All language subtitles for BBC.Life.on.Earth.03of13.The.First.Forests.XviD.AC3.www.mvgroup.org.ENG

The volcanoes of today
are mere feeble flickerings

compared with those that dominated the world
at the beginning of its history.

Then, enormous sheets of lava
welled out of craters,

titanic explosions blew mountains into fragments

and scattered them as dust and ash
over the surface of the land.

That sort of activity continued
for millions and millions of years.

I'm talking about a period
that was 4,500 million years ago.

The forces of erosion,
frost and rain, snow and ice,

shattered the volcanic rocks into fragments.

Rivers carried them
down to the edges of the continents

and deposited them
as sands and gravels and muds.

As the continents
drifted over the globe and collided,

new mountain ranges were built up
and, in their turn, worn down.

And throughout this immensity of time,
the land remained sterile.

Nowhere was there even the smallest of animals
or the tiniest speck of green.

If you condense the whole history of life,

from its beginnings until the present moment,
into a year,

then it wasn't until the end of September

that the first creatures of any size,
jellyfish and so on, appeared in the sea.

And it wasn't until the beginning of November
that the first life,

a few patches of green, appeared on land.

Maybe at the edge of water, like this.

These first plants were simple algae

that had developed cell walls thick enough
for them to survive on moist boulders and gravels.

Slowly, they spread
over the lake beaches and sandspits,

pioneers of the great revolution
that was to lead to the greening of the earth.

Moving out of water for the plants
presented a number of problems.

One of the most serious
was the question of support.

In water,
algae like this can grow into long strands,

but robbed of the support of water,
none has a sufficiently rigid stem

to allow it to grow upright.

So the first land plants remained lowly,

forming flat skins
like liverworts or cushions like mosses.

All of them lived in wet, moist places
and for a very good reason.

Their ancestors, the algae, had reproduced
in two ways, by budding and sexually,

and the sexual method involved sex cells

swimming through water
to find one another and fuse.

Well, mosses retain
very much the same sort of method.

It's this that keeps them tied to water.

So they can only live in places where at the very
least it's wet during some time of the year,

so that sexual reproduction can take place.

Of course, in places like this,
they are literally in their element.

Mosses and liverworts like this
both produce two kinds of sex cells.

These outgrowths on the liverwort, only a few
centimetres high, develop tiny mobile sperms

which actively swim.

These different growths
contain larger static sex cells, the eggs.

Under the microscope,
you can see the eggs at the base of tiny tubules

surrounded by a protective sheath
of smaller cells.

When the outgrowths are ripe and conditions
sufficiently wet, fertilisation begins.

The wriggling sperm are released and
swim in the film of water that covers the plant.

The sperm appears as a milky fluid.

At the same time, the female part of the liverwort
that bears the egg cells

releases a special chemical
that attracts the sperms.

Eventually, they reach the female organs.

Fertilisation occurs and the eggs develop,

repeatedly dividing to produce
a capsule full of microscopic grains: spores.

When they are ripe and the weather is dry,
the capsules burst.

Each minute spore is capable
of growing into a new liverwort plant.

Mosses also reproduce
by these two alternating methods.

The sexual stage provides the variety
of offspring necessary for continued evolution.

The asexual spores can be carried on the wind
to distribute the plant over great distances.

The spore capsules of mosses
are varied in shape,

and they have ingenious ways
of making sure they only release their contents

when the weather is suitably warm and dry.

Many species have detachable caps which
are blown off before the spores are released.

And beneath,
a perforated lid like a pepper pot.

The wind will now carry
the microscopic spores for miles.

With such mechanisms as these, the first plants
colonised the moist places of the world

and green carpets bordered the lakes and rivers.

Into these miniature jungles
came the first land animals.

Millipedes, then as now, were vegetarians,

and they must have found plenty to eat
among the mosses and liverworts.

The biggest today
are only a few inches long,

but many ancient forms that pioneered
life on land grew very much larger.

One, indeed, was as long as a cow.

Millipedes were descended from sea-living
creatures distantly related to crustaceans.

From them, they inherited segmented bodies
and an external skeleton

which gave them support
so they could move just as well in air, on land,

as their ancestors had done in the sea.

But breathing was another matter.

Their ancestors had extracted oxygen from water
with feathery gills alongside each leg.

But such things wouldn't work in air.

Instead, the first millipedes developed a system
of branching tubes within each segment,

along which air diffuses to all parts of the body
so the tissues can absorb oxygen directly.

These tubes open to the outside
through a tiny pore on the side of each segment.

But the amiable browsing millipedes
didn't have the land to themselves for long.

Very soon after they had colonised it,
hunters came up from the sea to prey on them.

These hunters are still today active,
mostly at night.

The scorpions.

They had evolved from a different group
of segmented sea creatures,

but again they had an external skeleton
which worked effectively on land.

With powerful nipping claws
and poisoned stings on their tails,

scorpions are well-armed and ferocious,

actively seeking out their prey
wherever it may be hiding.

Another closely related group
became day hunters in the miniature forests.

The spiders.

Although their sea-living ancestors
had many legs,

spiders and scorpions have only four pairs.
Better for speed.

Spiders have lost
most signs of division in their bodies,

except for some primitive ones
that live in South-East Asia.

Their abdomens show the last relics
of that ancestral segmentation.

Early on,
the spiders developed glands in the abdomen

with which they produce silk.

They use it in hunting,
sometimes laying long trip lines,

sometimes constructing dense sheets.

They manipulate the threads
with modified limbs, the spinnerets.

By the time it's finished,
any small creature trying to make its way here

will blunder into a silken trap.

And while it's still entangled,
the spider will pounce on it.

Reproduction for all these land creatures
presented new problems.

Without water to transport sperm to egg,
there was nothing for it:

male and female had to get together.

For the millipede,
this presented no real danger.

They're vegetarians, so when individuals meet,
neither risks being eaten by the other.

Their difficulties
are entirely ones of manipulation.

The sex glands of both male and female
are at the base of the second pair of legs.

The male has reached forward
with his seventh pair of legs

and collected from his second segment
a packet of sperm.

Now, if only
he can get it into the right position

alongside the female's pouch
in her second segment,

all will be well.

And there it goes.

The scorpion's sexual problems
are much more complicated

and potentially dangerous.

These hunters have to make sure
one doesn't regard the other

not as a mate but as a meal.

Courtship is necessary,
ritualised in a number of set movements.

First, those dangerous pincers
have to be neutralised.

Now, with the pincers held out of action,
more rituals follow.

The heads of male and female come close,

and even touch.

Now a strange heaving back and forth,

which will eventually lead
to the transfer of sperm.

The male's sex gland is on his underside,

and from it he has deposited
a packet of sperm on the ground.

Now he has to tug the female into a position
where her sexual pouch is directly above it.

If this ritual is not performed correctly,
the scorpion's hunting instincts are not pacified.

It's a delicate balance,
and here it seems to be going wrong.

This probing with the sting is probably
more to do with aggression than with mating.

And they break.

Spiders have the same kind of problem.

They too are hunters,
and a male advancing on a female

has to make sure
she knows who he is and what his intentions are.

The female jumping spider
has sharp eyes, eight of them.

He signals with his front legs as though
his life depended on it, which indeed it does.

She signals back...

..and he is encouraged.

At close range, the male uses
tactile signals rather than visual ones.

He must convince the female
of his good intentions.

He has to achieve a more intimate and direct
contact with the female than the scorpion did.

He's prepared for this by spinning
a tiny web of silk on which he's dropped sperm

from a gland under his abdomen.

He's taken up the sperm
in two special feelers, the palps.

Now he must reach over the female
to pump sperm from one palp

into one of the female's sexual pouches.

It's rather like liquid
being squeezed out of an eye dropper.

And there it goes.

Now the spider changes position
to pass sperm from the other palp

into the female's other sexual opening.

The wolf spider is a larger
and particularly aggressive species.

He too is courting a female.

His problem is especially dangerous
because the female lives in a burrow

from which she emerges only on hunting forays.

It's hardly surprising
that he approaches with the greatest caution.

At first, he uses a kind of semaphore.

If he doesn't keep this up,
the female may mistake him for prey

and rush out and pounce on him.

Within the confines of the burrow,
visual signals are difficult,

and so the male changes to delicate
and sensitive strokings with his front legs.

At last, she receives him
and he can take up his risky mating position,

reaching right round to the female's abdomen.

The early jungles, filled with such creatures,
were still only a few inches high,

no more than a thick, moist carpet
draping the sandspits and boulders.

For plants like mosses and liverworts
were still the only ones on land.

And this is just about as big
as any moss in the world ever grows.

A series of isolated stems.

It has no real roots. It absorbs
what moisture it requires through its surface.

And it doesn't have true leaves,
they're just simple scales.

And to see why it's so frail,
one has to look inside the stem.

Sliced and examined under
the electron microscope, this is how it appears.

The cells are thin-walled with no rigidity to them,
unable to support a tall plant.

But that structure was soon to be strengthened.

In the course of time, some plants developed
that were able to grow upright

and several feet tall.

The fossilised remains
of some of the earliest of them

have been found in the rocks
of these bleak Welsh hillsides.

To find fossils,
you sometimes have to use violent methods.

And here are some.

They're just thin branching filaments,

but they'll show up even better
if I wet this slab.

They look like tiny moss filaments,

but when these flattened,
400-million-year-old stems are sectioned,

the electron microscope
reveals quite different cells.

These have much thicker walls,
forming tubes in the stem.

A plumbing system,
up which the plant draws water.

And these new cells give the stem strength
and the ability to grow tall.

These very similar cells
come not from a fossil plant but from a living one,

from this plant,
which grows on another Welsh hillside.

It may look superficially like a moss,
in fact, its common name is clubmoss,

but actually, it's fundamentally different.

By virtue of those tough thick cells
in its stem, it's more rigid than any moss.

Today, it only grows to that sort of height.

But in the past, it grew to the size of trees
and formed great forests.

There were soon many kinds of plant
with the new cell walls,

and some of them, the horsetails,
are still common worldwide.

The highest, in South America,
reaches three or four metres,

but 300 million years ago,
they grew to 30 metres, 90 feet tall.

Then, as now, they developed
a hard outer skin to prevent desiccation.

Under the microscope, you can see
minute pores through which the plant breathes,

taking in carbon dioxide and giving out oxygen.

There was a third kind of plant that grew

with the giant horsetails
and the clubmoss trees in the first forests:

tree ferns.

But height for the horsetail and the tree fern
accentuated yet again

the problem of achieving sexual union
with a male cell that has to swim.

How could a microscopic cell
swim from the top of that tree fern

to the top of that one? Impossible.

The structures that are up there
produce spores,

reproductive cells that do not require
fertilisation in order to develop,

just like those
in the capsules developed by mosses.

The ferns produce their spores
from structures beneath the fronds.

Their shape and arrangement
varies with each fern species.

Ferns, like mosses,
release their spores when the weather is dry,

and the wind can carry them far.

Some fern spores are produced
in cups at the end of curled strips,

one side woody, the other thin-walled.

As these cups dry,
they shrivel, pulling back the strip

until the tension is too much, the strip snaps
back and the spores are catapulted free.

The spores have tiny spines and ridges
that help them catch the wind.

A few will fall on moist ground and then
germinate to produce a different kind of plant.

This is the stage in the fern's life cycle
that bears sex cells.

It has had to remain small
and close to the ground

in order that its sperm can swim
from plant to plant.

When wet weather comes,
the male organs release the sperm

which swim by thrashing their thread-like tails.

Hundreds of thousands are produced
from the underside of the flat plant

and carried away by the rainwater.

Eventually, some reach
the female organs of the plant

and swim up the tubes
that lead to the egg cells.

After fertilisation,
a new growth develops from the egg,

sending up a tiny stalk.

These green shoots eventually grow tall
and complete the cycle,

becoming once more
a familiar spore-bearing fern.

Then, about 400 million years ago,
as the forests began to rise,

new animals appeared.

These were descendants of the ancestral
millipedes, and several kinds still survive today.

This is a bristletail, and it lives in soil worldwide.

And this, the silverfish,
that now often lives in houses.

Faster than millipedes,
they have fewer body segments

and even fewer legs, just three pairs.

They all feed on vegetable matter.

But as plants grew taller, so leaves
and spores became more inaccessible.

And these little creatures doubtless clambered
up the stems and trunks after them.

The journey up must have been fairly easy,

but getting down again,
sometimes over upward-pointing spikes,

may have been more laborious.

Maybe that was the reason
for a dramatic development.

Some little creatures developed wings
for flying from plant to plant.

Just how wings evolved, we can't be certain,
but they may have first developed

as tiny lobes on the back.

Dragonflies today develop their wings
in just this way,

repeating millions of years of evolution
in just one night.

The wings are stretched taut
by blood pumping into the veins.

Later, the blood is drawn back into the body
and the gauzy wings slowly dry and harden.

Flight is the great achievement of the insects.

They were the first creatures to take to the air

and they had it almost to themselves
for 100 million years.

Dragonflies were among the first flyers,
and they are still superb aeronauts.

They can reach speeds
of 20 miles, 30 kilometres an hour.

They hunt in the air, holding their legs
crooked in front of them like a basket.

They even mate on the wing.

The females lay their eggs in water.

Their young, wingless larvae
will grow up on the bottom of the pond,

breathing through feathery gills
and feeding on other small water-living creatures

until the time comes for them too
to climb up a reed and spread their wings.

The dragonflies' smaller relative,
damselflies, also haunt ponds.

The wings of these insects beat so rapidly

that only a slow-motion camera
can show clearly how they fly.

This is the action slowed down 120 times.

The insect gets lift on the downbeat of the wing
by twisting it

so that the leading edge is inclined downwards.

But at the bottom of each stroke,
the wing is twisted back

so that it is effective on the upstroke as well.

It's an intricate set of mechanical movements
which man has never matched in the air.

Here, the insect is hovering. The wings sweep
alternately backwards and forwards,

again changing angle at the end of each sweep
to obtain lift on both strokes.

Man has achieved something similar
with a helicopter, whose blades rotate.

The insect can't rotate its wings,

but it's evolved a set of movements
which are even more complex.

The principal navigational equipment
of dragonflies and damselflies are their eyes.

Because they're so dependent on them,
dragonflies normally fly only during the day.

Today's splendid species
are among the biggest of insects,

but when the insects first had the air
to themselves, the dragonflies grew gigantic

and one appeared
that had a wingspan of 70cm, over two feet.

The largest insect that has ever existed.

While all this was happening,
some 300 million years ago,

the plants themselves
were on the brink of an important advance.

This tiny sexual stage of the fern's life cycle
is obviously very vulnerable.

It can only live
in moist conditions like these,

and down on the ground
it's easily cropped by plant-eating animals.

It would obviously be much safer if this stage
could take place in the top of the tree.

But that would require some way of transferring
the sex cells from tree to tree.

Well, they could be blown there by the wind.

But there was then, as there is now,
a regular traffic between the treetops.

Insects that go up there to seek the spores
as food and fly from one tree to another.

They could take them. And that's what happened.

New plants appeared
in which the sexual generation

remained fixed to the asexual tree stage.

And one of the first of them
was a plant like this, a cycad.

Cycads bear two kinds of cones,

each of which represent, in effect, part of the tiny
sexual stage that once grew on the ground.

The male cones produce pollen, the grains
of which germinate to produce the male cells,

and the female cones contain the large egg cells.

Insects help to transport the pollen
from the male cone to the female,

and there it produces a tube
down which swims the sperm.

At its tip, within the female cone,
a drop of water appears,

and in that the sperm swims, re-enacting
the journeys made through the primordial seas

by the sperm cells of their algal ancestors.

Only after several days does it fuse with the egg.

This cycad leaf is about 200 million years old.

That's to say it was fossilised
at the end of November in the "life on earth" year.

And at that time, a new and revolutionary plant
had appeared, growing alongside these cycads.

It was the conifer
and this is one of its trunks.

It's not wood as you might think, but solid stone.

I'm in the middle of one of the most spectacular
deposits of plant fossils in the world.

The petrified forest in Arizona.

These conifers grew to over 200 feet tall

and they stood in thick, dense, dark forests
alongside the swamps where the cycads grew.

When the trunks fell, they often dropped
into a river which swept them down here

so that they formed great logjams around here.

Then the river muds
and sands and silts buried them.

And the silts eventually formed mudstones
like those over there.

When the mudstones eroded away,
as they have done here,

they re-exposed these trunks
that have been turned to stone.

Conifers are built
on very similar lines to the cycads,

except that they have both the male
and the female cone on the same tree.

These are the male cones,
and they use wind to transport their pollen.

But to make sure that such a haphazard
method of fertilisation is successful,

they have to produce pollen in huge quantities.

One cone may produce several million grains,

and there are many thousands of cones
on an average-sized tree.

The female cones are fewer in number
and grow on the same branches.

They're small globes in conspicuous positions
on the tips of shoots,

where they can easily receive pollen.

Pollen falling on the female cone
is only the beginning of a long process.

It takes a year for the grains
to grow down to the eggs.

At the end of that year, the cone looks like that.

But even that's not the end of things.

During the next year,
the cone grows still more,

it develops wrappings
around the fertilised eggs

and then it dries out and opens up.

Out drop small, neatly packaged brown objects.

Seeds. They contain the first kind of plant eggs
to have been fertilised without the help of water.

Ancient though the conifers' technique
of reproduction is, it has proved a huge success.

Today, about a third of the forests in the world
are formed by conifers.

Firs, larches, cedars, pines.
They're all members of this group.

The biggest living organism of any kind
is a conifer,

the giant sequoia of California
that grows to 112 metres, 367 feet high.

Some have a diameter of 12 metres, 40 feet.

Conifers have a special way
of healing wounds to their trunks.

They seal them with resin.

When it first flows, it's runny,
but it soon forms a sticky lump

which not only covers the wound
but incidentally acts as an insect trap.

Lumps of resin from the ancient
coniferous forests survive as amber,

and in them are insects, as perfect now

as the day when they blundered
into the resin 100 million years ago.

From fossils like these,
we know that the insects by that time

had developed into an enormous variety of forms

that swarmed through the trees and over
the ground, feeding on every part of the plants.

Pollen and fruit,
leaves and wood, root and branch,

just as they do today.

Bugs stab stems with stiletto-like mouthparts
to reach the sap.

There are over 3,000 species of aphids alone

tapping this ready source of food
in plants all over the world.

They just pierce the plant vessels.

They don't even need to suck,
such is the pressure of the sap within the stem.

Locusts and grasshoppers chew the leaves.

Beetles munch through cuticles
and even manage to digest wood.

Some insects not only eat plants,
but in order to hide while doing so,

they've come to look like plants,
like leaves and sticks.

Hunters from the ground
pursue the insects up into the trees.

Spiders.

But lying in ambush on trunks and leaves
has its limitations.

Most insects fly.

Spiders never developed wings,
so were unable to pursue their prey into the air.

Instead, they set traps for them.

The silk they had spread in sheets
and trip lines on the ground

they now wove into nets,
setting them across the insect flyways.

With these elegant and varied constructions,
spiders began to take a heavy toll of flying insects

and today spiders are one of the most
effective predators on insect populations.

The insects developed their flying skills
in many different ways.

The two pairs of wings
used by the dragonflies and their relatives

were also used by other insects.
This is a lacewing.

But this design was modified
by other insects.

The caddis-fly, not needing
the speed of a dragonfly to catch prey,

overlapped its two pairs of wings,
producing a unified surface area.

On the other hand,
bees must have compact wings

which can be neatly folded back
when visiting flowers or in the hive.

To get the right lift,
their smaller wings must beat faster.

They look as though they only have
one pair of wings, but in fact they have two.

They're hitched together
to form what is virtually a single surface

by a line of hooks
along the front edge of the back wing.

Other insects spend more time
among dense foliage.

The front wings of this bug
have thickened bases

which strengthen them
and protect the rear ones when folded.

Beetles have gone one stage further.

Many burrow through litter and dense vegetation,

and their front wings
have become converted into protective covers.

In order to lift the heavy body during flying,
the operational wings have to be large.

To protect them when not in use,
they have to be folded,

and the trick is done with spring-loaded joints
in the veins of the wings.

Once in the air, the wing covers
have to be held up out of the way.

But they may also help in flight,
acting as stabilisers,

preventing rolling and yawing.

Like many insects, this beetle increases lift

by clapping its wings
at the top of the upstroke,

thereby improving airflow over the wings.

The chafer is the heavyweight
of the insect fliers.

Its wings beat comparatively slowly,
about 40 times a second.

And it's the least agile
of insects in the air,

ponderous
and unable easily to bank and swerve.

It holds its wing covers out of the way
along its back

and balances itself with outstretched legs.

Its wing structure is tremendously strong
in order to support a heavy insect,

and yet flexible enough
to change its angle on each stroke

and even fold back on itself
when the insect stops flying.

Even that is overshadowed by the feats
of the most skilled aeronauts of all, the flies.

This one, the hoverfly, is perhaps the champion.

It uses only one pair of wings, the front ones,

which it keeps in perfect condition
with frequent cleaning.

It can hang absolutely stationary in the air,
and does so even when it mates.

It can compensate for
any sudden current of wind to hold its position.

It can fly backwards and dart off at great speed
in any direction.

And to perform these manoeuvres, it beats
its wings at an astonishing 175 beats a second.

A normal slow-motion camera
still shows the wings as a blur.

They control flight with a device
which can be seen clearly in another fly,

the crane-fly, or daddy-long-legs.

Those two objects like drumsticks
swinging up and down

are their back pair of wings
after millions of years of evolution.

They're jointed to the body,
like the rear wings,

and act like gyroscopes.

By beating very fast,
and here they're slowed down 120 times,

they give the fly stability in the air.

Like gyroscopes
in the automatic controls of an aeroplane,

they enable the fly
to be aware of the attitude of its body

and to detect
when there's been a change in the flight path.

Houseflies also have these "drumsticks",
though they're much smaller.

It's these that enable flies to perform
such extraordinary and tantalising aerobatics.

And the same organs
perform similar functions for the hoverfly,

giving it that superb flight control.

The design of the insect body
is particularly suited not to great size

but to miniaturisation.

The hoverfly is one
of the most intricately constructed insects of all.

A marvel of microscopic machinery
that's built up from an egg in days

and is often crushed beneath a thumb.

Insect development took place at a comparatively
early stage in the history of life on earth.

At the time when these petrified forest trees
were alive, 200 million years ago,

every single main type of insect
we know today

was already in existence.

Here, for example,
is a piece of petrified wood,

and before it was turned to stone,
some beetle had bored holes into it,

just as beetles bore into dead wood today.

And now the stage was set
for a revolution.

One in which the insects
were to play a crucial part.

Charles Darwin called its history
"an abominable mystery".

Even today, we've only got a sketchy idea
of what happened.

But some of the plants developed flowers.

The woodlands and the lakes bloomed
and colour came to the earth.

Flowers became beautiful,

not to delight the eye of man,
but to attract insects.

This led to some of the most intimate
of all the relationships

that have evolved between plants and insects:
pollination.