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NARRATOR: What do we really know
about the planet we live on?

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This giant spinning ball
of rock.

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The truth is,

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something extraordinary is
going on deep inside the Earth.

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Powerful forces,
mysterious processes

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are happening thousands of miles
beneath our feet.

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And without them, life on
our planet would be impossible.

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The secret to life on Earth
lies inside.

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[Rumbling]

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To discover how and why, we need
to crack the Earth open...

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...and travel all the way
to the core.

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A century ago,

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Jules Verne's book "Journey
to the Center of the Earth"

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captured the world's
imagination.

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Of course, in reality,
it's an impossible journey.

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In the center of the Earth,

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there are titanic pressures
and extreme temperatures.

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They make 99%
of the planet beneath us

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inaccessible to humans.

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It is easier to design something
to descend into the sun

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than it is to design something

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to go to the center
of the Earth,

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because the temperatures
are as high or higher

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than the surface of the sun,

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but the pressures
are unimaginably large.

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NARRATOR: Because scientists
can't travel to the core

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and see for themselves,

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they have to work out other ways
to understand it.

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It's not easy studying something

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you'll never be able to see
or touch.

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LATHROP:
We can see hurricanes coming.

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We can see fronts coming that
will have violent thunderstorms.

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All of that predictive power

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comes because
we can observe the atmosphere.

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We don't have anything like that
in the interior of the Earth

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because we don't have
any detailed measurements

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of what's happening in the core.

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We don't really know
any of the motions in the core.

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We don't know how
the temperatures are varying.

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We don't know what storms
are brewing down there.

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NARRATOR: But Lathrop
is determined to find out,

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so he's building
his very own planet Earth

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at the University of Maryland.

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So we've been seven years in
construction of this experiment.

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Built to try to match
as many parameters as possible

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with the Earth's core.

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It's a model of both the outer
and inner cores of the Earth.

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NARRATOR: It might look like
a crazy experiment,

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but investigating
the Earth's interior

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is more than just
scientific curiosity.

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Life on Earth's surface,
where we live,

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actually depends
on processes taking place

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deep inside our planet.

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If we can figure them out,

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then we'll be closer
to understanding

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how and why life exists
and what its future could be.

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LATHROP:
And the hope is,

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by building a laboratory model
of a planetary core,

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or the Earth's core,

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that we can probe in detail
what's happening

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and work toward getting
a predictive science,

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being able to predict
what's going to happen

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toward the future
for the Earth's core.

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NARRATOR:
Lathrop is not alone.

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Around the world, scientists are
probing the planet

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in every way possible

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to solve the mysteries
of the deep Earth.

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They're studying volcanoes...

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...measuring vibrations
from earthquakes

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to perform seismic X-rays
of the planet...

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...building complex
laboratory models...

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...and discovering
that the world beneath our feet

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is stranger and more fantastic
than they could ever imagine.

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It's full of incredible riches,

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monumental structures,
and bizarre creatures.

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They've found there's actually
more life beneath the surface

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than above it...

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...and more water
than in all of the oceans.

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Down here,
there are even raging storms

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more violent than
the planet's worst hurricanes.

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And somehow this mysterious
world deep inside the planet

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shapes our own.

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But to discover how
is a huge challenge.

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LATHROP: Almost any basic
quantity that you imagine

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might be changing down there.

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There's a whole host
of interesting questions

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that you'd like to know
about the core

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but that you can't
unless you go there.

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NARRATOR: There are many
mysteries in the deep core

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but perhaps none so powerful
as gravity.

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Gravity keeps the moon and
thousands of man-made satellites

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in their orbits.

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And even out here

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it prevents molecules of gas
from floating off into space.

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This immense force

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comes from the massive
dense interior of our planet.

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The closer we get to Earth,
the stronger this force becomes.

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By 62 miles up,
gravity has collected enough gas

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to form a cocoon
around the Earth.

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This is the Earth's atmosphere.

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It protects us from meteorites,
absorbs lethal radiation,

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and insulates the Earth from the
freezing temperatures of space.

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And what's most important...

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It gives us the air
that we breathe.

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It's simple.
No gravity... no atmosphere.

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No atmosphere... no life.

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There's another force of nature
inside Earth

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that's just as vital to life.

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We take it for granted that life
gets its energy from the sun.

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True, its nuclear furnace
does warm our atmosphere,

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drive our weather,
and make our food grow.

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Without the sun, life on Earth
would quickly disappear.

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But forces
from deep inside the Earth

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played a vital role in creating
life in the first place.

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Life survives today
because of a careful balance

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between the energy of the sun
on the outside

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and the energy coming
from inside Earth's core.

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The most visible sign

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of the seething energy
inside our planet are volcanoes.

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They erupt through cracks
in the crust,

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the planet's
fragile outer shell.

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This layer
is only 30 miles thick.

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All of the Earth's volcanoes

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release just a tiny fraction
of the energy

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locked beneath the surface.

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The Earth's inner energy
is so powerful,

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it can thrust rock layers
high in the air,

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creating whole mountain ranges

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such as the Guadalupe Mountains
in New Mexico.

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These layers
were once a flat seabed

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until the Earth's heat pushed
them 8,000 feet into the sky.

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In this churning,
heaving action,

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cracks and fissures
let in water,

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which dissolves
the soft limestone rocks

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below the surface.

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Here in New Mexico are the
magnificent Carlsbad Caverns.

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One chamber is so large,

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it could comfortably accommodate
a jumbo jet.

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For Peter Scholle,

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these caverns are
a geological treasure trove.

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We're 850 feet below
the surface of the Earth here

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in the lower cave
of Carlsbad Caverns.

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We are amongst a bunch

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of limestone stalactites
and stalagmites.

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This cave has probably
a couple of miles of passage.

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There are other caves

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that have literally
hundreds of miles of passage.

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In many cases,
there are actually rivers

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that flow through them for tens
or even hundreds of miles.

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NARRATOR: The eerie stalactites
growing downward

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00:12:54,595 --> 00:12:56,882
and the stalagmites
growing upward

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were deposited by the water
over thousands of years.

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[Rumbling]

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Our journey
from the surface to the core

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reveals more
spectacular surprises

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as we head further downward.

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Just below the surface,
it's cold, dark, seemingly dead.

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Then, very quickly,
everything changes.

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As we go even deeper,
it gets warmer, then hot.

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The next stop on our journey...

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a mysterious cave
below the Mexican desert.

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This is what the Earth's
inner energy can do.

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At nearly 40 feet long,

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these are the largest known
crystals in the world.

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They're what's left
of an underground lake

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rich in minerals.

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The lake was turned into
a boiling cauldron

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by red-hot magma
erupting from below.

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00:14:02,596 --> 00:14:04,923
As the hot water
percolated through the crust,

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00:14:05,023 --> 00:14:06,421
these giant crystals

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00:14:06,530 --> 00:14:09,486
grew from the minerals
dissolved in the water.

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00:14:11,553 --> 00:14:15,747
Today, the chamber is still
a scorching 120 degrees...

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so hot, scientists can only work
30 minutes at a time,

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even in their
climate-controlled suits.

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LATHROP: But the deep interior
is quite unsuitable for people.

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Pressures are high,
temperatures are high.

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And early on,
people going to mines

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realize it gets hotter
as you go deeper.

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And so there's
this fascination then

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with this inhospitable interior

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to what is otherwise
a pleasant surface we live on.

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NARRATOR: But the energy
inside the Earth

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can do more than make mountains
and hollow out caves.

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In the 1960s,

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00:14:50,936 --> 00:14:54,960
scientists discovered
it can move entire continents.

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00:14:55,070 --> 00:14:57,197
The Earth's crust is formed

187
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from seven massive sections
called plates.

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00:15:00,831 --> 00:15:03,028
What researchers realized

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00:15:03,138 --> 00:15:05,724
is that these plates
were all shifting.

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In some places,
they're pulling apart,

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00:15:09,099 --> 00:15:11,685
in others, smashing together.

192
00:15:12,764 --> 00:15:15,819
Mountains are the crumple zones
of these collisions,

193
00:15:15,929 --> 00:15:19,224
and some are truly spectacular.

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These are the Swiss Alps,

195
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where two continents
crashed together.

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High peaks, like the Matterhorn,

197
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testify to the immense scale
of the forces unleashed.

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It's literally a piece of Africa
sitting on top of Europe.

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Every year, these mountains
grow by a quarter inch.

200
00:16:45,439 --> 00:16:48,195
The Earth is always in motion.

201
00:16:49,233 --> 00:16:52,928
Our mountains and continents
slide around the Earth's surface

202
00:16:53,028 --> 00:16:56,223
driven by energy
from deep inside the planet.

203
00:16:57,531 --> 00:17:00,517
But as this driving force
reshapes the surface,

204
00:17:00,627 --> 00:17:02,654
it reshapes life as well.

205
00:17:03,722 --> 00:17:07,556
It can change and transform
the course of life.

206
00:17:08,595 --> 00:17:10,213
The evidence is here...

207
00:17:10,322 --> 00:17:14,476
1.5 miles down inside
a vast coal seam.

208
00:17:17,023 --> 00:17:20,747
700 miles long
and 120 miles wide.

209
00:17:22,684 --> 00:17:26,010
212 million tons of coal.

210
00:17:27,747 --> 00:17:29,045
All the coal on Earth

211
00:17:29,145 --> 00:17:32,131
is the fossilized remains
of a superforest

212
00:17:32,250 --> 00:17:35,206
that once dominated
the surface of our planet.

213
00:17:40,478 --> 00:17:44,772
360 million years ago, there was
an explosion of life on Earth.

214
00:17:44,872 --> 00:17:46,030
It was more diverse,

215
00:17:46,140 --> 00:17:49,336
more abundant
than it's ever been since.

216
00:17:49,435 --> 00:17:50,873
And it was all because
of the way

217
00:17:50,973 --> 00:17:55,127
that forces inside planet Earth
had shaped the surface.

218
00:17:57,034 --> 00:17:58,402
Go back in time.

219
00:17:58,502 --> 00:18:01,058
That driving energy
at the heart of the planet

220
00:18:01,168 --> 00:18:02,686
had pushed
the continents together

221
00:18:02,796 --> 00:18:07,419
into a single giant landmass
wrapped around the equator.

222
00:18:09,796 --> 00:18:12,692
On this supercontinent,
known as Pangaea,

223
00:18:12,791 --> 00:18:16,486
there were vast lowland swamps
and tropical rainforests.

224
00:18:16,596 --> 00:18:18,213
It was a massive hothouse

225
00:18:18,323 --> 00:18:23,276
and led to the creation
of millions of new species.

226
00:18:26,092 --> 00:18:30,346
This period of time is known
as the Carboniferous era.

227
00:18:30,456 --> 00:18:32,073
The closest scientists can get

228
00:18:32,183 --> 00:18:35,778
to those conditions on Earth
millions of years ago is here...

229
00:18:35,888 --> 00:18:39,183
the Okefenokee nature reserve
in southern Georgia.

230
00:18:39,283 --> 00:18:42,738
Dr. Fred Rich is exploring
how the inner Earth and life

231
00:18:42,848 --> 00:18:44,405
are interconnected.

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00:18:47,511 --> 00:18:51,066
DR. RICH: There were
large landmasses at the equator.

233
00:18:51,175 --> 00:18:56,108
So you have to imagine this flat
landscape just above sea level,

234
00:18:56,208 --> 00:18:59,004
very well-watered,
in the tropics.

235
00:18:59,104 --> 00:19:04,166
And that paleogeography
and the weather conditions,

236
00:19:04,266 --> 00:19:07,032
the meteorology
that followed from that,

237
00:19:07,132 --> 00:19:10,897
led to the appearance of forests

238
00:19:10,997 --> 00:19:13,992
that were unlike anything that
had ever existed on the planet.

239
00:19:18,396 --> 00:19:21,661
NARRATOR: It wasn't just
that the forests were big.

240
00:19:21,761 --> 00:19:24,287
The trees were monsters, too.

241
00:19:26,564 --> 00:19:28,821
DR. RICH:
Huge plants...

242
00:19:28,930 --> 00:19:32,725
Some of these are reckoned
to have been 70 to 100 feet high

243
00:19:32,825 --> 00:19:36,220
and perhaps as much
as 5, 6 feet in diameter...

244
00:19:37,418 --> 00:19:42,610
...lived across
this immense moist landscape.

245
00:19:42,720 --> 00:19:46,045
And plants grew
until they got so big or so old

246
00:19:46,155 --> 00:19:47,583
that they simply fell over.

247
00:19:50,479 --> 00:19:53,035
NARRATOR: These huge trees
and dense forests

248
00:19:53,145 --> 00:19:55,701
had a profound effect
on the atmosphere.

249
00:19:56,980 --> 00:20:01,133
They sucked up carbon dioxide
and pumped out oxygen.

250
00:20:02,242 --> 00:20:04,139
DR. RICH:
High humidity.

251
00:20:04,239 --> 00:20:07,005
Tremendous amount
of oxygen exchange.

252
00:20:07,105 --> 00:20:09,042
I mean, these plants
were photosynthesizing.

253
00:20:09,142 --> 00:20:11,568
So, understandably,
these were oxygen pumps.

254
00:20:11,678 --> 00:20:14,264
And they were similarly
pulling huge amounts of CO2

255
00:20:14,374 --> 00:20:15,602
out of the air.

256
00:20:17,839 --> 00:20:20,026
NARRATOR:
360 million years ago,

257
00:20:20,136 --> 00:20:22,363
the proportion of oxygen
in the air

258
00:20:22,472 --> 00:20:25,698
was 60% greater
than it is today.

259
00:20:27,365 --> 00:20:29,232
The high levels of oxygen

260
00:20:29,332 --> 00:20:33,726
led to another dramatic effect
on the Earth's creatures.

261
00:20:34,864 --> 00:20:37,091
It supersized them.

262
00:20:38,898 --> 00:20:43,052
There were poisonous centipedes
6 feet long.

263
00:20:43,162 --> 00:20:44,590
2-foot cockroaches.

264
00:20:45,589 --> 00:20:48,355
Even dragonflies
the size of sea gulls.

265
00:20:49,323 --> 00:20:51,909
DR. RICH: Dragonflies that we
find in this swamp are large,

266
00:20:52,019 --> 00:20:53,317
and they're certainly numerous.

267
00:20:53,417 --> 00:20:54,975
But the dragonflies
of the Carboniferous

268
00:20:55,085 --> 00:20:56,213
would have been much bigger.

269
00:20:56,323 --> 00:20:58,180
Easily three, four times
the size,

270
00:20:58,290 --> 00:21:00,687
based on what we have
for fossil evidence.

271
00:21:03,213 --> 00:21:04,841
NARRATOR:
Instead of alligators,

272
00:21:04,950 --> 00:21:08,276
the dominant predators
were giant toads.

273
00:21:09,344 --> 00:21:13,368
Alligators would have been
replaced by large amphibians...

274
00:21:13,478 --> 00:21:16,234
amphibians probably as large
as the alligators

275
00:21:16,344 --> 00:21:17,971
that we have
in these modern swamps

276
00:21:18,081 --> 00:21:20,238
but looking differently,
perhaps.

277
00:21:21,746 --> 00:21:24,732
NARRATOR: New species that
changed the evolution of life,

278
00:21:24,841 --> 00:21:28,636
all because the energy inside
our planet reshaped its surface.

279
00:21:31,442 --> 00:21:35,456
This strange lost world
existed long before humans,

280
00:21:35,566 --> 00:21:39,999
but its story was sealed
into the Earth's rocks in coal.

281
00:21:42,266 --> 00:21:44,633
The forest first became peat.

282
00:21:44,732 --> 00:21:47,419
This was then squeezed
under tons of rock,

283
00:21:47,528 --> 00:21:49,585
where it started to dry out.

284
00:21:53,160 --> 00:21:57,184
Now, in the process
of this brown messy sediment

285
00:21:57,294 --> 00:21:58,912
becoming coal,

286
00:21:59,022 --> 00:22:02,357
the first thing we would need
to do is get rid of the water.

287
00:22:02,457 --> 00:22:05,612
Earthly processes do that simply
by loading the sediment.

288
00:22:05,722 --> 00:22:08,278
So the longer the sediment
is in the ground,

289
00:22:08,388 --> 00:22:11,643
the longer it has been buried,
subjected to geothermal heat

290
00:22:11,753 --> 00:22:14,050
that's coming from
the interior of the Earth,

291
00:22:14,150 --> 00:22:16,516
the more the sediment
is compacted,

292
00:22:16,616 --> 00:22:18,134
and the more the water
is driven out.

293
00:22:22,118 --> 00:22:23,736
NARRATOR:
So the Earth's internal energy

294
00:22:23,845 --> 00:22:26,402
had reshaped the landmass
to make life possible,

295
00:22:26,512 --> 00:22:30,965
then broke it apart and buried
the remains deeper and deeper

296
00:22:31,075 --> 00:22:32,473
until the heat and pressure

297
00:22:32,573 --> 00:22:35,698
transformed the ancient forests
into coal...

298
00:22:35,808 --> 00:22:38,434
fossilized remains
of a lost era.

299
00:22:44,805 --> 00:22:46,862
As we go deeper on our journey,

300
00:22:46,972 --> 00:22:49,798
there are other riches
for humans to exploit.

301
00:22:51,635 --> 00:22:53,362
2.5 miles down,

302
00:22:53,462 --> 00:22:57,087
we pass a glittering seam
of gold being formed.

303
00:22:58,595 --> 00:23:01,461
Boiling fluids
full of dissolved gold

304
00:23:01,560 --> 00:23:04,027
bubble up
through the cracks in the rock.

305
00:23:06,064 --> 00:23:08,720
The higher it rises,
the cooler it gets,

306
00:23:08,830 --> 00:23:12,055
until the dissolved gold
finally settles into seams.

307
00:23:14,761 --> 00:23:16,948
Earth's thin crust...

308
00:23:17,058 --> 00:23:21,312
home to life in all its complex,
colorful, infinite variety.

309
00:23:22,849 --> 00:23:26,684
Below it is an inhospitable,
lifeless world.

310
00:23:27,812 --> 00:23:29,480
Or so it seemed.

311
00:23:30,678 --> 00:23:34,742
Scientists are now finding life
deep inside Earth.

312
00:23:36,210 --> 00:23:41,442
It's a remarkable discovery made
in the world's deepest mines.

313
00:23:43,310 --> 00:23:46,864
This is the Witwatersrand region
of South Africa.

314
00:23:46,974 --> 00:23:52,636
The mines here reach
2.5 miles inside Earth's crust.

315
00:23:52,736 --> 00:23:56,500
It seems like they stretch
a long way down.

316
00:23:57,639 --> 00:24:01,363
But in reality,
they barely scratch the surface.

317
00:24:07,394 --> 00:24:10,061
This is a hostile environment
for a human being.

318
00:24:12,267 --> 00:24:16,162
It's 130 degrees Fahrenheit,
100% humidity,

319
00:24:16,262 --> 00:24:18,348
and extremely cramped.

320
00:24:20,655 --> 00:24:22,453
The mines are so deep,

321
00:24:22,562 --> 00:24:25,987
the miners have to descend
in two stages.

322
00:24:27,755 --> 00:24:30,810
A single elevator cable
stretching 2.5 miles

323
00:24:30,920 --> 00:24:32,977
would snap under the strain.

324
00:24:35,254 --> 00:24:38,579
It's so far down,
the journey can take two hours.

325
00:24:43,911 --> 00:24:44,940
Like the miners,

326
00:24:45,050 --> 00:24:47,945
these biologists
from Bloemfontein University

327
00:24:48,045 --> 00:24:51,670
risk heatstroke as they descend
into one of the mines.

328
00:24:54,306 --> 00:24:56,203
But they're not interested
in gold.

329
00:24:58,310 --> 00:25:01,176
They're looking for life...

330
00:25:01,276 --> 00:25:03,463
colonies of
extraordinary creatures

331
00:25:03,573 --> 00:25:06,129
that thrive
in these extreme conditions...

332
00:25:07,806 --> 00:25:10,532
...bacteria they believe
may be direct descendants

333
00:25:10,632 --> 00:25:13,628
of the very first
life-forms on Earth.

334
00:25:15,505 --> 00:25:18,621
Leading the team
is Professor Derek Litthauer.

335
00:25:18,730 --> 00:25:21,996
You've got
communities of bacteria.

336
00:25:22,096 --> 00:25:24,961
And possibly even fungi.

337
00:25:25,061 --> 00:25:26,090
We don't know yet.

338
00:25:26,200 --> 00:25:29,595
But probably mostly bacteria
living in there.

339
00:25:29,694 --> 00:25:31,662
And the kind of populations
you get in there

340
00:25:31,761 --> 00:25:32,690
are usually determined

341
00:25:32,790 --> 00:25:34,987
by the chemical composition
of the water.

342
00:25:35,097 --> 00:25:36,924
But our past experience

343
00:25:37,024 --> 00:25:41,417
has been that there's
some unique stuff in there.

344
00:25:46,051 --> 00:25:48,946
NARRATOR: The scientists tap
into ancient underground water

345
00:25:49,056 --> 00:25:52,282
released during
the mining process.

346
00:25:53,819 --> 00:25:56,006
The water
and the bacteria inside it

347
00:25:56,116 --> 00:26:01,009
have remained undisturbed
for billions of years.

348
00:26:02,147 --> 00:26:05,173
These bacteria are tough.

349
00:26:05,283 --> 00:26:10,735
All they need to survive is
rock, water, and scorching heat.

350
00:26:12,941 --> 00:26:15,767
LITTHAUER: There's an amazing
diversity of life underground,

351
00:26:15,877 --> 00:26:17,665
even in the deep subsurface.

352
00:26:17,774 --> 00:26:20,131
In some areas,
we can expect life

353
00:26:20,241 --> 00:26:23,137
possibly even down to
10 kilometers below surface.

354
00:26:24,135 --> 00:26:27,261
And they are
extremely sophisticated,

355
00:26:27,370 --> 00:26:30,266
very highly specialized for the
environment in which they live

356
00:26:30,366 --> 00:26:32,563
off the nutrients
that they can get in the rocks.

357
00:26:32,663 --> 00:26:34,820
NARRATOR:
It's an extraordinary discovery

358
00:26:34,929 --> 00:26:37,256
that has transformed
biologists' understanding

359
00:26:37,366 --> 00:26:39,263
of the origins of life.

360
00:26:39,363 --> 00:26:41,759
The bacteria
are the latest additions

361
00:26:41,859 --> 00:26:43,447
to a strange group of creatures

362
00:26:43,557 --> 00:26:45,654
that thrive
in extreme conditions

363
00:26:45,764 --> 00:26:47,950
called extremophiles.

364
00:26:48,060 --> 00:26:49,918
[Bubbling]

365
00:26:51,156 --> 00:26:52,684
In the 1960s,

366
00:26:52,793 --> 00:26:55,250
astonished scientists
found bacteria

367
00:26:55,360 --> 00:26:58,415
living in Yellowstone's
boiling acid pools.

368
00:26:59,823 --> 00:27:01,551
Then in the 1970s,

369
00:27:01,650 --> 00:27:05,445
biologists discovered life
1.5 miles down in the oceans

370
00:27:05,555 --> 00:27:09,140
close to vents in the seafloor
called black smokers.

371
00:27:10,318 --> 00:27:12,744
These life-forms thrive
on nothing more

372
00:27:12,844 --> 00:27:14,971
than volcanic gases.

373
00:27:16,409 --> 00:27:19,574
If life exists
in such hostile conditions...

374
00:27:20,613 --> 00:27:22,869
...it suggests
a teeming mass of life

375
00:27:22,979 --> 00:27:25,945
could exist beneath our feet.

376
00:27:26,974 --> 00:27:30,129
It's been estimated that all
the bacteria inside Earth

377
00:27:30,239 --> 00:27:34,063
could weigh more than all the
life aboveground put together.

378
00:27:35,241 --> 00:27:38,197
It also raises
an intriguing possibility...

379
00:27:38,307 --> 00:27:41,363
that life may have started
not on the surface

380
00:27:41,472 --> 00:27:43,629
but deep within the Earth.

381
00:27:46,395 --> 00:27:50,489
There's more diversity and more
life in the deep subsurface

382
00:27:50,599 --> 00:27:52,027
than we have above surface.

383
00:27:52,127 --> 00:27:54,094
The implications for this,

384
00:27:54,194 --> 00:27:56,660
in terms of the evolution
of life in the universe,

385
00:27:56,760 --> 00:27:57,659
are quite astounding,

386
00:27:57,759 --> 00:28:02,092
because the old concept
that life could have started

387
00:28:02,192 --> 00:28:06,316
in very calm, serene, warm pools
on the surface of the Earth...

388
00:28:06,426 --> 00:28:07,784
That may be completely wrong.

389
00:28:07,894 --> 00:28:09,881
Life may have started
in the subsurface.

390
00:28:12,457 --> 00:28:14,384
NARRATOR:
If life began underground,

391
00:28:14,484 --> 00:28:17,210
then somehow at some time
in Earth's history,

392
00:28:17,320 --> 00:28:19,747
it found a route to the surface.

393
00:28:21,115 --> 00:28:23,102
Perhaps the Earth's
inner energy,

394
00:28:23,212 --> 00:28:24,649
as it pushed through the crust,

395
00:28:24,749 --> 00:28:27,336
took the extremophiles
to the top.

396
00:28:28,684 --> 00:28:31,170
Or maybe it hitched a ride
on a black smoker...

397
00:28:31,280 --> 00:28:34,675
a kind of extremophile elevator
to ground level.

398
00:28:34,775 --> 00:28:37,471
Or floated up
in thermal hot springs,

399
00:28:37,571 --> 00:28:39,438
boiling up
from deep in the Earth.

400
00:28:41,605 --> 00:28:45,659
How far down primitive life
could survive is uncertain.

401
00:28:45,769 --> 00:28:48,565
But to explore what lies
beyond the deepest mine

402
00:28:48,674 --> 00:28:51,231
pushes technology to its limits.

403
00:28:52,968 --> 00:28:56,094
The only way down this far
is to drill.

404
00:29:00,098 --> 00:29:02,125
But pressure and heat
put a limit

405
00:29:02,235 --> 00:29:05,750
on even our most
sophisticated drill bits.

406
00:29:05,859 --> 00:29:09,384
The deepest hole ever drilled
bored just 7.5 miles

407
00:29:09,494 --> 00:29:12,390
into the Earth's 30-mile crust.

408
00:29:12,490 --> 00:29:15,425
In the 1970s,
the Soviets race

409
00:29:15,525 --> 00:29:18,391
to drill the world's
deepest borehole in Russia.

410
00:29:19,819 --> 00:29:21,087
The drill bit was so long,

411
00:29:21,187 --> 00:29:24,812
it bent and stretched
like a piece of elastic.

412
00:29:24,922 --> 00:29:26,549
But even at this depth,

413
00:29:26,649 --> 00:29:29,375
we are less than halfway through
the Earth's surface layer,

414
00:29:29,485 --> 00:29:31,382
the crust.

415
00:29:31,482 --> 00:29:35,207
It's only 1/500th
of our journey to the core.

416
00:29:35,316 --> 00:29:39,041
7.5 miles is like traveling
from downtown Chicago

417
00:29:39,151 --> 00:29:40,938
into the suburbs.

418
00:29:42,975 --> 00:29:47,379
But it's another 4,000 miles
to the center of the Earth.

419
00:29:47,479 --> 00:29:50,674
That's like commuting
from Chicago to London.

420
00:29:52,441 --> 00:29:54,029
Scientists may be restricted

421
00:29:54,139 --> 00:29:57,005
to exploring the thin top layer
of the Earth's crust,

422
00:29:57,105 --> 00:30:00,090
but their journey of discovery
isn't over.

423
00:30:00,200 --> 00:30:04,104
They've found other ingenious
ways of exploring inside Earth,

424
00:30:04,204 --> 00:30:06,171
and in the process

425
00:30:06,271 --> 00:30:08,498
discovered more
surprising connections

426
00:30:08,598 --> 00:30:10,655
with the evolution
of life itself.

427
00:30:15,927 --> 00:30:19,832
Life on Earth might have started
deep in the Earth's crust,

428
00:30:19,931 --> 00:30:22,687
but violent upheavals
even further down

429
00:30:22,797 --> 00:30:24,954
played a crucial role
in pushing life

430
00:30:25,064 --> 00:30:27,790
on to the next stage
of evolution...

431
00:30:27,890 --> 00:30:31,215
one that would lead to all life
as we know it.

432
00:30:31,325 --> 00:30:34,750
Remarkably, we know this
from the ancient rocks

433
00:30:34,860 --> 00:30:36,377
of the crust itself.

434
00:30:49,478 --> 00:30:50,467
These mountains

435
00:30:50,577 --> 00:30:53,173
in Western Australia's
Karijini National Park

436
00:30:53,283 --> 00:30:57,706
are made from rock
that's 3.5 billion years old.

437
00:30:57,816 --> 00:31:01,401
They used to be the bed
of an ancient sea.

438
00:31:01,511 --> 00:31:04,436
Their red color
comes from iron ore

439
00:31:04,546 --> 00:31:06,593
imbedded right in the rock.

440
00:31:07,911 --> 00:31:11,097
But the iron is evidence
of something remarkable...

441
00:31:12,904 --> 00:31:14,272
...because they were formed

442
00:31:14,372 --> 00:31:15,930
during one of
the most important events

443
00:31:16,040 --> 00:31:18,696
in the story of life on Earth.

444
00:31:24,228 --> 00:31:28,252
The bands of red iron ore
were once layers of sediments,

445
00:31:28,362 --> 00:31:31,916
and they contain evidence
of very primitive life-forms.

446
00:31:33,125 --> 00:31:35,821
Martin Van Kranendonk
is a geologist

447
00:31:35,931 --> 00:31:39,615
who's spent a lifetime
studying these rocks.

448
00:31:39,725 --> 00:31:41,283
Each one of these little bands

449
00:31:41,393 --> 00:31:43,549
is only about
the length of a thumbnail,

450
00:31:43,659 --> 00:31:45,487
and it was maybe deposited
in a year.

451
00:31:45,587 --> 00:31:46,615
So you can see here,

452
00:31:46,725 --> 00:31:49,651
you've got hundreds of feet
of deposited sediments.

453
00:31:49,750 --> 00:31:52,017
It represents
hundreds of thousands of years

454
00:31:52,117 --> 00:31:53,775
of geological time.

455
00:31:56,151 --> 00:31:58,548
NARRATOR: These were
no ordinary sediments.

456
00:31:58,647 --> 00:32:03,011
They contain fossils of rock
structures called stromatolites,

457
00:32:03,111 --> 00:32:05,837
created by some
of the earliest living things...

458
00:32:05,947 --> 00:32:08,243
simple bacteria.

459
00:32:10,211 --> 00:32:11,229
It's hard to imagine,

460
00:32:11,349 --> 00:32:14,275
but this immense volume
of iron-rich rocks

461
00:32:14,375 --> 00:32:17,670
was actually formed
by tiny microscopic organisms

462
00:32:17,780 --> 00:32:20,605
that formed structures
such as preserved here

463
00:32:20,705 --> 00:32:22,692
in this very old rock.

464
00:32:22,802 --> 00:32:24,829
This is an example
of a stromatolite

465
00:32:24,939 --> 00:32:28,394
that's built by single-celled
organisms in this rock,

466
00:32:28,504 --> 00:32:31,629
which is 3.45 billion years old.

467
00:32:31,739 --> 00:32:34,635
This is the oldest fossil
on the planet.

468
00:32:39,598 --> 00:32:41,525
NARRATOR:
Incredibly, these bacteria

469
00:32:41,635 --> 00:32:44,421
are still making these
distinctive rock formations

470
00:32:44,531 --> 00:32:47,187
just 400 miles to the west.

471
00:32:48,864 --> 00:32:52,050
These strange-looking mounds
are giant stromatolites

472
00:32:52,159 --> 00:32:54,316
built by the bacteria.

473
00:32:59,519 --> 00:33:01,416
VAN KRANENDONK:
Well, stromatolites are rocks,

474
00:33:01,526 --> 00:33:04,971
but they're rocks that are made
by living microorganisms

475
00:33:05,091 --> 00:33:07,048
or, as we call them, microbes.

476
00:33:09,255 --> 00:33:11,651
And so these stromatolites
actually grow

477
00:33:11,751 --> 00:33:13,648
by precipitating rock.

478
00:33:13,748 --> 00:33:18,042
So they build up layer by layer,
but only very slowly.

479
00:33:19,080 --> 00:33:22,136
NARRATOR: The bacteria
also produced something else,

480
00:33:22,246 --> 00:33:26,300
something which kick-started
a biological revolution...

481
00:33:26,410 --> 00:33:27,967
oxygen.

482
00:33:29,345 --> 00:33:31,332
If life did start underground,

483
00:33:31,442 --> 00:33:35,197
maybe it eventually
found its way to the surface,

484
00:33:35,307 --> 00:33:39,001
propelled upward
by those forces within Earth.

485
00:33:39,101 --> 00:33:41,438
And once
they'd reached the surface,

486
00:33:41,537 --> 00:33:44,833
those bacteria found a new way
to harness energy,

487
00:33:44,933 --> 00:33:48,417
not from the rocks
and the heat of the deep Earth,

488
00:33:48,537 --> 00:33:52,292
but from sunlight... the process
we call photosynthesis.

489
00:33:52,402 --> 00:33:56,126
And one of the most important
by-products of photosynthesis

490
00:33:56,226 --> 00:33:57,993
is oxygen.

491
00:33:58,093 --> 00:34:01,219
These stromatolites
are incredibly important for us.

492
00:34:01,329 --> 00:34:02,557
They're really the precursors

493
00:34:02,657 --> 00:34:06,112
to allow life to evolve
from the oceans on to land

494
00:34:06,221 --> 00:34:07,949
and to breathe air.

495
00:34:08,059 --> 00:34:09,856
NARRATOR:
Without oxygen,

496
00:34:09,956 --> 00:34:13,820
complex life as we know it
simply wouldn't exist.

497
00:34:13,920 --> 00:34:17,575
But oxygen also changed
the composition of the planet,

498
00:34:17,685 --> 00:34:20,650
creating the iron ore
in the crust.

499
00:34:20,750 --> 00:34:23,716
At the time,
most of the iron on the surface

500
00:34:23,816 --> 00:34:27,271
was dissolved in the oceans,
making them appear bright green.

501
00:34:28,849 --> 00:34:32,244
But the newly released oxygen
bonded with all the iron

502
00:34:32,343 --> 00:34:34,400
to make iron oxide, or rust.

503
00:34:35,748 --> 00:34:38,235
The iron oxide
fell to the seafloor,

504
00:34:38,345 --> 00:34:41,210
and the seas turned blue.

505
00:34:41,310 --> 00:34:44,066
Eventually, the iron oxide
formed the deposits

506
00:34:44,176 --> 00:34:46,643
we see
in the Karijini mountains.

507
00:34:47,741 --> 00:34:51,396
Layer upon layer of iron oxide
exists in the Earth's crust

508
00:34:51,505 --> 00:34:53,902
thanks to primitive bacteria.

509
00:34:55,240 --> 00:34:57,137
It's the ore
from which we extract

510
00:34:57,237 --> 00:35:00,293
1.7 billion tons of iron
each year,

511
00:35:00,403 --> 00:35:03,368
and it's also rich in oxygen.

512
00:35:05,136 --> 00:35:07,862
In fact,
there's 20 times more oxygen

513
00:35:07,961 --> 00:35:09,719
locked up in the bands
of iron ore

514
00:35:09,829 --> 00:35:12,525
than there is
floating in the atmosphere.

515
00:35:13,923 --> 00:35:16,449
It's another example
of how the world we know

516
00:35:16,559 --> 00:35:18,716
has been shaped
by the incredible forces

517
00:35:18,826 --> 00:35:20,553
deep inside the planet.

518
00:35:21,861 --> 00:35:24,717
But where do
these forces come from?

519
00:35:24,827 --> 00:35:26,874
We now enter
the part of the Earth

520
00:35:26,984 --> 00:35:29,820
that holds the answer...
the mantle.

521
00:35:29,919 --> 00:35:32,386
It's a dynamic mass
of churning rock

522
00:35:32,486 --> 00:35:34,972
kept moving by energy
from the core...

523
00:35:35,082 --> 00:35:37,918
the powerhouse of the planet.

524
00:35:40,484 --> 00:35:42,881
Below the 30 miles
of surface crust,

525
00:35:42,980 --> 00:35:46,875
we now move deeper, further
than any human has ventured,

526
00:35:46,975 --> 00:35:48,872
into the Earth's mantle.

527
00:35:48,982 --> 00:35:51,039
The mantle is the real key

528
00:35:51,149 --> 00:35:53,575
to understanding
how our world works.

529
00:35:53,675 --> 00:35:55,762
When you see flowing lava,

530
00:35:55,872 --> 00:35:58,468
it's easy to think
that the mantle is liquid.

531
00:35:58,578 --> 00:36:02,332
In fact, it's nearly
2,000 miles straight down

532
00:36:02,442 --> 00:36:04,229
of hot but solid rock.

533
00:36:04,339 --> 00:36:08,064
It makes up 80%
of the Earth's volume.

534
00:36:08,174 --> 00:36:09,791
Nothing can live here.

535
00:36:09,901 --> 00:36:14,225
But what happens at these depths
is vital to life on Earth.

536
00:36:14,335 --> 00:36:16,801
The mantle
may be beyond our reach,

537
00:36:16,901 --> 00:36:19,297
but sometimes it reaches us.

538
00:36:22,133 --> 00:36:23,621
The solid rock liquefies

539
00:36:23,731 --> 00:36:26,956
when the massive pressure on
the mantle is suddenly released

540
00:36:27,056 --> 00:36:28,953
through fissures and cracks
in the crust.

541
00:36:30,162 --> 00:36:35,244
The radical change in pressure
transforms the rock into lava.

542
00:36:36,423 --> 00:36:39,149
The rock of the mantle
beneath the Earth's crust

543
00:36:39,258 --> 00:36:40,307
is inaccessible.

544
00:36:40,417 --> 00:36:41,645
But against the odds,

545
00:36:41,755 --> 00:36:43,742
there are some places
where mantlerock

546
00:36:43,852 --> 00:36:45,909
has been forced to the surface.

547
00:36:47,047 --> 00:36:49,414
One of them
is on the Lizard Peninsula

548
00:36:49,513 --> 00:36:51,850
on the southernmost tip
of England.

549
00:37:02,814 --> 00:37:04,432
On this peaceful beach

550
00:37:04,542 --> 00:37:07,507
is evidence of something violent
and powerful...

551
00:37:07,607 --> 00:37:09,734
a piece of mantlerock
that broke away

552
00:37:09,844 --> 00:37:12,570
and was forced upward 30 miles

553
00:37:12,670 --> 00:37:15,266
by the churning movements
of the crust.

554
00:37:15,376 --> 00:37:17,732
For geologists like Robin Shail,

555
00:37:17,842 --> 00:37:20,458
it's the perfect place
to study mantlerocks,

556
00:37:20,568 --> 00:37:23,364
which are normally
way beyond his reach.

557
00:37:24,732 --> 00:37:27,828
How do they compare
with other rocks on the surface?

558
00:37:29,535 --> 00:37:33,120
What do they tell us about
what's inside planet Earth?

559
00:37:38,462 --> 00:37:41,687
DR. SHAIL: The rocks here
look completely different.

560
00:37:41,797 --> 00:37:44,284
They have colors which vary
from greens

561
00:37:44,393 --> 00:37:46,221
through to oranges and yellows.

562
00:37:46,321 --> 00:37:48,218
This is typical of mantlerocks

563
00:37:48,328 --> 00:37:51,513
wherever they're exposed
at the Earth's surface.

564
00:37:54,788 --> 00:37:56,686
NARRATOR:
Like no other rocks we know,

565
00:37:56,785 --> 00:37:59,841
mantlerock is very hard
and very heavy,

566
00:37:59,951 --> 00:38:02,577
nearly twice the weight
of granite.

567
00:38:07,480 --> 00:38:11,374
It's a dense mass of minerals
rich in heavy elements

568
00:38:11,484 --> 00:38:14,839
such as iron and magnesium.

569
00:38:14,949 --> 00:38:17,176
And it's the source of gemstones

570
00:38:17,276 --> 00:38:20,571
such as the distinctive
green peridot.

571
00:38:22,977 --> 00:38:25,134
Close up,
structures are revealed

572
00:38:25,244 --> 00:38:27,141
that could only have been formed

573
00:38:27,241 --> 00:38:29,867
under extreme temperature
and pressure.

574
00:38:37,606 --> 00:38:41,860
Here on the Earth's surface,
this rock seems solid enough.

575
00:38:43,827 --> 00:38:47,262
Deep underground, however,
it becomes very different,

576
00:38:47,362 --> 00:38:50,387
something that behaves
more like fudge.

577
00:38:50,497 --> 00:38:55,320
When we look at this mantle
peridotite, it appears solid.

578
00:38:55,430 --> 00:38:59,514
In contrast, when mantlerocks...
or fudge... are warmer,

579
00:38:59,624 --> 00:39:03,019
you can actually stretch
and make it flow.

580
00:39:03,119 --> 00:39:05,016
And the significance for this

581
00:39:05,126 --> 00:39:08,281
is that these weak layers
within the mantle

582
00:39:08,391 --> 00:39:11,906
allow the overlying plates
to move slowly across.

583
00:39:12,016 --> 00:39:15,141
NARRATOR: A solid that flows
may seem strange,

584
00:39:15,251 --> 00:39:19,045
but the mobility of the mantle
is vital to life on Earth.

585
00:39:19,145 --> 00:39:21,172
Because currents of heat
circulate upwards

586
00:39:21,282 --> 00:39:23,439
from the core
through the mantle,

587
00:39:23,549 --> 00:39:26,874
the plates of the crust
can move around on the surface.

588
00:39:26,974 --> 00:39:29,770
Without this shifting geology,
there'd be no continents,

589
00:39:29,880 --> 00:39:33,135
and the conditions for life
would never have existed.

590
00:39:33,245 --> 00:39:34,932
DR. SHAIL: Without these zones
in the mantle

591
00:39:35,042 --> 00:39:38,068
that allow the plates to move
across the Earth's surface,

592
00:39:38,178 --> 00:39:41,463
we would basically have
a geologically dead planet.

593
00:39:41,573 --> 00:39:43,040
We would have no plate movement.

594
00:39:43,140 --> 00:39:44,998
We would have
no mountain ranges.

595
00:39:45,107 --> 00:39:47,564
We would have
no major ocean basins.

596
00:39:47,674 --> 00:39:50,659
So the mantle
is absolutely critical.

597
00:39:52,966 --> 00:39:54,833
NARRATOR: These are
the deepest rocks visible

598
00:39:54,933 --> 00:39:56,331
on the Earth's surface.

599
00:39:56,431 --> 00:39:58,158
To look further into the mantle,

600
00:39:58,268 --> 00:40:00,884
scientists must find
another way.

601
00:40:05,957 --> 00:40:07,655
Inside the Earth's mantle,

602
00:40:07,764 --> 00:40:11,209
crushed beneath
100 miles of rock,

603
00:40:11,329 --> 00:40:14,085
the pressure
is 50,000 times more

604
00:40:14,195 --> 00:40:16,482
than we feel at the surface,

605
00:40:16,592 --> 00:40:20,106
like carrying 20 <i>Titanics</i>
on your shoulders.

606
00:40:22,483 --> 00:40:24,181
It's in this hostile environment

607
00:40:24,290 --> 00:40:27,645
that some of the Earth's
greatest treasures are forged.

608
00:40:29,553 --> 00:40:31,979
The pressure creates diamonds.

609
00:40:32,948 --> 00:40:35,414
It crushes carbon
into the hardest mineral

610
00:40:35,514 --> 00:40:38,410
known to science.

611
00:40:38,510 --> 00:40:42,234
But we don't have to dig
100 miles to find them.

612
00:40:42,344 --> 00:40:46,468
Diamonds exist just a few
hundred feet below the surface.

613
00:40:48,845 --> 00:40:50,332
They were forced up
through the crust

614
00:40:50,442 --> 00:40:52,739
by violent prehistoric eruptions

615
00:40:52,839 --> 00:40:55,235
triggered by
the Earth's internal heat.

616
00:40:57,073 --> 00:41:00,528
Today, miners excavate
these extinct volcanic vents

617
00:41:00,637 --> 00:41:03,623
in search of diamonds.

618
00:41:04,771 --> 00:41:06,059
The Letseng diamond mine

619
00:41:06,169 --> 00:41:08,855
is located in the mountain
kingdom of Lesotho...

620
00:41:10,094 --> 00:41:13,459
...a small country
in the heart of South Africa.

621
00:41:15,596 --> 00:41:19,150
The diamonds are imbedded
in rock called kimberlite

622
00:41:19,260 --> 00:41:21,727
inside an old volcanic pipe.

623
00:41:21,826 --> 00:41:23,814
It's the job
of company geologists

624
00:41:23,923 --> 00:41:25,791
like Claire Palmer
to find them.

625
00:41:26,859 --> 00:41:29,655
DR. PALMER:
We're standing within the pipe,

626
00:41:29,755 --> 00:41:32,621
the original
eruptive pipe that formed.

627
00:41:32,721 --> 00:41:35,277
And the original earth surface
would have been

628
00:41:35,387 --> 00:41:37,474
at least 200 meters
above our heads.

629
00:41:37,584 --> 00:41:39,950
And we're actually,
in the mining process,

630
00:41:40,050 --> 00:41:41,947
reexcavating that pipe.

631
00:41:43,585 --> 00:41:45,442
NARRATOR:
Most of the diamonds on Earth

632
00:41:45,552 --> 00:41:49,376
exploded through the surface
during huge volcanic eruptions

633
00:41:49,476 --> 00:41:51,503
one billion years ago.

634
00:42:01,978 --> 00:42:06,561
DR. PALMER: These volcanoes
erupted at supersonic speeds.

635
00:42:06,671 --> 00:42:10,296
So you can imagine the power
with which it explodes.

636
00:42:12,702 --> 00:42:15,069
Similar to that
of Mount St. Helens.

637
00:42:15,169 --> 00:42:16,427
But Mount St. Helens' eruption

638
00:42:16,537 --> 00:42:18,893
moved laterally
across the Earth,

639
00:42:19,003 --> 00:42:21,969
whereas these eruptions were
actually a lot more vertical

640
00:42:22,069 --> 00:42:24,026
in their expanse.

641
00:42:28,799 --> 00:42:30,526
NARRATOR:
These violent eruptions

642
00:42:30,626 --> 00:42:33,352
exploded minerals
from 100 miles down

643
00:42:33,462 --> 00:42:36,288
upward to the surface
in minutes.

644
00:42:38,724 --> 00:42:42,659
Today, the diamonds are locked
inside this volcanic rock.

645
00:42:42,758 --> 00:42:45,275
There's only one way
to get them out.

646
00:43:04,347 --> 00:43:07,472
Letseng is a valuable mine.

647
00:43:07,582 --> 00:43:09,480
All these diamonds
were recovered

648
00:43:09,579 --> 00:43:11,976
in just over two weeks.

649
00:43:12,076 --> 00:43:15,271
These diamonds
are known worldwide

650
00:43:15,371 --> 00:43:17,098
for their very high quality

651
00:43:17,208 --> 00:43:21,332
and yield the highest dollar
per carat in the world.

652
00:43:21,442 --> 00:43:22,960
The Letseng diamond mine

653
00:43:23,070 --> 00:43:25,596
is famous for its
very large diamonds.

654
00:43:25,706 --> 00:43:28,791
One of our most famous
is the Lesotho Promise...

655
00:43:28,901 --> 00:43:32,456
603 carats, which was recovered
in August 2006.

656
00:43:32,566 --> 00:43:36,790
And it sold on tender
for $12.4 million U.S.

657
00:43:36,900 --> 00:43:39,126
NARRATOR:
Not all diamonds are perfect.

658
00:43:39,226 --> 00:43:41,892
Some have microscopic flaws.

659
00:43:41,992 --> 00:43:44,758
A perfect diamond
is worth a lot more money.

660
00:43:44,858 --> 00:43:48,812
But for geologists, these flaws
are the real treasures.

661
00:43:48,922 --> 00:43:51,688
They're tiny fragments
of primitive mantle

662
00:43:51,788 --> 00:43:53,775
trapped inside the diamond,

663
00:43:53,885 --> 00:43:57,320
and they're the deepest samples
it's possible to capture.

664
00:43:57,420 --> 00:43:59,177
They tell a remarkable story.

665
00:43:59,287 --> 00:44:00,415
Like time capsules,

666
00:44:00,515 --> 00:44:02,782
they hold the key
to unlock secrets

667
00:44:02,882 --> 00:44:05,078
of the Earth's
very early history.

668
00:44:05,188 --> 00:44:06,776
From their chemistry,

669
00:44:06,886 --> 00:44:09,512
scientists can deduce
that most of these diamonds

670
00:44:09,612 --> 00:44:12,378
are 3.2 billion years old.

671
00:44:12,478 --> 00:44:16,771
They can even figure out
they were forged 100 miles down.

672
00:44:17,980 --> 00:44:19,877
Diamond samples from
different parts of the world

673
00:44:19,977 --> 00:44:22,673
show large variation
in their composition.

674
00:44:22,773 --> 00:44:26,328
That suggests the mantle
was a churning dynamic place,

675
00:44:26,437 --> 00:44:29,233
even in the early history
of the planet.

676
00:44:30,841 --> 00:44:32,499
From below 100 miles,

677
00:44:32,608 --> 00:44:36,333
very few rock samples
reach us on the surface.

678
00:44:36,433 --> 00:44:40,387
But this isn't the end
of our journey to the core.

679
00:44:40,497 --> 00:44:43,333
There is another way
to see what's down there.

680
00:44:45,100 --> 00:44:48,555
It's like an X-ray image
of planet Earth.

681
00:44:52,999 --> 00:44:54,726
Most of the time,

682
00:44:54,826 --> 00:44:58,221
we're unaware of the power
locked inside our planet.

683
00:44:58,331 --> 00:45:01,816
But sometimes
there are violent reminders.

684
00:45:01,926 --> 00:45:03,393
[Rumbling]

685
00:45:05,790 --> 00:45:07,917
Earthquakes are the result
of processes

686
00:45:08,027 --> 00:45:10,713
taking place
deep in the interior.

687
00:45:12,550 --> 00:45:15,146
Propelled by the slow movement
of the mantle,

688
00:45:15,256 --> 00:45:17,613
the great plates
that make up the Earth's crust

689
00:45:17,723 --> 00:45:21,707
constantly grind into, over,
and under each other.

690
00:45:23,145 --> 00:45:26,410
Pressure builds
until something snaps.

691
00:45:26,510 --> 00:45:30,534
When this happens, the Earth
shakes, heaves, and rolls.

692
00:45:30,644 --> 00:45:32,910
The results can be catastrophic,

693
00:45:33,010 --> 00:45:36,635
especially when they happen
in populated areas.

694
00:45:36,745 --> 00:45:39,331
This earthquake in China in 2008

695
00:45:39,441 --> 00:45:45,342
killed 70,000 people and cost
$150 billion worth of damage.

696
00:45:46,640 --> 00:45:49,436
Big earthquakes are disasters,

697
00:45:49,536 --> 00:45:54,090
but they're also windows on
the deep interior of the planet.

698
00:45:54,199 --> 00:45:58,094
Scientists can make use of the
shattering power of earthquakes

699
00:45:58,204 --> 00:46:01,688
to help understand
the Earth's most remote depths.

700
00:46:01,798 --> 00:46:05,233
They use a worldwide network
of devices called seismometers

701
00:46:05,333 --> 00:46:07,091
to trace earthquake vibrations

702
00:46:07,190 --> 00:46:09,487
as they travel
through the planet.

703
00:46:15,359 --> 00:46:18,344
The data produced
can help fill in our picture

704
00:46:18,454 --> 00:46:20,851
of the deep Earth.

705
00:46:20,960 --> 00:46:25,813
Professor Ed Garnero uses this
technique to study the mantle...

706
00:46:25,923 --> 00:46:28,849
all 1,800 miles of it.

707
00:46:28,949 --> 00:46:30,606
GARNERO:
When an earthquake happens,

708
00:46:30,716 --> 00:46:33,203
the waves travel away
from the earthquake

709
00:46:33,312 --> 00:46:35,649
through the planet in the
interior and on the surface...

710
00:46:35,749 --> 00:46:37,676
in the same way, when you drop
a rock in a pond,

711
00:46:37,786 --> 00:46:40,112
you see the rings getting
bigger and bigger and bigger

712
00:46:40,212 --> 00:46:42,269
from the drop zone.

713
00:46:42,379 --> 00:46:44,276
So, what we do in seismology is,

714
00:46:44,376 --> 00:46:46,773
we have these sensitive
microphones all over the planet

715
00:46:46,873 --> 00:46:49,309
that record the ground shaking.

716
00:46:49,409 --> 00:46:51,835
And so we keep track of
the precise time it gets here.

717
00:46:51,945 --> 00:46:54,202
So when you use a bunch
of these instruments in concert,

718
00:46:54,312 --> 00:46:56,469
you can start to say something

719
00:46:56,568 --> 00:46:59,694
about the material
the waves travel through.

720
00:46:59,804 --> 00:47:02,200
NARRATOR:
Just as doctors use sound waves

721
00:47:02,300 --> 00:47:03,858
to picture a baby in the womb,

722
00:47:03,968 --> 00:47:06,524
the waves from earthquakes
can tell scientists

723
00:47:06,634 --> 00:47:10,089
about the world concealed
deep beneath the Earth's crust.

724
00:47:11,267 --> 00:47:14,163
The waves travel through
and bounce off structures

725
00:47:14,263 --> 00:47:16,060
within the planet.

726
00:47:17,099 --> 00:47:20,394
GARNERO: So if you have
enough seismic data,

727
00:47:20,494 --> 00:47:22,521
you can start to characterize
the shapes of things

728
00:47:22,631 --> 00:47:26,685
inside the planet that are
reflecting the seismic energy.

729
00:47:28,622 --> 00:47:30,090
NARRATOR:
And because earthquake waves

730
00:47:30,189 --> 00:47:32,456
travel differently
through different materials,

731
00:47:32,556 --> 00:47:35,022
we know our planet
is made of many layers,

732
00:47:35,122 --> 00:47:37,379
like an onion.

733
00:47:37,489 --> 00:47:41,942
The waves show the mantle
extends downward for 1,800 miles

734
00:47:42,052 --> 00:47:45,747
and offer the first glimpse
of our ultimate destination...

735
00:47:45,847 --> 00:47:47,834
the Earth's core.

736
00:47:49,012 --> 00:47:50,380
Ed Garnero's results

737
00:47:50,480 --> 00:47:53,306
show intense activity
within the mantle.

738
00:47:53,416 --> 00:47:56,641
They reveal how convection
currents of hot solid rock

739
00:47:56,741 --> 00:47:59,676
constantly circulate
through the whole layer.

740
00:47:59,776 --> 00:48:02,103
It's too slow
to observe directly.

741
00:48:02,213 --> 00:48:04,470
But speed it up
and it's clear...

742
00:48:04,579 --> 00:48:09,033
over millions of years...
the mantle is in constant flux.

743
00:48:09,143 --> 00:48:10,870
Resembling mushrooms,

744
00:48:10,970 --> 00:48:13,197
the vertical columns
in his animations

745
00:48:13,307 --> 00:48:15,793
show the steady movements
of the Earth's interior.

746
00:48:15,903 --> 00:48:18,299
GARNERO:
So, what we're looking at here

747
00:48:18,399 --> 00:48:22,264
is a convection calculation
depicting things...

748
00:48:22,363 --> 00:48:25,030
When they get to the top,
they cool off, and fall back in.

749
00:48:25,129 --> 00:48:26,597
Just like a lava lamp,
you know,

750
00:48:26,697 --> 00:48:29,683
the blob goes up
and then its heat goes away

751
00:48:29,793 --> 00:48:31,021
and it falls back in.

752
00:48:31,131 --> 00:48:32,559
So that's
what's happening here...

753
00:48:32,658 --> 00:48:34,685
the cycling of material
in Earth's mantle

754
00:48:34,795 --> 00:48:35,884
over millions of years.

755
00:48:35,994 --> 00:48:38,390
And this is a process
that's happening today.

756
00:48:39,958 --> 00:48:42,324
NARRATOR: These convection
currents through the mantle

757
00:48:42,424 --> 00:48:46,119
transfer heat from the core
to the crust...

758
00:48:46,219 --> 00:48:49,114
heat that drives and pushes
the continental plates

759
00:48:49,224 --> 00:48:51,121
on Earth's surface.

760
00:48:51,221 --> 00:48:52,549
In this way,

761
00:48:52,649 --> 00:48:57,103
the roaring energy of the core
shapes the world we live in.

762
00:48:57,213 --> 00:48:59,939
The crust consists
of two kinds of plates...

763
00:49:00,048 --> 00:49:04,212
oceanic plates
and continental plates.

764
00:49:04,312 --> 00:49:07,108
Ocean plates are heavier,
so when the two collide,

765
00:49:07,208 --> 00:49:09,804
the oceanic plate
plunges downwards

766
00:49:09,914 --> 00:49:12,570
under the lighter
continental plate.

767
00:49:12,680 --> 00:49:14,667
Whole sheets of crustal plate

768
00:49:14,777 --> 00:49:17,643
extend right down
to the edge of the core.

769
00:49:19,270 --> 00:49:20,738
GARNERO:
As that plate descends

770
00:49:20,838 --> 00:49:22,925
and drags some of the water
down with it

771
00:49:23,035 --> 00:49:25,092
and the water...
some of the crust sediments

772
00:49:25,202 --> 00:49:28,397
are still saturated...
they make their way down.

773
00:49:28,507 --> 00:49:31,902
That water can actually
be stored in the mantlerock.

774
00:49:33,300 --> 00:49:36,395
NARRATOR: Over millions of
years, descending ocean plates

775
00:49:36,495 --> 00:49:38,692
have dragged
so much water into the mantle

776
00:49:38,802 --> 00:49:41,198
that scientists estimate
there's now more water

777
00:49:41,298 --> 00:49:44,524
<i>below</i> the Earth's surface
than above it.

778
00:49:45,592 --> 00:49:46,960
GARNERO:
Take all the water

779
00:49:47,060 --> 00:49:49,496
from the oceans and lakes
and glaciers...

780
00:49:49,596 --> 00:49:51,753
everything on the surface
of the Earth...

781
00:49:51,863 --> 00:49:57,844
and anywhere between
2 and 10 or 12 amounts of that

782
00:49:57,954 --> 00:50:00,550
can actually be stored
in the Earth.

783
00:50:00,660 --> 00:50:03,716
NARRATOR: If all this water
rose to the surface,

784
00:50:03,816 --> 00:50:06,811
there would be flooding
on a biblical scale.

785
00:50:08,289 --> 00:50:11,275
No land could survive.

786
00:50:11,384 --> 00:50:13,182
Eventually,
sea levels would rise

787
00:50:13,282 --> 00:50:17,506
21/2 miles above
the peak of Mount Everest.

788
00:50:17,615 --> 00:50:20,841
Luckily for us,
it will never happen.

789
00:50:20,951 --> 00:50:23,177
But some of this
underground water

790
00:50:23,277 --> 00:50:26,173
does make its way
back to the surface.

791
00:50:26,273 --> 00:50:29,678
The water carried down
by ocean plates into the mantle

792
00:50:29,778 --> 00:50:33,792
become superheated and drives
back toward the surface.

793
00:50:33,912 --> 00:50:36,967
A change in pressure liquefies
the hot mantlerock.

794
00:50:37,067 --> 00:50:38,964
Mixed with expanding water,

795
00:50:39,074 --> 00:50:42,000
the lava punches up
through the crust,

796
00:50:42,100 --> 00:50:45,934
where it erupts
with spectacular force.

797
00:50:54,661 --> 00:50:58,216
Mount St. Helens is
the most famous American volcano

798
00:50:58,326 --> 00:51:00,623
created at a plate boundary.

799
00:51:00,733 --> 00:51:04,088
The pulverized rock and steam
that billowed out of the volcano

800
00:51:04,198 --> 00:51:06,025
following its 1980 eruption

801
00:51:06,125 --> 00:51:10,019
was once part of the plate
beneath the Pacific Ocean.

802
00:51:14,652 --> 00:51:18,377
There's a ring of explosive
volcanoes like Mount St. Helens

803
00:51:18,487 --> 00:51:20,713
circling the Pacific Ocean.

804
00:51:20,823 --> 00:51:23,180
It's called the Ring of Fire.

805
00:51:24,488 --> 00:51:26,205
Each one marks the spot

806
00:51:26,315 --> 00:51:31,508
where the Pacific plate
dives into the mantle below.

807
00:51:31,618 --> 00:51:34,234
We're now entering
the lower mantle,

808
00:51:34,344 --> 00:51:37,739
a region at the edge
of scientific understanding.

809
00:51:37,848 --> 00:51:39,965
Nobody knows what it looks like,

810
00:51:40,075 --> 00:51:42,971
but scientists speculate
the hostile conditions here

811
00:51:43,071 --> 00:51:47,065
may create
bizarre chemical effects.

812
00:51:47,175 --> 00:51:50,400
GARNERO: If you were to be able
to go into the mantle,

813
00:51:50,500 --> 00:51:53,296
you would see exotic things,

814
00:51:53,406 --> 00:51:55,493
chemical things
that we're not quite

815
00:51:55,603 --> 00:51:58,588
we fully understand right now,
but there's evidence for it.

816
00:51:58,698 --> 00:52:01,534
And you'd see a lot of different
kinds of layering.

817
00:52:01,634 --> 00:52:04,000
Just like when
you're driving in your car

818
00:52:04,100 --> 00:52:07,395
and you see a roadcut,
you can see the layered rock.

819
00:52:09,093 --> 00:52:13,387
NARRATOR: But in a few places,
something disturbs these layers.

820
00:52:15,424 --> 00:52:20,217
Plumes of hot mantlerock rise up
from the core to the crust.

821
00:52:22,893 --> 00:52:25,789
If you happen to live above
one of these plumes,

822
00:52:25,888 --> 00:52:30,372
the result can be both creative
and destructive.

823
00:52:30,482 --> 00:52:33,607
So you would see
little isolated conduits...

824
00:52:33,717 --> 00:52:36,114
the details of which
we're not fully clear on,

825
00:52:36,213 --> 00:52:40,118
but we think they could be
100 miles in diameter...

826
00:52:40,218 --> 00:52:43,143
very hot material that works
its way to the surface

827
00:52:43,243 --> 00:52:48,196
and gives rise to these things
that we call hot spot volcanoes.

828
00:52:48,316 --> 00:52:49,334
You can see in this image,

829
00:52:49,444 --> 00:52:53,338
you have hot plumes of material
coming up to the surface.

830
00:52:53,438 --> 00:52:56,843
And the stuff that comes out
is what we see coming out

831
00:52:56,943 --> 00:52:59,669
of places like Hawaii
and Easter Island

832
00:52:59,769 --> 00:53:01,796
and Kerguelen Islands and such.

833
00:53:01,906 --> 00:53:05,461
And this animation was made
with things called tracers...

834
00:53:05,571 --> 00:53:06,939
these little black dots.

835
00:53:07,038 --> 00:53:10,404
So you can get an appreciation
for how slowly the material

836
00:53:10,503 --> 00:53:12,730
moves across
the core-mantle boundary

837
00:53:12,830 --> 00:53:16,285
until it finds its little plume
upwelling and then... foom...

838
00:53:16,395 --> 00:53:18,522
they shoot up quite rapidly.

839
00:53:27,089 --> 00:53:29,086
NARRATOR: Some of the world's
largest volcanoes...

840
00:53:29,196 --> 00:53:30,654
Yellowstone...

841
00:53:30,764 --> 00:53:32,621
Iceland...

842
00:53:32,721 --> 00:53:33,849
Hawaii...

843
00:53:33,959 --> 00:53:38,483
sit right above
these gigantic mantle plumes.

844
00:53:38,592 --> 00:53:42,716
Hawaii's Big Island is evidence
of their creative power.

845
00:53:42,816 --> 00:53:44,913
Measured from the ocean floor,

846
00:53:45,023 --> 00:53:47,479
this is the world's
tallest single mountain...

847
00:53:47,589 --> 00:53:51,144
4,000 feet higher
than Mount Everest.

848
00:53:51,254 --> 00:53:53,680
And every foot of it
is made from lava

849
00:53:53,780 --> 00:53:57,575
spewed out from the top
of a mantle plume.

850
00:53:57,685 --> 00:54:00,241
The surface plate
is constantly moving,

851
00:54:00,341 --> 00:54:02,278
while the mantle plume
stays still,

852
00:54:02,378 --> 00:54:04,774
so the magma
keeps punching through the crust

853
00:54:04,874 --> 00:54:06,072
in different places

854
00:54:06,172 --> 00:54:10,536
and leaves a chain of extinct
volcanic islands in its wake.

855
00:54:15,269 --> 00:54:17,166
But while mantle plumes
have the power

856
00:54:17,276 --> 00:54:20,032
to create entire island chains,

857
00:54:20,132 --> 00:54:24,066
they also have the power
to destroy vast amounts of land.

858
00:54:27,301 --> 00:54:30,826
Yellowstone's geysers and
mud pools may delight tourists,

859
00:54:30,936 --> 00:54:33,762
but they are signs
that the park sits on top

860
00:54:33,862 --> 00:54:36,558
of a vast mantle plume.

861
00:54:38,525 --> 00:54:42,459
With a crater 45 miles long
and 35 miles wide,

862
00:54:42,559 --> 00:54:46,953
this is one of the world's
largest supervolcanoes.

863
00:54:48,960 --> 00:54:52,884
Geologist Hank Heasler wants to
understand its behavior.

864
00:54:54,492 --> 00:54:58,746
DR. HEASLER: There's been many
destructive volcanic episodes

865
00:54:58,855 --> 00:55:02,011
in Yellowstone...
three massive eruptions...

866
00:55:02,121 --> 00:55:04,208
one at 2. 1 million years ago,

867
00:55:04,317 --> 00:55:07,543
which is one of the largest
that we as geologists can define

868
00:55:07,653 --> 00:55:09,011
on the face of the Earth,

869
00:55:09,110 --> 00:55:14,013
one at 1.3 million years ago,
and one at 640,000 years ago.

870
00:55:14,982 --> 00:55:17,708
NARRATOR: Yellowstone may not
look much like a volcano.

871
00:55:17,808 --> 00:55:19,905
It's more of a wide depression.

872
00:55:20,005 --> 00:55:24,169
But that's just because
of its sheer size.

873
00:55:24,278 --> 00:55:27,434
DR. HEASLER: Yellowstone
is such a big volcano

874
00:55:27,544 --> 00:55:31,298
that so much material
has been erupted...

875
00:55:31,408 --> 00:55:34,633
hundreds to thousands
of cubic kilometers of magma

876
00:55:34,733 --> 00:55:37,529
have been forcefully ejected
into the air.

877
00:55:37,639 --> 00:55:39,626
When all that magma is erupting,

878
00:55:39,736 --> 00:55:43,630
the ground actually subsides
into the void

879
00:55:43,730 --> 00:55:45,817
created by the erupting magma.

880
00:55:45,927 --> 00:55:49,222
NARRATOR:
It's been 640,000 years

881
00:55:49,332 --> 00:55:51,728
since Yellowstone last erupted.

882
00:55:51,828 --> 00:55:54,345
Heat emissions from the park
could be a sign

883
00:55:54,464 --> 00:55:57,081
that the next eruption
is overdue.

884
00:55:57,190 --> 00:56:00,176
If the Yellowstone volcano
does erupt,

885
00:56:00,286 --> 00:56:03,152
it will unleash billions of tons
of ash and gas

886
00:56:03,252 --> 00:56:04,979
into our atmosphere.

887
00:56:05,089 --> 00:56:07,915
It would block out the sun
and plunge the world

888
00:56:08,025 --> 00:56:10,811
into a devastating
volcanic winter.

889
00:56:15,813 --> 00:56:17,411
Mantle plumes are a key part

890
00:56:17,521 --> 00:56:20,207
of the Earth's
interior cooling system.

891
00:56:22,084 --> 00:56:23,302
They have the power to create

892
00:56:23,412 --> 00:56:25,000
some of the world's
most beautiful

893
00:56:25,110 --> 00:56:27,506
and dangerous landscapes.

894
00:56:29,713 --> 00:56:33,268
The question is,
what creates mantle plumes?

895
00:56:33,378 --> 00:56:35,305
Nobody knows for sure.

896
00:56:35,405 --> 00:56:37,701
But one thing is certain...

897
00:56:37,811 --> 00:56:41,995
The answer lies somewhere
in the boiling furnace

898
00:56:42,105 --> 00:56:44,072
of the Earth's core.

899
00:56:48,905 --> 00:56:51,631
1,800 miles
down into the Earth,

900
00:56:51,731 --> 00:56:54,028
just below us, is the core.

901
00:56:58,960 --> 00:57:02,395
The Earth's outer core
is a huge ball of liquid metal

902
00:57:02,495 --> 00:57:05,151
bigger than the moon.

903
00:57:05,261 --> 00:57:07,059
LATHROP:
The conditions of the outer core

904
00:57:07,158 --> 00:57:09,026
are really quite hostile.

905
00:57:09,126 --> 00:57:13,060
Temperatures more
than 3,000 degrees.

906
00:57:13,160 --> 00:57:15,886
The pressure
is just mind-boggling.

907
00:57:15,986 --> 00:57:18,781
More than a million atmospheres
of pressure.

908
00:57:19,820 --> 00:57:21,188
If you could
strip away the mantle

909
00:57:21,288 --> 00:57:22,875
and just have the raw core,

910
00:57:22,985 --> 00:57:25,641
it's quite hot
and would be glowing intensely,

911
00:57:25,751 --> 00:57:27,838
very much like the surface
of the sun is glowing.

912
00:57:27,948 --> 00:57:29,576
It's that hot.

913
00:57:30,554 --> 00:57:32,242
NARRATOR:
If we could open up a space

914
00:57:32,352 --> 00:57:37,005
between the mantle and the core,
this is what it might look like.

915
00:57:42,008 --> 00:57:43,665
LATHROP:
Just inside the mantle,

916
00:57:43,775 --> 00:57:45,572
liquid metal meets the mantle.

917
00:57:45,672 --> 00:57:48,368
There's probably, you know,
a bit of a mushy zone,

918
00:57:48,478 --> 00:57:50,305
where there's
liquid metal mixing in

919
00:57:50,405 --> 00:57:52,702
with the last bits
of mantle material.

920
00:57:52,802 --> 00:57:54,140
And then inside of that

921
00:57:54,240 --> 00:57:58,034
is just this vast, deep ocean
of liquid metal,

922
00:57:58,134 --> 00:58:01,859
which is red-hot, flowing,

923
00:58:01,968 --> 00:58:04,395
there's all this
churning motion,

924
00:58:04,505 --> 00:58:07,061
and probably things
that are analogous to clouds,

925
00:58:07,171 --> 00:58:09,857
in the sense of bits that
are more dense and less dense

926
00:58:09,967 --> 00:58:13,092
mixing about
as the core convects.

927
00:58:16,597 --> 00:58:20,112
NARRATOR: Seismologists can see
what the outer core looks like

928
00:58:20,222 --> 00:58:24,516
because seismic waves
bounce off its liquid surface.

929
00:58:27,821 --> 00:58:29,848
And scientists like Dan Lathrop

930
00:58:29,958 --> 00:58:33,013
are discovering what's going on
inside the core

931
00:58:33,123 --> 00:58:36,049
by measuring the powerful
electromagnetic energy

932
00:58:36,149 --> 00:58:40,313
it produces...
the Earth's magnetic field.

933
00:58:41,421 --> 00:58:43,648
LATHROP: If you look at
the pattern of magnetic field

934
00:58:43,748 --> 00:58:45,076
on the outside of the Earth,

935
00:58:45,185 --> 00:58:48,581
it's quite clear that
that pattern is slowly moving

936
00:58:48,680 --> 00:58:52,705
and slowing changing in a way
that would be easily described

937
00:58:52,814 --> 00:58:55,141
by it rising from a liquid metal

938
00:58:55,241 --> 00:58:57,677
that's also slowly moving
and slowly convecting.

939
00:58:57,777 --> 00:58:59,505
NARRATOR:
The Earth's magnetism

940
00:58:59,604 --> 00:59:02,540
has been known about
for more than 1,000 years.

941
00:59:02,640 --> 00:59:05,037
And for centuries,
explorers and sailors

942
00:59:05,136 --> 00:59:09,660
have kept detailed records of
our moving magnetic North Pole.

943
00:59:09,770 --> 00:59:12,735
We now know that birds
and animals use it to navigate

944
00:59:12,835 --> 00:59:17,528
on their epic migrations
across continents and oceans.

945
00:59:17,638 --> 00:59:18,826
By the 1950s,

946
00:59:18,936 --> 00:59:21,592
scientists understood
that something made of metal

947
00:59:21,702 --> 00:59:24,718
was responsible
for the magnetic field.

948
00:59:24,828 --> 00:59:26,485
It was the Earth's core.

949
00:59:28,363 --> 00:59:32,347
Dan Lathrop wants to know how
the field could be generated,

950
00:59:32,457 --> 00:59:34,354
so he's built
a model of the core,

951
00:59:34,464 --> 00:59:38,048
a sphere filled
with liquid metal.

952
00:59:39,726 --> 00:59:42,782
Not iron, but sodium.

953
00:59:46,286 --> 00:59:50,410
Iron would be too heavy
and dangerously hot.

954
00:59:52,947 --> 00:59:55,852
But sodium isn't perfect either.

955
00:59:58,549 --> 01:00:01,574
Well, sodium has its pros
and cons, without a doubt.

956
01:00:01,684 --> 01:00:03,232
It's a very good
electrical conductor...

957
01:00:03,342 --> 01:00:04,740
an excellent
electrical conductor...

958
01:00:04,849 --> 01:00:07,306
so it gets us closer
to being like a planet

959
01:00:07,416 --> 01:00:08,774
in the laboratory experiments.

960
01:00:08,873 --> 01:00:11,639
The cons are,
it's a reactive liquid.

961
01:00:11,739 --> 01:00:15,234
It is flammable,
burns readily in air,

962
01:00:15,344 --> 01:00:17,671
and also reacts violently
with water.

963
01:00:20,337 --> 01:00:24,131
NARRATOR: With the 13 tons
of sodium safely sealed inside,

964
01:00:24,241 --> 01:00:26,428
the 10-foot sphere
starts to spin

965
01:00:26,538 --> 01:00:28,365
to re-create
the Earth's rotation.

966
01:00:30,132 --> 01:00:32,958
Heaters keep the sodium molten.

967
01:00:37,232 --> 01:00:38,490
Minutes later,

968
01:00:38,600 --> 01:00:43,024
magnetic fields spill from
the sphere in all directions.

969
01:00:45,161 --> 01:00:46,818
Lathrop's experiment confirms

970
01:00:46,928 --> 01:00:49,654
the way the Earth's
magnetic field is generated.

971
01:00:49,754 --> 01:00:51,092
Driven by the heat,

972
01:00:51,192 --> 01:00:53,179
the convection currents
in the core

973
01:00:53,289 --> 01:00:54,687
combine with
the Earth's rotation

974
01:00:54,787 --> 01:00:58,451
to create a giant dynamo.

975
01:00:58,551 --> 01:01:00,578
LATHROP: The dynamo is like
an electrical generator,

976
01:01:00,688 --> 01:01:03,015
but it's being driven
by the motions

977
01:01:03,114 --> 01:01:05,481
of the liquid outer core.

978
01:01:05,581 --> 01:01:06,849
And that churning motion,

979
01:01:06,949 --> 01:01:09,106
sort of turbulent convection
in the core,

980
01:01:09,216 --> 01:01:10,843
couples with the magnetic field

981
01:01:10,953 --> 01:01:12,970
to continuously regenerate
the magnetic field.

982
01:01:13,080 --> 01:01:15,476
It's like the turning motion
of the generator,

983
01:01:15,576 --> 01:01:18,802
in this case then, is
the churning of the convection.

984
01:01:20,080 --> 01:01:21,508
NARRATOR:
The magnetic field

985
01:01:21,607 --> 01:01:24,333
is much more
than a geological curiosity.

986
01:01:24,443 --> 01:01:27,768
It's vital to life on Earth.

987
01:01:27,878 --> 01:01:31,633
The field protects us from
our closest, deadliest enemy...

988
01:01:31,743 --> 01:01:32,701
the sun.

989
01:01:34,209 --> 01:01:36,196
A giant nuclear reactor,

990
01:01:36,306 --> 01:01:39,431
enormous storms
rage on its surface.

991
01:01:41,339 --> 01:01:44,734
These storms fling
lethal radioactive particles

992
01:01:44,834 --> 01:01:46,162
into space.

993
01:01:46,262 --> 01:01:51,953
This is the solar wind, and
Earth lies right in its path.

994
01:01:52,063 --> 01:01:54,120
But like a stone in a stream,

995
01:01:54,230 --> 01:01:58,214
the Earth's magnetic field
parts the flow of radiation,

996
01:01:58,324 --> 01:02:00,591
diverting it around the planet.

997
01:02:04,824 --> 01:02:07,720
We sit in a protective pocket
of magnetism...

998
01:02:07,820 --> 01:02:09,258
the mystery of life

999
01:02:09,358 --> 01:02:13,811
made possible by the mysterious
core of the planet it inhabits.

1000
01:02:16,957 --> 01:02:19,613
The Earth's magnetic field
is absolutely critical

1001
01:02:19,713 --> 01:02:21,580
for Earth
to be a habitable planet,

1002
01:02:21,680 --> 01:02:25,474
in the sense that
the quite violent radiation

1003
01:02:25,584 --> 01:02:30,008
coming from the sun stream
around the outsides of a bubble

1004
01:02:30,108 --> 01:02:32,234
formed around the Earth
by the magnetic field.

1005
01:02:32,344 --> 01:02:34,811
So the magnetic field
extends a sort of shield,

1006
01:02:34,911 --> 01:02:39,803
the magnetosphere, which
protects us and the atmosphere

1007
01:02:39,903 --> 01:02:41,171
from most of the radiation.

1008
01:02:41,271 --> 01:02:43,328
If that weren't there,
the solar radiation

1009
01:02:43,438 --> 01:02:45,905
would be constantly
bombarding the atmosphere,

1010
01:02:46,004 --> 01:02:48,031
actually eating away
at the atmosphere,

1011
01:02:48,141 --> 01:02:50,997
and some of it then directly
making it down to ground level.

1012
01:02:52,765 --> 01:02:55,560
NARRATOR: About 40,000 miles
above the poles,

1013
01:02:55,670 --> 01:02:57,458
the charged solar particles

1014
01:02:57,568 --> 01:03:00,653
meet the outer reaches
of the magnetic field.

1015
01:03:01,632 --> 01:03:03,649
Here, some are diverted down

1016
01:03:03,769 --> 01:03:05,756
toward the Earth's
magnetic poles,

1017
01:03:05,865 --> 01:03:10,089
where they create spectacular
auroras that glow in the sky.

1018
01:03:10,189 --> 01:03:12,186
These dazzling displays happen

1019
01:03:12,296 --> 01:03:14,653
when the particles
slam into gas molecules

1020
01:03:14,762 --> 01:03:16,879
in the Earth's upper atmosphere.

1021
01:03:18,727 --> 01:03:19,885
Although beautiful,

1022
01:03:19,985 --> 01:03:22,182
these are a sign
of a ferocious battle

1023
01:03:22,292 --> 01:03:23,749
between the Earth's core

1024
01:03:23,859 --> 01:03:27,015
and an invading stream
of solar radiation.

1025
01:03:29,022 --> 01:03:31,818
Our magnetic field
protects us from other dangers,

1026
01:03:31,917 --> 01:03:34,174
not just from the sun.

1027
01:03:34,284 --> 01:03:37,409
Lethal cosmic rays
made of radioactive particles

1028
01:03:37,519 --> 01:03:40,445
permeate deep space.

1029
01:03:40,545 --> 01:03:42,911
Down on Earth,
we're unaware of them.

1030
01:03:43,011 --> 01:03:45,947
But up in space,
it's a different story.

1031
01:03:46,047 --> 01:03:49,302
On July 20, 1969,

1032
01:03:49,412 --> 01:03:54,395
Neil Armstrong was the first man
to set foot on the moon.

1033
01:03:56,102 --> 01:04:00,007
It was one of humankind's
greatest achievements.

1034
01:04:03,372 --> 01:04:05,389
But on their way to the moon,

1035
01:04:05,499 --> 01:04:07,795
Armstrong and co-pilot
Buzz Aldrin

1036
01:04:07,905 --> 01:04:11,799
saw flashes of light inside
the darkened <i>Apollo 11</i> module.

1037
01:04:15,164 --> 01:04:19,358
Bizarrely, they even saw the
flashes with their eyes shut.

1038
01:04:21,795 --> 01:04:25,320
When they returned to Earth,
they reported what they saw.

1039
01:04:25,429 --> 01:04:27,916
NASA scientists were mystified.

1040
01:04:30,921 --> 01:04:34,317
Six years later, they came
to believe these light flashes

1041
01:04:34,426 --> 01:04:37,043
were the result
of high-energy cosmic rays

1042
01:04:37,152 --> 01:04:41,047
penetrating the spacecraft
and the crew members' eyes.

1043
01:04:43,413 --> 01:04:46,249
Armstrong and Aldrin
were exposed to these rays

1044
01:04:46,349 --> 01:04:47,907
because the <i>Apollo</i> craft

1045
01:04:48,017 --> 01:04:49,914
was near the edge
of the safety shield

1046
01:04:50,014 --> 01:04:52,740
of the Earth's magnetic field.

1047
01:04:52,850 --> 01:04:55,036
MAN: 3, 2, 1.

1048
01:04:55,146 --> 01:04:57,802
And liftoff of <i>Discovery.</i>

1049
01:04:58,841 --> 01:05:00,309
NARRATOR:
In the years since,

1050
01:05:00,408 --> 01:05:02,066
at least 39 astronauts

1051
01:05:02,176 --> 01:05:04,233
have developed
some kind of eye cataract

1052
01:05:04,343 --> 01:05:08,037
a few years after exposure
to this dangerous radiation.

1053
01:05:11,902 --> 01:05:13,999
Without the Earth's
magnetic field,

1054
01:05:14,109 --> 01:05:17,394
we would all be exposed
to these dangers.

1055
01:05:17,504 --> 01:05:21,028
And it's the core
that is our great protector.

1056
01:05:22,696 --> 01:05:25,861
We know the magnetism comes from
the rotation of the core

1057
01:05:25,961 --> 01:05:29,326
and the turbulence
of the molten metal within it.

1058
01:05:29,426 --> 01:05:33,690
But how can we work out exactly
what's going on inside the core?

1059
01:05:33,800 --> 01:05:37,454
Peter Olson is one scientist
who's devised an experiment

1060
01:05:37,564 --> 01:05:39,322
that could offer an explanation.

1061
01:05:39,422 --> 01:05:40,760
Well, what we have here

1062
01:05:40,860 --> 01:05:44,414
is nothing more than a large
tank of water on a turntable.

1063
01:05:44,524 --> 01:05:47,919
And what it's
intending to simulate

1064
01:05:48,019 --> 01:05:50,416
is the Earth's outer core.

1065
01:05:50,525 --> 01:05:53,781
And we're going to inject
some heavy dye

1066
01:05:53,891 --> 01:05:56,786
into this big tank of water,

1067
01:05:56,886 --> 01:06:00,441
and we're going to see
the effects of the rotation

1068
01:06:00,551 --> 01:06:01,739
on the turbulence.

1069
01:06:03,816 --> 01:06:05,544
There's a turbulent plume

1070
01:06:05,643 --> 01:06:08,080
trying to sink
to the bottom of the tank.

1071
01:06:08,180 --> 01:06:11,006
But it starts to feel
the effect of the rotation,

1072
01:06:11,115 --> 01:06:15,839
and you can see it gets twisted
up into kind of a helix.

1073
01:06:15,938 --> 01:06:20,272
And it's this helical type
of flow in the Earth's core

1074
01:06:20,372 --> 01:06:22,269
that we think is so critical

1075
01:06:22,369 --> 01:06:25,494
for generating
the Earth's magnetic field.

1076
01:06:25,604 --> 01:06:27,432
Ordinary turbulent motions

1077
01:06:27,541 --> 01:06:30,527
don't have this kind
of helical structure to them.

1078
01:06:30,637 --> 01:06:33,762
But by virtue of the effect
of the Earth's rotation,

1079
01:06:33,872 --> 01:06:36,528
the turbulence in the core
is made helical.

1080
01:06:38,396 --> 01:06:39,993
NARRATOR:
These helical columns

1081
01:06:40,093 --> 01:06:42,859
might explain
the Earth's magnetic field.

1082
01:06:43,798 --> 01:06:46,094
They represent
liquid-iron columns,

1083
01:06:46,194 --> 01:06:50,218
which could work like the wire
coils inside an electromagnet.

1084
01:06:51,556 --> 01:06:55,920
As they move with the Earth's
rotation, they create magnetism.

1085
01:07:00,493 --> 01:07:03,549
2,500 miles
below the Earth's surface...

1086
01:07:03,659 --> 01:07:06,674
could there really be
molten columns of liquid iron

1087
01:07:06,784 --> 01:07:08,312
hundreds of miles high?

1088
01:07:08,422 --> 01:07:11,577
OLSON: As a consequence
of this turbulent motion

1089
01:07:11,687 --> 01:07:13,275
of the liquid iron,

1090
01:07:13,385 --> 01:07:16,011
electric currents
are flowing in the core.

1091
01:07:16,111 --> 01:07:18,507
And the geomagnetic field
that we see at the surface

1092
01:07:18,617 --> 01:07:21,203
is actually the result
of these electric currents.

1093
01:07:21,313 --> 01:07:24,339
So there is no bar-magnet
or permanent-magnet effect

1094
01:07:24,449 --> 01:07:27,344
of any significance
inside the core of the Earth.

1095
01:07:27,444 --> 01:07:31,398
The magnetic field there is
produced by electric currents.

1096
01:07:33,445 --> 01:07:35,932
NARRATOR:
This delicate feedback system

1097
01:07:36,042 --> 01:07:38,468
makes the core
seem extremely fragile.

1098
01:07:38,568 --> 01:07:42,522
Without heat or rotation,
it wouldn't work.

1099
01:07:46,496 --> 01:07:47,625
To demonstrate,

1100
01:07:47,735 --> 01:07:51,030
Olson simply switches off
the tank's rotation.

1101
01:07:51,130 --> 01:07:53,616
The water keeps moving,
but as it slows down,

1102
01:07:53,736 --> 01:07:58,030
the convection currents
gradually collapse.

1103
01:07:58,129 --> 01:07:59,687
If this happened in the core,

1104
01:07:59,797 --> 01:08:03,492
the Earth's magnetic shield
would soon disappear.

1105
01:08:06,258 --> 01:08:08,015
Deep inside the Earth's core,

1106
01:08:08,125 --> 01:08:10,711
something mysterious
is happening.

1107
01:08:10,821 --> 01:08:13,287
Swirling currents
of molten metal

1108
01:08:13,387 --> 01:08:17,721
are creating a magnetic field
that envelops the planet.

1109
01:08:17,821 --> 01:08:18,879
We depend on this field

1110
01:08:18,989 --> 01:08:22,783
to protect us
from deadly solar radiation.

1111
01:08:22,883 --> 01:08:24,281
But scientific data

1112
01:08:24,381 --> 01:08:27,547
shows that magnetic field
is weakening.

1113
01:08:29,014 --> 01:08:30,243
Over the past century,

1114
01:08:30,352 --> 01:08:32,180
the strength of the planet's
magnetic field

1115
01:08:32,280 --> 01:08:37,802
has declined by nearly 10%,
and scientists aren't sure why.

1116
01:08:37,911 --> 01:08:40,498
During most
of mankind's history,

1117
01:08:40,607 --> 01:08:43,264
the magnetic field
has been very strong.

1118
01:08:43,373 --> 01:08:45,271
And now it's weakening.

1119
01:08:45,371 --> 01:08:47,338
LATHROP:
The Earth's magnetic field

1120
01:08:47,438 --> 01:08:50,922
has been studied
for about 160 years.

1121
01:08:51,042 --> 01:08:53,089
And what people see is
that the magnetic field

1122
01:08:53,199 --> 01:08:56,255
has slowly and steadily dropped
in its strength.

1123
01:08:57,433 --> 01:08:58,661
NARRATOR: In one region,

1124
01:08:58,771 --> 01:09:01,397
the magnetic field
is a third weaker.

1125
01:09:02,735 --> 01:09:05,132
It's here
over the Atlantic Ocean,

1126
01:09:05,232 --> 01:09:07,698
just off the coast of Brazil.

1127
01:09:07,798 --> 01:09:11,423
It's known
as the South Atlantic Anomaly.

1128
01:09:11,532 --> 01:09:13,889
This disruption
in the magnetic field

1129
01:09:13,999 --> 01:09:16,455
stretches a quarter
of the way around the globe,

1130
01:09:16,555 --> 01:09:18,283
and it's growing.

1131
01:09:20,559 --> 01:09:22,147
Every day in this area,

1132
01:09:22,257 --> 01:09:26,211
cosmic radiation reaches closer
to the Earth's surface.

1133
01:09:27,519 --> 01:09:30,814
This protection that we get
from the solar radiation

1134
01:09:30,924 --> 01:09:33,780
from the magnetic field
is already weaker in that patch,

1135
01:09:33,890 --> 01:09:36,216
so it already
has implications...

1136
01:09:36,316 --> 01:09:40,710
mostly for astronauts
and people who run satellites.

1137
01:09:40,820 --> 01:09:42,577
OLSON:
It's really come into prominence

1138
01:09:42,677 --> 01:09:45,942
since the advent of long-term
orbiting spacecraft.

1139
01:09:46,042 --> 01:09:48,269
For example,
the Hubble Space Telescope

1140
01:09:48,379 --> 01:09:50,965
has had enormous problems
over the years

1141
01:09:51,075 --> 01:09:53,541
as it passes through
the South Atlantic Anomaly.

1142
01:09:53,641 --> 01:09:55,838
NARRATOR:
The problem is so bad

1143
01:09:55,938 --> 01:09:58,065
that when the billion-dollar
Hubble Space Telescope

1144
01:09:58,174 --> 01:09:59,403
is above the area,

1145
01:09:59,502 --> 01:10:02,598
vital instruments are routinely
shut down for protection.

1146
01:10:02,708 --> 01:10:05,064
<i>[Radio chatter]</i>

1147
01:10:08,869 --> 01:10:11,625
And near the core
under the South Atlantic,

1148
01:10:11,735 --> 01:10:15,030
something even stranger
is happening.

1149
01:10:15,130 --> 01:10:18,355
The magnetic field here
hasn't just weakened,

1150
01:10:18,465 --> 01:10:20,761
it has totally reversed.

1151
01:10:22,259 --> 01:10:23,747
LATHROP:
If you look at what

1152
01:10:23,867 --> 01:10:25,984
the magnetic field would be
at the edge of the core,

1153
01:10:26,094 --> 01:10:27,522
the magnetic field down there

1154
01:10:27,631 --> 01:10:30,957
has already reversed
in that patch.

1155
01:10:31,056 --> 01:10:32,784
Now, this could be a sign,

1156
01:10:32,894 --> 01:10:35,410
if this becomes
deeper and broader,

1157
01:10:35,520 --> 01:10:37,178
that we're headed
toward a reversal.

1158
01:10:38,286 --> 01:10:41,222
NARRATOR: A reversal is
a total change in polarity

1159
01:10:41,322 --> 01:10:43,119
of the Earth's magnetic shield.

1160
01:10:43,219 --> 01:10:45,276
The North Pole flips
to the south,

1161
01:10:45,386 --> 01:10:47,712
and the South moves north.

1162
01:10:47,822 --> 01:10:49,310
LATHROP: What a reversal is,

1163
01:10:49,420 --> 01:10:52,815
is when those
North and South Poles reverse

1164
01:10:52,915 --> 01:10:55,681
so that you have
a long, steady period

1165
01:10:55,780 --> 01:10:58,037
where they're
in one orientation,

1166
01:10:58,147 --> 01:10:59,545
and then there's a reversal

1167
01:10:59,645 --> 01:11:03,299
and then a long, steady period
in opposite reversal.

1168
01:11:05,077 --> 01:11:06,734
NARRATOR:
Reversals have happened before.

1169
01:11:06,844 --> 01:11:09,171
We know this because,
when lava cools,

1170
01:11:09,271 --> 01:11:12,396
it preserves evidence
of the Earth's magnetic field.

1171
01:11:12,506 --> 01:11:17,339
Crystals inside the molten lava
line up with the field.

1172
01:11:18,537 --> 01:11:19,865
When it solidifies,

1173
01:11:19,965 --> 01:11:21,962
it creates a record
of its strength and direction

1174
01:11:22,072 --> 01:11:24,259
at that exact moment in time.

1175
01:11:25,168 --> 01:11:27,324
Studies of
prehistoric lava flows

1176
01:11:27,434 --> 01:11:31,199
indicate that the last reversal
happened 700,000 years ago,

1177
01:11:31,299 --> 01:11:34,424
when our apelike ancestors
roamed the Earth.

1178
01:11:35,892 --> 01:11:38,388
You might think that,
if the field is so stable

1179
01:11:38,498 --> 01:11:40,925
that it can persist
for billions of years,

1180
01:11:41,024 --> 01:11:43,121
why should it
suddenly decide to change?

1181
01:11:43,221 --> 01:11:44,120
But it does.

1182
01:11:44,230 --> 01:11:45,817
We know that the Earth's
magnetic field

1183
01:11:45,927 --> 01:11:47,825
has reversed
many hundreds of times.

1184
01:11:47,924 --> 01:11:50,890
What we don't know is
when will it do it next?

1185
01:11:50,990 --> 01:11:53,576
NARRATOR: Neither do we know
what will happen when it does.

1186
01:11:53,686 --> 01:11:57,241
The weakening magnetic field
and the South Atlantic Anomaly

1187
01:11:57,351 --> 01:12:01,215
are the signs that we're about
to experience the next reversal.

1188
01:12:01,315 --> 01:12:04,910
It could happen
within the next 1,500 years.

1189
01:12:05,019 --> 01:12:10,841
OLSON: The rate of decrease
is about 6% per century.

1190
01:12:10,951 --> 01:12:13,707
Now, that doesn't sound
like very much, perhaps.

1191
01:12:13,817 --> 01:12:17,332
But in geologic terms,
that's extremely rapid.

1192
01:12:18,879 --> 01:12:21,106
NARRATOR: No one knows
what a reversal will mean

1193
01:12:21,206 --> 01:12:22,694
for life on Earth.

1194
01:12:24,311 --> 01:12:26,398
But while
the magnetic field reverses,

1195
01:12:26,508 --> 01:12:29,494
we would lose its protection
for several months.

1196
01:12:30,572 --> 01:12:34,327
Solar radiation would penetrate
our electrical systems.

1197
01:12:37,332 --> 01:12:41,127
Surges would overload
the world's power grids.

1198
01:12:46,868 --> 01:12:48,256
At the same time,

1199
01:12:48,366 --> 01:12:51,592
bats, birds, and whales
could become disoriented

1200
01:12:51,691 --> 01:12:55,526
as their internal navigational
systems are scrambled.

1201
01:12:57,363 --> 01:13:00,718
There could even be
an increased incidence of cancer

1202
01:13:00,828 --> 01:13:03,814
as solar radiation
attacks our cells' DNA.

1203
01:13:07,359 --> 01:13:11,912
We might see auroras appearing
all over the planet.

1204
01:13:13,050 --> 01:13:15,537
Even over our major cities.

1205
01:13:18,682 --> 01:13:22,077
No one knows exactly when
the next reversal will happen,

1206
01:13:22,177 --> 01:13:25,732
but the answer could lie
even deeper inside the Earth

1207
01:13:25,842 --> 01:13:28,468
in the inner core.

1208
01:13:28,578 --> 01:13:31,044
It's the least understood,
most remote,

1209
01:13:31,144 --> 01:13:34,130
and inaccessible place
on the planet.

1210
01:13:34,239 --> 01:13:37,335
And somewhere
in this hidden, hostile world

1211
01:13:37,445 --> 01:13:40,370
lies the key
to the Earth's future.

1212
01:13:41,469 --> 01:13:44,804
The inner core is
a rotating sphere of solid metal

1213
01:13:44,904 --> 01:13:47,890
floating inside
the liquid outer core.

1214
01:13:49,297 --> 01:13:53,661
Billions of amps of electricity
leap across its surface.

1215
01:13:53,771 --> 01:13:55,199
Hotter than the outer core,

1216
01:13:55,299 --> 01:13:58,594
the inner core's heat
is the ultimate driving force

1217
01:13:58,694 --> 01:14:01,250
behind the Earth's
magnetic shield.

1218
01:14:03,227 --> 01:14:05,254
OLSON:
The pressures are so high

1219
01:14:05,364 --> 01:14:07,191
towards the center of the Earth

1220
01:14:07,291 --> 01:14:10,776
because of the overlying weight
of so much material,

1221
01:14:10,896 --> 01:14:13,013
that despite the fact
that it's hot,

1222
01:14:13,123 --> 01:14:14,680
the material is still solid.

1223
01:14:15,789 --> 01:14:17,816
NARRATOR: Seismic studies
tell us something else

1224
01:14:17,926 --> 01:14:19,214
about the inner core...

1225
01:14:19,324 --> 01:14:22,908
slowly but surely,
it's growing.

1226
01:14:23,018 --> 01:14:26,174
Every year,
it expands by one millimeter

1227
01:14:26,284 --> 01:14:28,810
as the planet loses heat.

1228
01:14:28,920 --> 01:14:31,746
Nobody has ever seen this
process with the naked eye.

1229
01:14:31,845 --> 01:14:34,901
But in the lab, scientists can
use their imagination

1230
01:14:35,011 --> 01:14:37,637
to show something similar.

1231
01:14:37,747 --> 01:14:39,434
LATHROP:
So as the Earth cools,

1232
01:14:39,544 --> 01:14:44,038
the inner core grows
by iron crystallizing onto it.

1233
01:14:44,148 --> 01:14:46,933
We could imagine
what that looks like

1234
01:14:47,043 --> 01:14:51,996
by looking at ice crystallizing
onto this cool sphere.

1235
01:14:57,139 --> 01:14:59,865
A lot of people
who think about the core

1236
01:14:59,974 --> 01:15:02,990
sit around and argue about,
what's that surface like?

1237
01:15:03,100 --> 01:15:06,036
Is it rough? Is it smooth?
Is it mushy?

1238
01:15:06,135 --> 01:15:07,593
What we know is that,

1239
01:15:07,703 --> 01:15:09,560
from the earthquakes
passing through,

1240
01:15:09,660 --> 01:15:11,098
if it is rough,

1241
01:15:11,198 --> 01:15:15,851
the thickness of that
is less than a mile or so.

1242
01:15:15,961 --> 01:15:17,928
But that still leaves
lots of room

1243
01:15:18,028 --> 01:15:20,754
for mushy zones
or cavernous pits

1244
01:15:20,864 --> 01:15:22,452
and little mini mountains.

1245
01:15:22,562 --> 01:15:25,687
We really have no idea
what that surface looks like.

1246
01:15:25,787 --> 01:15:28,752
But if you look at any other
surface on the Earth,

1247
01:15:28,852 --> 01:15:30,839
on other planets
elsewhere in the solar system,

1248
01:15:30,959 --> 01:15:32,857
they're all rough.

1249
01:15:32,956 --> 01:15:34,854
Even the surface of the ocean
is rough,

1250
01:15:34,953 --> 01:15:36,471
of course,
moving about with the waves.

1251
01:15:36,591 --> 01:15:38,209
And so my expectation is

1252
01:15:38,319 --> 01:15:40,685
that things are quite rough
and quite complicated.

1253
01:15:42,313 --> 01:15:44,370
NARRATOR: Exactly how
rough and complicated

1254
01:15:44,480 --> 01:15:46,177
is open to debate.

1255
01:15:47,415 --> 01:15:49,782
Dan Lathrop believes
the inner core's surface

1256
01:15:49,882 --> 01:15:53,746
is probably covered in a forest
of metallic projections.

1257
01:15:55,074 --> 01:15:57,271
They're called dendrites.

1258
01:15:57,381 --> 01:16:00,436
LATHROP: There's most likely
a sort of rough surface

1259
01:16:00,546 --> 01:16:03,332
of these iron crystals,
perhaps dendrites poking out.

1260
01:16:03,442 --> 01:16:05,868
And the whole core itself

1261
01:16:05,968 --> 01:16:08,195
has a sort of crystalline order
to it.

1262
01:16:08,305 --> 01:16:10,272
So while it's roughly spherical,

1263
01:16:10,372 --> 01:16:13,238
it has crystalline bits
growing out from it,

1264
01:16:13,337 --> 01:16:15,395
continuously growing larger.

1265
01:16:17,072 --> 01:16:19,658
NARRATOR: As the core cools,
the dendrites grow.

1266
01:16:19,768 --> 01:16:22,824
It's a sign that heat is
constantly being transferred

1267
01:16:22,934 --> 01:16:25,560
from the inner
to the outer core.

1268
01:16:26,768 --> 01:16:30,023
The Earth is slowly cooling,
just from its origin.

1269
01:16:30,133 --> 01:16:32,220
And whenever you have something

1270
01:16:32,330 --> 01:16:35,156
which is hotter on the inside
and colder on the outside,

1271
01:16:35,256 --> 01:16:37,812
it tends to get
flows going, vortices.

1272
01:16:37,922 --> 01:16:39,479
You know,
think of them sort of like

1273
01:16:39,589 --> 01:16:41,556
big, tumbling,
cloudlike motions,

1274
01:16:41,656 --> 01:16:43,683
but it's in the liquid metal
in the core.

1275
01:16:45,950 --> 01:16:49,615
NARRATOR: This heat transfer is
fundamental to life on Earth.

1276
01:16:49,714 --> 01:16:53,120
It powers the outer core
and the Earth's magnetic shield.

1277
01:16:53,219 --> 01:16:55,706
But it won't last forever.

1278
01:16:57,783 --> 01:17:01,807
With planet Earth losing heat
every second, every day,

1279
01:17:01,917 --> 01:17:04,004
one thing is certain...

1280
01:17:04,113 --> 01:17:08,267
the inner core
will keep growing and cooling.

1281
01:17:08,377 --> 01:17:10,344
In the distant future,

1282
01:17:10,444 --> 01:17:13,899
the whole core
will freeze solid.

1283
01:17:14,009 --> 01:17:15,267
For life on Earth,

1284
01:17:15,377 --> 01:17:18,732
the consequences of that
are unthinkable.

1285
01:17:22,607 --> 01:17:26,091
The inner core of planet Earth
is a mysterious place,

1286
01:17:26,201 --> 01:17:28,069
hotter than the surface
of the sun,

1287
01:17:28,168 --> 01:17:30,425
yet it's solid metal.

1288
01:17:30,535 --> 01:17:33,730
The core radiates
incredible heat energy outward.

1289
01:17:33,830 --> 01:17:34,959
At the same time,

1290
01:17:35,068 --> 01:17:37,625
it crushes everything
down around it

1291
01:17:37,734 --> 01:17:39,522
with intense gravity.

1292
01:17:39,632 --> 01:17:42,647
There's no way to see it
or sample it.

1293
01:17:42,757 --> 01:17:46,282
How did it get there?
Where did it come from?

1294
01:17:46,392 --> 01:17:48,419
There are clues.

1295
01:17:49,727 --> 01:17:53,092
The Earth shares its origins
with the other rocky planets...

1296
01:17:53,192 --> 01:17:56,447
Mars, Venus, and Mercury.

1297
01:17:56,557 --> 01:17:59,643
In the beginning,
just after the sun lit up,

1298
01:17:59,752 --> 01:18:01,620
before the planets existed,

1299
01:18:01,720 --> 01:18:07,112
great clouds of cosmic debris
orbited the newly ignited star.

1300
01:18:07,221 --> 01:18:08,809
These early building blocks

1301
01:18:08,919 --> 01:18:12,044
crashed into each other
with massive force.

1302
01:18:14,151 --> 01:18:16,049
The bigger the objects became,

1303
01:18:16,148 --> 01:18:18,375
the greater
their gravitational pull,

1304
01:18:18,475 --> 01:18:22,200
until eventually
whole planets formed.

1305
01:18:22,309 --> 01:18:23,677
LATHROP:
When a planet forms,

1306
01:18:23,777 --> 01:18:25,405
it forms from a hodgepodge

1307
01:18:25,505 --> 01:18:27,372
of all sorts
of different materials.

1308
01:18:27,472 --> 01:18:30,408
And so the heavier bits would
tend to fall under gravity

1309
01:18:30,508 --> 01:18:32,874
and accumulate
into the interior of the Earth.

1310
01:18:32,974 --> 01:18:35,440
We know
that the bits of material

1311
01:18:35,540 --> 01:18:36,868
that made up
all of the inner planets

1312
01:18:36,968 --> 01:18:38,196
had quite a bit
of iron in them...

1313
01:18:38,306 --> 01:18:40,064
just raw, metallic iron.

1314
01:18:40,173 --> 01:18:42,191
And that would tend
to sink down eventually

1315
01:18:42,300 --> 01:18:46,594
to form this massive core
of the Earth.

1316
01:18:46,704 --> 01:18:49,460
NARRATOR: The solar system
is now complete and stable,

1317
01:18:49,560 --> 01:18:52,585
but the process of formation,
called accretion,

1318
01:18:52,695 --> 01:18:54,353
is not quite over.

1319
01:18:55,831 --> 01:18:57,348
The spare parts left over

1320
01:18:57,458 --> 01:18:59,046
from the creation
of the solar system...

1321
01:18:59,156 --> 01:19:01,522
asteroids,
comets, meteorites...

1322
01:19:01,622 --> 01:19:05,556
still orbit the sun
and still crash into the Earth,

1323
01:19:05,656 --> 01:19:07,883
like the one
that created this...

1324
01:19:07,993 --> 01:19:10,319
Meteor Crater in Arizona.

1325
01:19:12,357 --> 01:19:16,151
It was formed by an impact
50,000 years ago.

1326
01:19:18,518 --> 01:19:21,044
And for cosmochemist
Meenakshi Wadhwa,

1327
01:19:21,154 --> 01:19:24,169
it offers a glimpse
of the forces and the materials

1328
01:19:24,279 --> 01:19:26,805
that created the Earth's core.

1329
01:19:28,513 --> 01:19:30,999
WADHWA: So Meteor Crater
that you see here

1330
01:19:31,109 --> 01:19:34,045
was created by the impact
of an object

1331
01:19:34,145 --> 01:19:37,839
probably that was
about 300, 400 feet across.

1332
01:19:37,939 --> 01:19:42,562
And this was an event that was
a sudden, catastrophic event.

1333
01:19:42,672 --> 01:19:44,140
A lot of energy was released...

1334
01:19:44,240 --> 01:19:46,667
something like
20 megatons or so.

1335
01:19:50,601 --> 01:19:52,368
NARRATOR:
Lmagine a planet growing

1336
01:19:52,468 --> 01:19:54,695
from billions of impacts
like this one,

1337
01:19:54,805 --> 01:19:57,031
each one delivering
iron, nickel,

1338
01:19:57,131 --> 01:19:59,787
and the other elements
that make the world around us.

1339
01:19:59,897 --> 01:20:04,121
They also delivered an enormous
amount of heat energy.

1340
01:20:06,328 --> 01:20:08,265
WADHWA: You can see
that there were large blocks

1341
01:20:08,365 --> 01:20:09,823
that were ejected
out from the crater,

1342
01:20:09,933 --> 01:20:11,121
and there were
actually material

1343
01:20:11,231 --> 01:20:13,747
probably tossed out to hundreds
of miles from the crater

1344
01:20:13,857 --> 01:20:15,794
as a result of the impact.

1345
01:20:18,360 --> 01:20:20,647
NARRATOR:
The impact here was so powerful,

1346
01:20:20,757 --> 01:20:22,744
it vaporized the meteorite.

1347
01:20:22,854 --> 01:20:25,580
But a few fragments survived.

1348
01:20:25,690 --> 01:20:27,777
So this particular
meteorite is...

1349
01:20:27,886 --> 01:20:30,043
It's called
a Canyon Diablo meteorite,

1350
01:20:30,153 --> 01:20:34,587
and it's an iron-rich meteorite
which was part of the impactor

1351
01:20:34,687 --> 01:20:36,544
that created Meteor Crater.

1352
01:20:36,654 --> 01:20:38,171
It's very difficult, of course,

1353
01:20:38,281 --> 01:20:40,708
to actually sample a piece
of the Earth's core,

1354
01:20:40,818 --> 01:20:44,143
but these meteorites
right here provide us a window

1355
01:20:44,243 --> 01:20:46,869
into looking
at planetary interiors.

1356
01:20:46,979 --> 01:20:48,606
And you can
actually learn something

1357
01:20:48,706 --> 01:20:50,034
about core-formation processes

1358
01:20:50,144 --> 01:20:52,371
by looking
at iron-rich meteorites.

1359
01:20:52,471 --> 01:20:53,839
NARRATOR: Close up,

1360
01:20:53,938 --> 01:20:56,375
you can see the crystalline
structure of the metal

1361
01:20:56,475 --> 01:20:58,901
that exists right
at the heart of our planet,

1362
01:20:59,001 --> 01:21:02,296
a planet that's unique
in the solar system.

1363
01:21:02,406 --> 01:21:05,591
But what makes Earth so special?

1364
01:21:05,701 --> 01:21:08,427
If the other rocky planets
were made the same way,

1365
01:21:08,537 --> 01:21:11,093
how come
they're so different today?

1366
01:21:13,130 --> 01:21:14,528
What happened to them

1367
01:21:14,628 --> 01:21:18,223
might shed light on the future
of our own planet.

1368
01:21:19,561 --> 01:21:21,888
Scientists look to them
for clues

1369
01:21:21,998 --> 01:21:25,922
that can tell them more about
the fate of the Earth's core.

1370
01:21:26,022 --> 01:21:30,216
And the planet that
interests them most is Mars.

1371
01:21:31,294 --> 01:21:34,050
It's our nearest neighbor.

1372
01:21:34,160 --> 01:21:37,275
Like Earth, water once flowed
on its surface.

1373
01:21:37,385 --> 01:21:39,153
It had a thick atmosphere.

1374
01:21:39,252 --> 01:21:42,408
But that was
billions of years ago.

1375
01:21:42,518 --> 01:21:46,352
Today, the planet
is a frozen desert.

1376
01:21:46,452 --> 01:21:50,536
Most of its water and atmosphere
have vanished.

1377
01:21:50,646 --> 01:21:53,302
And even though Mars
has a metal core,

1378
01:21:53,412 --> 01:21:55,898
its magnetic field is tiny.

1379
01:21:57,216 --> 01:21:59,772
Are these conditions
a coincidence?

1380
01:21:59,882 --> 01:22:03,737
Or is Mars
a vision of Earth's future?

1381
01:22:05,804 --> 01:22:07,831
<i>MAN:in NASA's</i>
<i>Mars Global Surveyor.</i>

1382
01:22:07,941 --> 01:22:12,424
NARRATOR: In 1996, NASA launched
the Mars Global Surveyor.

1383
01:22:12,534 --> 01:22:16,658
Its mission... to unlock
the secrets of the red planet.

1384
01:22:16,768 --> 01:22:19,604
<i>MAN:as America begins its</i>
<i>journey back to the red planet.</i>

1385
01:22:19,703 --> 01:22:20,762
NARRATOR:
But in the process,

1386
01:22:20,872 --> 01:22:24,456
it unlocked some
of our own planet's secrets,

1387
01:22:24,566 --> 01:22:27,931
shedding new light on the very
center of the Earth...

1388
01:22:28,031 --> 01:22:30,288
the inner core.

1389
01:22:30,398 --> 01:22:35,121
The Global Surveyor's data
astonished scientists.

1390
01:22:35,231 --> 01:22:38,586
It showed Mars' magnetic field
is very weak,

1391
01:22:38,696 --> 01:22:42,710
but Mars' crust is
intensely magnetized.

1392
01:22:44,627 --> 01:22:48,422
The implications
for our planet are immense.

1393
01:22:51,058 --> 01:22:54,782
Like Earth, Mars once had
a powerful magnetic field.

1394
01:22:54,882 --> 01:22:58,746
But at some point, the Martian
core cooled and froze,

1395
01:22:58,846 --> 01:23:01,043
and its magnetic field
collapsed.

1396
01:23:03,020 --> 01:23:06,705
The question is,
could it happen to our planet?

1397
01:23:12,047 --> 01:23:14,014
Mario Acuna was
one of the scientists

1398
01:23:14,114 --> 01:23:17,299
who built the magnetic sensors
that gathered the Mars data.

1399
01:23:17,409 --> 01:23:21,503
He used it to create a map
of Mars' magnetized crust.

1400
01:23:21,603 --> 01:23:26,037
He discovered that in one area,
there is no magnetism at all.

1401
01:23:26,137 --> 01:23:29,462
And it corresponds with
a particular physical feature.

1402
01:23:29,572 --> 01:23:31,429
One of the things
that we observe

1403
01:23:31,539 --> 01:23:35,293
is this very large hole in Mars,

1404
01:23:35,403 --> 01:23:36,521
if we want
to call it a hole.

1405
01:23:36,631 --> 01:23:40,066
It's really the remnants
of a gigantic impact

1406
01:23:40,166 --> 01:23:42,852
that took place very early
in Mars' history.

1407
01:23:44,959 --> 01:23:48,414
NARRATOR: This hole is
an enormous meteor crater.

1408
01:23:48,524 --> 01:23:50,421
It was clear
that the rocks here,

1409
01:23:50,531 --> 01:23:52,578
unlike those in the rest
of Mars' crust,

1410
01:23:52,688 --> 01:23:54,915
hadn't been magnetized.

1411
01:23:55,024 --> 01:23:56,512
So the crater must have formed

1412
01:23:56,622 --> 01:23:59,248
after Mars' core
stopped working.

1413
01:24:01,685 --> 01:24:03,951
Scientists think
the meteor impact here

1414
01:24:04,051 --> 01:24:05,709
released so much energy,

1415
01:24:05,819 --> 01:24:08,585
it liquefied the planet's crust
at the point of impact.

1416
01:24:13,248 --> 01:24:15,235
Crystals in the cooling lava

1417
01:24:15,345 --> 01:24:18,111
would have recorded
the surrounding magnetic field,

1418
01:24:18,211 --> 01:24:20,547
just like they do on Earth.

1419
01:24:20,647 --> 01:24:22,904
But in the gigantic crater
on Mars,

1420
01:24:23,014 --> 01:24:26,908
the rocks bear no record
of being magnetized.

1421
01:24:27,008 --> 01:24:28,496
Scientists theorize

1422
01:24:28,606 --> 01:24:31,332
that's because the magnetic
field no longer existed

1423
01:24:31,441 --> 01:24:34,028
when the impact occurred.

1424
01:24:34,137 --> 01:24:39,070
The continent-sized crater was
created 4 billion years ago.

1425
01:24:39,170 --> 01:24:41,437
It means the dynamo
in Mars' core

1426
01:24:41,537 --> 01:24:46,230
stopped working when the planet
was in its infancy.

1427
01:24:46,340 --> 01:24:47,558
DR. ACUNA:
For the first time,

1428
01:24:47,668 --> 01:24:51,123
we could time
when the dynamo disappeared.

1429
01:24:51,233 --> 01:24:54,817
And since Mars was formed
only 41/2 billion years ago,

1430
01:24:54,927 --> 01:24:57,264
that means
that the dynamo only lasted

1431
01:24:57,364 --> 01:24:59,381
a few hundred million years.

1432
01:25:02,326 --> 01:25:04,523
NARRATOR: The reason
for Mars' premature death

1433
01:25:04,623 --> 01:25:06,990
lies in its size.

1434
01:25:09,186 --> 01:25:11,483
Mars is
half the diameter of Earth,

1435
01:25:11,593 --> 01:25:14,049
so it cooled more quickly.

1436
01:25:14,159 --> 01:25:15,677
Its core froze,

1437
01:25:15,787 --> 01:25:19,052
and its magnetic shield
collapsed.

1438
01:25:19,152 --> 01:25:23,046
The fate of life on Mars
was sealed.

1439
01:25:24,913 --> 01:25:27,679
The planet lay exposed
to the solar wind.

1440
01:25:31,344 --> 01:25:35,069
Its atmosphere and water
eroded away.

1441
01:25:36,147 --> 01:25:38,164
DR. ACUNA: The fact that
the magnetic field disappeared

1442
01:25:38,274 --> 01:25:41,669
had a tremendous effect
on the loss of water by Mars.

1443
01:25:41,779 --> 01:25:47,171
We are looking for something
like 1,500 feet of water

1444
01:25:47,271 --> 01:25:52,064
over the entire planet Mars
to have disappeared from Mars.

1445
01:25:55,938 --> 01:25:58,365
NARRATOR:
Earth is much larger than Mars,

1446
01:25:58,465 --> 01:26:01,690
so its core is still hot,
still working.

1447
01:26:01,800 --> 01:26:04,955
But the lesson of Mars
is unavoidable.

1448
01:26:05,065 --> 01:26:08,290
Eventually,
Earth's own core will cool

1449
01:26:08,400 --> 01:26:12,085
until the convection columns
inside the outer core collapse,

1450
01:26:12,194 --> 01:26:16,129
and then our magnetic shield
will come down.

1451
01:26:18,455 --> 01:26:21,251
Without it, solar radiation
will strip away

1452
01:26:21,361 --> 01:26:25,815
both our atmosphere
and liquid water.

1453
01:26:25,924 --> 01:26:30,178
Then Earth will become
a dead and desolate place.

1454
01:26:31,287 --> 01:26:34,043
But we don't need
to panic just yet.

1455
01:26:36,749 --> 01:26:38,945
The extreme temperatures
in the inner core

1456
01:26:39,045 --> 01:26:41,312
suggest we have
plenty of time left,

1457
01:26:41,412 --> 01:26:44,308
perhaps even billions of years.

1458
01:26:47,513 --> 01:26:50,269
Nearly 4,000 miles
from the surface,

1459
01:26:50,379 --> 01:26:52,176
we have reached
our destination...

1460
01:26:52,276 --> 01:26:54,742
the very center of the Earth.

1461
01:26:54,842 --> 01:26:57,468
This is the hottest part
of the planet.

1462
01:26:59,945 --> 01:27:02,841
Temperatures reach
12,000 degrees,

1463
01:27:02,941 --> 01:27:05,597
hotter than the surface
of the sun.

1464
01:27:07,035 --> 01:27:10,799
And with no gravity,
it's like nothing else on Earth.

1465
01:27:12,497 --> 01:27:14,094
The very center of the Earth is

1466
01:27:14,204 --> 01:27:17,599
probably the most un-Earthlike
place on the planet,

1467
01:27:17,699 --> 01:27:20,785
in the sense that gravity
gets weaker as you go down,

1468
01:27:20,894 --> 01:27:23,620
and when you hit the center,
there's no gravity left.

1469
01:27:23,730 --> 01:27:26,716
There's no direction
which means down.

1470
01:27:26,826 --> 01:27:28,124
Gravity is absent.

1471
01:27:28,224 --> 01:27:30,890
The temperature is
the hottest spot on the Earth.

1472
01:27:30,990 --> 01:27:33,985
And so it's this sort
of white-hot, gravityless,

1473
01:27:34,095 --> 01:27:36,651
very high-pressure...
just crushing pressures

1474
01:27:36,761 --> 01:27:38,848
of all of the weight
of the rest of the Earth

1475
01:27:38,958 --> 01:27:40,286
all pushing down on you.

1476
01:27:40,386 --> 01:27:42,513
So it's extremely inhospitable

1477
01:27:42,623 --> 01:27:45,638
and extremely strange
at the same time.

1478
01:27:47,715 --> 01:27:49,612
NARRATOR:
The world beneath our feet

1479
01:27:49,722 --> 01:27:51,440
may seem like an alien place,

1480
01:27:51,550 --> 01:27:53,207
but our journey has shown

1481
01:27:53,317 --> 01:27:55,574
it's very much
part of life aboveground.

1482
01:27:57,850 --> 01:28:00,307
Everything about it
is just right.

1483
01:28:01,515 --> 01:28:04,531
The Earth spins
at precisely the right speed,

1484
01:28:04,641 --> 01:28:06,608
and it's exactly the right size

1485
01:28:06,708 --> 01:28:11,111
to allow some heat loss
from the core, but not too much.

1486
01:28:13,078 --> 01:28:16,164
As a result,
we have our magnetic field.

1487
01:28:16,274 --> 01:28:18,600
The mantle is just mobile enough

1488
01:28:18,700 --> 01:28:21,097
to allow currents of heat
to move upward

1489
01:28:21,206 --> 01:28:23,463
so we have our continents
to live on.

1490
01:28:26,439 --> 01:28:28,925
And our gravity
is just the right strength

1491
01:28:29,035 --> 01:28:32,989
to bind our atmosphere
and oceans to the surface.

1492
01:28:34,028 --> 01:28:36,924
From the crust to the core,

1493
01:28:37,033 --> 01:28:40,648
every layer, every rock,
every piece fits together

1494
01:28:40,758 --> 01:28:44,023
to make life
upon the surface possible.

1495
01:28:44,123 --> 01:28:47,089
The secret of all life
as we know it

1496
01:28:47,189 --> 01:28:50,054
lies deep inside planet Earth.