50x13 - Ancient Earth: Life Rising

[bunniefuu]

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

created by the much
closer moon at that time.

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


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.

♪ ♪

[expl*si*n 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


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.

NARRATOR: They were
able to live on the land

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.

It was shaped like
a chunk of wood.

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

was also quite dry, and
maybe rocky or very sandy.

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


♪ ♪

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


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

of carbon dioxide
from the atmosphere.

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,

we definitely would
not be here today.

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.

[expl*si*n 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 ♪

♪ ♪

♪ ♪

♪ ♪

♪ ♪

♪ ♪