All language subtitles for NOVA.S50E15.Ancient.Earth.Humans.1080p.WEB.h264-BAE_track3_[eng]

NARRATOR:
From a fiery hellscape

to a thriving oasis

filled with life,

our planet has played host
to a vast array of creatures.

STEVE BRUSATTE:
It is one unfolding story

with so many twists and turns

and new characters coming in,

and old characters
going extinct.

It's like the longest-running
television show of all time.

♪ ♪

NARRATOR:
Throughout Earth's history...

(eruption roars)

...powerful geological forces
shape the course of evolution.

And 66 million years ago...

(explosion roars)

...one catastrophe sparks
the beginning of a new era.

AISHA MORRIS:
One major event

can have these ripple effects
throughout the rest of history,

and this event
is almost unmatched.

NARRATOR:
An era in which
a species emerges

that changes the planet
faster than any before it.

AMELIA VILLASEÑOR:
Humans have modified the planet
in a geological blink of an eye.

We have basically altered every
part that there is to alter.

♪ ♪

NARRATOR:
What extraordinary series
of events gave rise to us?

MÓNICA CARVALHO:
This is one of those scenarios

in which we see geology
driving the evolution of life.

NARRATOR:
And can lessons
from our planet's past

help secure our future?

ZERAY ALEMSEGED:
Our survival as a species

is intricately linked
to the future of the planet.

NARRATOR:
"Ancient Earth: Humans."

♪ ♪

Right now, on "NOVA."

♪ ♪

♪ ♪

♪ ♪

NARRATOR:
Over the course of Earth's

four-and-a-half-billion-year
history,

countless species
have come and gone.

But for over 160 million years,
it was dominated by creatures

amongst the largest
to have ever evolved.

This is the age of dinosaurs.

MORRIS:
I think it would interesting,
humbling, and a bit terrifying

to be walking amongst

some of these massive creatures

that were roaming around

and munching
on these huge plants

that were growing at the time.

(dinosaurs bellowing
in distance)

JANE FRANCIS:
The sounds, I think,

would have been
really interesting.

Bird-like chattering.

Definitely a lot of loud and
hoarse noises.

(dinosaurs lowing)

BRUSATTE:
The whole fantastic variety

of meat-eating dinosaurs,
plant-eating dinosaurs,

long-necked dinosaurs,

dinosaurs with horns and spikes,

and dinosaurs
with feathers and wings.

(dinosaur screeching)

NARRATOR:
But the reign of the dinosaurs
nears its end,

as a looming disaster will set
the stage for our own evolution.

♪ ♪

("Never Close Enough"
by SIPHO. playing)

♪ Oh, we won't ever hear
the silence ♪

♪ Or ever see the colors ♪

(exploding)

♪ That never lived in
our minds ♪

♪ ♪

♪ Just a moment ♪

♪ Never too far out ♪

♪ Never close enough ♪

♪ ♪

NARRATOR:
An asteroid
the size of Mount Everest

is on a direct collision
course with Earth.

♪ ♪

(dinosaurs calling)

(explosion rumbling)

NARRATOR:
The blast from the impact

annihilates
everything in its path.

(shock wave rushing)

MORRIS:
The energy released
when this asteroid struck

was the equivalent
of ten billion nuclear bombs.

MARK MASLIN:
It caused earthquakes
100 times more powerful

than any earthquake

that humans have ever
encountered.

a second sun on the horizon,
a huge ball of fire.

It certainly wouldn't
have been possible

to bathe in its beauty,

because if you were unfortunate
enough

to be able to see it,
you were toast.

(shock wave rushing)

JESSICA WATKINS:
It is difficult to imagine

what it would have been like to
be a dinosaur

on the surface that day.

Um, not a great day to be a
dinosaur.
(laughs)

This was probably
the biggest asteroid

that's hit the Earth in at least
the last half a billion years.

And the dinosaurs
had no idea what was coming.

♪ ♪

(thunder rumbling)

NARRATOR:
After billions
upon billions of tons

of super-heated debris
are thrown up

into the atmosphere,
it begins to rain.

Not water,

but bullets of rock
known as spherules.

♪ ♪

In an asteroid impact,

the molten rock
vaporizes to form a gas.

That gas expands to form
a plume, and inside the plume,

that gas condenses,
solidifies, and cools,

and becomes these
rounded droplets

that then rain down on
the surrounding environment.

COLLINS:
These particular spherules
were found

about 300 miles away
from the impact site.

It's amazing to think
that these tiny spherules

were produced
in this intense fireball.

♪ ♪

NARRATOR:
The impact formed a vast crater

over 110 miles wide.

(wind blowing, birds chirping)

But, over time,

this was buried under
more than 1,600 feet of rock.

Today, at ground zero
of the impact,

the jungles
burst with biodiversity.

It's hard to imagine
the devastation

inflicted 66 million years ago.

♪ ♪

To uncover the true extent
of the catastrophe...

...scientists study
geological clues it left behind.

♪ ♪

CHRIS LOWERY:
I'm standing in this beautiful
geological formation

called a cenote.

Cenote is a Mayan word

which means
"a hole filled with water."

These cenotes form

as rainwater trickles through
cracks in the rock,

slowly eroding those cracks,

and they get wider and wider
until they collapse,

and a big sinkhole forms.

NARRATOR:
Taking a satellite image
of the Yucatán Peninsula

and overlaying a map
of the cenotes on top of it

reveals a subtle pattern.

LOWERY:
Each of these
yellow dots is a cenote.

You can see
thousands of cenotes.

There's as many as 10,000.

And if we look
at the northwestern part

of the Yucatán over here,

we see about 400
of these cenotes

that form this cluster.

NARRATOR:
Scientists call this cluster
the Ring of Cenotes,

because if the arc it forms
is extended into the ocean,

it creates a circle.

LOWERY:
This cluster of cenotes
actually corresponds

very closely to the inner rim
of the crater itself.

Almost like a bull's eye
of the impact crater.

NARRATOR:
The asteroid impact
weakened the rock

around the crater's rim.

(birds chirping)

So, over millions of years,

rainwater eroded
the weakened layers,

creating caves, which collapsed
to form the Ring of Cenotes.

LOWERY:
So, these amazing
natural features

are some of the only
visual reminders

we have left of the impact.

♪ ♪

NARRATOR:
But how could an impact
on one side of the planet

wipe out species
on the other side?

To solve this mystery,
scientists need to understand

what happened in the days
and months that followed.

In the hours after the chaos
of the initial impact,

debris and dust
thrown up by the collision

combine with soot and ash
from wildfires,

forming a vast, gray cloud,

which engulfs the entire planet

and causes death and destruction

on a global scale.

One of the big mysteries is

that the heavier particles
rained out

of the atmosphere within a few
months,

maybe a year, tops,

but that doesn't really explain

the extent of
the extinction that followed.

So, there has been this global
detective chase

to understand how the extinction
unfolded.

♪ ♪

NARRATOR:
But it wasn't in the atmosphere

that scientists
found the smoking gun.

It was deep underground.

LOWERY:
So, beneath our feet
is the Earth's crust.

The Earth's crust
is layers of rock,

20 miles thick in most places,

and these layers of rock,
uh, can be read

like a story
of the Earth's history.

We can drill into
these layers, and we can

recover samples, and we can
use that to understand

how things
have changed through the past.

NARRATOR:
In the 1950s and '60s,

oil drilling
in the Yucatán Peninsula

unearthed samples that were rich
in a particular type of rock.

LOWERY:
So, this is a rock
called anhydrite.

It might look very boring,

but it's actually very rich
in an element called sulfur.

And the sulfur is what's really
important about this story.

♪ ♪

NARRATOR:
In 2016, Chris Lowery
and a team of scientists

drilled through the seafloor
into the impact crater.

LOWERY:
When we drilled into the crater,

we got the cores back
from the layers of rock

where the asteroid actually hit.

We found
that there was no anhydrite.

What we think this means
is all this anhydrite

was vaporized
by the force of the impact.

This would have put, we think,
about 325 billion tons of sulfur

into the upper atmosphere,
and this is where this impact

really had
its devastating effect.

MORRIS:
So, we end up
with a lot of sulfur

in the upper atmosphere,

and the atmospheric circulation

moves this material
around the planet.

CARVALHO:
Unlike carbon dioxide,

that traps the heat
from the sun,

sulfur does the opposite,

and it actually reflects a lot
of the radiation

that's coming in from the sun.

(wind blowing)

NARRATOR:
With less sunlight
reaching the surface,

it becomes dark and cold,

plunging the planet
into a global impact winter.

CARVALHO:
With very little light,

there's barely no
photosynthesis.

And photosynthesis
is the main process

by which plants are
able to produce the food

that's feeding all the animals
that live in ecosystems.

BRUSATTE:
What I have here is
a replica of a skull.

It's a type of dinosaur
called an ornithomimid,

and it was thriving

during those last glory days
before the asteroid hit.

And it probably ate
a lot of plants.

The dinosaurs and
other animals that ate plants,

they didn't have any food,
so they died.

And the meat-eaters
then died, and so on.

Ecosystems collapsed
like houses of cards.

So it was really
that global impact winter

that sealed the fate
of most of the dinosaurs.

NARRATOR:
But it isn't just the dinosaurs
that are wiped out.

AMMIE KALAN:
We have an estimate that about

75% of all living plants
and animals

at that time went extinct

as a result of the asteroid's
impact.

This was one of the worst

mass extinctions in Earth
history.

♪ ♪

NARRATOR:
The asteroid impact
wipes out all of the dinosaurs

except for some smaller ones
that are the ancestors of birds.

And, crucially,
some mammals also survive.

FRANCIS:
Extinctions are really important
because they change things.

They give us a change

in the direction of evolution,

and it gives an opportunity

for new species
of animal and plants

to evolve into the landscape.

(birds calling)

NARRATOR:
You don't have to look into
the past to find examples

of the types of animals
that survived that long winter,

because areas of ecological
destruction on Earth today

demonstrate that
with a depleted habitat,

but just enough opportunity,

there is always a chance
that some species

will find a way to exploit
the devastation that is left.

BRUSATTE:
There are some types
of organisms,

because they're adaptable,
because they can grow fast,

because they can eat
lots of different things,

they are well suited
for living in conditions

that other animals
and plants just can't handle.

This was a huge catastrophe
for mammals,

but just enough survived
that they were able to

inherit a planet
that was barren of dinosaurs.

So, these are replica fossils

of a tiny early mammal
called Purgatorius.

Purgatorius is one
of these early mammals

that thrived
once the dinosaurs went extinct.

So, here is Purgatorius's jaw,

and you can even see
the teeth there,

and the tiny little heel bone,
which is minute,

and its ankle bone here.

And it's really on the backs

of these really tiny
small mammals

that the evolution of the rest
of mammals really lies on.

♪ ♪

NARRATOR:
It is thought that
the cold, dark conditions

last for over a decade.

But as the skies clear

and the sunlight returns
to full strength,

temperatures rise again,

creating a climate warmer
than the one we have today.

♪ ♪

And mammals, which have lived
in the shadows

of the dinosaurs
for around 140 million years,

find a way to gain a foothold.

BRUSATTE:
And this new world
was a world of prime opportunity

for the mammals that survived.

It was their springboard
to an entirely new future.

NARRATOR:
A new chapter for life
is beginning:

the age of mammals.

But it's not
an asteroid from space

that will spur
the next big change

in the course of evolution.

It's powerful forces
within Earth itself.

♪ ♪

Deep beneath
the North Atlantic Ocean,

volcanic activity
starts to bake organic matter

within the seafloor.

As this carbon-rich
material is heated,

bubbles of the greenhouse gases
carbon dioxide and methane

stream out
and warm the atmosphere.

FRANCIS:
Methane acts much faster
and much more strongly

than carbon dioxide.

So, if we're releasing
methane from the seafloor,

it would have caused
rapid warming.

NARRATOR:
As this warming releases
other reserves of methane,

it nudges the climate
past a tipping point.

We had what we think was a
runaway effect.

LOWERY:
The rate of things
really matters

when you're talking
about warming,

and this global temperature
spike 56 million years ago

is a example of that sort of
runaway effect

and the devastating consequences
of that

in terms of climate.

(thunder clapping)

NARRATOR:
On an already warm planet,

global temperatures rise by at
least nine degrees Fahrenheit,

a dramatic spike...

(thunder claps)

...that triggers chaos
in Earth's climate.

Violent storms batter the planet

with flash floods...

...prolonged droughts,

and destructive hurricanes.

JAMES ZACHOS:
The warming event

had impacts on virtually

every environment on Earth.

With the combination of
warming and ocean acidification,

there was one of the largest

deep sea mass extinctions
in recent Earth history.

NARRATOR:
Alongside catastrophic impacts
in the deep oceans

are surprising changes
in life near the poles,

where temperatures now rise
above 70 degrees Fahrenheit.

BRUSATTE:
There were alligators
above the Arctic Circle,

trying to take shade underneath
palm trees.

So, I've been to the Arctic

and collected fossil plants,

and I have a leaf
about 45 million years old

from the forest that once
grew close to the North Pole.

Here we are,
standing among banks of snow,

and my hands are freezing cold,

and yet here is a leaf
that's telling me

that millions of years ago,

there was warmth and
lush life in the polar regions.

It's incredibly exciting to find
fossils

from this time period,

because it's an unimaginable
thing.

And for the first time,
you are looking at these plants

that were actually
thriving in these ecosystems.

NARRATOR:
This warmer world
brings new opportunities

for mammals on land,

because now, for the first time,

across vast areas of
North America, Europe, and Asia,

one habitat starts to flourish
and spread out from the Equator.

CARVALHO:
Tropical rain forests,
as we know them today,

started spreading
north and south.

And from the pollen record,
we see many new types of pollen

showing up
during this time period,

which is reflecting
many new species of plants.

♪ ♪

NARRATOR:
This rich environment
would play a vital role

in the emergence
of a new type of mammal.

One that is more like us.

(birds chirping)

Tropical forests evolved

into some of the most
biodiverse habitats on Earth.

(birds chirping)

Home to countless species
of animals and plants.

♪ ♪

And 56 million years ago,

many of these plants were
providing a crucial ingredient.

In my hand, I have a
fossilized flower,

and it's pretty
incredible.

It's really tiny.

(chuckling):
It's only about the size
of my fingernail.

And it was found in
Utah, in North America,

and it's been dated to
around 51 million years old.

So, flowering plants

have been on Earth
for over 130 million years.

But during this
period of time on Earth,

which was really hot and humid,

the tropical forests
were spreading,

and at that time,
we think the flowering plants

also continued
to evolve and diversify.

♪ ♪

NARRATOR: Flowering plants

are one of the great drivers of
biodiversity,

and, following the spike in
global temperature,

Earth's blossoming forests were
full of them.

♪ ♪

KALAN: As flowering plants
flourished,

such as insects,
but also birds and mammals.

And that's really significant,
because flowering plants

also produce fruit.

And we think fruit

was one of the factors
that drove the evolution

of our mammal ancestors.

NARRATOR:
Against a thriving backdrop
of opportunity and reward,

a new branch
of mammals is evolving,

which takes full advantage
of this rich food source.

They are known
as the first true primates.

♪ ♪

KALAN:
So, I have in my bag
an illustration

of one of the first true
primates, called Teilhardina.

And it would have evolved
around 56 million years ago,

during this period
of climate change,

where there was
a lot of warming.

And we know from the fossils

that this primate
would have been very small,

only around maybe
two ounces or so.

And you can see here they had
very big, forward-facing eyes

and these
grasping hands and feet,

very much in line

with modern-day
primate characteristics.

NARRATOR:
It took millions of years
of evolution,

but this was the first time
a species had evolved

that truly resembled
the primates

we see around the world today.

KALAN:
They're climbing

and leaping through the canopy.

And right now
they're watching us.

I have one looking
right at me right now.

(chuckles)

Showing their curiosity.

And their acrobatic skills.
(chuckles)

(animals calling in background)

These are the
black howler monkeys,

and they are basically
a tree canopy-adapted species.

They use their
grasping hands and feet

and this
amazing prehensile tail

to make their way through
the canopy.

(animals calling in background)

So, the first true primates,

like Teilhardina, would
have had traits

very similar to the howler
monkeys that we see here today.

♪ ♪

NARRATOR:
Abundant fruit may have
helped these true primates

evolve some of their
distinctive characteristics.

KALAN:
Fruit is essentially a wonderful
source of energy for them

that's packed with calories,

and it can be really hard to
find these small fruits

in this large,
dense, green canopy,

and that's where their big eyes
and their hands

help them to be able to find
and pick out ripe fruits.

And this would have been
essential for them

to be able to adapt to
a life in the trees.

♪ ♪

♪ ♪

So, with this
global temperature spike,

forests started to spread
further and further,

even up into
the northern hemispheres,

and, with that, primates
were then able to expand

into Europe, North America,
Asia, and Africa.

MASLIN:
We enter the golden age
of primates.

We have them evolving

into lots of different species.

This was perhaps, at that moment
in time,

the pinnacle of primate
diversity.

At this time,
it really was

not really
"Planet of the Apes,"

but it definitely was
"Planet of the Primates."

♪ ♪

NARRATOR:
But the global spread of
primates

is about to come to an end.

They have thrived
for over 20 million years

on a warm Earth.

But now, the planet's climate
is cooling dramatically.

♪ ♪

FRANCIS:
The mechanism is still debated,

but we think natural cycles

reduced carbon dioxide levels
in the atmosphere.

And there were other impacts,
as well,

such as the movement of the
tectonic plates

that changed ocean circulation,

that had an impact on the
atmosphere,

and gradually, the polar regions
began to,

to cool, particularly
Antarctica.

NARRATOR:
Across the northern continents,
cooler, drier conditions

decimate
the lush forest ecosystems,

and the habitats where
the first true primates emerged

begin to disappear.

KALAN:
This was really bad for
primates,

because it meant that
their habitat was shrinking.

Along with that
comes the fact, then,

that they cannot get access

to all the food resources
that they need.

NARRATOR:
Primate populations
plummet in Europe

and disappear completely
from North America.

But around Earth's warm Equator,

their habitat
continues to thrive.

The critical thing
about those primates in Africa

is that we can trace
our evolutionary lineage

all the way back to them.

♪ ♪

NARRATOR:
As primates prosper in the
warmth of East Africa...

♪ ♪

...tectonic forces
deep within the Earth's crust

begin to
tear the continent apart.

♪ ♪

Hot magma wells up,

driving the creation of
a new environment.

♪ ♪

Over millions of years,

deep valleys are forged and
mountain ranges rise.

♪ ♪

Until,

running thousands of miles

through present-day Ethiopia
in the north

to Mozambique in the south,

the East African Rift Valley
is formed.

♪ ♪

APRIL NOWELL:
The Rift Valley system created

both these deep valleys and, of
course,

these really high mountain
ranges,

so it blocked the monsoon rains
from coming across,

and that created
a whole new landscape.

CARVALHO:
So, this is one of the
perfect scenarios

in which we see
geology and tectonics

actually driving
the evolution of life.

With this drier climate,
all the vegetation changes.

You go from a complete cover
of forest

to having a mosaic of
environments.

Patches of forests
connected by grasslands.

NARRATOR:
This shifting landscape

presents these primates
with new challenges.

KALAN:
This was really an evolutionary
fork in the road for primates.

Food resources
became more dispersed,

which meant that primates had to
travel further

in order to find enough food
to survive.

And what we see is that that
likely led to

ALEMSEGED:
Africa is fundamental
to our origin story

because most of our development
happened in Africa.

The conditions were unique

not only for the flourishment
of our species

and our lineage in general,

but for the preservation of
their remains.

(talking indistinctly)

NARRATOR:
The fossils discovered here

help paleontologists like
Zeray Alemseged

retrace the complex story
of our evolution.

VILLASEÑOR:
There is evidence

in the fossil record that
there's a mix of

walking and climbing traits,

and so our ancestors
were experimenting with

walking on two legs.

NARRATOR:
They were still spending time in
the trees, but a specimen

almost three-and-a-half-million
years old,

which Zeray named Selam,
adds to evidence

that our ancestors were
regularly walking upright.

What I'm holding here is

a replica of a skull of Selam,

which is earliest child
ever discovered.

This hole here,
which is where the spine

would insert
and connect to the brain,

is more centralized,
and that is what happens

when you have a upright,
walking individual.

By studying
the skull in general,

we were able to comprehend

that the species
to which she belonged

was at the cusp of being human.

The ability to walk upright

changed everything
for our ancestors.

It allowed us to run,

it allowed us to have shoulders

that we could actually throw
things, so we could hunt.

Over time, tool use
becomes much more complex.

So, for example, I have here
something called a hand axe.

This one here

was used to butcher a horse,

and we know that because

we were able to extract
blood residue from the edge.

These stone tools tell us
that our ancient ancestors

were much more
cognitively, socially,

technologically sophisticated

than we ever thought before.

Every time we find a new fossil
or a new artifact,

it's like adding a new page
to that human story.

♪ ♪

(animal trumpeting)

NARRATOR:
The fossil record reveals that
around 300,000 years ago,

a number of human-like species
are thriving.

And it's in Africa

that our own ancestors
eventually emerge--

Homo sapiens.

But the world humans encounter
as they leave Africa

is vastly different from the one
their predecessors inhabited.

♪ ♪

Over millions of years,

Earth has continued to cool...

...and is now in the thick of
the Ice Age.

♪ ♪

FRANCIS:
There were times when about
25% of the land surface

would have been covered by ice.

Particularly in the Northern
Hemisphere,

glaciers and glacial landscapes

extended as far as
New York and London.

So much water
was locked up as ice

that the oceans dropped
by hundreds of feet.

♪ ♪

ALEMSEGED:
As Homo sapiens moved from
one place to another,

they would be facing
many challenging conditions.

Remember,
we are a tropical species.

But at the same time,
there seem to have been

some type of shift
in terms of our behavior.

Humans were doing
all sorts of things

that you wouldn't have
imagined to have happened

during the Ice Age.

(birds chirping)

♪ ♪

NARRATOR:
Today, we uncover hidden
evidence of these behaviors.

♪ ♪

Clues that our ancestors

had evolved impressive
powers of creativity.

Wow!

The panel of
the spotted horses

is one of my absolute favorite
in all of cave art,

and I've seen it reproduced
a thousand times

in books and so on,

but nothing compares to
standing right in front of it.

You see the colors,
you see the textures.

In some ways,
it looks deceptively simple,

but these lines
are so carefully placed

that you immediately know
that this is a horse,

just from looking at
its contour.

It's a real combination of

what they're seeing
in their environment,

as well as maybe
some symbolic meaning

through the placement of
the dots around them.

And then with
the hand prints around it.

I look at those hands,

and you know that's us,
you know that's a human.

That's what connects us to

the people who made
these 25,000 years ago.

♪ ♪

NARRATOR:
Ancient art like this

has been found
all over the world.

Within the caves of Indonesia

are paintings dated
to around 45,000 years ago--

the world's oldest
known images of animals.

Studying this expanding
footprint of creativity

helps scientists piece together

the puzzle
of what makes us human.

♪ ♪

NOWELL:
Prehistoric people
around the world

chose to recreate nature
through their art.

And, of course,
the big question is, why?

For me, the most
compelling explanation

is that these images were
probably part of

an oral storytelling
tradition.

That they were
the illustrations

that went along with
their stories.

And they're not just
for entertainment value,

but they actually also
communicate a lot of

really important information.

In order to be able to survive
in a particular environment,

one person's knowledge
isn't enough.

♪ ♪

But humans live in communities,

and we share our knowledge.

It's not one mind,
but many minds working together.

It's this grand total,
this sum of all the knowledge

that we have
that we then pass on

from generation
to generation over time,

and that's what archaeologists
call cumulative culture.

For me, this is key.

This is what
makes humans unique,

and it's really
what has allowed us

to move out into all
different kinds of environments

and essentially live in

basically every corner
of this planet.

♪ ♪

NARRATOR:
The most extreme cold
and dry conditions

of the Ice Age don't last.

Because subtle changes
in Earth's orbit

alter the amount of sunlight
reaching its surface.

This, along with
increasing carbon dioxide

in the atmosphere,
drives temperatures up

and causes much of the ice
to melt.

♪ ♪

And as it retreats,

humans apply their skills
in a revolutionary new way.

They begin to farm.

♪ ♪

VILLASEÑOR:
Farming was a major turning
point for humans.

We started to modify the
landscape

in a way that we'd never done
before.

With farming, we transitioned

from using the environment

to owning the environment

through domesticating animals,

but also having a permanent
landscape that we control.

NARRATOR:
Within a few thousand years of
those first seeds being sown,

humans are farming
across the planet

on an ever-increasing scale.

♪ ♪

Today, about half of
the habitable land on Earth

is used for agriculture,

and our takeover of
the natural world

has had
an unprecedented impact.

♪ ♪

We have cut down three trillion
trees--

that's half the trees on the
planet--

to make way for agriculture
and our cities.

♪ ♪

NARRATOR:
Humans now have a greater effect
on shaping Earth's surface

than many of its natural
processes,

and human-made materials like
concrete and plastic

outweigh the combined biomass
of all life on the planet.

♪ ♪

MORRIS:
Humans have done a lot to
create a place where

they can thrive in relative
comfort.

We have cars, buses, trains.

We've conquered the sky.

♪ ♪

NARRATOR:
And the engine of this progress

is powered by
materials deposited

over the course of
Earth's history.

MASLIN:
Modern human society

is built on
the use of fossil fuels.

Coal, oil, and natural gas,

you can see them
as fossilized sunlight.

♪ ♪

Plants and animals have
trapped energy from the sun,

stored it in their carbon,

and then been laid down
in geological strata.

VILLASEÑOR:
Humans have basically mined the
geological record to fuel

many of the technologies
that we depend on today.

NARRATOR:
Humanity is acting as
a geological force,

adding greenhouse gases
to the atmosphere

around ten times faster
than the volcanic activity

that caused global warming
56 million years ago.

We've driven 20,000 years' worth
of climate change

in only 170 years.

As someone who studies natural
events,

it's remarkable,
the change that we have made.

We're changing every aspect of
the planet.

The oceans, the land,
the atmosphere, the ice.

♪ ♪

MORRIS:
I think this would be

an unrecognizable planet
to our ancestors.

NARRATOR:
The planet we have transformed

now supports more than
eight billion people.

A remarkable milestone
for a species

that was unlikely
to have evolved at all.

MASLIN:
Every single one of
your ancestors

must have survived and
reproduced to produce you.

The chances that any one of us
actually exists,

the chances of our own species
existing, are so, so small,

it must make us realize
how lucky we are.

♪ ♪

NARRATOR:
Since Earth formed

four-and-a-half billion years
ago,

the evolution of humanity
has been far from inevitable.

Life has been
threatened by asteroids.

(explosions roar)

♪ ♪

Catastrophic
volcanic eruptions.

♪ ♪

And the almost complete
glaciation of Earth's surface.

BRUSATTE:
In the history of the Earth,
the history of life,

it is one unfolding story

with so many
twists and turns and plot lines

and new characters
coming in,

and old characters going
extinct.

It's like the longest-running
television show of all time.

♪ ♪

NARRATOR:
But from a barren environment
once devoid of an atmosphere...

♪ ♪

...to thriving ecosystems

bursting
with plants and animals,

our planet's
geology and climate

shaped a world where
Homo sapiens could evolve,

the first species

able to look not only
into Earth's past...

...but also toward its future.

♪ ♪

MISSION CONTROL:
T minus 15.

NARRATOR:
In 2021, NASA launched
a rocket...

MISSION CONTROL:
Ten...

ANNOUNCER:
Nine, eight, seven...

NARRATOR:
...toward an asteroid
seven million miles from Earth.

ANNOUNCER:
Three, two, one...

And lift-off of
the Falcon 9 and DART,

on NASA's first
planetary defense test

to intentionally
crash into an asteroid.

♪ ♪

NARRATOR:
Even though this asteroid was
a fraction of the size

of the one that
wiped out the dinosaurs,

humanity was about to
make history.

Oh, my goodness!
(applauding)

(applause continues)

(cheering and applauding)

We have impact!

(cheering and applauding)

COLLINS:
As someone that studies
asteroid impacts and knows

how disastrous

their consequences can be,

it was really exciting

to watch the NASA DART
spacecraft

(cheering and applauding)

♪ ♪

NARRATOR:
Our technology allows us to
consider a future free from

the threat of a
cataclysmic asteroid impact.

But it also gives us
a perspective

never experienced by
our ancestors.

One that brings into sharp focus
threats far closer to home.

♪ ♪

WATKINS:
It takes 90 minutes to orbit
the Earth on the I.S.S.

So, we see 16 sunrises
and sunsets every day.

It is hard to pull yourself away

from watching the world go by.

♪ ♪

We're up in...

...the Canadian plains now.

(interview):
Seeing the Earth for the
first time

from the cupola windows

was just
absolutely breathtaking.

It's difficult to describe.

Just really
seeing the planet as one body.

Getting to see how

all of the different climates
and environments of the Earth

are really connected.

And also,
how fragile that ecosystem is.

It really drives home

the importance of
taking care of this planet

and the responsibility
we've been given to do so.

♪ ♪

I think oftentimes we as a
species

focus too much on the bombastic.

On the big, bold, brash things.

When it comes down to it,

the risk of an asteroid
hitting us is tiny,

but the risk that
climate and environmental change

pose to us right now,
every day, day in and day out,

that risk is so much higher,
it's so much more real.

We do have a responsibility
to look in the past

and use that information wisely
to make decisions

about our future
and the future of this planet.

It is our responsibility.

We are the only species
that understands

the consequence of our actions.

WATKINS:
I think, as human beings,
we've been given a gift,

and that is our intelligence

and capability to investigate

our impact on
the environment around us,

and I think using that gift

to understand how we can
affect our future

is really imperative.

♪ ♪

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