Original subtitles

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.

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 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.

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--

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 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 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

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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