The Living Planet

Water: Hundreds of thousands of tons of it,

lying frozen on the world's mountains.

It covers not only the poles, but caps great peaks on the equator.

Water molecules, distilled from the sea by the sun's heat, condense in the sky.

As they fall through the air, they pack together into shapes

that echo their six-fold symmetry and form infinitely varied crystals of ice.

They settle on the high mountains and compact into snow and ice

that is, chemically, almost pure water,

much purer than the sea from which it came.

On Mount Rainier in the United States,

permanent snow begins at 7,000 feet.

You might think that this was one of the most inhospitable places on earth for life.

After all, no vegetation grows on these snowfields,

so there can be no animals that feed on it, like marmots or mice or rabbits,

and if there are no herbivores, there can't be any predators like hawks or weasels.

But in fact, there is a surprising amount of life here.

There is some life actually within this snowfield itself,

because this snow is not white, but red.

The colour comes from microscopic plants: Algae.

The redness is produced by light reflected from their cell walls,

and is almost invisible when, under the microscope, light shines through them.

Internally, they're green with chlorophyll.

With its aid, they convert carbon dioxide and water into sugars.

These, and the minerals dissolved in the melt water,

are all the algae need to grow and reproduce.

The winter snow will bury them feet deep,

but in spring, when the surface melts, they divide, develop tiny beating hairs

and swim up towards the sunshine.

As they age and the minerals are used up, they change colour,

forming huge smears of red in snowfields all over the world.

Eventually, the snow algae produce spores as fine as dust

and in that form they are blown from one snowfield to another.

But other, bigger animals, also brought up by the wind,

blow across the snows of Mount Rainier.

Ladybirds. Thousands of them.

Nobody knows why they come up in such numbers and assemble like this.

But in late summer they fly up from the valleys up to these high peaks

and here assemble in the rocks.

When the winter snows come, the ladybirds remain underneath the snow in the rocks,

and then in the spring, as now, the snow melts and the sun warms the ladybirds,

and they become active and fly off back to the valley to feed on aphids.

The ladybirds are only temporary residents of the Mount Rainier snowfields.

Other insects manage, almost unbelievably,

to live all their lives in this seemingly inhospitable snow.

The best time to find them is at night.

A whole community lives here,

feeding on pollen grains and the bodies of dead insects blown up on the wind.

Some, like this primitive relation of the cockroach, a grylloblattid,

have a body chemistry so well adjusted to low temperatures

that if you pick them up, your hand's warmth will kill them.

Permanent snow lies directly on bare rock,

but lower down, where it comes and goes, there can be a little vegetation to be grazed.

Mountain sheep. These on Mount McKinley are the kind known as Dall Sheep.

Little ground squirrels live up here too.

Unlike the sheep, which retreat to lower altitudes in winter,

the squirrels are permanent residents,

insulated in their burrows from the frosts by the cover of snow.

There are sheep like these in mountains all through North America, Asia and Europe.

All carry big horns, and the senior males, in autumn,

indulge in the most alarming courtship battles.

It's hard for plants to grow on steep, high slopes

The warming by day and freezing by night makes the gravelly soil slip downwards,

so it's difficult for plants to keep a hold.

With few plants, grazing animals are rare,

though there may be more than there appear to be at first sight.

These, in the Himalayas, are blue sheep,

so nimble and sure-footed they can reach almost any vegetation on the steep slopes.

But if these are rare, rarer still is the animal that preys on them, the snow leopard.

In summer it stays at between 12,000 and 15,000 feet,

hunting small rodents and birds as well as mountain sheep.

Snow leopards have been seen as high as 18,000 feet in summer.

But with winter's heavy snowfalls, it retreats to the valleys.

Game is now so scarce that there's barely enough to support more than one leopard,

so this animal hunts alone.

Its thick, dense fur is now paler.

It has a thick, woolly undercoat and cushions of hair under its paws

which prevent it from sinking in the snow.

The mountains of Africa, although so near the equator, are permanently snow-capped.

Kilimanjaro, 19,000 feet high, is a volcano.

Mount Kenya, also volcanic, is 2,000 feet lower but still has its own glaciers

Each has its own animals and plants

specially adapted to life at low temperatures.

Here, at about 13,000 feet, grow some most beautiful and dramatic plants:

Giant groundsels and giant lobelias.

At these altitudes, plants like these

have to face two totally conflicting problems every 24 hours.

Every night the temperature falls so low that they're in danger of freezing solid.

And every day the sun beats down so strongly in this very thin air

that it threatens to rob them of their moisture by evaporation.

But look how this lobelia deals with those problems.

This little pond of water in the leaf rosette freezes over every night,

and this shield of ice prevents the water beneath from freezing,

so that it acts as a liquid jacket, preventing the frost from reaching the heart of the plant.

But as the day wears on and it gets warmer, this water is in danger of evaporating

and the plant of losing its night-time insulation.

But it isn'tjust rainwater that's accumulated in this rosette.

It's been secreted by the plant itself and it's slightly slimy.

It contains pectin, a colloidal substance which greatly reduces evaporation.

But there's another kind of lobelia

which deals with these two problems in a quite different way.

This one grows very tall and has extremely long leaves,

each fringed with tiny hairs which act like an animal's fur,

trapping air between them, insulating the stem from chills.

They also prevent the wind from robbing the plants of moisture.

Each group of lobelias is owned by a pair of sunbirds

which collect the insects the plants attract.

They keep themselves warm with fluffed-up feathers.

And among the rocks are hyrax.

The reason these little creatures are so tame and I can get so close to them

is just because they're living so high up.

Up here, there are few creatures to prey on them.

An occasional leopard may come up and hunt them, but apart from that, nothing.

And so they can come out during the few brief hours of sunshine

and bask on the rocks without any fear,

just as they're doing now.

Hyrax also live down on the hot plains below,

but these, in response to the cold, have developed particularly long fur.

Despite their shape, they often climb trees to crop leaves.

But at these altitudes, there's only grass and lobelias,

and they share it with the little furry-eared rat.

Mount Kenya, like its neighbours Kilimanjaro and Ruwenzori,

is an isolated patch of snow and ice surrounded by the baking hot African plains.

But the great mountains of South America,

like Cotopaxi, 19,000 feet high, are very differen

These volcanoes, some active, some dormant, are not isolated peaks

but part of a continuous range that runs the length of the continent

and is surrounded by the high, cold plains of the altiplano,

so their flanks support a large and varied population of animals,

all adapted to life at high altitudes and low temperatures.

Here lives a wild South American camel, the vicuna.

Its coat is fine, silky and protected so well from the cold,

that it has, paradoxically, led to its near-extinction.

Men have recognised that vicuna wool has an unexcelled softness and warmth

and hunted the animal for it until it's close to extinction.

The people of the Andes have domesticated another wild camel, the guanaco,

to produce heavy-fleeced versions which produce excellent wool

and serve as beasts of burden.

Here, in Ecuador and Peru, near the equator, wild camels live at around 14,000 feet.

But as you travel south down the Andes, the snowline gets lower.

Half-way down, 2,000 miles south of Cotopaxi,

the line of permanent snow has dropped from 16,000 feet to 13,000 feet.

A thousand miles farther south still, the mountains are not so high

but are almost completely covered with snow, to within a few hundred feet of the sea.

So, on the southernmost tip of South America, in Patagonia and Tierra del Fuego,

the guanaco doesn't live at great altitudes, but almost at sea level.

Yet it needs its warm coatjust as much, for here, even in summer, it's very cold,

and during the winter the whole land is snowbound.

The reason it gets colder nearer the pole is not complicated.

The sun's rays strike the earth at the equator at right angles.

But as you travel round the earth,

the rays become more and more glancing.

So a given amount of heat falling on the equator

is distributed over a much greater area in the polar regions

and has to travel through more of the earth's atmosphere, which weakens it still further.

So down in Patagonia, the sun's rays are very much less intense and carry much less heat,

and the glaciers flow right down to the sea.

Farther south still, across the near-frozen seas off Cape Horn,

you reach chains of small volcanic islands

that run down towards the Antarctic continent itself:

Remote, little-known archipelagos

such as the South Sandwich and, here, the South Orkneys.

There are only two flowering plants that can manage to survive in this bleak, icy country.

One is a kind of thrift and the other is a small, stunted grass.

And apparently, no land-living animals of any kind.

But when the snows melt in summer, they reveal that the rocks and the boulders

are covered with over 100 different kinds of mosses and lichens,

some of them rounded green cushions, others like miniature trees.

The capacity of these simple plants to endure cold is phenomenal.

Some species can even survive being frozen solid for weeks on end.

Within this miniature tangled jungle lives a whole menagerie of tiny animals.

Primitive creatures little bigger than pinheads

manage to survive by slowly chewing away at the lichens and mosses during summer.

In winter they almost grind to a halt,

yet they survive unfrozen because their blood contains a kind of antifreeze

and remains liquid even when the temperature falls well below zero.

The majority are vegetarians, but there are also carnivorous mites among them

which clamber around the grazing herds,

picking off individuals as they fancy.

In this extreme cold, the processes of life are greatly slowed down,

not only those of growth, but those that lead to old age and death.

So such tiny creatures, which elsewhere might live for merely months,

survive for two or three years within the green mossy carpets.

The seas around these Antarctic islands are strewn with ice.

The pack ice that litters the surface is frozen sea water,

and in winter forms a solid cover to the sea.

The icebergs are different.

They're made of fresh water and have broken away from glaciers flowing into the sea.

This is the source of those bergs: The edge of a glacier.

Beyond it, the continent of Antarctica.

It's huge, bigger than the whole of Europe,

and, for the most part, it seems totally devoid of life.

But not all of Antarctica is snow-covered.

In parts of the interior there are valleys where almost no snow ever falls.

This is as desolate a part of the earth as exists.

The cold is extreme, it's drier even than the centre of the Sahara,

it's dark for half the year

and it's scoured by a never-ending howling wind.

And the wind is responsible for these carvings in the solid granite.

Crystals of salt form beneath tiny flakes on the surface,

and grow slowly, but so powerfully that particles are broken loose.