A Perfect Planet - First Season

A Perfect Planet.

There is only one planet in the universe, as far as we know,

where there is life.

The Earth.

Our home.

The perfect planet.

Life here is only possible

because of a unique balance of natural forces.

Energy from the sun powers the living world.

Weather systems transport fresh water around the globe.

And powerful ocean currents circulate life's essential nutrients.

This series will reveal

how these global forces have worked together

to create our planet's fragile life-support system.

One of these forces is so important

that life would never have even started without it.

Across the surface of our planet,

there are over 1,500 active volcanoes.

This is the most active - Kilauea in Hawaii.

Here, magma - liquid rock from the planet's hot interior -

bursts out through fractures in the Earth's crust.

And it's been flowing for months.

Nothing can stand in the lava's way.

Volcanoes are certainly destructive,

but without these powerful underground forces,

there would be no breathable atmosphere.

No oceans.

No land.

No life.

We can't control volcanoes,

but they're vital for all living things on Planet Earth.

This is Ol Doinyo Lengai in Tanzania.

It's one of Africa's most active volcanoes,

and has erupted over 15 times in the last hundred years.

On its northern flank lies Lake Natron,

400 square miles in extent,

and one of the world's most corrosive bodies of water.

The water wells up from deep below,

carrying such a concentration of chemicals that it can burn skin.

But one animal thrives here.

Volcano birds.

Nearly two million lesser flamingos live in East Africa

and all of them come here to breed.

But they can only nest here when the lake's level drops so far

that in the centre its bed is exposed.

And that rare moment is now.

How they know when the conditions are right is a mystery.

But some have flown thousands of miles to be here.

The flamingos head for the middle of the lake,

where the intense evaporation has created islands of salt.

It's here that the birds build their nests,

over three miles from the lake's edge

and safe from land predators, which are unable to cross

the surrounding moat of caustic soda.

The single egg is laid on a mount of hardened salt

built by the adults,

its height an insurance against

a sudden rise in water level...

...Which often happens on Lake Natron.

As the centre dries and enlarges,

more and more flamingos arrive to nest on it.

In good years, such as now,

as many as half a million pairs breed here.

After 28 days of incubation,

a chick emerges into Natron's harsh glare.

Here, temperatures can rise to 55 degrees Celsius.

Mother's wing, however, can serve as a sun-shield.

The chick is fed a rich liquid

made of the lake's barely digested algae

and traces of its parent's blood.

After a few days, the chick is strong enough to stretch its legs.

It then joins a growing creche made up of chicks of different ages.

Soon, the need for fresh water will force the infant birds

to trek to springs on the lake's edge...

...a journey they have to make on foot, as their flight feathers

have yet to develop.

Every day, the adults fly to these springs to feed.

Here, on the lake's margins, they collect algae that flourish

in the volcanic water - vital food for the flamingos.

It's the algae that turn the flamingos' feathers pink.

It even colours their eyes.

The adults spend most of their day at the springs,

and now their chicks are going to join them there.

No-one wants to get left behind.

It's a three-mile march over razor-sharp flakes of soda

and sticky, caustic mud...

...a life-threatening trial, especially for the youngest chicks.

The groups merge into one giant creche.

For some, the challenges are just too great.

Exhaustion overcomes the weakest.

And now there is yet another threat.

Marabou storks.

They have long legs like a flamingo,

but a beak like a Roman sword.

And they are patient, waiting for an easy target.

Their very presence creates panic among the chicks.

The smallest avoid being trampled underfoot

by travelling on the outside of the group.

But that exposes them to attack.

Their only defence is to run.

But you have little chance

when you're barely ankle-high to your pursuer.

Stragglers will almost certainly be taken.

But there comes a point when every stork has had its fill.

This little chick is very lucky.

At last, the youngsters reach the freshwater springs

at the lake's margin to rejoin their parents.

Almost unbelievably, each chick has a unique call

that its parent can recognise.

It's not just lesser flamingos that depend on volcanoes.

Ultimately, so do all living things.

Over 80% of the Earth's surface

is the result of magma bursting up from the molten interior.

The process started four billion years ago

and it still continues today.

When lava cools, it solidifies into rock

and eventually weathers into land that can support life.

All the Galapagos Islands in the Pacific are volcanic,

and Fernandina is the youngest of them...

...and still growing.

At its centre, a volcanic crater four miles wide...

...and over 800 metres deep.

It seems dormant, but it was erupting only two weeks ago.

Even so, there are some who depend on the heat from this volcano.

A female land iguana, heavy with eggs, approaches the crater's rim.

It took her ten days to climb up here,

but the toughest part of her journey is still ahead.

She's going to descend into the crater itself.

Frequent tremors make the crater walls unstable.

More people have travelled in space

than have visited the bottom of Fernandina's crater.

But instinct drives her on.

The warm volcanic ash on the crater floor

has the perfect temperature for incubating her eggs.

But there are no clear paths down.

Any made last year have been destroyed by rockfalls.

The slope is steep and unstable.

Tumbling rocks quickly become an avalanche.

With the boulders falling down away from her,

she's not in immediate danger.

But behind her, higher up,

two other females have also started the descent.

And now she is in the firing line.

She's safe.

Others before her haven't been so lucky.

But she's undeterred.

At last, after an eight-hour descent,

she reaches the crater floor.

Now she must find a suitable place to dig her nest.

The best sites are already taken.

And nesting females are very aggressive.

A nodding head means keep away.

Push off!

Ignored warnings are met with force.

But she's come a long way, and she's not going to give up now.

She, too, starts to dig a hole in which to lay her eggs.

That done, she will head back,

leaving the volcano to provide the warmth her eggs need

if they are to hatch.

Sometimes, of course, the volcano erupts

and destroys not only eggs, but many nesting adults.

But for the iguanas, the benefits of nesting in the crater are so great

that it's worth all the risks.

Volcanic islands make up just 5% of the planet's land,

but they're home to nearly 20% of its species.

Animals often evolve very swiftly on islands,

cut off from their mainland relatives

and faced with the challenges of isolation.

This is Wolf, an extinct volcano

and one of the most remote islands of the Galapagos,

800 miles from the nearest large landmass

and over a million years old.

A finch.

A female.

Its ancestors doubtless were blown here by storms many centuries ago.

Like most finches, they feed on seeds, nectar and insects.

But there's little food of any kind on Wolf.

And since they aren't strong enough fliers to leave the island,

they've had to find food from a very unusual source.

They depend on another of the island's inhabitants.

Nazca boobies.

Every day, these seabirds commute

between the island and their fishing grounds out in the open ocean.

Each time a pair meet, they renew their bond...

...and then catch up with the neighbours.

Now is the time...

...to hop into action.

Blood.

They are vampire finches.

These little birds have become one of the world's newest species.

She cuts the quill of a large flight feather,

and the blood flows.

The sight of it attracts the attention of others.

Blood is very nutritious - worth fighting for.

So, with this never-ending supply of food,

the vampire finches can flourish on an island

where otherwise they could not survive.

Why the boobies don't object, nobody knows.

Perhaps the finches' behaviour started

when they helped the boobies to remove parasites from their plumage.