01x05 - When the Forests Collapsed

[bunniefuu]

[thunder rumbling]

NARRATOR:
The story of life on Earth...

[loud roar]

has been marked by a series of
catastrophic extinction events.

Natural disasters which have
threatened to wipe out

many of the creatures
that call our planet home.

But, after every brush with
death, life has come back

even stronger.

[peaceful music]

NARRATOR: One such event took
place 305 million years ago,

when huge swamp forests
dominated much of the earth.

And were home to strange
new creatures.

[loud growling]

But the forests were
so astonishingly successful,

they changed the planet,

making Earth colder and drier.

Unfortunately, this then
drove them to extinction.

But life returned
more resilient and diverse...

than ever.

[theme song]

[insects buzzing]

[soft roar]

NARRATOR:
Long before the dinosaurs

the world is dominated
by plants.

Lush, water-logged swamp
forests cover the land.

And down among the roots,

live countless strange
and wonderful creatures.

A little amphibian
called Diplocaulus.

This is a very special
night for her.

It's that time of year

when she looks for a burrow
to lay her eggs.

[Diplocaulus croaks]

But this riverbank
is fully booked.

Every mother is taking
advantage of the damp night

to find their own nesting spot.

[loud croaks]

All the burrows are occupied.

As morning dawns,

she realizes she waited
too long to book a burrow.

So, she makes her own.

[bright music]

The world she lives in is
a triumph of plant power.

Herbivores have yet to evolve

so the vegetation can grow
untouched by all but insects.

Horsetails and tree ferns
stretch as far

as the eye can see.

Towering above are scale trees,
the giants of this forest,

but they are nothing
like the trees we know today.

Their trunks are rigid hollow
tubes that can grow as tall

as a 14 story building
in less than 15 years.

[crickets chirping]

The extent of these forests
is staggering.

For 50 million years

plants have been the dominant
life force on land.

As the continents have drifted
together vast lowland basins

have formed along the equator

and these have filled with
billions of swamp trees.

These forests have released
so much oxygen,

that they've supercharged
the Earth's atmosphere.

Oxygen levels are the highest
the planet has ever seen.

This has boosted the animals.

Some insects have grown
enormous,

like the Griffinfly...

with a wingspan
as big as a crow's.

[Griffinfly buzzing]

But oxygen doesn't just
fuel growth.

But it also fuels fire.

Even in this wet swamp,

a single lightning strike
can set off a forest inferno.

Our little Diplocaulus
will be safe here

in a labyrinth
of drowned roots.

But water isn't
the natural habitat

for many forest dwellers.

Dendromaia.

Her dry scaly skin shows
she is a reptile,

one of the first vertebrates
to leave the water

and live permanently on land.

[wood cracking]

So, for her,
the fire is a huge threat.

In this oxygen rich atmosphere,

one ember can quickly
become a raging blaze.

[tense music]

To save herself she needs
to run now but she has a nest

full of babies nearby
and she won't abandon them.

[dramatic music]

The fire is moving so fast
she only has seconds.

[babies Dendromaiae chitters]

She and her babies
are surrounded by chaos.

[babies Dendromaiae chitters]

[wood cracking]

NARRATOR: 305 million years ago

dense fast-growing forests
cover the equator.

They are so successful they
have pushed up the amount of

oxygen in the atmosphere
to record levels.

But all this oxygen has
intensified forest fires

so much so that even
waterlogged wood burns.

The fire has cut this mother
off from her babies.

[babies Dendromaiae chitters]

[dramatic music]

She is desperately trying to
reach them before the flames.

She's got them, but now she
needs to get them out of there.

[wood cracking]

[calming music]

She's done it.

As the wind changes direction,

it starts to drive
the fire away.

Our heroic mother has saved
her babies from the flames.

The next morning,

it looks as though
the smoke is still lingering.

But this isn't smoke.

It's something very different.

Spores, billions of them,

So small they are almost
invisible to the naked eye.

These tiny spores are

how these extraordinary
scale trees begin life.

They need just the right
conditions to germinate,

and the damp soil here
is perfect.

Our Diplocaulus mom
has been busy digging.

And she's made her own burrow
in the riverbank.

Here, water from the swamp
has created a tiny pool.

This is where
she has laid her eggs.

Over the next few weeks this
mom will dedicate herself

to protecting her brood
until they hatch.

Because these swamps
are filled with predators.

[predator growling]

They can be heard calling
through the forest.

[growling]

The calls are coming from giant
amphibians called Eryops.

They are carnivores and
can grow up to eight feet long.

These beasts are among
the largest land animals

on the planet and things are
about to get steamy.

It's time for their
annual courtship.

[Eryops calling]

Their calls are booming
through the forest

for one purpose...

to attract a female
and it's worked.

[soft growling]

Let the serenading begin!

[Eryops calling]

Hardly a classic love
ballad but it'll do.

Now a couple of the males want
to show off different skills.

One male starts a new contest.

[Eryops deep calling]

His low frequency rumbles
make the water... dance.

Interesting.

But the other guy
can do that too.

[Eryops deep calling]

She's still not sure
who to choose.

This could get ugly.

NARRATOR: Over 300 million years
before humans evolve,

the Earth's equatorial regions
are cloaked

in dense swamp forests dominated
by mosses and ferns.

The animals here thrive in the
damp, oxygen-rich atmosphere.

These Eryops are amphibians

and among the largest creatures
on land.

Each as big
a silverback gorilla,

they are formidable predators

with a mouthful
of curved fangs.

But they are not here to hunt,

they are here to win a mate.

These two suitors are
sumo wrestling, swamp-style.

Battling to impress
a potential mate.

[Eryops cries]

[growling]

[loud growling]

Finally, a champion.

[Eryops calling]

The winner will stay
firmly attached

in a slippery embrace
for hours.

When she finally lays
her eggs,

he will be ready
to fertilize them.

Then, both parents abandon them.

Of the 500 eggs she lays,

only about 10 will survive
to adulthood.

Down in her burrow our
Diplocaulus mom

is a much more caring parent.

Two weeks on and she's still
devotedly tending her eggs.

But she can tell something's
not right.

When she laid her eggs
they were underwater,

now some are exposed.

The water level is dropping

and the reason lies far
beyond her little burrow.



while the endless forests are
producing loads of oxygen,

they are also absorbing
huge amounts of carbon dioxide,

a greenhouse gas that keeps
the planet warm.

As each tree falls,
and submerges into the swamp,

it locks the carbon away
underground.

For millions of years,

these trees have been rotting
down on top of each other.

Eventually, this one period
in Earth's history

will create 90 per cent
of all our coal.

This also means carbon dioxide
levels in the atmosphere

have been dropping

and the whole planet
has started to cool.

Several ice sheets
have begun to grow

over the southern continents,

and they are expanding towards
the equator.

With cooler seas,
there is less evaporation,

less water in the atmosphere,
and, therefore, a drier climate.

This means dry seasons
are getting longer

and droughts worse
in the swamp forest.

The consequences
could be devastating

for our caring mother.

As the swamp drains,

she tries everything to keep
her babies from drying out.

And she's not the only one.

If this drought continues
much longer,

her baby-filled burrow
will become a tomb.

But a drier swamp is not a
problem for all creatures here.

Down under the ferns
a Dendromaia shows

how reptiles managed to escape
being so dependent on water.

They lay eggs with
waterproof shells.

So they can stay on land

without the fear of their eggs
drying out.

[crickets chirping]

[soft instrumental music]

As night falls moonlight picks
out the glowing wing cases

of a million insects.

The deep forests belong
to the creepy crawlies,

and the biggest of these
is perhaps

the most bizarre creature
in an already weird world.

Arthropleura, a giant millipede,
eight feet long.

Using her antenna,

she probes
the forest floor for food...

creeping closer and closer

to our young mom's burrow
full of babies.

[squeaking]

[dramatic instrumental playing]

[chirping]

[insects chirping]

Deep in the swamp forest,

a Diplocaulus mom has laid
her eggs in a flooded burrow

to protect them from
the many predators outside.

Unfortunately, tonight,
the entrance has been discovered

by an eight-foot-long
Arthropleura,

a monstrous millipede.

[tense instrumental playing]

[chirping]

[chirping angrily]

But this eight-foot monster

hasn't met our fiercely
protective mother.

In fact,
she is no threat at all.

She's a gentle giant.

[wondrous instrumental playing]

Soon, she finds the food
she was looking for all along...

something rich in nutrients.

Eryops droppings.

[expansive instrumental playing]

The drought is intensifying.

The drier soil
no longer holds enough water

to sustain
the giant scale trees.

[loud crash]

The swamp is
no longer wet enough

for the spores
to germinate,

and the trees cannot recover.

The once endless groves
are becoming patchy and sparse.

[chirping quietly]

Against all the odds,

our Diplocaulus mom has managed
to keep enough water

in her burrow for her
eggs to survive.

[sweeping instrumental playing]

And now,
they're starting to hatch.

A miracle of new life.

But unlike their mother,

they can only breathe
underwater.

For now,
they have feathery gills

that absorb all
the oxygen they need.

It will be eight weeks
before their lungs develop

and they can breathe on land.

Despite all her hard work,

their birthing pool
is shrinking.

Our mom is running out of time,

and digging around on this bank
just got riskier.

Forced by the drought to hunt
in these shallow waters...

Orthacanthus,
a freshwater shark.

Aquatic animals here
are now pushed

into smaller
and smaller pockets.

Global cooling has brought
the forests to a tipping point.

These baby Eryops,
abandoned by their parents,

are now stuck.

Thousands of them,
with no space and no food.

It's not long before
they turn on each other.

[sorrowful instrumental playing]

Just one tiny tragedy in
a world that is falling apart.

In her underground nursery,

our Diplocaulus mom
is also desperate.

To save her remaining babies,

she carries them in her mouth
down to the stream.

She has spent weeks fiercely
defending these little ones.

Now, there's
nothing more she can do.

They are on their own.

But they're not
the ones in danger.

[menacing instrumental playing]

NARRATOR: After an unnaturally
long dry season,

the swamp forest is suffering.

Our Diplocaulus mom
has had to abandon her burrow

to save her babies.

Holding them in her mouth,

she has carried
them down to the river.

She has no idea
she's being stalked.

[tense instrumental playing]

[fraught instrumental playing]

The starving shark
has overreached.

His last mistake.

[chirping quietly]

Our mom returns
to her empty burrow.

Her best hope now is to wait
out the dry season underground.

[poignant instrumental playing]

The swampland forests

are the architects of
their own destruction.

By absorbing so much carbon
dioxide from the atmosphere,

they set in motion
unstoppable global cooling.

And a cooler world
is a drier world.

Inside her burrow,
our Diplocaulus

has made herself
a mucus cocoon to hibernate.

But her time has passed.

She will raise
no more babies in this forest.

Outside, the age of plants
is coming to an end.

Millions of years pass.

From the west to the east,

nearly 90% of
swamp forest trees are lost.

And along with them,

many of the strange
and wonderful creatures

that depended on them.

Eventually, the earth warms
and the ice starts to melt.

But the land remains
a drier place.

[sweeping instrumental playing]

Instead of scale trees,

other trees
now dominate the landscape.

Conifers.

Their crucial advantage

is that instead of
using spores to reproduce,

they use seeds.

These simple packets of food
give seedlings a head start.

[dramatic instrumental playing]

The animals
that live in and around

these conifer forests
have evolved...

and become much, much bigger.

[growling]

[dramatic instrumental playing]

This is a Dimetrodon.

As long as a dump truck,

she is the apex predator
in these forests.

And she smells something
in the ground.

An amphibian.

Even in this new world,

amphibians can survive
drier periods

by hibernating underground.

Unless a giant reptile with
a good sense of smell

finds them first.

[distant bellowing]

A curious call reaches the
Dimetrodon like a dinner bell.

[bellowing continues]

Cotylorhynchus.

A cumbersome,
plant-eating machine.

His ancestors were carnivores,

but his species has evolved
to become one of

the first large herbivores.

In the time of
the swamp forests,

the only creatures
that ate plants were insects.

But plants aren't
as nutritious as meat,

so he needs a massive gut
to break down his tough diet.

Today, though,
something is wrong.

Dizziness.

Drooling.

- Gas.
- [flatulence]

All the signs of poisoning.

The moment animals
started eating plants,

plants started producing toxins
to put the herbivores off.

And today, he swallowed
the wrong kind of leaves.

Another symptom?

Collapse.

[quiet flatulence]

He'll have to sleep it off.

But this could be fatal.

Nearby,
hungry eyes are watching.

[growling]

NARRATOR: It is 20 million years

since the collapse of
the swamp forests.

Conifers now cover the land.

Beneath their branches,
reptiles have thrived,

and some have grown enormous.

[distant bellowing]

This giant herbivore has eaten
some poisonous plants

and decided to sleep it off.

But this
has left him vulnerable,

and he has attracted
the attention

of a predatory Dimetrodon.

[Dimetrodon exhaling]

[growling]

[hissing]

[hissing]

[distant growling]

Luckily, he has friends.

Big friends.

[dramatic instrumental playing]

[growling]

[hissing]

The Cotylorhynchus
is part of a herd,

a new social grouping
herbivores use

to defend themselves.

Some other time.

The collapse of
the swamp forests

ushered in
a new era on land.

It is the dawn of
the age of reptiles.

And there are more
and more large herbivores

who are starting
to break up the forests.

And their dung
helps fertilize the ground.

For the first time,

animals are beginning
to shape their habitats

on a massive scale.

It's the way of the future.

[sweeping instrumental playing]

[soft instrumental playing]

NARRATOR: Today,
rainforests once again

dominate the Earth's
tropical regions.

They have evolved to be

the most diverse
environments on Earth.

Home to half of all our plant
and animal species.

It's only recently they have
come under threat from humans.

The rate at which
they are now shrinking

is greater than any time
in Earth's history.

Could our impact cause
a tipping point,

like the ancient swamp forests,

that brings about
a complete collapse?

Hope for the rainforests lies in
their incredible biodiversity.

No one part of the forest
is quite like another.

Along with this diversity

comes a powerful ability
to regenerate.

Where humans abandon land,
the forest recovers.

Two-thirds of
today's global rainforests

are secondary regrowth.

Bouncing back
after human impact.

Modern tropical rainforests

have proven themselves
to be remarkably resilient.

Humans just need
to give them space to recover.

♪ I see trees of green ♪

♪ Red roses too ♪

♪ I watch them bloom
for me and you ♪

♪ And I think to myself ♪

♪ What a wonderful world ♪

♪ Yes, I think to myself ♪

♪ What a wonderful world ♪