Inside Planet Earth Page #4

to this geological cataclysm

that tore Pangaea apart.

The supercontinent

looked like this,

made up of

the present-day continents

of Africa, South America, India,

Antarctica, and Australia.

The cracking started here

and split the continent

into the present-day continents

of South America and Africa.

In geological terms,

it happened incredibly fast.

The crack opened northward at

a speed of 2 inches per year,

the split unzipping the land

as it went along.

Fountains of volcanic fire

leapt through the crack.

The entire process took only

5 million years to complete.

Evidence of the unzipping

is clear.

The shorelines of South America

and Africa match perfectly.

And under the ocean,

the mid-Atlantic ridge

divides the 2 continents

almost exactly down the middle,

where it still

pushes them apart.

Until recently, scientists had

never visited the place

where this spreading occurred.

But now even the depths

are giving up their secrets.

Alvin, the world's first

deep-sea submersible,

led the way

to this unexplored terrain.

Atlantis, Alvin.

The valve is open.

The light is on.

The hatch is shut.

Oxygen's on.

One of the first regions visited

was the East Pacific Rise,

part of the spreading area

called the mid-ocean ridge.

They expected to find evidence

of the Earth at work.

What they actually discovered

lay beyond imagination.

From this pioneering work,

scientists worldwide

are able to study

the extraordinary

geological systems

4 miles beneath our feet.

Lindsay Parson heads a team

at the Southampton

Oceanographic Centre.

These are really

some of the most amazing images

that I think we have

of the ocean floor.

They're taken from

about 3,000 meters down.

They're in some of the deepest

parts of the ocean floor.

And we're here looking

at hydrothermal systems,

where bottom water of the sea

is being sucked

into the ocean floor.

It's being heated from there,

the heat engine

inside the Earth.

And it's being delivered out

into the ocean floor again

once it's dissolved

and leeched out minerals

and chemical compounds

from the rock itself,

which is why the smokers,

as we call them,

are black

and densely colored here.

The pressure

is an immense

2 tons per square inch.

Water is superheated

to over 700 degrees.

It's highly acidic,

full of hydrogen sulfide

and heavy metals.

The equivalent volume

of the world's oceans

is siphoned through

the vent systems

every 30 million years.

Samples prove that

the seafloor along the ridges

is the youngest on Earth,

endlessly reborn.

But an even greater surprise

lay in store.

Even in this harshest

of terrain, life takes hold.

The black smokers

are warm-water oases

around which familiar species--

shrimps, foot-long clams,

and mussels--

thrive alongside

more bizarre forms--

6-foot-long tube worms

and strange fish.

The majority of the life-forms here

depend not on light

to maintain their existence.

They absorb and fix chemicals

from the hydrothermal vents

to keep them alive.

They are

chemosynthetic communities

rather than

photosynthetic communities.

Far from the sun

and the air,

these creatures have evolved

in a self-contained environment

separated from the rest

of the biosphere.

They have managed to survive

the endless geological upheavals

that wrack the world above them.

Maybe one day,

long after we are gone,

they will inherit the earth.

of the seabed

actually creating itself.

The hydrothermal systems lie

along the mid-ocean ridge.

The mid-ocean ridge is the line

along which the tectonic plates

move apart from one another,

allowing hot, molten rock

from the interior of the Earth

to well up and to form

new ocean floor--

the youngest part of the world

as we know it.

The mid-ocean ridge is

the Earth's crust factory.

New molten magma

endlessly emerges

to force the cold, older lava

away from the ridges.

Enough lava is created each year

to bury New York

over 100 feet deep.

And this unrelenting pressure

is like a wedge

between the plate boundaries,

driving them

and their continents

on their unstoppable journey.

Accurate mapping of the seafloor

is now possible

and crucial to understanding

the system on a grand scale.

By careful monitoring,

scientists can calculate

just how fast the seafloor is

spreading and the plates moving.

A sonar sledge is towed

across the ocean bed.

Individual snapshots

are processed by computer

and a photomontage created.

That information is turned

into 3-dimensional maps.

What emerges

is that the seafloor

is full of great valleys

and deep trenches,

and that here is the largest

and tallest range

of volcanic mountains on Earth,

40,000 miles long,

sometimes 5 miles high,

stretching around the globe

like a seam on a baseball.

Oceanographic research

is difficult.

But there is a country

that might have been designed

as a geological laboratory--

the one place

where the mid-Atlantic ridge

becomes exposed on land.

Iceland.

The land here

is being torn apart.

The rift shows exactly

where the plates

carrying America and Europe

are being forced away

from each other,

at about an inch per year.

And Iceland is in the middle.

The land is continually reshaped

through eruption and rifting.

The lava from the flows

forms vertical dikes

and horizontal beds,

just as it does

on the ocean floor.

Geysers and mud pools

are evidence

of the heat and pressure

just beneath the surface

continually seeking

a way to escape.

Ice and fire is a deadly mixture.

In 1996, part of the mid-ocean

ridge erupted under the ice cap.

It rapidly melted its way

through 300 feet of ice,

forming a deep gorge.

The meltwater raced away

to fill a subglacial lake

until it could no longer

be contained.

In the catastrophic flood

that followed,

10 square miles of land

was drowned.

This time the damage

was only to roads and bridges.

But in Iceland,

the earth is always menacing.

In 1975, the Krafla volcanic

eruptions began,

lasting 9 years.

14 square miles of basalt

spewed out,

in some places widening

the land itself by 28 feet.

In 1973, the town of Heimaey

was almost overwhelmed

when the nearby volcano

woke from a 5,000-year sleep.

5 months later, the lava and

ash had destroyed 300 houses,

reshaped the harbor,

and added nearly a square mile

of new land.

Living in a laboratory

can be hard.

But if new land

is continually being made

at the crust factory

along the ridges,

why isn't the world itself

constantly expanding?

The reason is subduction,

the giant recycling process

that has been going on

since the world began

and which causes

most volcanoes and earthquakes.

Subduction zones

are the graveyards

of the old, dense oceanic floor.

Where it collides with

the lighter continental crust,

it's forced down.

It pulls the rest

of the plate with it,

to be melted in the ferocious

furnace of the inner earth.

The plates don't die peacefully.

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