All language subtitles for How the Universe Works (2022) - S10E04 - Dark History of Earth_track3_[eng]

[narrator] The earth is
over 4.5 billion years old.

Its history is shaped
by disaster...

...after disaster.

[Paul M. Sutter] Asteroid
and comet collisions,

flares from the Sun.

[Jani Radebaugh]
Mass extinctions,

supernova explosions,

cosmic ray bombardment.

You name it,
we've experienced it.

It's kind of a miracle
we're here at all.

[narrator]
These violent events
could be why Earth has life

[Nina Lanza] We tend to thin
of disaster as a bad thing,

but out of chaos
can come possibility.

When we destroy something,

we can also create
something new.

[narrator] Earth has walked
the line between survival..

...and destruction.

It's tipping that fine
balance of luck

between a good disaster
and a bad disaster.

[narrator]
Could catastrophe and chaos
be the essential ingredient

for life?

2021.

Scientists investigate
something mysterious

buried deep inside the earth

It's a long hidden clue
to our violent past.

[Michelle Thaller] Deep down

1,800 miles
below the surface
of the earth,

our core is surrounded
by fluid rock,

but inside that,

600 miles high

and thousands of miles across

are two denser regions,

and they kind of cup
the core of our planet
like two hands.

One of them is, you know,
half the size of Australia,
for crying out loud.

So, I mean, they're
big lumps down there.

There's no reason
they should be there.

It's a mystery to us.

[narrator] To solve
this mystery,

scientists need
to examine the rocks

buried over 1,000 miles
beneath the surface.

We don't really know
what these two big rocks
are made of,

sitting there on the core.

However, we've been
able to sample them.

How in the world
is that possible?

Well, these blobs are actual
feeding mantle plumes

that are rising
up through the mantle.

[Dan Durda] So, volcanoes
in Iceland and Samoa,
for instance,

will dredge up some
of these lumps of rock
from the mantle.

It's a precious chance
for us to sample some
of that deep rock

that we'd normally not
get a chance to see.

[narrator] These rocks
are old.

Very old.

[Radebaugh] It turns out
that the samples in the lav

that we think came
from these blobs of rock
in the mantle

are 4.5 billion years old.

That is as old
as the age of the earth.

[Durda] So, they tell us
something about, you know,

how the internal
structure of our planet
was, uh, arranged

in the earliest days
of the formation
of our planet,

so getting samples
from that time is
very, very important.

[narrator] The age
of the rocks may be
a clue to their origin.

They date back to a time
of monstrous cosmic mayhem.

[Kevin Walsh]
4.5 billion years ago,

the solar system was
still a pretty wild place.

We're approaching the end
of the formation of planets.

Earth would still be growing.

[James Bullock] Back then,
you wouldn't necessarily
recognize the earth.

In fact, you wouldn't
recognize the earth at all.

For example, no moon.

The earth did not have a moon
when it first formed.

[narrator]
The young earth orbits the S
with other infant planets.

One of them is an object
scientists call Theia...

...and it's
on a collision course
with our home.

[Bullock]
The Theia collision would ha
been a spectacular event.

It would've been one
of the coolest things

you could possibly witness

in the origin
of the solar system,

certainly the biggest event
in the history of the earth.

[Konstantin Batygin]
The Theia event is

something that completely
reshaped the earth.

The planet that the earth
was before the Theia event

is gone forever.

[narrator] The impact
melts rock

and throws out over a billio
billion tons of debris.

[Thaller] During
this incredible collision,

these two planets were
literally broken apart

and combined
into one big planet.

Huge chunks of Theia
stayed together

as the now molten earth
began to form anew.

[Radebaugh] Now, we can
kind of paint a picture

of where these big lumps
of rock might have come from.

They're very old.

They're, in fact, the same age
as that large impact event.

They could be pieces of Thei

[narrator] The giant slabs
of Theia sink down
into our planet...

...and lie undiscovered
for billions of years.

Earth reforms from the ruin
of both planets.

Now, you might think
that a collision like this
is just devastating,

there's no upside at all,

but there's some
things that came out
of this collision

that may have led
to the possibility of life.

[narrator] When these two
planets combined,

parts of Theia's iron core
merged with Earth's.

So, that means that Earth
collected a much bigger core

than it might have
possessed on its own.

This is good news for us

because the core is the source
of the magnetic field

that protects us.

[narrator] Liquid metal
flowing around
in the outer core

generates Earth's
magnetic field...

...a protective shield
from the Sun.

[Thaller] The Sun can actual
output billions of tons

of high-energy
protons and electrons
in a single burp.

That, eventually, would hav
stripped away our atmosphere

If it weren't
for that active core

and that magnetic field,

we would look like Mars,

just sort of a bare
and barren desert.

[narrator] Thanks
to Theia's extra iron,

Earth's molten
outer core is large...

...so it cools slowly,

staying molten,

and keeps on generating
a strong magnetic shield.

[Thaller]
Because of that collision,

the extra iron,
the extra heat,

we've stayed active.

We have a magnetic field.

We are protected,

and, in fact, that's why we're
here talking about it.

[narrator]
The catastrophic impact
helped life in other ways.

[Walsh] The Theia event
was absolutely huge,

and not an impact like
a 100-mile asteroid making
a big crater in the desert,

but a planet hitting a planet,

causing a huge disk of debris
spread out from the earth,

out of which formed the Moon

[narrator]
After the collision,

the earth tilts on its side

and spins incredibly fast.

A day only lasts a few hours

The earth itself rotates
slightly on its side,

and, if left to its
own devices,

would, in fact,
experience unpredictable,
chaotic wobbling.

The fact that the Moon
is there

stabilizes the earth,

stabilizes our climate.

[narrator] The Moon's
gravitational pull
on our oceans

creates tides and slows
down the earth's spin...

...creating a world
primed for life.

We actually owe quite a bit
to the Moon and Theia,

its progenitor,

for making Earth
a hospitable planet
for life.

[Sutter] A giant collision
4.5 billion years ago

sounds like a catastrophe,

but it was probably the best
thing to happen to the earth.

Theia, I would shake your ha

because we have
a lot to owe you.

[narrator] We also owe
the science of chance

because we lucked out

with a one
in a million impact.

If the impact from Theia
had been a little bit harder,

the earth may not have
recovered as well as it did,

and we may not be here
to talk about it right now.

If it had been a little bit
less forceful,

then the impact of it may no
have made the changes

that we think were needed
for us to be here now.

We got lucky.

Most planets
don't get to survive
a collision like that

and get a bonus moon
out of the deal.

[narrator] Earth's
huge collision with Theia

was not our planet's
first brush with danger.

An earlier explosive event

could have stopped
the solar system

from sparking into life...

...and the earth from formin

[narrator] Supernovas
are one of the universe's
most destructive events...

...releasing, in one second.

...as much energy
as our sun will

in its entire lifetime.

But rather than wipe us out

supernovas may have
kick-started the solar syste

4.6 billion years ago,

the solar system's not even
really the solar system.

It's the precursor
of the solar system.

[Phil Plait] So, what we ha
was a cloud of gas and dust
collapsing in on itself,

forming the Sun in the cente

a big, flat disk around it

out of which all the planets
were forming.

[Thaller] There are all kind
of vast clouds of dust and g
floating around the Galaxy.

What actually causes them
to start collapsing

and forming new stars?

Well, you have to give
that cloud a push.

[narrator] Scientists
think this push could
be a stellar blast...

...a supernova.

[Sarafina Nance] Supernova
are some of the most powerfu
events in the universe.

One explosion can light up
brighter than a galaxy.

So, not only do they eject
elements and material,

they also eject a lot
of light and energy.

[narrator]
A supernova explosion
sends a shock wave

racing out into space
at 18,000 miles per second.

The shock wave
from a nearby supernova

compresses material together

until it begins to collapse
under its own gravity.

[narrator] Was this how
our solar system started?

[Bullock] So far,
it's been really difficult
to find, uh, evidence

that there was some supernova,

or point to something
that happened

that really kick-started
the solar system.

[narrator] The ancient
supernova blast faded
away a long time ago.

[Plait] Imagine a crime scen

Now, imagine waiting
4.6 billion years

after the crime is committed,

and looking at it and going,

"There's... There's
nothing here.

What are we doing?"

Uh, that's kinda what
we're trying to do here.

[narrator] Researchers from
the University of Minnesota

tried to solve
this ancient crime...

...by studying asteroids
that fell to Earth
as meteorites.

Asteroids are critical
for understanding
the early solar system,

and this is because they
have frozen in place
all the conditions

that existed
in that very early
solar nebula,

right at 4.5 billion
years ago.

[narrator] The asteroids
contain information

about the time leading
up to the birth of the Sun
and the solar system.

When a massive star ends
its life as a supernova,

it undergoes what we
call nucleogenesis.

In fact, we call it
explosive nucleogenesis.

Literally, the explosion
is generating new types
of nuclei,

new elements,
heavier elements.

Well, it turns out the types
of elements it makes

depends on the star
that blew up.

[narrator] The Minnesota tea
ran computer simulations

to investigate
which elements form

when a star up to 12 times
the mass of the Sun explodes

Then, they compared
the results

with analysis of elements
found in asteroids

dating back to the birth
of the solar system.

They match.

[Nance] So, the remains
of this supernova was actual
under our noses all along

in the elements that have been
in our solar system for ages.

[narrator] And perhaps
in the earth as well.

[Thaller] The earth has
lots of rocks that's made
of, uh, silicon.

That's only produced
in supernova explosions,

and the very core
of our earth,

the thing that keeps us alive,

that's iron, nickel.

Again, you only get that
in supernova explosions.

[narrator] In February 2021

scientists shed light
on the supernova explosions

that helped seed
our solar system

and provided the materials
to build our planet.

The research
examined fragments

blasted off the giant
space rock, Vesta...

...4.5 billion years ago,

and later landed on Earth.

These asteroid fragments
contain the fingerprints

of not one,

but at least two
supernova explosions.

Our solar system was seeded,
was enriched, by at least two
separate supernova explosions.

That's incredibly lucky

because that is what
delivers the ingredients
necessary for life.

[narrator] Scientists believ
that these two supernovas

may have enriched
different parts

of the infant solar system.

One provided the materials

that helped form
the outer gas planets.

The other supernova seeded
the inner solar system

with elements that built
the rocky planets,

including the earth.

Once again, our fate
came down to pure chance.

A series of extraordinarily
violent supernova blasts

gave the solar system
the kick-start it needed

and the elements
to build the planets

without destroying
our future home.

It's a fine line between being
too close to a supernova,

which will just shred
your pre-stellar cloud...

...and not too far away
that you don't get any
of the good stuff.

Supernova play both
creation stories

and destruction stories.

They play both roles.

[narrator] We lucked out.

This chapter
of the story ends well.

The solar system gets
the ingredients it needs
to build planets.

Earth forms
in a good location,

close to its star.

The future looks bright,

but then,

the biggest bombardment
in history

smashes into the earth.

[narrator] From the moment
our planet formed...

...we've been under fire.

2021.

A fireball streaks
across the night sky
in Europe.

2018.

A 1,500-ton meteor explodes
over the Bering Sea

with 10 times the energy
of an atomic bomb.

2013.

An asteroid explodes
over Russia,

injuring over 1,000 people.

The earth is hit
by quite a few asteroids
every day.

You see them
as shooting stars,

meteors in the sky.

[narrator] These events
are violent and destructive

but these space invaders
also brought something
every living planet needs:

volatiles.

[Radebaugh] When we
say volatiles,

what we mean are elements
that are really light

and easily moved around.

Often, they're gases,

so that's oxygen, and water,
and carbon dioxide,

and just all
those light elements

that are really important
building blocks for life.

[narrator] These elements ar
abundant on our planet today

but were not
when it first formed.

[Thaller] From observing
other solar systems forming
all around us in space,

we know that planets
as close to their stars
as we are to the Sun,

when they form,
they're very hot and dry.

There's probably some littl
bit of water around there,

but really not very much.

[Hakeem Oluseyi] So,
what this means

is any volatiles will
basically be boiled away.

If you have a molten surface,

anything like water is
gonna get boiled away.

[narrator] Young Earth
was a dry planet,

devoid of all the precious
volatiles needed for life.

These materials must have
been delivered to Earth
after its formation.

We think volatiles
arrived in the early days
of the solar system...

...when the giant planets,
including Jupiter,

moved around...

...and stirred up the conten
of the solar system.

[Plait] As Jupiter moves,

its gravity is pulling
on all the objects in there

basically speeding them up,

and there's a little
bit of chaos there
in the first place,

but now, Jupiter is basically
supercharging it.

[narrator] Jupiter's
path sends countless
asteroids and comets

on a collision course
with the earth.

[Radebaugh] It would have
been utterly chaotic.

This is a rain
of large objects

onto all of the inner planets,

but these objects that came
screaming into Earth
were gigantic.

[narrator] Four billion
years ago,

a storm of giant
asteroids and comets

hits the earth.

Some are tens of miles wide

They bring the volatiles

that help fill
the earth's oceans

and build its atmosphere...

...but cosmic deliveries
can both give

and take.

The importance of impacts
for atmosphere

could go either way.

You could have a...
A really big,

really powerful impact...

...that blows away
the atmosphere

of a small, fledgling planet

or you could have
a bunch of small impacts
of water-rich asteroids

that are simply
contributing water,
and volatiles,

and new chemicals
to the surface

that might help the atmosphe
that's already there.

[Oluseyi] When you
think about an object
coming to Earth,

is it gonna land on Earth,

and if it does land,

is it gonna be a...
An erosive event,

where material is lost
from the earth,

or is it gonna be
an accretion event,

where the earth
gains material?

Well, the devil's
in the details.

[narrator] Details like
the size of the impactor.

One study suggests

that asteroids between 60 fe
and 3,300 feet wide

add more to the atmosphere
than they take away.

And speed at the point
of impact also matters.

Asteroids are orbiting
the sun.

And when they fall
towards the sun,
they are gaining speed,

they're gaining velocity.

Imagine dropping
a coin into one of those
spiral wells.

As the coin gets
closer and closer
to the middle,

it spins up faster and faste

[narrator] The closer
an asteroid gets to the sun

the stronger
the sun's
gravitational pull...

...and the faster
the asteroid travels.

[Jessie Christiansen]
So proximity to your star

is a vital factor
in how intense
any impacts will be.

[James Bullock] It's possibl
that the Earth

is the right distance
from its host star

so that when
an impact happens,

the energy
isn't insanely high.

It's just the right amount
that it's the right speed
to make everything work.

[narrator] Supernovas seed
the solar system

with the elements
to build the planets.

Asteroids and comets delive
volatile chemicals
to the surface of the Earth

Together they create
a habitable environment.

So we need
those impacts to happen
to have life on Earth.

[narrator] Disasters create
a planet primed for life.

But it appears that even mor
mayhem and chaos

are needed
to trigger life itself.

[narrator] An asteroid tear
through the solar system,

hurdling through space
at 40,000 miles an hour.

It's destination,

Earth.

Will this space rock inflic
unimaginable damage...

...or will it bring
the spark of life?

This idea of a spark of life,

we've all kinda seen it

in the Frankenstein movies,
right? "It's alive!"

This comes from legend,
from myth, from history

that there's some sort of
a spark that differentiates

cold inanimate matter
from living stuff.

And in some sense
it's kind of true.

[narrator] On Earth, we thin
this spark may have arrived

over 4 billion years ago.

The Hadean Eon
was the time
from the Earth's formation

about 4.6 billion years ago

to about 4 billion years ago.

It's named
after literally Hades.

So the conditions on Earth
were literally hellish.

[Dan Durda]
It was hot and soupy,
a lot of water vapor around

high pressure atmosphere,
very intense heat.

You wouldn't survive.

The planet would
literally kill you back then.

It's shocking.
And I mean, really shocking

that the evidence
of first life that we have
on Earth

dates to the Hadean Eon.

This was a terrible place,

molten and poisonous
and awful.

And yet life somehow arose
in all of that mess.

[narrator] June 2020,

Japanese scientists simulat
the conditions

of this hellish planet...

...and then try to recreate
the spark of life.

So what the scientists
were trying to do was mimic
those conditions

and see what would happen.

If you smash a meteorite
into the ocean back then,

could it produce sort of
the same chemicals

that we see life using today?

[narrator] They use a mix
of carbon dioxide, nitrogen
water, and iron

to replicate
the Hadean environment.

Firing a mini meteor
at 2,000 miles an hour
into this chemical soup

triggers a reaction between
the basic organic elements..

...creating amino acids.

We call amino acids
the building blocks of life.

Really they're
the building blocks
of proteins.

And life needs
proteins to exist.

But that's why
they're so important.

Without amino acids,
there's no proteins,

without proteins,
no life as we know it.

[narrator]
The experiment proves

that meteorite impacts
can help build
the components for life.

But for these building block
to come together

and create life,

we need more.

It's like making a cake.

You can put together
the oil, and the flour,
and the butter, and the sugar,

but if you don't put it
in an oven,

you're not gonna end up
with a cake.

You're gonna end up
with something else.

[narrator] We thought
that the violence
of asteroid impacts

prevented life from forming

Now, we think they could be
an essential ingredient.

[Phil Plait]
If the asteroid impact
is big enough and fast enoug

it can punch
right through the crust.

Then you're getting
geothermal heat,

heat the bubbles up
from the mantle.

And it is certainly possibl
to get an asteroid impact
that big.

[narrator]
Large meteorite impacts
can create hydrothermal vent

which some scientists believ
were the cradles of life.

They provide
warm, wet environments

and bring up chemicals
from deep inside
the Earth's crust...

...the perfect place
for life to begin.

As bad as those conditions
seem to us,

to the molecules
that are beginning to combin
and do their thing,

that was
a wonderful place to be.

That could actually be
that the conditions

that are best for early life

might actually be those
just after an impact.

So you have sort of
this petri dish environment

in which life
could really thrive.

[narrator] These vents
might be similar

to those we see
in the oceans today.

[Lewis Dartnell]
These hydrothermal vents
provide little window

into what the conditions
on the primordial Earth
would've been like.

And the sort of chemistry

that goes on
in those hydrothermal fluids

seems to be the right
kind of chemistry
for creating life.

[narrator] Once again,
Earth got lucky.

Impacts that could've
destroyed everything...

...may have helped
spark life into existence.

[Hakeem Oluseyi] I once hear
this quote from Confucious..

...that creation is quiet
but destruction is loud.

Well, these impacts

were both destructive,
but they also
may have been creators.

[narrator] Earth leaves behi
the Hadean age.

The planet calms,
and life takes hold.

But disaster
is our constant companion

as we prepare to face a stor
of deadly cosmic bullets.

[narrator] The universe
is a dangerous place for lif

There are asteroid impacts..

...black holes...

...and exploding stars.

But public enemy No. 1

cosmic rays...

...lethal energic particles
born in violent events.

Cosmic rays
are incredibly small

but travel so fast,
near the speed of light,

but they can tear
through our DNA and damage i

Your full of DNA.

If that DNA gets broken apart,
guess what happens?

That could lead
to cancer and death.

At first glance,
these cosmic rays
are the worst things for life.

They're terrible.

[narrator] Despite
their frighting rap sheet,

cosmic rays may have played
a crucial roll
in the evolution of life.

2020,

scientists at New York
and Stanford universities

investigate
biological molecules
that have a twin...

...mirror image versions
called chiral molecules.

The concept of chirality
in chemistry

is when you have
two molecules, two chemicals,

that are physically the same

They're made
of exactly the same things,

but their structure
is different.

And they're
not just different,

they're reflections
of each other.

It's literally
called handedness

because look
here's my right hand

with my thumb over here
and my fingers over here,

here's my left hand
with my thumb over here
and my fingers over here.

I can't wear a left glove
on my right hand.

There's nothing I can do
to make these guys the same.

And it turns out this
is true not just for hands,

but also for large number
of simple organic compounds,

things like amino acids
or sugars,

which are the building blocks
of all life on Earth.

[narrator]
Billions of years ago,
early life may have had

both left- and right-handed
DNA and RNA.

But life chose to use
mostly right-handed molecule

The reason may have been
cosmic rays.

When cosmic rays hit
Earth's atmosphere...

...they degrade
into even smaller
subatomic particles

called muons.

Most muons spin
in one direction.

So we have these little muons,
which are very energetic,

and they're spinning
a certain way.

And when they hit a molecule
they interact with it.

They can disrupt it.
They can change it.

[narrator]
Some scientists believe
these spinning muons

interact more readily
with right-handed DNA
and RNA...

...triggering mutations.

[Plait]
Some mutations are beneficia
but they have to get a chanc

So if you have
right-handed molecules
and left-handed molecules,

and they're both being hit
by muons,

the one that's hit more gets
more chances to have
a beneficial mutation.

[narrator] Cosmic rays
may have given
right-handed life

an evolutionary advantage.

Left-handed life
could not compete.

It's like throwing dice.

If you're trying
to get double sixes,

and the left hand only gets
to throw ten times,

and the right hand gets
to throw 100 times,

more likely to get
double sixes

with the right hand
than the left hand.

[narrator] But the dice
don't always land
in our favor.

359 million years ago,
Earth's luck ran out.

And cosmic rays
may have lived up
to their reputation

as the baddest particle
on the block.

[Dartnell] Earth's oceans
were teeming with marine lif

And by this period as well,

plants had started
to colonize onto the contents
and landmasses,

attracting animal life,
insects, millipedes.

And it's in this environmen

the Earth experienced
one of the greatest
mass extensions

in the history of life.

[narrator] Something
killed off 97%
of all vertebrae species.

We call this wipeout
the end Devonian extinction

One possible explanation,
a supernova.

When some dying stars explod
they fire out cosmic rays.

[Dartnell] This radiation
bombards the upper atmospher
of the Earth

and drives the chemistry
of nitrogen, turning
into nitrogen dioxide,

a gas which itself
then reacts
with the ozone layer

and destroys it.

[narrator]
Without the protective
ozone layer,

ultra violet radiation
from the sun bombards Earth

Radiation rains down
for thousands of years...

...damaging the DNA
of plants and animals.

Many species die out.

[Dartnell] The end Devonian
mass extinction
mostly effected marine life

This is where we see
the greatest percentage
of deaths.

[narrator] The oceans
once populated by fish
the size of school buses...

...now host fish
no bigger than a sardine.

These smaller fish
reproduce quickly.

In the challenging
environment,

they adapt and diversify
faster than larger species.

Mass extinction
is not only
wipe the slate clean

and provide other animals
and other life forms
an opportunity,

it creates a sort of chaoti
and complex environment

that drives natural selectio
and evolution.

[narrator] If a supernova
was to blame
for this extinction event,

scientists believe
that the culprit
was 65 light years away.

Any closer and Earth's luck
would've run out completely

It seems the existence of life

is always balanced
on a knife edge.

When an exploding star
goes off a little bit
too close to us...

...and we are all destroyed

So there's
this wonderful balance

between just violent enough
and too violent.

And we have been lucky enough
to dance on that edge
for 4.5 billion years.

[narrator]
This mass extinction
reset life on Earth

and paved the way
for four-legged creatures,

our distant ancestors.

Cataclysmic events
go hand in hand

with human evolution.

Some knocked us back

and others like the event
66 million years ago

gave us a push forward.

[narrator]
66 million years ago

a massive asteroid crashes
into the Earth.

It triggers
a huge extinction event.

Without it humans
may have never evolved.

[Nina Lanza] At this time
in Earth's history,

we had
these enormous plants
and gigantic insects

that actually would be
incredibly terrifying
if we saw them today.

[Christiansen] Pterosaurs sa
through the air.

Huge marine reptiles dominat
the oceans.

And the T. rex is the king
of the world.

[narrator]
Then a glowing object appear
in the sky.

[Durda] I'm sitting
on the beach

what was then gonna be
the Yucatan of Mexico

enjoying a drink
with a, you know,
a little umbrella,

but up there in the sky
all of sudden

approaching me
at 40,000 miles an hour

is Mount Everest glowing
thousands of times
more intensity than the sun...

...and it's just seconds away
from dropping on my head.

[narrator]
A 6 mile wide asteroid...

...slams into the Earth.

The impact throws
trillions of tons
of rock and dust into the ai

The rocks heat up
as they fall back to Earth..

...setting the planet on fir

That beach holiday
suddenly turns into
absolute nightmare.

[narrator] The impact
also throws up soot,

chocking the atmosphere.

Now, the skies are blotted out
by all these materials,

so the sun
is no longer shining brightly
on the surface.

[narrator] Plants need
sunlight to photosynthesize

Without this
vital energy source,

many species die out.

With their food source gone

plant eating dinosaurs starv
to death,

followed by their predators

It was a huge disruption
to all of life on Earth.

The dinosaurs have been
around for 160 million years
at this point.

That's astronomical
amount of time.

And in one event,
[snaps fingers] they're gone.

[narrator] Again the dice ro
is in our favor.

Most dinosaurs become extinc

paving the way
for the evolution
of mammals...

...leading eventually
to humans.

Without the asteroid impact
we wouldn't be here.

As a furry primate
on this planet, I kinda like
the K-Pg impact, right?

I'm here because of it.

We all are.

[narrator]
Some plants benefited
from the asteroid strike.

To learn out plants changed
after the impact,

Smithsonian scientist
examined thousands
of tropical plant fossils

from the time of the die off

This disaster opened the way
for new types of plants
to develop.

[Christiansen] It transforme
the plant kingdom...

...producing a richer
and more diverse
global ecosystem.

[narrator]
Before the asteroid strike,

conifers and ferns dominate
the tropical forests
of South America.

But afterwards,
falling ash from the impact

enriched the soil.

And fast growing
flowering plants took over.

[Lanza] The impact
was very hard to recover fro

but it actually opened
the opportunity

for a greater diversity
of plant life,

which ultimately has benefited
us as humans

because it has allowed us
to have more food sources.

[narrator]
This new world order
eventually gave rise

to the modern
Amazon Rainforest,

home to 10%
of all species on Earth.

[Christiansen]
It really destroyed and rema
our entire environment.

The world grew back,
of course it did, here we are,

but it changed everything.

[narrator] And another age
may be just around the corne

[Dartnell] We should
absolutely expect

that at some point
in the future,

and I'm not saying
you should lose sleep over it,

but at some point
there will be
another mass extinction.

Maybe that will be
the end our days.

It's intriguing question is

what might come after humans
on planet Earth?

[narrator] Catastrophe may b
the universe's recipe for li

throughout the cosmos...

...one that every planet
must follow.

[Plait] Looking
at our own history,

life thrives on catastrophes

We need these disasters
for evolution to work.

So, hopefully,
and I hate saying this,
I know how it sounds,

hopefully, these other plane
have had terrible disasters
as well.

[Michelle Thaller] Think abo
the word disaster.

It means bad star.

It means that something
has gone wrong,

something that's dangerous.

We are children of disasters

There's no way you get us
without planets colliding...

...without asteroids
and comets streaming
through the atmosphere...

...without even
stars exploding
and supernovas.

You are a child
of that violence.

That's part of the environment
that we grew up in
in a cosmic way.

And I think that
is tremendously beautiful.