All language subtitles for How.the.Universe.Works.S02E06.480p.HDTV.x264-mSD.HI

Narrator:
Comets are a celestial mystery.

They are messengers
from deep space itself --

time machines
from the early Universe.

Narrator: Comets could unlock the deepest
secrets of our cosmos.

If we can establish
a correlation

between amino acids on comets
and life on Earth,

that would be one of the most
significant findings in science.

Narrator:
They threaten our very survival.

We're talking about something
the size of a mountain,

so the amount of energy

that this thing would release
upon impact is devastating.

Narrator:
Yet without comets,

we might not be here.

We may owe
a great cosmic debt to comets

because
they may have been responsible

for bringing the chemicals
that we require for life

to the Earth.

♪ How the Universe Works 2x06 ♪
Comets
Original Air Date on August 15, 2012

== sync, corrected by elderman ==

[ dramatic music plays ]

Narrator: A dramatic streak
of light across the sky,

a passing comet
is an astonishing sight.

Dr. Plait: They're beautiful,

these fuzzy, glowing balls
with the tail coming off.

It's really something.

You just don't get to see
an object like that very often.

Comets are extraordinary.

If you get to see a comet
for the very first time,

it'll stick with you forever.

The journey of a comet as it
sails through the solar system

is the most fantastic
of all astronomical objects.

Narrator: It loops in toward the
Sun from the depths of space --

an odyssey that can last
millions of years.

Many pass by the Earth so often,
they're almost like old friends.

Every comet is a frozen mass
of rock and ice

several miles across.

But all we see
is a glowing ball of light...

And a long, sweeping tail.

Yet comets
are more than cosmic fireworks.

They could help unlock

some of the deepest mysteries
in science.

We're trying to figure out, as
scientists, where we came from,

and that means everything from
the beginning of the Universe

to the beginning of the solar
system to how life started.

Comets really fit into that.

They really give us clues about
how the solar system formed.

If we can't understand comets,

we don't understand
how we got here.

Narrator: Comets may even be
the source of life itself.

We may owe our existence
to the fact that comets,

billions of years ago,

came to Earth and brought the
necessary ingredients for life.

Narrator: They can also cause
enormous destruction.

Comets could kill us all.

If a comet were
to hit the Earth, watch out.

It would be a planet-buster.

It would be an object sufficient
to wipe out

all life as we know it
on the planet.

Narrator: Learn about comets,

and just maybe we will learn
how to survive them...

...and begin to understand
how the Universe works.

Dr. Plait:
When we study them,

we're learning
what the solar system was like

when it was first forming.

And we can learn about what
other solar systems were like,

as well.

And, hopefully, that will teach
us a tremendous amount

about how stars form
and how planets form

and how comets themselves
were originally formed.

[ Dramatic music plays ]

Narrator: Comets date back to
the birth of our solar system

4 1/2 billion years ago.

They were made by the same force
that created the solar system --

gravity.

It began
in a maelstrom of chaos.

A giant cloud of gas and dust

collapsed to form
a whirling disc.

Close to the Sun,
it was burning hot.

But further out,

it was cool enough for gas
clouds to condense and freeze.

Ice crystals fused
with grains of dust.

They slowly pull together
into larger and larger masses.

Over time,
these sort of snowballed,

like a snowball
rolling downhill,

picking up more and more
and more material.

Narrator: Eventually,
they formed gas giants

like Jupiter and Saturn.

But not all the debris in
the disk turned into planets.

Trillions of lumps of dirty ice
were left behind -- the comets.

You could almost think of comets
as sort of the frozen leftovers

of the formation
of the solar system.

Narrator: They're almost
unchanged to this day.

They're pristine time capsules,

and if you could crack one open
and see what was inside,

you could literally see

what the solar system
was first made out of.

That's remarkable.

Narrator:
But the comets did not stay put.

Several hundred million
years later,

the solar system plunged
into turmoil once again.

Encounters with debris pulled
the gas giants out of position.

The giants' immense gravity

then hurled comets
in every direction,

flinging trillions of tons
of material

from the dawn
of the solar system

into the cold
outer reaches of space.

Some comets settled in a region

4,000 million miles
from the Sun --

the Kuiper Belt.

But most were tossed
even farther out

to form a giant sphere
around the entire solar system.

We call it the Oort cloud.

This is a region
of our solar system

that's farthest away
from the Sun.

The Sun is just a tiny
little dot, one of many stars.

And the whole area of space
around you is virtually empty.

There's nothing there --
very little.

And just occasionally,
you'll find the odd comet

floating out there
in deep freeze --

cold, dark, and very much alone.

Narrator:
In this remote ice cloud,

there are more
than a trillion comets.

They can take millions of years
to orbit the Sun.

But they don't always stay here.

The orbit of every comet is a
delicate gravitational balance.

The smallest nudge
can tip the scale.

Most comets
spend their entire life-span

billions of miles from the Sun

motionless, inert,

simply waiting
for something to happen.

But then, perhaps,
a random collision takes place.

Perhaps a passing star
nudges it,

and then the gravitational
force of the Sun

inevitably pulls it toward
the inner solar system.

Narrator: Gravity, the force
that created the comets,

then flung them
to the edge of the solar system,

now pulls them back in.

Our comet begins
its epic odyssey

to spread life or death
across the solar system.

Narrator: More than a trillion
comets circle the Sun

at the frozen edges
of our solar system.

But many do not stay here.

The smallest
gravitational disruption

can knock them
out of their orbit.

It could be
a nearby star going by.

It could be us going through
a denser part of the galaxy.

Anything that just gives

a little gravitational hit
to a comet

can cause it
to fall in towards us.

Narrator:
Our comet has been disturbed.

Now the Sun's immense gravity
takes over.

You could think of the gravity
of our solar system

sort of like being a hillside.

At the bottom, there's the Sun.

And comets are way
at the top of that hill.

When they get dislodged, there's
only one way for them to go.

They have to fall down in
towards the Sun.

Narrator: Our comet
accelerates towards the Sun,

but its path
is far from straight.

Gravity from the planets
can throw comets off course

or out of the solar system
completely.

If they escape these obstacles,

comets continue their journey
toward the Sun.

Now they begin one of the most
remarkable transformations

known to science.

Dr. Thaller:
A chrysalis to a butterfly.

They become
the most spectacular things

the Universe has to offer.

Narrator: As it passes Jupiter,
our comet begins to change.

As it starts to move
a little bit faster

and starts getting closer
and closer to the Sun

and it starts feeling
the heat of the Sun,

that's when things
really start to change.

Narrator:
500 million miles from the Sun,

heat brings our comet to life.

Frozen gases start to vaporize.

Grains of ice and dust
rise from the surface.

As the comet
continues to approach the Sun

and gets warmer,

more and more gas is released.

The comet becomes a fuzzy ball.

There's a solid part in there,
but it's surrounded

by a much larger
sort of cloud of material.

Narrator:
This cloud of dust and gas

forms an atmosphere,
or coma, around the comet.

And it also creates
the comet's huge tail.

It's all driven by the Sun,

and it's not over yet.

Dr. Thaller: There's something
called the solar wind.

It's actually a huge wave
of charged particles

originating from the Sun.

This fills our solar system,

and as a comet begins to move
further and further

in towards the Sun,

the solar wind gets stronger.

Narrator:
Like a cosmic hurricane,

the solar wind blasts
gas molecules

from our comet out into space.

They form a second giant tail.

The solid part of the comet

might only be
a few miles across,

and the fuzzy part might be

a few thousand or tens
of thousands of miles across.

The tail that gets swept back

as that material is blown off
by the solar wind

can be millions or
tens of millions of miles long.

Narrator: Our comet hurtles through space
at 50,000 miles an hour.

It's about to enter the most
violent phase of its journey.

200 million miles from the Sun,

water ice begins to vaporize.

The ground would start
to shift and quake,

and as the material beneath
my feet is literally thawing,

we'd have great big jets
of carbon dioxide

and water ice
starting to come out,

and that would not be a very
good place to be standing.

Narrator:
The surface cracks open.

Gases explode.

Debris fires in all directions.

The force of these eruptions

makes the comet tumble
erratically.

Every jet that turns on

is literally like a little jet
engine attached to the comet.

Narrator:
Like a dragster on a racetrack,

our comet explodes to life.

[ Engine revs ]

Incredible speed,

irresistible energy,
and a vast plume of debris.

Our comet transforms
into a cosmic hot rod,

but speed and energy
are a volatile mix.

Our comet could blow apart
at any moment.

The cloud around our comet
is now bigger than Jupiter.

Its tail stretches
for 100 million miles.

An object 4.5 billion years old
emerges from the dark.

Every arrival of a new comet is
like a gift from the Universe.

We've never seen this little bit
of the solar system before,

this little building block,
this little baby picture.

It's completely new to us.

Narrator: It's a chance to study
the origin of our solar system,

and what we're learning
is a revelation.

Comets are far more hostile
and alien than we imagined.

Narrator:
With modern telescopes,

we can study comets
in more detail than ever before.

But to really understand them,

we need to get close
to the very heart of a comet --

its nucleus.

One of the holy grails of comet
science is to really understand

what is in a comet's nucleus.

What is actually on the surface?

What is
the chemical composition?

What are the characteristics of
the rocks and the materials --

the volatiles
that are on that surface?

The nucleus is
the fundamental building block

of the solar system

that we, as scientists,
really want to investigate.

That's where
the mysteries really are.

Narrator: There have been more
than a dozen missions to comets

in the past three decades.

Every one of them
has been a revelation.

We've learned
about the chemistry of them.

We've learned about

the physical interaction
they have with the Sun.

We've learned about their
physical surface, their terrain,

and how they're different,

even if you were to go from
one spot on a comet to another.

So, we're really learning

that these things
are worlds unto themselves.

Narrator: Scientists thought comets
were white like a snowball.

That changed in 1986,
when the Giotto Space probe

beamed back
these images of Halley's Comet.

For the first time in history,

we had a snapshot of
the very center of that comet,

that comet that entered
human history on many occasions,

and we found a cold, dead world.

We found an object
shaped like a peanut.

Narrator:
Halley was no snowball.

A thick layer of black dust
covered its surface.

There were pits and hills,

and Halley was 9 miles long,

far bigger than anyone expected.

Scientists thought
that all comets were the same.

They were wrong.

In 2004, the Stardust probe flew
into the tail

of comet Wild 2

and captured thousands
of tiny dust particles.

When Stardust brought
those samples back on Earth,

we realized that, in fact,
every comet is a unique object.

Just like
every planet is different,

it looks like
every comet is different.

It has its own history to tell.

Different materials
went into its formation.

Different heat sources
were injected into its interior.

Different chemical processes
and geologic processes occurred.

Each one is a unique world
waiting to be explored.

Narrator:
Some comets are truly strange.

These are real images
of Hartley 2,

a comet so weird,

it snows.

Dr. Mainzer:
It's so strange.

We were able to see

that there are golf-ball-sized
chunks of dry ice

that are following
the comet around

up to a million miles away
from the nucleus.

This thing
is just making a big mess.

[ Chuckles ]

Hartley 2 is just amazing!

It looked like you were
in the middle of a snow globe

and you shook it up and there
were all these little things,

kind of like flies
buzzing around food,

just kind of floating out there.

That's just not right.

Narrator: Hartley 2
is a hyperactive comet.

It tumbles faster
and spits out more debris

than most others its size.

Comets are alien worlds.

On comet Tempel 1,

there are smooth plateaus...

Craters,
and cliffs 60 feet high,

layers of rock
lie on top of each other

like a stack of pancakes.

Each comet seems to have
its own unique history.

Tempel 1 gave scientists
their biggest breakthrough.

In 2005,
the deep impact space probe

slammed a projectile
into its surface.

The explosion dug out a crater

150 yards across.

Talk about
a spectacular 4th of July.

I mean,
can you imagine anything better?

We actually blew a hole
in a comet.

I mean, that's got to be
one of the more amazing things

that NASA has ever done.

Narrator:
The material the impact ejected

allowed us to see
inside a comet's nucleus

for the first time.

Thaller:
It was completely unexpected.

We found things like rubies
and peridot, gemstones --

tiny little things
inside the comet.

And we found
all kinds of organic molecules,

the very sorts of things
we're made of.

Narrator:
Scientists now believe

that comets play a critical role
in our Universe.

Kaku: Where do the ingredients
of life come from?

Where were they all mixed
together?

Where did all this liquid water
come from?

Comets could hold the key

to understanding
the nature of life itself.

Narrator: But opportunities to
study them up close are rare.

Our comet is now moving
at incredible speed

toward a place where no
spacecraft could ever survive --

the Sun.

Narrator:
4 billion years ago,

gravity hurled comets to
the edges of our solar system.

The same force
can pull them back in.

Our comet passes Earth

and enters the most violent
stage of its journey.

It rockets toward the Sun
at 100,000 miles per hour.

The surface of the comet
is now sizzling,

sizzling with activity.

Blistering temperatures
are being created.

Enormous geysers
of ice crystals and gas

being shot off the surface.

Jets are erupting all over
the place, it's tumbling,

the rotational state
is changing,

and the very surface is kind of
cracking up underneath our feet.

Narrator: Inside the comet,

pockets of gas explode
and fling huge rocks into space.

Dr. Mainzer: It's losing mass.

It's shrinking.

And as we get closer and closer
to the Sun

and more and more
of the volatiles

are starting to come off
of its surface,

this can actually change the
rotational state of the comet.

It can make it tumble.

It can actually even push it
in its orbit.

It can actually change the orbit
of the comet.

Narrator: Comets can shed 50 tons
of ice and gas every second.

Ormous pressures build up
inside the nucleus.

Kaku:
It could become unstable.

It could even break apart
into pieces at any time.

Narrator: As comets reach
their closest point to the Sun,

their existence
is on a knife edge.

Many will not survive.

We've been able to actually see
images of comets

just getting
swallowed up by the Sun,

and you can actually see them
just pelting in there.

And the whole body,

whether it's a mile across
or 10 miles across,

just gets completely
and utterly destroyed.

Narrator: A solar observatory recorded
these extraordinary images.

They show small comets
called "sun grazers"

diving towards the sun.

[ Dramatic music plays ]

Here they're exposed
to immense gravity

and torched by
the ferocious heat of the Sun.

Many are vaporized.

Even in deep space,

vast explosions
can tear comets apart.

In 2007, comet Holmes was
heading away from the Sun

when something extraordinary
happened.

In less than a day, it grew
half a million times brighter.

The cloud around it
ballooned into space.

It's actually relatively
common for a coma --

the fuzzy part around a comet --

to expand large enough
to be bigger than Jupiter,

100,000 miles across.

But that can take days and weeks
and months to build up.

To have a single event,
something that happened,

boom, all at once,
some catastrophe

to create this shell
around comet Holmes

that could be bigger
than Jupiter is amazing to me.

We had never seen
something like this before.

In fact, the coma of the comet

was actually larger
than the Sun itself.

Briefly,
it was the largest object

in the entire solar system,

something
that was unprecedented.

Narrator: Without warning,
comet Holmes blew apart --

the largest cometary explosion

ever recorded.

The debris stretched
for a million miles.

What caused it is still unclear.

One theory is
that perhaps comet Holmes

slammed into an asteroid
of some sort,

creating this gigantic megaflare
in outer space.

Another possibility is
perhaps the comet was unstable

and perhaps
there was an explosion

caused by expanding gas and
ripped the entire comet apart.

At the present time,
we simply don't know.

Narrator: The life of all comets
hangs by a thread.

Our comet survives
its encounter with the Sun...

but it's paid a price.

Its geography
has been totally rearranged.

Huge chunks, mountaintops'
worth, of rock have disappeared.

An object which could be
perhaps 10, 20 miles across

has lost literally hundreds,
perhaps thousands of tons

of rock and ice on its journey.

Narrator: As our comet
leaves the Sun behind,

activity on its surface
subsides.

On its outward journey, a comet
gradually begins to shut down.

It becomes cooler, less active,
the jets begin to turn off,

the coma begins to blow away.

And you're left with this
little ball of ice and dirt.

Narrator: It returns
to the depths of space,

dormant once again.

But the Sun
is just one of many challenges.

Comets must also survive

the gravitational pull
of the planets.

Our gravity is way too small to
have any effect on this comet.

But Jupiter
is a very large planet.

It has 300 times
the mass of the Earth.

If the comet passes within even
a few million miles of Jupiter,

that can change its orbit.

Narrator: The consequences
can be catastrophic.

In 1994, a comet
called Shoemaker-Levy 9

flew too close to Jupiter.

Scientists watched the planet's
immense gravity tear it apart.

The remains
headed straight toward Jupiter.

Dr. Mainzer: Many people thought
that the impacts

wouldn't do anything to Jupiter,

that Jupiter would just sort of
swallow it up without a burp.

And that's
not what happened at all.

Narrator:
21 comet fragments

smashed
into Jupiter's atmosphere.

Each impact released more energy

than all the world's
nuclear arsenals combined.

Comet Shoemaker-Levy 9 was not
a particularly massive comet,

and it wasn't
even a very dense one.

It actually had the consistency
of cotton candy.

You could have pulled bits of it
apart with your fingers.

But this rather tenuous
little icy creature

created
unimaginable destruction.

Narrator: The impacts
hurled plumes of debris

thousands of miles high...

and scarred Jupiter's atmosphere
with dark lesions.

The event rocked
the scientific community.

To actually see it
for ourselves,

to actually see
the immense destructive power

by an object that's really
not that much bigger than a hill

was really pretty terrifying.

Even though we knew the math,

to see it for ourselves
was amazing.

The Shoemaker-Levy 9 impact
really woke astronomers up

to the fact
that impacts can happen now

and they can happen here.

Narrator: If a comet just a few
miles across hit our planet,

the result
would be catastrophic.

Tidal waves
would devastate the land.

Debris would rain from the sky.

Life as we know it would end.

Yet comet impacts
can also be a creative force.

Narrator:
Across the Universe,

comets cause
massive destruction.

They could be moving
50 or more times faster

than a rifle bullet.

And we're talking
about something

the size of a mountain.

So, the amount of energy

that this thing would release
upon impact is devastating.

Narrator: But they're
not always destructive.

They have another side.

Scientists believe
they can shape entire worlds.

This is Titan --
the largest of Saturn's moons.

It's the only moon in our solar
system with a thick atmosphere.

Rivers and lakes
of liquid methane

cover its surface.

Titan was transformed by comets.

Radar images reveal a moon
shaped by a blizzard of comets

that rained down
over millions of years.

Each comet
vaporized when it hit,

releasing gases
from inside its nucleus.

Gradually, they built up
a rich organic atmosphere

and this strange
liquid landscape.

Comets turned a space rock
into an earth-like world.

Comets, in some sense,
are the ultimate engineers

of the solar system.

Cometary impacts could give us
the chemicals

which give us the atmosphere
not just of Titan

but even, perhaps,
the Earth itself.

Narrator: So, if comets have the
power to reshape entire worlds,

what part did they play in
the history of our own planet?

To find out,

we need to get closer
to a comet than ever before.

We need to land on one.

In March 2004,
the Rosetta mission launched.

The Rosetta mission is named
after the Rosetta stone

because just like the stone

gave linguists the keys
to the ancient language,

we're hoping that the comet
will give us the keys

to understanding
the ancient solar system.

Narrator:
November 11, 2014,

will be a landmark
in space exploration.

For the very first time,

a spacecraft will touch down
on the surface of a comet.

Previous missions to comets
were basically flybys,

and they basically gave us
tantalizing evidence

that there was a greater mystery
yet to be solved.

Now we're gonna land on a comet.

We're gonna be
up close and dirty

with a live comet
streaming through outer space,

and this is unprecedented.

Narrator: Rosetta is
around the size of a car.

It's flying through space
at 20,000 miles per hour.

It's heading for this...

...a comet with a nucleus
3 miles wide

orbiting the Sun
every 6 1/2 years.

A robotic lander
will drop down to the surface,

beginning the most detailed
study of a comet ever attempted.

It's going to look at
what the surface looks like.

It's going to take samples.

It's going to look
at the terrain.

It's going to be able to
actually probe inside the comet

and see what it's made of
and how it's put together.

We're hopefully going to learn
more from this mission

about one comet

than we have about
just everything we've known

about comets for centuries.

Narrator: Rosetta should answer
some very simple questions.

Dr. Alexander:
Is it porous?

Is it like a sponge?

Is it like a bunch of tubes?

Is it like a snowflake,

you know, with this sort of
fairy-castle structure?

These things
will help us to understand

how the heat flows within

and maybe what causes
certain portions of it

to become a jet
and other portions not.

Narrator:
But this is just the beginning.

For an entire year,
Rosetta will study the comet

on its epic journey
'round the Sun,

using technology so advanced,

it mimics the five human senses.

Dr. Alexander: We've got
instruments that can see.

We've got a kind of
an ultrasound experiment,

instruments that are
the equivalent of your hands.

So, we'd like to understand
everything possible

about this comet's journey
around the Sun

from when it's quiet to
when it's at its most active.

Narrator: But we'll have to
get there first.

Just to reach the comet,

scientists must overcome
enormous technical challenges.

Rosetta must hit a target
just 3 miles wide,

traveling
at 34,000 miles per hour.

Landing on it
will be even harder.

Comets have very little gravity.

There's not anything that you
know is gonna pull you down

to the surface.

And there's no atmosphere,

so you can't unfurl a parachute

and just sail down
until you touch down.

You've got to figure out a way

to get your lander to actually
reside and rest on the surface.

Narrator: Technicians
have an ingenious solution.

The lander is equipped with
shock absorbers and a harpoon.

Dr. Alexander: When it makes
contact with the surface,

at the same time,

the harpoon will be released
down into the substrate,

and it will have prongs
that will open

that will prevent it
from coming back up.

Narrator:
Rosetta will attempt to solve

some of science's
deepest mysteries.

We would very much like to know

why is it that Earth has
liquid water and so much of it

compared to any place else
that we've ever seen.

So how is it
that the water got here?

Now, there is a theory that says

that comets delivered the water
to the Earth long ago,

but the question is,
can we actually prove it?

Narrator: To find out,

the lander
will collect water molecules

to compare with water
from Earth.

But scientists
hope to go even further.

We're on the brink of making
an extraordinary discovery.

We may find proof

that life itself
has an extraterrestrial origin,

that it was brought to Earth
by comets.

Narrator:
Life has existed on our planet

for at least
3 1/2 billion years.

But we still don't understand
its beginnings.

We used to think
life originated on Earth itself,

that volcanic gases
and water vapor

formed oceans and an atmosphere.

Lightning added the creative
spark for early life to begin.

Now we think that's wrong,
and the evidence is in space.

In 1997,
comet Hale-Bopp appeared,

one of the biggest and
brightest comets ever recorded.

Scientists found it was packed
with water, gases, and carbon --

the basic ingredients for life.

That discovery
raised profound questions.

We're all used to the idea that
life originated here on Earth,

and it probably did --
at least, complex life.

But where did
the building blocks come from?

Where did the water
that makes up our body,

the organic molecules that make
up the very essence of life --

they actually may not have been

intrinsically part of the Earth
to begin with.

They came from somewhere else.

[ Flutes play dissonantly ]

Narrator: Hale-Bopp suggested
that the raw materials for life

might have
an extraterrestrial origin.

Since then, scientists
have found further evidence.

Astrobiologist Dante Lauretta

discovered that dust from comet
Wild 2 contained minerals

that could only form
in heat and liquid water.

Lauretta: We had the sulfide minerals,
we had iron oxides,

we had carbonate minerals --

which are the same kind of
materials that marine organisms

use to build their shells --

unlike anything we thought
was possible to be formed

in the early solar system.

Narrator:
Scientists have even found

that comet Wild 2
contains amino acids.

That's incredibly exciting,

because amino acids are
the building blocks of proteins,

and proteins
are essential biomolecules

for all life on Earth.

Narrator: These discoveries
have transformed

our understanding of comets.

Many scientists now believe

they're more than
just frozen time capsules.

Perhaps they play a central role
in the history of our planet.

We have learned
from a study of a single comet

and the results
of the stardust mission

that they are
complex chemical laboratories

where the ingredients of life
could form.

These materials
likely did not arise naturally

on the surface of the Earth

from processes on our planet.

Instead, they had to be
delivered by these messengers

from the outer solar system.

Narrator: The idea
that we may owe our existence

to comet impacts is astounding.

But not everyone is convinced.

There's pretty good
circumstantial evidence

that a comet might have been
important to life,

but we don't really have --

if we're C.S.I.,

if we're
the comet science investigators

trying to prove it,

we haven't got the proof
lined up yet.

It's quite possible
that what we have out there

has nothing to do with life
as we know it on Earth.

Narrator: Scientists hope the Rosetta
mission will resolve the issue.

If we can establish
a correlation

between amino acids on comets

and the amino acids
we have on Earth, life on Earth,

that would be one of the most
significant findings in science.

Narrator: The story of life on Earth
began 4 1/2 billion years ago.

When our planet formed,
it was a barren, hostile world.

700 million years later,

the solar system
plunged into turmoil.

Gravity ripped comets
from their orbits

and hurled them
in all directions,

many into
the inner solar system.

They rained down
on the early Earth

for 300 million years.

They released
gases and organic material,

creating an atmosphere
and the oceans.

Finally, life could begin.

It's a dramatic story.

But is it true?

Only time is gonna tell,

if we keep studying
these mysterious objects,

whether or not we can really pin
down exactly the mechanisms

and find out
how it all got started.

Dr. Alexander:
In 100 years' time,

hopefully,
we'll look back and say,

"wouldn't it be cool to
have been living at that time,

"to be a witness,

to be one of the first to make
these incredible discoveries"?

Narrator: In the meantime,

the search for proof continues.

I can't say for sure
if comets brought

all of these raw ingredients
to the Earth

and that we evolved
from these materials,

but it's certainly possible,

and it's absolutely poetic

to think that we came
from out there.

[ Dramatic music plays ]

== sync, corrected by elderman ==