24 Hours on Earth Page #3

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

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