Walking with Monsters

This is Earth. Four point four billion years ago.

A toxic world with no hope of life.

Then everything changed.

Another planet, Thea, smashed into Earth

and the two planets fused,

creating a brand new world.

Our world.

Even today, Thea lies right beneath our feet.

A smaller chunk of Thea became our moon.

And slowly our oceans formed.

Until life on Earth was ready to begin.

But who would inherit this blue planet?

This series tells the extraordinary story of life before the dinosaurs.

A time when strange and savage

creatures fought a ruthless battle to rule the Earth.

Amongst them were our own earliest ancestors,

whose survival would decide whether we humans would exist at all.

As they evolved,

these bizarre creatures created the blueprint

not only for our bodies,

but for everything living today.

This is life's forgotten story.

An epic war for our world.

A war between monsters.

This is our planet,

five hundred and thirty million years ago.

Nothing yet lives on land,

but in the ocean it's a different story.

Life has already been evolving for millions of years

at a slow and steady pace.

The seas are full of simple,

soft bodied creatures,

blindly drifting in the currents.

Now, however, in the coastal shallows below,

evolution has stepped on the accelerator.

Predators have taken their first bite.

This is Anomalocaris, Earth's first super predator.

This two metre long monster owes his success

to a monumental evolutionary landmark.

Eyes.

They may look bizarre but they're not unique.

Many predators in the Cambrian seas

have also evolved eyes.

And so have their prey.

The consequences have been explosive.

Being able to see and react to enemies

has triggered an arms race between hunter and hunted.

This battle continues today

and is a major force behind the variety of life.

To combat being visible and vulnerable,

eighty percent of creates in these shallow seas

have sturdy skeletons on the outside of their bodies.

These armoured animals are called Arthropods.

In the future,

they'll give rise to insects and spiders.

But in these crowded waters

there's competition everywhere,

and even the mighty Anomalocaris's defences are constantly put to the test.

Rigid armour splits if bent too far,

leaving the loser vulnerable.

To a completely different threat.

This is Haikouichthys.

He's the size of your thumbnail,

but he's an evolutionary giant.

He's the first ever fish.

Our earliest known ancestor.

He's unique,

because instead of having armour on the outside,

he's tough inside.

He's evolved a primitive backbone.

He's the very first vertebrate.

Forerunner of all future backboned animals,

from the dinosaur, to the elephant, to us.

His flexible backbone makes him

more manoeuvrable than spineless Anomalocaris.

He can scavenge flesh, then dart away unharmed.

Our tiny backboned ancestors have survived a sea of monsters,

but there are still many more battles ahead.

They must adapt or die.

Evolution takes over.

As millions of years pass,

fish build on their basic design.

The muscles around their backbone

evolve into a powerful tail and fins appear.

They evolve a distinct head.

He may not look like you or I,

but this odd fish is becoming the blueprint for our own bodies.

This is Cephalaspis.

She's a peaceful grazer who sucks up algae through her jawless mouth.

But she's also developed a tough protective head and thick scales.

Our ancestor's arthropod enemies have also been evolving

and they're ready for round two.

A hundred million years have passed

and the fight for survival has filled the Silurian seas with variety.

Some creatures here would be recognisable today.

Sponges filter food alongside sea urchins.

The orthocone is a distant relative of squid and cuttlefish,

but he's as long as a truck.

This world is terrorised by

a new improved generation of armoured arthropods.

Meet Brontoscorpio.

He's a metre long monster scorpion with gills

and a stinger the size of a light bulb.

He zeros in on his next meal.

But Cephalaspis has evolved an early warning system.

Special sensors on her skin detect the tiniest vibrations in the water.

We've inherited similar senses.

They make us sensitive to touch.

With her defensive headgear, Cephalaspis can't swim fast for long.

She must rest frequently.

Soon she'll tire completely.

Cephalaspis suddenly changes her path.

She's picking up bad vibrations.

Something Brontoscorpio can't detect.

Pterygotus is the Titan of sea scorpions.

The biggest arthropod of all time.

More than three metres long,

she's the size of a crocodile.

She has turned the tables on Brontoscorpio.

He'll make a good meal for her young.

In such dangerous seas there's nowhere to hide.

When breeding seasons comes,

the Cephalaspis congregate to head for the one place

they might escape a scorpion's grasp.

Fresh water, inland.

Land at this time is like an alien planet.

It's a barren expanse of roasting rock hotter than the Sahara.

The air would be toxic to us.

It has much less oxygen

and three hundred times more carbon dioxide than today.

But some forms of life have gained a foothold in this furnace.

The first pioneering plants.

Cooksonia has a unique survival strategy.

It's the first plant to send shoots upwards, trapping extra light to help it grow.

This basic design will eventually lead to our tallest forests.

The Cephalaspis convoy ploughs upriver, away from the sea.

They're making the marathon journey

back to the spawning grounds where they hatched.

Incredibly our fish ancestors already use memory.

They use familiar landmarks to navigate.

Their toughened heads protect a vital weapon.

One of the first complex brains.

It's much more developed than their scorpion rivals

who have no memory at all.

It's thanks to these primitive fish

that we can think and solve problems today.

But the fish have underestimated their enemy.

It is the arthropods and not our ancestors

who have taken the first momentous steps out of the sea into dry land.

Brontoscorpio has a huge advantage.

As well as gills

he has simple lungs made up of hundreds of thin layers of tissue.

He can't breath in and out like we do.

He just absorbs the oxygen into his blood.

Equipped to maximise the little oxygen available

and with their armour to protect them from the sun,

the scorpions patrol the shoreline,

scavenging on whatever the sea washes up next.

Finally the fish approach their destination.

They've navigated their way back to the spawning pool,

where their lives began.

Weak from their long journey,

now they have to cross a ridge of rock

to make it from the river, to the pool.

The first fish make it through and start to lay their eggs.

But the exhausted Cephalaspis have company.

Passing scorpions have stumbled on this bounty.

But the fish have numbers on their side.

The clever Cephalaspis have navigated their way,

while Brontoscorpio are only here by luck.

They're soon stuffed to the gills while the fish keep jumping.

One scorpion is still hungry, but he can't feed.

He's become a prisoner in his own skin.

His rigid skeleton is now a handicap.

It can't grow with his body.

He needs to shed his hard skin and then grow another,

expanding while the new one is still soft.

For such a large creature, this is a long process.

Next morning, there's no sign of life in the spawning pool.

The scorpion has missed his chance.

Our ancestors have survived.

They've laid their eggs and are returning to the sea.

Brain has triumphed over brawn,

and soon they won't be such soft targets.

Evolution starts to give them weapons to fight back.

Over millions of years,

the fish's gills adapt to form the first jaw with the very first teeth.

Now they're equipped to go on the attack.

Some develop tougher bones and muscles in their fins and shoulders,

which become the first limbs.

This is where our arms and legs began.

With this four-limbed design,

our ancestors finally haul themselves out of water on to land.

This is the giant amphibian, Hynerpeton.

The prototype land dweller for the next three hundred million years.

Hynerpeton are over a metre and a half in length,

much larger than most amphibians today.

They've carved out a home along the water's edge.

Arthropod enemies still exist,

but they've shrunk since their Brontoscorpio glory days.