Original subtitles

♪ ♪

NARRATOR: 252 million years ago,

a catastrophe killed nearly all life on Earth.

This is closest our planet has ever been

to going back to square one.

As many as 90% of species across the Earth died.

SURESH SINGH: This extinction was much greater

than the one that ended the age of the dinosaurs.

NARRATOR: But an asteroid wasn't to blame.

SONIA TIKOO: It is not easy to kill so many species,

so this had to be something utterly catastrophic.

(rumbling)

NARRATOR: The culprit was lurking

just beneath the surface.

We're finally able to piece together

clues from this ancient crime scene.

Now we finally know the culprit:

enormous volcanic eruptions.

TIKOO: It is as if the Earth itself turned on life.

NARRATOR: Yet some life stubbornly hung on.

♪ ♪

And when the threat passed,

thrived again.

PAUL WIGNALL: Mass extinction events,

although terrible, provide new opportunities for life.

Death and extinction

shaped the biodiversity of the living world.

♪ ♪

NARRATOR: From the ashes of a lost world

comes the story of

"Ancient Earth: Inferno."

Right now, on "NOVA."

♪ ♪

♪ ♪

NARRATOR: In a time long before

the rise of human civilization...

♪ ♪

Before the last glacial period...

♪ ♪

Before an asteroid impact wiped out the dinosaurs...

♪ ♪

In fact, a time before dinosaurs even existed at all...

An apocalypse destroyed nearly all life on Earth,

and it may hold lessons for our future.

♪ ♪

Over a quarter of a billion years ago,

the disaster looms.

♪ ♪

("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: 253 million years ago.

Earth looks very different than it does today.

On one side, a water world.

No land in sight.

♪ ♪

But on the other side,

Earth's landmasses are clustered

into a colossal supercontinent.

♪ ♪

This is Pangaea.

♪ ♪

Lush forest ecosystems flourish.

(animals grunting)

♪ ♪

And its waters teem with

weird and wonderful creatures.

♪ ♪

The Permian Earth is rich, diverse,

and full of life.

♪ ♪

There are no ecosystems on Earth today

that look exactly like those of the Permian period,

but some share a few similarities.

♪ ♪

Life at the end of the Permian was beautiful.

We had a very diverse ecosystem,

both in the marine realm, but also on land.

EMMA DUNNE: It doesn't contain any mammals,

any birds, any flowers,

so completely different.

♪ ♪

JEFFREY BENCA: But you would recognize

some of the early forerunners

to our modern conifers, for example.

♪ ♪

So, the rock I'm holding here

has a lot of fossil leaves

from a plant called Glossopteris--

one of the tree-forming plants

that lived in the Southern Hemisphere.

It's pretty cool to hold a fossil from that time period.

It's like going back

in a, in a time machine.

♪ ♪

NARRATOR: Pangaea is dominated by animals that lived before

dinosaurs and mammals evolved.

(animals grunting)

Forgotten creatures that scientists only know about

from the fossil record.

You would have had

these giant armored herbivores

with these crazy, big, bony sort of processes

on their skulls called pareiasaurs.

BRANDON PEECOOK: And the big predators are called gorgonopsians.

They've got a mouth full of sharp teeth.

Smaller sharp teeth up in the front,

and then these incredible sabers.

This is the first time that we know of predators

evolving saber teeth to kill their prey.

On land during the Permian, we had insects, as well.

We see wings, some of which span

more than a foot long.

Much larger than the ones we see today.

♪ ♪

DUNNE: And we also see the very first beetles.

The beetles haven't appeared yet in the fossil record

until about the Permian.

NARRATOR: There is also great diversity to be found in the oceans.

The oceans would look

completely different to now,

but with a couple of familiar characters,

ray-finned fish and sharks.

There were lots of reefs,

but made of very different types of organisms.

And there would have been trilobites

scuttling about on the ocean floor--

more or less seafloor bugs.

By the end of the Permian, life had become

very rich and diverse in, in a whole range

of habitats, both on land and in the sea.

SINGH: I would love to go back

and see all these animals living together.

It would be a great prehistoric safari.

♪ ♪

NARRATOR: But life is about to change forever.

Deep beneath Northern Pangaea,

superheated liquid rock-- magma-- is rising.

It pushes up against

the Earth's rigid upper layer, the crust,

until it can take no more.

♪ ♪

The crust splits open.

(erupting)

Within hours,

the local landscape is torn apart.

Cracks grow, forming great curtains of fire,

as lava floods onto the surface.

♪ ♪

The insides of Earth spew out.

The eruptions came from a giant volcanic system

in Northern Pangaea called the Siberian Traps.

♪ ♪

The remnants, the rock record

of these volcanic eruptions,

still exists in Siberia.

♪ ♪

There's a huge footprint of lava left behind,

covering a huge area of modern-day Siberia.

BURGESS: I've actually been to the Siberian Traps

and floated down rivers where both sides of the river

were huge cliffs of stacked-up lava flows.

♪ ♪

NARRATOR: These rocks reveal that the Siberian Traps

erupted on and off for around two million years...

♪ ♪

...emitting about 700,000 cubic miles of magma and rock.

The eruptions at the end of the Permian are absolutely huge.

They're, they're vastly greater in scale

than anything that we've seen today.

WHITESIDE: This is a planetary-scale eruption that would

cover the United States in lava around 300 yards deep.

♪ ♪

NARRATOR: We can try to grasp the scale of these eruptions

by comparing them to recently active volcanoes.

Witnessing a volcanic eruption

just gives you a sense of how powerful

the Earth is.

MATHER: The explosions make the ground throb,

so you can feel sound traveling through your whole body.

♪ ♪

And the smell and the fumes can be really intense.

♪ ♪

NARRATOR: In 2021,

the volcano Tajogaite erupted and released around

300 million cubic yards of material.

That's enough to fill... 80 football stadiums?

NARRATOR: Other eruptions in human history,

like the Krakatau Volcano, were much bigger.

MATHER: So, when Krakatau erupted in the 1880s,

it spewed out about two cubic miles of magma.

YING CUI: The eruption was so large

that it led to global temperature decrease

because of the gases emitted.

NARRATOR: But even Krakatau was minuscule compared to the eruptions...

(eruption roars)

...of the Siberian Traps.

♪ ♪

WHITESIDE: The Siberian Traps would be like a Krakatau erupting

every year for 300,000 years.

NARRATOR: Eruptions on this vast scale

are devastating to life nearby.

♪ ♪

Fire fountains blast volcanic material

up into the atmosphere.

Untold numbers of creatures perish in the forest fires

that burn close by.

Sulfur dioxide builds up and reacts in the atmosphere,

partially blocking out the sun.

Plants wilt and die as a volcanic winter sets in.

♪ ♪

Ash falls on a dying landscape.

After each eruption,

vast swaths of Northern Pangaea are scorched.

But is it enough to cause mass extinction?

♪ ♪

Although these early eruptions are huge,

Pangaea is big, too.

Most of the supercontinent

remains untouched by deadly lava.

Elsewhere in Pangaea, something curious is happening.

♪ ♪

A strange haze hangs in the air.

♪ ♪

Created by nutrient-rich volcanic ash and sulfur,

blown here from the eruptions

happening thousands of miles away.

♪ ♪

At first, plant life seems unaffected,

and may have even benefited from the nutrients and the ash.

There is no mass extinction.

For now.

But death is coming.

♪ ♪

These rocks, formed 252 million years ago,

contain evidence of a massive die-off.

As we go up in this section,

we are traveling forward in time.

So, these rocks here are older than the ones on the top.

♪ ♪

NARRATOR: These ancient rocks were formed on the ocean floor,

before being pushed up to make these mountains.

Rocks not only tell us about

the environment in which they were formed,

but something extraordinary about them,

it's that they are full of fossils.

So, for example, clams, marine snails,

shelled organisms, and other fossils,

like this nautilus,

that were living during that time.

NARRATOR: The diverse fossils in these rocks show that this

was a vibrant marine ecosystem.

But that was about to change.

So, all the complex ecosystem

that we are seeing here, full of life,

after

this level, it becomes, like, super-hard to find fossils.

And the things that we do find are really tiny,

and we see how all the diversity that we have below

seems to have just disappeared.

NARRATOR: Over just a few hundred years--

a geological blink of an eye--

almost all life here vanishes.

This is death on an astounding scale.

But curiously, these rocks show no direct evidence

of this volcanic activity.

GÓMEZ CORREA: So it's actually really surprising

that here we are, thousands of miles away

from the eruptions going on in the north of Pangaea,

and still you see the consequences going on there.

This event,

it's not only found here,

but also across the planet.

Life just vanished.

You will see this line of that.

You will see how life seems to just vanish.

♪ ♪

NARRATOR: How could volcanic eruptions in the north

wipe out so much life across the entire planet?

Scientists think that the Siberian Traps

was erupted in different phases.

Phase one was characterized by lava flows

for around 300,000 years.

♪ ♪

NARRATOR: It's not just Earth's surface

that is affected by the eruptions.

They also eject billions upon billions

of tons of gas and tiny particles into the air.

♪ ♪

Water vapor, sulfur dioxide,

toxic heavy metals, and carbon dioxide,

which begin to disperse in the atmosphere.

So, what we want to understand is,

how were these gases affecting the planet?

♪ ♪

TIKOO: Sulfur dioxide and carbon dioxide have opposite effects

on the Earth's atmosphere.

Sulfur dioxide reflects sunlight

back into outer space,

causing global cooling,

whereas carbon dioxide is a greenhouse gas

and can lead to global warming.

NARRATOR: The cooling and heating effects of these gases in the atmosphere

act on different timescales.

Sulfur dioxide tends to stay in the atmosphere

for a shorter period of time,

because it can get rained out.

TIKOO: But carbon dioxide can stay in the Earth's atmosphere

for hundreds, if not thousands, of years.

(rumbling)

NARRATOR: After each pulse or surge of volcanic activity,

any cooling effects from sulfur dioxide wouldn't last long.

But for heat-trapping carbon dioxide,

it's a different story.

Carbon dioxide released during one pulse

of the Siberian Traps volcanism

would have stuck around

for the next pulse.

NARRATOR: And as carbon dioxide builds up in the atmosphere,

it affects the entire planet.

BURGESS: So, the biggest driver of environmental change

that leads to mass extinction is not the lavas themselves.

It's the gases that they release into the atmosphere.

♪ ♪

NARRATOR: We're witnessing the impacts

of increasing levels of greenhouse gases today,

but at a much smaller scale.

CUI: As we are adding

more carbon dioxide to the atmosphere today,

the global temperature is rising,

which lead to a series of environmental changes.

NARRATOR: Studying our oceans and the impacts of modern climate change

gives clues as to how life might have been affected

by the warming 252 million years ago.

We can see right now, in our own world,

coral reefs affected by climate change.

The oceans are getting warmer

and they're getting more acidic.

SHUKLA: This is really stressful for corals,

and it causes vast swaths of places

like the Great Barrier Reef to bleach,

turning corals white.

NARRATOR: Bleached corals are more likely to die,

and this can have devastating consequences.

Coral reefs are a poster child ecosystem

for one that's complex and full of life.

If you start taking away those corals,

it's really easy to see

how ecosystems like that can collapse.

NARRATOR: But it's not just coral reefs

that are being pushed off balance

by present-day climate change.

As temperatures rise in the ocean,

that allows algae to reproduce really quickly.

And when it rains,

that pushes nutrients that we have on land into the ocean,

and the algae feed on that and grow,

resulting in these enormous algal blooms.

♪ ♪

NARRATOR: These vast algal blooms today

have consequences for life in the oceans.

And in this case,

it's not the rising temperatures that kill.

As algal blooms occur,

they actually take up the oxygen in the ocean,

leaving less oxygen behind,

and therefore, organisms can't live in it.

NARRATOR: Changes in modern-day ecosystems

show how the process of extinction can play out.

FORMOSO: So, these subtle changes

may not seem so striking at first:

the loss of one species here,

the change in this environment over there.

But given enough time

and given enough of these subtle changes,

you can have drastic negative impacts on ecosystems.

This slow relentless change is likely what led to

the huge loss of life at the end of the Permian.

♪ ♪

NARRATOR: Mass extinction can take place slowly

over thousands or even millions of years,

as environmental changes become too much

for many species to adapt to.

♪ ♪

In Pangaea, as greenhouse gases build up

over hundreds of thousands of years,

the temperature rises.

MONARREZ: During the mass extinction,

it is thought the ocean warmed up

between 14 and 18 degrees Fahrenheit,

and on land, they warmed up even more.

NARRATOR: On the supercontinent, trees begin to die.

(trunk cracking slowly)

(creaking)

♪ ♪

Holes appear in the canopy,

bathing the ground in sunlight.

For some life, it's an opportunity.

Weed-like lycophyte plants

flourish in this new environment.

And with the warmer temperatures,

other species migrate.

Woody, seed-bearing plants called cycads

that are believed to have once grown in the tropics

now thrive closer to the poles.

♪ ♪

Fossil evidence suggests that some ecosystems

are now more diverse than before the warming began.

♪ ♪

But this ecosystem is still vulnerable.

A few more degrees of warming and it could crumble.

♪ ♪

But then, something strange happens.

A silence descends on the Siberian Traps.

♪ ♪

Greenhouse gas emissions,

including carbon dioxide, taper off.

After 300,000 years of lava flows,

the eruptions finally stop.

For now.

♪ ♪

When scientists try to calculate the amount of

greenhouse gases released by the eruptions,

and then compare that to the amount of global warming

implied in the rock record,

something doesn't add up.

When we add up all the carbon

we think we would have got from the magmas,

making our best guess,

it's not enough to account for the level of climate devastation

that the geological record suggests.

♪ ♪

BURGESS: About half of the greenhouse gases

needed to drive the extinction to

the end of the Permian are missing.

NARRATOR: So, where do all the extra greenhouse gases come from?

♪ ♪

One answer can be found underground.

♪ ♪

It's quiet on the surface.

But beneath the Siberian lava field...

...reaching almost eight miles deep...

...hot magma still flows,

forming great reservoirs underground,

encountering rocks hundreds of millions of years old

deep below.

The amount of lava that, over time,

was released from the Siberian Traps

was so immense

that it caps the Earth's surface eventually.

NARRATOR: After 300,000 years of lava

building up on Earth's surface,

the path of the magma changes.

The volcanism enters phase two.

BURGESS: Instead of lavas flowing on the surface,

magma started to spread laterally underground.

MATHER: The Earth's crust is in some ways

like a layer cake.

So as the magma forced its way up,

it encountered different layers of rock.

♪ ♪

NARRATOR: One such rock was coal.

WHITESIDE: In this case, the magma literally

started burning fossil fuels

similar to the way we're burning them

through our pistons and power plants.

NARRATOR: But carbon dioxide doesn't act alone.

It isn't just coal in the Earth's crust.

TIKOO: Beneath the volcanic rocks released

by the Siberian Traps eruptions

lies an ancient seabed that contains the salt

left behind whenever the sea dried up.

In some places, the salt layers

were 650 feet thick.

Now, that's quite a lot of salt.

NARRATOR: When salt and magma make contact,

the consequences can be devastating.

So, salt is-- I have a piece with me here.

On its own, salt's a fairly sort of innocuous,

not very dangerous-looking rock type, as we know.

We put salt on our food and so on.

But it can be very dangerous.

So, when the hot magma comes into contact

with these salt layers, it, it bakes them,

releasing all sorts of horrible gases.

TIKOO: The burning coal

and the heated-up deposits of salt

that were triggered by these eruptions

just basically created a huge time bomb.

♪ ♪

NARRATOR: The salt and coal underground are heated

to as much as 1,400 degrees Fahrenheit.

And begin to release their toxins.

The pressure beneath the surface increases.

Until the land above can take no more.

(rock cracking)

♪ ♪

(eruption roars)

Volcanic material flies miles into the air.

Each eruption releases more greenhouse gases

from burning coal.

This is thought to be the missing link that accounts

for the full extent of global temperature rise.

And the scorching salt releases deadly chemicals, too.

Toxic gases called halogens,

which can spell trouble if they reach the ozone layer.

WIGNALL: It's a layer high in our atmosphere,

and what it does is,

it protects our planet from ultraviolet radiation

from the sun, which is very harmful for all life.

SINGH: When these halogens react with the ozone layer,

they weaken it,

and that allows harmful radiation

from the sun to come through.

NARRATOR: We've seen the Earth's ozone layer temporarily degraded

in recent history.

In the 1980s,

industrial activity created a hole in the ozone layer

over Antarctica.

One that is now closing.

But during the extinction event at the end of the Permian,

the halogens damaged

the ozone layer on a devastating scale,

bathing life with a massive dose

of harmful ultraviolet radiation.

The loss of ozone is thought

to have contributed to the extinctions.

But can scientists find a way to prove it?

BENCA: A way we can really understand

the mass extinction is by looking at

fossilized pollen grains,

microscopic reproductive structures

plants left behind in the fossil record.

NARRATOR: Some tree pollen has remained relatively unchanged

for hundreds of millions of years.

So modern-day pollen should look the same

as that in the fossil record.

So, I have a picture here

of a modern pollen grain of a pine tree.

It's basically one central body,

and there are these two structures on the side

that are called sacci.

These help this grain catch the wind and fly.

And this is very much what the pollen grains

in the end-Permian trees would have looked like

under normal conditions.

NARRATOR: But the fossil pollen from the extinction event

doesn't look the same.

So, during the mass extinction at the end of the Permian,

the pollen grains start looking more like this,

and, boy, they're strange.

This one here has three sacci when it should have two.

And this one has four sacci.

This here is two grains that are stuck together.

They come in all sorts

of strange shapes and forms that really deviate

from what a healthy pollen grain should look like.

They're malformations.

NARRATOR: Could increased ultraviolet radiation be the cause?

To find out,

paleobotanist Jeffrey Benca grew modern pine trees

under high ultraviolet radiation in a lab.

BENCA: We wondered if the plants

would just die on us under these extreme conditions.

But that's not what we found.

Instead, we found the exact same types of malformations

in the fossil record were produced by our modern pines.

NARRATOR: Although this high ultraviolet radiation

didn't kill the plants outright,

malformations in the pollen did have catastrophic consequences.

The results of this experiment are telling us

that at the end of the Permian,

the forests would have been sterilized,

unable to reproduce.

NARRATOR: It is a slow march to extinction.

♪ ♪

The Permian forests have been exposed

to extreme ultraviolet radiation.

Healthy-looking trees are now sterile.

♪ ♪

As trees die and are not replaced,

animals lose precious habitat and food supplies dwindle.

♪ ♪

During the mass extinction,

life on land is under threat from all sides.

The mass extinction at the end of the Permian

is like "Murder on the Orient Express."

There's not one killer that can do it all.

SINGH: There's still a lot of debate

about how all these killers came together

to kill off life on land.

We're talking global warming, heavy metal poisoning,

acid rain, wild fires, deadly U.V. radiation.

This was hell on Earth.

♪ ♪

BENCA: There probably were pulses of ozone weakening

that were happening throughout the duration

of the Siberian Traps activity,

but over even longer time spans,

global warming was kicking in

and really driving ecosystems to full collapse.

NARRATOR: The collapse of life in the oceans

is even more dramatic.

The warmer, nutrient-rich waters contain less oxygen.

Oxygen that marine life uses to breathe.

And as carbon dioxide reacts with seawater,

the oceans become more acidic.

Algae and bacteria bloom across the planet,

poisoning the oceans with the hydrogen sulfide they release.

Creatures across the oceans die.

Huge stretches of the seafloor become fetid beds of death.

MONARREZ: So, in the oceans,

the combination of increases in temperature,

loss of oxygen, and acidification

all contributed to the loss of life

we see at the end of the Permian.

These ocean killers could have worked together

to be exceptionally devastating to ocean life.

NARRATOR: Exactly how much life died is debated by scientists,

because the fossil record is incomplete.

But evidence shows

that the great Glossopteris forests,

the giant sabertooth predators,

and almost all marine life disappears.

♪ ♪

By the time the eruptions finally stop,

the average global atmospheric temperature

has risen as much as 22 degrees Fahrenheit.

Countless species have gone.

The rich complexity of life on Earth has vanished.

The words "mass extinction" are not

lightly put together by scientists.

They carry real weight.

And the extinction at the end of the Permian

was the most severe of all of these.

It's been called the mother of mass extinctions,

it's been called the Great Dying.

It's, it's by far the worst thing

that's, that life has ever had to endure.

♪ ♪

NARRATOR: With so much death and destruction,

how could any life hold on at all?

Life on Earth is adapted to living on Earth.

It has evolved that way.

And if circumstances change,

organisms can adapt to that change.

(hisses)

And those that cannot adapt will eventually go extinct.

♪ ♪

NARRATOR: If species can adapt to the new conditions,

it gives them an opportunity to thrive.

Death and extinction shape the evolution of life.

It's through this act

of creative destruction, where one species go extinct,

that allows for another species to actually rise.

Over time, the combination of these interactions,

of extinction, adaptation, and evolution,

create resilient ecosystems.

NARRATOR: But even resilient ecosystems aren't indestructible.

An ecosystem is a lot like a Jenga tower,

where each brick is its own species.

And as you remove one to two species,

the ecosystem stays relatively intact.

But the more species you lose,

the more unstable the ecosystem becomes

until it fully collapses.

PEECOOK: Today, organisms are really struggling

to adapt to an ever-changing planet.

SHUKLA: And it's not just climate change.

It's also things like habitat destruction.

Loss of coral reefs, loss of sea ice.

Deforestation.

Loss of wetlands.

Loss of grasslands and prairies.

NARRATOR: But even after ecosystems collapse,

like they did 252 million years ago,

some life survives.

If it can adapt, there's a chance to rebuild.

♪ ♪

The Permian apocalypse isn't just the end of one world.

It's the beginning of a new one.

♪ ♪

Fossil evidence is patchy,

so scientists don't know exactly where life holds on.

On land, some life likely survived near the cooler poles.

And many creatures could have sought refuge underground,

sheltering from blistering temperatures

and intense solar radiation.

And some life survives above ground, too.

A single type of plant dominates

much of the post-extinction landscape.

Pleuromeia.

A hardy plant that makes it through the apocalypse.

This ecosystem provides

just enough sustenance for the cockroaches,

who also make it through.

Life endures.

But the searing heat does, too.

The period immediately after the Permian

is the Triassic period, and it was very, very hot.

NARRATOR: Scientists know about these conditions

from studying fossils

and the chemical composition of rocks formed at the time.

It's incredible what we can get from rocks.

They look so unassuming, but actually,

they hold so many clues

to past environments and past life.

LOOY: We, for instance, know that there were forests growing

on the South Pole, and to make that happen,

you need a warm planet.

WHITESIDE: Temperatures on land would be 120 degrees Fahrenheit,

possibly up to 140, with heat waves on top of that.

LOOY: And that is so hot that in several places of the world,

complex life would not have been possible anymore.

NARRATOR: It's also hot in the oceans.

Surface ocean temperature may have reached as high

as 100 degree Fahrenheit,

and that's as hot as a hot tub.

These extreme ocean temperatures would have been

inhospitable to most ocean life.

MONARREZ: The mass extinction at the end of the Permian

was so devastating to coral reefs

that for about 14 million years into the Triassic,

we don't see corals anywhere on the planet.

NARRATOR: For life to bounce back, the planet needs to cool down.

♪ ♪

Normally, over vast timescales,

Earth's temperature naturally resets itself.

Carbon dioxide is removed from the atmosphere,

in part by reacting with rainwater.

But vast areas of Central Pangaea are desert.

Little rain falls.

It takes millions of years for Earth to cool.

♪ ♪

Much of the supercontinent remains barren and dry.

But 18 million years after the mass extinction began,

life is about to get an enormous boost.

(thunder rumbling)

And traces of what that was can still be seen today.

♪ ♪

These mountains are largely made of a hard rock called dolomite.

But hidden within them

are layers of an altogether different rock.

One that holds clues

to an extraordinary time in Earth's history.

EVELYN KUSTATSCHER: This is the rock that formed

during this strange period of time.

This is a sandstone.

It's a relatively soft stone, and you can see

all the single grains of the sand.

And if we take this ones in here,

this is a softer stone still,

and it easily breaks down in my fingers,

because it's a mudstone.

These rocks in here are looking completely different

from the ones below and above us,

because these are sandstones and mudstones,

whereas those above and below are dolomites.

NARRATOR: The secret of this unusual layer of rock

is how it was formed.

Sandstones and mudstones are sediments

that are typically formed

by the erosion of sand and mud on the continents

which were washed into the ocean.

NARRATOR: All over the Dolomites,

there are examples of this

strange layer of softer rocks made from sand and mud.

KUSTATSCHER: So now, of course, we have to ask ourself,

what caused this dramatic change?

NARRATOR: The answer came from the sky.

And it was rain, a lot of rain.

This episode lasted for a long time.

About two million years.

NARRATOR: A deluge on this scale seems so unlikely

that when scientists first discovered the evidence,

some believed it was just a local event.

KUSTATSCHER: But later on, evidence of it popped up

also at China, Iran, North America.

So nowadays, it is believed to be a global event.

This period of time is called the Carnian Pluvial Episode.

(thunder rumbling)

NARRATOR: 18 million years after the mass extinction began,

the skies become heavy with moisture...

...until the clouds burst.

(rain falling, thunder rumbling)

Rain falls across Pangaea.

And Earth is changed once more.

♪ ♪

Lush forests grow again.

This two-million-year event lasted just as long

as the volcanism that preceded it

and may have marked the rise of a new life form.

The Carnian Pluvial Episode set the stage

for the dawn of the age of dinosaurs.

♪ ♪

SINGH: My research suggests that this era of warm,

wet conditions really boosted plant diversity.

And from the plants, we get

more herbivores, more carnivores,

and dinosaurs are part of that growth.

So, this is Herrerasaurus, this is one of the first dinosaurs

to appear just after the Carnian Pluvial Episode,

and as you can see by the sharp teeth here,

this was a meat-eater, one of the top predators.

The Carnian Pluvial Episode,

and what it might have meant for dinosaurs,

is a brand-new avenue of research.

DUNNE: We see a lot of fossils that we can't quite

figure out exactly how they fit into the grand family tree

of ancient life, and so we are working with

some very difficult fossils,

and putting all this stuff together

is very, very difficult for scientists.

(rain falling, thunder rumbling)

PEECOOK: We can see that the ecosystems were changing.

We can see that the climate was changing.

But how those interact,

what actually would have affected the dinosaurs,

what would have caused them to be successful,

we don't know yet.

This is why there are so many paleontologists

doing active research.

NARRATOR: What scientists do know today

is that the world of the dinosaurs will persist

for over 160 million years.

♪ ♪

Life on our planet...

(explosion roars)

...has been punctuated by catastrophes.

And although the extinction at the end

of the Permian might seem like a distant nightmare,

it holds lessons for our own future.

CUI: Both the end of the Permian and today,

we are seeing rising global temperatures,

lower oxygen levels in the sea, and ocean acidification.

Today, there's no volcano-- it's just us.

TIKOO: While we're not releasing as much greenhouse gas

as was released during

the entirety of the Siberian Traps eruptions,

the fact is, we're releasing them a lot faster today.

NARRATOR: And our fast-changing environment

is affecting life everywhere.

We are driving things to extinction

at, at an extremely rapid rate.

SHUKLA: If the loss of life

continues to go unchecked, we may very well

be in the midst of another mass extinction on this planet.

NARRATOR: But even after the worst catastrophes

in Earth's history,

life recovers.

DUNNE: The extinction at the end of the Permian

both shows us the fragility of life,

but also shows us how resilient life can be.

FORMOSO: The most amazing thing about life

is how it bounces back from these devastating events.

However, it comes back differently.

BENCA: It takes a long time

for life to rebound from these sorts of events.

MONARREZ: If we continue on our current path,

we risk altering life as we know it.

We also risk our place as humans on this planet.

NARRATOR: And yet hope remains.

Human beings are an ingenious species.

SINGH: We've gone from hunter-gatherers to traveling through space.

If we can do all that,

I'm confident we can sort out our current problems.

NARRATOR: What does the legacy of mass extinction

mean for our future?

Whether it's a massive eruption of lava

or human beings burning fossil fuels,

the Earth is going to be fine-- it's the species

that are living on the Earth at the time

that might not make it through.

In the long term, the Earth will come back

from where we are today.

The question is just whether we as a species

will be here to see it.

♪ ♪

NARRATOR: On "NOVA: Ancient Earth"...

AISHA MORRIS: One major event

can have these ripple effects

throughout the rest of history,

and this event is almost unmatched.

STEVE BRUSATTE: In the history of life, it is one unfolding story--

so many new characters coming in

and old characters going extinct.

ZERAY ALEMSEGED: What I'm holding is the earliest child ever discovered.

This species was at the cusp of being human.

NARRATOR: "Humans" on "NOVA."

Next time.

SINGER: ♪ Wish I could go back in time ♪

♪ ♪

♪ ♪

♪ ♪

♪ ♪

♪ ♪