24 Hours on Earth

The sun.

It creates the daily rhythm for life on Earth.

A player in almost every drama that unfolds across our planet.

Hour by hour,

its exact position is critical.

For some, it brings moments of enormous opportunity.

For others, it can spell disaster.

All over the world, animals' lives are governed

by the sun's journey through the sky.

How they respond can make the difference between success

and failure,

life or death.

This is just an ordinary day

on our extraordinary planet.

It's dawn.

The sun hasn't arrived yet,

but its power will soon be felt,

and the world is waking.

HOOTING

The day starts with a love song.

HOOTING

HOOTING

Lar gibbons.

With each note, they renew their bond after the long night,

and remind other gibbons that this patch of forest is theirs.

They've discovered that the hour before sunrise is the perfect time

for their duet...

HOOTING

..because sound travels furthest in cool air.

And at dawn, a warm layer sits above the cool air,

reflecting and amplifying every note.

It's the best time of the day to be heard,

and the gibbons aren't the only ones making the most of it.

BIRD SQUAWKS

BIRDS CALL

All over the planet, nature's dawn chorus heralds the moment

the world's been waiting for.

SCREECHING

PENGUINS TRUMPET

Our star,

a burning giant,

reappears above the horizon.

Its rays, travelling at over 180,000 miles per second...

..flick the switch

and the world is flooded with light.

This meerkat family is up early to greet the sunrise.

THEY CHIRRUP

It's not high enough to warm them up just yet...

..and they're finding it difficult to get going.

But unbeknown to them, the early light

is having an extraordinary effect inside their bodies.

Sunlight triggers the brain to shut off drowsy hormones,

replacing them with waves of energising ones,

kick-starting their metabolism

and preparing them for the day ahead.

Suddenly, they're wide awake.

Time to find breakfast.

All over the world, the rising sun is making its presence felt,

forcing animals into action.

For the last eight months, South Africa's rocky shoreline

has been a nursery for this young Cape fur seal.

He, too, is hungry, but the need to fuel his body

is about to get him into trouble.

Each morning, with the rising sun,

the current moving past the mouth of the bay brings rich pickings.

But with opportunity comes danger.

A killer patrols these waters...

..waiting for inexperienced pups to take the plunge.

The older seals know the great whites are out there,

but by midday, the biggest fish shoals will be out of range.

The seals must leave now.

The pups' best chance is to fall in with a convoy of adults.

Experienced seals are notoriously hard to catch.

But in the first two hours of the day,

the great white has a better chance, thanks to an ally.

The sun itself.

The early-morning light is strong enough

to silhouette the pup from below.

But the slanting rays can't penetrate the depths.

The shark can see the pup,

but the pup can't see the shark.

This time, the pup is just small

and speedy enough to slip through the shark's jaws.

Away from the coastline, he's safe.

And as the sun rises higher,

illuminating the shadowy depths,

the shark's window of opportunity closes.

At least, until tomorrow.

As the sun climbs higher in the sky,

its character is changing.

For the first time in the day, it's not just sensed as light,

but as radiant heat.

BIRDS CHIRP

Clusters of Monarch butterflies huddle close together

against the chilly Mexican night.

Up until now, the morning has been too cold to leave the branches.

But as the sun hits their wings,

warming their bodies to a crucial 12 degrees, they can finally fly.

Each cluster revealing tens of thousands

of individual butterflies.

The first warmth of the day is just as important to small mammals.

These Madagascan lemurs aren't meditating.

They're sunbathing.

Too small to regulate their body temperature well...

..they lie back and soak up the warmth

through their thinly coated underbellies.

A much-needed morning heat fix.

But nowhere is the warming of the landscape felt more keenly

than in the desert...

..of Namibia.

Overnight, the temperature hit freezing point.

But this morning, the sun

is radiating heat directly onto the sand dunes.

Three hours after sunrise

and, already, the temperature has climbed by 30 degrees.

Exactly what this desert inhabitant has been waiting for.

The Namaqua is unusual...

which, for a chameleon, is really saying something.

Somewhere in its evolution, it drew the short straw.

So whilst its cousins around the world live hidden in trees,

the Namaqua is exposed on sand-blasted dunes.

Just surviving the freezing night

has left the cold-blooded chameleon sluggish.

Its energy supplies so drained

that breakfast passes right under its nose.

It's going to need to get warm before it can eat.

By angling its dark brown, scaly skin towards the light,

it becomes a reptilian solar panel.

An hour or two on charge and it will be good to go.

In less extreme parts of Africa,

this change in air temperature has burnt the hanging morning haze away.

In just a couple of hours, the ground will become so hot

that it will begin to generate a heat haze of its own.

But right now, in this brief window of clarity,

with nothing to spoil her view,

conditions for this cheetah

are perfect.

She's a mother, with responsibilities.

Three of them.

They're growing fast

and they're hungry.

Mum needs to make a kill.

The lions who share her territory

have excellent night vision.

But the cheetah's eye is designed for sunlight.

Packed full of colour receptors,

she sees the world in razor-sharp detail.

The lions could threaten her cubs,

but they're stuffed full from the night's hunt.

Right now is her best chance.

Black tear stains under her eyes

combat glare and help her focus

in the crisp morning air.

Just in time.

The heat haze will soon be shimmering above the ground...

..making it difficult to see in any detail.

Then the time for hunting will be over.

The best option?

To spend the rest of the day

in the shade.

In more temperate parts of the world,

plants have been working hard since dawn...

..photosynthesising light into energy.

In the next hour, the sun's intensity will peak.

These light harvesters are gearing up for what should be

the most productive moment of the day...

..but it's also when the sun becomes its most dangerous.

As damaging to plant cells as it is to our skin.

As the sun blasts down from overhead...

..these sunflowers are carefully monitoring

its intensity,

flooding each leaf with a sunscreen,

protecting the plant from sun damage.

At 90 degrees, directly overhead...

..the sun's rays pass through the least atmosphere.

Millions of watts of energy beat down onto the Earth.

In the Australian outback,

temperatures have soared past 50 degrees.

Out in the open, these kangaroos

are becoming dangerously hot.

The shade gives some relief,

but it's not enough.

The air surrounding them is baking.

To prevent heatstroke,

these roos have a trick or two up their sleeves.

Along their forearms, vessels full of hot blood run close to the skin.

They lick themselves.

As their saliva evaporates, a little body heat is lost with it.

And by digging away the hottest layers of earth...

..and resting on the cooler layers below...

..these resourceful roos have found a way to survive the midday onslaught.

Shade is hard to come by in the Namibian sand dunes.

Our cold-blooded chameleon

is in danger of being cooked in his own skin.

But life in this uncompromising place

has forced an incredible adaptation.

Doing what chameleons all over the world do best,

it's changed colour.

Dark brown to brilliant white.

Reflecting the heat off its skin

and keeping its internal temperature

just cool enough to survive...

..and to hunt.

A solar-powered, turbo-charged chameleon.

Well, relatively speaking.

Not everyone finds the midday sun such a challenge.

In a lake, on a remote island in the Pacific...

..a golden jellyfish is sunbathing.

This is no ordinary jelly.

Over 12,000 years ago,

its ancestors were marooned here.

Faced with starvation,

this seafarer became a farmer.

Absorbing lake algae into its body

and cultivating them.

The algae use light to photosynthesise,

sharing the energy generated with their hosts.

The jellies carefully tend the algae,

following the path of the sun

across the lake.

It's such a successful relationship

that now, there are 13 million jellies...

..all clustered under the midday sun.

Gently spinning, to give their crop

just the right amount of light.

From midday onwards,

the angle of the sun begins to wane.

But it becomes no less dangerous.

The ground temperature carries on rising.

While most animals wait for the Earth to cool...

..amongst the craggy peaks of the Ethiopian mountains...

..a quirky-looking crowd is gathering.

Lammergeyers are vultures, scavengers.

Collectors of bones.

Partial to the marrow found inside them.

Heavy duty stomach acid dissolves small bones,

but they're not exactly nutritious.

A lamb femur full of marrow is much more like it.

But there's a problem -

the bone's far too big to swallow.

In the warmth of the afternoon,

this lammergeyer senses an opportunity.

Heat, radiating from the plains below,

has built into huge columns

rising into the atmosphere.

Warm-air thermals - perfect for flight.

The lamb bone matches her own bodyweight,

but the early-afternoon thermals create an invisible elevator,

making flight possible.

At any other time, this manoeuvre would prove dangerous

and costly in energy.

But by seizing her chance, she's been rewarded.

Delicious.

While the lammergeyer rides early-afternoon thermals

close to the Equator...

..a polar bear, right at the top of the Earth,

is facing a very different challenge.

Because of the tilt of the Earth on its axis,

the Arctic summer is filled with almost endless light.

Hunting seals under the sea ice, he's in no rush.

At three o'clock in the afternoon,

the sun is still high in the sky...

..but the radiant heat from days of endless summer

is melting his Arctic world.

The sun will stay high over the Arctic for another two months.

Soon, there'll be no ice left to hunt on.

He will have to fast until the seasons change again.

It's this seasonal journey of the sun in the sky

that causes the greatest movement

of animals across the planet.

Driven by changes in weather,

by opportunity,

and danger,

migrants criss-cross the planet.

Across continents and through oceans.

WHALE SINGS

Even the lives of the greatest travellers are ruled by the sun.

This family of humpback whales

spent the winter breeding in tropical waters...

..which made the perfect nursery for the new calf...

..but are low on stocks of krill and small fish,

the things 30-tonne adults like to eat.

The calf is now strong enough to swim the 3,000 miles north

towards the family's next big meal.

Navigating across thousands of miles of featureless ocean

is an incredible challenge.

And with the adults running on empty,

they can't afford to get lost.

But the sun throws them a lifeline.

Humpbacks are expert navigators.

They use the sun to keep their bearings.

Its changing position in the sky,

combined with information sensed from the Earth's magnetic field,

creates a reliable compass.

So effective is their reckoning

that between sunrise and this point in the afternoon,

the family will have deviated less than one degree

from last year's course.

Late afternoon.

The sun's time in the sky is running out.

Its power is fading.

Animals face an urgent new challenge -

to make the most of the remaining light and warmth

before it disappears.

Back in Namibia, the sand is beginning to cool...

..and the chameleon has undergone his most bizarre transformation yet.

He's split himself right down the middle.

Black side faced towards the sun

to absorb every last bit of remaining warmth.

White in the shade, to stop his body heat being lost.

Being two chameleons at once

will help him survive the cold night ahead.

And he's not the only animal torn between the heat of the day

and a chilly desert night.

In the mountains of Oman,

a rock hyrax family

are soaking up all the late-afternoon heat they can get.

They could also be accused of having

a bit of an identity problem.

Hyrax look like rodents,

but their closest relative is actually an elephant.

And although they're mammals,

they need to bask to keep warm,

just like lizards.

Sunbathing in the late afternoon is a serious business.

Every extra minute spent absorbing warmth from the rocks

gives them a better chance of surviving

the cold night ahead.

But stretching out in the open like this is dangerous.

They've no choice but to make themselves targets.

And stonebaked hyrax is a black eagle favourite.

The family are on high alert.

The eagle's only chance is a stealth attack...

..and the afternoon sun provides the perfect disguise.

Diving at the same angle,

the glare is an invisibility cloak.

But hyrax have a unique adaptation.

In their eye,

the coloured iris slightly shields the top of the pupil.

An in-built sun visor,

perfect for eagle spotting.

There won't be hyrax on the menu tonight.

There's less than two hours left before sunset.

The sun has lost its strength,

but it has not lost its grip on our planet.

It has one last hand to play.

The phenomenal energy absorbed by the ground

during the hottest parts of the day

is released back into the atmosphere.

Fast-rising, unstable, hot air

colliding with higher, colder air

creates weather.

THUNDER ROARS

If you live near the Equator,

rain in the afternoon is just something you've got to put up with.

A waterproof makes it all much more bearable.

Although...

this young orangutan

hasn't quite got the hang of making his just yet.

But over drier parts of our planet,

all this pent-up heat energy can spell disaster.

Turbulent air creates static charges.

Lightning.

Each strike five times hotter than the surface of the sun.

Parched forests take like tinder to a match.

The fire will eventually burn itself out,

but the smoke lingers,

scattering all but the very longest wavelengths of light -

reds and oranges.

While the Earth smoulders,

the sunset burns extra deep.

It takes, on average, just two minutes

for the sun to sink below the horizon.

Such a short time, in which everything changes for life on Earth.

The sun's great energy,

its light and heat, is suddenly lost.

All over our planet, families regroup

and find the safety of their beds...

..as drowsy hormones flood back into their bodies,

pulling them into sleep.

But not everyone's quite ready to let the day go.

Above a limestone cave in Borneo,

a hawk, a day flyer,

has not yet flown to its roost.

What it's waiting for is just beginning to stir.

Inside the cave, a storm is brewing.

The beating wings of millions of wrinkle-lipped bats.

They use sound more than sight to navigate,

so leaving the cave before dark

won't help them find food.

But there's just so many of them

that flying any later would cut into valuable feeding time.

By pushing out into this last, brief window of light,

they're taking a huge risk.

The hawk is just one of many

that's ready for them.

Our eyes would struggle in this twilight.

But the hawk's eyes can pick out fast-moving objects

in the faintest glimmer of light.

It's a twilight battle of the senses -

sonar versus eyesight.

In the last moments before complete blackness,

eyesight still wins.

As the very last of the sun's rays are lost behind the horizon...

..for the first time, the planet is in true darkness.

The night-time world.

The darkness holds allure for a whole host of permanent night dwellers.

They've acquired very different senses...

that don't rely on sunlight.

This scorpion has spent the daylight hours hiding deep in crevices,

to avoid being eaten.

But when the sun is quite absent, she becomes the predator.

Her small eyes are all but useless in the darkness.

Instead, she senses prey through vibrations.

VIBRATIONS PULSE

The movement of a single grain of sand

gives her all the information she needs to attack.

But just as she closes in on

her first meal of the night,

she freezes.

Sensing danger.

Even in the dead of night,

our sun is still not lost.

Its rays pass by the dark side of the Earth...

..and reflect off its moon.

A ghost sun.

The full moon rises high and bright...

..and the scorpion begins to glow.

Ultraviolet light reacts with fluorescent chemicals

in the scorpion's armour.

Her eyes can't see moonlight, but her whole body is a warning system,

telling her that her cover is blown.

She needs to hide, before a predator sees her.

So she uses the fluorescence to her advantage...

..as a light sensor.

Any part of her armour in shadow will stop glowing...

..telling her she's found safety.

The scorpion is not alone in her fear of the moon.

Known as lunar phobia,

many nocturnal species around the world will hide away...

..and choose to go hungry,

rather than risk coming out

under the reflected sunlight.

But to a hunter in Southeast Asia,

a bright-lit night is an opportunity to be seized.

Every night, the rainforest's insect population comes under attack

from a palm-sized primate.

Don't let the wide eyes fool you,

this family of spectral tarsiers are ruthless hunters.

With saucer-like eyes, each as big as their brain,

this family use the faintest of starlight

to see the forest in incredible detail.

And when your eyes are this sensitive,

all this reflected sunlight is a gift.

The family aren't about to miss a moment of

the best hunting night of the month.

In the moonlit forest, the family might triple their hunting success.

But it's all too easy for a tarsier

to have eyes bigger than its stomach.

In the early hours, full to bursting,

the family call it a night.

It's nearly morning.

The moon is hanging just above the horizon.

Soon, it will be overwhelmed by the first light of dawn.

But in the Arctic, the sun is casting

a new and different power over the last few hours of darkness.

Particles thrown from the sun's surface across 90 million miles

of empty space, to reach the Earth.

They are directed by the Earth's magnetic field to the poles.

This cosmic storm creates a magical aurora.

The spectacular Northern Lights.

But behind this beautiful light show...

..is a sinister force...

..that impacts on whales, with potentially lethal consequences.

The humpbacks have been relying on the Earth's magnetic field

to chart their night-time course.

WHALE SONG

But the Earth's magnetism is becoming distorted

under this barrage of solar energy.

It's believed whales can become disorientated.

Thrown off course.

They might even strand onto the land.

But soon, it will be morning,

and the sun compass will bring them back on track.

Dawn.

The very first light of a new day.

The sun's power will soon be felt...

..and the world is waking...

..ready to begin another ordinary day...

..on our extraordinary planet.