1 00:00:57,791 --> 00:01:00,885 Most of the time the surface of our World gives no hint 2 00:01:01,027 --> 00:01:03,427 of What lies beloW 3 00:01:09,402 --> 00:01:10,869 but there are a feW places on earth 4 00:01:11,004 --> 00:01:12,232 Where We can get a glimpse 5 00:01:12,372 --> 00:01:15,307 of What's happening inside the planet. 6 00:01:15,742 --> 00:01:18,905 That is just one fantastic sight. 7 00:01:19,045 --> 00:01:22,481 You can really see hoW much of this cone has fallen in 8 00:01:23,016 --> 00:01:25,780 These taller slopes are all very recent. 9 00:01:25,919 --> 00:01:28,683 Like all the loose boulders We see doWn here 10 00:01:28,822 --> 00:01:33,418 have fallen off the crater Walls since March. 11 00:01:34,828 --> 00:01:38,559 This is Mount Kilauea on the island of HaWaii. 12 00:01:52,479 --> 00:01:55,073 Scientists from the US Geological Survey 13 00:01:55,215 --> 00:01:59,515 regularly fly up here to take the pulse of the volcano. 14 00:02:06,860 --> 00:02:10,853 They need to get as close to the active crater as possible. 15 00:02:17,036 --> 00:02:19,129 lt's not a place Where you Want to hang around 16 00:02:19,272 --> 00:02:21,604 if you don't have to. 17 00:02:28,715 --> 00:02:30,945 lt's the pond of lava at the bottom of the crater 18 00:02:31,084 --> 00:02:33,416 Which they need to keep an eye on. 19 00:02:36,422 --> 00:02:40,791 Any change in level could be Warning of an imminent eruption. 20 00:02:45,398 --> 00:02:48,834 We're standing on the crater rim of Pu'u'O'o cone. 21 00:02:48,968 --> 00:02:50,435 This is the active vent 22 00:02:50,570 --> 00:02:53,630 on the eastern slope of Kilauea volcano. 23 00:02:53,773 --> 00:02:57,038 Potential hazard here is the, When the pond is so loW 24 00:02:57,177 --> 00:02:59,941 there's not much supporting the inside of the crater 25 00:03:00,079 --> 00:03:02,013 so We'll have large chunks of the crater rim 26 00:03:02,148 --> 00:03:05,413 that fall and if that happens pond level 27 00:03:05,552 --> 00:03:07,281 Would then rise and fall, rise and fall 28 00:03:07,420 --> 00:03:10,617 and you'll also get spatter and, 29 00:03:10,757 --> 00:03:13,453 and of course you don't Want to be standing on a chunk 30 00:03:13,593 --> 00:03:16,653 of rim that might actually go doWn in. 31 00:03:19,465 --> 00:03:24,027 Mount Kilauea is the World's most active volcano. 32 00:03:25,071 --> 00:03:27,335 Geologists suspect that all this vulcanism reflects 33 00:03:27,473 --> 00:03:32,240 some remarkable phenomenon deep Within the planet. 34 00:03:33,446 --> 00:03:34,879 But the problem scientists face 35 00:03:35,014 --> 00:03:39,075 is that the Earth's interior is totally inaccessible. 36 00:03:47,060 --> 00:03:49,620 Yet in a sense scientists have managed 37 00:03:49,762 --> 00:03:52,822 to descend to the very centre of the Earth. 38 00:03:52,966 --> 00:03:54,593 ln a remarkable series of experiments 39 00:03:54,734 --> 00:03:58,170 they've probed our planet to its core. 40 00:04:03,276 --> 00:04:05,005 They've shoWn hoW the same process 41 00:04:05,144 --> 00:04:07,169 that created this volcano 42 00:04:07,313 --> 00:04:09,907 also keeps the entire surface of our planet 43 00:04:10,049 --> 00:04:12,017 in constant motion. 44 00:04:28,001 --> 00:04:33,268 There's no better place to see that motion than lceland. 45 00:04:34,073 --> 00:04:35,472 The island sits astride 46 00:04:35,608 --> 00:04:38,168 an extraordinary break in the crust, 47 00:04:38,311 --> 00:04:41,439 a rift that marks the boundary betWeen tWo of the vast plates 48 00:04:41,581 --> 00:04:44,778 that make up the planet's outer skin. 49 00:04:46,819 --> 00:04:48,753 Up close this rift appears 50 00:04:48,888 --> 00:04:50,947 as a series of deep and narroW cracks 51 00:04:51,090 --> 00:04:52,887 in the surface. 52 00:04:58,131 --> 00:05:00,531 Here geologists like Bob White 53 00:05:00,667 --> 00:05:04,194 can study at first hand the Way the plates move. 54 00:05:04,337 --> 00:05:07,864 This fissure here is one of the, the many sWarm of fissures 55 00:05:08,007 --> 00:05:10,100 across about a 50 kilometre-Wide zone 56 00:05:10,243 --> 00:05:13,269 Where the motion betWeen the American plate on that side 57 00:05:13,413 --> 00:05:16,280 is moving aWay from the Eurasian plate on that side 58 00:05:16,416 --> 00:05:18,407 at a rate of about 20 millimetres a year, 59 00:05:18,551 --> 00:05:21,816 on average, about that much per year. 60 00:05:21,954 --> 00:05:24,115 The movement that's so visible in lceland 61 00:05:24,257 --> 00:05:27,249 is in fact happening all over the World. 62 00:05:29,729 --> 00:05:31,026 By the late 60s 63 00:05:31,164 --> 00:05:33,462 scientistshad Worked out that beneath the crust 64 00:05:33,599 --> 00:05:35,965 the entire surface of the planet is divided up 65 00:05:36,102 --> 00:05:39,902 into a small number of pieces - plates. 66 00:05:40,740 --> 00:05:43,208 These plates are all sloWly moving 67 00:05:43,343 --> 00:05:46,335 carrying the continents With them. 68 00:05:52,719 --> 00:05:54,414 The theory that described this motion 69 00:05:54,554 --> 00:05:58,183 Was called plate tectonics. 70 00:06:00,059 --> 00:06:02,254 lt Was the biggest step forward scientists 71 00:06:02,395 --> 00:06:06,058 had ever made in understanding the Earth. 72 00:06:09,135 --> 00:06:11,035 But there Was something missing. 73 00:06:11,170 --> 00:06:12,933 They kneW the plates Were moving, 74 00:06:13,072 --> 00:06:15,097 but scientists had no idea 75 00:06:15,241 --> 00:06:17,573 Why they Were moving. 76 00:06:22,482 --> 00:06:24,416 Nobody Was more Worried about this problem 77 00:06:24,550 --> 00:06:26,711 than one of the architects of the theory; 78 00:06:26,853 --> 00:06:29,014 Dan McKenzie. 79 00:06:29,689 --> 00:06:31,816 By the beginning of the 70s 80 00:06:31,958 --> 00:06:35,325 We had some understanding of 81 00:06:35,461 --> 00:06:36,928 What Was going on the surface 82 00:06:37,063 --> 00:06:39,759 'cos We'd been able to map the motions of the plates 83 00:06:39,899 --> 00:06:43,357 really in quite some detail all over the, the World, 84 00:06:43,503 --> 00:06:46,700 but What We really didn't have at that stage 85 00:06:46,839 --> 00:06:49,831 Was any decent understanding 86 00:06:49,976 --> 00:06:52,240 of hoW these motions Were maintained, 87 00:06:52,378 --> 00:06:53,902 and the obvious place to look is, 88 00:06:54,046 --> 00:06:56,514 is underneath the plates in the mantle 89 00:06:56,649 --> 00:06:58,116 'cos it clearly, they clearly Weren't being driven 90 00:06:58,251 --> 00:07:00,776 by the Winds from the outside, right. 91 00:07:00,920 --> 00:07:03,912 lt had to be an internal process. 92 00:07:08,694 --> 00:07:11,458 The first hint of What lies inside our planet 93 00:07:11,597 --> 00:07:14,498 came from scientists like Bryndis Brandsdottir, 94 00:07:14,634 --> 00:07:16,226 Who spends much of her time monitoring 95 00:07:16,369 --> 00:07:19,497 the many earthquakes Which shake lceland. 96 00:07:23,276 --> 00:07:25,437 We use different kind of sensors 97 00:07:25,578 --> 00:07:28,342 to monitor different things Within the Earth. 98 00:07:28,481 --> 00:07:30,278 For instance you can see earthquakes 99 00:07:30,416 --> 00:07:33,544 Which occurred in the region late last night 100 00:07:33,686 --> 00:07:35,984 and early this morning. 101 00:07:37,023 --> 00:07:38,354 But With the right equipment 102 00:07:38,491 --> 00:07:40,015 scientists can do far more 103 00:07:40,159 --> 00:07:43,651 than locate and record local earth tremors. 104 00:07:44,096 --> 00:07:46,758 With better senses We can record earthquakes 105 00:07:46,899 --> 00:07:48,059 from all over the globe 106 00:07:48,201 --> 00:07:51,102 and if they're big enough to send Waves through the earth 107 00:07:51,237 --> 00:07:53,432 those Waves can give us information 108 00:07:53,573 --> 00:07:56,633 about various places Within the Earth 109 00:08:03,516 --> 00:08:04,847 By putting together information 110 00:08:04,984 --> 00:08:06,713 from thousands of earthquakes, 111 00:08:06,853 --> 00:08:09,378 scientists built up their first complete picture 112 00:08:09,522 --> 00:08:11,683 of the Earth's interior. 113 00:08:14,126 --> 00:08:16,492 At its centre lies the core, 114 00:08:16,629 --> 00:08:18,893 an immense ball of liquid iron, 115 00:08:19,031 --> 00:08:21,864 the size of the planet Mars. 116 00:08:22,368 --> 00:08:24,996 Beyond the core is the vast bulk of the planet, 117 00:08:25,137 --> 00:08:28,937 the mantle, Which is composed of solid rock. 118 00:08:29,642 --> 00:08:32,236 The plates are simply the upper layer of the mantle 119 00:08:32,378 --> 00:08:35,905 With the crust just a thin veneer on top. 120 00:08:43,990 --> 00:08:47,016 But this picture gave no hint of any movement in the mantle 121 00:08:47,159 --> 00:08:50,492 that could be driving the motion of plates. 122 00:08:50,630 --> 00:08:52,063 To make progress 123 00:08:52,198 --> 00:08:55,497 scientists needed a different approach. 124 00:09:04,176 --> 00:09:05,507 Here in Lovgrun, 125 00:09:05,645 --> 00:09:07,374 SWedish island in the Baltic, 126 00:09:07,513 --> 00:09:09,413 scientists have long been intrigued 127 00:09:09,549 --> 00:09:12,347 by a mysterious phenomenon. 128 00:09:13,052 --> 00:09:15,577 Canadian geophysicist Dick Peltier 129 00:09:15,721 --> 00:09:17,154 has made the journey from Toronto 130 00:09:17,290 --> 00:09:18,882 to meet Martin Eckman 131 00:09:19,025 --> 00:09:21,653 and see things for himself. 132 00:09:24,263 --> 00:09:26,322 The sea has alWays been important here. 133 00:09:26,465 --> 00:09:29,593 People notice When it changes. 134 00:09:30,636 --> 00:09:34,663 ln 1940 Lisa Nygren Was a young Woman. 135 00:09:35,541 --> 00:09:40,103 Lisa tell us that she is about 35 years old here 136 00:09:40,246 --> 00:09:43,044 and you can see that in front of the boathouse here 137 00:09:43,182 --> 00:09:46,049 there is a lot of Water. 138 00:09:46,185 --> 00:09:49,018 NoWadays there is no Water here in the long ridge. 139 00:09:49,155 --> 00:09:53,114 lt's completely dry, just gravel and grass. 140 00:09:54,927 --> 00:09:56,224 lt seemed to the people here 141 00:09:56,362 --> 00:09:59,957 that the sea Was sloWly ebbing aWay. 142 00:10:05,638 --> 00:10:07,663 She tells me that When she Was young 143 00:10:07,807 --> 00:10:09,536 there Was Water here, 144 00:10:09,675 --> 00:10:11,040 it Was filled With Water, 145 00:10:11,177 --> 00:10:13,441 a small inlet from the bay. 146 00:10:13,579 --> 00:10:14,443 You mean you could bring boats 147 00:10:14,580 --> 00:10:16,047 right up into What are noW fields. 148 00:10:16,182 --> 00:10:19,015 Yes, roWing boats. 149 00:10:21,921 --> 00:10:23,946 Peltier and Eckman are not the first scientists 150 00:10:24,090 --> 00:10:25,990 to study the phenomenon. 151 00:10:26,125 --> 00:10:27,558 TWo and a half centuries ago 152 00:10:27,693 --> 00:10:30,719 the famous SWedish physicist Anders Celsius 153 00:10:30,863 --> 00:10:32,956 noticed the same thing. 154 00:10:45,478 --> 00:10:48,413 This is the famous rock of Lovgrun 155 00:10:48,547 --> 00:10:51,141 and here is the sea-level mark made by Celsius 156 00:10:51,283 --> 00:10:53,581 in 1 731 , 157 00:10:53,719 --> 00:10:57,450 so 250 years ago sea-level Was here. 158 00:10:57,590 --> 00:10:59,956 Today it's doWn there. 159 00:11:02,595 --> 00:11:05,689 Thanks to Celsius' foresight, Peltier and Eckman 160 00:11:05,831 --> 00:11:09,164 can calculate the rate of apparent sea-level drop here - 161 00:11:09,301 --> 00:11:12,429 over one centimetre each year. 162 00:11:16,909 --> 00:11:19,434 The problem is there's absolutely no evidence of 163 00:11:19,578 --> 00:11:24,038 any significant change to global sea-levels for 10,000 years, 164 00:11:24,183 --> 00:11:27,949 since levels rose at the end of the lce Age. 165 00:11:29,088 --> 00:11:31,386 Perhaps it's not the sea that is falling, 166 00:11:31,524 --> 00:11:34,584 but Scandinavia Which is rising. 167 00:11:35,861 --> 00:11:38,159 On the SWedish mainland Peltier and Eckman 168 00:11:38,297 --> 00:11:42,233 have found evidence that this is indeed What's happening. 169 00:11:50,109 --> 00:11:52,202 lt's astonishing. 170 00:11:54,413 --> 00:11:57,314 Believe it or not, this is a beach. 171 00:11:57,450 --> 00:12:00,010 We are noW 200 metres up a mountain 172 00:12:00,152 --> 00:12:02,985 and 30 kilometres from the sea. 173 00:12:03,122 --> 00:12:06,819 9,000 years ago this Was at sea-level 174 00:12:06,959 --> 00:12:08,984 and this Was the seashore. 175 00:12:09,128 --> 00:12:10,322 You can see the stones here 176 00:12:10,463 --> 00:12:13,364 have been reWorked by the sea Waves. 177 00:12:13,499 --> 00:12:17,128 Over the years this has been lifted up nearly 200 metres 178 00:12:17,269 --> 00:12:19,169 and this is the result. 179 00:12:24,877 --> 00:12:26,344 All the evidence suggests that 180 00:12:26,479 --> 00:12:29,346 since the ice melted 10,000 years ago 181 00:12:29,482 --> 00:12:34,419 Scandinavia has sloWly but steadily been rising out of the sea. 182 00:12:37,656 --> 00:12:39,214 lt may seem completely bizarre 183 00:12:39,358 --> 00:12:40,825 but When you think about it 184 00:12:40,960 --> 00:12:43,827 there's a very simple and Wonderful explanation 185 00:12:43,963 --> 00:12:45,988 that has to do With the Earth's mantle 186 00:12:46,132 --> 00:12:48,623 and With lce Ages. 187 00:12:51,670 --> 00:12:52,728 20,000 years ago 188 00:12:52,872 --> 00:12:55,602 the Earth Was in the midst of an lce Age. 189 00:12:56,175 --> 00:12:59,770 At that time all of Scandinavia Was covered by ice. 190 00:12:59,912 --> 00:13:02,574 Over central SWeden the ice Was about 3 kilometres, 191 00:13:02,715 --> 00:13:05,445 almost 2 miles deep. 192 00:13:06,318 --> 00:13:10,448 The great Weight of the ice load forced Scandinavia to sink. 193 00:13:10,923 --> 00:13:13,084 Just like loading a boat in the sea, 194 00:13:13,225 --> 00:13:15,750 the greater the Weight of the load put in the boat 195 00:13:15,895 --> 00:13:18,363 the deeper it sinks into the sea. 196 00:13:21,700 --> 00:13:25,431 But by 9,000 years ago the ice had melted. 197 00:13:28,240 --> 00:13:30,435 As time passes the land begins to rise 198 00:13:30,576 --> 00:13:32,737 rebounding back to its original outline, 199 00:13:32,878 --> 00:13:34,573 just as a boat bobs upWards 200 00:13:34,713 --> 00:13:37,147 When load is removed. 201 00:13:39,852 --> 00:13:43,344 So What Celsius first measured 21/2 centuries ago 202 00:13:43,489 --> 00:13:45,184 Was not the sea ebbing aWay 203 00:13:45,324 --> 00:13:46,621 but the land bobbing up 204 00:13:46,759 --> 00:13:50,126 as the great Weight of the ice disappeared. 205 00:13:50,262 --> 00:13:52,787 HoWever, this explanation, neat as it is, 206 00:13:52,932 --> 00:13:55,230 requires that beneath Scandinavia 207 00:13:55,367 --> 00:13:59,133 the earth's solid mantle is acting very strangely. 208 00:13:59,271 --> 00:14:01,102 Like the Water beneath a boat 209 00:14:01,240 --> 00:14:03,800 it must be floWing. 210 00:14:11,083 --> 00:14:15,383 What sort of stuff is rock solid yet floWs? 211 00:14:15,888 --> 00:14:17,913 Understanding that Would turn out to be the key 212 00:14:18,057 --> 00:14:20,651 to the mystery of Why the plates move, 213 00:14:20,793 --> 00:14:22,090 but to get that key 214 00:14:22,228 --> 00:14:23,855 scientists Would have to perform 215 00:14:23,996 --> 00:14:26,123 an ingenious series of experiments 216 00:14:26,265 --> 00:14:30,167 Which Would take them deep into the planet's interior. 217 00:14:34,673 --> 00:14:38,473 The first step Was to get hold of some rock from the mantle. 218 00:14:38,611 --> 00:14:39,578 lt's rare stuff 219 00:14:39,712 --> 00:14:42,010 but just occasionally olcanic eruptions 220 00:14:42,147 --> 00:14:43,239 bring to the surface 221 00:14:43,382 --> 00:14:47,250 small unmelted fragments of the mantle. 222 00:14:48,487 --> 00:14:52,548 lt's a green crystalline material called olivine, 223 00:14:52,691 --> 00:14:55,159 but to tell hoW this stuff behaves in the mantle 224 00:14:55,294 --> 00:14:57,626 scientists need to simulate the enormous 225 00:14:57,763 --> 00:14:59,993 temperatures and pressures of the Earth's interior 226 00:15:00,132 --> 00:15:01,963 in the lab 227 00:15:02,101 --> 00:15:04,592 so a tiny sample of olivine is squeezed 228 00:15:04,737 --> 00:15:07,331 betWeen the jaWs of a specialised vice 229 00:15:07,473 --> 00:15:10,306 called a diamond anvil. 230 00:15:12,211 --> 00:15:14,805 To understand hoW pressure affects the sample, 231 00:15:14,947 --> 00:15:16,608 Eckhard Salje needs to look 232 00:15:16,749 --> 00:15:18,979 deep to the structure of the crystal. 233 00:15:19,118 --> 00:15:20,551 The Way We are doing that 234 00:15:20,686 --> 00:15:24,486 is to bounce off the sample here X-rays, 235 00:15:24,623 --> 00:15:26,921 so radiation is coming in here, 236 00:15:27,059 --> 00:15:29,357 it's bounced off here into a detector 237 00:15:29,495 --> 00:15:30,792 and that Will tell us 238 00:15:30,930 --> 00:15:34,127 What the actual atoms are doing. 239 00:15:38,337 --> 00:15:40,703 As Eckhard uses these techniques to descend 240 00:15:40,839 --> 00:15:42,739 ever deeper into the Earth, 241 00:15:42,875 --> 00:15:45,366 he's revealing hoW the behaviour of our planet 242 00:15:45,511 --> 00:15:48,105 is governed by What happens at the atomic level 243 00:15:48,247 --> 00:15:50,340 inside the mantle. 244 00:16:01,493 --> 00:16:03,984 Although the sample alWays remains solid 245 00:16:04,129 --> 00:16:05,153 the intense pressures 246 00:16:05,297 --> 00:16:08,960 can disrupt the structure of the crystals 247 00:16:10,469 --> 00:16:12,596 and that means the solid material 248 00:16:12,738 --> 00:16:15,605 can sloWly floW. 249 00:16:16,141 --> 00:16:18,473 Suppose this is a piece of the Earth's mantle. 250 00:16:18,610 --> 00:16:19,599 Seismologists tell us, 251 00:16:19,745 --> 00:16:21,007 based on earthquake observations, 252 00:16:21,146 --> 00:16:22,909 that this material is solid. 253 00:16:23,048 --> 00:16:25,983 lt's elastic, it's resilient. 254 00:16:26,552 --> 00:16:29,817 What could be more elastic or more resilient. 255 00:16:29,955 --> 00:16:31,820 HoWever on a longer timescale 256 00:16:31,957 --> 00:16:35,085 its behaviour is completely different. 257 00:16:52,411 --> 00:16:55,744 So the mantle of the Earth is both a solid and a fluid. 258 00:16:55,881 --> 00:16:58,543 lt's all a question of timescale. 259 00:16:59,351 --> 00:17:01,251 So over long periods of time 260 00:17:01,387 --> 00:17:04,015 the solid mantle is floWing, 261 00:17:04,156 --> 00:17:05,418 but What does this floW have to do 262 00:17:05,557 --> 00:17:07,923 With the motion of the plates? 263 00:17:08,060 --> 00:17:09,652 Scientists Would find the ansWer to that 264 00:17:09,795 --> 00:17:12,059 When they voyaged even deeper, 265 00:17:12,197 --> 00:17:14,722 doWn to the iron core. 266 00:17:16,668 --> 00:17:17,896 We have here a piece of iron 267 00:17:18,037 --> 00:17:19,470 in Which We're going to re-create ignitions 268 00:17:19,605 --> 00:17:21,436 at the centre of the earth. 269 00:17:22,674 --> 00:17:25,507 And We have to do that by generating very high pressures 270 00:17:25,644 --> 00:17:26,838 and We have to melt it 271 00:17:26,979 --> 00:17:29,243 under those very high pressures. 272 00:17:30,182 --> 00:17:31,706 Then We're going to stick it in this - 273 00:17:31,850 --> 00:17:33,943 the hydrogen gas gun. 274 00:17:37,923 --> 00:17:39,584 NoW Keith is loading the gun noW 275 00:17:39,725 --> 00:17:41,955 With about 7lbs of gunpoWder. 276 00:17:42,094 --> 00:17:43,425 When the gun is fired 277 00:17:43,562 --> 00:17:45,530 it pushes this heavy piston 278 00:17:45,664 --> 00:17:48,030 doWn this hydrogen-filled tube 279 00:17:48,167 --> 00:17:51,068 Which starts out at 10 times atmospheric pressure, 280 00:17:51,203 --> 00:17:53,535 but the time We arrive here 281 00:17:54,006 --> 00:17:56,372 it's about 2,000 times atmospheric pressure. 282 00:17:56,508 --> 00:17:58,840 Takes this disc, bursts it, 283 00:17:58,977 --> 00:18:00,467 hydrogen comes out of here 284 00:18:00,612 --> 00:18:02,239 and pushes on this projectile 285 00:18:02,381 --> 00:18:04,975 accelerating it doWn this tube 286 00:18:05,117 --> 00:18:07,381 up at, at about 10,000 Gs 287 00:18:07,519 --> 00:18:09,817 up to a velocity of about 8 kilometres a second 288 00:18:09,955 --> 00:18:12,185 Which is Why We call it the fastest gun in the West. 289 00:18:12,324 --> 00:18:14,622 Once it gets here it impacts on the target 290 00:18:14,760 --> 00:18:16,057 generating very high pressures, 291 00:18:16,195 --> 00:18:18,095 melting the, melting the iron target 292 00:18:18,230 --> 00:18:21,028 and has about 50 billionths of a second 293 00:18:21,166 --> 00:18:23,134 to measure that temperature. 294 00:18:24,736 --> 00:18:26,636 l'll zero the counters. 295 00:18:26,772 --> 00:18:28,603 Neil Holmes is going to all this trouble 296 00:18:28,740 --> 00:18:29,900 because he Wants to ansWer 297 00:18:30,042 --> 00:18:33,409 a very basic question about the Earth's core. 298 00:18:33,545 --> 00:18:35,513 HoW hot is it? 299 00:18:35,647 --> 00:18:37,137 Yeah, everything looks good over here... 300 00:18:37,282 --> 00:18:38,306 Since scientists are pretty sure 301 00:18:38,450 --> 00:18:40,714 that the core contains molten iron, 302 00:18:40,853 --> 00:18:42,844 the thinking is that its temperature must be close 303 00:18:42,988 --> 00:18:45,047 to the melting point of iron. 304 00:18:45,190 --> 00:18:47,283 Calibrate target chamber... 305 00:18:48,727 --> 00:18:52,254 But not the melting point at the surface. 306 00:18:52,998 --> 00:18:54,295 Bringing up X-rays... 307 00:18:54,433 --> 00:18:56,993 The melting point under the stupendous pressures 308 00:18:57,136 --> 00:18:58,831 at the centre of the planet. 309 00:18:58,971 --> 00:19:00,336 Whenever you're ready. Ready to fire. 310 00:19:00,472 --> 00:19:02,440 Let's go ahead, Yeah. 311 00:19:18,957 --> 00:19:22,449 Well, there's not much left in here. 312 00:19:23,495 --> 00:19:25,429 That used to be a part of some of it. 313 00:19:25,564 --> 00:19:27,191 l don't knoW What. 314 00:19:27,332 --> 00:19:29,425 So the Whole target, everything We started With, 315 00:19:29,568 --> 00:19:31,126 is destroyed, 316 00:19:31,270 --> 00:19:34,034 but When the projectile hit the iron, 317 00:19:34,173 --> 00:19:37,108 the iron made a brief flash of light. 318 00:19:39,311 --> 00:19:42,542 The colour of that light tells us What the temperature Was. 319 00:19:42,681 --> 00:19:44,512 What it tells us is that melting temperature 320 00:19:44,650 --> 00:19:47,517 is 6,200 Centigrade 321 00:19:47,653 --> 00:19:48,984 This is over 1 ,000 degrees 322 00:19:49,121 --> 00:19:51,055 hotter than the surface of the Sun. 323 00:19:51,190 --> 00:19:53,181 What this means is the core of the Earth 324 00:19:53,325 --> 00:19:55,293 is a gloWing ball of hot iron, 325 00:19:55,427 --> 00:19:58,191 3,000 miles in diameter 326 00:19:58,330 --> 00:20:00,821 and sloWly over the aeons that, 327 00:20:00,966 --> 00:20:03,093 that heat is gradually moving out 328 00:20:03,235 --> 00:20:05,430 to the surface of the Earth. 329 00:20:07,072 --> 00:20:09,870 So at the Earth's centre beneath the mantle 330 00:20:10,008 --> 00:20:14,377 there's a heat source hotter than the surface of the Sun. 331 00:20:18,984 --> 00:20:20,849 Of course, as anyone Who's ever placed 332 00:20:20,986 --> 00:20:23,682 a pan of Water on a stove Will knoW, 333 00:20:23,822 --> 00:20:27,588 When you heat a fluid from beloW it starts moving. 334 00:20:27,726 --> 00:20:30,320 A little bit of dye shoWs What happens. 335 00:20:30,462 --> 00:20:32,953 Hot material comes up from the bottom, 336 00:20:33,098 --> 00:20:35,566 rises to the surface Where it cools 337 00:20:35,701 --> 00:20:37,999 and sinks back again. 338 00:20:38,136 --> 00:20:41,003 This is the process knoWn as convection. 339 00:20:41,139 --> 00:20:44,404 Could this be happening in the Earth's mantle? 340 00:20:54,853 --> 00:20:56,480 To ansWer this question 341 00:20:56,622 --> 00:20:58,180 scientists have had to put together 342 00:20:58,323 --> 00:21:01,781 everything they've learnt about the Earth's interior; 343 00:21:02,828 --> 00:21:04,955 the temperature of the core 344 00:21:05,964 --> 00:21:08,398 size of the mantle 345 00:21:09,468 --> 00:21:12,164 the properties of mantle rock 346 00:21:14,806 --> 00:21:17,775 and the rate at Which they can floW. 347 00:21:19,411 --> 00:21:20,742 Adding all this together 348 00:21:20,879 --> 00:21:24,110 scientists came to an amazing conclusion. 349 00:21:24,249 --> 00:21:27,082 Like Water in a gigantic saucepan, 350 00:21:27,219 --> 00:21:30,814 the planet's interior is ceaselessly churning aWay 351 00:21:30,956 --> 00:21:33,049 as it convects heat from the core 352 00:21:33,191 --> 00:21:35,318 toWards the surface. 353 00:21:35,460 --> 00:21:36,518 So the situation noW 354 00:21:36,662 --> 00:21:38,220 is really very much more interesting 355 00:21:38,363 --> 00:21:41,059 because We have this mobile Earth 356 00:21:41,199 --> 00:21:44,691 Which is mobile because it's transporting heat 357 00:21:44,836 --> 00:21:48,567 from the interior toWards the surface 358 00:21:48,707 --> 00:21:51,073 both upWards by hot material rising 359 00:21:51,209 --> 00:21:53,575 and doWnWards by cold material sinking 360 00:21:53,712 --> 00:21:56,772 and the thing acts really just like a, an engine. 361 00:21:56,915 --> 00:21:59,406 lt's converting heat, right, 362 00:21:59,551 --> 00:22:01,246 the heat Which it's transporting, 363 00:22:01,386 --> 00:22:02,819 into some sort of Work 364 00:22:02,954 --> 00:22:04,945 and it's this Work Which is driving 365 00:22:05,090 --> 00:22:07,718 the plates round on the surface. 366 00:22:08,560 --> 00:22:11,324 lt's not difficult to see hoW the motion of the plates 367 00:22:11,463 --> 00:22:14,432 relates to convection in the mantle. 368 00:22:14,900 --> 00:22:17,994 At the mid-ocean ridges hot mantle is floWing up 369 00:22:18,136 --> 00:22:20,297 and as it cools it forms neW plate 370 00:22:20,439 --> 00:22:23,374 Which moves aWay from the ridge. 371 00:22:23,508 --> 00:22:25,339 Eventually it's cold and dense enough 372 00:22:25,477 --> 00:22:29,914 to sink back doWn again into the planet's interior. 373 00:22:34,653 --> 00:22:36,518 So the complex motion of the plates 374 00:22:36,655 --> 00:22:39,249 is actually part of a simple process 375 00:22:39,391 --> 00:22:41,222 by Which the Earth is sloWly losing 376 00:22:41,360 --> 00:22:44,124 its massive store of heat. 377 00:22:51,837 --> 00:22:55,773 But What about the vulcanism in places like HaWaii? 378 00:22:55,907 --> 00:22:59,274 HoW did that fit into mantle convection? 379 00:23:06,284 --> 00:23:08,275 The ansWer to that started to become clear 380 00:23:08,420 --> 00:23:13,016 When Dan McKenzie began experimenting With convection. 381 00:23:13,158 --> 00:23:15,285 His idea Was to simulate the behaviour 382 00:23:15,427 --> 00:23:18,988 of the Earth's interior in the laboratory. 383 00:23:22,801 --> 00:23:24,462 The heat source, the core, 384 00:23:24,603 --> 00:23:27,538 Was represented by a Waster bath. 385 00:23:31,743 --> 00:23:33,734 For the mantle above McKenzie 386 00:23:33,879 --> 00:23:36,404 chose a rather surprising material; 387 00:23:36,548 --> 00:23:39,574 a layer of golden syrup. 388 00:23:40,519 --> 00:23:44,148 What We Wanted Was to look at convection in something 389 00:23:44,289 --> 00:23:46,723 Which had a very large range of viscosity 390 00:23:46,858 --> 00:23:49,418 like the Earth does because We, We kneW that, 391 00:23:49,561 --> 00:23:52,223 that plates on the Earth's surface 392 00:23:52,364 --> 00:23:53,854 are really very viscousb and strong 393 00:23:53,999 --> 00:23:57,730 because they move as units over huge areas, 394 00:23:57,869 --> 00:23:59,894 but underneath that We knoW 395 00:24:00,038 --> 00:24:03,474 from the Way in Which Scandinavia recovers 396 00:24:03,608 --> 00:24:05,132 after the ice melted that, 397 00:24:05,277 --> 00:24:07,268 that the viscosity underneath 398 00:24:07,412 --> 00:24:10,313 there is very much loWer than the surface plates, 399 00:24:10,449 --> 00:24:11,882 so What We Wanted Was a material 400 00:24:12,017 --> 00:24:14,508 Which had a huge range of viscosity 401 00:24:14,653 --> 00:24:18,180 and Lyle's golden syrup is ideal. 402 00:24:20,058 --> 00:24:22,117 But When McKenzie ran the experiment 403 00:24:22,260 --> 00:24:24,820 the result Was a tremendous surprise. 404 00:24:24,963 --> 00:24:27,124 lnstead of large plates he found 405 00:24:27,265 --> 00:24:28,960 that the convection organised itself 406 00:24:29,100 --> 00:24:31,660 into an interlocking pattern of small cells 407 00:24:31,803 --> 00:24:35,068 each centred around a rising plume of hot material 408 00:24:35,207 --> 00:24:39,439 surrounded by sheets of cold sinking treacle. 409 00:24:41,580 --> 00:24:43,275 We could heat it in different Ways, 410 00:24:43,415 --> 00:24:44,643 right, We could do all kinds of different things. 411 00:24:44,783 --> 00:24:46,148 We could alter the top temperature 412 00:24:46,284 --> 00:24:47,683 and alter the viscosity contrast. 413 00:24:47,819 --> 00:24:49,787 Really doesn't make much difference, right. 414 00:24:49,921 --> 00:24:51,479 You alWays get this pattern, 415 00:24:51,623 --> 00:24:53,022 lots of little cells, 416 00:24:53,158 --> 00:24:56,218 not really at all like What We Wanted for plates, 417 00:24:56,361 --> 00:24:59,353 but this then gave us the idea that, 418 00:24:59,498 --> 00:25:00,988 that maybe on Earth 419 00:25:01,132 --> 00:25:02,861 the same thing Was going on 420 00:25:03,001 --> 00:25:05,231 and that underneath these big plates 421 00:25:05,370 --> 00:25:06,860 there Were perhaps lots of little cells 422 00:25:07,005 --> 00:25:09,701 like this Which Were convecting. 423 00:25:27,392 --> 00:25:28,450 Could one of Dan McKenzie's 424 00:25:28,593 --> 00:25:32,120 convecting cells lie beneath HaWaii? 425 00:25:41,239 --> 00:25:43,332 lf so, then all this lava 426 00:25:43,475 --> 00:25:45,466 is coming from a plume of mantle rock 427 00:25:45,610 --> 00:25:48,602 that has risen from deep Within the planet. 428 00:25:54,886 --> 00:25:57,286 Why don't you stand about here and give me enough coil... 429 00:25:57,422 --> 00:25:59,287 Lava floWs in underground channels 430 00:25:59,424 --> 00:26:00,948 doWn from the main vent. 431 00:26:01,092 --> 00:26:04,357 That gives Carl Thornber and Dave Bercovici 432 00:26:04,496 --> 00:26:07,431 a chance to go fishing for a sample. 433 00:26:07,566 --> 00:26:11,332 Perfect, absolutely perfect shot. 434 00:26:11,469 --> 00:26:14,267 OK, noW We are ready to go ahead With this sample? 435 00:26:14,406 --> 00:26:17,967 OK, take care to hang on to the end of that. 436 00:26:21,680 --> 00:26:24,877 OK, looks good. 437 00:26:28,486 --> 00:26:31,250 We're at the top of that lava fall 438 00:26:31,389 --> 00:26:32,754 and it's in. 439 00:26:34,025 --> 00:26:36,892 Oh Jesus, that's moving. 440 00:26:39,931 --> 00:26:41,956 OK, l'm trying to get a good sample. 441 00:26:42,100 --> 00:26:43,761 Man it's hot. 442 00:26:48,006 --> 00:26:49,598 Come on baby. 443 00:26:51,142 --> 00:26:52,939 OK, We're coming up. 444 00:26:53,378 --> 00:26:55,209 We've got a big one. 445 00:26:57,048 --> 00:26:59,573 OK We're ready to pull and clinch. 446 00:26:59,718 --> 00:27:00,514 OK, here We go. 447 00:27:00,652 --> 00:27:05,055 1 , 2, 3. Let's go. 448 00:27:09,094 --> 00:27:09,992 That Was a good sample. 449 00:27:10,128 --> 00:27:11,493 Yeah. 450 00:27:13,331 --> 00:27:15,322 Anyone for tea? 451 00:27:20,138 --> 00:27:22,971 Routine analysis of fresh lava samples 452 00:27:23,108 --> 00:27:25,770 alloWs us to predict What the volcano might do next, 453 00:27:25,910 --> 00:27:28,208 but perhaps more significantly - 454 00:27:28,346 --> 00:27:29,335 some of these are still hot - 455 00:27:29,481 --> 00:27:31,608 more significantly in terms of, 456 00:27:31,750 --> 00:27:33,911 of Where all these basalts come from 457 00:27:34,052 --> 00:27:37,351 this stuff contains an extraordinary proportion of helium 3 458 00:27:37,489 --> 00:27:40,583 Which is relatively rare in volcanic rocks. 459 00:27:40,725 --> 00:27:44,855 NoW one might Wonder Where this helium 3 comes from. 460 00:27:44,996 --> 00:27:46,827 One source Where helium 3 is, 461 00:27:46,965 --> 00:27:48,193 is still present Within the Earth today 462 00:27:48,333 --> 00:27:49,698 is at the core mantle boundary 463 00:27:49,834 --> 00:27:53,167 and if that's the case then one might expect that this stuff 464 00:27:53,304 --> 00:27:55,499 came from Way doWn there. 465 00:28:03,415 --> 00:28:05,212 The composition of the lava indicates 466 00:28:05,350 --> 00:28:07,045 that it's come from mantle rock 467 00:28:07,185 --> 00:28:10,916 that has risen rapidly from deep doWn in the Earth, 468 00:28:11,056 --> 00:28:12,284 and there's another line of evidence 469 00:28:12,424 --> 00:28:15,416 that HaWaii sits above a plume. 470 00:28:21,499 --> 00:28:24,434 This evidence comes not from the erupting lava, 471 00:28:24,569 --> 00:28:28,300 but from the shape of the HaWaiian archipelago. 472 00:28:30,809 --> 00:28:33,277 One of the major clues that We are standing above a mantle plume 473 00:28:33,411 --> 00:28:35,311 is that the HaWaiian islands themselves 474 00:28:35,447 --> 00:28:37,210 form an almost perfectly linear chain 475 00:28:37,348 --> 00:28:40,010 that goes off to the north-West. 476 00:28:40,151 --> 00:28:42,346 The plume is sitting under the Pacific plate 477 00:28:42,487 --> 00:28:46,617 Which has been moving across it for 100 million years, 478 00:28:46,758 --> 00:28:49,784 so the volcanic islands the plume created in the past 479 00:28:49,928 --> 00:28:53,625 have been carried aWay by the moving plate. 480 00:28:55,567 --> 00:28:58,536 ln time an entire line of volcanic islands 481 00:28:58,670 --> 00:29:01,537 Was effectively burnt into the Pacific plate. 482 00:29:01,673 --> 00:29:04,073 ln fact this island and Kilauea volcano 483 00:29:04,209 --> 00:29:05,642 are moving off the centre of the plume 484 00:29:05,777 --> 00:29:08,439 and giving Way to a neW volcano Loihi 485 00:29:08,580 --> 00:29:09,842 Which is forming under Water 486 00:29:09,981 --> 00:29:12,950 about 15 miles to the south-east of this island 487 00:29:13,084 --> 00:29:16,212 and in about 200,000 years Loihi Will breech sea-level 488 00:29:16,354 --> 00:29:19,517 and become the next HaWaiian island. 489 00:29:36,374 --> 00:29:37,500 Once scientists realised 490 00:29:37,642 --> 00:29:40,110 that mantle plumes really do exist, 491 00:29:40,245 --> 00:29:42,907 they began to see them everywhere. 492 00:29:43,047 --> 00:29:44,674 Where the plumes are coming up 493 00:29:44,816 --> 00:29:46,613 they push up the surface a little bit 494 00:29:46,751 --> 00:29:49,345 and so What We've been able to do, 495 00:29:49,487 --> 00:29:50,818 quite recently actually, 496 00:29:50,955 --> 00:29:53,924 is to, to map the Whole of the, 497 00:29:54,058 --> 00:29:56,288 the convective circulation underneath the plates 498 00:29:56,427 --> 00:29:59,191 and you can see that very clearly here in the Pacific. 499 00:29:59,330 --> 00:30:02,356 Here's South America & North America & Australia 500 00:30:02,500 --> 00:30:04,695 and Japan and HaWaii in the middle 501 00:30:04,836 --> 00:30:06,827 and you can see these red patches 502 00:30:06,971 --> 00:30:08,666 Where plumes are coming up 503 00:30:08,807 --> 00:30:10,240 and the biggest of these is HaWaii 504 00:30:10,375 --> 00:30:11,740 and What you're looking at here 505 00:30:11,876 --> 00:30:13,366 essentially the fact that the sea floor's 506 00:30:13,511 --> 00:30:14,910 all being pushed up, right, 507 00:30:15,046 --> 00:30:17,514 by the plume coming up. 508 00:30:19,284 --> 00:30:21,878 So HaWaii oWes its existence to the fact 509 00:30:22,020 --> 00:30:23,715 that the plume beneath the island 510 00:30:23,855 --> 00:30:27,985 pushes up the overlying plates into a large dome 511 00:30:28,126 --> 00:30:29,525 and Where this happens on land, 512 00:30:29,661 --> 00:30:33,825 the effects can be unexpected and far-reaching. 513 00:30:34,899 --> 00:30:37,367 These patterns make sort of dimples 514 00:30:37,502 --> 00:30:39,595 and even though they're very small 515 00:30:39,737 --> 00:30:42,672 they control the, the, the floW of the, 516 00:30:42,807 --> 00:30:45,503 of the largest rivers on Earth 517 00:30:45,643 --> 00:30:50,137 and probably one of the best examples is, is the Nile 518 00:30:50,281 --> 00:30:52,715 Where it floWs out from Lake Victoria here, 519 00:30:52,851 --> 00:30:56,116 it floWs out through the depression, the dimple 520 00:30:56,254 --> 00:30:58,051 betWeen these tWo plumes here 521 00:30:58,189 --> 00:30:59,656 and then goes northWards 522 00:30:59,791 --> 00:31:03,249 and it goes again through exactly betWeen these tWo 523 00:31:03,394 --> 00:31:05,885 and then goes off into the Mediterranean, 524 00:31:06,030 --> 00:31:09,830 so the convective circulation from the plumes 525 00:31:09,968 --> 00:31:11,560 is actually much more important 526 00:31:11,703 --> 00:31:14,399 in terms of hoW rivers floW than We thought before 527 00:31:14,539 --> 00:31:18,635 and We can see this pattern of, of, of rising plumes 528 00:31:18,776 --> 00:31:22,974 all over the Earth's surface everywhere We look. 529 00:31:27,685 --> 00:31:30,984 So beneath the crust, beneath the plates 530 00:31:31,122 --> 00:31:34,819 the rocks of the mantle move to their oWn rhythm. 531 00:31:38,096 --> 00:31:40,929 Rising from deep Within the planet's interior 532 00:31:41,065 --> 00:31:45,229 plumes of hot rock push up toWards the surface. 533 00:31:48,139 --> 00:31:49,936 Less than 20 years ago plumes 534 00:31:50,074 --> 00:31:53,202 Were no more than a theoretical possibility. 535 00:31:53,344 --> 00:31:55,676 Today they are recognised as major features 536 00:31:55,813 --> 00:31:58,976 of the planet Which can remain stable for tens, 537 00:31:59,117 --> 00:32:02,018 perhaps hundreds of millions of years, 538 00:32:02,153 --> 00:32:03,381 and it's becoming clear 539 00:32:03,521 --> 00:32:06,319 that over Earth history they've played a major role 540 00:32:06,457 --> 00:32:09,915 in shaping the surface of the planet. 541 00:32:35,453 --> 00:32:38,388 These are the Kanheri Caves in Western lndia, 542 00:32:38,523 --> 00:32:41,583 a large temple complex carved by Bhuddist monks 543 00:32:41,726 --> 00:32:44,923 out of a single vast lava floW. 544 00:32:45,063 --> 00:32:47,531 This floW is the result of a volcanic eruption 545 00:32:47,665 --> 00:32:49,758 far bigger than anything humanity 546 00:32:49,901 --> 00:32:52,563 has ever Witnessed. 547 00:32:52,704 --> 00:32:55,104 Yet this is just one of dozens of such floWs 548 00:32:55,239 --> 00:32:58,572 Which blanket much of Western lndia. 549 00:32:59,210 --> 00:33:00,871 Piled one on top of the other, 550 00:33:01,012 --> 00:33:03,310 they form this extraordinary mountain range, 551 00:33:03,448 --> 00:33:06,212 the so-called Deccan Traps. 552 00:33:08,886 --> 00:33:13,346 Here is evidence of vulcanism on a truly gigantic scale. 553 00:33:15,360 --> 00:33:17,385 Most geologists assumed that the eruptions 554 00:33:17,528 --> 00:33:18,825 Which produced this landscape 555 00:33:18,963 --> 00:33:22,524 must have continued for tens of millions of years, 556 00:33:23,134 --> 00:33:24,829 but in 1985 557 00:33:24,969 --> 00:33:27,403 the French geophysicist Vincent Courtillot 558 00:33:27,538 --> 00:33:29,631 came to the Deccan. 559 00:33:29,774 --> 00:33:32,675 He Was interested in the Way the Earth's magnetic field 560 00:33:32,810 --> 00:33:35,176 has changed over time. 561 00:33:35,880 --> 00:33:37,370 When We first came here our purpose 562 00:33:37,515 --> 00:33:38,948 Was to measure the magnetisation 563 00:33:39,083 --> 00:33:41,210 of the lava in the Deccan. 564 00:33:41,352 --> 00:33:44,412 When a lava floW cools beloW a certain critical temperature 565 00:33:44,555 --> 00:33:48,082 it Will lock in the direction of the Earth's magnetic field. 566 00:33:48,226 --> 00:33:50,023 lt has a memory of What the Earth's field 567 00:33:50,161 --> 00:33:52,095 Was like at the time of cooling 568 00:33:52,230 --> 00:33:54,130 and We knoW the Earth's field has been reversing, 569 00:33:54,265 --> 00:33:55,664 flipping many times, 570 00:33:55,800 --> 00:33:59,258 approximately once every million years. 571 00:34:01,039 --> 00:34:03,132 So frozen into the lava layers 572 00:34:03,274 --> 00:34:06,675 should be a history of these magnetic reversals. 573 00:34:06,811 --> 00:34:09,109 Courtillot Was expecting to find dozens of them 574 00:34:09,247 --> 00:34:12,341 recorded in the Deccan lava floWs. 575 00:34:17,188 --> 00:34:20,555 What he actually found astonished him. 576 00:34:29,700 --> 00:34:31,327 When We came here the estimates 577 00:34:31,469 --> 00:34:32,993 for ages of the Deccan lava 578 00:34:33,137 --> 00:34:36,368 ranged over as Wide as 50 million years, 579 00:34:36,507 --> 00:34:38,407 so We expected to have recorded 580 00:34:38,543 --> 00:34:41,842 maybe 50/60 reversals of the field. 581 00:34:42,346 --> 00:34:43,938 When We had completed the sampling 582 00:34:44,082 --> 00:34:45,481 and the Work in our laboratory 583 00:34:45,616 --> 00:34:47,345 much to our surprise We found 584 00:34:47,485 --> 00:34:50,386 that only 2 reversals had been frozen 585 00:34:50,521 --> 00:34:52,079 in the lava. 586 00:34:52,223 --> 00:34:54,555 That only 2 reversals had been recorded 587 00:34:54,692 --> 00:34:56,819 Was proof that the Whole vulcanism 588 00:34:56,961 --> 00:35:00,192 could not have lasted much more than say a million years. 589 00:35:00,331 --> 00:35:02,526 This Was an enormous out rate indeed. 590 00:35:02,667 --> 00:35:05,261 l could only have been caused by the massive eruption 591 00:35:05,403 --> 00:35:08,668 at the Earth's surface of a mantle plume head. 592 00:35:11,175 --> 00:35:13,040 Enough lava Was erupted here 593 00:35:13,177 --> 00:35:14,906 to cover the United States 594 00:35:15,046 --> 00:35:18,413 to a depth of nearly one kilometre. 595 00:35:21,152 --> 00:35:24,212 Vincent Courtillot believes such a stupendous event 596 00:35:24,355 --> 00:35:26,983 can only have been the result of a poWerful neW plume 597 00:35:27,125 --> 00:35:28,422 splitting the crust 598 00:35:28,559 --> 00:35:30,959 and breaking through to the surface. 599 00:35:31,095 --> 00:35:32,153 When a mantle plume 600 00:35:32,296 --> 00:35:33,695 comes to the surface of the Earth 601 00:35:33,831 --> 00:35:36,629 the plume head Will bulge, deform the crust 602 00:35:36,767 --> 00:35:38,826 and then burst out as a lava floW 603 00:35:38,970 --> 00:35:41,302 With enormous volumes. 604 00:35:42,740 --> 00:35:45,174 These plumes Which are born inside the mantle 605 00:35:45,309 --> 00:35:47,038 and erupt to th surface of the Earth 606 00:35:47,178 --> 00:35:49,806 Will modif the Whole landscape of a continent 607 00:35:49,947 --> 00:35:52,347 in a very durable fashion. 608 00:35:57,121 --> 00:36:00,147 And it hasn't happened only in lndia. 609 00:36:02,827 --> 00:36:07,389 lceland too shoWs the unmistakable fingerprints of a plume, 610 00:36:07,532 --> 00:36:10,660 but here the plume has done more than change the landscape. 611 00:36:10,801 --> 00:36:11,665 There's evidence that 612 00:36:11,802 --> 00:36:13,929 it's changed the motion of the plates, 613 00:36:14,071 --> 00:36:17,768 reshaping an entire region of the globe. 614 00:36:25,750 --> 00:36:29,151 lceland occupies a unique position on the Earth. 615 00:36:29,287 --> 00:36:31,517 The fissure that runs across the island 616 00:36:31,656 --> 00:36:34,887 is in fact, part of the vast mid-ocean ridge, 617 00:36:35,026 --> 00:36:36,891 the great rift that runs up the centre 618 00:36:37,028 --> 00:36:38,052 of the Atlantic 619 00:36:38,196 --> 00:36:41,393 Where the ocean basin is sloWly opening up. 620 00:36:41,532 --> 00:36:43,022 lceland is above Water 621 00:36:43,167 --> 00:36:47,126 only because it is buoyed up by a mantle plume. 622 00:36:54,612 --> 00:36:57,775 The influence of that plume is felt right across the island 623 00:36:57,915 --> 00:37:00,475 in all sorts of Ways. 624 00:37:02,720 --> 00:37:04,585 The Whole of lceland oWes its existence 625 00:37:04,722 --> 00:37:06,189 to the mantle plume. 626 00:37:06,324 --> 00:37:09,760 lt's elevating the Whole area something like 500 metres 627 00:37:09,894 --> 00:37:11,725 above sea-level Where We're standing noW, 628 00:37:11,862 --> 00:37:13,523 but the very hottest part of the plume 629 00:37:13,664 --> 00:37:16,098 is right behind me underneath Vatna Jokull, 630 00:37:16,234 --> 00:37:18,725 a huge glacier. 631 00:37:19,203 --> 00:37:20,101 NoW the glacier's there 632 00:37:20,238 --> 00:37:22,832 because that's the very highest point of lceland. 633 00:37:22,974 --> 00:37:23,804 lt's the highest point of lceland 634 00:37:23,941 --> 00:37:26,239 because the hottest material is underneath. 635 00:37:26,377 --> 00:37:27,366 The mantle plume itself 636 00:37:27,511 --> 00:37:29,741 is hotter than the rest of the mantle round it 637 00:37:29,880 --> 00:37:32,940 so it's a little bit more buoyant and that buoyancy, 638 00:37:33,084 --> 00:37:34,312 because it's less dense, 639 00:37:34,452 --> 00:37:35,714 pushes up that region 640 00:37:35,853 --> 00:37:38,014 and makes the very highest region, 641 00:37:38,155 --> 00:37:39,884 the region Where the glacier forms. 642 00:37:40,024 --> 00:37:41,958 NoW that particular glacier is the, 643 00:37:42,093 --> 00:37:45,028 the largest glacier outside the Arctic or the Antarctic, 644 00:37:45,162 --> 00:37:46,322 so it's a big feature 645 00:37:46,464 --> 00:37:48,864 and it's another 1 ,000 metres above us, 646 00:37:49,000 --> 00:37:51,468 so it's something like 4,000 metres 647 00:37:51,602 --> 00:37:54,093 above its normal level. 648 00:37:54,572 --> 00:37:56,767 lt's sort of ironic that the coldest part of the lceland 649 00:37:56,907 --> 00:38:00,468 is sitting right above the hottest part of the mantle. 650 00:38:01,846 --> 00:38:05,213 The hot mantle plume also creates volcanoes, 651 00:38:05,349 --> 00:38:09,445 a dangerous combination of fire and ice. 652 00:38:09,587 --> 00:38:11,384 ln fact there's 5 major volcanic systems 653 00:38:11,522 --> 00:38:12,921 underneath Vatna Jokull 654 00:38:13,057 --> 00:38:14,615 and it's those volcanic systems 655 00:38:14,759 --> 00:38:15,817 that have been responsible 656 00:38:15,960 --> 00:38:17,086 for some of the biggest eruptions 657 00:38:17,228 --> 00:38:19,788 in lceland over the past centuries. 658 00:38:19,930 --> 00:38:22,262 ln fact the, the biggest historic eruption 659 00:38:22,400 --> 00:38:26,530 in the World occurred from a volcano underneath Vatna Jokull 660 00:38:26,671 --> 00:38:28,036 in 1 783 661 00:38:28,172 --> 00:38:29,662 and that particular eruption 662 00:38:29,807 --> 00:38:31,035 didn't actually kill anybody 663 00:38:31,175 --> 00:38:34,167 from the lava that floWed out from it 664 00:38:34,312 --> 00:38:36,212 but such a lot of dust and ash 665 00:38:36,347 --> 00:38:40,044 and other toxic gases Were erupted at the same time 666 00:38:40,184 --> 00:38:42,209 that the majority of the livestock 667 00:38:42,353 --> 00:38:44,321 on lceland Was, Was killed 668 00:38:44,455 --> 00:38:47,982 and the next Winter in 1 783 and 1 784 669 00:38:48,125 --> 00:38:51,151 25% of the population of lceland died 670 00:38:51,295 --> 00:38:54,230 as a direct result of that eruption. 671 00:38:59,804 --> 00:39:01,396 ln 1996 672 00:39:01,539 --> 00:39:05,771 the volcanoes under Vatna Jokull spoke once again. 673 00:39:05,910 --> 00:39:07,639 This time fortunately the ash fall 674 00:39:07,778 --> 00:39:10,872 Was mainly confined to the ice cap itself, 675 00:39:11,015 --> 00:39:13,779 but as the heat from the eruption melted the ice above, 676 00:39:13,918 --> 00:39:16,546 a tremendous deluge of melt Water floWed out 677 00:39:16,687 --> 00:39:20,316 from under the glacier sWeeping all before it. 678 00:39:30,701 --> 00:39:32,726 As roads and bridges Were sWept aWay 679 00:39:32,870 --> 00:39:34,667 lcelanders Were once more reminded 680 00:39:34,805 --> 00:39:37,365 that the plume that has created their homeland 681 00:39:37,508 --> 00:39:41,069 also harbours aWesome destructive energy. 682 00:39:53,257 --> 00:39:54,690 lt's the poWer of mantle plumes 683 00:39:54,825 --> 00:39:56,315 to drive enormous changes to 684 00:39:56,460 --> 00:40:00,920 continents and oceans that intrigues geologists. 685 00:40:01,065 --> 00:40:03,363 The material erupted from its volcanoes 686 00:40:03,501 --> 00:40:05,935 has built up the crust of lceland, 687 00:40:06,070 --> 00:40:07,298 but scientists noW suspect 688 00:40:07,438 --> 00:40:09,770 that the plume may have shaped the environment here 689 00:40:09,907 --> 00:40:12,501 in a far more profound Way. 690 00:40:12,643 --> 00:40:14,201 They've started to ask themselves 691 00:40:14,345 --> 00:40:15,937 Whether it's merely coincidence 692 00:40:16,080 --> 00:40:18,014 that here a mantle plumesits right 693 00:40:18,149 --> 00:40:21,175 underneath the great mid-ocean ridge. 694 00:40:21,318 --> 00:40:23,548 Could the lceland plume have caused he rift 695 00:40:23,687 --> 00:40:25,985 in the first place and triggered the opening 696 00:40:26,123 --> 00:40:30,355 of the Atlantic 58 million years ago? 697 00:40:34,865 --> 00:40:37,698 Clues to What happened then can still be found, 698 00:40:37,835 --> 00:40:42,067 not in lceland but on the West coast of Scotland. 699 00:40:48,179 --> 00:40:50,773 Here geologists have found that the Western lsles 700 00:40:50,915 --> 00:40:53,907 are largely composed of volcanic rock. 701 00:40:54,051 --> 00:40:57,543 Above the Atlantic surf rise great cliffs of basalt 702 00:40:57,688 --> 00:41:01,988 With its characteristic hexagonal columns. 703 00:41:04,795 --> 00:41:06,422 All these formations have been dated 704 00:41:06,564 --> 00:41:08,429 to a relatively brief period, 705 00:41:08,566 --> 00:41:11,399 58 million years ago. 706 00:41:11,535 --> 00:41:13,765 Volcanic activity on this scale is evidence 707 00:41:13,904 --> 00:41:15,201 for an event similar to that 708 00:41:15,339 --> 00:41:17,364 Which caused the Deccan Traps, 709 00:41:17,508 --> 00:41:21,535 a neW mantle plume head Which split the crust 710 00:41:24,048 --> 00:41:26,744 and 2,000 kilometres aWay to the West, 711 00:41:26,884 --> 00:41:31,514 Greenland too has similar huge basalt formations. 712 00:41:33,424 --> 00:41:35,790 So the rocks on both sides of the Atlantic 713 00:41:35,926 --> 00:41:37,951 bear Witness to the impact of a plume 714 00:41:38,095 --> 00:41:40,825 from deep Within the mantle. 715 00:41:46,871 --> 00:41:50,170 As the plume pushed up against the crust it split, 716 00:41:50,307 --> 00:41:53,299 rifting Greenland off from Europe. 717 00:41:53,811 --> 00:41:54,800 Once split, 718 00:41:54,945 --> 00:41:57,413 Europe and Greenland continued to move apart 719 00:41:57,548 --> 00:42:01,644 creating a neW ocean basin in the North Atlantic. 720 00:42:01,785 --> 00:42:03,844 Ever since then the plume has been sitting 721 00:42:03,988 --> 00:42:06,923 under the rift producing lceland, 722 00:42:07,057 --> 00:42:10,356 the largest volcanic island on the planet. 723 00:42:22,506 --> 00:42:25,498 The plume under lceland has produced some enormous changes 724 00:42:25,643 --> 00:42:28,510 in the 60 million years or so since it started to rise 725 00:42:28,646 --> 00:42:30,739 through the Earth's mantle. 726 00:42:30,881 --> 00:42:33,315 Without that event in the planet's interior 727 00:42:33,450 --> 00:42:34,940 the Whole of the northern hemisphere 728 00:42:35,085 --> 00:42:36,609 Would look totally different 729 00:42:36,754 --> 00:42:39,985 and North America Would still be joined to Europe, 730 00:42:40,124 --> 00:42:42,820 but plumes may have even more significant effects 731 00:42:42,960 --> 00:42:45,895 than the shaping of the planet's surface. 732 00:42:48,265 --> 00:42:50,597 Some scientists are beginning to suspect 733 00:42:50,734 --> 00:42:54,067 that they may change the course of evolution. 734 00:43:16,760 --> 00:43:19,661 The vast Deccan lava floWs Were all erupted in, 735 00:43:19,797 --> 00:43:23,858 geologically speaking, a blink of an eye, but When? 736 00:43:24,001 --> 00:43:26,026 Usually they may extend up to 100 metres 737 00:43:26,170 --> 00:43:28,604 you knoW and if We look very carefully... 738 00:43:28,739 --> 00:43:30,969 Palaeontologist Ashok Sahni 739 00:43:31,108 --> 00:43:33,736 has helped Vincent Courtillot pin doWn exactly 740 00:43:33,877 --> 00:43:36,778 When the plume head hit the surface. 741 00:43:37,781 --> 00:43:42,775 Could this event have had global consequences for living things? 742 00:43:45,289 --> 00:43:48,281 These here are the teeth of mammals. 743 00:43:48,425 --> 00:43:53,021 These mammalian teeth Were recovered in sediments 744 00:43:53,163 --> 00:43:55,688 lying in-betWeen the Deccan floWs. 745 00:43:55,833 --> 00:43:58,199 They belong to very primitive mammals 746 00:43:58,335 --> 00:44:02,396 Which are related to the present-day shreWs. 747 00:44:02,539 --> 00:44:06,031 These mammals evolved at a fairly fast rate 748 00:44:06,176 --> 00:44:07,700 and it's possible to tell 749 00:44:07,845 --> 00:44:10,871 from these teeth exactly Where We are in time. 750 00:44:11,015 --> 00:44:13,108 They give us a date 751 00:44:13,250 --> 00:44:16,447 for the initiation of the Deccan volcanics 752 00:44:16,587 --> 00:44:21,854 and this date happens to be 65 million years. 753 00:44:21,992 --> 00:44:25,155 They belong to an era that is What 754 00:44:25,295 --> 00:44:27,126 We call the Cretaceous period 755 00:44:27,264 --> 00:44:30,233 and surprisingly it is this Cretaceous period, 756 00:44:30,367 --> 00:44:31,994 the end of this Cretaceous period 757 00:44:32,136 --> 00:44:36,197 Which also saW the extinction of the dinosaurs. 758 00:45:00,497 --> 00:45:02,863 lf you ask someone What killed the dinosaurs 759 00:45:03,000 --> 00:45:04,729 he or she is likely to tell you Well, 760 00:45:04,868 --> 00:45:06,392 it Was the impact of an asteroid 761 00:45:06,537 --> 00:45:09,062 and they might Well be right. 762 00:45:09,206 --> 00:45:12,073 But that cannot explain all of the extinctions. 763 00:45:12,209 --> 00:45:13,471 Palaeontologists tell us that 764 00:45:13,610 --> 00:45:15,703 Well before the impact hit the earth 765 00:45:15,846 --> 00:45:18,212 species had begun sloWly disappearing. 766 00:45:18,348 --> 00:45:19,337 When l mean sloWly 767 00:45:19,483 --> 00:45:21,178 l mean in the course of tens of thousands 768 00:45:21,318 --> 00:45:23,013 or hundreds of thousands of years. 769 00:45:23,153 --> 00:45:26,554 This is precisely the timescale of the Deccan eruptions. 770 00:45:26,690 --> 00:45:29,853 This is What makes me prefer that explanation. 771 00:45:31,729 --> 00:45:34,425 As the large plume head came from inside the Earth 772 00:45:34,565 --> 00:45:38,399 it started erupting lava floW after lava floW. 773 00:45:41,071 --> 00:45:42,834 You should imagine these lava floWs 774 00:45:42,973 --> 00:45:47,034 pumping into the atmosphere vast amounts of gases 775 00:45:49,012 --> 00:45:51,071 sulphur dioxide, carbon dioxide, 776 00:45:51,215 --> 00:45:53,479 chlorine and also large amounts 777 00:45:53,617 --> 00:45:56,518 of dust obscuring the skies. Obscurity Would cause cold, 778 00:45:56,653 --> 00:45:59,588 possibly freezing and then acid rains Would folloW. 779 00:45:59,723 --> 00:46:02,487 Real hell everywhere. 780 00:46:09,166 --> 00:46:11,134 And When the Deccan had finished erupting 781 00:46:11,268 --> 00:46:13,429 60% of the species had disappeared 782 00:46:13,570 --> 00:46:16,130 from the surface of the Earth. 783 00:46:19,409 --> 00:46:22,936 Among the survivors Were those tiny shreW-like mammals, 784 00:46:23,080 --> 00:46:24,547 our oWn ancestors, 785 00:46:24,681 --> 00:46:26,546 Who Were to flourish in a World freed 786 00:46:26,683 --> 00:46:29,811 from the grip of the large reptiles. 787 00:46:33,023 --> 00:46:35,082 lf Vincent Courtillot is right, 788 00:46:35,225 --> 00:46:38,626 then in a sense We human beings oWe our existence 789 00:46:38,762 --> 00:46:41,788 to events deep Within the Earth. 790 00:46:43,066 --> 00:46:44,590 The link betWeen the Earth's activity 791 00:46:44,735 --> 00:46:45,997 and the course of evolution 792 00:46:46,136 --> 00:46:49,731 is something We'll be exploring later in the series. 793 00:47:00,150 --> 00:47:02,812 The scientists Who've explored the Earth's interior 794 00:47:02,953 --> 00:47:05,786 have made a profound discovery. 795 00:47:05,923 --> 00:47:07,550 Beneath all the complex changes 796 00:47:07,691 --> 00:47:09,352 We see at the surface 797 00:47:09,493 --> 00:47:11,893 there is an underlying simplicity - 798 00:47:12,029 --> 00:47:15,692 the vast churning heat engine of the Earth's mantle, 799 00:47:15,833 --> 00:47:19,132 an engine Which drives the dance of plate tectonics 800 00:47:19,269 --> 00:47:20,896 and reforms our World 801 00:47:21,038 --> 00:47:23,939 in a myriad different Ways. 802 00:47:27,511 --> 00:47:29,536 Here in lceland scientists can Witness 803 00:47:29,680 --> 00:47:33,241 the Workings of that engine at first-hand. 804 00:47:33,851 --> 00:47:35,944 As the Earth cools by convection 805 00:47:36,086 --> 00:47:40,580 so the continents shift over its surface and rift apart, 806 00:47:40,724 --> 00:47:44,319 but plate tectonics means that continents don't just separate, 807 00:47:44,461 --> 00:47:46,759 they must also collide 808 00:47:46,897 --> 00:47:49,457 and it's What happens When tWo continents collide 809 00:47:49,600 --> 00:47:52,933 that's the subject of our next programme.