All language subtitles for The universe S06E05 Crash Landing on Mars

Male narrator: In the beginning,
there was darkness,

and then, bang,

giving birth to an endless
expanding existence

of time, space, and matter.

Every day, new discoveries
are unlocking the mysterious,

the mind-blowing,
the deadly secrets

of a place we call
The Universe.

Throughout its more than
4 billion years of existence,

planet Earth has endured
some extremely rough days.

But what were the very worst?

Was it a shattering encounter
with a planet

that got too close?

- Had anything been there,

it definitely
wouldn't have survived.

Narrator: Or a hot shower
of deadly rays

that almost scoured the planet
clean of life?

- The blast from the impact
would have laid waste

a thousand miles
in every direction.

It's literally the sound
heard around the world.

Narrator: From runaway volcanism
that led to vast extinctions

to tiny microbes that triggered
a global deep freeze,

life has teetered
perilously close to the brink

time and time again.

- More life died then
than any time since

and maybe any time before.

This was the biggest
and the baddest of them all.

Narrator:
Are the darkest hours behind us

or lurking
in the distant future?

Take cover as we count down

the seven worst days
on planet Earth.

[dramatic music]

J J

You may think you've had
some really rough days...

Stuck in gridlocked traffic,

dodging a sea of humanity
on the way to work,

or trapped
in a torrential downpour

or blizzard.

But they can't even begin
to compare

to the seven worst days
on planet Earth.

- Throughout its history,

Earth has experienced
some really bad days,

days that have killed off life,
created life,

restructured the planet
as a whole.

All of this together has formed
the Earth that we live on today.

But during
those really bad days,

we certainly wouldn't want
to be here.

- From our point of view,

Earth has been through
some pretty rough days,

catastrophic impacts
that have really changed

the face of the planet

and changed the makeup
of the flora and fauna—

The animals and plants—
on the planet.

Narrator:
One of Earth's worst days

came early in its history,

when an uninvited guest
barged into our neighborhood

and threatened
to destroy the planet

before life had a chance
to blossom.

Blasting in as the
seventh-worst day on Earth...

About 4 1/2 billion years ago,

our solar system
was a battle zone.

Giant boulders collided
and coalesced

to form planets.

Infant Earth
took hit after searing hit.

- If we could somehow magically
transport ourselves back in time

to be on the early Earth,
it'd be very interesting,

I think, to watch one
of these large-impact events.

The surface of the Earth itself
was probably heated

to a near molten state.

The atmosphere
would be very dusty.

It would be very hot.

So it would be a very alien
world to us,

one that we actually
couldn't survive on

just standing
like we are here today.

Narrator:
Pounded by incoming rocks,

Earth slowly grew
to nearly its present size,

developing a solid crust,
a thick mantle, an iron core,

and a hot, stormy atmosphere.

Some speculate that life
may have taken a tenuous hold,

but then.. disaster.

A neighboring planet named Theia

had been edging
into Earth's orbital path.

The intrusion ended in the most
disastrous way imaginable:

a collision of worlds.

- It was a very violent event.

Imagine something
the mass of Mars,

about 10% the mass
of the Earth,

whacking in from space
and blowing all its material in.

Whatever was on the Earth
at that time

was radically changed
by this event.

- When a Mars-sized object
whacked into the Earth,

that was a bad day
on Earth.

Had anything been there,

it definitely
wouldn't have survived.

Narrator: It took hours

for the full scope
of the catastrophe to unfold.

As the cores
of the two planets melded,

Earth's atmosphere
was blasted into space,

its crust liquefied at
over 2,000 degrees Fahrenheit,

and vast portions of both
Earth's and Theia's mantles

were ejected into orbit.

- It's not at all like
what you see in the movies.

You can sit down
and have a cup of coffee,

and it's still going on!

These are—you know,

big objects
take a long time to occur.

So these aren't the normal
flashes that you think about,

of bullets hitting the wall.

Narrator:
The plume of ejected material

created a vast orbital ring
before coalescing

into a new companion
for the Earth:

the newborn Moon.

- That fully fledged planet
merged with the Earth.

The iron cores
would have come together,

and the silicate mantles
were left on the Earth

and also accreted into a disc
that was orbiting the Earth.

This disc, most of it, came back
and crashed back onto the Earth,

but then a portion of it
re-formed

and, over time,
has been pushed out

and has become the Moon.

Narrator:
It took about 150 million years

for Earth to stabilize

and its molten crust
to re-harden.

But although the Theia impact
was a very bad day on Earth,

it was a very good day
for its ability to sustain life.

- When the Moon formed,

it stabilized
Earth's axis of rotation.

Otherwise, gravitational tugs
from other planets

would have caused it
to chaotically vary,

and that would have been bad
for long-term climate stability.

- Would we even have life
as we know it

if that impact
had not taken place?

Without a moon, you could really
have a case

where your tropics,

within hundreds
of thousands of years,

could rotate and become
the arctic or the Antarctic,

and you kill everything.

Narrator: With the impact over

and the Moon now providing
orbital stability,

the stage seemed set
for a quiet future.

But that was not to be.

- You form the planets.
You form the Moon.

Everybody's happy.

And all of a sudden,
something terrible happens.

Narrator:
Earth was suddenly caught

in the crossfire once again.

Number six on our countdown
of worst days...

Approximately 150 million years
after the Theia impact,

the Earth's crust cooled.

Some speculate that early oceans
and even life may have evolved.

But another cataclysm
would wipe the slate clean.

In the far reaches
of the solar system,

the orbits
of the outer gas giants

began to fluctuate,

disrupting vast swarms
of asteroids and comets.

Trillions broke loose
from their orbits

and plunged inwards
towards the rocky planets,

launching an era
of fiery destruction

known as
the Late Heavy Bombardment.

- We know asteroids
the size of Texas hit the Earth.

Any impact or that big causes
the entire ocean to go away.

We sterilized the Earth
over and over and over,

so the inference we have

is that life evolved
over and over and over

just to be snuffed out again
by these large impacts.

Narrator:
The relentless bombardment

gouged out craters
thousands of miles wide,

and the hits just kept coming

for at least 200 million years.

Today billions of years
of erosion

and shifting plate tectonics

have erased any trace
of the cataclysm

from the Earth's surface.

But it's a different story

on the cratered face
of the Moon.

- We can see very clearly

its record
on the face of the Moon.

The lava-filled basins
were formed

during the giant impact events

that occurred during
the Late Heavy Bombardment.

And so we know that
large objects hit the Earth

during this time.

Narrator:
But this celestial rain of fire

may have had a silver lining,
literally.

New evidence suggests
the Late Heavy Bombardment

delivered precious metals
to the surface of the Earth;

things like silver,
gold, and platinum.

Earth's original store
of these elements

had sunk
into its molten iron core

as the planet slowly cooled.

But now, with our planet
already solidified,

this new supply of materials
remained near the surface,

able to be mined
by future humans.

- Today's technologies depend
on a lot of the heavy elements

that were delivered to the Earth
through impacts.

So it may have been
very difficult for the life,

if there were life on Earth,
during the heavy bombardment.

But it was very good
for the Earth's crust

to have all of these materials
that we now depend on

delivered to the surface
of Earth through impacts.

Narrator:
The Late Heavy Bombardment

was Earth's true
baptism by fire.

But now, as we reach
number five in our countdown

of the planet's worst days,

Earth catches
the worst cold in history,

a climactic crisis so chilling
that life itself

was in danger
of being frozen in its tracks.

Both the Theia impact
and the Late Heavy Bombardment

turned Earth into an inferno.

But now, as we continue
our countdown

of the seven worst days
on Earth,

we skate forward in time
to a catastrophe not of fire

but of all-encompassing ice.

Number five on our countdown:;

the frozen cataclysm
known as snowball Earth.

- We had these bad days,

and a snowball Earth
is much longer than a bad day.

It's a bad
hundreds of thousands of years.

Snowball Earth is that
the planet becomes a snowball.

It cools enough
that the oceans freeze

down to 10 feet,
20, 50 feet thick.

Imagine the arctic sea ice
we see now,

except the whole planet
has that.

Narrator:
During a typical ice age,

glaciers invade
the temperate zones,

often reaching as far south
as modern New York or Paris.

But during snowball Earth,

the glaciers
just kept coming

until they had encircled
the entire planet

and frozen the oceans
to a depth of up to a mile.

As average temperatures plunged
to minus 75 degrees Fahrenheit,

the equator grew as cold then
as the South Pole is today.

And this global deep freeze

may have happened
not once but twice,

the first episode beginning
2.4 billion years ago.

- During
the snowball Earth phase,

the entire Earth has a climate

quite similar
to modern-day Antarctica.

It's extremely cold,
extremely dry, extremely windy,

extremely inhospitable to life.

Narrator:
The snowball Earth hypothesis

helps explain the discovery
of glacial deposits

in areas that were once
at the equator.

It's theorized
that as the glaciers

marched on
from the polar regions,

they reflected sunlight
back into space

and created
a powerful feedback loop,

turning the thermostat
relentlessly lower.

- If the polar regions
get too large,

if the snow and highly
reflective ice coatings

get too far down in latitude,

they reflect more light
back into space,

the Earth gets cooler,

the ice goes closer and closer
and closer to the equator.

So it's thought to be
kind of a runaway process.

So this leaves a freeze-over
of the Earth.

Narrator: But what caused
the first snowball Earth?

Scientists think the culprit

actually may have been
life itself.

- The gas
that was most prevalent

when life first appeared
on the Earth

wasn't oxygen;
it was methane.

Creatures at that time,
single-celled bacteria,

would have used methane

as part of their normal
living processes.

- Methane is a phenomenal
greenhouse gas.

So if you had a lot of methane
in the atmosphere,

you had, likely,
very warm temperatures.

Narrator:
But 2.4 billion years ago,

a new group
of underwater microbes

began absorbing energy
from the Sun

in a process called
photosynthesis.

By converting carbon dioxide
and water into energy,

photosynthesis
polluted the Earth

with a toxic new waste product:

oxygen,

vast amounts of it.

- Prior to 2.4 billion
years ago,

oxygen was a poison.

And any life that was on Earth
did not use oxygen.

It was considered
a waste gas.

All of that life
that didn't like oxygen

was exposed
to this rich oxygen environment,

and it caused
a great deal of stress.

- Methane creatures were happy
to live

in this oxygen-free world.

Now, when oxygen
finally does appear,

it was like the worst calamity
in their history.

Narrator. As oxygen
flooded the world,

it oxidized methane,

turning it into carbon dioxide.

The methane-consuming creatures
died off

in a vast extinction event

called
the great oxygen catastrophe.

And as Earth lost

its warming blanket
of methane gas,

the planet froze over.

But if oxygen-producing life
was the primary trigger

of the first snowball Earth,

that life now needed
to find a warm place

to escape the disaster
it had caused.

- The Earth at that time

was even more energetic
tectonically

than it is now.

The formation of the Earth
produced enormous heat.

That heat comes to the surface.
It's slowing.

But back then,
many more volcanoes.

Around every volcano,
there would have been

this melted lake-like zone
where life could have thrived.

Narrator:
To show how volcanism

could have carved out
cozy niches for life,

all you need is a blowtorch
and a big ball of ice.

- We're here at Carving Ice,

an ice house
owned by Roland Hernandez,

an amazing ice sculptor
who's created for us

this hemisphere of solid ice

which represents
snowball Earth.

We've placed it up here
on this dolly

so that we can heat it
from below

with an industrial blowtorch,

to represent the type of heating
that we would experience

on snowball Earth

from volcanism
deep beneath the surface.

- Now let me
just light this up.

[torch hissing]

Al right.

Passing you the torch.

- Okay.

[torch hissing]

Narrator: Scientists suspect
that the extreme heat pressure

generated by volcanism
beneath the Earth's surface

would have created
cracks in the ice

for life to take refuge.

- Okay, so you can see how
the cracks have formed

all throughout the ice
along the top here.

These are very similar
to the types of cracks

that would form
during a snowball Earth event.

It's in these cracks
where you can get

the mixture
of a little bit of liquid,

a little bit of heat,
a little bit of chemistry—

In other words,
the perfect ingredients

for generating an environment

where life can take root
and even thrive.

Narrator:
Volcanism wasn't just key

to life's survival
during snowball Earth.

It also may have forced
the glaciers

to finally retreat.

- So you've got
all of these gases

that are coming
out of the volcanoes—

Things like water vapor,
carbon dioxide,

sulfur dioxide,
for example—

Which are
escaping into the atmosphere.

And over time,
over tens of millions of years,

you're building up

these levels
of greenhouse gases.

At some point,

it's going to get so warm
in the atmosphere

that the ice begins to melt.

Narrator. Both episodes
of snowball Earth—

The first
2.4 billion years ago

and the second
600 million years ago—

Placed profound stresses
on early life.

But oddly, both were followed

by enormous flowerings
of new species.

- We know
from the sedimentary record

that just before animals
bloomed into existence,

an enormous amount
of phosphorous

came into the ocean.

There were big rocks
of phosphorous.

They eroded.

As that erosion occurred,

phosphorous levels
in the ocean rose.

All of a sudden,
life is able to just bloom.

This may have really caused
the diversification two times—

Of the microbial world
at 2.3 billion years ago,

but more importantly to us,

it really probably helped
the diversification of animals

at 600 million years ago.

Narrator:
Although snowball Earth

produced some of the planet's
harshest weather,

life not only managed
to survive;

it bounced back
stronger than ever,

which is why this disaster

only ranks as number five
on our list of worst days.

So far, on our countdown

of the seven worst days
on Earth,

we've seen our planet battered

during the moon-forming
impact,

baked by
the Late Heavy Bombardment,

and almost completely
frozen over by snowball Earth.

Now we travel forward
over 100 million years

as the world is rocked

by one of the greatest
mass killings in its history.

Number four on our list...

In the billion of years
of life on Earth,

99% of all species
that ever lived

have ultimately vanished,

mostly due to five
mass-extinction events.

The first was during
the Ordovician period

450 million years ago.

- The mass extinction
during the Ordovician

is the most mysterious
of the so-called big five,

simply because it was the one
that was the oldest.

Every one after that
was closer to us in time,

and the further
back in time you go,

the more fuzzy our
scientific view of the past is.

Narrator:
During the Ordovician period,

the globe was covered
with three major oceans

and four super continents.

The land was still barren,

but the oceans teemed with life,

including brilliant corals
and the planet's first fish.

Then a mysterious cataclysm
swept the seas,

and 60% of life on Earth
vanished.

- There's a couple
of possibilities.

Number one:
it got cold again.

So why would it
have gotten cold?

Well, it could have been
that plate tectonics

moved all
of the formerly warm continents

down to the polar regions,

and that dropped the temperature
of everything.

Narrator: For years,

scientists blamed
the Ordovician extinction

on a devastating ice age.

But now some researchers propose
that the mass killer

could have been something
from the cosmos,

like a gamma ray burst,

the biggest blast
in the universe.

- A gamma ray burst is
a colossal explosion of a star

that occurs asymmetrically.

There are two
oppositely directed beams

of very energetic
high-speed particles

and radiation
that go zipping through space,

kind of like a laser beam.

If that beam is aimed
right at Earth,

it can cause
significant damage here.

Narrator: A large burst
would vaporize

1/3 of the planet's
protective ozone layer,

and creatures
on the side of the Earth

facing the onslaught

would suffer
lethal radiation exposure.

The destructive energy
of a gamma ray burst

can be demonstrated
here on Earth.

- Here's our globe
representing the Earth

at the end
of the Ordovician period,

a time when
one group of scientists thinks

that a gamma ray burst

may have triggered
a mass extinction.

The paper represents
the Earth's ozone layer,

and the gamma ray burst

is represented
by this propane torch.

[gas hisses]

[click]

Eight, nine,
ten seconds' worth.

That's all they say
it would take

to destroy about 1/3
of the Earth's ozone.

So of course,
the gamma ray burst

didn't actually torch the Earth,

but it did destroy the ozone
that it encountered.

And it would have messed
with the chemistry

of the ozone molecules
on this side of the globe.

And when the ozone
was destroyed,

UV radiation could penetrate
to the surface.

And the ultraviolet radiation
is very lethal to life.

It's very destructive to DNA.

So it may be that
a gamma ray burst

destroying the ozone layer

contributed to,
or maybe even triggered,

a mass extinction
at the end of the Ordovician.

Narrator: In addition
to depleting the ozone layer,

a large gamma ray burst
also could have ripped apart

nitrogen and oxygen molecules
in the atmosphere,

producing a gaseous smog
of nitrogen dioxide

that blocked sunlight

and set off
a secondary disaster:

an ice age.

- It's not clear whether
that could have been caused

by a gamma ray burst.

But at least part
of the Ordovician extinction

seems to have been marked

by a huge decrease in the number
of surface-dwelling creatures,

like on the Earth's surface

or in the surface layers
of the ocean.

That may well indicate that
it was ultraviolet radiation

that killed them off
rather than some other factor.

Narrator: A gamma ray burst
could be one explanation

for the first mass annihilation
of life on Earth.

But a startling new hypothesis

points to a different
cosmic force:

a bizarre and potentially deadly
phenomenon

known as a bow shock.

- A bow shock forms when
there's compression of material

in front of a moving object.

So for example, if you have
a boat zooming along,

it creates a wave,

a compression in front of it

that then bends around
as the boat moves through.

Well, our galaxy is moving
rapidly through space,

so it can compress
intergalactic gas

in front of it,
heating it up,

creating cosmic rays.

And some of those cosmic rays
can then hit the Earth.

Narrator:
Our solar system oscillates

through the Milky Way,

traveling above and below
the main disk of the galaxy

every 64 million years.

Once outside the galaxy's
protective magnetic field,

our planet is vulnerable
to deadly cosmic rays

generated
by the galactic bow shock...

much like a wake boarder
on a lake.

- Wake boarding would be
a reasonable example

of a bow shock in space.

Hit it!

While the wake boarder
is well within the confines

of the bow wake of the boat,

the water is very calm
and smooth,

and he has no trouble
standing up.

But during those periods
when he moves

out toward the edge
of the wake,

the water becomes
a bit more turbulent

and a bit more chaotic,

and he has trouble standing up.

The same thing is true in space.

For most of the time,

the Earth and Sun
are well within

the protective confines

of the Milky Way galaxy's
magnetic field,

protecting it
from the cosmic rays

and other radiation that's
coming in from the bow shock.

But during those periods

when the Earth and the Sun
rise above the galactic plane,

it's much more vulnerable

to all of these cosmic rays
coming from the bow shock.

Narrator:
Fossil records indicate

that the biodiversity
of many species

may increase and decrease
in 62-million-year cycles,

those cycles closely coinciding

with the times
of greatest exposure

to cosmic rays
from galactic bow shock,

which occur
every 64 million years.

Could the two events
be connected?

- Two of the mass extinctions

happened to have occurred
at about the time

when the Sun was highest
above the plane of our galaxy.

That suggests
that there's something

about that particular location
that's special.

Causing these
mass extinctions.

Narrator: During
the Ordovician extinction,

Earth could have been blasted
with enough deadly radiation

from the galactic bow shock

to unleash genetic mutations
and DNA damage

that wiped out
over half of all species.

- This is not yet
a well-tested idea.

It's just out there
on the drawing board.

But it could explain

some of the possible periodicity
in Earth's mass extinctions.

Narrator: But while
the Ordovician extinction

was fatal to most species,

some grasped
at the opportunity.

- It's like pulling weeds
out of a garden.

You sort of clean out
and weed out and thin out.

That seems to have happened

in the Ordovician
mass extinctions.

Some creatures which died out
allowed others to diversify.

Narrator: The Ordovician was
the first mass extinction

but hardly the worst.

Number three on our countdown
of the worst days on Earth:

it's the most famous die-off
in prehistory.

But if you think you know
what killed the dinosaurs,

you may be in for a surprise,

because some scientists

now argue that
the common explanation

of a single giant impact
on a single disastrous day

is itself
about to be blasted away.

In our countdown
to the very worst day on Earth,

no catastrophe has been
the subject

of more public fascination
and sensational headlines

than the bombardment

that ultimately cleared the path
for mankind.

But today
controversial new hypotheses

challenge the concept
that a single disastrous impact

wiped out the dinosaurs

and led to the third-worst day
on Earth...

- 65 million years ago,

we would have seen a world
something like Africa

in terms of the number
of animals out there.

But instead of big mammals,
we have big dinosaurs,

herds of triceratops,
herds of duckbill dinosaurs,

small to big predators,
the largest being T. Rex.

[dinosaur roaring]

Narrator: Dinosaurs ruled
the prehistoric world

for almost
200 million years.

Then something took out
2/3 of all living creatures,

including the giant beasts.

After years of searching
for clues,

most experts now agree

that a single cataclysm
doomed the dinosaurs.

- The evidence for an impact
of a six-mile-wide asteroid

65 million years ago

is about as good
as anything gets in science.

Narrator:
65 million years ago,

a rock the size of Mount Everest
barreled down from the sky

and slammed
into the Yucatan peninsula,

near modern Chicxulub,
Mexico.

The impact unleashed

an unstoppable chain
of destruction,

first locally
then across the globe.

- The k-t is
an asteroid-driven extinction.

A big rock from space came down,

clunked a few dinosaurs
on the head,

but the kill mechanism

was really
the secondary effects of this.

There would have been
darkening of the atmosphere,

acid rain, a change
in the entire biosphere.

Narrator. Proponents
of this single-impact theory

point to a convincing array
of evidence,

including high levels
of the asteroid element iridium

at the k-t event's
geological boundary,

or death layer,

and, of course,
the smoking gun itself,

the underwater crater
in modern Mexico.

But is this cold case
finally closed?

Some scientists now argue

the Yucatan asteroid
had accomplices.

- There seem to be
various causes

that can trigger these,

and in some cases,
several causes come together

in sort of a confluence
of bad circumstances

to provide a particularly
damaging extinction event.

Narrator: Millions of years
before the k-t extinction,

vast lava flows had been pouring
out of the Deccan traps,

a series of lava beds
now located in southwest India.

These flood basalts
once spewed out enough magma

to cover a million square miles

and belched up
a toxic brew of gases

that could have altered
the climate around the world.

- That period of eruption
is pretty coincident

with the extinction
65 million years ago as well.

And in fact, they were going on
for millions of years

before the k-t impact
and before the extinctions

and so perhaps could be
a complicating factor.

Narrator: In this scenario,

the dinosaurs received
a double knockout blow...

First the rampant volcanism
of the Deccan traps

then the Yucatan impact.

And a small group of dissenters
goes even further,

claiming that multiple asteroids
struck Earth

at roughly the same time
65 million years ago.

According to them,
the Yucatan impact

wasn't the largest,
only the best documented.

- Some people think

that there may have been
multiple impacts,

a shower of impacts,
for example.

Perhaps they came from a single
object that broke apart.

Narrator:
Supporters of this hypothesis

point to a suspicious
geologic feature,

a 370-mile basin
off the coast of India

more than three times larger
than the Yucatan impact site.

But controversy swirls around
this so-called Shiva crater—

Named after the Hindu
god of destruction—

Including whether
it's even a crater at all.

- While this feature
certainly looks circular

and looks crater like,

there's no other evidence

that it's an actual
impact structure.

Narrator. For some,

the dinosaur die-off debate
rages on.

But most scientists agree
the apocalyptic event

was a very fortunate day
for small mammals

that were no longer dinner
for T. Rex.

- Had it not been
for the k-t impact

and the volcanism that was also

at the time of the extinction
of the dinosaurs,

the mammals probably
wouldn't have risen

to the prominence
that they did.

And thank heaven
for the rise of mammals,

because that led
to the rise of humans.

Narrator: The k-t extinction
raises a sobering question.

Could humans one day
go the way of the dinosaurs?

That's what viewer Tom Moore
from Adrian, Michigan,

wanted to...

- Well, Tom,
Earth could definitely be hit

by another k-t sized comet
or asteroid.

They're out there.

The good news is,
we're tracking the positions

of most of the big ones.

So if we ever find one
with Earth's name written on it,

hopefully, we'll be able
to deflect it

before it reaches Earth.

Narrator:
The k-t event toppled T. Rex,

but it only ranks
as number three

on our countdown
of worst days on Earth.

Number two was the mother
of all extinctions,

the greatest die-off

that life on Earth
has ever suffered.

It's also been

one of the biggest
unsolved mysteries in science...

until now.

As we near the climax
of our countdown,

we reopen
one of the oldest cold cases,

an unsolved murder mystery

that happened
250 million years ago,

almost 200 million years before
the downfall of the dinosaurs.

The second-worst day witnessed
the greatest mass extinction

in the planet's history,

a cataclysm known
as the Great Dying.

During the Permian period,

Earth was a wondrous world
of mammal-like reptiles

and exotic sea creatures.

Then 90% of all life disappeared
from the planet.

- This was a bad
few hundred thousand years

on planet Earth.

But it was certainly
the most catastrophic.

More life died then
than any time since

and maybe any time before.

This was the biggest
and the baddest of them all.

Narrator: For decades,

scientists have sifted
through clues,

struggling to solve the mystery
of the Great Dying,

when the survival of life itself
seemed to hang by a thread.

One of the prime suspects:

a super volcano
that tore Siberia open

for hundreds of miles,

erupted for at least
a million years,

and produced the greatest
lava flows ever known,

enough to bury
the entire United States

thousands of feet deep.

- This wasn't
a single giant volcano.

It was simply cracks
in the Earth,

and you're, like,
pumping out lava.

It's like a fire hose
spewing lava everywhere.

Well, that certainly would have
killed anything in its way.

- It's believed that
you had these beds of coal

in what is now Siberia,

which then have
lava erupting underneath them,

burning the coal,

putting all sorts of noxious
greenhouse and other toxic gases

into the atmosphere,

and really putting strong stress
onto the biosphere.

Narrator:
The increased global warming

was fatal to most animals.

But plants usually thrive
on carbon dioxide.

So why did they also succumb

at rates that have never
been equaled?

- There's a second killer
in the story

that we think—
and just now are discovering—

And that's the presence
for the first time on the planet

of massive amounts
of hydrogen sulfide gas,

the same stuff you see
with rotten eggs.

That's a true poison.

And it, with the heat,
combined, I think,

to cause this greatest
of mass extinctions.

Narrator: If the scientific jury
is still debating

the cause of the
Permian-Triassic extinction,

no one disputes that those were
the darkest days

for life on our planet...
so far.

But life on Earth cannot
and will not survive

an event that scientists predict

is as unavoidable
as death itself,

the number one worst day
on planet Earth...

In 5 billion years,

our sun will reach
the end of its life.

As it exhausts its nuclear fuel,

it will undergo
a disastrous transformation,

bloating into a red giant star

200 times its original size.

As it swells,
it will first engulf Mercury

then Venus.

The incinerated Earth

will either be pushed
to a higher orbit

or swallowed itself.

The good news:

humans won't be around

the day our sun
incinerates Earth.

The bad news: we will have been
roasted long before.

- The Sun gets brighter
about 10% every billion years.

And so in less
than a billion years,

the Sun will be bright enough

that it's predicted that
it will pump basically all—

Well, most of the carbon dioxide
out of the atmosphere,

and so things that rely
on carbon dioxide,

like plants, are going to have
a hard time

surviving in a natural world.

Narrator: As plants shrivel
and oceans evaporate,

biologists predict a future
mega mass extinction.

The age of animals will end
in about 500 million years.

- We have as much time
in the future

to be alive as an animal
as we've had in the past.

We're halfway through.

That's a sobering thought.

Narrator: We've seen Earth

smacked by the giant
moon-forming impact,

strafed and sterilized during
the Late Heavy Bombardment,

then frozen
into a giant snowball.

A cosmic force ravaged
an ancient water world

during the first
mass extinction,

followed by
a near total extinction

during the Great Dying

and the spectacular fall
of the dinosaurs.

What else lies in store

before our planet
is ultimately baked by the Sun?

- Earth will certainly continue
to experience disasters

all the way
up until the very end,

when the Sun's red giant phase
brings an end to the story.

Narrator: History has proven

that Earth is
an unpredictable planet,

orbiting in a very dangerous
galactic neighborhood.

To survive, mankind must learn
from the worst days of our past

and try to prepare for whatever
the cosmos might throw at us.

Only by increasing our knowledge
of the universe

can we hope to thrive
and fully enjoy

our final 500 million years
of life on Earth.