All language subtitles for NOVA.S50E13.Ancient.Earth.Life.Rising.1080p.WEB.h264-BAE_track3_[eng]

NARRATOR:
A young world.

The atmosphere toxic.

The land barren and forbidding.

Until the arrival of a life form
that changed everything.

Plants.

DORI CONTRERAS:
Everything about the landscape

was influenced by plants
moving onto the land.

NARRATOR:
Evolving in the oceans,

they eventually partner
with fungi

to turn an alien world...

One of the most bizarre
prehistoric landscapes of all.

NARRATOR:
...into one we recognize today.

(eruption roars)

Along the way, they're subjected
to cataclysm after cataclysm...

LYNN SOREGHAN:
Ice could have covered
the entire planet.

NARRATOR:
...and alter
the very Earth itself.

CHRISTOPHER JACKSON:
This interplay between biology

and geology has utterly
transformed our land.

NARRATOR:
How did an inhospitable
rocky planet...

...become an oasis for life?

"Ancient Earth: Life Rising."

Right now, on "NOVA."

♪ ♪

♪ ♪

NARRATOR:
Viewed from above, planet
Earth is a riot of colors.

But there is one color
that is special.

One that reminds us our home is
a living, breathing planet,

unique in our solar system.

♪ ♪

Green.

(wind howling)

This is the story
of how Earth transformed...

♪ ♪

...from a hostile
and inhospitable world...

...into a haven of opportunity
for life.

Our green planet
wasn't preordained.

It's the result of an immense
struggle over millions of years.

NARRATOR:
How plant life rose from
the oceans

to dominate a rugged
and desolate landscape.

ALY BAUMGARTNER:
Everything that you know
about the planet,

everything that you think
of when you look outside,

is because of plants.

NARRATOR:
And how plants reshaped
Earth itself.

CONTRERAS:
Without plants,

Earth would be nothing like
it is today.

JACKSON:
Plants are literal
terra-formers.

They transformed bare rock
into life-giving soil.

♪ ♪

KIRK JOHNSON:
Plants are elaborate,
beautiful little machines.

These are the most
amazing things in the world.

("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:
Half a billion years after
Earth was formed...

...the planet is
covered by an endless ocean...

...broken up only by a few
remote volcanic islands,

with no trace of life
on the surface.

But this is a living world.

To find ancestors of modern
life, many scientists believe

you would have to leave
the surface behind...

♪ ♪

...and travel
to the depths of the oceans.

It's thought early life thrived
in superheated geothermal vents.

♪ ♪

These single-celled organisms
would've been

uniquely adapted to life
in this harsh environment,

and would ultimately give rise
to plants

and everything
that will ever live on Earth.

♪ ♪

But for now,
they're stuck in the ocean,

because large landmasses...

(eruption roaring,
water hissing)

...do not yet exist.

So there's a theory that four
billion years ago,

the only land on Earth were just

a few black volcanic islands

scattered in the ocean.

♪ ♪

This early land was made
of basalt,

which is cooled lava.

And it contains magnesium,
calcium--

things that life requires.

AISHA MORRIS:
The problem was that
these small early

volcanic islands were
short-lived,

because they were smashed to
pieces by the tides

NARRATOR:
For dry land to form
and persist,

one of the world's
most powerful geologic forces

had to begin:

plate tectonics.

(eruption roars)

MORRIS:
Plate tectonics really
tries to explain

the land forms that we see
on Earth:

things like volcanoes,
events such as earthquakes.

And it's really based
on the idea that plates

on the surface of the Earth
move around in relation

to one another, and sometimes
go beneath each other,

sometimes crash into each other,

and sometimes slide past
each other.

NARRATOR:
This geologic process
would prove

to be the key that would change
the surface forever.

♪ ♪

But its beginnings
are shrouded in mystery.

HAZEN:
The beginnings of plate
tectonics is so controversial.

Some people think it was

density differences and crust
being pulled down by gravity.

NARRATOR:
But some incredible new
evidence has been discovered

that suggests
an extra-terrestrial origin.

Sometimes geology gives us
great clues

about how early processes
occurred.

NARRATOR:
Scientists have found
microscopic structures

called spherules,
thought to be formed

by asteroid impacts

3.2 billion years ago,
hidden in ancient rocks.

These are located
alongside rocks

that show indications
of plate tectonics.

So it's really hard
to know for sure,

because this happened
so long ago,

but one of the things that
may have happened

is that these impacts

may have actually
started the magma moving.

These asteroid impacts
would've ruptured the crust.

They may have played
some role in starting the plates

moving and allowing plates
to sink.

This may have
started plate tectonics.

♪ ♪

NARRATOR:
Data suggest that one of these
giant asteroids

is as much as 30 miles across.

♪ ♪

More than three times the size
of the one

believed to have
wiped out the dinosaurs.

♪ ♪

(explosion roars)

Early life forms in its path
would be lost to oblivion.

But somehow,

in its deep ocean hideaway,

some early life clings on,

and its odds for making it onto
land have just gotten better.

Because with
the advent of plate tectonics

comes an entirely
new kind of rock...

...that could
allow life to get a foothold.

This rock forms during
a process called subduction.

Subduction is when one slab of
rock,

a tectonic plate, is forced down

beneath another tectonic plate.

EDMONDS:
The subducting plate brings
water down

into the interior
of the Earth, and that water

is a bit like adding salt
to an icy road.

So adding water to hot rock
makes it melt,

but this melt is really special.

It's really rich
in silica and oxygen,

and when it rises
to the surface,

it forms granite.

NARRATOR:
A rock that shapes the surface
of Earth as we know it today.

Now, you may think of granite
as just a speckled

gray rock, but it actually
has a really special property

that make it a wonderful
land-building material.

NARRATOR:
Granite has a low density.

HAZEN:
So we all understand density

because we put ice cubes
in our drink,

and when we do,
about ten percent of that ice

sticks above the water,

'cause ice is ten percent
less dense than water.

And in the exact same way,

granite is about ten percent
less dense than basalt,

so ten percent of the granite

sticks up above basalt.

♪ ♪

This means that after
granite's formed,

this hard, heavy rock

actually floats on top

of the partially molten basalt
beneath it.

(wind howling)

♪ ♪

NARRATOR:
As plate tectonics continue,
over billions of years,

vast swathes of rock

gradually emerge
across the planet.

Earth's first landmasses
are born.

A couple of billion years

after the inception of
plate tectonics...

...a multitude of
continental-scale landmasses

are strewn across
the surface of the planet.

A vast frontier.

A rocky world with plenty
of minerals

containing nutrients like
potassium and phosphorus,

key elements for life.

♪ ♪

For any organism that can adapt
to this new territory,

incredible opportunities await.

♪ ♪

Dwelling in the shallows,

within touching
distance of the land...

...are recognizable,
plant-like life.

Marine algae.

Descendants of the early life

that originated
in geothermal vents.

They bask in
the light-filled shallows,

having adopted
an absolutely incredible way

to harvest energy
directly from the sun:

photosynthesis.

Photosynthesis is a chemical
reaction

by which plants take light from
the sun

and combine it with water and
carbon dioxide

to make oxygen and glucose,
the sugar they use for energy.

NARRATOR:
Marine algae have evolved to use

a crucial cellular
innovation called chloroplasts,

specialized structures
filled with chlorophyll,

a compound that helps
harness the sun's energy

and gives them
their distinctive green hue.

But they are still confined
to the water.

An environment which they
are perfectly adapted to.

A watery environment is lovely

if you're a plant.

It's like being surrounded

by a bath of your food.

You've got nutrients available
to you,

there's no danger of drying out,

and you don't have to worry
about gravity or soil.

NARRATOR:
Migrating onto land
at this point

would require
a huge evolutionary leap.

For plants to live outside of
water,

it's a bit like me trying to
live on Mars

without a space suit.

NARRATOR:
But while marine algae can't
quite make it from the ocean

onto dry land,

they can adapt to another,
more accessible environment:

fresh water.

Eventually,
the algae take up residence

in the lakes,
streams, and rivers.

From there, around
half a billion years ago...

...the algae begin their
slow journey onto the land.

We may never know
the combination of factors

that spurred
green algae on land.

NARRATOR:
Maybe it was the changing of
Earth's landscapes

to more clement conditions,

or the time needed
for profound genetic change.

But whatever the reason, green
algae begins to come ashore.

The journey is likely
to have started

at the pebbly shorelines
of freshwater lakes and rivers.

Some eventually evolve
a thick waxy coating

that stops them from drying out
in their harsh new environment.

But this effective adaptation
is a double-edged sword...

...making it more
difficult to absorb nutrients

from their surroundings,
like they did in the water,

and making success
on land nearly impossible.

So, how did plants come
to thrive on land?

♪ ♪

Though this may look like an
ordinary field,

it contains one of the world's
most important geological sites,

and the secret to what
helped plants survive on land.

This is an incredibly exciting
place for me to be,

because more than a hundred
years ago, this site

where we are today
was excavated to reveal

the most incredible set of 400-
million-year-old plant fossils.

What's special about the fossils
from this particular site was,

the degree of preservation

of the plant material meant
that we got some amazing clues

as to how they actually made
landfall in the first place.

♪ ♪

NARRATOR:
Around 400 million years ago,

this area looked completely
different

from how it looks today.

It resembled
Yellowstone National Park,

where boiling mineralized waters

cascade down rocky terraces.

FIELD:
So the ancient hot springs
that were here at Rhynie

turned any plant material
that they touched into rock,

and that got buried
over millions of years.

The resulting bed of fossils is
what we call the Rhynie Chert.

♪ ♪

This fossil is really amazing.

If you look closely,
you can see these circles

in the surface of the fossil.

And those circles
are actually cross sections

through the stems of
ancient plants

that grew all around here.

NARRATOR:
And you can see
something unusual

when you look at them
under a microscope.

What we see is,
there's this light banding

around the top,
and that's plant tissue,

but if you look even more
closely,

you see these dark brown
thread-like structures

weaving between the cells

and actually invading
some of the plant cells.

And those thread-like
structures are actually fungi.

NARRATOR:
This incredible evidence shows

that plants actually
teamed up with another

kind of life form
to help get onto the land--

fungi.

Rhynie Chert fossils are
some of the only

fossils on Earth where you can
see this ancient link

between plants and fungi.

♪ ♪

NARRATOR:
Fungi, however,
were not newcomers

to the land surfaces.

Fungi made its way onto
terrestrial land

probably hundreds of millions of
years

before plants.

consuming bacteria
and drawing minerals

directly from the rocks below.

FIELD:
So fungi are able to get hold
of these nutrients

by exuding organic acids
out of their fungal hyphae,

which are thread-like filaments

that form
the majority of the fungus.

NARRATOR:
Even though the Rhynie Chert
fossils

are around
400 million years old,

this union of plants and fungi

must have occurred
millions of years earlier.

CONTRERAS:
Plants benefited
from the partnership

because they got the nutrients
from the rock's surface

that were broken down

by the fungi.

And then the fungi
benefited because

they got to use the sugars
that were supplied

from the plants
doing photosynthesis.

NARRATOR:
Bolstered by this
new relationship with fungi,

plants evolved
the ability to exchange sugars

for vital nutrients
like nitrogen and phosphorus.

Even with their thick,
water-retentive coating,

they can still get all
the nutrients they need.

The emergence of this newly
evolved mutual relationship,

or symbiosis,

is a key turning point
for plants' journey.

Now plants can finally survive
out of the water on the land.

The symbiosis between land
plants and fungi

is super-important.

It's essential
for how ecosystems evolved

and how they work today.

BAUMGARTNER:
After millions of years

and lots of evolutionary tries,

plants were
finally onto the land.

♪ ♪

NARRATOR:
Plants and fungi created
one of Earth's

first complex
terrestrial ecosystems.

♪ ♪

And their partnership
continues to this day.

♪ ♪

It's often easy to
spot mushrooms,

which are the reproductive
part of some types of fungi.

But most fungi live underground,
where we can't see them.

So this plant has grown

with a fungal partner,
and you can see that,

with the plant roots being
intermingled

with fungal filaments,

and these wrap themselves
around the plant roots

and form these
intimate associations.

NARRATOR:
These associations are so vital

that nearly 90% of plants living
today are dependent on them.

FIELD:
It's really easy
to overlook fungi because,

for the most part,
they live underground,

whilst plants grow much taller
and are more obvious.

NARRATOR:
But some fossil evidence

from around
420 million years ago

suggests that this balance
once looked quite different.

♪ ♪

Something utterly astonishing
has happened to some fungi.

They have become giants.

♪ ♪

Colossal fungal spikes tower
over the landscape.

They're called Prototaxites.

Standing over 20 feet high,

they reproduce
by releasing spores

that are carried by the wind.

CONTRERAS:
The Prototaxites landscape
would've been an alien world.

NARRATOR:
So alien

that when the fossils were
first discovered back in 1843,

scientists were not
even sure what they were.

It was a very strange

and odd thing when people
found it.

NARRATOR:
But when they took
a much closer look,

they discovered
something incredible.

So what this is

is a very thin slice of
Prototaxites.

♪ ♪

And we find that, unlike a log,

which would be full of
woody cells,

instead we find a mass of these
fungal filaments,

reminiscent of fungi today.

JOHNSON:
It creates,

in my mind, one of the most
bizarre prehistoric landscapes

of all, 'cause there's
nothing like it today.

NARRATOR:
The towering Prototaxites
dominate the landscape.

Plants, by contrast,
are still tiny,

measuring just
a few inches or less.

Stuck by the water's edge,

near to where
they first made landfall.

LYDON:
So, even though plants

have made it out of the water,

they're still confined to
the edges

of lakes and rivers.

A lot of the land surface on
Earth at this time

NARRATOR:
With no way of holding on to
that water inland,

Earth could've remained
a fungal paradise.

For plants to establish
themselves

away from the water,

they were gonna have to change,

to evolve new traits that
allowed them

to live in the new environment.

NARRATOR:
But there is a vital ingredient
missing.

♪ ♪

Something that seems like it has

always been part
of the fabric of Earth.

♪ ♪

Soil.

Just one teaspoon of this
crumbly brown stuff

includes more living organisms

than there are people on the
planet,

and that is absolutely
unbelievable.

Despite the fact that soils

only make up a small portion of
the Earth's surface,

there are thousands
of varieties,

including more than 20,000
in the U.S. alone.

♪ ♪

NARRATOR:
Soil is formed by the combined
action

of organisms
like bacteria and fungi

working on biological matter
like fallen leaves.

Combined with
particles like sand or clay,

it is the
perfect material to hold

all the ingredients
plants need to thrive.

Soil traps and holds on to water
and nutrients

so that plants
can use them all year round.

If we look in the fossil record,

we see something
absolutely remarkable.

About 470 million years ago,

soils as we know them today
did not exist.

Instead, we had the earliest
version of soils,

what we call proto-soils.

They were only
maybe a millimeter thick.

They were formed from
very thin layers

of bacterial or fungal mats;
they just didn't have

the same kind of building
blocks that soils today have.

NARRATOR:
Early fungi do not need soil
to thrive.

But plants need something
to support and nourish them

if they are to survive
farther away from the water.

Soon, they start making soil.

♪ ♪

They begin slowly,

over millions of years,

breaking down the bare rock

with tiny root-like
structures called rhizoids,

mixing in nutrients
from their fungal partners.

♪ ♪

But the true
transformative ingredient...

...is the plants themselves.

Generation after generation
breaks down after death,

building up a bed of soil.

Turning once inert rock
into a living layer.

♪ ♪

Fast-forward 20 million years.

And with the growing
soil layers,

plants are transforming.

♪ ♪

They're much bigger.

And their ability to move water
through their tissues

by a kind of plumbing

has allowed them to live
farther away from the water.

They're now more varied,
with deeper roots

to support their taller stems.

Prototaxites, the giant fungi,

still tower over them.

But soil makes it possible

for plants to thrive
much farther inland.

Their wind-borne spores
reach drier upland areas.

♪ ♪

Without the barrier that kept

terrestrial plant life
near the water's edge,

plants scale new heights,

and diversify
as they occupy new environments.

♪ ♪

For the first time,

significant parts of Earth's
land are turning green.

FIELD:
Plants changed our landscape

by terra-forming bare rock

into living matter.

Life and Earth,

they're not separate entities--

they're totally interconnected.

So, these changes that plants
caused to the Earth's surface

had huge consequences.

Pretty much everything
about the landscape

was influenced
by plants moving onto the land.

NARRATOR:
But plants don't
just alter Earth's surface.

♪ ♪

CARVALHO:
As plants are creating

this beautiful green planet,

carbon dioxide levels in the
atmosphere

actually start going down.

Part of the reason
has to do with plants.

As plants are growing,

they're accumulating
carbon dioxide

as they're transforming it
into sugars,

and making up
their plant bodies.

As plants had exploded across
the landscape,

CO2 in the atmosphere
decreased by upwards of 25%.

NARRATOR:
Ironically, this
poses a problem to plants.

Because carbon dioxide
is plant food.

They absorb the CO2
for photosynthesis

through structures
called stomata.

CONTRERAS:
Stomata are these cellular
complexes

that have a pore in the middle,

and these are the gas exchange
pores for plants,

so it's the way they move
carbon dioxide

in and out of the plant body.

If you look at stomata under the
microscope, it almost looks like

they're breathing
as they open and close.

JOHNSON:
In early land plants,

between 420 and 390 million
years ago,

most land plants had

their stomata on their stems.

The falling carbon dioxide
levels

had a huge impact on plants.

In order to get as much
carbon dioxide

as they were before,
they would need more stomata.

But where to put them?

CONTRERAS:
The answer was as elegant
as it was revolutionary.

♪ ♪

Leaves.

♪ ♪

NARRATOR:
Leaves came about as an
adaptation

to cope with
the changing atmosphere.

Leaves make plants more
efficient

by providing
greater surface area

for photosynthesis and for
taking up CO2 for gas exchange.

♪ ♪

NARRATOR:
In a relatively short time,

most plants
had evolved leaves,

but this seemingly
small innovation would trigger

an entirely new dynamic
between plants.

When we have plants
growing close to each other,

these big surfaces
that capture sunlight

are creating competition because
of the shading of each other.

NARRATOR:
This started a race for light

that will ultimately transform
the landscape once again.

♪ ♪

With leaves supporting this
increased photosynthesis,

some plants begin building
their bodies

out of tougher
biological material,

wood,

which leads to the rise of a
whole new type of organism--

biological machines unlike
anything

Earth has seen before.

Trees are photosynthesizing
powerhouses.

With strong wooden trunks,
they can grow much taller,

effectively pushing
past the competition

towards the sunlight they need.

Trees were a huge step forward

for terrestrial plant life.

Trees were remarkable

at exploiting resources.

They had enormous, deep
rooting systems,

allowing them
to access water and nutrients,

they had these giant stems for
stability, and on top of that,

a canopy of leaves
for photosynthesis.

Archaeopteris, like this one
here,

was one of the earliest trees,

and they formed many
of the Earth's first forests.

Here's one branch of
Archaeopteris.

It has big woody stems,

but the leaves kind of look
like ferns,

but kind of not.

BAUMGARTNER:
The ability of Archaeopteris

to consume vast amounts of
carbon dioxide

allowed them to grow to be

almost 100 feet tall.

♪ ♪

JOHNSON:
I often like to say
that trees are made out of gas.

They absorb carbon dioxide
from the atmosphere

to make the carbohydrate
in their plant bodies.

♪ ♪

NARRATOR:
Earth is on its way
to becoming a forest world.

♪ ♪

The Prototaxites are gone,
never to return.

♪ ♪

And the majority of the fungi
retreats from the surface,

thriving in giant networks
below the ground,

where they have remained
ever since,

a vital partner
to the plant life above them.

The spread of plants
from the water's edge

across the planet's surface
is dramatic.

♪ ♪

Plants transform
the face of the planet.

But in doing so,

they also set the stage
for global upheaval.

♪ ♪

This beautiful coastal
redwood forest

is part of a dynamic ecosystem,

with trees playing
an essential role,

even after they can
no longer stand tall.

A fallen coastal redwood
locals call the Phoenix Tree

is a rare instance of being able
to see

the interconnectedness
of the forests above the ground.

So this tree fell over about
86 years ago,

and the special thing about it

is that that wasn't a death
sentence.

Instead,
beneath each separate branch

are roots that are forming,

and these branches are
eventually going to become

their own independent trees.

♪ ♪

These spread-out, shallow roots

allow them to basically
hold hands with each other

for stability, and they can
even share resources

like water and nutrients.

NARRATOR:
But this tree is just
one small piece

of a vast
and interconnected system.

It's a living bridge
that connects the atmosphere

with the soil
and the life within it.

When trees are alive,
they are homes,

they are food,
and they provide moisture

to the environment around them.

But they actually
provide the same things

after they've decomposed.

NARRATOR:
Dead trees are broken down
by organisms

that return the carbon
that was locked in them

back into the atmosphere
through respiration.

And this equilibrium helps keep
the atmospheric CO2 in balance.

But around
350 million years ago,

that balance was interrupted.

Leading to a crisis
that would threaten the survival

of all life on Earth.

♪ ♪

The rapid spread of
terrestrial plant life

has left Earth a changed planet.

In the Southern Hemisphere,
ice sheets form.

But in the equatorial regions,

the climate is still very hot
and wet.

♪ ♪

As the ice sheets expand
and contract,

over millions of years,
sea levels fluctuate,

creating huge deltas

where vast swamp forests
spring up...

...covering millions
of square miles...

...and giving rise to a whole
host of new plant species

that thrive
in these wet conditions.

The largest among them,
Lepidodendrons,

grow over 160 feet tall.

These are part
of a group called lycopods,

or scale trees.

It looks like it's not a plant.

People often find these things,
say,

"These thing's got scales.

"It looks like a garfish,
or a dinosaur,

or some kind of snake,
a reptile."

And in fact,
these are called scale trees.

NARRATOR:
The swamp forests these trees
grew in

would've looked
similar to today's,

except those trees would've
grown incredibly quickly,

creating a huge amount

of plant mass
in a very short time.

HETHERINGTON:
Lepidendron trees could be
enormous,

and one hypothesis is
that they reach

this amazing height
in as little as 15 years.

So this rapid plant growth

would've removed enormous
amounts

NARRATOR:
But this was not the only impact

these trees
had on the atmosphere.

CARVALHO:
So when these massive trees

fell into waterlogged
conditions,

which typically are very low
in oxygen,

they become really, really hard
to break down.

Through time,

all this organic matter
accumulates.

NARRATOR:
This huge amount of plant mass
was not broken down

and returned to the atmosphere,
as typically happens today.

Instead, it was locked away

in the sludge of the
swamp forests.

This would have immense
consequences

for the Earth's climate.

♪ ♪

NARRATOR:
The deep basins
of the tropical swamp forests

were log-jammed with
fallen trees

and partially decayed plant
matter that formed peat.

This carbon-rich mixture
was then buried

and compressed under millions
of tons of marine sediment,

deposited by
fluctuating sea levels.

All the ingredients were
in place,

slowly transforming...

(birds squawking)

...into an incredible type
of rock.

We can see that substance
in the black seam

behind me, within the cliff
face, within the rock records.

And that substance
is actually coal.

And this coal forms
when that plant material

is buried within the Earth

and subjected to the Earth's
intense heat

and the intense pressure.

And it forms this midnight
black, energy-rich material.

So coal is very, very rich
in carbon,

and it's this period
of geological time

which is associated with the
deposition

of these thick coal deposits,

so it's no surprise
that this period got its name,

the Carboniferous, which means
coal-bearing or coal-producing.

♪ ♪

NARRATOR:
During the 60 million years
of the Carboniferous,

plant life locked away
100 billion tons

of carbon per year
in the form of coal.

JACKSON:
We know that present day,

the burning of coal is having
a dramatic impact

on the Earth's climate,
but actually,

the formation of coal back in
the Carboniferous

had an equally
as profound effect.

NARRATOR:
With so much plant matter
locked away underground,

atmospheric
carbon levels dropped.

And this is why massive
sustained coal production

kicked the whole system
out of balance.

NARRATOR:
And the impact was dramatic.

♪ ♪

Over millions of years,

CO2 levels plummet, and
global temperatures nosedive,

in a reverse
of the greenhouse effect...

(wind howling)

...causing vast icy expanses.

The consequences
of carbon hoarding

by the equatorial swamp forests

leave plants
teetering on the edge.

In the frozen south,
the forests die off en masse.

SOREGHAN:
As carbon dioxide
continued to drop,

it would've become very,
very cold,

and up to a quarter of the
world's landmasses

would've been covered in ice.

NARRATOR:
If this process had continued,

it would've
had dire consequences.

It could've potentially caused
a Snowball Earth,

or what we call
a runaway glaciation,

where ice could have
covered the entire planet.

NARRATOR:
Which would've set plants back

hundreds of millions of years.

But that isn't what happens.

Beneath the frozen surface,

the giant tectonic plates
are continuing

their perpetual movement.

SOREGHAN:
Over the 60 million years
or so of the Carboniferous,

plate tectonics
had been creating

a new supercontinent.

They were zippering together,

essentially along the Equator,
and moving northward.

Mountains were being formed,

new weather patterns were
being altered

and adjusted as a result

of this change
in the landmass on Earth.

NARRATOR:
And with this change...

♪ ♪

...about 300 million years ago,

most of the swamps dry up and
cease their production of coal.

SOREGHAN:
When coal formation

essentially ended, it meant that

we weren't locking away as much
carbon dioxide,

and yet, volcanoes were
still belching out CO2,

but we weren't
drawing it down as much.

And therefore carbon dioxide
began rising

in the atmosphere,
the Earth began warming...

...and the glaciers started
melting.

♪ ♪

NARRATOR:
The ice sheets recede
and eventually disappear.

This set the stage
for a plant renaissance.

Plant life
exploded in diversity,

leading eventually
to the green world we see today.

NARRATOR:
Over the following
few hundred million years,

plants would overcome
one challenge after another,

developing flowers
and fruit,

co-evolving with insects,

and eventually
forming grasses and grains.

Plants transform the land from
green

into every vivid color of the
spectrum.

♪ ♪

NARRATOR:
Earth's transformation

from a barren, rocky world
to the living planet

we see today is spectacular.

Rocks breathed life
into the land,

but then life altered the rocks,
and changed them,

and diversified and enriched our
planet in so many ways.

If plants hadn't conquered the
land,

BAUMGARTNER:
The chair that I am
sitting in is from plants.

The food that you eat,

the clothes that you wear,

everything you know

is because of plants.

♪ ♪

So, no matter how we try,

we can't escape the fact

that this is a plant planet.

♪ ♪

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

PAUL WIGNALL:
It's the mother
of mass extinctions.

Something utterly catastrophic.

SURESH SINGH:
Much greater than the one

that ended the age
of the dinosaurs.

Now we finally know the culprit.

(explosion pounds)

JEFFREY BENCA:
We are finally able to piece
together clues

from this ancient crime scene.

SINGH:
We're talking wildfires,
acid rain,

deadly U.V. radiation.

This was hell on Earth.

NARRATOR:
"Inferno" on "NOVA."

Next time.

SINGER:
♪ Wish I could go back in time ♪

♪ ♪

♪ ♪

♪ ♪

♪ ♪

♪ ♪