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.

On planet Earth,

there's an invisible force...

Whoa!

...governing

everything.

It gave me enough energy

to be able to go through

all the loops and twists

and turns of this amazing track.

It's called gravity,

a phenomenon that

permeates the planet,

wielding secret power over

the continents and oceans,

plants and people.

But in a remote part

of North America,

some of it has

turned up missing,

and it could be gone forever.

If you suddenly

turn off gravity,

we would be flung

into outer space.

Without gravity,

there would be no you,

and there would be no me.

The case of

the missing gravity

on Secrets of the Earth.

On this planet called Earth,

something strange is happening.

Gravity, a fundamental

force of nature,

is actually missing

in some places.

In fact, Canada's Hudson Bay

has lost a lot of gravity,

more than almost anywhere else

on the planet.

It is a mystery tied to one

of the most important forces

in the cosmos.

Gravity is the glue that

holds the universe together.

Gravity is assisting us

in--in all of the actions

and things that we do

as human beings.

Without gravity,

there would be no galaxies,

there would be no stars,

there would be no planets.

There would be no you

and no me.

For over a half-century,

scientists on Earth

have been on a mission

to solve the case of

the missing gravity

and what secrets

it might reveal

about the planet.

It is a quest

that has taken them

to one of the most

remote outposts

along the Hudson Bay,

Churchill, Manitoba.

No roads lead here.

The only way in is by train

or small aircraft.

The subarctic community

of only 600 people

is the polar bear capital

of the world.

Tourists flock here

in the summer and fall

when the massive white beasts

move inland off the melted ice.

But for much of the year,

Churchill is a desolate town

where winter temperatures

can dip

to minus 30 degrees Fahrenheit,

and the modes of transportation

are snowmobile

and dogsled.

We're in Churchill

in northern Canada,

one of the world's largest

gravity lows.

The missing gravity

in the Hudson Bay region

is so large that you can

observe it from space.

Understanding what

caused this bizarre abnormality

in the Hudson Bay

requires decoding the secrets

of gravity on Earth

and in the universe.

Gravity is an attractive force

that causes

any two objects with mass to

be pulled toward each other.

This force is stronger

for more massive objects,

and it's stronger the closer

you are to that object,

and that's the way

gravity works.

So really big things

like planet Earth

have lots of gravity

that pulls everything

towards their center.

The rocks forming

this cliff here

attract me gravitationally,

but I don't feel an attraction

toward them.

Instead, I'm firmly planted

on Earth here because

Earth's mass

pulling me down

is so much greater

than the mass of those rocks

pulling me to the side.

The Earth,

like all planets, was formed

when gravity pulled together

bits of rock, dust, and gas

over millions of years,

gradually forming a sphere.

Gravity holds the Earth

together

and keeps it orbiting

around the sun.

To understand

how important gravity is,

let's turn it off.

If you suddenly

turn off gravity,

we would be flung

into outer space

at a thousand miles per hour.

The power of gravity

isn't just reserved

for shaping the universe.

Humans sometimes harness it

for a thrill.

Here I am

on the Xcelerator ride

at Knott's Berry Farm

in southern California,

and this incredible

roller coaster is gonna show us

the amazing power of gravity.

Here I go. Who-oa!

Whoo! Whoo!

Oh, man!

Ah!

And now gravity

is gonna take me down!

Whoa! Whoa!

And the rest

of the ride is powered by

nothing but gravity.

Oh, ho-ho! Whoo!

Oh, man!

So I got accelerated to

80 miles an hour,

and then launched

nearly vertically.

So I was doing work

against gravity.

Got to the top

of the track,

and then gravity

brought me down.

Whoa!

Gravity gave me enough energy

to be able to go through

all the loops

and twists and turns

of this amazing track.

Since the mass of an object

determines how much