All language subtitles for The.UnXplained.Mysteries.of.the.Universe.S01E03.1080p.WEB.h264-EDITH_track3_[eng]

WILLIAM SHATNER:
A blue oasis

formed by cosmic collisions.

Vast secrets hidden beneath
hundreds of miles of rock.

And mysterious forces

with the power to either protect

or destroy life as we know it.

We walk on its surface,

breathe its air,
drink its water.

But the blue marble
we call Earth

remains in large part a mystery

to the eight billion people
who live on it.

The story of our planet
is extraordinary,

and there are many questions
we still haven't answered.

How was the Earth made?

What are the secrets
of its survival?

And how long

will humans be able
to call it home?

Well, that's what we'll try
and find out.

♪ ♪

Earth.

It is the third planet
from the Sun

in a gravitationally bound
system of eight planets

we call the solar system.

It has a surface area of
nearly 200 million square miles,

which is covered
in continental landmasses

and liquid surface water.

And it is the mysterious home

to the only known life
in the universe.

(birds singing)

MICHIO KAKU: When you look
at the Earth today,

it looks so calm,
serene, beautiful.

These are
ideal conditions for us.

And it seems
like everything's normal.

But we're beginning to realize,
much to our shock,

that the Earth is an oddball.

ROD PYLE:
Space is a really big place,

and it's pretty clear
that planets are everywhere.

We've discovered something like
5,340 planets in the universe,

and not one of them
appears to be similar to Earth

to any meaningful extent.

We're not finding
an atmosphere like ours.

We're not finding a planet

that can support liquid water
on the surface,

oxygen, the things we think
that life might need.

We've been very lucky
to be where we are.

ANNA GÜLCHER:
The Earth is definitely a puzzle
that needs to be solved.

In that sense,
you could think of-of it

as trying to get
little pieces of evidence

to try to understand how the
Earth has evolved over time,

especially of the early Earth.

SHATNER:
While mankind has survived
and even thrived

by learning to harness
Earth's resources

and adapt
to its ever-changing conditions,

there is
surprisingly very little

we know about how
and why Earth is the way it is.

Based on uranium-lead
dating methods

used on a meteorite
in the 1950s,

scientists have maintained

that the Earth
is 4.5 billion years old.

But just how Earth was created
remains a mystery.

GRAHAM LAU:
The origins of Earth started
4.5 billion years ago.

So we really have
to be detectives

and sleuth our way through

to look back into time
to understand

the early formation of Earth.

There have been different ideas
over time.

And the truth is, we
really don't know for sure yet

where Earth came from.

REBECCA BOYLE:
There's a lot of mysteries

that make this planet
really special.

And going back
to the very beginning,

we don't really know how Earth
got here in its present form.

It's the only planet
that can host life.

But it shows
that we have a lot to learn

about the fundamental processes
that built this planet.

SHATNER:
How can we unravel
the early history of Earth?

Curiously, a simple experiment
gave scientists

an unexpected clue that
might help solve this mystery.

The International Space Station,
250 miles above Earth.

While conducting
a simple science experiment

for television viewers,

NASA astronaut Don Pettit
makes a major

and unexpected discovery.

PYLE:
In 2003,

NASA started
a Saturday morning program

by which the astronauts would
do citizen science for kids.

Don Pettit wanted to see
what would happen

with small grains of salt if
they were shaken up in zero-g.

So he thought this would be
an interesting experiment.

LAU: By taking a little
plastic bag of salt crystals

and shaking them up,

salt crystals
started clumping together

and making larger gloms
inside of this bag, basically,

showing off some of the things
that happen in microgravity,

this experience
of weightlessness

that the astronauts feel.

SHATNER:
At first, when the grains
of salt floated together

in zero gravity,

Don Pettit thought it was merely
a strange space anomaly.

But when he repeated the
experiment with other materials,

including sugar...

...he realized that his Saturday
morning science presentation

had revealed the process

of how Earth's very first
particles began to bind together

billions of years ago.

LAU:
For a long time,

we weren't really sure

how all of the dust and the gas

around our Sun

coalesced together
and formed our Earth.

And so, these experiments
where particles

start to aggregate together

and-and grow larger clumps
actually helps us to solve

a really old problem
for understanding

the early evolution
of our planet.

SHATNER:
If, 4.5 billion years ago,

particles of space dust
came together

and started to build
the foundation of our planet,

then what happened next?

How did Earth become
the enormous celestial body

that it is today?

On the surface,
this remote countryside

may appear to be a simple valley
dotted by rolling hills.

But, curiously, in July of 2005,

the area was designated
as a UNESCO World Heritage Site.

So what's special
about this rural landscape?

As it turns out,

Vredefort is home
to an important clue

about Earth's origins
that can only be seen

from space.

LAU:
When we look at Vredefort
from space,

what we see is
an asteroid impact crater

made by an extremely large
impactor.

That impactor might have been
20 to 25 kilometers in diameter.

So this giant structure

striking the Earth...

...with so much force that,
if it happened today,

it could have obliterated
all of the life on Earth.

But the Vredefort impact

was slightly over
two billion years ago...

...a much different time
in Earth's history.

The very early Earth would
have been a molten ball of rock.

It would have looked hot
from space.

You would have seen
all this energy coming off.

And so, our world was a much
different place back then.

SHATNER:
Scientists believe
that the Vredefort Crater

is just one
of many asteroid impacts

that occurred
in Earth's early history.

And while not every one
of these giant space rocks

made a mark
that is still visible...

...they all contributed

to Earth's growing into
the massive planet it is today.

KAKU: If you take a look at all
the craters on the planet Earth,

they are reminders
of the fact that we live

in the middle
of a cosmic shooting gallery.

Given the fact that the Earth
is 8,000 miles across,

it means that there
must have been hundreds

of other cataclysmic impacts

that eventually gave rise
to the planet Earth.

And it was created
by the slow accumulation

of tremendous amounts of debris,
rocks and asteroids

from all these collisions.

GÜLCHER:
There are hints everywhere

across the surface of the Earth

that give us clues about how
it has evolved over time.

We generally agree that,

ultimately, all these collisions

of bigger and bigger material

is really key for how the Earth
has been formed

to what we already know today.

SHATNER:
When you consider
that our world was formed

by random collisions
in the void of space,

it's clear that Earth's
formation is a cosmic puzzle

that we're just beginning
to piece together.

But the origin of Earth
is only the first chapter

in the ongoing story
of our planet.

In fact,
the greatest enigma may lie

in how this rocky globe
became...

an ocean world.

SHATNER: NASA's Apollo 8
spacecraft is halfway

through completing the first
manned voyage around the Moon.

As the craft circles back from
the far side of lunar orbit,

the crew glimpses
a breathtaking view of Earth.

Astronaut Bill Anders
documents the experience

with a stunning color photograph

that would come to be known

as Earthrise.

PYLE:
The Apollo 8 Earthrise picture

was stunning.

It was amazing.
It was transformative.

When you look at the picture,

in the lower part
of the Earthrise photo,

you've got this dead limb
of the Moon.

Dry, lifeless, gray.

Clearly not a place
that anybody could live,

certainly not
that life could arise.

And then in the distance,

here is the Earth rising,
just this astonishing planet,

with liquid water
on the surface.

Within days, this picture was
on the cover of every newspaper

and every major magazine
in the free world.

It's really hard to overstate
the importance of that picture.

And it really moved people.

SHATNER:
The iconic Earthrise photo

showed us that our world
is truly a giant blue marble

floating in space.

70% of Earth's surface
is covered in water,

which is remarkable
when compared to most planets.

CLARK:
One of the really clear things

that we see that sets
Earth apart from everybody else

is that we're blue.

When we look
at the planets around us,

we're not these browns of clays
on the surfaces.

We're not the grays
of icy worlds.

We have this very unique color.

So, water is really important

for the Earth being the planet
that we see today.

LAU:
The Earth is the only world
we know of

to have such a deep
and voluminous ocean

of liquid water, and honestly,
there's still a lot of debate

as to how Earth got its water.

We don't really know
how we became an ocean world.

SHATNER:
Where did all of
Earth's water come from?

And why does our world
have so much water

when other planets don't?

Experts point to a rare
and remarkable event

that may hold a clue
to solving this mystery.

In this small town,

some local boys are playing
basketball, when suddenly...

...a chunk of rock

slams into the ground
only 40 feet away.

Incredibly, this small rock

fell to Earth from outer space.

CLARK:
When this meteorite fell
next to these kids playing,

one of the really
interesting things is that

this was the fastest recovered
meteorite that we know of.

And so, they were able
to get this meteorite

really quickly into the lab,

and one of the things
that was surprising at the time

is that it had small amounts
of liquid water inside of it.

So, the fact that there
was liquid water in space

is really mind-blowing.

It changes things,

because when you go to space,
it should be dry,

and the fact that there's enough
water to actually have a droplet

is really incredible.

As we look at meteorites
that fall on Earth,

we're finding more and more
that it's very common

to have water on some meteors
and on some asteroids.

And in fact, the current theory
is that this, apparently,

is where we think
the water came from

to get on Earth.

SHATNER:
If it's true that meteors
brought water to Earth,

as scientists theorize,

then it's likely
that other planets

have also received water
from space rocks.

So how does the Earth
retain so much liquid

when other planets
can't even keep a drop?

The answer lies
in our planet's distance

from the Sun.

TIMOTHY LYONS:
One of the things about Earth
that we perhaps take for granted

is that Earth lies
within the habitable zone.

The habitable zone is defined
as a band around a star

that could support liquid water.

And the Earth's orbit
around the Sun

is just right
to support liquid water.

Not too hot, like Venus;

not too cold, like planets
as distant as Mars.

So, as we think about
what's so special about Earth,

it's really that simple.

SHATNER:
While Earth
is the perfect distance

from the Sun to allow it
to maintain

the life-giving liquid
in various forms,

despite our ideal location,

Earth did not always appear
as a big blue marble.

Earth has been
many different planets

over its four and a half
billion years of history.

And there's a popular idea

that the Earth may have
gone into a deep cool

around 700 million years ago.

So much so
that the surface oceans

may have almost
completely frozen over.

And so, were you to be looking
at Earth from space,

you might have seen
this giant white sphere.

This is called a Snowball Earth
for obvious reasons.

In the distant geologic past,

the Earth had
a very different atmosphere.

It had much higher
concentrations

of greenhouse gases,
like carbon dioxide.

And then
that cools the planet down,

freezing some
of the ocean into ice.

That ice then reflects
more of the light from the Sun,

leading to the formation
of more ice.

And so, you have this
feedback loop that leads

to the total glaciation
of the planet.

SHATNER:
The idea that Earth

was once covered in ice
is chilling

in more ways than one.

But according
to a remarkable discovery,

an even more surprising fact
about our planet's water

may lie deep inside our world.

In this remote mining area,

several workers uncover
a tiny diamond.

But this is
no ordinary gemstone,

because when it was
later analyzed in a lab

by geologist Graham Pearson,

he determined that it's
a so-called "superdeep" diamond

that first formed
550 miles underground,

far deeper
than most precious stones.

CLARK:
This discovery
is really exciting

because Graham Pearson's group
found a lot of water

trapped inside this diamond.

And so, this is coming together
to basically say,

"Maybe we have
vast amounts of water stored

in the Earth's deep interior."

And in fact, there have been
a lot of news stories

that have come out
over the past decade or so

that we have somewhere between

three and five oceans' worth
of water inside the Earth.

LAU:
Based on our current knowledge,

some researchers have suggested
there's several times more water

in the interior than we have

on the surface of our planet.

And so, Earth really is
a very wet world.

And water has been important
for life

throughout the history
of our planet.

It's mind-blowing to think
that there are literally

oceans of water
in the center of the Earth.

But water's not the only part
of our world

that warrants a deeper dive.

The rocky surface of our planet
is also full of surprises.

For instance,
a recent discovery has revealed

that Mount Everest
is actually getting taller.

SHATNER:
The Himalayas.

Located along the border
of China and Nepal,

this sprawling chain
of mountains

is home to Mount Everest,
the highest summit on Earth,

which reaches
over five miles into the sky.

But curiously,
according to recent studies,

the world's tallest mountain
is actually growing.

In 2020,

Chinese and Nepalese
scientists announced

that Mount Everest
stands more than two feet taller

than its previously
measured height.

SAFFER:
This study in 2020,
it's a really interesting story

because we have a tendency
to think that the land surface--

we live on it--
that it's stable.

Yet we know, uh,
in detail, it's actually, uh,

constantly changing
in subtle but measurable ways.

SHATNER:
What are the unseen forces
of nature

that subtly raised Mount Everest
even higher into the sky?

Scientists call this
gradual movement of the Earth

"plate tectonics."

Plate tectonics is the theory

that the Earth can be divided
into distinctive plates

that are separated
by very narrow plate boundaries,

along which plates
can move towards each other,

which really creates
all of the big landforms

we see on our planet,

such as mountains
and huge volcanoes.

But plate tectonics
is also very crucial

in the earthquakes that form
when two plates move together

and one plate is forced
underneath the other.

So, much of the surface
of the Earth

is changing constantly
over time.

The Himalayas are an example of
this scenario where you've got

two tectonic plates colliding
continuously over time.

And so, that land surface
continues to get squeezed,

which played a role
in the uplift of Mount Everest.

And that mountain peak
is still rising right now.

SHATNER:
Thanks to our understanding
of plate tectonics,

we know that the Earth's surface

has been moving
for billions of years.

And in fact, tectonics are
yet another feature of our Earth

that makes it so different
from other planets.

JACOB HAQQ-MISRA:
There are no other planets
in the solar system

that's this vibrant,
active world

with plate tectonics
the way we have it on Earth.

That is unique.

And so, it seems
that this is necessary

or at least an important
condition for life on Earth

in order to keep a planet
from becoming stagnant.

SHATNER:
As technology helps us
monitor the subtle changes

happening on our world,
it makes you wonder,

what did Earth look like
in the distant past?

How different was it

from the planet we know today?

It's a fascinating question,
and in the early 20th century,

scientists went to great lengths

to solve this mystery.

Geologist Alfred Wegener
publishes a book titled

The Origin of Continents
and Oceans.

In it, Wegener makes
a shocking claim.

He argues that
the continents we live on,

which seem solid
and unchanging to us,

have actually been
moving around our planet

for billions of years.

Alfred Wegener had
a broad range of skills.

He was talented and bright
enough to be able to understand

lots of different types
of observations.

And so, he looked first
and foremost at the fit

of the continents and recognized

that they fit together
like a puzzle.

So, Wegener really had
a sense that the continents

we see distributed
throughout the world today,

at times in the past
were together.

SHATNER:
At first glance,
Wegener's insight about

the position
of the continents seems

like a perfectly logical
conclusion.

However, at the time, experts

at the British Royal
Geographical Society disagreed

because they felt strongly
that the continents moved only

up or down, and did not shift
across the Earth.

Proof of Wegener's revolutionary
idea would ultimately come

from a remarkable discovery
not on Earth's surface

but deep underwater.

Scientists at the Lamont
Geological Observatory

of Columbia University

decide to launch
an ambitious new program

to map the bottom of the ocean.

The team sends numerous ships
around the world

to take sonar readings
of the ocean floor.

This vast amount of data is
analyzed by a young geologist

named Marie Tharp,

who was hired by the university
for her map-drafting skills.

CLARK:
When Marie Tharp
started looking at the data

of the ocean floor,

one of the things
that she noticed is that,

first of all, it-it's not flat.

There's actually giant
mountain ranges

that are hiding
beneath the Earth's oceans.

One of these is the mid-Atlantic
Ridge that travels, basically,

like a baseball seam across
the length of the Atlantic.

However, nobody believed her
for quite some time.

SHATNER:
Initially, Marie's colleague
Bruce Heezen

dismissed her discovery
of underwater mountains,

calling it "girl talk."

But ultimately he and the rest
of the scientific community

had to admit that
Marie was right.

In 1957, she published a map
of the mid-Atlantic Ridge,

and her breakthrough proved
that the continents

shift over time...

just as Alfred Wegener
had theorized

more than 40 years earlier.

CLARK:
One of the things that
Marie Tharp was able

to demonstrate is that
the mid-Atlantic Ridge,

this giant mountain range,
was built from

volcanic activity
that is occurring because

the Earth's plates
are spreading apart.

And it's this mid-Atlantic
Ridge that actually helped push

apart South America
and Africa through time,

from the starting place
of them being connected

during the supercontinent
period of the Earth.

So that they're now separate,

and we have the Atlantic Ocean
fitting in.

LAU:
There's still so much
that we're learning about

the processes
of plate tectonics

and the evolution of our planet.

There's even still debate
as to when

the continents first formed.

But we do know that our Earth
is extremely unique to have

plate tectonics currently
going on actively on our world.

It's intriguing to think that
the ground under our feet

is alive, and that
the continents

on our planet are
always shifting.

But what's hidden beneath
this ever-changing surface?

Perhaps the answer
can be found by examining

mankind's attempts to journey

to the center of the Earth.

SHATNER:
Just east of the border
of Norway,

near the coast
of the Barents Sea,

lies the ruins of a Soviet-era
engineering facility.

Among the crumbling walls
of this long-abandoned site

is a metal cap, sealed shut
by 12 rusted bolts.

Beneath it is the Kola
Superdeep Borehole.

It is the deepest
human-made hole on Earth

and one of the 20th century's

greatest scientific
accomplishments.

In the 1970s, the Soviet Union

attempted to break the world
record of deep drilling,

to go well past the typical

three to four to five
kilometers of deep drilling

that is normally done
for oil, for example.

And their aim was to achieve
a depth of about 15 kilometers.

It's not a very big hole.
It's only nine inches wide,

but it's a testament to what
is possible with technology.

The Kola Superdeep Borehole is
just a really thin, narrow hole

straight down into the Earth.

One of the reasons why
they made the hole that shape is

that the wider the space
it is that you're drilling,

the more resistance
that you run into.

And as you dig down deeper,
strange things start to happen.

One of the biggest obstacles
to digging that hole

was, the temperature increases
about 60 degrees Fahrenheit

for every kilometer
that you go down.

These teams found,
when they were drilling down,

that the rock started
to behave like plastic.

And that the solid rock
was actually gumming up

the works of their drills.

ROBERT SCHOCH:
There's so much pressure there,

there's so much heat there,

eventually
they could drill no deeper

and they had to abandon it.

And since then,
there has been no project

that has gotten deeper.

It's actually the deepest hole
that has ever been drilled

to this day by humans.

SHATNER:
By the end of the project,
in 1995,

scientists had recorded reaching
an unprecedented 12,000 meters,

or 7.6 miles,
deep into the Earth's crust.

But despite this remarkable
feat of engineering,

the Kola Superdeep Borehole
penetrated less than one percent

of the 4,000 miles between
the planet's surface

and inner core.

If we've only been able
to explore a tiny portion

of Earth's crust,
what do we really know

about the inner workings
of our planet?

Since time immemorial,
people have created mythologies

and stories to explain
what was underneath our feet.

However, the first person
to use mathematics and physics

to decode the mystery of
the Earth was Edmond Halley,

famous for discovering and
understanding Halley's Comet.

He thought that the Earth
might be hollow.

CLARK:
Edmond Halley was really
interested in the idea that

there were basically
these concentric shells

inside the Earth

and that each one of these
shells had different properties.

They could spin independent of
each other inside of the planet.

When we think about
something like Halley's theory,

we forget that things
like the Hollow Earth

were valid scientific thought.

It wasn't just
a science fiction idea.

It was one that was still
the best explanation at the time

to try and fit the data
and information they had.

And the reality is
different from that,

but it's still an exciting idea.

SHATNER:
While we now know our planet
is not hollow,

Halley's concept of concentric
layers has become

an accepted theory.

For decades, experts have
proposed that our world

is comprised of four parts:
the inner core,

the outer core,
the mantle and the crust.

But how did we determine this

if we can barely scratch
Earth's surface?

LAU:
Today, we analyze the way
that waves from earthquakes

move through the Earth

and we see how they bounce off
of certain rocks

or are deflected
deep underground.

And that tells us about
the structure,

what the interior
of the Earth looks like.

But at the same time,
it's interesting that we've

never seen the inside
of our world in person.

SHATNER:
While it may be impossible
for humans to physically reach

the center of the Earth,
we have made some

fascinating discoveries

in the world's deepest mine.

The deepest mine is located

in South Africa,
and this is deep.

It's about four kilometers deep,

But the excitement is all about
the unintended discoveries.

For example, about two
and a half kilometers down,

a whole new species of
bacteria was discovered.

And this bacteria is the only
living thing down there.

And so, you don't know
what you're gonna find

until you get down there
and take a good look.

SHATNER:
Will we ever really know
what lies beneath our feet?

Our understanding of what
our planet is made of

is ever-changing.

For example, in February 2023,

geologists at Australian
National University

made a stunning announcement

when they detected a surprising
fifth layer that lies

within Earth's core.

There is now
a innermost inner core,

inside what we thought of
as being the core.

Part of why this is exciting
is that this is very, very new.

So we don't know
where this is gonna go.

We're still
in this age of discovery,

and really, there's some
very fundamental information

that we still need to learn
about the Earth's interior.

KLINGER:
The more we're able to explore
the depths of the Earth,

the more we're able
to understand

about the planet itself,

about the cosmos

and our place in it.

Will we ever be able to reach
the center of the Earth?

(chuckles)
It's fun to think about.

But experts warn there are

more pressing mysteries
to explore,

such as our planet's
relationship with the Sun

because, while the Sun
is vital to our existence,

it also has the power

to destroy all life
as we know it.

SHATNER:
While excavating
a construction site,

workers unearth
a massive kauri tree

that has been buried
in the soil of an ancient swamp

for thousands of years.

Fused into
the preserved tree rings

are clues to solving
a 42,000-year-old mystery

of one of the deadliest
solar events

ever recorded on our planet,
called the Adams Event.

BEN McGEE:
The Adams Event is

what scientists think is
a small magnetic pole reversal

around 42,000 years ago.

And why is this important?

Well, when a magnetic field
flips on our planet...

...it effectively goes away
for a little while.

And this lets
solar radiation come in

and, basically,
wreak havoc around the globe.

HAQQ-MISRA:
Earth has a magnetic field
with two poles.

The way you think
of a bar magnet--

there's a north pole
and a south pole,

and it's roughly aligned

with our geographic
north and south pole.

Earth's magnetic field is
like a protective blanket

that protects our planet
from dangerous solar flares

coming from the Sun.

In order to power
a magnetic field,

a planet needs a molten hot core

that is full of electrically
charged particles

that are spinning around.

And so, this is how the Earth
generates its magnetic field.

Honestly,
when it comes to planets,

we've got it pretty good.

The Earth's magnetic field

is our force field.

SHATNER:
But what happens if
our force field is unstable?

When geoscientists

at the University
of New South Wales

in Sydney, Australia

found unusually high levels
of radiation from the Sun

baked into the rings
of the ancient kauri tree,

it revealed that Earth's
last magnetic field disruption--

42,000 years ago--

caused drastic
and deadly consequences.

McGEE:
Without the Earth's
magnetic field,

you could have had intense
charging of the atmosphere...

...leading to auroras...

...blue sky lightning...

... and increased
radiation doses.

And it's possible
that the Adams Event caused

widespread ecosystem disruption

and even extinction
as the Earth adjusted

to, suddenly, a world
whose deflector shield

against all the radiation
from the rest of the universe

suddenly went down.

SHATNER:
It's estimated
that during the Adams Event,

the Earth's magnetic field
shrank to as low as five percent

of its current strength,

exposing the planet
to powerful solar winds,

galactic cosmic rays,
and unfiltered radiation...

...that destroyed
the ozone layer.

McGEE:
Some have hypothesized

that the Adams Event
contributed

to the extinction
of the Neanderthals,

possibly because their pale skin
may not have been able

to withstand increased levels
of ultraviolet radiation.

Or maybe they were just
not as adept at adapting

to changes in the ecosystem.

But in either case, it looks
like this had something to do

with taking out
the Neanderthals.

BETH SHAPIRO:
We don't really know why it is

that Neanderthals became extinct

by around 39,000 years ago.

But perhaps they were just
simply not as well-adapted

to the extremely dramatic shifts

that were happening to their
environment at the time.

SHATNER:
According
to the U.S. Geological Survey,

the reversal of Earth's
magnetic fields are random

and can occur as often
as every 10,000 years

or as infrequently
as every 50 million years.

It's hard to comprehend
how such an event

would alter life as we know it

and transform our source
of life on this planet

to a reaper
of global destruction.

The Sun's energy is the source
of all life on Earth.

The Sun, though, doesn't
entirely help life on Earth.

It can also threaten it.

The Sun gives off
ultraviolet radiation,

and that can be extremely
damaging to life on Earth.

It can destroy DNA.

As the Adam's Event showed,

the Sun is at once
the source of light

and heat and warmth

and, ultimately,
of life on the Earth,

but the Sun is also

this raging monster...

...in that when we drop
our planetary defenses,

we are in danger.

SHATNER:
Will a solar disaster
like the Adams Event

strike the Earth again?

It's among
the many possibilities

that could change life
as we know it.

And as we seek to understand
the history of our world,

many have turned to the stars

to see if there could be
another planet

just like Earth
somewhere in the universe.

SHATNER:
Aerospace company
Blue Origin prepares

to launch a spacecraft

that will take four civilians
on an 11-minute trip

into orbit around Earth,
and I had the privilege

of being one
of those passengers.

After we blasted into space

and entered zero gravity,

looking down
upon our planet was perhaps

the most exhilarating
experience of my life.

Oh, wow.

When we returned to Earth...

(group cheering)

...I felt overwhelmed
by a deep sense

of awe and wonder.

(crying): It was
the most profound experience

I can imagine.

I-I'm so filled with emotion
about what just happened.

I-I just...

It's extraordinary.

Extraordinary.

Now that I've seen
our world from space,

it's hard for me to imagine
that there could be a planet

as extraordinary as Earth.

But on the other hand,
the universe is a vast expanse

filled with
a countless number of planets.

So it begs the question,

could there actually be
another Earth?

In 2014, scientists got
one step closer to the answer,

when they identified the first
potential Earth-like planet,

which is 582 light-years
away from Earth

and has been named Kepler-186f.

Kepler-186 was one
of the first rocky planets

detected orbiting another star.

This is a planet

that's in the outer region
around its star,

so it doesn't receive
as much light

as the Earth does
from the Sun...

...but enough that

the surface of that planet
could be habitable.

SHATNER:
In addition to Kepler-186f,

scientists have discovered
54 more Earth-like planets.

But while these worlds may bear
some similarity to ours,

that doesn't mean we've found
another Earth just yet.

PYLE:
How truly unique Earth is
is still kind of a mystery.

We've got tools
that could help us

to try and figure out
how many other

Earth-like planets
might be out there.

But, ultimately,
we're not gonna know

until we move further out.

We're gonna have
to send probes there

to really understand what
these planets are all about.

SHATNER:
While we look to find

other planets like Earth
out in the vast universe,

our blue marble offers
plenty of mysteries

just waiting
for humanity to solve.

CLARK:
The mystery
in understanding the Earth is,

on one hand, we know that

the fundamental building blocks
that made the Earth are

spread throughout the universe.

On the other hand,

we don't see life
in other places.

The exciting thing for us
as scientists is when

the Earth does something new.

We're able to take that evidence

and add a new piece
of the puzzle

of trying to understand
what makes the Earth tick.

It seems that, in spite
of everything we've learned,

Earth still holds
many mysteries.

If we continue to investigate
the origins of our world,

will we be able
to fully understand

what makes it so special?

Let's hope so because
our future may depend on it.

But for now,

Earth's place in the universe
will remain...

unexplained.

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