[tranquil music]
DAVID: A Perfect Planet.
[sizzles, splutters]
DAVID: There is a nuclear reactor 93 million miles away.
We call it the Sun.
Its rays, travelling through space,
reach the Earth in just eight minutes
and give power to life throughout the planet.
[whale squeals]
DAVID: Its daily and yearly rhythms
shape the existence of every creature on Earth.
[tranquil music]
DAVID: And has done so for over three billion years.
[waves crashing]
[grand music]
DAVID: In the beginning...
there was light.
Surprisingly perhaps,
almost every part of the Earth's surface
receives the same quantity of sunlight each year.
4,380 hours of it.
But it's delivered in varying amounts,
at different times of the year, depending on where you are.
[birds chirping]
It's only here in the tropics, close to the Equator,
that there are 12 hours of guaranteed
daily sunlight the year round.
[animal squeaks]
[birds chirping]
And here that has created a great richness of life,
the tropical forest.
Each leaf is a natural solar panel,
which collects the sun's energy and fuels a multitude of plants.
And in southeast Asia, gibbons live here.
[howling]
DAVID: A five-year-old female
and her lifelong partner
are on a mission.
Every morning, they head out across their territory
to look for ripe fruit.
[gibbons howling]
DAVID: There is one kind of tree here
that they need more than any other.
The fig tree.
These are the only plants in the entire forest
that produce fruit all year round.
Their flowers grow in dense clusters
inside undeveloped figs.
But these have not yet been pollinated
and are not yet edible.
The gibbons
will have to wait.
To produce ripe fruit,
the fig still needs two things.
A large dose of sunlight
and some of the smallest creatures in the forest.
Tiny fig wasps.
They're only two millimetres long.
The figs have a unique partnership with these insects.
A female wasp has the space of just a single day
when the fig will allow her to burrow
into the undeveloped fruit.
It's such a tight squeeze that her wings are ripped off,
but she's not going to use them again.
Once inside,
she makes her way to the tiny tightly packed internal flowers.
And here within,
she lays hundreds of eggs.
She then carefully unpacks fig pollen from her abdomen
and with it, fertilises the tiny flowers.
When she's finished laying,
she dies
inside the unripe fig,
alongside her eggs.
The sunlight now slowly ripens the figs
and helps the young wasps inside to develop.
After just five weeks,
the eggs start to hatch.
The first to emerge are the golden wingless males.
Things now become stranger than fiction.
These males start to mate
with their unhatched sisters.
To reach them, they use a telescopic penis
that's twice their body length.
While their now pregnant sisters
are beginning to hatch,
the males themselves burrow their way to the outside world.
[tranquil music]
The brother's final act
is a chivalrous one.
They sacrifice themselves to marauding ants.
They're serving as decoys,
so their sisters can take to the skies.
The young females, loaded with pollen,
live for just 48 hours
in which time they must find another fig tree
at just the right stage
into which they themselves can burrow as their mothers did.
With the sun's helping hand,
the figs are now ready to eat.
[grand music]
DAVID: The gibbons know all the fig trees
in their territory,
and each day, they travel up to two miles to find one
with fruit that's ready to eat.
Ripe figs at last,
a major part of their diet and available the year round.
Thousands of animals rely on fig trees.
This abundance is only possible
in a world without seasons,
and constant daily sunlight.
But this 12-hour cycle of light and darkness
only happens close to the Equator.
Elsewhere, the amount of sunlight
fluctuates across the year.
That is because the Earth does not spin in an upright way.
Its axis is on a tilt.
23.5 degrees.
So as the Earth makes its annual orbit around the Sun,
keep your eye on the North Pole.
For the first half of the year, its angled away from the Sun,
bringing darkness and winter to the Northern Hemisphere.
For the second part of the year,
the North Pole swings towards the Sun bringing summer.
The Earth's tilt gives us the seasons.
And life has adapted
to deal with even the most extreme changes in light.
The high Arctic.
After six months of being angled towards the Sun,
it begins six months of freezing darkness.
[eerie music]
DAVID: This is Ellesmere Island,
the closest land to the North Pole.
It's winter,
and for the last four long months,
the only light here has come from the moon.
Few creatures can survive this sustained darkness.
They have become specialists in living for months
without sunlight.
[wind howling]
DAVID: Muskox,
remnants of the last ice age.
Having grazed all summer, they've built up fat reserves
that will enable them to survive the brutal cold of winter.
And this makes them
a prime target for other sub-zero specialists.
Arctic wolves.
The moon provides just enough light for them to see.
[ominous music]
DAVID: This alpha female leads the hunt.
Target in sight.
If her pack is to survive,
they need to make a large kill
at least once every three weeks.
[grunting]
[low growls]
The alpha female signals the start of the attack.
[suspenseful music]
They run at the muskox
and the herd panics.
The muskox close ranks.
The wolves look for weakness.
[low growl]
[roars louder]
Charging risks isolation from the crowd.
And that is just what the wolf pack wants.
[muskox roars continue]
[wolves whimper]
DAVID: The wolves can sense victory.
But the herd comes to the rescue.
And once again, they close ranks.
Most winter hunts end in failure for the wolves.
As the long polar nights drag on,
the hungry wolves turn
to their only other source of food.
Arctic hares.
[whimsical music]
They've gathered together in their hundreds, for safety.
Trying to catch one hare amongst hundreds
is harder than you might think.
Even if they do catch one, it's not much of a meal.
Sometimes,
you just have to admit defeat.
But life is about to get better for the wolves.
[tranquil music]
For the first time in six months,
the sun rises above the horizon.
Its appearance marks the beginning
of half a year of continuous light.
The sun's warmth will allow the muskox to give birth,
and that will provide easier hunting for the wolves.
[tranquil music]
It's early spring
and much of North America
is still locked in ice.
As our tilted planet orbits the Sun,
the Northern Hemisphere receives increasing sunlight,
and wakens an animal
with an almost supernatural ability.
[suspenseful music]
It is frozen solid, like a block of ice,
and has been all winter.
An ordinary looking frog,
but an extraordinary one.
A Wood Frog.
Its heart has stopped beating completely.
But as the sun's power increases,
almost miraculously, it begins to change.
Its frozen blood is melting
and begins to flow through its veins...
as his heart begins to beat again.
The Wood Frog is cryogenic.
In just 12 hours, it thaws
and comes back to life as if by magic.
This defrosting ability
means it's ready for the moment when, at last,
spring arrives.
All across the Northern Hemisphere,
the sun's warmth is bringing dramatic change.
[grand music]
[bird chirping]
As the sun rises higher
and spring takes hold,
the warming air reaches the ground
and the rocks beneath.
Here, thousands of animals begin to stir.
Garter Snakes,
one of Canada's most northerly reptiles.
[suspenseful music]
After six months of hibernation,
the males are the first to emerge.
They haven't eaten for months.
Even so, it's not food that is on their minds.
It's something else.
Females.
But they stand no chance of doing anything about that
until they've charged their batteries.
Snakes are cold-blooded and they need to absorb the sun's heat
before they're able to move quickly.
After a few hours, the males are raring to go.
Twenty thousand snakes.
The largest emergence of reptiles anywhere on Earth.
Now, a few females appear.
They're much bigger than the males
and warming will take them longer.
She releases a scent, a pheromone,
that attracts the males.
They outnumber her a hundred to one.
To speed her own return to activity,
she will absorb heat from them.
Intoxicated by her scent,
the males compete for her, wrapping themselves around her.
She now has hundreds of males on top of her,
making mating near impossible.
But she has a way of weeding out the men from the boys.
She'll make a daring ascent
of the nearby cliff.
She barges her way through the crowd to get to the rock face.
As she climbs, only the strongest, fittest males
can keep up with her.
[suspenseful music]
[music rising]
DAVID: She's made it to the top.
Only a few of her suitors have managed to rise to the occasion.
And she may reward them all.
This entire mating jamboree
only lasts for one short week in the year.
And when it's over,
they all move off into the forest.
There, they disperse to lead solitary lives
searching for food, until winter drives them back
to the shelter of the rocks below ground.
[birds chirping]
[animal cawing]
It's June,
halfway through the Earth's annual journey around the Sun,
and summer has arrived in the Northern Hemisphere.
Karrak Lake, in Canada,
north of the Arctic Circle.
The summer will be brief,
but there is sunlight for 24 hours every day.
So, the next few months are vital
for every living thing here.
And this Arctic fox knows it.
[squeals]
Winter has been hard for her,
and now with a new family to support,
she must make the most of the summer's abundance.
Her three-week-old pups
have just emerged from the den.
[squealing]
DAVID: Each of these little bundles of fur
needs nearly 300 calories of food every day.
A tall order for Mum.
But a solution for her problem is just arriving.
[honking]
Snow Geese.
They have flown over a thousand miles from the United States,
timing their arrival to coincide with the end of the snow.
[honking continues]
DAVID: More than half a million will spend the summer here,
nesting and feeding on the grass.
There's fierce competition between couples
for the safest nesting sites.
[honking]
The losers will have to nest on the outskirts of the colony,
the first part to be raided by the foxes.
[tranquil music]
[geese honking in the distance]
Mother is after eggs.
But getting them is not going to be easy.
[suspenseful music]
[honking]
DAVID: The geese will risk their lives to protect their eggs.
If they lose them,
they can't produce another clutch this season.
The fox wins.
[honking]
DAVID: She gives the first eggs to her young pups.
And then, heads back for more.
[geese honking, hissing]
DAVID: Some of the eggs, she stashes away.
They will be food to help her through the coming winter.
In just three weeks,
she will steal over 800 eggs from the geese.
But eating a big egg is not easy
if one is rather small.
It's a technique
the pups haven't quite yet cracked.
Mum shows how it's done.
[squeaks]
Goslings are now hatching all across the colony.
And they will need all the food they can get
to build up their fat before their journey south.
Now that the chicks have hatched,
they can all find safety on the water.
In these brief sunlit months,
there's time for the cubs to play.
But there is no playtime for mum.
But the Arctic is warming
and the timing of the seasons and the migration of the geese
is becoming unpredictable.
Although the sun stays above the horizon
continuously throughout the Arctic summer,
its rays are comparatively feeble.
Closer to the Equator, in our planet's deserts,
cloud cover is rare.
[eerie music]
DAVID: The sun here is not a friend,
but an enemy.
Africa.
The Sahara.
Few creatures can live here.
Get caught out in the open, at the wrong time of day,
and it's game over.
By ten in the morning,
the temperature on the surface of the sand
is pushing 60 degrees Celsius.
Even the toughest will soon have to take cover.
But one creature is waiting underground
for the sun to get even hotter.
Temperatures are now so high
that everything else has to shelter.
[rumbling, explosion]
DAVID: The desert now belongs
to the Earth's greatest solar specialist.
The Saharan Silver Ant.
At midday, when the sun is at its fiercest,
they emerge to look for creatures
killed by the scorching heat.
They're one of the fastest insects on Earth.
And they need to be with just five minutes to find food
before the heat kills them.
Getting lost would mean certain death.
So, every few seconds, they spin round,
taking a bearing from the sun.
When others are frying,
these ants have solar tech
to stop them from overheating.
Special glassy hairs and shining bodies
that reflect the sun's lethal rays.
It buys them precious time.
To get their prize back as quickly as possible
to their underground den
demands teamwork.
But shelter is a long way away.
Any technique will do.
The push and slide.
The spin.
Even dune surfing.
[suspenseful music]
DAVID: The nest is still 70 metres away.
Some are already collapsing in the heat.
Reinforcements are needed urgently.
Now, the heat
whips up violent gusts of hot desert air.
[wind roaring, rumbling]
For an ant, these are hurricanes.
[ground rumbling]
DAVID: They must get their prize underground as soon as possible,
and blown sand has blocked the entrance to their den.
Any longer out here and they will be toast.
One final effort.
The last of the team race home.
Shade at last.
Much of the land on our planet
could become as scorched and lifeless as this
if we allow our activities
to continue to change the atmosphere.
The Sahara alone has expanded
by an area twice the size of France
in just the last hundred years.
[wind hissing]
Part of a global desert invasion
that threatens a third of all land.
The sun can certainly be a lethal threat.
But it could also be our saviour.
The solar energy that strikes our planet in just an hour,
contains more power than that used by all of humanity
in an entire year.
By October,
as the Earth completes
its annual journey around the Sun,
day lengths in the Northern Hemisphere
are shortening once again.
[birds chirping, cawing]
DAVID: The sun's power is diminishing.
Trees are beginning to shut down their solar panels.
The green chlorophyll with which they collected the sun's energy
is broken down chemically and reabsorbed.
[tranquil music]
And the forests turn from emerald to gold.
It's autumn.
Once again, the living world away from the tropics
is transformed.
Plants stop growing
and many animals begin to prepare
for tough times ahead.
[animal honking]
The forests of Central China.
Home to the golden snub-nosed monkey.
[monkeys squeaking]
They will not survive the fast approaching winter,
unless they stock up on calorie-rich food.
Top of their autumn menu,
pine cones.
They grew during the summer sunlight and are rich in fats.
Few are now left
and time to gather them is running out.
Dominant males patrol the troop,
making sure they get the pick of the crop.
[squealing]
As the number of pine cones dwindles,
tensions between rival families increase.
[high-pitched squeals]
Mere threats between two males
may not be enough to settle disputes.
Conflict is in the air.
There's going to be a fight.
[suspenseful music]
[loud squeals]
Vital food is at stake,
so every pine cone is worth fighting for.
[squeals continue]
The victor and his family enjoy the spoils of war.
The losers get no more than a few dead leaves,
and will have fewer energy reserves for the coming winter.
The sun's power dims.
Temperatures drop.
Everything slows down.
Ahead lies months of crippling cold.
[squeaks softly]
[dramatic music]
DAVID: Most of the life on Earth away from the tropics
has managed to adapt to the changing seasons.
But there are some creatures
that have found a way to avoid the cold of winter altogether.
Snares Islands, New Zealand,
deep in the Southern Hemisphere.
[loud caws]
Here, sooty shearwaters
have been nesting throughout the long summer
and gorging themselves on fish.
As a result, they have piled on quite a few pounds.
But the sun is now fading
and the southern winter is approaching.
No time to hang around.
When you're a touch tubby,
launching into the air...
[birds cawing]
DAVID: ...is a leap of faith.
They won't see land again for four weeks.
Setting off across the Pacific,
they're starting on one of the longest journeys
made by any living thing.
Their aim,
to avoid the consequences of the Earth's tilt,
and follow the sun's warmth,
as it dwindles in the south and increases in the north.
For those who survive the 10,000 mile marathon,
there will be a great prize.
The reward for travelling from
one end of the planet to the other
is long summer days the year round.
This is their destination.
Alaska's Aleutian Islands.
While the south of our planet is slipping into autumn,
here, summer is just beginning.
[water flowing]
DAVID: Below the waves,
vast clouds of plankton are blooming
triggered by the sunlight.
These tiny marine organisms
are food for crustaceans.
Krill.
This is the sun-fuelled bounty
for which the shearwaters have crossed the planet.
[birds cawing]
DAVID: By cheating the tilt,
they're able to enjoy the riches of summer the year round.
But shearwaters are not the only ones to visit the warming seas.
[whales moaning]
Humpback whales.
[whale blows]
DAVID: They've been breeding in the tropics
and haven't fed for six months.
Up to 6,000 whales are now heading for these islands.
The only place where they can find food
in the quantities they need.
The shearwaters begin to dive into a huge shoal of krill.
[grand music]
DAVID: The humpbacks attack from below.
[strong blow]
Each year, a million shearwaters join the whales
in these dramatic feeding frenzies.
[shearwaters cawing]
[whales moaning]
DAVID: It's one of the greatest gatherings of life on Earth.
And it only happens
because some whales and some birds
have found a way to live in a summer that never ends.
[uplifting music]
