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THE LIVING PLANET
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A PORTRAIT OF THE EARTH
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Our planet, the earth, is, as far
as we know, unique in the universe.
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It contains life. Even in its most
barren stretches, there are animals.
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Around the equator, where
those two essentials for life,
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sunshine and moisture, are most
abundant, great forests grow,
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and here plants and animals
proliferate in such numbers
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that we still have not even
named all the different species.
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Here, animals and plants,
insects and birds, mammals and man
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live together in intimate
and complex communities,
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each dependent on one another.
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00:01:58,482 --> 00:02:02,643
Two thirds of the surface of this
unique planet are covered by water,
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00:02:02,707 --> 00:02:06,084
and it was here indeed
that life began.
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From the oceans, it has spread even to
the summits of the highest mountains,
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as animals and plants have responded
to the changing face of the earth.
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THE BUILDING OF THE EARTH
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This river, the Kali Gandaki, has cut
its way, in the most remarkable fashion,
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right through the highest range of
mountains in the world, the Himalaya.
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To the east of me rises Annapurna,
over 26,000 feet high.
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To the west, Dhaulagiri,
even higher.
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Their two summits are
a mere 22 miles apart,
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and I am four vertical
miles below them.
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00:03:09,712 --> 00:03:12,810
And that makes this the
deepest valley in the world.
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00:03:12,874 --> 00:03:17,155
At this altitude,
about 7,000 feet, it's quite warm,
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and animal and plant life on the flanks
of the valley is both rich and abundant.
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The blossoms on these trees
may well look familiar.
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Flowers like them grow in
gardens all over the world.
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But these are wild plants and this is
their original home. They're rhododendrons.
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And here they are food for monkeys,
grey langurs,
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reminders that the hot plains of
Southern Nepal and the tropics
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are not far away to the south.
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But they aren't just monkey food. They
are the rhododendrons' advertisements,
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attracting birds and insects which will
sip their nectar, gather their pollen,
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and so bring about
their fertilisation.
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The ring-necked parakeet
also comes from the tropics.
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00:04:23,279 --> 00:04:28,709
Here, it's at the top of its range. Any higher
and the weather will be too cold for it.
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00:04:29,781 --> 00:04:32,540
Beneath the rhododendrons
live several species
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of those most splendid of
Asia's birds, the pheasants.
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The blood pheasant, for all its delicate
beauty, is a plainer member of the family.
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The cock Tragopan is surely
the most magnificent.
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Until, that is,
you see a cock Impeyan pheasant,
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with the coronet of a
peacock and the burnished,
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metallic iridescence of
a tropical butterfly.
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The Impeyan's hen, like those of all
pheasants, is comparatively dull.
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This deepest of all valleys in the world
enables you to walk within a few days
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from the tropics,
in its lower reaches,
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to the equivalent of the poles
on the slopes high above,
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and to see as you make the journey
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how closely animals and plants are
matched to the changing circumstances.
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As you walk higher, the rhododendron forest
gets thinner and becomes hung with moss.
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The air is still moist and it
can be quite warm during the day.
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And now, in summer,
there are orchids here.
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On the ground beneath, flowers
appear in close-packed bunches,
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protecting one another
from the night frosts.
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The little Himalayan panda is certainly
very well protected against the cold.
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Not only does it have warm,
dense fur, but, like many animals
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that spend some of their time in the snow,
it has hair on the soles of its feet.
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That not only keeps its feet warm on the
snow but stops it from sliding around on ice.
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Now, in the summer, it also helps in
getting a grip on wet, slippery branches.
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00:06:53,758 --> 00:06:57,933
It's primarily a vegetarian,
collecting buds and leaves and fruit,
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but it also takes eggs from a
bird's nest, if it can find one.
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00:07:06,739 --> 00:07:09,817
On the ground,
and scarcely bigger than the panda,
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one of the shyest animals of the
Himalayan forests, a musk deer.
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In these tangled trees, antlers
would be a considerable handicap,
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and the musk deer
doesn't develop them.
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00:07:26,337 --> 00:07:30,321
A male fights instead with the
short sharp tusks in his upper jaw.
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They feed on moss,
lichen and leaves,
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and are so agile and
well-adapted to a mountain life
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that they can climb steep
cliffs in search of food.
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When a musk deer or any other animal
of any size dies, the vultures come.
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These are griffons, very similar
to those that circle the skies
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above Indian villages
down in the hot foothills.
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00:08:02,444 --> 00:08:06,339
They are common in this forest
up to 7,000 or 8,000 feet.
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So the lives of all these
creatures are connected,
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one with the other,
either directly or indirectly,
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and all are ultimately
dependent upon the vegetation.
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00:08:43,483 --> 00:08:45,766
But of course,
both animals and plants
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are also greatly affected
by the physical environment.
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I've climbed several thousand feet now
and things are beginning to change.
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00:08:54,456 --> 00:08:59,960
It's getting colder, and the
rhododendrons are giving way to fir trees,
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00:09:00,024 --> 00:09:04,187
and that will mean a change
in the animals that live here.
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00:09:07,875 --> 00:09:11,235
The yellow-throated martin has
a fairly broad taste in food.
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It takes fruit on occasion, catches
the few insects now and then,
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00:09:15,447 --> 00:09:19,742
but it relishes above all small
rodents, like mice and squirrels,
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00:09:19,806 --> 00:09:22,306
and there are quite a
lot their found here.
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00:09:22,489 --> 00:09:27,261
Even when winter comes, when the forests
are deep in snow, it will remain active.
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00:09:27,470 --> 00:09:30,775
But it's a great traveller, and if
the weather becomes very cold indeed,
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00:09:30,839 --> 00:09:34,074
it will descend to lower
altitudes for a spell.
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00:09:45,459 --> 00:09:49,630
The Himalayan bear is capable
of living very high indeed.
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00:09:49,694 --> 00:09:53,300
Its thick fur protects it
against really severe cold,
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00:09:53,364 --> 00:09:57,791
but its range is not limited by
temperature so much as by food supply.
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00:09:58,045 --> 00:10:02,578
In spite of its huge size, it seldom
tackles any animal bigger than a mouse,
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00:10:02,642 --> 00:10:07,693
and it lives for most of the time on
just ants, grubs, nuts and leaves,
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00:10:07,757 --> 00:10:11,638
so it seldom goes any higher
than the forest can grow.
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00:10:18,906 --> 00:10:24,516
And now, getting on for 10,000 feet
up, the forest is beginning to thin.
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00:10:24,705 --> 00:10:29,533
In summer, there's not much rain here,
for it most has fallen at lower altitudes.
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00:10:29,783 --> 00:10:32,711
In winter, it gets extremely cold.
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00:10:32,775 --> 00:10:38,860
Those conditions don't suit rhododendrons.
Here only conifers flourish in large numbers.
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High though we are, the Kali
Gandaki is still a very broad river.
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00:10:44,718 --> 00:10:47,225
Remarkably,
and indeed mysteriously,
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it doesn't rise from the flanks of these
giant mountains but cuts right through them.
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00:10:53,273 --> 00:10:56,231
The people of the foothills
have long since recognised
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the value of this extraordinary corridor
that leads right through the Himalayas,
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00:11:00,896 --> 00:11:04,608
and all summer trains of
mules trudge up the valley,
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00:11:04,672 --> 00:11:09,694
taking barley and buckwheat to trade
with Tibetans for wool and salt.
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00:11:12,820 --> 00:11:17,412
All the way up the valley there are villages
where the muleteers can stay and rest,
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00:11:17,723 --> 00:11:20,440
but during the summer few do so.
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00:11:20,827 --> 00:11:24,765
Most trudge tirelessly upwards
for as long as there's daylight.
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00:12:13,182 --> 00:12:16,499
A lammergeier, the bearded vulture,
a mountain bird
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that soars around the high valleys of Asia
and still in a few remote parts of Europe,
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00:12:22,160 --> 00:12:24,653
but nowhere higher than this.
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00:12:30,435 --> 00:12:34,793
And a sign that now we are
getting really high: Snow cock.
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00:12:34,857 --> 00:12:38,977
Its dappled white plumage gives it
good camouflage against the broken snow
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00:12:39,041 --> 00:12:42,970
that even now, in summer,
can fall at these altitudes.
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00:12:43,034 --> 00:12:46,621
They forage for seeds and
rootlets in the thin turf.
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00:12:58,029 --> 00:13:02,803
There are no trees now, just a few
small shrubs and dry, withered grass.
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00:13:02,867 --> 00:13:05,125
But that's enough for the tahr.
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00:13:05,189 --> 00:13:09,988
It is neither a true sheep nor a true
goat, but related equally to them both.
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00:13:10,052 --> 00:13:15,781
It will eat almost anything that's green, and
is grateful to find it in this bleak land.
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00:13:16,446 --> 00:13:21,067
Another typically mountain creature:
The red-billed chough, a kind of crow.
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00:13:21,131 --> 00:13:26,939
They search the rocks for insects, grubs,
odd seeds. They will take most things.
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00:13:35,256 --> 00:13:40,044
Their cousins, yellow-billed choughs,
go as high as any bird in the world,
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00:13:40,108 --> 00:13:45,453
riding the rising wind currents to the
height of the snow peaks themselves.
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00:14:10,509 --> 00:14:15,225
Flowers at this altitude can only
come from small cushion plants,
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00:14:15,289 --> 00:14:17,815
huddled together against the cold.
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00:14:18,773 --> 00:14:22,005
Higher still,
little can grow except lichens.
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00:14:22,069 --> 00:14:26,967
Now it's so cold that growth may only
be possible for a few days in the year.
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00:14:29,664 --> 00:14:34,072
And yet, in these bleak regions,
people live.
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00:14:34,331 --> 00:14:37,180
To help plough the fields,
they use the yak,
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00:14:37,244 --> 00:14:41,403
a domesticated creature that once
roamed wild on the plains of Tibet,
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00:14:41,467 --> 00:14:46,092
the only large mammal that lives
permanently as high as man.
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00:14:48,770 --> 00:14:53,781
The people, Bhotias and Sherpas,
grow not only barley but potatoes,
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00:14:53,845 --> 00:14:57,341
a crop that was first cultivated
by the Incas in the Andes
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00:14:57,405 --> 00:15:01,247
and was introduced here
a century or so ago.
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00:15:02,039 --> 00:15:06,350
These highland people are well-adapted
to life at these altitudes.
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00:15:06,751 --> 00:15:11,115
Their blood contains a particularly
high number of red corpuscles
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00:15:11,494 --> 00:15:16,043
and so can carry more oxygen
in it than a lowlander's can.
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00:15:17,019 --> 00:15:21,803
Certainly, when it comes to
walking at these high altitudes,
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00:15:22,344 --> 00:15:25,816
they're very much better
adapted than I am.
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00:15:26,619 --> 00:15:32,096
So, all the living creatures
in these high valleys
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00:15:32,347 --> 00:15:36,605
are adapted to their environment,
both their biological environment
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00:15:36,669 --> 00:15:41,946
and their physical environment. And
yet, in terms of biological history,
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those adaptations are
very recent indeed.
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00:15:46,782 --> 00:15:51,114
These immense mountains,
the eternal hills,
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00:15:51,178 --> 00:15:54,350
are in fact far from eternal.
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00:15:55,166 --> 00:15:59,956
They are younger than the
plains of India to the south
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00:16:00,165 --> 00:16:02,876
or the plateau of
Tibet to the north.
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00:16:02,975 --> 00:16:09,587
They were raised to their present
height about 65 million years ago
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00:16:09,651 --> 00:16:11,852
from the bottom of the sea.
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00:16:11,947 --> 00:16:15,780
And what is the evidence for
that extraordinary statement?
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00:16:15,942 --> 00:16:20,252
It can be found all over the place,
just up here.
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These slopes are littered
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00:16:33,887 --> 00:16:39,023
with fragments like these.
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00:16:40,365 --> 00:16:45,444
This is obviously a shell that's
been turned to stone, a fossil.
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00:16:45,728 --> 00:16:50,690
Although there are no molluscs
alive today exactly like this one,
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00:16:50,754 --> 00:16:56,427
there are some which are sufficiently similar
for us to be sure that it lived in water.
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00:16:56,558 --> 00:17:00,684
And if we analyse the rock
in which it's embedded,
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00:17:00,822 --> 00:17:06,226
it's clear that that was mud
laid down at the bottom of a sea.
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00:17:06,901 --> 00:17:10,721
But I am about as far as possible
is it's to be from the sea.
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00:17:10,785 --> 00:17:14,741
Not only am I in the middle of Asia,
hundreds of miles from the sea,
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00:17:14,963 --> 00:17:18,663
but I am over two vertical
miles above it's level.
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00:17:18,727 --> 00:17:23,631
What forces could possibly have
raised the seabed to these heights?
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00:17:24,037 --> 00:17:27,462
We now know that those
forces are still in action,
164
00:17:27,526 --> 00:17:34,415
that these mountains are still rising
and that land is still being created.
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00:17:58,435 --> 00:18:02,899
I'm in Iceland.
This fantastic fountain of fire
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00:18:02,963 --> 00:18:08,307
rising 200 feet or so into the
air behind me is molten rock.
167
00:18:09,079 --> 00:18:15,159
Fine ash is falling all around, there
are gusts of choking, poisonous gas,
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00:18:15,223 --> 00:18:20,635
and it's so hot that this is just
about as close as I can get to it.
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00:18:35,402 --> 00:18:39,090
The sheer weight of these
molten ingots of rock
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00:18:39,154 --> 00:18:43,097
prevents them being swept away
from the vent by the gale,
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00:18:43,161 --> 00:18:46,632
so there's little danger of
them suddenly coming our way.
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00:18:51,832 --> 00:18:56,192
Less dramatic than the fire
fountain but perhaps more sinister
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00:18:56,256 --> 00:19:02,646
is this tide of black slag that is slowly
creeping over the surface of the land.
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00:19:02,886 --> 00:19:07,197
In parts it's red-hot and
molten and flows like treacle,
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00:19:07,353 --> 00:19:12,289
but on the edges it's cooled enough
for me to be able to handle it.
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00:19:12,561 --> 00:19:17,012
It's black,
it's heavy and it's called basalt.
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00:19:17,227 --> 00:19:22,327
Basalt like this has been welling
up from deep in the earth's crust
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00:19:22,391 --> 00:19:25,816
ever since the beginning of
the history of our planet.
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00:19:35,959 --> 00:19:39,786
A flow may travel for
as much as 25 miles.
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00:19:39,850 --> 00:19:43,167
Sometimes it moves no
faster than a man can walk,
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00:19:43,231 --> 00:19:47,154
but sometimes it races along
at an extraordinary speed,
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00:19:47,218 --> 00:19:51,271
40 miles an hour, and nothing...
nothing... can stop it.
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00:20:03,890 --> 00:20:06,496
Sometimes so much lava is produced
184
00:20:06,560 --> 00:20:10,382
that it accumulates in
flows 100 feet or so thick.
185
00:20:10,533 --> 00:20:15,075
Then the centre layers of it cool
exceptionally slowly and very evenly,
186
00:20:15,603 --> 00:20:17,937
and this is the result.
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00:20:19,648 --> 00:20:24,622
Here, at the Giant's Causeway island, the
top of the lava flow has been eroded away,
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00:20:24,686 --> 00:20:28,100
for the eruptions took
place 50 million years ago.
189
00:20:28,327 --> 00:20:32,748
The cooling contractions have produced the
effect you can sometime see in drying mud,
190
00:20:32,835 --> 00:20:35,658
though here the cracks extend
to a much greater depth
191
00:20:35,722 --> 00:20:39,994
to produce six-sided columns
about a foot and a half across.
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00:20:42,886 --> 00:20:46,214
Over the sea, in the Hebrides,
there's another lava flow
193
00:20:46,278 --> 00:20:50,454
that erupted at about the same
time and formed Fingal's Cave.
194
00:20:55,790 --> 00:21:01,415
The blanceting layer of lava that slowed down
the cooling of the interior is still uneroded,
195
00:21:01,479 --> 00:21:06,768
and beneath it the near-perfect basalt
columns rise almost 20 feet high.
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00:21:30,749 --> 00:21:36,378
Basalt that doesn't contain very much
gas wells out from below almost quietly.
197
00:22:07,941 --> 00:22:10,963
But if the lava has been
extruded under great pressure,
198
00:22:11,027 --> 00:22:15,503
it may be full of gas, and then
it behaves very differently.
199
00:22:23,711 --> 00:22:29,609
Sometimes a flow sweeps down over a
forest, incinerating the trees in its path.
200
00:22:51,163 --> 00:22:57,663
Most dramatic of all, the lava sometimes wells
up inside the deep crater and can't escape.
201
00:22:57,727 --> 00:23:02,541
Then it forms that most fearsome of
nature's spectacles, a lava lake,
202
00:23:02,605 --> 00:23:05,520
like this one in
Nyiragongo in Africa.
203
00:23:05,802 --> 00:23:12,053
This lava is over 1,000 degrees
centigrade, 2,000 degrees Fahrenheit.
204
00:23:12,180 --> 00:23:16,830
The bubbles of gas that burst from
its surface may be 50 feet across.
205
00:23:17,204 --> 00:23:21,851
Sometimes, having got rid of much of
its gas, like beer losing its fizz,
206
00:23:21,915 --> 00:23:25,405
it sinks back down the
vast pipe up which it roses
207
00:23:25,469 --> 00:23:29,690
and returns to the lava
chamber a mile or so below.
208
00:23:31,754 --> 00:23:35,053
But lava lakes fed by
pipes are not common.
209
00:23:35,183 --> 00:23:40,757
Basalt more usually comes to the surface
of the Earth in a rather different way.
210
00:23:51,794 --> 00:23:57,958
These Icelandic volcanoes erupt
from huge cracks or fissures
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00:23:58,022 --> 00:24:03,837
which regularly open up in a line which
runs right across the width of the island.
212
00:24:04,019 --> 00:24:09,740
But that line itself is only the
northern end of a huge line of weakness
213
00:24:09,804 --> 00:24:14,023
that runs for thousands of
miles southwards from Iceland
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00:24:14,087 --> 00:24:16,480
right round the side of the globe.
215
00:24:18,830 --> 00:24:22,984
Iceland lies between Norway and
Greenland, south of the Arctic Circle.
216
00:24:23,048 --> 00:24:27,029
The crack, ridged over by lava,
is mostly underwater,
217
00:24:27,093 --> 00:24:31,365
which is why its existence wasn't known
until the beginning of this century.
218
00:24:31,625 --> 00:24:35,285
From Iceland it runs midway between
Europe and Africa to the east
219
00:24:35,349 --> 00:24:39,354
and the Americas to the west. In
places, it rises above the sea
220
00:24:39,418 --> 00:24:43,497
to form volcanic islands:
The Azores, the Cape Verdes,
221
00:24:43,561 --> 00:24:47,181
Ascension, St Helena,
Tristan da Cunha.
222
00:24:47,272 --> 00:24:51,336
But below the surface the lava
is also continually erupting,
223
00:24:51,400 --> 00:24:55,168
unseen by human eyes until
only a few years ago.
224
00:25:27,166 --> 00:25:30,090
The clouds of gas come
from the lava itself.
225
00:25:30,154 --> 00:25:35,405
They're not steam. The pressure of the
water prevents that from being produced.
226
00:25:35,588 --> 00:25:39,436
The heat is rapidly absorbed by
the vastness of the ocean itself
227
00:25:39,500 --> 00:25:44,379
so that the lava cools and congeals much
more quickly than it would do in the air.
228
00:25:53,035 --> 00:25:57,535
Eruptions like these, at great
depths, built the Atlantic ridge.
229
00:25:57,599 --> 00:26:03,747
But the basalt forms not only the ridge
itself but the sea floor on either side.
230
00:26:04,153 --> 00:26:07,786
By dating it chemically,
we know that the farther way it is
231
00:26:07,850 --> 00:26:10,863
from the centre of the ridge,
the older it is.
232
00:26:11,127 --> 00:26:15,351
This means that basalt is welling
up in a molten state at the ridge
233
00:26:15,415 --> 00:26:20,076
and then, as it solidifies,
is moving away on either side.
234
00:26:20,508 --> 00:26:24,349
We still don't fully understand
the forces that power the process,
235
00:26:24,413 --> 00:26:28,491
but it seems that 50 to 60
miles below the earth's surface
236
00:26:28,555 --> 00:26:31,575
it's so hot that
the rocks are molten
237
00:26:31,639 --> 00:26:36,382
and currents in them are welling up
beneath the ridge, causing eruptions,
238
00:26:36,446 --> 00:26:39,143
and then flowing
away on either side,
239
00:26:39,207 --> 00:26:42,360
pulling the great plates of
the ocean floor with them.
240
00:26:42,543 --> 00:26:46,695
It was this movement that dragged
apart Africa and South America
241
00:26:46,759 --> 00:26:49,490
and created the Atlantic Ocean.
242
00:26:53,346 --> 00:26:55,877
Similar things have
happened in the Pacific.
243
00:26:55,988 --> 00:26:59,740
The great plate that forms the
eastern part of the ocean floor
244
00:26:59,804 --> 00:27:02,930
is moving towards the
west coast of America.
245
00:27:03,133 --> 00:27:06,888
But where it meets the continent,
it dives downwards,
246
00:27:06,952 --> 00:27:10,300
perhaps pulled by the descending
current in the crust below,
247
00:27:10,364 --> 00:27:13,714
producing a deep trench
in the ocean floor.
248
00:27:15,478 --> 00:27:18,757
As it goes down, it takes
with it some of the sediments
249
00:27:18,821 --> 00:27:22,913
that accumulated of the bottom
of the ocean and also some water.
250
00:27:23,652 --> 00:27:27,179
These new ingredients melt with
the basalt as they get deeper
251
00:27:27,243 --> 00:27:30,808
and interact with the rocks of
the interior to produce a mixture
252
00:27:30,872 --> 00:27:35,318
that is crucially different from the
lava that erupted at the ocean ridge.
253
00:27:35,663 --> 00:27:40,463
For one thing, it contains much
more dissolved gas and steam.
254
00:27:42,219 --> 00:27:45,200
As it rises up in the cracks
on the edge of the continent,
255
00:27:45,264 --> 00:27:48,867
it cools and solidifies,
choking the vents.
256
00:27:49,703 --> 00:27:53,826
The effect is like screwing down
the safety valve of a boiler.
257
00:28:11,938 --> 00:28:15,218
Mount St Helens on the Pacific
coast of North America.
258
00:28:15,502 --> 00:28:17,793
On May 18th 1980,
259
00:28:17,857 --> 00:28:22,948
with an explosion 500 times as powerful
as the atomic blast at Hiroshima,
260
00:28:23,041 --> 00:28:26,975
it blew away three-quarters
of a cubic mile of rock.
261
00:28:28,789 --> 00:28:32,520
The forests around the mountain
were totally destroyed.
262
00:28:32,584 --> 00:28:36,998
Trees 200 feet tall lay
scattered like matchsticks.
263
00:28:38,216 --> 00:28:40,629
Geologists, weeks beforehand,
264
00:28:40,693 --> 00:28:44,143
watching a huge bulge develop
on the side of the mountain,
265
00:28:44,207 --> 00:28:46,879
had warned of the
coming catastrophe.
266
00:28:47,196 --> 00:28:51,796
Even so, over 60 people
stayed and were killed.
267
00:29:03,147 --> 00:29:07,968
On the northern side of the volcano,
there were not even trees to be seen.
268
00:29:08,054 --> 00:29:11,990
A huge avalanche of rock,
blown out by the blast,
269
00:29:12,054 --> 00:29:17,581
had slid for 15 miles down the side
of the mountain, burying everything.
270
00:29:21,367 --> 00:29:24,683
Behind it,
Mount St Helens lay wrecked.
271
00:29:24,747 --> 00:29:27,339
Its summit was over
1,000 feet lower,
272
00:29:27,403 --> 00:29:32,033
and at the back of a huge amphitheatre,
a mile wide from which the rock had come,
273
00:29:32,152 --> 00:29:37,339
another ominous bulge was
developing, swathed in jets of steam.
274
00:29:52,941 --> 00:29:56,935
Almost a century earlier, on the
opposite side of the Pacific,
275
00:29:56,999 --> 00:30:02,541
another catastrophic eruption had taken
place on the tiny island of Krakatau,
276
00:30:02,605 --> 00:30:07,823
in the straits between Java to
the east and Sumatra to the west.
277
00:30:08,263 --> 00:30:12,949
In 1883 it was an island five
miles long and three miles wide,
278
00:30:13,013 --> 00:30:18,445
with three volcanic peaks on it, the
highest of which rose to almost 3,000 feet.
279
00:30:18,871 --> 00:30:23,548
But those peaks were dormant. There had been
no sign of any volcanic activity on Krakatau
280
00:30:23,612 --> 00:30:28,245
within living memory.
But then, in August of that year,
281
00:30:28,309 --> 00:30:32,186
people on the coast of Java began
to hear series of explosions.
282
00:30:32,250 --> 00:30:35,865
A great column of smoke
rose above Krakatau.
283
00:30:36,814 --> 00:30:41,913
Pieces of lava the size of a house
were being thrown high into the air.
284
00:30:42,019 --> 00:30:45,488
The explosions
continued day after day.
285
00:30:45,552 --> 00:30:52,064
The column of smoke rose up until it
was five miles or so up into the sky.
286
00:30:52,444 --> 00:30:57,573
Ships that were sailing nearby had
their decks covered in ash and pumice,
287
00:30:57,637 --> 00:31:01,824
and at night electric flames
played over the rigging.
288
00:31:02,033 --> 00:31:05,503
Day after day this continued.
And as it was doing so,
289
00:31:05,567 --> 00:31:10,784
it was emptying the lava chamber
deep in the crust beneath the sea,
290
00:31:10,848 --> 00:31:14,787
and that was the cause of the
greatest catastrophe of all.
291
00:31:14,936 --> 00:31:20,700
Because on the morning of August
27th, Monday, at 10 o'clock,
292
00:31:21,063 --> 00:31:24,783
the roof of that lava
chamber collapsed.
293
00:31:25,183 --> 00:31:28,545
Millions of tons of sea water
poured onto the red-hot lava.
294
00:31:28,609 --> 00:31:31,909
So did millions of tons of rocks.
295
00:31:31,973 --> 00:31:35,639
And this produced a
titanic explosion.
296
00:31:36,416 --> 00:31:39,371
The noise was almost
certainly the loudest noise
297
00:31:39,435 --> 00:31:43,595
that has ever echoed round
the earth in recorded history.
298
00:31:43,943 --> 00:31:47,640
It was heard 2,000
miles away in Australia.
299
00:31:48,185 --> 00:31:53,877
3,000 miles away on the small island
of Rodriguez in the South Atlantic,
300
00:31:53,941 --> 00:32:00,485
the commander of the garrison heard it
and thought it was distant gunfire at sea.
301
00:32:01,190 --> 00:32:04,840
The explosion also
produced a tempest of wind,
302
00:32:04,904 --> 00:32:10,003
which swept out entirely round
the globe seven and a half times
303
00:32:10,067 --> 00:32:12,279
before it finally died away.
304
00:32:13,218 --> 00:32:18,243
But most catastrophic of all, the
explosion produced a tidal wave.
305
00:32:18,598 --> 00:32:21,510
It swept towards the
coasts and as it approached
306
00:32:21,574 --> 00:32:25,329
it became a wall of
water over 100 feet high.
307
00:32:25,741 --> 00:32:28,369
It crashed into the
harbours of little villages,
308
00:32:28,433 --> 00:32:31,789
it picked up a naval
gunboat with a crew of 28
309
00:32:31,853 --> 00:32:37,534
and lifted it bodily for over a mile
inland and dumped it on the top of a hill.
310
00:32:37,716 --> 00:32:41,408
And it overwhelmed
village after village.
311
00:32:41,472 --> 00:32:46,290
Over 36,000 people were killed.
312
00:32:47,566 --> 00:32:51,145
The pall of ash brought darkness
313
00:32:51,209 --> 00:32:55,307
over an area of 100 miles
or so for several days.
314
00:32:55,752 --> 00:33:01,769
But when it cleared away, they found that
the island of Krakatau was unrecognisable.
315
00:33:02,907 --> 00:33:05,872
Three-quarters of the main
island had disappeared.
316
00:33:05,945 --> 00:33:10,139
The two nearby islets were buried
beneath massive deposits of ash.
317
00:33:10,203 --> 00:33:15,031
And where the tallest peak had
stood, the sea was 900 feet deep.
318
00:33:15,143 --> 00:33:21,606
But not for long. 44 years later another
island rose from the boiling sea.
319
00:33:31,536 --> 00:33:35,544
They called it Anak Krakatau:
The child of Krakatau.
320
00:33:35,657 --> 00:33:38,202
Compared with the
explosions of its parent,
321
00:33:38,266 --> 00:33:41,687
its eruptions are still
trivial bubblings.
322
00:34:08,430 --> 00:34:12,135
Now, after more than 50
years of fitful activity,
323
00:34:12,199 --> 00:34:16,099
Krakatau's child has
built itself a new cone.
324
00:34:16,163 --> 00:34:19,743
It's still not very big,
less than 1,000 feet high.
325
00:34:20,098 --> 00:34:26,099
Sporadically, it explodes. But often
it's easy enough to walk round its rim.
326
00:34:36,196 --> 00:34:42,259
The fumes that boil up from its crater are
partly steam and partly sulphurous gas,
327
00:34:42,327 --> 00:34:46,771
and the sulphur condenses on
the rocks, coating them yellow.
328
00:34:49,001 --> 00:34:53,042
All volcanic eruptions spew out
sulphur in one form or another,
329
00:34:53,106 --> 00:34:55,514
including those underwater.
330
00:34:57,631 --> 00:35:00,151
Here it doesn't form
yellow crystals,
331
00:35:00,215 --> 00:35:05,198
but reacts with the sea water to
produce clouds of black sulphides.
332
00:35:08,875 --> 00:35:13,094
These smokers, nearly two miles
deep on the floor of the Pacific,
333
00:35:13,158 --> 00:35:17,653
are one of the most extraordinary
scientific discoveries of recent years.
334
00:35:17,875 --> 00:35:22,300
The sulphides they produce are
food for microscopic bacteria.
335
00:35:22,750 --> 00:35:27,521
They, in turn, are consumed by a
group of creatures, quite unlike any
336
00:35:27,585 --> 00:35:30,036
that have been seen before.
337
00:35:31,650 --> 00:35:34,855
These are giant
tube-worms 11 feet long.
338
00:35:34,919 --> 00:35:40,349
They have neither mouth nor gut but
absorb bacteria through their thin skin.
339
00:35:42,356 --> 00:35:47,543
And these are clams, two feet across.
They too consume the bacteria.
340
00:35:47,847 --> 00:35:50,935
The heated water rising
above the smokers
341
00:35:50,999 --> 00:35:55,971
causes currents along the sea bottom that
sweep small particles towards to the vents
342
00:35:56,035 --> 00:35:59,423
so there's a whole community
of creatures feeding on them.
343
00:35:59,487 --> 00:36:05,269
Small, white, blind crabs.
Strange fish, hitherto unknown.
344
00:36:07,386 --> 00:36:10,092
Until this bizarre
colony was discovered,
345
00:36:10,156 --> 00:36:12,639
we had believed that
all creatures on earth
346
00:36:12,703 --> 00:36:16,021
derived their energy
through plants from the sun.
347
00:36:16,244 --> 00:36:22,159
Even the deep sea creatures we knew of fed
on fragments falling from the sunlit surface.
348
00:36:22,223 --> 00:36:26,343
But here were animals that
owed nothing to the sun
349
00:36:26,407 --> 00:36:32,351
and were sustained through bacteria
by the chemical energy of volcanoes.
350
00:36:39,258 --> 00:36:43,378
But volcanoes don't
remain active for ever.
351
00:36:43,464 --> 00:36:47,336
Eventually, there is some
shift deep in the earth's crust
352
00:36:47,400 --> 00:36:51,254
and the focus of the intense
heat moves away slightly
353
00:36:51,318 --> 00:36:53,912
and the eruptions come to an end.
354
00:36:54,172 --> 00:36:58,313
But if water should percolate down
from the surface through the rocks
355
00:36:58,377 --> 00:37:01,403
and approach to the magma chamber,
it's still so hot
356
00:37:01,467 --> 00:37:05,494
that the water is superheated
and forced up again,
357
00:37:05,558 --> 00:37:08,480
like water in the spout
of a boiling kettle.
358
00:37:09,002 --> 00:37:13,884
On the way, it may well dissolve minerals
from the rocks through which it passes,
359
00:37:13,948 --> 00:37:20,362
and then, as it emerges as hot springs,
the minerals will be deposited in terraces,
360
00:37:20,426 --> 00:37:23,502
like these in Rotorua,
in New Zealand.
361
00:37:32,497 --> 00:37:36,107
In some parts, the superheated
steam on its way to the surface
362
00:37:36,171 --> 00:37:38,976
has dissolved the softer rocks
through which it is passes
363
00:37:39,040 --> 00:37:41,763
and brings them up as boiling mud.
364
00:37:48,244 --> 00:37:52,353
Elsewhere, the boiling water shoots
spasmodically into huge fountains,
365
00:37:52,417 --> 00:37:55,295
and the whole area
is wreathed in steam.
366
00:37:55,721 --> 00:38:00,878
Such a place is typical parts of land
where volcanic fires are on the wane.
367
00:38:01,120 --> 00:38:05,066
The famous hot springs of Yellowstone
in the Rocky Mountains of North America
368
00:38:05,130 --> 00:38:08,383
are also heated by a vast
chamber of molten rock
369
00:38:08,447 --> 00:38:11,316
some distance down
beneath the surface.
370
00:38:22,852 --> 00:38:27,059
The water welling up from these
crystal-clear, chemically rich pools
371
00:38:27,123 --> 00:38:30,902
is so scaldingly hot that no
creature can live in them.
372
00:38:31,206 --> 00:38:33,845
But when they trickle over
the brim, they begin to cool,
373
00:38:33,909 --> 00:38:38,860
and there rich colonies of bacteria
and mats of algae begin to grow.
374
00:38:39,285 --> 00:38:42,813
In places they flourish so thickly
that they break the surface
375
00:38:42,877 --> 00:38:49,077
and divert the flow of water so that in parts
they're cool enough to allow brine flies.
376
00:38:58,892 --> 00:39:01,373
The flies come to
feed on the algae.
377
00:39:07,153 --> 00:39:09,418
And here, too, they mate.
378
00:39:24,640 --> 00:39:28,833
They lay their eggs directly
in the warm mat of the algae.
379
00:39:28,897 --> 00:39:32,847
Each has a long white thread
to its case, like a seed.
380
00:39:41,110 --> 00:39:43,988
The eggs, however,
are far from safe.
381
00:39:44,052 --> 00:39:47,825
They're seized by mites that
clamber about over the algae.
382
00:39:58,465 --> 00:40:02,438
Spiders, too,
prowl around the grazing herds.
383
00:40:08,585 --> 00:40:11,862
A slightly larger fly moves
among the brine flies.
384
00:40:11,926 --> 00:40:15,251
It too is a killer,
devouring the grubs.
385
00:40:29,162 --> 00:40:33,758
So the algal mats support a
closely-knit interdependent community,
386
00:40:33,822 --> 00:40:38,822
all nourished by chemicals in the water
and energised by the volcanic heat.
387
00:40:38,974 --> 00:40:42,238
But in the end it's
destroyed by its own success.
388
00:40:42,302 --> 00:40:47,195
Increasing numbers of grubs munch away
the algae and begin weaken the mat.
389
00:40:47,259 --> 00:40:53,230
Eventually it gives way, the channel clears
and lethal scalding water gushes down,
390
00:40:53,294 --> 00:40:58,785
killing an entire generation of grubs and
many hunters and parasites that live on them.
391
00:41:02,701 --> 00:41:06,222
Now the process has to
start all over again.
392
00:41:23,115 --> 00:41:26,193
The hot volcanic springs of
the Rift Valley in Africa
393
00:41:26,257 --> 00:41:32,215
also support their own crops of bacteria and
the small floating algae that feed on them.
394
00:41:32,481 --> 00:41:36,159
But here the creatures that come
to harvest them are much bigger.
395
00:41:36,367 --> 00:41:41,495
Flamingoes, sometimes as many as a
million of them on this one lake.
396
00:41:49,678 --> 00:41:53,552
These lesser flamingoes feed
entirely on single-celled algae
397
00:41:53,616 --> 00:41:58,433
that proliferate in vast quantities
in these steaming soda-rich waters.
398
00:41:58,555 --> 00:42:01,846
Flocks like these remove 150 tons
399
00:42:01,910 --> 00:42:05,491
of these microscopic plants
from this lake every day.
400
00:42:11,651 --> 00:42:15,508
Their bills have sieves inside
them which strain off the algae
401
00:42:15,572 --> 00:42:17,883
as the water passes through them.
402
00:42:22,320 --> 00:42:24,818
It's easy to see how living
creatures can benefit
403
00:42:24,882 --> 00:42:30,070
from the chemical riches of volcanoes when
thay dissolved in the waters of hot springs.
404
00:42:30,930 --> 00:42:34,068
It's more difficult to
imagine how any living thing
405
00:42:34,132 --> 00:42:37,713
could derive nourishment
from a basalt lava flow.
406
00:42:42,292 --> 00:42:46,758
Its surface in many places is
as smooth and as hard as glass,
407
00:42:46,822 --> 00:42:52,136
and neither frost nor roots of plants
can initially make any impression on it.
408
00:43:00,865 --> 00:43:03,267
Centuries may pass
after an eruption
409
00:43:03,331 --> 00:43:08,119
before there's any sign of the surface
of such a flow beginning even to weather.
410
00:43:08,219 --> 00:43:14,744
This flow for example on the flanks of Mount
Kilauea in Hawaii is some 3,000 years old,
411
00:43:14,808 --> 00:43:20,678
and yet still it shows the rippled, ropy
surface that formed when it was liquid.
412
00:43:20,742 --> 00:43:26,842
But in the end the surface does erode and
plants do manage to get root in the cracks.
413
00:43:26,906 --> 00:43:30,452
They in turn can support
all kinds of other life,
414
00:43:30,516 --> 00:43:34,036
and so the lava flow is
eventually colonised,
415
00:43:34,100 --> 00:43:37,372
not only on its surface
but in its depths.
416
00:43:37,436 --> 00:43:42,302
For these basaltic lava flows are
often not as solid as they seem.
417
00:43:43,957 --> 00:43:47,951
When the lava first flows
out of the vent like a river,
418
00:43:48,015 --> 00:43:53,058
that on the outside of the flow
will cool quicker and solidify,
419
00:43:53,122 --> 00:43:56,037
forming walls on either
side of the flow.
420
00:43:57,903 --> 00:44:04,168
The top too cools quicker, and that
causes a crust to form over the flow,
421
00:44:04,232 --> 00:44:09,023
so that eventually the lava
is flowing down a long tunnel.
422
00:44:09,871 --> 00:44:14,749
When that happens, the walls and
ceiling of the tunnel act as insulation,
423
00:44:14,813 --> 00:44:18,857
keeping the heat in, so that
the lava flow remains liquid
424
00:44:18,921 --> 00:44:21,952
and so continues
for mile after mile.
425
00:44:27,043 --> 00:44:30,116
When eventually the
supply of lava stops,
426
00:44:30,180 --> 00:44:36,699
that tunnel may drain, leaving
a long cavern like this one.
427
00:45:20,317 --> 00:45:23,884
Out of the reach of rain
and frost and even dust,
428
00:45:23,948 --> 00:45:27,359
the surface of the lava looks
exactly as it must have done
429
00:45:27,423 --> 00:45:31,445
when the last trickle was draining
away and the floor was so hot
430
00:45:31,509 --> 00:45:34,877
that anything touching it
would be turned to a cinder.
431
00:45:54,760 --> 00:45:59,835
Molten lava had dripped from the
ceiling, it had swilled round the sides
432
00:45:59,899 --> 00:46:04,459
and spurted out in little dribbles from
cracks in the newly congealed walls.
433
00:46:04,605 --> 00:46:07,872
But living organisms
have already moved in.
434
00:46:08,475 --> 00:46:14,019
These roots belong to trees that are
growing on the surface of the lava flow.
435
00:46:14,083 --> 00:46:18,549
They've found their way down through
the cracks, and here they dangle,
436
00:46:18,613 --> 00:46:23,020
catching water as it percolates through
the lava and trickles down them.
437
00:46:23,191 --> 00:46:29,678
Among the rootlets, there are animals
that live nowhere else in the world.
438
00:46:34,193 --> 00:46:37,467
Normally, these creatures
are in total darkness.
439
00:46:37,636 --> 00:46:41,671
Nearly all of them, like this
cricket, have lost their pigment.
440
00:46:41,892 --> 00:46:45,511
Many of them have also lost
their wings and their eyes.
441
00:46:46,007 --> 00:46:49,469
In the blackness,
they find their way about by touch,
442
00:46:49,601 --> 00:46:52,365
and, like many cave insects
elsewhere in the world,
443
00:46:52,429 --> 00:46:56,299
have consequently developed
long legs and antennae.
444
00:47:03,695 --> 00:47:06,648
Some, like this bug,
are scavengers.
445
00:47:09,160 --> 00:47:12,626
Others, like the centipede, hunt.
446
00:47:18,095 --> 00:47:20,965
And the millipedes
feed on the roots.
447
00:47:40,330 --> 00:47:43,721
So, in these extraordinary
lava caverns,
448
00:47:43,785 --> 00:47:47,101
there is yet another community
of interdependent creatures
449
00:47:47,165 --> 00:47:51,681
that have come into existence
since the volcanoes erupted.
450
00:48:03,699 --> 00:48:08,412
The colonisation of volcanic
ash presents different problems.
451
00:48:08,587 --> 00:48:12,069
The difficulty here is not the
glassy hardness of the rock
452
00:48:12,133 --> 00:48:16,246
but quite the reverse,
its insubstantial dustiness.
453
00:48:16,593 --> 00:48:20,239
Mount St Helens is
still a wasteland.
454
00:48:22,004 --> 00:48:26,324
It's now, as I speak,
some two and a quarter years
455
00:48:26,388 --> 00:48:28,714
since the volcano erupted.
456
00:48:29,422 --> 00:48:33,178
I'm some three miles
from the crater,
457
00:48:33,242 --> 00:48:38,925
and still the scene is one
of devastation and sterility.
458
00:48:38,989 --> 00:48:44,385
It's not just that this unweathered
ash is not very fertile,
459
00:48:44,449 --> 00:48:49,417
but it's also so loose that it's
difficult for plants to get root.
460
00:48:49,481 --> 00:48:52,964
But that possibility
is always here.
461
00:48:53,256 --> 00:48:59,738
Here, for example, in this crevice,
there are the seeds of the willow herb,
462
00:48:59,802 --> 00:49:03,222
or, as they call it in these parts,
fireweed,
463
00:49:03,286 --> 00:49:06,985
that have been blown up
from the valleys below.
464
00:49:07,049 --> 00:49:11,248
I don't suppose these particular
ones will manage to get root here,
465
00:49:11,312 --> 00:49:13,819
but in the end some plant will,
466
00:49:13,883 --> 00:49:18,476
and in the end the process
of colonisation will begin.
467
00:49:22,025 --> 00:49:25,199
Krakatau's child is
just 57 years old.
468
00:49:25,263 --> 00:49:28,299
Its flanks too are covered
for the most part with ash,
469
00:49:28,363 --> 00:49:32,267
and they're still being buried regularly
with new layers from fresh eruptions,
470
00:49:32,331 --> 00:49:36,456
yet the process of colonisation
is already under way.
471
00:49:37,059 --> 00:49:41,393
Not only are there giant grasses,
like this wild sugar cane,
472
00:49:41,818 --> 00:49:44,487
but trees: A casuarina.
473
00:49:44,551 --> 00:49:50,175
If you want to see what a whole century
of colonisation by plants can bring about,
474
00:49:50,548 --> 00:49:54,873
have a look at that fragment
of old Krakatau over there.
475
00:50:04,227 --> 00:50:07,210
We know from first-hand
reports that 100 years ago
476
00:50:07,274 --> 00:50:11,358
there was nothing here at all
but sterile ash many feet deep.
477
00:50:11,693 --> 00:50:16,594
Within three years, 34 different
species of plants had reappeared.
478
00:50:17,210 --> 00:50:20,028
Ten years later there
were twice that number,
479
00:50:20,092 --> 00:50:23,588
and over 100 species of
birds and insects as well.
480
00:50:24,064 --> 00:50:28,424
Some seeds must have floated here
from Java, some 20 miles away,
481
00:50:28,488 --> 00:50:31,070
and they still continue to do so.
482
00:50:32,352 --> 00:50:36,052
Other smaller ones were
probably carried here by birds,
483
00:50:36,116 --> 00:50:39,172
either on their feet
or in their stomachs.
484
00:50:51,465 --> 00:50:56,672
But the ash is still here beneath the
lattice of roots of the jungle trees.
485
00:51:01,732 --> 00:51:07,352
Somehow or other, rats and lizards
and pythons have all reached here.
486
00:51:07,581 --> 00:51:11,259
There are now many hundreds of
different species of plants,
487
00:51:11,344 --> 00:51:15,937
and the winds have assisted the passage
of great number of flying insects,
488
00:51:16,001 --> 00:51:20,348
whose descendants now form
large and permanent populations,
489
00:51:20,412 --> 00:51:23,925
pollinating the flowers,
feeding on their fruits,
490
00:51:23,989 --> 00:51:28,779
collecting their rotting leaves
and indeed feeding on one another.
491
00:51:48,387 --> 00:51:52,599
As yet there are no larger mammals,
no monkeys or squirrels,
492
00:51:52,663 --> 00:51:57,331
no hunting cats or mongoose,
as there are in Java or Sumatra.
493
00:51:57,617 --> 00:52:00,069
But as far as smaller
creatures are concerned,
494
00:52:00,133 --> 00:52:03,495
the number of species is
increasing all the time.
495
00:52:17,117 --> 00:52:20,465
And on the flanks of
volcanoes all round the world,
496
00:52:20,529 --> 00:52:23,895
men clear fields and plant crops,
497
00:52:23,959 --> 00:52:27,637
even though they know they
may be sitting on a time bomb.
498
00:52:34,720 --> 00:52:39,135
These rice fields lie on the flanks
of one of Krakatau's near neighbours,
499
00:52:39,199 --> 00:52:43,841
Gunung Agung in Bali.
Only 20 years ago it erupted,
500
00:52:43,905 --> 00:52:49,027
killing 2,000 people and
leaving 150,000 homeless.
501
00:52:49,530 --> 00:52:53,299
But the Balinese will not leave
fields that are so fertile
502
00:52:53,363 --> 00:52:58,314
they can produce two or three
rich harvests of rice every year.
503
00:52:59,789 --> 00:53:05,417
Gunung Agung, Krakatau and the rest of the
long line of violently explosive volcanoes
504
00:53:05,481 --> 00:53:10,826
that run in a chain along Sumatra and
Java and rest of the Indonesian islands
505
00:53:10,890 --> 00:53:14,255
stand on the line of the
crack in the earth's crust
506
00:53:14,319 --> 00:53:17,526
where the basalt plate forming
the floor of the Indian Ocean
507
00:53:17,590 --> 00:53:21,395
meets the partly submerged
edge of the continent of Asia.
508
00:53:21,507 --> 00:53:25,451
This junction already
existed 65 million years ago,
509
00:53:25,515 --> 00:53:29,685
when India was an isolated island
in the middle of that ocean.
510
00:53:30,182 --> 00:53:33,944
Since then, as the ocean
floor has continued to spread,
511
00:53:34,008 --> 00:53:38,087
the continents have shifted and
India has moved towards Asia.
512
00:53:38,393 --> 00:53:42,617
As the two continents approached,
the sediments between them crumpled
513
00:53:42,681 --> 00:53:45,615
and eventually piled
up over the junction,
514
00:53:45,713 --> 00:53:49,868
so instead of the line between them
being marked by chain of volcanoes,
515
00:53:49,932 --> 00:53:55,439
it's buried deep beneath an immense
range of mountains, the Himalaya.
516
00:53:58,065 --> 00:54:04,454
So these great peaks of sandstone and
limestone rising five miles into the sky
517
00:54:04,518 --> 00:54:09,183
are not only the highest mountains
in the world, but among the youngest.
518
00:54:09,247 --> 00:54:13,175
What is more, the process
has not yet come to an end.
519
00:54:13,389 --> 00:54:18,049
India is still moving north at the
rate of about two inches a year,
520
00:54:18,113 --> 00:54:23,614
compacting itself ever more tightly
against the great continental mass of Asia,
521
00:54:24,003 --> 00:54:29,062
and the Himalaya are, infinitesimally,
getting higher and higher.
522
00:54:30,216 --> 00:54:34,203
And that is how this ammonite,
this sea-living creature,
523
00:54:34,267 --> 00:54:38,797
came to rest over two
miles high in the Himalaya.
524
00:54:38,986 --> 00:54:42,877
That too is the explanation
of how the Kali Gandaki river
525
00:54:42,941 --> 00:54:48,455
managed to cut its way clean through the
highest range of mountains in the world.
526
00:54:49,315 --> 00:54:53,085
It was flowing south from
the ancient plateau of Tibet
527
00:54:53,149 --> 00:54:57,536
even before the great mass
of India collided with Asia.
528
00:54:58,544 --> 00:55:03,864
As the sediments between the two land masses
buckled and rose over millions of years,
529
00:55:03,928 --> 00:55:06,611
the river maintained its course,
530
00:55:06,675 --> 00:55:10,666
cutting down through the
rocks as swiftly as they rose.
531
00:55:11,142 --> 00:55:15,080
And so now it still flows
south to the plains of India,
532
00:55:15,206 --> 00:55:19,408
and does so through the
deepest gorge in the world.
533
00:55:21,241 --> 00:55:25,792
Mountain ranges have been created in this
way several times during history the Earth.
534
00:55:25,856 --> 00:55:28,632
The Himalaya are
just the most recent.
535
00:55:28,696 --> 00:55:32,493
As they are worn down, so they
create different environments
536
00:55:32,557 --> 00:55:35,072
in which animals
and plants can live.
52811
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