Inside Planet Earth Page #2

an active volcano.

Many choose to

because volcanic soil

is so fertile and productive.

But will the people

of Montserrat ever be able

to return to their fields

and old ways of life?

Or has that gone,

as lost as Pompeii?

People and politicians

would like clear-cut answers.

But scientists know

that's impossible.

If the eruption stops tomorrow,

the dome is still up

on top of the volcano.

It's still unstable, and it will

still retain its heat.

And it might stay like that

for 5 years

after the eruption finishes.

Or it might cool down

exceptionally quickly

and, within one year,

people could move back.

We don't really know.

Montserrat's disaster

is caused by something

that happened

over 4 billion years ago,

when the Earth's crust

broke into gigantic sections,

forming the tectonic plates.

Understanding Earth's

tumultuous history

is like reading

an intricate detective story,

for the Earth is unlike

any other planet.

Its restless surface

is changing constantly,

destroying the evidence

of the past.

But if you know where to look

for them,

the clues are still there.

About 18,000 meteorites

hit the Earth every year,

hurtling down

at 70,000 miles an hour.

Most are small

and do little damage,

but each brings clues

to the catastrophic formation

of our planet.

Geologist Roger Buick is working

in northwestern Australia.

Even though it's just arrived,

this is the oldest thing

on Earth.

It's a chondrite--

a type of stony meteorite--

and it's been wandering

around the solar system

for about 4,500 million years.

It's stuff like this

that the Earth is made of--

space junk glued together.

4.6 billion years ago,

the molten Earth grew

as a continual rain

of mega-meteorites

pummeled it

on its orbit around the sun.

Each strike brought with it

raw rock,

the material

from which Earth could grow.

It also brought

explosive energy,

raising the surface temperature

of the primitive planet

to over 1,800 degrees.

A vast ocean of molten rock

100 miles deep

covered the globe.

Internal radioactivity raised

the temperature even further.

Earth became a melting pot.

The meteoric iron

began to sink to the center,

dragged by the relentless tug

of gravity.

A kilometer sphere of molten

iron would make the journey

from the surface

to the center of the Earth

in less than a million years--

a blink of geological time.

The constituents of the Earth

were forming.

It had an iron core

surrounded by molten rock.

On the surface,

a thin crust was developing.

It behaved

like these lava ponds.

And the turbulent forces beneath

began to fracture the crust.

These are the tectonic plates--

vast sheets

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