50x15 - Ancient Earth: Humans

[bunniefuu]

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...

[expl*si*n 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]

[expl*si*n 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.

GARETH COLLINS: It
would have looked like

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 b*ll*ts 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 g*n.

It was deep underground.

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

The Earth's crust
is layers of rock,



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


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


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.

It's the warmest the planet
has been in 180 million years.

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,

so did the species
that relied on them,

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,

and that would have
created this rain shadow,

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

evolving more efficient ways of
moving through the landscape.

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...

h*m* 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 h*m* 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 buildings, we
have very tall buildings.

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
h*m* 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

slam into the asteroid
and successfully deflect it.

[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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