The Living Planet (1984–…): Season 1, Episode 1 - The Building of the Earth - full transcript
Our planet, the earth, is,
as far as we know, unique in the universe.
It contains life. Even in its most barren stretche
there are animals.
Around the equator,
where those two essentials for life,
sunshine and moisture, are most abundant,
great forests grow,
and here plants and animals
proliferate in such numbers
that we still have not even named
all the different species.
Here, animals and plants,
insects and birds, mammals and man
live together in intimate and complex communities,
each dependent on one another.
Two thirds of the surface of this unique planet
are covered by water,
and it was here indeed that life began.
From the oceans, it has spread
even to the summits of the highest mountains,
as animals and plants have responded
to the changing face of the earth.
This river, the Kali Gandaki,
has cut its way, in the most remarkable fashion,
through the highest range of mountains
in the world, the Himalaya.
To the east of me rises Annapurna,
over 23,000 feet high.
To the west, Dhaulagiri, even higher.
Their two summits are a mere 22 miles apart,
and I am four vertical miles below them.
And that makes this
the deepest valley in the world.
At this altitude, about 7,000 feet, it's quite war
and animal and plant life on the flanks
of the valley is both rich and abundant.
The blossoms on these trees
may well look familiar.
Flowers like them
grow in gardens all over the world.
But these are wild plants and this is
their original home. They're rhododendrons.
And here they are food for monkeys, grey langurs,
reminders that the hot plains of Southern Nepal
and the tropics
are not far away to the south.
But they aren'tjust monkey food.
They are the rhododendrons' advertisements,
attracting birds and insects
which will sip their nectar, gather their pollen,
and so bring about their fertilisation.
The ring-necked parakeet
also comes from the tropics.
Here, it's at the top of its range.
Any higher and the weather will be too cold for it
Beneath the rhododendrons
live several species
of those most splendid of Asia's birds,
The blood pheasant, for all its delicate beauty,
is a plainer member of the family.
The cock Tragopan
is surely the most magnificent.
Until, that is,
you see a cock lmpeyan pheasant,
with the coronet of a peacock
and the burnished, metallic iridescence
of a tropical butterfly.
The lmpeyan's hen,
like those of all pheasants, is comparatively dull
This deepest of all valleys in the world
enables you to walk within a few days
from the tropics, in its lower reaches,
to the equivalent of the poles
on the slopes high above,
and to see as you make the journey
how closely animals and plants are matched
to the changing circumstances.
As you walk higher, the rhododendron forest
gets thinner and hung with moss.
The air is moist
and it can be quite warm during the day.
And now, in summer, there are orchids here.
On the ground beneath,
flowers appear in close-packed bunches,
protecting one another from the night frosts.
The little Himalayan panda is certainly
very well protected against the cold.
Not only does it have warm, dense fur,
but, like many animals that spend time
in the snow, it has hair on the soles of its feet.
That keeps its feet warm on the snow
and stops it from sliding on ice.
Now, in the summer, it also helps
in getting a grip on wet, slippery branches.
It's primarily a vegetarian,
collecting buds and leaves and fruit,
but it also takes eggs from a bird's nest,
if it can find one.
On the ground,
and scarcely bigger than the panda,
one of the shyest animals
of the Himalayan forests, a musk deer.
In these tangled trees,
antlers would be a considerable handicap,
and the musk deer doesn't develop them.
A male fights instead
with the sharp tusks in his upperjaw.
They feed on moss, lichen and leaves,
and are so agile
and well-adapted to a mountain life
that they can climb steep cliffs
in search of food.
When a musk deer or any other animal
of any size dies, the vultures come.
These are griffons,
similar to those that circle the skies
above Indian villages
down in the hot foothills.
They are common in this forest
up to 7,000 or 8,000 feet.
So the lives of all these creatures are connected,
one with the other,
either directly or indirectly,
and all are ultimately dependent
upon the vegetation.
But both animals and plants are also
greatly affected by the physical environment.
I've climbed several thousand feet now
and things are beginning to change.
It's getting colder, and the rhododendrons
are giving way to fir trees,
and that will mean
a change in the animals that live here.
The yellow-throated martin
has a broad taste in food.
It takes fruit on occasion,
catches insects now and then,
but it relishes small rodents, like mice
and squirrels, and there are quite a lot here.
Even in winter, when the forests
are deep in snow, it will remain active.
But it's a great traveller,
and if it gets very cold,
it will descend to lower altitudes for a spell.
The Himalayan bear is capable
of living very high indeed.
Its thick fur protects it against severe cold,
but its range is not limited by temperature
so much as food supply.
In spite of its size,
it seldom tackles any animal bigger than a mouse,
and it lives for most of the time
on ants, grubs, nuts and leaves,
so it seldom goes any higher
than the forest can grow.
And now, getting on for 10,000 feet up,
the forest is beginning to thin.
In summer, there's not much rain here,
for most has fallen at lower altitudes.
In winter, it gets extremely cold.
Those conditions don't suit rhododendrons.
Here only conifers flourish in large numbers.
High though we are,
the Kali Gandaki is still a very broad river.
Remarkably, and mysteriously,
it doesn't rise from the flanks of these
giant mountains but cuts right through them.
The people of the foothills
have long since recognised
the value of this extraordinary corridor
that leads right through the Himalayas,
and all summer
trains of mules trudge up the valley,
taking barley and buckwheat
to trade with Tibetans for wool and salt.
All the way up the valley
are villages where the muleteers can rest,
but during the summer few do so.
Most trudge tirelessly upwards
for as long as there's daylight.
A lammergeier, the bearded vulture,
a mountain bird
that soars around the high valleys of Asia
and a few remote parts of Europe,
but nowhere higher than this.
And a sign that now we are getting really high:
Its dappled white plumage gives it camouflage
against the broken snow
that even now, in summer,
can fall at these altitudes.
They forage for seeds and rootlets
in the thin turf.
There are no trees now,
just a few small shrubs and dry, withered grass.
But that's enough for the tahr.
It is neither a sheep nor a goat,
but related equally to both.
It will eat almost anything that's green,
and is grateful to find it in this bleak land.
Another typically mountain creature:
The red-billed chough, a kind of crow.
They search the rocks for insects, grubs,
odd seeds. They will take most things.
Their cousins, yellow-billed choughs,
go as high as any bird in the world,
riding the rising wind currents
to the height of the snow peaks themselves.
Flowers at this altitude
can only come from small cushion plants,
huddled together against the cold.
Higher still, little can grow except lichens.
Now it's so cold that growth may only be possible
for a few days in the year.
And yet, in these bleak regions,
To help plough the fields,
they use the yak,
a domesticated creature
that once roamed wild on the plains of Tibet,
the only large mammal
that lives permanently as high as man.
The people, Bhotias and Sherpas,
grow not only barley but potatoes,
a crop that was first cultivated
by the Incas in the Andes
and was introduced here a century or so ago.
These highland people are well-adapted
to life at these altitudes.
Their blood contains a particularly high number
of red corpuscles
and so can carry more oxygen in it
than a lowlander's can.
Certainly, when it comes to walking
at these high altitudes,
they're very much better adapted than I am.
So, all the living creatures in these high valleys
are adapted to their environment,
both their biological environment
and their physical environment.
And yet, in terms of biological history,
those adaptations are very recent indeed.
These immense mountains, the eternal hills,
are in fact far from eternal.
They are younger
than the plains of India to the south
or the plateau of Tibet to the north.
They were raised to their present height
about 35 million years ago
from the bottom of the sea.
And what is the evidence
for that extraordinary statement?
It can be found all over the place, just up here.
These slopes are littered
with fragments like these.
This is obviously a shell
that's been turned to stone, a fossil.
Although there are no molluscs alive today
exactly like this one,
there are some which are sufficiently similar
for us to be sure that it lived in water.
And if we analyse the rock
in which it's embedded,
it's clear that that was mud
laid down at the bottom of a sea.
But I am as far as I can be from the sea.
I am in the middle of Asia, miles from
the sea, and over two vertical miles above it.
What forces could possibly have raised
the seabed to these heights?
We now know that those forces
are still in action,
that these mountains are still rising
and that land is still being created.
I'm in Iceland.
This fantastic fountain of fire
rising 200 feet or so into the air behind me
is molten rock.
Fine ash is falling all around,
there are gusts of choking, poisonous gas,
and it's so hot
that this is just about as close as I can get to i
The sheer weight
of these molten ingots of rock
prevents them being swept away
from the vent by the gale,
so there's little danger of them
suddenly coming our way.
Less dramatic than the fire fountain
but perhaps more sinister
is this tide of black slag that is slowly
creeping over the surface of the land.
In parts it's red-hot and molten
and flows like treacle,
but on the edges it's cooled enough
for me to handle it.
It's black, it's heavy and it's called basalt.
Basalt like this has been welling up
from deep in the earth's crust
since the beginning
of the history of our planet.
A flow may travel for as much as 25 miles.
Sometimes it moves no faster
than a man can walk,
but sometimes it races along
at an extraordinary speed,
40 miles an hour,
and nothing... nothing... can stop it.
Sometimes so much lava is produced
that it accumulates
in flows 100 feet or so thick.
Then the centre layers of it
cool exceptionally slowly and very evenly,
and this is the result.
Here, at the Giant's Causeway,
the top of the lava flow has been eroded away,
for the eruptions took place
50 million years ago.
The cooling contractions have produced
the effect you see in drying mud,
though here the cracks
extend to a greater depth
to produce six-sided columns
a foot and a half across.
In the Hebrides, there's another lava flow
that erupted at about the same time
and formed Fingal's Cave.
The layer of lava that slowed down
the cooling of the interior is still uneroded,
and beneath it the near-perfect
basalt columns rise almost 20 feet high.
Basalt that doesn't contain very much gas
wells out from below almost quietly.
But if the lava has been extruded
under great pressure,
it may be full of gas,
and then it behaves very differently.
Sometimes a flow sweeps down
over a forest, incinerating the trees in its path.
Most dramatic of all, the lava sometimes
wells up inside a crater and can't escape.
Then it forms that most fearsome
of nature's spectacles, a lava lake,
like this one in Nyiragongo in Africa.
This lava is over 1,000 degrees centigrade,
2,000 degrees Fahrenheit.
The bubbles of gas that burst from its surface
may be 50 feet across.
Sometimes, having got rid of much of its gas,
like beer losing its fizz,
it sinks back down the pipe and returns
to the lava chamber a mile or so below.
But lava lakes fed by pipes are not common.
Basalt more usually comes to the surface
in a rather different way.
These Icelandic volcanoes erupt
from huge cracks or fissures
which regularly open up in a line
which runs right across the width of the island.
But that line itself is only
the northern end of a huge line of weakness
that runs for thousands of miles
southwards from Iceland
right round the side of the globe.
Iceland lies between Norway and Greenland,
south of the Arctic Circle.
The crack, ridged over by lava,
is mostly underwater,
which is why its existence wasn't known
until the beginning of this century.
It runs between Europe and Africa
to the east and the Americas to the west.
In places, it rises above the sea
to form volcanic islands:
The Azores, the Cape Verdes, Ascension,
St Helena, Tristan da Cunha.
But below the surface
the lava is also continually erupting,
unseen by human eyes
until only a few years ago.
The clouds of gas come from the lava itself.
They're not steam. The pressure of the water
prevents that from being produced.
The heat is rapidly absorbed
by the vastness of the ocean itself
so that the lava cools and congeals
much more quickly than it would do in the air.
Eruptions like these, at great depths,
built the Atlantic ridge.
But the basalt forms not only the ridge itself
but the sea floor on either side.
By dating it chemically,
we know that the farther it is
from the centre of the ridge, the older it is.
Basalt is welling up
in a molten state at the ridge
and then, as it solidifies,
is moving away on either side.
We still don't fully understand
the forces that power the process,
but 50 to 30 miles below the earth's surface
it's so hot that the rocks are molten
and currents in them are welling up
beneath the ridge, causing eruptions,
and then flowing away on either side,
pulling the plates of the ocean floor with them.
It was this movement that dragged apart
Africa and South America
and created the Atlantic Ocean.
Similar things have happened in the Pacific.
The great plate
that forms the eastern part of the ocean floor
is moving towards the west coast of America.
But where it meets the continent,
it dives downwards,
perhaps pulled by the descending current
in the crust below,
producing a deep trench in the ocean floor.
As it goes down, it takes with it
sediments from the bottom of the ocean
and also some water.
These new ingredients melt
and interact with the rocks of the interior
to produce a mixture crucially different
from the lava that erupted at the ridge.
For one thing,
it contains much more dissolved gas and steam.
As it rises up on the edge of the continent,
it cools and solidifies, choking the vents.
The effect is like screwing down
the safety valve of a boiler.
Mount St Helens on the Pacific coast
of North America.
On May 18th 1980,
with an explosion 500 times as powerful
as the atomic blast at Hiroshima,
it blew away three-quarters
of a cubic mile of rock.
The forests around the mountain
were totally destroyed.
Trees 200 feet tall
lay scattered like matchsticks.
Geologists, weeks beforehand,
watching a huge bulge develop
on the side of the mountain,
had warned of the coming catastrophe.
Even so, over 30 people stayed and were killed.
On the northern side of the volcano,
there were not even trees to be seen.
A huge avalanche of rock,
blown out by the blast,
had slid for 15 miles down the side
of the mountain, burying everything.
Behind it, Mount St Helens lay wrecked.
Its summit was over 1,000 feet lower,
and at the back of a huge amphitheatre,
from which the rock had come,
another ominous bulge was developing,
swathed in jets of steam.
Almost a century earlier,
on the opposite side of the Pacific,
another catastrophic eruption had taken
place on the tiny island of Krakatau,
in the straits between Java to the east
and Sumatra to the west.
In 1883 it was an island
five miles long and three miles wide,
with three volcanic peaks on it,
the highest rising to almost 3,000 feet.
But those peaks were dormant.
There had been no sign of any volcanic activity
within living memory.
But in August of that year,
people on the coast of Java
began to hear explosions.
A great column of smoke
rose above Krakatau.
Pieces of lava the size of a house
were being thrown high into the air.
The explosions continued day after day.
The column of smoke rose up
until it was five miles or so up into the sky.
Ships that were sailing nearby
had their decks covered in ash and pumice,
and at night
electric flames played over the rigging.
Day after day this continued.
And as it was doing so,
it was emptying the lava chamber
deep in the crust beneath the sea,
and that was the cause
of the greatest catastrophe of all.
Because on the morning of August 27th,
Monday, at 10 o'clock,
the roof of that lava chamber collapsed.
Millions of tons of sea water
poured onto the red-hot lava.
So did millions of tons of rocks.
And this produced a titanic explosion.
The noise was almost certainly the loudest noise
that has ever echoed round the earth
in recorded history.
It was heard 2,000 miles away in Australia.
3,000 miles away on the small island
of Rodriguez in the South Atlantic,
the commander of the garrison heard it
and thought it was distant gunfire at sea.
The explosion also produced a tempest of wind,
which swept out entirely round the globe
seven and a half times
before it finally died away.
But most catastrophic of all,
the explosion produced a tidal wave.
It swept towards the coasts
and became a wall of water over 100 feet high.
It crashed into the harbours,
it picked up a naval gunboat with a crew of 28
and lifted it for over a mile inland
and dumped it on a hill.
And it overwhelmed village after village.
Over 33,000 people were killed.
The pall of ash brought darkness
over an area of 100 miles or so
for several days.
But when it cleared away,
the island of Krakatau was unrecognisable.
Three-quarters of the main island
The two nearby islets were buried
beneath massive deposits of ash.
And where the tallest peak had stood,
the sea was 900 feet deep.
But not for long. 44 years later
another island rose from the boiling sea.
They called it Anak Krakatau:
The child of Krakatau.
Compared with the explosions of its parent,
its eruptions are still trivial bubblings.
Now, after more than 50 years of fitful activity,
Krakatau's child has built itself a new cone.
It's still not very big, less than 1,000 feet high
Sporadically, it explodes.
But often it's easy enough to walk round its rim.
The fumes that boil up from its crater
are partly steam and partly sulphurous gas,
and the sulphur condenses on the rocks,
coating them yellow.
All volcanic eruptions spew out sulphur
in one form or another,
including those underwater.
Here it doesn't form yellow crystals,
but reacts with the sea water
to produce clouds of black sulphides.
These smokers, nearly two miles deep
on the floor of the Pacific,
are one of the most extraordinary
scientific discoveries of recent years.
The sulphides they produce
are food for microscopic bacteria.
They, in turn, are consumed by a group
of creatures unlike any seen before.
These are giant tube-worms 11 feet long.
They have neither mouth nor gut
but absorb bacteria through their thin skin.
And these are clams, two feet across.
They too consume the bacteria.
The heated water rising above the smokers
causes currents along the sea bottom
that sweep small particles to the vents
so there's a whole community
of creatures feeding on them.
Small, white, blind crabs.
Strange fish, hitherto unknown.
Until this bizarre colony was discovered,
we had believed that all creatures on earth
derived their energy
through plants from the sun.
Even the deep sea creatures
fed on fragments falling from the sunlit surface.
But here were animals
that owed nothing to the sun
and were sustained through bacteria
by the chemical energy of volcanoes.
But volcanoes don't remain active for ever.
Eventually, there is some shift
deep in the earth's crust
and the focus of the intense heat
moves away slightly
and the eruptions come to an end.
But if water percolates down
through the rocks to the magma chamber,
it's still so hot that the water
is superheated and forced up again,
like water in the spout of a boiling kettle.
On the way, it may dissolve minerals
from the rocks through which it passes,
and then, as it emerges as hot springs,
the minerals will be deposited in terraces,
like these in Rotorua, in New Zealand.
In some parts, the superheated steam
on its way to the surface
has dissolved the softer rocks
and brings them up as boiling mud.
Elsewhere, the boiling water
shoots spasmodically into huge fountains,
and the whole area is wreathed in steam.
Such a place is typical of land
where volcanic fires are on the wane.
The famous hot springs
of Yellowstone in the Rocky Mountains
are also heated
by a vast chamber of molten rock
some distance down beneath the surface.
The water welling up
from these crystal-clear, chemically rich pools
is so hot that no creature can live in them.
When they trickle over the brim, they cool,
and there rich colonies of bacteria
and mats of algae begin to grow.
They can flourish so thickly
that they break the surface
and divert the flow of water
so that in parts they're cool enough for brine fli
The flies come to feed on the algae.
And here, too, they mate.
They lay their eggs
directly in the warm mat of the algae.
Each has a long white thread to its case,
like a seed.
The eggs, however, are far from safe.
They're seized by mites
that clamber about over the algae.
Spiders, too, prowl around the grazing herds.
A slightly larger fly moves among the brine flies.
It too is a killer, devouring the grubs.
So the algal mats support
a closely-knit interdependent community,
all nourished by chemicals in the water
and energised by the volcanic heat.
But in the end it's destroyed by its own success.
Increasing numbers of grubs eat the algae
and weaken the mat.
Eventually it gives way, the channel clears
and scalding water gushes down,
killing a generation of grubs
and many hunters and parasites that live on them.
Now the process has to start all over again.
The hot volcanic springs
of the Rift Valley in Africa
also support their own crops of bacteria
and the small algae that feed on them.
But here the creatures
that come to harvest them are bigger.
Flamingoes, sometimes as many
as a million of them on this one lake.
These lesser flamingoes
feed entirely on single-celled algae
that proliferate in vast quantities
in these steaming soda-rich waters.
Flocks like these remove 150 tons
of these microscopic plants
from this lake every day.
Their bills have sieves inside them
which strain off the algae
as the water passes through them.
It's easy to see how creatures can benefit
from the chemical riches of volcanoes
dissolved in the waters of hot springs.
It's more difficult to imagine how any living thin
could derive nourishment
from a basalt lava flow.
Its surface in many places
is as smooth and as hard as glass,
and neither frost nor roots of plants
can initially make any impression on it.
Centuries may pass after an eruption
before there's any sign of the surface
of such a flow beginning even to weather.
This flow on the flanks of Mount Kilauea
in Hawaii is some 3,000 years old,
and yet still it shows the rippled, ropy surface
that formed when it was liquid.
But in the end the surface does erode
and plants do get root in the cracks.
They in turn can support all kinds of other life,
and so the lava flow is eventually colonised,
not only on its surface but in its depths.
For these basaltic lava flows
are often not as solid as they seem.
When the lava first flows
out of the vent like a river,
that on the outside of the flow
will cool quicker and solidify,
forming walls on either side of the flow.
The top too cools quicker,
and that causes a crust to form over the flow,
so that eventually
the lava is flowing down a long tunnel.
When that happens, the walls and ceiling
of the tunnel act as insulation,
keeping the heat in,
so that the lava flow remains liquid
and so continues for mile after mile.
When eventually the supply of lava stops,
that tunnel may drain,
leaving a long cavern like this one.
Out of the reach of rain and frost and even dust,
the surface of the lava looks as it did
when the last trickle was draining away
and the floor was so hot that anything
touching it would be turned to a cinder.
Molten lava had dripped from the ceiling,
it had swilled round the sides
and spurted out in little dribbles
from cracks in the newly congealed walls.
But living organisms have already moved in.
These roots belong to trees
that are growing on the surface of the lava flow.
They've found their way down
through the cracks, and here they dangle,
catching water as it percolates through the lava
and trickles down them.
Among the rootlets, there are animals
that live nowhere else in the world.
Normally, these creatures are in total darkness.
Nearly all of them,
like this cricket, have lost their pigment.
Many of them have also lost
their wings and their eyes.
In the blackness,
they find their way about by touch,
and, like many cave insects elsewhere,
have developed long legs and antennae.
Some, like this bug, are scavengers.
Others, like the centipede, hunt.
And the millipedes feed on the roots.
So, in these extraordinary lava caverns,
there is yet another community
of interdependent creatures
that have come into existence
since the volcanoes erupted.
The colonisation of volcanic ash
presents different problems.
The difficulty here is not the hardness of the roc
but quite the reverse,
its insubstantial dustiness.
Mount St Helens is still a wasteland.
It's now, as I speak,
some two and a quarter years
since the volcano erupted.
I'm some three miles from the crater,
and still the scene
is one of devastation and sterility.
It's notjust that
this unweathered ash is not very fertile,
but it's also so loose
that it's difficult for plants to get root.
But that possibility is always here.
Here, for example, in this crevice,
there are the seeds of the willow herb,
or, as they call it in these parts, fireweed,
that have been blown up from the valleys below.
I don't suppose these particular ones
will manage to get root here,
but in the end some plant will,
and in the end
the process of colonisation will begin.
Krakatau's child is just 57 years old.
Its flanks too are covered with ash,
and they're still buried regularly
with new layers from fresh eruptions,
yet the process of colonisation
is already under way.
Not only are there giant grasses,
like this wild sugar cane,
but trees: A casuarina.
If you want to see what a century
of colonisation by plants can bring about,
have a look at that fragment
of old Krakatau over there.
We know from first-hand reports
that 100 years ago
there was nothing here
but sterile ash many feet deep.
Within three years,
34 different species of plants had reappeared.
Ten years later there were twice that number,
and over 100 species
of birds and insects as well.
Some seeds must have floated here from Java,
some 20 miles away,
and they still continue to do so.
Other smaller ones
were probably carried here by birds,
either on their feet or in their stomachs.
But the ash is still here
beneath the lattice of roots of the jungle trees.
Somehow or other, rats and lizards and pythons
have all reached here.
There are now many hundreds
of different species of plants,
and the winds have assisted the passage
of many flying insects,
whose descendants now form
large and permanent populations,
pollinating the flowers,
feeding on their fruits,
collecting their rotting leaves
and indeed feeding on one another.
As yet there are no larger mammals,
no monkeys or squirrels,
no hunting cats or mongoose,
as there are in Java or Sumatra.
But as far as smaller creatures are concerned,
the number of species is increasing all the time.
And on the flanks of volcanoes
all round the world,
men clear fields and plant crops,
even though they know
they may be sitting on a time bomb.
These rice fields lie on the flanks
of one of Krakatau's near neighbours,
Gunung Agung in Bali.
Only 20 years ago it erupted,
killing 2,000 people
and leaving 150,000 homeless.
But the Balinese will not leave fields
that are so fertile
they can produce two or three rich harvests
of rice every year.
Gunung Agung, Krakatau
and the rest of the violently explosive volcanoes
that run in a chain along Sumatra
and Java and the Indonesian islands
stand on the line of the crack in the earth's crus
where the basalt plate
forming the floor of the Indian Ocean
meets the partly submerged edge
of the continent of Asia.
This junction already existed 35 million years ago
when India was an isolated island
in the middle of that ocean.
Since then, as the ocean floor
has continued to spread,
the continents have shifted
and India has moved towards Asia.
As the two continents approached,
the sediments between them crumpled
and eventually piled up over the junction,
so instead of the line between them
being marked by volcanoes,
it's buried deep beneath
an immense range of mountains, the Himalaya.
So these great peaks of sandstone
and limestone rising five miles into the sky
are not only the highest mountains in the world,
but among the youngest.
And the process has not yet come to an end.
India is still moving north
at the rate of two inches a year,
compacting itself ever more tightly
against the continental mass of Asia,
and the Himalaya are, infinitesimally,
getting higher and higher.
And that is how this ammonite,
this sea-living creature,
came to rest over two miles high in the Himalaya.
That too is the explanation
of how the Kali Gandaki river
managed to cut its way clean through
the highest range of mountains in the world.
It was flowing south
from the ancient plateau of Tibet
even before the great mass of India
collided with Asia.
As the sediments between the two land masses
buckled and rose over millions of years,
the river maintained its course,
cutting down through the rocks
as swiftly as they rose.
And so now it still flows south
to the plains of India,
and does so
through the deepest gorge in the world.
Mountain ranges have been created
in this way several times.
The Himalaya are just the most recent.
As they are worn down,
they create different environments
in which animals and plants can live.
So we have begun our portrait
of the planet up on the roof of the world,
and we will go from high altitudes to low,
from the poles to the equator.
And in the next programme we'll go even higher,
to the most inhospitable environment of all,
the world of snow and ice.