All language subtitles for Eons.Life.and.Death.on.Pangea.S01E01.How.The.Formation.of.Pangea.Changed.the.World.1080p.AMZN.WEB-DL.DDP5.1.H.264-RAWR_track3_[eng]

Viewers like you make
this program possible.

Support your local PBS station.

252 million years ago,

in the dying days
of the Permian Period,

life on Earth
was brought to its knees.

In the northern reaches
of the supercontinent Pangea

in what's now Siberia,

colossal volcanic eruptions

burst through
the planet's crust,

and they didn't stop erupting

for hundreds
of thousands of years.

An area nearly the size
of Western Europe

was blanketed in lava,

and the knock-on effects
of these eruptions

baked the planet
into a hellscape that,

for most of the species
of the Permian,

was not survivable.

Blake de Pastino: On land,
relentless heat, drought,

and acid rain
collapsed whole ecosystems

and scorched
the straggling survivors.

More than 70%
of terrestrial species

were lost forever.

Life in the oceans
was devastated, too,

as the water rapidly
heated, acidified,

and was stripped of its oxygen.

Over 80% of all marine species
went extinct

in an evolutionary blink
of an eye.

Michelle Barboza-Ramirez:
An entire ancient world

of diverse living creatures

was brought to a sudden
and brutal end by this event,

a catastrophe known
in the study of deep time

simply as the Great Dying.

The Great Dying was
the single worst mass extinction

in the entire history
of life on Earth,

a level of death
that has no known equal

in the fossil record,

even more severe
than the asteroid impact

that ended
the reign of the dinosaurs.

It was perhaps the closest
that complex life ever came

to being extinguished
altogether.

Gabriel-Philip Santos: But what
really made the Great Dying

at the end of the Permian
such a disaster was that

in the Permian Period itself,

life had been thriving in ways

that it had
never thrived before.

The Permian was a chapter
when ancient life on Earth

conquered new realms
for the first time,

faced and overcame
new ecological challenges,

and pioneered
entirely new ways of living.

These species rose and fell

long before the first blade
of grass sprouted,

the first dinosaur hatched,
or the first flower bloomed.

And the vastness of time
that separates us

makes them seem both strange
and familiar to our eyes.

Kallie Moore: But the story
of their evolutionary ascent

and, in particular,
of their catastrophic fall

is one of the most
important and dramatic

in all of natural history--

a story about how a chain
of geological, climatic,

and evolutionary events
erased an ancient world

and created the modern one
we know today.

And it's a story about us.

Our direct ancestors
were shaped by the Permian

and somehow survived

the disastrous way
that it ended,

when few other species could.

But to understand the full story

of the time that
almost everything died,

we'd have to start tens
of millions of years earlier,

before the Permian Period
even began,

in an ancient swampy forest
here,

in what's now
Joggins, Nova Scotia,

at a time when planet Earth

would have looked...
oddly familiar.

The history

of complex life on Earth

is split into three main eras,

each composed of
multiple periods of time.

Currently,
we're in the Cenozoic Era,

or the era of recent life,

the heyday of flowering plants,
birds, and mammals.

In fact, you might also
sometimes hear

the Cenozoic Era simply called
the "age of mammals."

Before that was the Mesozoic,
or life's middle era,

famous for its dinosaurs,

and so sometimes called
the "age of reptiles."

And even further back
was the Paleozoic,

the era of ancient life,

when species
were far older and stranger

and rarely got
the attention they deserve.

Now, the final chapter
of the Paleozoic

was the Permian Period.

It was brought to a close
by the Great Dying,

and it began with the formation

of the supercontinent Pangea.

We'll get back to that
a little later,

but to set the scene,

let's rewind just a bit further
to the end of the period,

just before the Permian,

the Carboniferous Period.

While the Paleozoic seems
so far in the distant past

that Earth would barely
be recognizable,

at first glance,

the resemblance
would actually be

pretty uncanny at times.

Because the way our planet
looks now,

blue, green, and white

is actually pretty rare
for Earth.

And the last time it had
that classic Earth look

was during
the Late Paleozoic Ice Age,

when the planet had glacial ice
covering large areas of land,

as it does now.

And for most of that ice age,

the world even had
distinct continents,

like it does today.

The supercontinent of Pangea,

on which the story
of the Permian would play out,

had yet to fully form,

though it would soon enough.

It's hard to imagine our world
looking any different,

but this combination of features
is an unusual occurrence

from a deep time perspective,

and a connection we share

with those ancient days
of the planet's history.

For the last few days,
we've been here in Boston

at the Museum
of Comparative Zoology in...

Harvard.

Sorry, Boston.

It's been really fun,

because I've been able
to go into the collection

and see
some really amazing fossils.

It was this museum kid's dream
come true to be in there.

Yeah. From the outside,
it's like,

"Oh, that's
just another rock."

And then someone thought,

"Oh, let me crack
this thing open.

Oh, I wonder if there's
anything inside."

And lo and behold,

an early tetrapod from
the Late Carboniferous.

At the peak of
this ancient ice age,

near the end
of the Carboniferous Period,

the world didn't just look
geologically familiar,

it had started to look
ecologically familiar, too.

Christina Byrd:
What we're looking at here

are some plant fossils
from the Carboniferous.

In particular, we're
finding a lot of ferns.

See, while the world
was in a rare deep freeze

with huge glaciers covering
much of the southern hemisphere,

the area around
the equator was covered

in lush, humid tropical swamps
and rainforests,

teeming with complex life.

In earlier periods
of the Paleozoic,

complex life had been found
only in the oceans,

where it had originally evolved.

But eventually,
plants and invertebrates

colonized the land,

and by the Carboniferous Period,

we vertebrates
had joined them, too.

Thanks to the head start
that invertebrates got over us

in moving onto land, though,

the Carboniferous
is often remembered

as the golden age of giant bugs,

like Arthropleura, for example,

a nearly 2.5-meter long,
50-kilogram millipede relative

that had few, if any,
competitors or predators

to worry about in the swamps
of the Carboniferous.

And ruling the skies
was Meganeura,

a pigeon-sized
dragonfly relative,

and one of the largest
known insects to ever fly.

The vertebrate invasion of land

was still only in
its earliest stages,

and we couldn't yet challenge
the dominance of the giant bugs.

But our arrival meant

that the swampy equatorial
wetlands of the Carboniferous

were among the earliest
ecosystems on land

to broadly resemble
the ones we have today,

with those three groups--

plants, invertebrates,
and vertebrates--

all coexisting and interacting

as they have ever since.

Basically, back
in the Carboniferous

with things moving onto land
and evolving onto land,

we're seeing the start

of what today's rainforests
started as

and what they will
eventually become.

But these ecosystems had
some big differences, too,

because during
the ancient ice age,

life on land was
still finding its feet.

So, where exactly are we?

We're at
the Joggins Fossil Cliffs.

It's a UNESCO
World Heritage Site.

And it's 15 kilometers
of beach exposure that's

the Late Carboniferous
or Pennsylvanian.

And it's the best
Carboniferous exposure

in the world.

I've wanted
to go to Joggins

for a very long time,

because I really just love
the Carboniferous.

When I was a kid,

the very first fossils
I collected

were Carboniferous fossils.

I even collected
little, tiny Crinoid stems

from the playground gravel
when I was in grade school.

And I still have them.

When we first pulled up
for the very first shoot here,

I was, like,
shaking the back of the car,

and I was just like,
"Let me out, let me go see it."

You see, the stars

of the Carboniferous
fossil record are its plants,

fossils that fuel
the modern world

as we know it today.

So, if we were able to go
back 300 million years ago,

what would it look like?

300 million years ago,

Nova Scotia was located
at the equator,

so it was
a tropical rainforest

with a lot of rivers
flowing through.

So, the best environment
to think of today would be

the Amazon rainforest.

The swamps
were dominated

by towering club mosses,

relatives of
horsetails and ferns,

all of which reproduced
by using spores

that needed to find
their way to moisture

to become fertilized and grow.

Spores were an ancient feature
in these plants.

They'd been using them

since their
small and spongy ancestors

first colonized the land.

And by the Carboniferous,
they'd grown and diversified

to create complex rainforests,

which included giants
like Lepidodendron

that had evolved into
a towering tree-like form

over 50 meters tall.

Oh, my gosh, look.
It's quite big.

Holy smokes.

And it's in that thick
sandstone layer there.

And then if we move over,
there's a second stump.

There's another one!

These are visible
in the cliffs

for about
three to four years,

and then they weather out.

And because it's a forest,

new stumps will be visible
in different parts.

Seeing the Lepidodendron
tree stumps in the cliffs

was pretty amazing.

We walked for quite some time,

and everybody was kind of like,

"Are we actually
going to see any?"

And then all of a sudden,

Dr. Jade Atkins was like,
"Oh, look. There they are."

And everybody in the crew--
everybody was like

"There they are,
there they are."

Knowing that these trees

would have been flooded
and buried

305 million years ago or so,

and here they are just eroding
out of the coast today

is really special.

So, we found a really cool
fossil on the beach here.

Can you tell us
what it is?

So, this would be
part of a stump

of one of those scale trees,

so Lepidodendron
or Sigillaria.

Cool.

Each hole here would be
a secondary branch in life.

The carbon dioxide
drawn down from the atmosphere

and incorporated into

these photosynthesizing
swamp plants

is what gives
the Carboniferous its name,

the coal-bearing age.

No, you can still see
plant in it.

Yes. Yes, in most of it,
you can still see plant.

As they died,
they sank into the murky depths

generation after generation,

where the conditions
kept them from decomposing.

And as the glaciers
of the Late Paleozoic Ice Age

waxed and waned,

these coastal swamps
and their drowned plant material

were regularly submerged,

when the melting ice
raised sea levels.

This plant material then formed
peat that was buried,

and after enough time,

heat, and pressure, eventually
transformed into coal.

The same vast coal deposits

that we would eventually
find, dig up, and burn

to power the world

were created here in the swamps
of the Carboniferous Period

over 300 million years ago.

So, what was life like
when the coal layer

was first being
laid down?

So, this was
a really lovely time

for animals that might
breathe through their skin.

So, amphibians,
but also insects

were having a great time
at this time.

Everybody was getting
very big,

and it was just a really moist
rainforest environment.

That allows amphibians
to be more widespread,

because they are
reliant on water

to lay
their gelatinous eggs.

They cannot lay them
in a dry environment.

One group
of amphibious creatures

called temnospondyls

was especially widespread
and abundant in these swamps.

Over the course
of the Carboniferous,

they flourished and diversified

into a range of different sizes
and ecological niches.

Some early temnospondyls
were small and salamander-like,

hunters of insects
and other tiny prey

in the forest undergrowth,

like Dendrerpeton
or "Tree-creeper," for example.

Dendrerpeton is
one of the oldest members

of a lineage that probably
contains today's amphibians.

So, the frogs, salamanders,
and caecilians that we know,

this is one of their oldest
known relatives, probably.

Dendrerpeton is
named for the way its fossils

have often been found,

preserved
in the hollowed-out stumps

of swamp trees that
individuals crawled into

only to become
trapped and buried.

Others, like the big
and powerful Eryops

from the very end
of the Carboniferous,

were more crocodile-like.

What is that?

This is
Eryops megacephalus.

Now, Eryops first evolved
in the Late Carboniferous,

but it didn't really get
to this kind of size

until the Permian.

The lush swamps
of the Carboniferous were

ideal for amphibians,

and in their damp,
waterlogged paradise,

they thrived.

Some even began spending
so much time on land

that they became
almost fully terrestrial,

reliant on watery habitats

for only one last
big part of life--

reproduction.

But among both the plants
and vertebrates

of the Late Carboniferous,

a revolution was underway.

New groups had arisen

that could break their ties
to water entirely.

I have spent
my entire adult life

in the American West,

which I love.

And that means
I've spent a lot of time

hiking in the woods
among pine trees

and spruce and fir.

And over that time,
I've become enamored

with a particular tree,
the Ponderosa pine.

Part of what I love about them
is the scent that they produce

a certain time of year.

I'll be out on a hike,

and the woods smell
like butterscotch and vanilla.

And whenever I smell that
and I'm on a hike,

I know that spring is coming.

Alongside the ferns,
horsetail relatives

and club mosses of the swamps
were another group of plants

known scientifically
as gymnosperms.

Rather than reproducing
like those other plants did

via spores, which are
tiny naked reproductive cells

exposed to the world,

they had evolved seeds.

Today, I'm at the Montana
Conservation Seedling Nursery,

and I met a fellow
named Benjamin Jones,

whose title
is Grower of Seeds.

And his job is to turn
these little, tiny seeds

into giant Ponderosa pine trees.

Benjamin Jones:
At the nursery, we grow

about a million seedlings
a year

for anything from
wildfire rehabilitation

to just increasing
wildlife habitat.

And you've been
working here how long?

18 years.

So, you personally
are responsible

for growing 18 million trees,
give or take.

I'll take partial credit.

That's amazing.

You must be very proud.
Yeah.

So I understand you're going
to put me to work today.

What are we going
to be doing?

We're going to sow
Ponderosa pine

into a styro block
using a shutter box.

Okay, while I'm doing this,
explain to me,

why are seeds
so important?

Why are they
so successful?

Seeds are sort of
an all-inclusive package.

They contain
their own nutrients,

they have their own
moisture content,

and they
will only germinate

when conditions are ideal.

Having seeds had helped
early seed plants

gain an increasing foothold
in parts of the rainforests

over the course
of the Carboniferous.

It allowed them to tolerate

the occasional
seasonal dry spell,

while spore-producing plants
struggled to reproduce.

And by the Late Carboniferous,

some of the gymnosperms
were beginning to look

kind of like the ones
we have today.

The earliest conifer trees
had evolved by this time,

with many of the same traits
as today's species.

They were woody,
with needle-like leaves

that retain water,

and cones containing
seeds and pollen

that rely less on water
for reproduction.

These adaptations helped
primitive conifers

and other gymnosperms thrive

in drier areas of forest,
where they had an advantage.

But plants were not
the only ones

that had stumbled on
this same general solution

for surviving
in drier environments.

Around that same time,

vertebrates had given rise

to a new group that evolved
a similar trick of their own--

the amniotes,
with their shelled eggs.

Unlike the naked,
gelatinous eggs

of their amphibious
ancestors and cousins

that had to hatch
in an aquatic environment,

these amniotic eggs provided

a self-contained aquatic
environment internally.

The embryo was encased
in an outer shell

and an amniotic membrane

that protected
the developing young,

just like the seeds
of gymnosperms.

When this trait first arose,

it was just a weird
reproductive ability,

albeit a useful one
in areas of forests

that seasonally dried out.

Yet this bizarre
and unusual trait

would go down in deep time

as one of
the single most game-changing

evolutionary innovations ever,

because it was
the final push needed

for vertebrates to become
fully terrestrial.

And it gave rise to one
of the greatest animal dynasties

the world ever saw--

the amniotes.

So, amniotes lay eggs.
Mm-hmm.

What makes these eggs
such a big deal

in the grand story
of life?

Eggs were basically

a key innovation
of amniotes,

and it allowed amniotes

to break their ties
with water,

so that they could
reproduce on land

and not have to rely on
going back to the water,

like amphibians do.

All living and extinct
reptiles, birds, and mammals

are amniotes.

And even though we mammals
mostly don't lay eggs anymore,

we've essentially internalized
our amniotic egg,

losing the shell but keeping
the amniotic membrane

that surrounds the offspring
inside the mother,

though this extension
of the process wouldn't develop

for more than another
100 million years.

These earliest amniotes
in the Carboniferous are

who every vertebrate that
isn't a fish or an amphibian--

from humans to hummingbirds
to humpback whales--

can trace our ancestry to.

The rise of eggs and seeds
played out around the same time

in similar places,
and for similar reasons, too.

But they also have
one more thing in common.

They've both left
lasting legacies

on the world ever since.

So, you would say,
like, the egg is what led

to the success of, like,
amniotes through time?

I would definitely say
the egg is

one of the key things

that allowed amniotes
to become so successful.

And the egg definitely came
before the chicken, then?

Well, that's still up
for debate.

And among
one lineage of amniotes,

an event was about to take place

that seemed subtle at first

but had consequences
that still define

the modern world today--

one ancestral population
branched into two.

We don't know
exactly how it happened.

Perhaps one group
was cut off from another

by an environmental barrier,,

like a newly-formed river,

setting them on different
evolutionary journeys.

Or maybe one group
changed their behavior,

becoming active
at a different time of day,

a different level
of the forest canopy,

or hunting a different type
of insect prey,

eventually drifting apart

from the other group
ecologically.

But we do know

that the early species
from each side

still looked pretty much
identical at first glance.

Yet from one side
of the family split

would come all reptiles--

from crocodiles to turtles
to snakes to dinosaurs,

including birds.

And from the other side would
eventually come all mammals--

from manatees to mammoths
to bats and wombats to us.

During
the Late Carboniferous,

it was really hard
to tell the difference

between these two groups,

and it wasn't
until later on

in their evolutionary
history where we see

the defining traits
of these two groups

starting to evolve.

Think of
all the iconic differences

between both sides
of the family tree today--

our skin, our teeth,
our behaviors, our diets.

At this point, none of
these differences exist yet.

The only reason
we can tell them apart

is because their fossil skulls

have some subtle
differences in structure

that had begun
to distinguish the two sides

from one another.

As we'll see over the course
of the Permian to come,

the changes in sauropsid
and synapsid anatomy

will eventually become clear
as they

continue on their
parallel evolutionary journeys.

So, by this time,

egg-laying amniotes
and seed plants,

including gymnosperms,

had independently developed
similar solutions

to the same problem
in the same environments,

reproducing during times
when land became dry land.

And while they were only
ecological side characters

compared to their more
water-reliant cousins

in the Carboniferous swamps,

that was all about to change.

As the Carboniferous
drew to a close,

those oddball seed-
and egg-producing species

found themselves
in the right place

at the right time,

and with the right traits

to rise to prominence
as the Permian approached.

This opportunity came

in the form of
a sudden ecological shift

around 305 million years ago,

an event known

as the Carboniferous
Rainforest Collapse.

Just before
the Carboniferous Period

came to a close, the planet
started to dry out and warm up,

which reshaped
ecosystems on land.

The big swampy rainforests
of the equator

began to break up
into isolated pockets,

giving way to drier
and more open environments.

Forests of conifers
and other seed plants

began to spread,
replacing the wet swamps

that had been
so prevalent before.

And big forests of seed plants,
like conifers,

have stuck around
in much the same way ever since.

These forests provide habitats
for countless species

and represent one of the
planet's major stores of carbon.

It's hard to imagine
the world without them,

but they might have stayed
on the ecological margins

if the Late Carboniferous
had played out

just a little differently.

Instead, they became a familiar
feature of the modern world

that we can trace directly back

to a 300-million-year-old
climate shift

in the era of ancient life.

And we, too, can trace the story

of our rise
to the same climate shift,

because it was also the moment

that the two lineages
of amniotes

found themselves
perfectly placed

to move into
the new drier niches

that were now available.

So, as we start to move
into the Permian,

things start to get drier.

So, we start to move
into an environment

where amniotes--

so animals that have the water
with them in their egg--

start to thrive,

because they're
not tied to water

the way the amphibians are.

Those animals actually had
an opportunity to grow

and diversify
into these new niches

that were opening

because the old systems
were starting to fail

with this change
in climate.

And this led to a rapid
diversification of amniotes

into all sorts of shapes
and sizes during the Permian.

And the Carboniferous
Rainforest Collapse was

just part of a longer-term trend
in the Late Paleozoic climate

that would suit
both these groups.

The world was heating up,

and the ice age
was beginning to end.

Glaciers started to recede
from the higher latitudes

as the deep freeze ended,

allowing species to spread
from the fragments of the swamps

into these new regions
reclaimed from under the ice.

The Carboniferous had ended,

and the Permian had begun
hot and dry,

and it would only become
more so over time.

And it wasn't the only
planetary-scale trend

in the Early Permian shaping
the evolution of life,

and, quite literally,
shaping the world itself.

The continents we know today

had gradually been fused
into one by plate tectonics--

the movement of chunks of
the Earth's crust and mantle

over geologic time.

By the Early Permian,
these forces had created

a single huge, continuous
landmass--Pangea--

which literally means
"all the lands."

Pangea had been hundreds
of millions of years

in the making,

and on it would play out
the final chapter

of the Paleozoic Era.

A chapter that would begin
with bands of ancient wanderers

leaving the shrinking swamps
of the equator

to venture into the new habitats
that Pangea had to offer--

ecological opportunities
beyond count,

open to any species

adventurous and hardy enough
to survive the journey.

But Pangea brought with it
new challenges for life, too.

The ancient world's weather
and climate

entered a new phase--

one marked by
intense seasonal extremes.

It's fair to say the way
the Permian Period began--

with the collapse
of the rainforest,

the end of an ice age,
and the formation of Pangea--

was pretty chaotic.

But as we'll see,

it's nothing compared to the way
the Permian will conclude,

with the Great Dying

and the end of
the Paleozoic world.