Earth

---

Of all the planets in our universe,

we know of only one

that can support life.

Just the right distance from the sun,

it has a perfect climate.

Earth rests at an angle

of exactly 23 and a half degrees

to the sun.

Without that crucial tilt,

everything as we know it

would be different.

For by it, the seasons are created,

the extremes of climate, hot and cold,

and landscapes of spectacular beauty.

We spend a year with our fellow creatures

as they struggle to raise their young

in a world that is ever-changing.

January.

It's the dead of winter in the high Arctic,

and there has been no sun

for over a month.

A father, alone in an icy wilderness.

He scavenges for food

in the permanent darkness.

But there is little to eat.

Every living thing is waiting.

At long last,

the sun makes its first appearance

over the horizon.

And something else makes

an appearance for the first time too.

A mother polar bear has been

underground in her den the whole winter.

It's fresh-powder conditions up here,

and, after being cooped up

under the snow for so long,

she can't help but enjoy the slopes.

But she's not alone.

They're 2 months old now,

and this is the very first time

they've seen the light of day.

It's breakfast time for the little ones.

Mom uses the promise of food

to coax them across the slopes.

But it's not the easiest place

to take your first steps.

Milk is the breakfast of choice here.

In fact, it's the only choice here.

It's all the cubs have known since birth.

Mom hasn't eaten for five months,

and she's lost half her body weight.

But still, she'll stay at home

on these slopes

and nurse the cubs

until they find their footing.

Which, as you can see,

might take a little while.

Every year at this time,

they need food desperately.

They'll have to get down

and join Dad on the ice

before it starts to melt

in the warming sunlight.

The sea ice is the only place

the bears can hunt for seals.

If they don't make it in time,

they'll lose their hunting platform,

and the family could starve.

So far, the ice is strong enough

to support their dad.

But he won't be much help

to Mom and the kids.

Instinct leads him to hunt for himself.

This race to reach the sea ice

is more urgent than ever.

Our planet is warming,

and the ice is melting earlier every year.

It's ten days later

and time for Mom to lead

the growing cubs down to the sea ice.

They've found their feet now,

but they seem to be taking them

in the wrong direction.

Unlike humans, polar-bear cubs

don't always listen to their moms.

Finally, everybody is pointed

in the right direction,

and the journey to the ice begins.

Just a few miles from the coast,

the ice is already breaking up.

Mom leads her cubs to start their life

at the edge

of this increasingly dangerous new world.

What they don't know

is the harsh reality of life in the Arctic.

It's unlikely that both cubs

will survive their first year.

A thousand miles south of the bears,

stunted conifers are still locked in ice.

They mark the tree line of our planet

and the start of the boreal forest.

This vast belt of trees

forms an almost unbroken circle

around the north of the globe.

These conifers

have needle-shaped leaves,

virtually inedible,

so the forest supports

very little animal life.

In this silent world,

footprints rarely mark the snow.

And those who do live here

are so hard to glimpse,

they're like spirits.

The lynx roams hundreds of miles

in search of prey.

It may never visit

the same patch of forest twice.

This creature

is the very essence of wilderness.

One-third of all the trees on Earth

are here,

as many trees as in all

the world's rain forests combined.

As the planet tilts toward the sun,

spring creeps up from the south,

and the boreal is unveiled

from a blanket of snow.

The forest produces so much oxygen

that it refreshes the atmosphere

of the entire planet.

April, and life starts returning

to the warming north.

Visitors flock to this haven

from all corners of our planet.

They've come to make the most

of the brief flush of spring food.

And to have their babies.

In our changing world,

every new generation is precious.

As the snow melts

and the days grow longer,

caribou,

more than three million of them,

start their migration across the tundra.

It's the longest overland migration

on Earth,

with some herds traveling 2,000 miles

in a single year.

And it's totally dependent

on vast open spaces.

The herd stays on the move,

so newborn calves have to be on their feet

and running from the day they are born.

But these vast herds don't travel alone.

Wolves shadow them all along the way,

and they're hungry.

At first, the attack seems casual

and random,

but this running at the herd

is a tactic to generate panic.

In the chaos,

a calf is separated from her mother.

The calf is young,

but it's capable of outrunning the wolf

as long as it keeps its footing.

At this point, the odds are even.

Either the caribou will make a mistake,

or after a mile or so,

the wolf will give up.

Spring in the Arctic,

and already the sun never sets.

And further south, the sunlight begins

to work her glorious magic.

These are the forests

that we know well,

the broad leaf woodlands

of Europe and North America.

More than any other,

these have been crowded out

by towns and farmlands.

Only fragments remain.

The summers are longer here,

and deciduous trees can flourish.

They're far more edible

than the conifers of the north,

so these forests bustle with life.

Spring also means flight school

for the mandarin ducks.

Mom is in her nest high in the treetops,

and it's her job to lead the way.

It's their first flight.

Actually, I wouldn't call it flying,

as much as falling with style.

Wait. There are two missing.

A perfect landing, sort of.

With one big adventure behind them,

what other challenges are in store

for our planet's newest recruits?

The rhythm of the seasons

is a glorious legacy that we've inherited,

thanks to that all-important tilt

of the Earth.

As the seasons parade past,

the same forest

will show her spectacular fall colors

and eventually give up her leaves

to the snows of winter.

There are parts of the world

that have no seasons.

Here in the tropics,

the sun shines for 12 hours a day

every day of the year.

This is what allows the jungle

to grow unchecked

and support so much life.

Rain forest now covers

just 3 percent of our planet's surface,

but contains more than half

of all the plants and animals on Earth.

The rain forests of New Guinea

are especially precious.

They are home to 42 different kinds

of birds of paradise,

each more exotic than the last.

This is a particularly rich forest,

so the six-plumed bird of paradise

has no problem finding food.

He can concentrate

on more important tasks,

like cleaning up for his big date tonight.

He's obsessed with housework.

Everything has to be spick and span

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