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 are only beginning

to unlock its secrets.

The planet Earth

is a haven for life.

Conditions are perfect.

I mean, they really are perfect.

Oceans of liquid

water make life possible.

But that's not enough.

A complex secret

gives Earth its life,

while hundreds of other

known planets fall short.

Not a single one

of these planets

look just like the Earth.

What makes Earth

so perfect?

Why does it depend on

the moon, volcanoes,

even the planet Jupiter?

What puts Earth in the ultimate

Goldilocks Zone for life?

...on Secrets of the Earth.

May 19, 2012.

In the Arizona desert,

a 35-year-old visitor

from Germany is overcome by

105-degree temperatures,

the first of two hikers

to die this weekend

from early-season heat.

Water makes up 60%

of the human body.

As little as two to three

percent decrease in body water

can onset the symptoms

of dehydration.

Humans on Earth

exist on a knife's edge

between life and death,

surviving only in a narrow

range of temperatures.

So, too, in the solar system,

there is only a narrow range

in which planets

can support complex life.

This place--not too hot,

not too cold--

is called the Goldilocks Zone.

Estimates put

the Goldilocks Zone

between 67 million

and 279 million miles

from the sun,

and it's just right

for the one thing

life seems to need,

liquid water.

You're not so close

that water boils away.

You're not so far away

that water turns to ice.

Perfect Goldilocks.

We're in the Ka'u Desert

on the island of Hawaii.

When you look at

dry places like this,

it really makes you appreciate

how vital water is

to animals and plants.

Hawaii's Big Island

is also home to rainforests,

waterfalls,

seacoast,

and even snowcapped mountains,

where the secrets

of life's success on Earth

play out.

Among those secrets,

a recipe for life

that needs far more

than just liquid water.

One of the biggest

surprises of the last 20 years

is the large number of

conditions the Earth needs

to maintain its state

as being habitable.

Besides Earth's

distance from the sun,

life also depends

on the planet's volcanoes,

its large moon,

and even the planet Jupiter.

Liquid water is important,

but that's possible

at a wide range

of temperatures,

not all of them good for life.

The highest temperature

that complex life can live at

is very, very different

from that of microbes.

We animals really can't live

much above 113

to 115 degrees Fahrenheit.

The Nahuku

rainforest on Hawaii

is a Goldilocks Zone

on a Goldilocks planet.

There are more species

packed around me right now

than any other place

I could go to.

This rainforest

and others like it

represent the apex of species

diversity on planet Earth.

The diversity

springs from conditions

that are not only wet

but also warm

without being too hot.

Life likes to be warm.

Seventy to 80 to 90 degrees,

that's ideal.

That's where you want to be.

The Earth's volcanoes

hold the secret

of the planetary thermostat.

If it weren't for these

mountains of fire,

this entire planet

would freeze.

January 3, 1983.

Hawaii's Kilauea volcano

begins its longest eruption

in recorded history

as lava flows through

residential areas.

The first homes

destroyed there were 16 homes

shortly after that

initial eruption,

a vivid reminder

of the destructive power

of the volcano.

The volcano's fury

fuels mankind's fear.

But the erupting mountains

hold a secret.

They are essential to life

and play a central role

in making Earth

a Goldilocks planet.

Volcanoes are commonplace

in the solar system.

They have erupted on Mars,

on Jupiter's moon Io,

and may number

in the thousands on Venus.

But unlike other planets,

Earth's volcanoes are coupled

to plate tectonics,

the planet's method

of resurfacing its crust.

Earth is the only known planet

whose crust

actively moves around

with many distinct plates.

Many scientists now believe

plate tectonics

is the most important secret

other than water

in making Earth

just right for life.

It all has to do

with carbon dioxide.

Right now, it may be

making the planet too warm,

but life actually needs

some of that warming.

Without CO2, the Earth

would be very cold.

It would be

zero degrees Fahrenheit,

32 degrees below freezing.

Without that carbon dioxide,

the entire planet would be

a frozen wasteland.