Secrets of the Earth

We have

uncovered a remarkable planet,

a world of extreme weather,

alien landscapes,

and bizarre phenomena.

It's the most complex system

we know of in the universe.

That planet is Earth...

...and we're only beginning

to unlock its secrets.

It seems like

a most familiar sight,

but, in fact,

it's one of the strangest

phenomena in the universe,

and humans

couldn't live without it.

The water

that is in our bodies right now

has been around

for millions of years,

and all of us probably

have water

that passed

through Albert Einstein,

George Washington.

It's called rain.

Created by powerful

but little-known forces,

it teems with mystery

and even sometimes with life.

Rain decoded

on Secrets of the Earth.

Even from space,

it's clear that Earth

is a special planet.

It's unique

in this solar system

because it has massive oceans

and it rains water

from the sky.

When you look

down at the Earth from space

the two things that jump

out at you are

the white--the clouds--

and the blue--the oceans.

Canada's Vancouver Island,

the wettest place

in North America.

Here it can average

an astonishing

256 inches of rain a year.

The oceans, the clouds,

and even the water

on the moss around me here,

it's all part of

the same water cycle,

the cycle that sustains life

on the planet.

This cycle includes everything

from my breath

adding moisture to the air

to the water hanging

on this moss

to a river like this

flowing towards the ocean.

Or this.

Even

the world's driest deserts,

like Death Valley,

are shaped by rain.

Here in Death Valley,

even though

it's an extremely dry place,

everywhere we look,

we see evidence

of the work of water

that it sculpts the landscape.

It creates these fantastic

shapes that we see here,

and this arroyo

that's located behind me

that's deeply carved, deeply

incised into this hillside is

caused by torrential rains

that flood down the slope,

carve into the landscape,

and move

those sediments downstream.

Rain may seem simple,

but few people

on the planet understand

how it actually works,

how it relies

on visitors from outer space

and strange creatures

from Earth

to make it fall from the sky.

The secret life of rain

begins with a basic fact--

that across most of the Earth,

rain starts out not

as a liquid but as a solid.

Here in the rainforest

on Vancouver Island,

it's raining on me right now,

but these rain droplets

didn't actually start as rain.

They started

in the clouds as snow,

which is a combination

of ice, air,

and little droplets of water.

Most rain on the planet

actually starts as snow.

High in Earth's atmosphere,

it's far below 32 degrees,

and as every child

on Earth is taught,

water freezes at 32 degrees,

except that it doesn't.

It wants to freeze

because it's below the

freezing point, but it can't.

It needs an impurity,

an impurity around

which ice crystals can form

and then a solid can take place.

And this planet's atmosphere

is full of tiny impurities

that play this vital role.

The particulates

that we find in the atmosphere

come from many

different places--

from sea spray from the ocean,

from forest fires and the smoke

that they produce,

and even here in Death Valley

in a sand storm,

it's gonna pick this sand up,

toss it into the air,

and carry it into the clouds.

And some rain-making particles

actually zoom in

from outer space.

Every day, 6,000 pounds

of tiny micrometeorites

crash into Earth's atmosphere.

It's hard to believe,

but it's estimated

that the Earth may get heavier

by perhaps 10,000 tons

or so every year

because it's sweeping

through this dust cloud

of tiny micrometeorites.

They're very tiny.

A micrometeorite is

less than the width

of a piece of human hair,

and what that means

is that there's

not that much friction

as they're falling.

So they don't burn up

in the atmosphere

like a big meteorite would.

This micrometeorite,

once part of the tail

of an ancient comet,

hits the atmosphere.

It slows down

and eventually drifts into

a cloud full of microdroplets.

They're below freezing,

but they can't crystallize

without coming into contact

with an impurity

like this tiny space invader.

They encounter

one of these particles

in the atmosphere

and crystallize

around a single particle.

This happens

billions of times a day,

and the proof

is everywhere on Earth.

You can actually look

for micrometeorites yourself.

All you want to do

is collect some rainwater.

You get yourself

a really strong magnet.

You take your magnet and just

swish it around in the water

for a couple minutes

to make sure you pick up