.

narrator: RESEARCHERS STUDYING
PAST CLIMATE CHANGES

IN GUATEMALA FOUND
THAT LONG DROUGHTS OCCURRED

AT THE HEIGHT OF
THE ANCIENT MAYA CIVILIZATION,

FROM 3,000 TO 1,000 YEARS AGO.

THIS MAY HAVE BEEN A BIG FACTOR

IN THE MAYA CIVILIZATION'S
MYSTERIOUS COLLAPSE.

BECAUSE GLOBAL WARMING IS
AGAIN CREATING SERIOUS PROBLEMS

FOR PEOPLE AND ECOSYSTEMS,

SCIENTISTS ARE ENGAGED
IN AN URGENT EFFORT

TO STUDY PAST CLIMATE CHANGES

IN ORDER TO PREDICT
WHAT MIGHT HAPPEN IN THE FUTURE.

ONE OF THEIR BEST TOOLS
IS THE STUDY OF GASES

THAT CAUSE GLOBAL WARMING,

ESPECIALLY CARBON DIOXIDE,
OR CO2.

THESE GASES ARE DETECTED
IN ANCIENT GLACIAL ICE

HUNDREDS OF THOUSANDS
OF YEARS OLD IN ANTARCTICA.

- ATMOSPHERIC GASES
GET TRAPPED IN THE ICE,

AND YOU GET THESE TRAPPED
BUBBLES OF ATMOSPHERE

THAT ARE PRESERVED,

AND SO WHEN YOU TAKE
THE ICE CORE,

YOU HAVE THIS SORT OF
ANCIENT ATMOSPHERE.

AND SO THEY CAN RELEASE THAT
AND MEASURE THE AMOUNT OF CO2

THAT WAS AROUND.

AND ALSO HOW IT CHANGED
SINCE THE LAST ICE AGE.

SO WE KNOW FROM THE ICE CORES
THAT THE NATURAL LEVEL OF CO2

SHOULD BE
ABOUT 280 PARTS PER MILLION,

AND TODAY IT'S
ABOUT 390 PARTS PER MILLION,

AS HUMANS HAVE BEEN BURNING
FOSSIL FUELS AND RELEASING CO2.

THAT'S A REALLY BIG RISE.

WE'VE NEVER SEEN THIS RAPID
A RISE OF CO2

IN THE ATMOSPHERE

OVER, YOU KNOW,
100 MILLION YEARS.

narrator: SO IT APPEARS
THAT ONE NATURAL EARTH SYSTEM,

THE CLIMATE,

MAY INDEED BE ENTERING
A PERIOD OF INTENSE UPHEAVAL.

[rumbling]

WHAT ABOUT THE OTHER
NATURAL EARTH SYSTEMS,

LIKE THOSE THAT CAUSE
EARTHQUAKES AND VOLCANOES?

- ICELAND'S MOST ACTIVE VOLCANO
HAS STARTED ERUPTING.

narrator:
HAVE ANY OF THESE

BEGUN A PERIOD
OF INCREASED ACTIVITY?

- HAS BEEN SPEWING ASH AND SMOKE
12 MILES INTO THE AIR.

narrator:
LOOKING BACK 100 YEARS,

THE NUMBER OF VOLCANIC ERUPTIONS
EACH YEAR

HAS ACTUALLY HELD STEADY.

- IN GENERAL, THE PUBLIC ONLY
HEARS ABOUT VOLCANIC ERUPTIONS

WHEN THEY'RE PARTICULARLY BIG,
WHEN THEY KILL PEOPLE,

BUT, IN FACT, THERE ARE USUALLY
COUPLE DOZEN VOLCANIC ERUPTIONS

GOING ON EVERY MONTH.

AND SOME VOLCANOES HAVE BEEN
ERUPTING FOR DOZENS OF YEARS,

LIKE KILAUEA--

OR EVEN HUNDREDS
OR THOUSANDS OF YEARS

LIKE AETNA IN ITALY.

SO THERE IS A LOT OF VARIATION

IN TERMS OF SOMETIMES WE HAVE
REALLY BIG VOLCANIC ERUPTIONS,

AND THEN WE MIGHT GO FOR MONTHS
OR YEARS WITHOUT ONE OF THOSE.

BUT, IN FACT,
VOLCANOES ARE ERUPTING

AROUND THE EARTH ALL THE TIME.

narrator: A SIMILAR SCENARIO
HOLDS FOR EARTHQUAKES.

THE NUMBER OF BIG QUAKES
GREATER THAN MAGNITUDE 7

AVERAGES 18 PER YEAR.

- AT LEAST 250 PEOPLE HAVE DIED

AFTER A MAJOR EARTHQUAKE
HIT SOUTHWESTERN PAKISTAN.

narrator:
ONE OF THESE QUAKES

IS HIGHER THAN MAGNITUDE 8
EACH YEAR.

THIS NUMBER HAS HELD STEADY
SINCE THE YEAR 1900.

BUT IT MAY SEEM THAT EARTHQUAKES
HAVE BECOME MORE FREQUENT

FOR SEVERAL REASONS.

- YO!

EXCUSE ME!

narrator: FIRST, MORE ARE BEING
RECORDED AND PINPOINTED.

MORE THAN 8,000 STATIONS
LISTEN FOR QUAKES WORLDWIDE.

IN 1931,
THERE WERE JUST 350.

EARTHQUAKES ALSO SEEM
MORE NUMEROUS

BECAUSE OF THE SOARING
POPULATION

AND NEAR-INSTANT REPORTING
OF NEWS WORLDWIDE.

- THE EARTHQUAKE THAT KILLED
1/4 MILLION PEOPLE IN HAITI

WOULD ONLY HAVE KILLED
1/10 THAT NUMBER 100 YEARS AGO,

AND WE WOULDN'T HAVE KNOWN
ABOUT IT.

- THIS IS SOME OF WHAT I SAW
ON THE STREETS.

- NOW WE HEAR
ABOUT THESE THINGS INSTANTLY.

WE HAVE THE LIVE FOOTAGE
OF THE TSUNAMIS

ARRIVING ON THE JAPANESE COAST,

AND THE WHOLE WORLD
KNOWS ABOUT IT.

narrator: THE RECORDED NUMBER
OF TSUNAMIS HAS INCREASED

IN THE PAST 100 YEARS,

BUT SCIENTISTS ATTRIBUTE THIS
TO EVER-IMPROVING DETECTION.

AND WITH BETTER WARNING SYSTEMS
BEING INSTALLED,

THE LOSS OF LIFE IS DECREASING.

SO DO SCIENTISTS SEE AN UPTICK

IN INCREASED
GEOLOGICAL ACTIVITY?

- NO, THE EARTH'S DOING
THE SAME THING

IT'S BEEN DOING FOR BILLIONS
OF YEARS.

WE NOTICE THE EVENTS MORE

BECAUSE OUR MORE COMPLEX SOCIETY

AND OUR FAR MORE
POPULATED PLANET

ARE MUCH MORE VULNERABLE
TO THESE DISASTERS.

[rumbling]

THERE'S NO REAL EVIDENCE THAT
WE'RE LIVING THROUGH A PERIOD

OF ENHANCED ACTIVITY.

IN ANY ONE AREA,

THERE MAY BE REGIONS WHERE
WE HAVE A FEW MORE EARTHQUAKES

FOR A FEW HUNDRED YEARS,
AND THEN AFTER THAT CLUSTERING,

SEISMICITY WILL DIE AWAY.

BUT ON A PLANET-WIDE SCALE,
THERE'S NO EVIDENCE FOR THAT.

narrator: LOOKING DEEPER
INTO EARTH'S GEOLOGIC PAST,

FAR BIGGER UPHEAVALS
HAVE OCCURRED

THAN ANYTHING KNOWN BY HUMANS.

A SUPERVOLCANO
THOUSANDS OF TIMES BIGGER

THAN THE HUGE MOUNT SAINT HELENS
ERUPTION OF 1980

WENT OFF AT YELLOWSTONE
640,000 YEARS AGO.

SUPERVOLCANOES ARE EXCEEDINGLY
RARE IN HUMAN TERMS.

NONE HAVE ERUPTED
FOR 26,000 YEARS.

EARTH'S HISTORY BOOK CHRONICLES
OTHER MASSIVE UPHEAVALS

LIKE THE SIBERIAN TRAPS.

THERE WAS SNOWBALL EARTH,
WHEN THE WHOLE WORLD FROZE OVER.

IN MORE RECENT TIMES,

OUR DISTANT ANCESTORS
EXPERIENCED THE BITTER COLD

OF THE ICE AGES,

WHEN CHICAGO LAY
UNDER A MILE-THICK SHEET OF ICE.

IF PLANET EARTH WERE ACTING UP
MORE THAN USUAL RIGHT NOW,

IT WOULD BARELY REGISTER

IN THE ANNALS
OF MAJOR EARTHLY EVENTS.

THE EXCEPTION IS THE CLIMATE,

WHICH IS CHANGING IN WAYS
NEVER BEFORE SEEN

IN THE GEOLOGIC RECORD.

PEOPLE MAY HAVE SOME INFLUENCE
OVER THIS PROCESS,

BUT DEEP EARTH PROCESSES

LIKE EARTHQUAKES
AND VOLCANIC ERUPTIONS

ARE BEYOND ANYONE'S CONTROL.

SO SCIENTISTS ARE FOCUSING ON

WAYS TO LIVE
WITH THESE POWERFUL FORCES

AND REDUCE THEIR THREATS.

- THE PUBLIC WOULD LOVE IT
IF WE COULD PROVIDE

SHORT-TERM PREDICTIONS
OF HOURS TO DAYS

BEFORE AN EARTHQUAKE,
AND WE CAN'T DO THAT.

BUT WHAT WE CAN DO IS PROVIDE
LONG-TERM ESTIMATES--

DECADAL ESTIMATES, PERHAPS.

THAT SHOULD BE IMPORTANT TO US,
TO OUR SOCIETY,

TO PLAN FOR THESE EVENTS.

[bell clanging]

IN MY LIFETIME,
THERE'S A 3/4 CHANCE

THERE WILL BE A MAJOR EARTHQUAKE
IN THE BAY AREA WHERE I LIVE,

AND THAT SHOULD BE ENOUGH
TO ENCOURAGE ME

TO PLAN WISELY
FOR THAT EARTHQUAKE

THAT I NEED TO EXPECT.

narrator: WITH EARTHQUAKE
PREDICTIONS STILL IN THE FUTURE,

EARTHQUAKE-PRONE JAPAN
HAS DEVELOPED

THE WORLD'S FIRST EARTHQUAKE AND
TSUNAMI EARLY WARNING SYSTEM.

ITS FIRST MAJOR TEST CAME WITH
THE MASSIVE EARTHQUAKE IN 2011.

[alarm buzzing]

RESIDENTS OF TOKYO WERE WARNED

EIGHT TO NINE SECONDS
BEFORE THE QUAKE HIT.

- AT 2:46 IN THE AFTERNOON.

THE SHAKING WENT ON
FOR MORE THAN 2 MINUTES.

- THE CLOSEST MAJOR CITY,
SENDAI...

narrator: RESIDENTS OF THE
NEAREST COASTAL CITY OF SENDAI

HEARD TSUNAMI WARNINGS
EIGHT MINUTES BEFORE

THE 33-FOOT TSUNAMI CAME ASHORE.

JAPAN'S ADVANCED STATE
OF PREPAREDNESS

AND STRONG BUILDING CODES
WERE THE CRITICAL FACTORS

IN SAVING COUNTLESS LIVES
DURING THIS DISASTER.

AND THE EARLY WARNING SYSTEM

SAVED AN UNTOLD NUMBER
OF LIVES AS WELL.

[phone rings]

THE JAPAN METEOROLOGICAL
AGENCIES EARLY WARNING SYSTEM

ALSO DOUBLES AS JAPAN'S VOLCANIC
ERUPTION WARNING SYSTEM.

ERUPTIONS ARE EASIER TO PREDICT
THAN EARTHQUAKES.

- WE ARE GETTING BETTER
ALL THE TIME

AT PREDICTING
VOLCANIC ERUPTIONS,

BUT IT'S BY NO MEANS PERFECT.

AND IT'S STILL A VERY DIFFICULT
THING TO DO.

WE HAVE MUCH BETTER
INSTRUMENTATION.

WE CAN MEASURE THE INFLATION
OF THE GROUND.

SEISMOGRAPHS SEE HOW MAGMA
IS MOVING UP.

EVEN TEMPERATURES OF FUMAROLES,
CHANGES IN THE GASES.

SO WE ARE GETTING BETTER
ALL THE TIME.

narrator: MEANWHILE EARTH'S
INNER AND OUTER FORCES

WILL KEEP REWORKING THE PLANET,

FROM THE CENTER
OF THE INNER CORE

TO THE HIGHEST PEAKS
ON THE SURFACE.

NO OTHER PLANET KNOWN TO US

HAS SO MANY DIFFERENT
NATURAL FORCES AT WORK.

THE EARTH WE SEE TODAY

HAS BEEN 4 1/2 BILLION YEARS
IN THE MAKING

AND HAS NEVER LOOKED
QUITE THIS WAY BEFORE,

AND IT WILL NEVER LOOK
THE SAME AGAIN.

- I THINK THE WAY THE EARTH
LOOKS NOW AS A PLANET

IS UNIQUE IN HISTORY,

AS IS ALMOST EVERY PERIOD
IN GEOLOGIC HISTORY.

THE EARTH IS CONSTANTLY
UNDERGOING CHANGE.

- WHAT ARE THE GREENS?

- THE GREENS ARE COUNTRY ROADS,

AND THE YELLOWS ARE LOCAL ROADS.

- FROM A GEOLOGIST'S
POINT OF VIEW,

THE EARTH IS REALLY,
REALLY INTERESTING

BECAUSE, ON EARTH,
WE SEE ALL THE MAJOR PROCESSES

THAT FORM THE SURFACE
OF A PLANET ACTUALLY GOING ON.

WE HAVE VOLCANISM.

WE HAVE IMPACT CRATERS FORMED
NOT THAT LONG AGO.

WE HAVE AN ATMOSPHERE,

WHICH MEANS WE HAVE
LIQUID WATER.

WE HAVE WIND.
WE HAVE EROSION.

WE HAVE PLATE TECTONICS ON EARTH

WHICH APPEARS TO BE UNIQUE
IN THE SOLAR SYSTEM.

SO IT'S VERY GEOLOGICALLY
DIVERSE AND VERY DYNAMIC.

SO I THINK WE ARE LUCKY,
ACTUALLY, TO LIVE HERE.

[jangly guitar music]

¶ ¶