Inside Planet Earth Page #4

are buried in the ground.

We're digging 3 holes

for the geophones that we're

going to be putting in here

so that we can have

a 3-component

orientation system

to measure the seismic wave

that comes in.

We have a vertical geophone

which will measure the vertical

component of the arriving wave.

There is a north-south geophone

that will measure

the north-south component

of the incoming wave.

And we have

an east-west geophone

to measure

the east-west component

of the incoming seismic wave.

10, 9,

8, 7,

6, 5,

4, 3,

2, 1.

As the shock wave races down

through the ground,

they hit something hard--

much harder

than the surrounding rock.

The shock waves are reflected

and speed back to the surface,

taking their precious

information to the geophones.

Analysis of the result

shows that under the Rockies

are the buried remains

of ancient volcanic islands.

Over the last 200 million years,

hundreds of these islands

were grafted

onto the North American

continent.

They form much of the land

west of the Rockies,

stretching from Mexico

to Alaska.

This is a clue as to how the

first landmasses were created.

But until very recently,

science was at a loss

to say just when it happened.

Then, one day,

prospecting for minerals

in northwestern Australia,

Roger Buick made

a startling discovery.

This rock is part of the oldest

land surface on Earth.

It has miraculously survived

the never-ending cycle

of formation and destruction

of the crust.

The vertical stripes

have endured

for over 3.6 billion years.

At the same time,

the Earth began to cool.

condensing in pockets,

but not enough

to create oceans or rivers.

There was no oxygen in the air.

It was inhospitable,

with no trace of life.

A new theory suggests that,

in time, water--

maybe enough

to fill the world's oceans--

arrived from deep space,

brought on ice comets.

Cosmic rain continues today with

small, 20-to-40-ton ice comets

striking the Earth's atmosphere

once ever 3 seconds.

They add one inch of water

over the entire surface of

the globe every 20,000 years.

When the atmosphere was

saturated, the rain began.

An endless ocean grew.

And when the skies

finally cleared,

the Earth had been transformed

into a watery globe.

This is the time when life

is thought to have begun.

Echoes of those beginnings

can still be heard today.

Our most ancient ancestors,

the most resilient creatures

ever evolved,

have survived unchanged

for billions of years

living in solid rock.

Drilling to great depths

into the rocks at Idaho Falls,

Princeton microbiologist

Tullis Onstott

is hoping to take a closer look

at their descendants.

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