1 00:00:50,283 --> 00:00:55,744 Our planet, the earth, is, as far as we know, unique in the universe. 2 00:00:55,989 --> 00:01:01,450 It contains life. Even in its most barren stretche there are animals. 3 00:01:12,872 --> 00:01:15,898 Around the equator, where those two essentials for life, 4 00:01:16,076 --> 00:01:20,672 sunshine and moisture, are most abundant, great forests grow, 5 00:01:20,880 --> 00:01:23,713 and here plants and animals proliferate in such numbers 6 00:01:23,883 --> 00:01:28,081 that we still have not even named all the different species. 7 00:01:39,699 --> 00:01:44,830 Here, animals and plants, insects and birds, mammals and man 8 00:01:45,004 --> 00:01:47,871 live together in intimate and complex communities, 9 00:01:48,041 --> 00:01:50,202 each dependent on one another. 10 00:01:53,379 --> 00:01:57,281 Two thirds of the surface of this unique planet are covered by water, 11 00:01:57,450 --> 00:02:00,510 and it was here indeed that life began. 12 00:02:11,131 --> 00:02:14,999 From the oceans, it has spread even to the summits of the highest mountains, 13 00:02:15,168 --> 00:02:19,935 as animals and plants have responded to the changing face of the earth. 14 00:02:36,756 --> 00:02:41,716 This river, the Kali Gandaki, has cut its way, in the most remarkable fashion, 15 00:02:41,895 --> 00:02:45,888 through the highest range of mountains in the world, the Himalaya. 16 00:02:46,266 --> 00:02:51,033 To the east of me rises Annapurna, over 23,000 feet high. 17 00:02:51,237 --> 00:02:53,865 To the west, Dhaulagiri, even higher. 18 00:02:54,040 --> 00:02:58,033 Their two summits are a mere 22 miles apart, 19 00:02:58,211 --> 00:03:01,578 and I am four vertical miles below them. 20 00:03:01,848 --> 00:03:04,544 And that makes this the deepest valley in the world. 21 00:03:04,851 --> 00:03:08,719 At this altitude, about 7,000 feet, it's quite war 22 00:03:08,888 --> 00:03:13,825 and animal and plant life on the flanks of the valley is both rich and abundant. 23 00:03:15,595 --> 00:03:18,792 The blossoms on these trees may well look familiar. 24 00:03:18,998 --> 00:03:21,193 Flowers like them grow in gardens all over the world. 25 00:03:21,367 --> 00:03:27,033 But these are wild plants and this is their original home. They're rhododendrons. 26 00:03:29,576 --> 00:03:32,568 And here they are food for monkeys, grey langurs, 27 00:03:32,745 --> 00:03:35,441 reminders that the hot plains of Southern Nepal and the tropics 28 00:03:35,615 --> 00:03:38,049 are not far away to the south. 29 00:03:50,029 --> 00:03:54,261 But they aren'tjust monkey food. They are the rhododendrons' advertisements, 30 00:03:54,434 --> 00:03:58,370 attracting birds and insects which will sip their nectar, gather their pollen, 31 00:03:58,538 --> 00:04:00,972 and so bring about their fertilisation. 32 00:04:09,282 --> 00:04:12,251 The ring-necked parakeet also comes from the tropics. 33 00:04:12,452 --> 00:04:17,412 Here, it's at the top of its range. Any higher and the weather will be too cold for it 34 00:04:18,558 --> 00:04:20,924 Beneath the rhododendrons live several species 35 00:04:21,094 --> 00:04:24,530 of those most splendid of Asia's birds, the pheasants. 36 00:04:24,797 --> 00:04:29,598 The blood pheasant, for all its delicate beauty, is a plainer member of the family. 37 00:04:30,603 --> 00:04:34,095 The cock Tragopan is surely the most magnificent. 38 00:04:42,715 --> 00:04:46,481 Until, that is, you see a cock lmpeyan pheasant, 39 00:04:47,520 --> 00:04:49,351 with the coronet of a peacock 40 00:04:49,555 --> 00:04:53,116 and the burnished, metallic iridescence of a tropical butterfly. 41 00:05:00,867 --> 00:05:05,304 The lmpeyan's hen, like those of all pheasants, is comparatively dull 42 00:05:19,319 --> 00:05:24,450 This deepest of all valleys in the world enables you to walk within a few days 43 00:05:24,624 --> 00:05:26,649 from the tropics, in its lower reaches, 44 00:05:26,826 --> 00:05:30,227 to the equivalent of the poles on the slopes high above, 45 00:05:30,530 --> 00:05:32,259 and to see as you make the journey 46 00:05:32,432 --> 00:05:37,062 how closely animals and plants are matched to the changing circumstances. 47 00:05:37,437 --> 00:05:41,806 As you walk higher, the rhododendron forest gets thinner and hung with moss. 48 00:05:42,041 --> 00:05:45,533 The air is moist and it can be quite warm during the day. 49 00:05:45,712 --> 00:05:48,647 And now, in summer, there are orchids here. 50 00:05:56,489 --> 00:06:00,516 On the ground beneath, flowers appear in close-packed bunches, 51 00:06:00,693 --> 00:06:03,594 protecting one another from the night frosts. 52 00:06:07,433 --> 00:06:11,494 The little Himalayan panda is certainly very well protected against the cold. 53 00:06:11,671 --> 00:06:14,504 Not only does it have warm, dense fur, 54 00:06:14,674 --> 00:06:20,704 but, like many animals that spend time in the snow, it has hair on the soles of its feet. 55 00:06:21,114 --> 00:06:26,313 That keeps its feet warm on the snow and stops it from sliding on ice. 56 00:06:26,619 --> 00:06:31,682 Now, in the summer, it also helps in getting a grip on wet, slippery branches. 57 00:06:36,662 --> 00:06:40,598 It's primarily a vegetarian, collecting buds and leaves and fruit, 58 00:06:40,767 --> 00:06:44,498 but it also takes eggs from a bird's nest, if it can find one. 59 00:06:49,008 --> 00:06:51,806 On the ground, and scarcely bigger than the panda, 60 00:06:51,978 --> 00:06:56,574 one of the shyest animals of the Himalayan forests, a musk deer. 61 00:07:01,120 --> 00:07:05,147 In these tangled trees, antlers would be a considerable handicap, 62 00:07:05,324 --> 00:07:07,554 and the musk deer doesn't develop them. 63 00:07:07,860 --> 00:07:11,660 A male fights instead with the sharp tusks in his upperjaw. 64 00:07:11,931 --> 00:07:14,729 They feed on moss, lichen and leaves, 65 00:07:14,901 --> 00:07:17,597 and are so agile and well-adapted to a mountain life 66 00:07:17,770 --> 00:07:21,069 that they can climb steep cliffs in search of food. 67 00:07:24,310 --> 00:07:29,612 When a musk deer or any other animal of any size dies, the vultures come. 68 00:07:35,922 --> 00:07:38,982 These are griffons, similar to those that circle the skies 69 00:07:39,158 --> 00:07:42,093 above Indian villages down in the hot foothills. 70 00:07:42,562 --> 00:07:46,054 They are common in this forest up to 7,000 or 8,000 feet. 71 00:08:09,188 --> 00:08:14,023 So the lives of all these creatures are connected, 72 00:08:14,193 --> 00:08:17,492 one with the other, either directly or indirectly, 73 00:08:17,663 --> 00:08:21,258 and all are ultimately dependent upon the vegetation. 74 00:08:21,501 --> 00:08:26,871 But both animals and plants are also greatly affected by the physical environment. 75 00:08:27,173 --> 00:08:31,872 I've climbed several thousand feet now and things are beginning to change. 76 00:08:32,245 --> 00:08:37,444 It's getting colder, and the rhododendrons are giving way to fir trees, 77 00:08:37,617 --> 00:08:41,553 and that will mean a change in the animals that live here. 78 00:08:45,324 --> 00:08:48,487 The yellow-throated martin has a broad taste in food. 79 00:08:48,728 --> 00:08:52,357 It takes fruit on occasion, catches insects now and then, 80 00:08:52,532 --> 00:08:58,994 but it relishes small rodents, like mice and squirrels, and there are quite a lot here. 81 00:08:59,305 --> 00:09:03,639 Even in winter, when the forests are deep in snow, it will remain active. 82 00:09:04,010 --> 00:09:06,444 But it's a great traveller, and if it gets very cold, 83 00:09:06,612 --> 00:09:09,945 it will descend to lower altitudes for a spell. 84 00:09:21,360 --> 00:09:25,126 The Himalayan bear is capable of living very high indeed. 85 00:09:25,398 --> 00:09:28,765 Its thick fur protects it against severe cold, 86 00:09:28,935 --> 00:09:32,928 but its range is not limited by temperature so much as food supply. 87 00:09:33,406 --> 00:09:37,342 In spite of its size, it seldom tackles any animal bigger than a mouse, 88 00:09:37,510 --> 00:09:42,538 and it lives for most of the time on ants, grubs, nuts and leaves, 89 00:09:42,848 --> 00:09:46,284 so it seldom goes any higher than the forest can grow. 90 00:09:53,359 --> 00:09:58,626 And now, getting on for 10,000 feet up, the forest is beginning to thin. 91 00:09:58,965 --> 00:10:03,459 In summer, there's not much rain here, for most has fallen at lower altitudes. 92 00:10:03,803 --> 00:10:06,431 In winter, it gets extremely cold. 93 00:10:06,606 --> 00:10:12,306 Those conditions don't suit rhododendrons. Here only conifers flourish in large numbers. 94 00:10:14,080 --> 00:10:17,743 High though we are, the Kali Gandaki is still a very broad river. 95 00:10:18,017 --> 00:10:20,417 Remarkably, and mysteriously, 96 00:10:20,586 --> 00:10:25,421 it doesn't rise from the flanks of these giant mountains but cuts right through them. 97 00:10:26,258 --> 00:10:28,818 The people of the foothills have long since recognised 98 00:10:28,995 --> 00:10:33,398 the value of this extraordinary corridor that leads right through the Himalayas, 99 00:10:33,566 --> 00:10:37,024 and all summer trains of mules trudge up the valley, 100 00:10:37,203 --> 00:10:41,833 taking barley and buckwheat to trade with Tibetans for wool and salt. 101 00:10:45,111 --> 00:10:49,309 All the way up the valley are villages where the muleteers can rest, 102 00:10:49,782 --> 00:10:52,273 but during the summer few do so. 103 00:10:52,718 --> 00:10:56,415 Most trudge tirelessly upwards for as long as there's daylight. 104 00:11:43,035 --> 00:11:45,902 A lammergeier, the bearded vulture, a mountain bird 105 00:11:46,072 --> 00:11:51,339 that soars around the high valleys of Asia and a few remote parts of Europe, 106 00:11:51,577 --> 00:11:53,704 but nowhere higher than this. 107 00:11:59,485 --> 00:12:03,546 And a sign that now we are getting really high: Snow cock. 108 00:12:03,756 --> 00:12:07,624 Its dappled white plumage gives it camouflage against the broken snow 109 00:12:07,827 --> 00:12:11,319 that even now, in summer, can fall at these altitudes. 110 00:12:11,697 --> 00:12:14,757 They forage for seeds and rootlets in the thin turf. 111 00:12:26,045 --> 00:12:30,505 There are no trees now, just a few small shrubs and dry, withered grass. 112 00:12:30,783 --> 00:12:32,648 But that's enough for the tahr. 113 00:12:32,818 --> 00:12:37,448 It is neither a sheep nor a goat, but related equally to both. 114 00:12:37,656 --> 00:12:42,650 It will eat almost anything that's green, and is grateful to find it in this bleak land. 115 00:12:43,629 --> 00:12:47,929 Another typically mountain creature: The red-billed chough, a kind of crow. 116 00:12:48,200 --> 00:12:53,661 They search the rocks for insects, grubs, odd seeds. They will take most things. 117 00:13:01,680 --> 00:13:06,208 Their cousins, yellow-billed choughs, go as high as any bird in the world, 118 00:13:06,519 --> 00:13:11,149 riding the rising wind currents to the height of the snow peaks themselves. 119 00:13:35,447 --> 00:13:39,850 Flowers at this altitude can only come from small cushion plants, 120 00:13:40,019 --> 00:13:42,249 huddled together against the cold. 121 00:13:43,422 --> 00:13:46,323 Higher still, little can grow except lichens. 122 00:13:46,559 --> 00:13:50,962 Now it's so cold that growth may only be possible for a few days in the year. 123 00:13:53,866 --> 00:13:57,802 And yet, in these bleak regions, people live. 124 00:13:58,337 --> 00:14:00,965 To help plough the fields, they use the yak, 125 00:14:01,173 --> 00:14:05,041 a domesticated creature that once roamed wild on the plains of Tibet, 126 00:14:05,344 --> 00:14:09,246 the only large mammal that lives permanently as high as man. 127 00:14:12,251 --> 00:14:16,745 The people, Bhotias and Sherpas, grow not only barley but potatoes, 128 00:14:16,922 --> 00:14:20,221 a crop that was first cultivated by the Incas in the Andes 129 00:14:20,459 --> 00:14:23,690 and was introduced here a century or so ago. 130 00:14:24,396 --> 00:14:28,765 These highland people are well-adapted to life at these altitudes. 131 00:14:29,435 --> 00:14:33,030 Their blood contains a particularly high number of red corpuscles 132 00:14:33,205 --> 00:14:37,835 and so can carry more oxygen in it than a lowlander's can. 133 00:14:39,211 --> 00:14:43,773 Certainly, when it comes to walking at these high altitudes, 134 00:14:44,149 --> 00:14:47,641 they're very much better adapted than I am. 135 00:14:48,320 --> 00:14:55,852 So, all the living creatures in these high valleys are adapted to their environment, 136 00:14:56,095 --> 00:14:59,963 both their biological environment and their physical environment. 137 00:15:00,132 --> 00:15:07,265 And yet, in terms of biological history, those adaptations are very recent indeed. 138 00:15:07,940 --> 00:15:14,869 These immense mountains, the eternal hills, are in fact far from eternal. 139 00:15:15,781 --> 00:15:20,013 They are younger than the plains of India to the south 140 00:15:20,185 --> 00:15:22,915 or the plateau of Tibet to the north. 141 00:15:23,188 --> 00:15:29,650 They were raised to their present height about 35 million years ago 142 00:15:29,828 --> 00:15:31,295 from the bottom of the sea. 143 00:15:31,530 --> 00:15:35,466 And what is the evidence for that extraordinary statement? 144 00:15:35,768 --> 00:15:39,704 It can be found all over the place, just up here. 145 00:15:47,947 --> 00:15:51,781 These slopes are littered 146 00:15:52,885 --> 00:15:57,948 with fragments like these. 147 00:15:59,158 --> 00:16:03,959 This is obviously a shell that's been turned to stone, a fossil. 148 00:16:04,196 --> 00:16:08,929 Although there are no molluscs alive today exactly like this one, 149 00:16:09,101 --> 00:16:14,403 there are some which are sufficiently similar for us to be sure that it lived in water. 150 00:16:14,740 --> 00:16:18,267 And if we analyse the rock in which it's embedded, 151 00:16:18,444 --> 00:16:23,746 it's clear that that was mud laid down at the bottom of a sea. 152 00:16:24,683 --> 00:16:28,084 But I am as far as I can be from the sea. 153 00:16:28,253 --> 00:16:36,058 I am in the middle of Asia, miles from the sea, and over two vertical miles above it. 154 00:16:36,295 --> 00:16:40,732 What forces could possibly have raised the seabed to these heights? 155 00:16:41,066 --> 00:16:44,297 We now know that those forces are still in action, 156 00:16:44,470 --> 00:16:50,773 that these mountains are still rising and that land is still being created. 157 00:17:13,999 --> 00:17:15,261 I'm in Iceland. 158 00:17:15,901 --> 00:17:21,305 This fantastic fountain of fire rising 200 feet or so into the air behind me 159 00:17:21,473 --> 00:17:23,441 is molten rock. 160 00:17:24,309 --> 00:17:29,906 Fine ash is falling all around, there are gusts of choking, poisonous gas, 161 00:17:30,082 --> 00:17:35,145 and it's so hot that this is just about as close as I can get to i 162 00:17:49,468 --> 00:17:52,528 The sheer weight of these molten ingots of rock 163 00:17:52,704 --> 00:17:56,606 prevents them being swept away from the vent by the gale, 164 00:17:56,909 --> 00:18:00,140 so there's little danger of them suddenly coming our way. 165 00:18:05,184 --> 00:18:09,280 Less dramatic than the fire fountain but perhaps more sinister 166 00:18:09,455 --> 00:18:15,394 is this tide of black slag that is slowly creeping over the surface of the land. 167 00:18:15,894 --> 00:18:19,921 In parts it's red-hot and molten and flows like treacle, 168 00:18:20,132 --> 00:18:24,626 but on the edges it's cooled enough for me to handle it. 169 00:18:24,970 --> 00:18:29,430 It's black, it's heavy and it's called basalt. 170 00:18:29,641 --> 00:18:34,305 Basalt like this has been welling up from deep in the earth's crust 171 00:18:34,480 --> 00:18:37,608 since the beginning of the history of our planet. 172 00:18:47,626 --> 00:18:50,993 A flow may travel for as much as 25 miles. 173 00:18:51,263 --> 00:18:54,528 Sometimes it moves no faster than a man can walk, 174 00:18:54,733 --> 00:18:58,134 but sometimes it races along at an extraordinary speed, 175 00:18:58,303 --> 00:19:01,932 40 miles an hour, and nothing... nothing... can stop it. 176 00:19:14,386 --> 00:19:16,479 Sometimes so much lava is produced 177 00:19:16,655 --> 00:19:20,182 that it accumulates in flows 100 feet or so thick. 178 00:19:20,726 --> 00:19:24,992 Then the centre layers of it cool exceptionally slowly and very evenly, 179 00:19:25,164 --> 00:19:27,223 and this is the result. 180 00:19:29,501 --> 00:19:34,336 Here, at the Giant's Causeway, the top of the lava flow has been eroded away, 181 00:19:34,506 --> 00:19:37,304 for the eruptions took place 50 million years ago. 182 00:19:37,876 --> 00:19:41,778 The cooling contractions have produced the effect you see in drying mud, 183 00:19:41,947 --> 00:19:44,381 though here the cracks extend to a greater depth 184 00:19:44,550 --> 00:19:48,714 to produce six-sided columns a foot and a half across. 185 00:19:51,757 --> 00:19:56,626 In the Hebrides, there's another lava flow that erupted at about the same time 186 00:19:56,795 --> 00:19:58,786 and formed Fingal's Cave. 187 00:20:04,169 --> 00:20:09,436 The layer of lava that slowed down the cooling of the interior is still uneroded, 188 00:20:09,608 --> 00:20:14,443 and beneath it the near-perfect basalt columns rise almost 20 feet high. 189 00:20:37,669 --> 00:20:43,073 Basalt that doesn't contain very much gas wells out from below almost quietly. 190 00:21:13,438 --> 00:21:16,339 But if the lava has been extruded under great pressure, 191 00:21:16,508 --> 00:21:20,342 it may be full of gas, and then it behaves very differently. 192 00:21:28,420 --> 00:21:33,881 Sometimes a flow sweeps down over a forest, incinerating the trees in its path. 193 00:21:54,913 --> 00:22:01,284 Most dramatic of all, the lava sometimes wells up inside a crater and can't escape. 194 00:22:01,486 --> 00:22:05,513 Then it forms that most fearsome of nature's spectacles, a lava lake, 195 00:22:05,691 --> 00:22:08,319 like this one in Nyiragongo in Africa. 196 00:22:08,960 --> 00:22:14,626 This lava is over 1,000 degrees centigrade, 2,000 degrees Fahrenheit. 197 00:22:15,000 --> 00:22:19,061 The bubbles of gas that burst from its surface may be 50 feet across. 198 00:22:19,438 --> 00:22:23,772 Sometimes, having got rid of much of its gas, like beer losing its fizz, 199 00:22:23,942 --> 00:22:31,508 it sinks back down the pipe and returns to the lava chamber a mile or so below. 200 00:22:33,752 --> 00:22:36,721 But lava lakes fed by pipes are not common. 201 00:22:37,055 --> 00:22:42,459 Basalt more usually comes to the surface in a rather different way. 202 00:22:52,771 --> 00:22:58,607 These Icelandic volcanoes erupt from huge cracks or fissures 203 00:22:58,777 --> 00:23:04,272 which regularly open up in a line which runs right across the width of the island. 204 00:23:04,649 --> 00:23:09,916 But that line itself is only the northern end of a huge line of weakness 205 00:23:10,088 --> 00:23:13,956 that runs for thousands of miles southwards from Iceland 206 00:23:14,126 --> 00:23:16,151 right round the side of the globe. 207 00:23:18,797 --> 00:23:22,927 Iceland lies between Norway and Greenland, south of the Arctic Circle. 208 00:23:23,135 --> 00:23:26,536 The crack, ridged over by lava, is mostly underwater, 209 00:23:26,705 --> 00:23:30,573 which is why its existence wasn't known until the beginning of this century. 210 00:23:31,209 --> 00:23:36,078 It runs between Europe and Africa to the east and the Americas to the west. 211 00:23:36,548 --> 00:23:39,949 In places, it rises above the sea to form volcanic islands: 212 00:23:40,118 --> 00:23:45,852 The Azores, the Cape Verdes, Ascension, St Helena, Tristan da Cunha. 213 00:23:46,291 --> 00:23:49,954 But below the surface the lava is also continually erupting, 214 00:23:50,128 --> 00:23:53,529 unseen by human eyes until only a few years ago. 215 00:24:24,463 --> 00:24:26,988 The clouds of gas come from the lava itself. 216 00:24:27,165 --> 00:24:32,125 They're not steam. The pressure of the water prevents that from being produced. 217 00:24:32,471 --> 00:24:35,702 The heat is rapidly absorbed by the vastness of the ocean itself 218 00:24:35,874 --> 00:24:40,743 so that the lava cools and congeals much more quickly than it would do in the air. 219 00:24:49,221 --> 00:24:53,453 Eruptions like these, at great depths, built the Atlantic ridge. 220 00:24:53,725 --> 00:24:59,357 But the basalt forms not only the ridge itself but the sea floor on either side. 221 00:24:59,931 --> 00:25:03,230 By dating it chemically, we know that the farther it is 222 00:25:03,401 --> 00:25:06,199 from the centre of the ridge, the older it is. 223 00:25:06,571 --> 00:25:10,371 Basalt is welling up in a molten state at the ridge 224 00:25:10,542 --> 00:25:15,002 and then, as it solidifies, is moving away on either side. 225 00:25:15,447 --> 00:25:19,144 We still don't fully understand the forces that power the process, 226 00:25:19,351 --> 00:25:25,779 but 50 to 30 miles below the earth's surface it's so hot that the rocks are molten 227 00:25:25,957 --> 00:25:30,724 and currents in them are welling up beneath the ridge, causing eruptions, 228 00:25:30,896 --> 00:25:36,163 and then flowing away on either side, pulling the plates of the ocean floor with them. 229 00:25:36,735 --> 00:25:40,432 It was this movement that dragged apart Africa and South America 230 00:25:40,605 --> 00:25:43,073 and created the Atlantic Ocean. 231 00:25:47,112 --> 00:25:49,103 Similar things have happened in the Pacific. 232 00:25:49,481 --> 00:25:52,939 The great plate that forms the eastern part of the ocean floor 233 00:25:53,118 --> 00:25:56,019 is moving towards the west coast of America. 234 00:25:56,388 --> 00:25:59,915 But where it meets the continent, it dives downwards, 235 00:26:00,091 --> 00:26:03,083 perhaps pulled by the descending current in the crust below, 236 00:26:03,261 --> 00:26:06,321 producing a deep trench in the ocean floor. 237 00:26:08,266 --> 00:26:13,431 As it goes down, it takes with it sediments from the bottom of the ocean 238 00:26:13,605 --> 00:26:15,163 and also some water. 239 00:26:16,241 --> 00:26:21,611 These new ingredients melt and interact with the rocks of the interior 240 00:26:21,780 --> 00:26:27,241 to produce a mixture crucially different from the lava that erupted at the ridge. 241 00:26:27,752 --> 00:26:32,155 For one thing, it contains much more dissolved gas and steam. 242 00:26:33,992 --> 00:26:36,586 As it rises up on the edge of the continent, 243 00:26:36,761 --> 00:26:39,958 it cools and solidifies, choking the vents. 244 00:26:41,166 --> 00:26:44,727 The effect is like screwing down the safety valve of a boiler. 245 00:27:02,320 --> 00:27:05,380 Mount St Helens on the Pacific coast of North America. 246 00:27:05,757 --> 00:27:07,657 On May 18th 1980, 247 00:27:07,826 --> 00:27:12,854 with an explosion 500 times as powerful as the atomic blast at Hiroshima, 248 00:27:13,098 --> 00:27:16,625 it blew away three-quarters of a cubic mile of rock. 249 00:27:18,603 --> 00:27:22,095 The forests around the mountain were totally destroyed. 250 00:27:22,307 --> 00:27:26,368 Trees 200 feet tall lay scattered like matchsticks. 251 00:27:27,646 --> 00:27:29,637 Geologists, weeks beforehand, 252 00:27:29,814 --> 00:27:33,045 watching a huge bulge develop on the side of the mountain, 253 00:27:33,218 --> 00:27:35,743 had warned of the coming catastrophe. 254 00:27:36,254 --> 00:27:40,350 Even so, over 30 people stayed and were killed. 255 00:27:51,536 --> 00:27:55,973 On the northern side of the volcano, there were not even trees to be seen. 256 00:27:56,207 --> 00:27:59,734 A huge avalanche of rock, blown out by the blast, 257 00:27:59,911 --> 00:28:04,871 had slid for 15 miles down the side of the mountain, burying everything. 258 00:28:09,154 --> 00:28:12,021 Behind it, Mount St Helens lay wrecked. 259 00:28:12,257 --> 00:28:14,521 Its summit was over 1,000 feet lower, 260 00:28:14,693 --> 00:28:18,959 and at the back of a huge amphitheatre, from which the rock had come, 261 00:28:19,130 --> 00:28:24,033 another ominous bulge was developing, swathed in jets of steam. 262 00:28:39,384 --> 00:28:42,842 Almost a century earlier, on the opposite side of the Pacific, 263 00:28:43,054 --> 00:28:48,321 another catastrophic eruption had taken place on the tiny island of Krakatau, 264 00:28:48,560 --> 00:28:53,395 in the straits between Java to the east and Sumatra to the west. 265 00:28:53,865 --> 00:28:58,393 In 1883 it was an island five miles long and three miles wide, 266 00:28:58,636 --> 00:29:03,505 with three volcanic peaks on it, the highest rising to almost 3,000 feet. 267 00:29:03,975 --> 00:29:05,533 But those peaks were dormant. 268 00:29:05,710 --> 00:29:10,272 There had been no sign of any volcanic activity within living memory. 269 00:29:10,582 --> 00:29:13,016 But in August of that year, 270 00:29:13,184 --> 00:29:16,984 people on the coast of Java began to hear explosions. 271 00:29:17,222 --> 00:29:20,214 A great column of smoke rose above Krakatau. 272 00:29:20,492 --> 00:29:26,089 Pieces of lava the size of a house were being thrown high into the air. 273 00:29:26,364 --> 00:29:29,561 The explosions continued day after day. 274 00:29:29,734 --> 00:29:35,798 The column of smoke rose up until it was five miles or so up into the sky. 275 00:29:36,174 --> 00:29:41,043 Ships that were sailing nearby had their decks covered in ash and pumice, 276 00:29:41,212 --> 00:29:45,148 and at night electric flames played over the rigging. 277 00:29:45,517 --> 00:29:47,542 Day after day this continued. 278 00:29:47,919 --> 00:29:51,719 And as it was doing so, it was emptying the lava chamber 279 00:29:51,890 --> 00:29:53,755 deep in the crust beneath the sea, 280 00:29:53,925 --> 00:29:57,622 and that was the cause of the greatest catastrophe of all. 281 00:29:57,896 --> 00:30:03,095 Because on the morning of August 27th, Monday, at 10 o'clock, 282 00:30:03,268 --> 00:30:07,204 the roof of that lava chamber collapsed. 283 00:30:07,472 --> 00:30:10,873 Millions of tons of sea water poured onto the red-hot lava. 284 00:30:11,042 --> 00:30:14,307 So did millions of tons of rocks. 285 00:30:14,679 --> 00:30:17,614 And this produced a titanic explosion. 286 00:30:17,949 --> 00:30:21,112 The noise was almost certainly the loudest noise 287 00:30:21,286 --> 00:30:25,245 that has ever echoed round the earth in recorded history. 288 00:30:25,657 --> 00:30:29,252 It was heard 2,000 miles away in Australia. 289 00:30:29,561 --> 00:30:34,828 3,000 miles away on the small island of Rodriguez in the South Atlantic, 290 00:30:34,999 --> 00:30:41,529 the commander of the garrison heard it and thought it was distant gunfire at sea. 291 00:30:42,273 --> 00:30:45,765 The explosion also produced a tempest of wind, 292 00:30:45,944 --> 00:30:50,574 which swept out entirely round the globe seven and a half times 293 00:30:50,748 --> 00:30:52,739 before it finally died away. 294 00:30:53,518 --> 00:30:58,649 But most catastrophic of all, the explosion produced a tidal wave. 295 00:30:58,957 --> 00:31:05,328 It swept towards the coasts and became a wall of water over 100 feet high. 296 00:31:05,697 --> 00:31:11,533 It crashed into the harbours, it picked up a naval gunboat with a crew of 28 297 00:31:11,703 --> 00:31:16,868 and lifted it for over a mile inland and dumped it on a hill. 298 00:31:17,208 --> 00:31:20,609 And it overwhelmed village after village. 299 00:31:20,879 --> 00:31:25,373 Over 33,000 people were killed. 300 00:31:26,451 --> 00:31:30,012 The pall of ash brought darkness 301 00:31:30,188 --> 00:31:33,988 over an area of 100 miles or so for several days. 302 00:31:34,459 --> 00:31:40,420 But when it cleared away, the island of Krakatau was unrecognisable. 303 00:31:41,566 --> 00:31:44,160 Three-quarters of the main island had disappeared. 304 00:31:44,402 --> 00:31:48,304 The two nearby islets were buried beneath massive deposits of ash. 305 00:31:48,539 --> 00:31:52,839 And where the tallest peak had stood, the sea was 900 feet deep. 306 00:31:53,211 --> 00:31:59,172 But not for long. 44 years later another island rose from the boiling sea. 307 00:32:08,960 --> 00:32:12,691 They called it Anak Krakatau: The child of Krakatau. 308 00:32:12,997 --> 00:32:14,988 Compared with the explosions of its parent, 309 00:32:15,166 --> 00:32:18,431 its eruptions are still trivial bubblings. 310 00:32:44,329 --> 00:32:47,730 Now, after more than 50 years of fitful activity, 311 00:32:47,899 --> 00:32:51,426 Krakatau's child has built itself a new cone. 312 00:32:51,736 --> 00:32:55,035 It's still not very big, less than 1,000 feet high 313 00:32:55,540 --> 00:33:01,172 Sporadically, it explodes. But often it's easy enough to walk round its rim. 314 00:33:10,989 --> 00:33:16,552 The fumes that boil up from its crater are partly steam and partly sulphurous gas, 315 00:33:16,794 --> 00:33:20,890 and the sulphur condenses on the rocks, coating them yellow. 316 00:33:23,401 --> 00:33:26,928 All volcanic eruptions spew out sulphur in one form or another, 317 00:33:27,105 --> 00:33:29,039 including those underwater. 318 00:33:31,442 --> 00:33:33,842 Here it doesn't form yellow crystals, 319 00:33:34,012 --> 00:33:38,449 but reacts with the sea water to produce clouds of black sulphides. 320 00:33:42,253 --> 00:33:46,087 These smokers, nearly two miles deep on the floor of the Pacific, 321 00:33:46,257 --> 00:33:50,489 are one of the most extraordinary scientific discoveries of recent years. 322 00:33:50,995 --> 00:33:54,988 The sulphides they produce are food for microscopic bacteria. 323 00:33:55,533 --> 00:34:01,870 They, in turn, are consumed by a group of creatures unlike any seen before. 324 00:34:04,075 --> 00:34:07,067 These are giant tube-worms 11 feet long. 325 00:34:07,245 --> 00:34:12,683 They have neither mouth nor gut but absorb bacteria through their thin skin. 326 00:34:14,419 --> 00:34:17,183 And these are clams, two feet across. 327 00:34:17,388 --> 00:34:19,322 They too consume the bacteria. 328 00:34:19,657 --> 00:34:22,182 The heated water rising above the smokers 329 00:34:22,360 --> 00:34:27,195 causes currents along the sea bottom that sweep small particles to the vents 330 00:34:27,365 --> 00:34:30,596 so there's a whole community of creatures feeding on them. 331 00:34:30,835 --> 00:34:36,273 Small, white, blind crabs. Strange fish, hitherto unknown. 332 00:34:38,443 --> 00:34:40,638 Until this bizarre colony was discovered, 333 00:34:40,812 --> 00:34:43,042 we had believed that all creatures on earth 334 00:34:43,214 --> 00:34:46,308 derived their energy through plants from the sun. 335 00:34:46,851 --> 00:34:52,483 Even the deep sea creatures fed on fragments falling from the sunlit surface. 336 00:34:52,723 --> 00:34:56,454 But here were animals that owed nothing to the sun 337 00:34:56,627 --> 00:35:02,156 and were sustained through bacteria by the chemical energy of volcanoes. 338 00:35:08,973 --> 00:35:12,739 But volcanoes don't remain active for ever. 339 00:35:12,944 --> 00:35:16,539 Eventually, there is some shift deep in the earth's crust 340 00:35:16,714 --> 00:35:20,309 and the focus of the intense heat moves away slightly 341 00:35:20,485 --> 00:35:22,680 and the eruptions come to an end. 342 00:35:22,920 --> 00:35:28,984 But if water percolates down through the rocks to the magma chamber, 343 00:35:29,160 --> 00:35:33,859 it's still so hot that the water is superheated and forced up again, 344 00:35:34,031 --> 00:35:36,761 like water in the spout of a boiling kettle. 345 00:35:37,235 --> 00:35:41,934 On the way, it may dissolve minerals from the rocks through which it passes, 346 00:35:42,106 --> 00:35:48,238 and then, as it emerges as hot springs, the minerals will be deposited in terraces, 347 00:35:48,412 --> 00:35:51,108 like these in Rotorua, in New Zealand. 348 00:36:00,091 --> 00:36:03,219 In some parts, the superheated steam on its way to the surface 349 00:36:03,394 --> 00:36:08,593 has dissolved the softer rocks and brings them up as boiling mud. 350 00:36:15,139 --> 00:36:19,041 Elsewhere, the boiling water shoots spasmodically into huge fountains, 351 00:36:19,243 --> 00:36:21,711 and the whole area is wreathed in steam. 352 00:36:21,946 --> 00:36:27,111 Such a place is typical of land where volcanic fires are on the wane. 353 00:36:27,518 --> 00:36:31,147 The famous hot springs of Yellowstone in the Rocky Mountains 354 00:36:31,322 --> 00:36:34,223 are also heated by a vast chamber of molten rock 355 00:36:34,392 --> 00:36:36,952 some distance down beneath the surface. 356 00:36:48,239 --> 00:36:52,198 The water welling up from these crystal-clear, chemically rich pools 357 00:36:52,376 --> 00:36:55,868 is so hot that no creature can live in them. 358 00:36:56,347 --> 00:36:58,645 When they trickle over the brim, they cool, 359 00:36:58,816 --> 00:37:03,583 and there rich colonies of bacteria and mats of algae begin to grow. 360 00:37:04,121 --> 00:37:07,386 They can flourish so thickly that they break the surface 361 00:37:07,558 --> 00:37:13,292 and divert the flow of water so that in parts they're cool enough for brine fli 362 00:37:22,907 --> 00:37:25,068 The flies come to feed on the algae. 363 00:37:30,815 --> 00:37:32,783 And here, too, they mate. 364 00:37:47,665 --> 00:37:51,465 They lay their eggs directly in the warm mat of the algae. 365 00:37:51,736 --> 00:37:55,194 Each has a long white thread to its case, like a seed. 366 00:38:03,381 --> 00:38:05,872 The eggs, however, are far from safe. 367 00:38:06,250 --> 00:38:09,708 They're seized by mites that clamber about over the algae. 368 00:38:19,897 --> 00:38:23,492 Spiders, too, prowl around the grazing herds. 369 00:38:29,774 --> 00:38:32,800 A slightly larger fly moves among the brine flies. 370 00:38:32,977 --> 00:38:35,844 It too is a killer, devouring the grubs. 371 00:38:49,427 --> 00:38:53,761 So the algal mats support a closely-knit interdependent community, 372 00:38:53,931 --> 00:38:58,391 all nourished by chemicals in the water and energised by the volcanic heat. 373 00:38:58,936 --> 00:39:01,962 But in the end it's destroyed by its own success. 374 00:39:02,239 --> 00:39:06,505 Increasing numbers of grubs eat the algae and weaken the mat. 375 00:39:06,744 --> 00:39:12,512 Eventually it gives way, the channel clears and scalding water gushes down, 376 00:39:12,683 --> 00:39:17,711 killing a generation of grubs and many hunters and parasites that live on them. 377 00:39:21,592 --> 00:39:24,789 Now the process has to start all over again. 378 00:39:41,278 --> 00:39:43,974 The hot volcanic springs of the Rift Valley in Africa 379 00:39:44,148 --> 00:39:49,711 also support their own crops of bacteria and the small algae that feed on them. 380 00:39:50,154 --> 00:39:53,351 But here the creatures that come to harvest them are bigger. 381 00:39:53,791 --> 00:39:58,785 Flamingoes, sometimes as many as a million of them on this one lake. 382 00:40:06,704 --> 00:40:10,265 These lesser flamingoes feed entirely on single-celled algae 383 00:40:10,441 --> 00:40:14,639 that proliferate in vast quantities in these steaming soda-rich waters. 384 00:40:15,179 --> 00:40:18,171 Flocks like these remove 150 tons 385 00:40:18,349 --> 00:40:21,546 of these microscopic plants from this lake every day. 386 00:40:27,758 --> 00:40:29,555 Their bills have sieves inside them 387 00:40:29,727 --> 00:40:33,185 which strain off the algae as the water passes through them. 388 00:40:37,935 --> 00:40:40,199 It's easy to see how creatures can benefit 389 00:40:40,371 --> 00:40:45,206 from the chemical riches of volcanoes dissolved in the waters of hot springs. 390 00:40:46,010 --> 00:40:48,877 It's more difficult to imagine how any living thin 391 00:40:49,046 --> 00:40:52,447 could derive nourishment from a basalt lava flow. 392 00:40:57,154 --> 00:41:01,352 Its surface in many places is as smooth and as hard as glass, 393 00:41:01,525 --> 00:41:06,053 and neither frost nor roots of plants can initially make any impression on it. 394 00:41:14,939 --> 00:41:17,100 Centuries may pass after an eruption 395 00:41:17,274 --> 00:41:21,506 before there's any sign of the surface of such a flow beginning even to weather. 396 00:41:22,046 --> 00:41:28,076 This flow on the flanks of Mount Kilauea in Hawaii is some 3,000 years old, 397 00:41:28,252 --> 00:41:33,986 and yet still it shows the rippled, ropy surface that formed when it was liquid. 398 00:41:34,258 --> 00:41:39,753 But in the end the surface does erode and plants do get root in the cracks. 399 00:41:39,997 --> 00:41:43,057 They in turn can support all kinds of other life, 400 00:41:43,234 --> 00:41:46,635 and so the lava flow is eventually colonised, 401 00:41:46,804 --> 00:41:49,898 not only on its surface but in its depths. 402 00:41:50,174 --> 00:41:54,235 For these basaltic lava flows are often not as solid as they seem. 403 00:41:56,180 --> 00:41:59,946 When the lava first flows out of the vent like a river, 404 00:42:00,117 --> 00:42:04,816 that on the outside of the flow will cool quicker and solidify, 405 00:42:04,989 --> 00:42:07,549 forming walls on either side of the flow. 406 00:42:09,693 --> 00:42:15,529 The top too cools quicker, and that causes a crust to form over the flow, 407 00:42:15,766 --> 00:42:20,430 so that eventually the lava is flowing down a long tunnel. 408 00:42:21,005 --> 00:42:25,567 When that happens, the walls and ceiling of the tunnel act as insulation, 409 00:42:25,743 --> 00:42:29,645 keeping the heat in, so that the lava flow remains liquid 410 00:42:29,813 --> 00:42:32,407 and so continues for mile after mile. 411 00:42:37,521 --> 00:42:40,217 When eventually the supply of lava stops, 412 00:42:40,391 --> 00:42:46,421 that tunnel may drain, leaving a long cavern like this one. 413 00:43:28,772 --> 00:43:32,105 Out of the reach of rain and frost and even dust, 414 00:43:32,276 --> 00:43:37,612 the surface of the lava looks as it did when the last trickle was draining away 415 00:43:37,781 --> 00:43:42,650 and the floor was so hot that anything touching it would be turned to a cinder. 416 00:44:01,739 --> 00:44:06,073 Molten lava had dripped from the ceiling, it had swilled round the sides 417 00:44:06,243 --> 00:44:10,805 and spurted out in little dribbles from cracks in the newly congealed walls. 418 00:44:11,382 --> 00:44:14,146 But living organisms have already moved in. 419 00:44:14,952 --> 00:44:20,049 These roots belong to trees that are growing on the surface of the lava flow. 420 00:44:20,324 --> 00:44:24,317 They've found their way down through the cracks, and here they dangle, 421 00:44:24,495 --> 00:44:28,625 catching water as it percolates through the lava and trickles down them. 422 00:44:28,899 --> 00:44:34,963 Among the rootlets, there are animals that live nowhere else in the world. 423 00:44:39,643 --> 00:44:42,544 Normally, these creatures are in total darkness. 424 00:44:42,913 --> 00:44:46,644 Nearly all of them, like this cricket, have lost their pigment. 425 00:44:47,017 --> 00:44:50,214 Many of them have also lost their wings and their eyes. 426 00:44:50,921 --> 00:44:53,685 In the blackness, they find their way about by touch, 427 00:44:53,857 --> 00:45:00,558 and, like many cave insects elsewhere, have developed long legs and antennae. 428 00:45:07,971 --> 00:45:10,667 Some, like this bug, are scavengers. 429 00:45:13,110 --> 00:45:16,238 Others, like the centipede, hunt. 430 00:45:21,585 --> 00:45:24,418 And the millipedes feed on the roots. 431 00:45:43,006 --> 00:45:46,237 So, in these extraordinary lava caverns, 432 00:45:46,410 --> 00:45:49,379 there is yet another community of interdependent creatures 433 00:45:49,546 --> 00:45:53,505 that have come into existence since the volcanoes erupted. 434 00:46:05,395 --> 00:46:09,798 The colonisation of volcanic ash presents different problems. 435 00:46:10,033 --> 00:46:13,264 The difficulty here is not the hardness of the roc 436 00:46:13,437 --> 00:46:17,305 but quite the reverse, its insubstantial dustiness. 437 00:46:17,741 --> 00:46:20,733 Mount St Helens is still a wasteland. 438 00:46:22,980 --> 00:46:26,973 It's now, as I speak, some two and a quarter years 439 00:46:27,151 --> 00:46:29,119 since the volcano erupted. 440 00:46:30,187 --> 00:46:33,418 I'm some three miles from the crater, 441 00:46:33,590 --> 00:46:38,823 and still the scene is one of devastation and sterility. 442 00:46:39,096 --> 00:46:44,227 It's notjust that this unweathered ash is not very fertile, 443 00:46:44,401 --> 00:46:49,168 but it's also so loose that it's difficult for plants to get root. 444 00:46:49,439 --> 00:46:52,465 But that possibility is always here. 445 00:46:52,743 --> 00:46:59,114 Here, for example, in this crevice, there are the seeds of the willow herb, 446 00:46:59,283 --> 00:47:02,275 or, as they call it in these parts, fireweed, 447 00:47:02,452 --> 00:47:05,785 that have been blown up from the valleys below. 448 00:47:06,023 --> 00:47:09,891 I don't suppose these particular ones will manage to get root here, 449 00:47:10,060 --> 00:47:12,494 but in the end some plant will, 450 00:47:12,663 --> 00:47:16,656 and in the end the process of colonisation will begin. 451 00:47:20,571 --> 00:47:23,335 Krakatau's child is just 57 years old. 452 00:47:23,640 --> 00:47:26,370 Its flanks too are covered with ash, 453 00:47:26,543 --> 00:47:30,411 and they're still buried regularly with new layers from fresh eruptions, 454 00:47:30,681 --> 00:47:34,276 yet the process of colonisation is already under way. 455 00:47:34,918 --> 00:47:38,820 Not only are there giant grasses, like this wild sugar cane, 456 00:47:38,989 --> 00:47:41,822 but trees: A casuarina. 457 00:47:42,025 --> 00:47:47,122 If you want to see what a century of colonisation by plants can bring about, 458 00:47:47,297 --> 00:47:51,757 have a look at that fragment of old Krakatau over there. 459 00:48:00,978 --> 00:48:03,606 We know from first-hand reports that 100 years ago 460 00:48:03,780 --> 00:48:07,546 there was nothing here but sterile ash many feet deep. 461 00:48:08,185 --> 00:48:12,554 Within three years, 34 different species of plants had reappeared. 462 00:48:12,923 --> 00:48:15,915 Ten years later there were twice that number, 463 00:48:16,093 --> 00:48:19,460 and over 100 species of birds and insects as well. 464 00:48:19,863 --> 00:48:23,924 Some seeds must have floated here from Java, some 20 miles away, 465 00:48:24,101 --> 00:48:26,228 and they still continue to do so. 466 00:48:27,938 --> 00:48:31,374 Other smaller ones were probably carried here by birds, 467 00:48:31,541 --> 00:48:34,271 either on their feet or in their stomachs. 468 00:48:46,290 --> 00:48:51,159 But the ash is still here beneath the lattice of roots of the jungle trees. 469 00:48:56,033 --> 00:49:01,266 Somehow or other, rats and lizards and pythons have all reached here. 470 00:49:01,772 --> 00:49:04,866 There are now many hundreds of different species of plants, 471 00:49:05,042 --> 00:49:09,604 and the winds have assisted the passage of many flying insects, 472 00:49:09,780 --> 00:49:13,739 whose descendants now form large and permanent populations, 473 00:49:13,917 --> 00:49:17,250 pollinating the flowers, feeding on their fruits, 474 00:49:17,421 --> 00:49:21,915 collecting their rotting leaves and indeed feeding on one another. 475 00:49:40,911 --> 00:49:44,506 As yet there are no larger mammals, no monkeys or squirrels, 476 00:49:44,681 --> 00:49:49,243 no hunting cats or mongoose, as there are in Java or Sumatra. 477 00:49:49,720 --> 00:49:51,984 But as far as smaller creatures are concerned, 478 00:49:52,155 --> 00:49:55,215 the number of species is increasing all the time. 479 00:50:08,472 --> 00:50:11,805 And on the flanks of volcanoes all round the world, 480 00:50:11,975 --> 00:50:14,808 men clear fields and plant crops, 481 00:50:14,978 --> 00:50:18,436 even though they know they may be sitting on a time bomb. 482 00:50:25,322 --> 00:50:29,258 These rice fields lie on the flanks of one of Krakatau's near neighbours, 483 00:50:29,426 --> 00:50:31,326 Gunung Agung in Bali. 484 00:50:31,728 --> 00:50:33,923 Only 20 years ago it erupted, 485 00:50:34,097 --> 00:50:38,864 killing 2,000 people and leaving 150,000 homeless. 486 00:50:39,503 --> 00:50:42,836 But the Balinese will not leave fields that are so fertile 487 00:50:43,006 --> 00:50:47,705 they can produce two or three rich harvests of rice every year. 488 00:50:49,579 --> 00:50:54,642 Gunung Agung, Krakatau and the rest of the violently explosive volcanoes 489 00:50:54,818 --> 00:50:59,915 that run in a chain along Sumatra and Java and the Indonesian islands 490 00:51:00,090 --> 00:51:02,923 stand on the line of the crack in the earth's crus 491 00:51:03,093 --> 00:51:06,119 where the basalt plate forming the floor of the Indian Ocean 492 00:51:06,296 --> 00:51:09,925 meets the partly submerged edge of the continent of Asia. 493 00:51:10,300 --> 00:51:13,861 This junction already existed 35 million years ago 494 00:51:14,037 --> 00:51:17,905 when India was an isolated island in the middle of that ocean. 495 00:51:18,208 --> 00:51:21,905 Since then, as the ocean floor has continued to spread, 496 00:51:22,179 --> 00:51:26,013 the continents have shifted and India has moved towards Asia. 497 00:51:26,283 --> 00:51:28,217 As the two continents approached, 498 00:51:28,385 --> 00:51:33,015 the sediments between them crumpled and eventually piled up over the junction, 499 00:51:33,190 --> 00:51:37,217 so instead of the line between them being marked by volcanoes, 500 00:51:37,394 --> 00:51:42,593 it's buried deep beneath an immense range of mountains, the Himalaya. 501 00:51:45,268 --> 00:51:51,207 So these great peaks of sandstone and limestone rising five miles into the sky 502 00:51:51,374 --> 00:51:55,834 are not only the highest mountains in the world, but among the youngest. 503 00:51:56,146 --> 00:51:59,411 And the process has not yet come to an end. 504 00:51:59,883 --> 00:52:04,047 India is still moving north at the rate of two inches a year, 505 00:52:04,221 --> 00:52:09,420 compacting itself ever more tightly against the continental mass of Asia, 506 00:52:09,593 --> 00:52:14,724 and the Himalaya are, infinitesimally, getting higher and higher. 507 00:52:15,999 --> 00:52:19,526 And that is how this ammonite, this sea-living creature, 508 00:52:19,703 --> 00:52:24,072 came to rest over two miles high in the Himalaya. 509 00:52:24,307 --> 00:52:28,004 That too is the explanation of how the Kali Gandaki river 510 00:52:28,178 --> 00:52:33,411 managed to cut its way clean through the highest range of mountains in the world. 511 00:52:34,351 --> 00:52:37,752 It was flowing south from the ancient plateau of Tibet 512 00:52:37,921 --> 00:52:42,085 even before the great mass of India collided with Asia. 513 00:52:42,559 --> 00:52:48,225 As the sediments between the two land masses buckled and rose over millions of years, 514 00:52:48,398 --> 00:52:50,696 the river maintained its course, 515 00:52:50,867 --> 00:52:54,633 cutting down through the rocks as swiftly as they rose. 516 00:52:55,338 --> 00:52:58,796 And so now it still flows south to the plains of India, 517 00:52:58,975 --> 00:53:03,105 and does so through the deepest gorge in the world. 518 00:53:04,915 --> 00:53:09,352 Mountain ranges have been created in this way several times. 519 00:53:09,519 --> 00:53:11,919 The Himalaya are just the most recent. 520 00:53:12,222 --> 00:53:15,749 As they are worn down, they create different environments 521 00:53:15,926 --> 00:53:17,951 in which animals and plants can live. 522 00:53:18,261 --> 00:53:23,324 So we have begun our portrait of the planet up on the roof of the world, 523 00:53:23,500 --> 00:53:29,370 and we will go from high altitudes to low, from the poles to the equator. 524 00:53:29,673 --> 00:53:32,801 And in the next programme we'll go even higher, 525 00:53:32,976 --> 00:53:37,970 to the most inhospitable environment of all, the world of snow and ice.