All language subtitles for Earth s01e03.eng

Viewed from above, Planet Earth
is a riot of colours.

But there's one particular colour
that marks Earth out as special.

The colour that shows it's a living,
breathing planet.

Green.

Here we go.

Take a look at this little beauty.
This is Lysimachia glutinosa.

And I know it's not the most

glamorous plant in the world,

but its claim to fame is that
it grows here

and only here,

on this one side of this
one small island,

which makes it sound very fragile,
very vulnerable.

That couldn't be further
from the truth.

Because in the story of this plant,
indeed all plants,

lies the story of our Earth.

It's a story that begins
billions of years ago...

..in the chaos of Earth's
early years...

..before plant life
transformed it...

..into a world of opportunity...

..as plants rose from the oceans...

..to conquer a hostile
and alien land,

fighting and evolving through
triumph and disaster.

And just as they finally built
the perfect garden world,

their global domination almost
wiped out all life on the planet.

The story of plants begins deep
in Earth's ancient history.

Four billion years ago.

When the planet was an inhospitable
world...

..shrouded in a noxious atmosphere
of methane clouds...

..and covered by an endless ocean...

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

..with no sign of life.

But to find plants' ancestors,

you'd have to go about as far from
the surface as you can get.

In the depths of the oceans...

..sheltered inside geothermal
vents...

..are something miraculous.

Extremophiles.

An extraordinary form of
single-celled life.

The ancestors of every living
organism on Earth,

including plants.

But they are stuck here.

At this point, their chances of
making the leap onto dry land...

..are virtually nil.

CHRIS SIGHS

Four billion years ago,

any dry land on Earth would have
looked like this -

black, barren, volcanic islands
peeping out of a vast ocean.

If plants had any aspirations
to leap out onto land,

it was going to be very rapidly
disappointed,

because this land was
very short-lived.

The Earth's earliest islands
were made up of basalt.

Solidified lava...

..that was easily devastated
by explosive eruptions...

..smashed by extreme tides.

This was no place for life.

So the question is,

and it's a big question,

how did plants forge a permanent
base on the land?

Because, if the Earth's only trick

when it came to land-building
was volcanism,

it's very likely that
that life

would've never made it out
of the ocean.

What was needed was another
land-creating force,

and it came in the form of a
celestial intervention.

The culprits were giant asteroids.

Some nearly 60km in diameter.

More than four times the size
of the one

believed to have caused
the extinction of the dinosaurs.

The consequences were
earth-shattering.

Fracturing our planet's crust...

..and triggering a process that
would re-write Earth's story.

Plate tectonics.

Vast subterranean plates
were formed,

and where they meet and collide,

rocks like basalt,

along with sea water and sediment,

are pulled into Earth's
fiery mantle...

..where they're transformed
into a new type of rock.

A rock with a superpower.

Granite.

So what is it about this
hard, heavy,

unforgiving rock that sets it
apart from the crowd?

Well, rather counterintuitively,
it's its buoyancy.

Now, we know that ice is less dense
than water,

therefore ice floats in water,

therefore we have icebergs.

But it turns out that granite, here,
is 10% less dense than basalt.

So, when it's formed deep down
inside the Earth,

it naturally rises to the surface.

So you could say that the continents
on which we are walking

are vast floating granite icebergs.

So, when the tectonic plates collide

and the basaltic crust
is forced down,

granite isn't.

Granite is pushed up,

where it's crumpled into these giant
mountain ranges that we see today.

And over the course of
geological time,

more and more granite accumulates
on the surface,

perched on those tectonic plates,

which are gyrating around
the planet

in a grand continental dance.

Now, you may be wondering
how we know this.

Ten, nine...

Ignition sequence started.

Part of the answer is that,
since the 1960s...

Zero, all engines running.

..the space programme has provided
a unique insight

into the workings of our planet.

For the last 42 years,

we've been able observe the movement
of the Earth's tectonic plates

from orbit.

In 1976, Nasa launched Lageos -

the Laser Geodynamic Satellite -

which used a high precision
laser measuring system

and thousands of reflectors...

..to confirm the theory
that the continents

are constantly moving.

Nothing on Earth is staying still.

And by combining this data
with other measurements,

we've been able to rewind the clock,

to see how the continents
have evolved

over hundreds of millions of years.

And what this tells us

is that one billion years ago...

..the surface of the Earth
was a place

full of possibility and promise.

Vast granite landmasses
covered the planet.

All a potential home for life.

If only it could find
its way there.

And, fortunately,

one life form was waiting
in the wings,

ready to seize its opportunity.

Plants.

Life had migrated from the depths
to the shallows...

..in the form of marine algae.

The first instantly recognisable
plant-like organism on Earth.

They had mastered a revolutionary
new art.

Harvesting energy from the sun...

..using photosynthesis.

But before these plants could
escape the ocean,

they needed to overcome a hurdle...

..greater than anything they'd
faced before.

It's quite difficult to get
your head around

just what a challenge getting onto
dry land was for plant life.

The world that it would have to
overcome was harsh, hostile,

gravity bound, constantly battered
by storms, wind, rain,

UV light, pounded by hot sunlight.

So, just like these contemporary
relatives,

green algae rapidly chose
the easy pickings,

living in those freshwater rivers
and lakes that formed

on the early landmasses.

Cocooned in the safety of the water,

where nutrients and minerals
were abundant.

Life stayed in the water
for 500 million years...

..until a moment about
half a billion years ago,

when, for reasons we don't
entirely understand,

plants' ancestors set off
into the unknown.

Making base camp on rocky sediments
at the water's edge.

Having evolved a thick waxy coating

to stop themselves drying out in
their harsh new environment.

But this brilliant adaptation proved
to be a double-edged sword...

..making it much harder to absorb
the nutrients they needed.

So, despite their best efforts,

they slowly dried out,

dying on the rocks.

But plants aren't the type
to give up easily.

They just needed to find something
to help them.

And they did,

because, as it turned out...

..they were not alone.

Half a billion years before plants

successfully made it onto dry land,

it's believed that another group
of organisms were surviving

on these hostile early landmasses.

In this small rock are the
fossilised remains

of Tortotubus protuberans,

a 440-million-year-old species.

Now, you can't see it.

It's 200 micrometres in length.

But its earlier ancestors were those
that were surviving on that land.

Their ongoing success was down
to their ability

to chemically degrade that substrate
to get nutrients.

They were feasting on the
bare rock itself.

Now, if that sounds otherworldly,
I've got to tell you,

you probably know these organisms
very well.

You might have even had some
on toast

for breakfast this morning.

Because they're fungi.

The next waves of plant life making
their way onto the land

developed a new trick.

They evolved specialised cells that
could connect with fungi,

allowing them to trade resources

like nutrients and food
between each other.

And this new, mutually beneficial
partnership

turned out to be a match
made in heaven.

This was truly a pivotal moment.

Fungi and plants had come together
to produce

the first complex terrestrial
ecosystem on Earth.

Now, the plants got from the fungi

the nutrients they could extract
from the rocks -

and they repaid their fungal
partners with glucose,

the sugar product of photosynthesis,

using energy from the sun and CO2
from the atmosphere.

And this symbiosis meant that
plants could survive

permanently on these
new landmasses.

They'd finally made it
out of the water,

and they were ready to start
conquering the world.

It's incredible to think that
that first collaboration

between fungi and plants
would lead to such

an extraordinary relationship,

and one which would endure
till today.

Look at this bracket fungus here,
growing on this log.

This species is all about decay
and decomposition,

but we mustn't think about fungi
being about death.

Here in the forest, they're very
much about life.

There's an extensive network
of their hyphae,

their roots if you like, stretching
out into the woodland here,

intrinsically linking with the roots
of all of the trees.

And they are allowing them
to share nutrients,

even communicate with one another.

And the key thing is that none of
these plants could survive

without the fungi

and the fungi couldn't survive
without the plants.

And yet we always think of them
being down here in the damp,

in the undergrowth, very much
subservient to the plants

which are up here, towering
above them.

But in the earliest days
of terrestrial plants,

the situation couldn't have been
more different.

The clues were strange
circular fossils.

At first, scientists thought
they were ancient trees.

But, looking closer, they found
microscopic filaments,

revealing them to be fungi,

but on a scale bigger than anything
we know today.

70 million years after plants
and fungi first teamed up,

something utterly astonishing
has happened to fungi.

They are now giants.

In the staggering form
of Prototaxites.

Gargantuan, leathery, spore-bearing
fungal monsters

standing an incredible
eight metres tall.

They towered over the tiny plants

still clinging to the water's edge.

Before plants could challenge
the dominance of fungi,

they needed to come up with yet
another cunning plan.

The problem was that most
of the planet's surface

was just rock.

So, away from the water's edge,

where plants had ready access
to that water,

they really had no hope.

As soon as any moisture appeared
on those impervious surfaces,

it drained away into the streams,
into the rivers, into the lakes,

leaving the rock too exposed,
too dry for plants to survive.

So, at this point, it did appear
as if the Earth would be

a fungal paradise for all eternity.

If the plants wanted to compete,

if they wanted to stake their claim
on the land,

they would have to change
their equation.

They needed some magic.

Today, plants are everywhere.

In every niche and every
environment.

But almost all plants have one thing
that allows them to thrive.

Soil.

In the modern world, there are many
different types of soil.

Most, like this crumbling brown
wonder stuff here,

are made through the activities
of invertebrates, fungi,

bacteria, enzymes, all breaking
down organic matter -

like leaf litter or animal
excrement -

and then mixing it with minerals
that have eroded

from the bedrock below.

And the result is this
magical substance,

packed full of nutrients and,
essentially, able to hold moisture,

meaning that plants can get what
they want from it all year round,

those nutrients and that water.

But 450 million years ago,

there was no soil.

No soil because there were few
or no animals living on land

and precious little organic matter
for anything to work with.

The very idea of making soil
was seemingly impossible.

But plants weren't going to let a
little thing like that stop them.

So they began scratching the rock
with tiny root-like hairs...

..turning it to dust...

..which they mixed with enzymes
secreted by fungi.

But the truly transformative
ingredient...

..was the plants themselves.

Generation after generation...

..laying themselves down to form
the magical substance

that would set their
descendants free.

Fast forward 30 million years
and, thanks to soil,

plants have transformed.

They are much bigger

and in possession of brand-new
evolutionary tricks.

A vascular system that allows them
to move water

through their tissues.

And the first true roots that draw
nutrients from the soil

and support taller stems.

The colossal Prototaxites
still tower over them.

But now the soil offers
fertile ground

for countless wind-borne, seed-like
spores released by plants.

Thanks to this, plants can finally
break free

and move away from the water...

..riding the wind far and wide,

spreading across plains
and hillsides.

For the first time in history,

Planet Earth was turning green.

Ironically, there was a very
real danger

that this new-found success
could have instigated

the beginning of the end.

You see, no matter how big
we think it is,

the Earth is essentially
a closed system.

So any massive increase or decrease
in the amount of plants

wouldn't occur in isolation,

it would have a profound effect
both then and now.

I mean, just imagine, if we were
monumentally stupid enough

to cut down all of the trees and
poison all of the plants,

then the amount of CO2
in the atmosphere

would rocket up, along with
the global temperature,

and the amount of oxygen
would decrease.

So ultimately we wouldn't be able
to breathe.

But of course, we wouldn't be silly
enough to do that.

400 million years ago, however,

the situation was the polar
opposite,

there was a massive increase
in the amount

of terrestrial plants.

And as a consequence,

the amount of carbon dioxide
in the atmosphere

began to plummet.

In fact, in the first 30 million
years of the Devonian period,

it went down by 25%.

Now, given that CO2 is one
of the most important

resources for terrestrial plants,

this had the potential to develop
into a very real problem.

You see, if plants wanted to
continue to grow bigger,

they were going to need some new,
well, inspiration.

The funny thing about plants

is that we generally think of them
as fairly inanimate.

But look closer and there's
an awful lot going on.

Such as the photosynthetic dance
of green chloroplast,

excited by the sunlight
they capture.

But most incredibly,

looked at the right way,

you might almost swear

you can see them breathing.

Stomata - like tiny green mouths...

..taking in carbon dioxide

and exhaling oxygen and
water vapour.

Back in the Devonian period,

most stomata existed only
in plant stems.

But falling atmospheric carbon
dioxide meant they needed

more stomata to absorb the same
quantity to survive.

The problem was where to put them.

The answer was as elegant as
it was revolutionary.

Leaves.

Just look at these beauties.

These are called elephant's ear.

Now, of course, the earliest leaves
were nowhere near as big,

but they were a similar triumph
of botanical form and function.

Waxy on top, keeping them
waterproof.

And underneath, these strong ribs
to keep them flat.

Also, a greater surface area,

allowing many more stomata in here
for better gas exchange.

And on the top, that surface area
provides more room

for more chlorophyll to harvest
more sunlight from the sun.

But there is one problem
with leaves -

they generate shade,

which promotes competition.

And this fired the starting gun
on a race for light

that once again would completely
transform

the surface of the Earth.

Leaves did far more than just
allow plants to harvest

more carbon dioxide.

They made photosynthesis
more efficient,

which boosted energy...

..leading to the birth of a new
magic ingredient

in the form of wood.

This wonder material led
to the creation

of biological machines,

unlike anything Earth
had ever seen.

With strong, durable trunks
that could push past

the competition towards
the sunlight.

Trees.

For terrestrial plants,

trees represented a quantum leap
forwards.

I suppose we could say

they were the epitome of everything
that plants had learned

up until this point.

Deep-rooted, long-lived

photosynthetic powerhouses,

perfectly adapted to exploiting
all of the resources

that they required.

And perhaps most ahead of its time
was Archaeopteris,

considered by many to be
the first true tree -

enormously successful,

fossils found all over the world.

And just like this contemporary
Sitka spruce,

it had a timber trunk, thick bark
and lateral branches

covered with masses of green
photosynthetic leaves

competing for light.

And with that competition came the
need to grow ever taller.

And they did.

Until they towered above
everything else,

reaching heights of 30 metres.

Earth was now on its way to
becoming a forest world.

A home for countless new species
of plants

and insects at every level,

from the canopy to the forest floor.

The former masters of the land,
Prototaxites,

were gone, never to return.

Fungi were reduced to life
in the shadows,

where they've remained,

working their quiet magic,
ever since.

The meteoric rise of plant life,

from uncertain pioneers

to undisputed masters of the land,

was complete.

It was a new chapter
in Earth's story.

But this triumph brought with it

the threat of global catastrophe.

If you've never stood and gazed up
into the high canopy of a forest,

then it's something that I can
thoroughly recommend.

Because if you're in the right place
at the right time,

with the right species, you might
see something special.

So stand, stare and blink,

and look for a unique pattern.

You see, all of the branches
and leaves

from neighbouring trees
don't quite meet,

leaving a silvery line between them.

It's almost as if they're being kind
to their neighbours.

It's a phenomenon called
crown shyness,

part of a peaceful process
of evolution

which has allowed all of the species
in this ecosystem

to come together and live
harmoniously.

And it works.

It's beautiful.

And when they're living,

these magnificent trees are
providing homes,

shelter and food for a whole range
of different animals,

other species of plants and fungi.

And you know, even when
they're dead,

even when they are dead,

they just keep giving.

Through this process of
decomposition,

again, they're feeding animals,
other species of plants and fungi.

But it hasn't always been like this.

There was a time when
it was different,

when intense competition was driving
an arms race

that produced a very
dangerous substance,

a substance which could have led to
the end of all life on Earth.

The rapid spread of terrestrial
plants has changed the Earth.

Atmospheric carbon dioxide
has fallen even further,

causing global cooling.

In the southern hemisphere,

ice sheets have formed for
the first time

in more than a quarter of
a billion years.

But near the equator,

the climate is still extremely hot
and very wet.

Fluctuating sea levels have caused
huge deltas to form,

where vast carbon-hungry swamp
forests have sprung up...

..covering as much as 20 million
square kilometres.

A sweltering jungle paradise

teeming with life...

..where intense competition
for light

has given rise to a whole host
of new plant species...

..who would go on to threaten
the future

of terrestrial life on Earth.

The largest amongst them
were Lepidodendrons,

known as "scale trees",

towering up to an incredible
50 metres tall.

In many ways, we can see this
as the modern equivalent

of a carboniferous swamp forest.

It's certainly very swampy,
soft underfoot.

And in spring and summer,

green, lush, very productive -
as it was back then,

when large scale trees proliferated

because their roots had adapted
to allow them to grow

on the land and beneath the surface
of the water.

But unlike these modern day
cypresses -

and Archaeopteris, which
preceded them -

their trunks were very different.

They weren't made of wood.

The interior was a soft,
corky material

and the exterior, a very robust,
tough structural shell,

which allowed them to perhaps grow
to 50 metres

in as little as 15 years.

But maybe that tough
structural shell

was just a little too
indestructible.

Because when they finally matured
and died and toppled

into this oxygen depleted ooze,

they didn't decompose as
modern trees do -

breaking down slowly, giving their
carbon back to the system.

No, those scale trees hung on to it,
they hoarded that carbon,

and the consequences
for planet Earth

were astonishingly dire.

The floor of the swamp forests
became log-jammed

with fallen trees and decaying
plant matter.

When this carbon-rich mixture
was then buried

under millions of tonnes
of sediment,

all the elements were in place
for a remarkable alchemy.

Under intense heat and pressure,

and consumed by the passage of time,

this vast swathe of plant material
was transformed

by the Earth into a new type
of rock,

a type of rock that would come back
to haunt us.

Here we are.

It's coal.

Yes, coal.

And there's a seam of coal running
through this cliff here -

that black line -

which is constantly being eroded
by the wind, waves and rain.

Now, throughout the 60 million
years of the Carboniferous,

plants fixed carbon in the form
of coal

to the tune of 100,000 million
tonnes every single year,

taking an enormous amount of free
carbon out of the carbon cycle.

And what this added up to was
a deadly downward spiral.

These carbon-hoarding swamp forests

had pushed the Earth to the brink.

In the frozen south,

the Archaeopteris forests
are long dead.

And to make matters worse,

atmospheric carbon dioxide
is plummeting fast.

Nearly a quarter of
the world's land

is now buried beneath a blanket
of ice.

Earth sits within a hair's breadth
of descending

into a snowball event...

..where reflection of the sun's rays
by the frozen surface

could lead to the total glaciation
of the planet...

..threatening almost all life
on Earth.

This could've been the end
of plants' journey...

..but for another timely
intervention.

Beneath the frozen surface,

the giant tectonic plates that set
all these events in motion

in the first place

had been continuing their
perpetual dance.

And over the 60 million years
of the Carboniferous,

they'd slowly been shifting
the landmasses

where the swamp forests thrived...

..raising huge granite mountains
in their place,

which changed weather patterns,

denying water to the deltas below.

And with this intervention

about 280 million years ago,

most of the coal-producing swamps
dried up for good.

Atmospheric carbon dioxide
began to rebound.

Temperatures rose...

..melting the southern glaciers...

..which eventually disappeared...

..setting the scene for a plant
renaissance.

Allowing plants to diversify,

developing flowers and fruit,

grasses and grains.

Transforming their signature green
into a kaleidoscope of colour.

Evolving new species to exploit
every niche on the planet.

Right down to one side of one
small island.

Like our old friend,
Lysimachia glutinosa.

Plants' long journey has been
an astonishing

four-billion-year struggle
from humble beginnings...

..through the deadly fight to escape
the water...

..to the countless generations
that have reshaped

the surface of our planet.

Transforming it from bare rock

to a lush and verdant
home for life.

In the aftermath of all of these
tumultuous events

came a new world order.

That partnership of forces which had
been shaping the planet

found a harmony.

Even plants finally found a balance,

instinctively aligning the amount
of biomass on Earth

with the carbon cycle

and the composition of
the atmosphere.

And this equilibrium has lasted more
than a quarter of a billion years.

You see, plants had taken up
that role as guardians

of the Earth's climate,

breathing in and out as
and when required

and paving the way for the world
that we've inherited today.

This bountiful, blooming miracle.

This blue-green jewel.

This Eden.

How do scientists piece together
what was happening on our Earth

millions or even billions
of years ago?

Our planet has a 4.5-billion-year
history of change.

And when I say change, I mean
radical, dramatic,

just astonishing change.

This episode featured the bizarre
giant fungi, Prototaxites,

that dominated land over 400 million
years ago.

Prototaxites was a fossil
fungal spike.

They could grow up to be
about 26 feet tall.

So about the size of a
two-storey house.

Not only are these one of
the strangest organisms

ever to grace the planet,

the only clue to their existence
were a series

of mysterious fossils first
discovered in 1843.

So here you have this great
big thing.

And when they started finding more
of them, they were like,

"Well, this is kind of like a trunk,

"or it's shaped like a chunk
of wood."

But there's no wood.

There's no trees.

So what is this?

Until, in 2007,

when microscope technology was able
to take a closer look,

revealing a cellular structure
that was strangely familiar.

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.

Looking at it more closely,

they realised the structures were
actually more similar to fungi.

These were gigantic tree-like fungi.

It creates, in my mind, one of
the most bizarre

prehistoric landscapes of all.

And it's a great example of how
ancient organisms

sometimes look completely different
from anything that's alive today.

Sometimes the challenge isn't
identifying what a fossil is,

it's figuring out how the parts
fit together.

As it was with Archaeopteris,

one of the earliest trees on Earth.

Archaeopteris has a remarkable
fossil history.

So, first, the stem was discovered,

and they recognised it because of
its distinct type of wood.

And then, at the same time, they
found lots of fern-like foliage.

However, we didn't think
they were connected

because they looked so drastically
different.

Scientists initially thought they
had two distinct plants.

Eventually, someone found a specimen
that showed

the two structures connected.

And that's how we discovered
that this was all

part of the same plant.

And so Archaeopteris
was discovered...

..and another chapter of the story
of plants came into focus.

Archaeopteris fundamentally changed
the Earth's landscape.

For the first time,

we had forests that we're
so familiar with today.

Now, finding ancient fossilised
plant life is one thing.

How do we begin to learn about
geological processes

billions of years in the past?

Like the origin of plate tectonics,
an event still shrouded in mystery.

Studying the onset of
plate tectonics

is a hugely controversial area,

and that's because the evidence
is just so scant.

An eye-catching new idea leads
some scientists to think

plate tectonics started with a bang.

I would so love to have been there
to watch

a 30-mile asteroid smash into Earth.

Now, I'd want to be out
in space someplace,

maybe on the moon.

But what's the evidence for such
a cataclysmic event?

One thing that geologists can do
is they can pick out

small minerals from rocks and date
them using isotopes.

For example, there are now evidence
for very large asteroid impacts -

in Australia, in South Africa -

and that seems to correlate
with some of the starting

of plate tectonics.

Inside ancient rocks, geologists
have discovered spherules,

tiny droplets of melted material
that form

under the intense heat and pressure
of asteroid impacts.

Modelling of these impacts indicates
that these massive bombardments

played a role in triggering
plate tectonics.

What happens if an asteroid hits
that crust?

Well, it smashes it like a plate
falling on the floor,

and those pieces get pushed down
and moved around.

And that's how the mantle
and the crust

could begin plate tectonics.

By hunting down clues today,

scientists can unlock the secrets
of the Earth's deep history,

allowing us to tell our planet's
story like never before.

We journey back to where it
all began...

..to tell the story of
our atmosphere.

How it emerged from a toxic
orange hell

and transformed a violent ball
of rock

into a beautiful, life-sustaining
blue bubble,

unique in the universe.

If the Earth could talk,
what would it tell us?

Well, the Open University imagine
how it might answer

some of our questions.

To experience this interactive
presentation,

go to the website on the screen

and follow the links to
the Open University.

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