1 00:00:00,000 --> 00:00:04,162 WWW.MY-SUBS.CO 1 00:00:12,280 --> 00:00:14,340 Whoo hoo! 2 00:00:14,375 --> 00:00:16,807 I'm here! 3 00:00:16,842 --> 00:00:19,205 This is it. 4 00:00:19,240 --> 00:00:21,040 There's the top just there. 5 00:00:24,440 --> 00:00:27,800 Ah, this is fantastic! What a view! 6 00:00:27,835 --> 00:00:29,320 I'm back. 7 00:00:30,960 --> 00:00:33,640 I was last here 25 years ago. 8 00:00:33,675 --> 00:00:35,765 25 years! 9 00:00:35,800 --> 00:00:38,280 And somewhere around here I left my hammer. 10 00:00:38,315 --> 00:00:41,880 Ah, look at this! Here we are! 11 00:00:41,915 --> 00:00:44,685 Whoo! 12 00:00:44,720 --> 00:00:46,805 Would you look at this? 13 00:00:46,840 --> 00:00:49,365 Look at this view. This is what I remember. 14 00:00:49,400 --> 00:00:54,080 This is our ancient heritage laid out before our very eyes. 15 00:00:57,280 --> 00:01:01,000 Scotland's landscape has an epic and violent past. 16 00:01:03,200 --> 00:01:06,760 Hidden in these mountains and glens is the history of the planet. 17 00:01:06,795 --> 00:01:10,805 I'm going to show you how this landscape was used 18 00:01:10,840 --> 00:01:17,440 by a bunch of brilliant, maverick, eccentric scientists to solve the greatest mysteries of the Earth. 19 00:01:21,280 --> 00:01:24,760 I'm following in the footsteps of these pioneers 20 00:01:24,795 --> 00:01:28,240 who blazed a trail where no-one had been before. 21 00:01:34,880 --> 00:01:39,280 They showed vision and determination... 22 00:01:41,160 --> 00:01:44,365 .. to piece together baffling evidence 23 00:01:44,400 --> 00:01:48,880 and uncover the forces that shape our world. 24 00:01:48,915 --> 00:01:51,565 Wow! God, that's so hot! 25 00:01:51,600 --> 00:01:54,805 It's all out there if you know what to look for. 26 00:01:54,840 --> 00:01:59,320 Written into the Scottish landscape is the story of the entire planet. 27 00:02:16,920 --> 00:02:20,000 The remote northwest Highlands of Scotland. 28 00:02:25,080 --> 00:02:31,120 Ever since people were first drawn to these mountains, they wondered how they were formed. 29 00:02:31,155 --> 00:02:33,640 How did they come to be so high? 30 00:02:33,675 --> 00:02:35,920 So dramatic? 31 00:02:45,520 --> 00:02:50,160 For thousands of years, people believed these were the work of a divine creator. 32 00:02:55,120 --> 00:02:59,960 But by the 19th century, a new branch of science had emerged - geology. 33 00:03:02,400 --> 00:03:07,960 Scientists began to ask bold new questions about how our Earth was formed. 34 00:03:09,480 --> 00:03:16,240 In 1855, a geologist named Roderick Murchison was on his way to the Highlands. 35 00:03:17,920 --> 00:03:20,605 Roderick Murchison was an establishment man. 36 00:03:20,640 --> 00:03:25,080 He'd started off in the Army and then he married into money, and it was at his wife's suggestion 37 00:03:25,115 --> 00:03:31,160 that he took up geology as a more purposeful pursuit than his hobby of fox hunting! 38 00:03:34,080 --> 00:03:36,525 Murchison was the most famous geologist of the day. 39 00:03:36,560 --> 00:03:43,760 Head of the British Geological Survey, he was an authority throughout the British Empire. 40 00:03:43,795 --> 00:03:48,000 And he started the process that led, over the next century, 41 00:03:48,035 --> 00:03:52,445 to a true understanding of the way the planet works. 42 00:03:52,480 --> 00:03:58,880 Murchison believed that he could explain how the magnificent Scottish landscape had been formed. 43 00:04:04,760 --> 00:04:12,080 Murchison has come up his own big grand scheme, which he claims can unlock Scotland's geological past, 44 00:04:12,115 --> 00:04:19,680 the story of its landscapes and mountains, and it's based on one very simple idea. 45 00:04:24,440 --> 00:04:28,800 The start point for Murchison's grand scheme was very logical. 46 00:04:31,920 --> 00:04:33,965 All of Scotland's mountains and landscape 47 00:04:34,000 --> 00:04:39,040 were made up of layers of rock, laid one on top of another over time. 48 00:04:43,640 --> 00:04:46,720 There was much to be said for this idea. 49 00:04:48,640 --> 00:04:54,800 You can see why if you come to one of the most dramatic and inaccessible landforms in Britain... 50 00:04:56,320 --> 00:05:00,720 .. the Old Man of Stoer on the northwest coast of Scotland. 51 00:05:02,760 --> 00:05:08,285 First, there's just the small matter of getting to the top. 52 00:05:08,320 --> 00:05:13,360 I dare say that what I'm about to do wouldn't have fazed Murchison at all 53 00:05:13,395 --> 00:05:19,080 but, for me, this is a bit of a leap into the blue, really. 54 00:05:19,115 --> 00:05:21,320 Literally! 55 00:05:24,080 --> 00:05:28,800 What could possibly, possibly go wrong? 56 00:05:28,835 --> 00:05:30,445 Ah! 57 00:05:30,480 --> 00:05:32,540 Look at this! 58 00:05:32,575 --> 00:05:34,600 Whoo hoo! 59 00:05:37,440 --> 00:05:39,960 Oh, it's quite far, isn't it? 60 00:05:39,995 --> 00:05:42,360 Blooming 'eck! 61 00:05:45,280 --> 00:05:47,445 This may seem rather extreme, 62 00:05:47,480 --> 00:05:54,160 but when I get there, this stack will show something very important about how the landscape is formed. 63 00:05:54,195 --> 00:05:56,400 Whoo! Ah! 64 00:06:00,120 --> 00:06:02,000 Final push. 65 00:06:04,880 --> 00:06:06,360 Here we go. Let me touch it. 66 00:06:07,360 --> 00:06:09,600 The stack of Stoer! 67 00:06:10,000 --> 00:06:12,800 I'm here! Almost! 68 00:06:21,880 --> 00:06:26,400 This sea stack I'm standing on has been scoured by the sea 69 00:06:26,435 --> 00:06:30,445 so that it's completely detached from the headland 70 00:06:30,480 --> 00:06:36,320 and that means it gives this wonderful three dimensional slice right down through the landscape. 71 00:06:36,355 --> 00:06:40,760 You feel as if you are on the top of the world here! 72 00:06:46,720 --> 00:06:53,240 As I abseil down this stack, a close look reveals something crucial about the way it was created. 73 00:06:56,720 --> 00:07:00,325 These bands of rock around me are like layers on a cake. 74 00:07:00,360 --> 00:07:06,680 Murchison and the early geologists recognised that rocks like these started out as soft sediment 75 00:07:06,715 --> 00:07:09,085 laid down by water and then solidified, 76 00:07:09,120 --> 00:07:13,005 building up one after another over millions of years. 77 00:07:13,040 --> 00:07:19,160 So that means that the rocks 20 metres below me are millions of years older than the ones here 78 00:07:19,195 --> 00:07:24,560 and maybe tens of millions of years older than the ones at the top of the stack. 79 00:07:28,640 --> 00:07:34,880 This idea of young rock on top of old was the foundation for Murchison's thinking. 80 00:07:37,680 --> 00:07:40,040 But he took it much further. 81 00:07:42,720 --> 00:07:48,600 As he travelled across Scotland, he saw how exposed rock lay in angled layers. 82 00:07:51,600 --> 00:07:54,605 He believed these layers were piled up in a simple pattern, 83 00:07:54,640 --> 00:07:59,200 with the oldest rocks on the west of the country and the youngest rocks on the east. 84 00:08:02,040 --> 00:08:05,605 For Murchison, it was all so beautifully simple. 85 00:08:05,640 --> 00:08:08,720 He was convinced that the northwest Highlands were built up 86 00:08:08,755 --> 00:08:11,560 layer upon layer, just like this stack of slate here. 87 00:08:11,595 --> 00:08:14,965 And if you walked inland from west to east, 88 00:08:15,000 --> 00:08:17,960 you travelled through a cross section of younger and younger rocks. 89 00:08:17,995 --> 00:08:22,640 Because Murchison was the top dog of geology for 40 years, 90 00:08:22,675 --> 00:08:26,560 this grand, but simplistic scheme becomes dogma. 91 00:08:29,240 --> 00:08:34,080 It was all very logical and plausible and the evidence seemed to stack up. 92 00:08:35,920 --> 00:08:40,205 Murchison was so sure he was right, he used his influence 93 00:08:40,240 --> 00:08:44,640 to out-manoeuvre his rivals and quash any alternative theories. 94 00:08:46,160 --> 00:08:48,560 But if only it had been that simple. 95 00:08:50,640 --> 00:08:55,005 That mountainside over there seems at first glance to be the perfect example 96 00:08:55,040 --> 00:09:00,205 of Murchison's regular succession of layers of rock stacked on top of each other. 97 00:09:00,240 --> 00:09:05,760 But actually a discovery made in the hills around here would shatter that neat little picture. 98 00:09:21,160 --> 00:09:26,100 In 1882, a former schoolteacher came to a windblown shepherd's hut 99 00:09:26,135 --> 00:09:31,040 overlooking Loch Eriboll on the very tip of Scotland's north coast. 100 00:09:34,320 --> 00:09:40,480 Charles Lapworth was a passionate amateur geologist, modest and self-taught. 101 00:09:41,480 --> 00:09:46,880 What he discovered here would demolish Murchison's theory. 102 00:09:50,920 --> 00:09:54,285 When Lapworth came here, he stayed in this old shepherd's hut 103 00:09:54,320 --> 00:10:00,005 and for weeks braved the elements and went up daily wandering into the hills to do his work. 104 00:10:00,040 --> 00:10:06,560 And the key to the phenomenal success that he had up in those hills was his painstaking methods. 105 00:10:06,595 --> 00:10:13,320 He even would wear this special coat which had all these pockets in it. 106 00:10:13,355 --> 00:10:15,885 It's kind of like a portable filing cabinet! 107 00:10:15,920 --> 00:10:22,485 And in there he would collect little samples of rocks and samples of fossils and tuck them away. 108 00:10:22,520 --> 00:10:28,840 That allowed him to cover the ground inch by inch, collecting samples as he went in incredible detail, 109 00:10:28,875 --> 00:10:34,800 far more detail than that practised by the so-called expert geologists of the time. 110 00:10:37,200 --> 00:10:41,280 Lapworth suspected that Murchison's theory was too simplistic 111 00:10:41,315 --> 00:10:45,725 and he was unwilling to accept the established view. 112 00:10:45,760 --> 00:10:51,160 So he set off into the hills in a bid to solve the riddle of the rocks. 113 00:11:02,720 --> 00:11:10,080 With little more than a compass and a handful of tools, for six weeks, he trudged over these hillsides. 114 00:11:10,115 --> 00:11:11,845 WIND BLOWING 115 00:11:11,880 --> 00:11:17,800 Rob Butler has been studying the very same mountains around Loch Eriboll for decades. 116 00:11:17,835 --> 00:11:21,440 Do you think Lapworth did this - whoo hoo! 117 00:11:25,400 --> 00:11:29,320 How on earth do you work in these conditions? It's unbelievable! 118 00:11:29,355 --> 00:11:31,285 It's a little light breeze, a light breeze! 119 00:11:31,320 --> 00:11:34,285 A light breeze! It's the strongest wind I've ever had! 120 00:11:34,320 --> 00:11:38,080 I hope you had your porridge for breakfast. Weighing me down! 121 00:11:41,120 --> 00:11:43,005 Lapworth was driven. 122 00:11:43,040 --> 00:11:47,960 He surveyed the landscape in much more detail than the Victorian professionals. 123 00:11:49,480 --> 00:11:53,405 And on this cliff face on the flanks of Ben Arnabol, 124 00:11:53,440 --> 00:11:58,720 he found the evidence that changed our idea of how mountains were formed. 125 00:11:58,755 --> 00:12:01,800 So, is this it? Yeah, this is where Lapworth came. 126 00:12:01,835 --> 00:12:04,525 Fantastic. Yeah. Let's go and have a look. 127 00:12:04,560 --> 00:12:09,645 You can imagine Lapworth seeing this place, and he could recognise 128 00:12:09,680 --> 00:12:14,920 these should be simply layered and they should simply go up into younger and younger and younger rocks. 129 00:12:14,955 --> 00:12:19,600 That's what Murchison thought - that it just goes up and up. But up there, 130 00:12:19,635 --> 00:12:23,677 he went, hang on a minute! Those don't look like younger rocks to me! 131 00:12:23,712 --> 00:12:27,856 That stuff is the oldest rocks in Britain, so how could you possibly 132 00:12:27,891 --> 00:12:31,965 get the old rocks sitting on top of the young rocks that are down here? 133 00:12:32,000 --> 00:12:36,440 So for people like Murchison, they were quite happy that was just a regular stacked sequence of rocks, 134 00:12:36,475 --> 00:12:38,725 but Lapworth could tell that it was wrong. 135 00:12:38,760 --> 00:12:44,640 Lapworth had to establish how come you've got the older rocks sat on top of the younger? 136 00:12:44,675 --> 00:12:48,960 What's going on at this contact? That's where the action is. 137 00:12:51,760 --> 00:12:58,880 When Lapworth examined the cliff carefully, he spotted something no one had noticed before - 138 00:12:58,915 --> 00:13:04,685 a thin layer sandwiched between the old rock above and the young rock below. 139 00:13:04,720 --> 00:13:09,160 What Lapworth recognised was that the old rocks had been reprocessed and ground, 140 00:13:09,195 --> 00:13:12,560 rather like an industrial mill, processing and grinding it down 141 00:13:12,595 --> 00:13:17,205 into sort of a very streaky-looking, smeared-out material. 142 00:13:17,240 --> 00:13:20,920 And this is the brilliant bit because he realised that this processing 143 00:13:20,955 --> 00:13:23,925 involves a grinding and, therefore, a horizontal motion. 144 00:13:23,960 --> 00:13:30,205 This thin streaky layer showed Lapworth something then almost unthinkable. 145 00:13:30,240 --> 00:13:37,360 The ancient rocks above had been grinding slowly sideways up and over the younger rocks below. 146 00:13:37,395 --> 00:13:40,245 So that slab of rock above has been sliding towards us really, 147 00:13:40,280 --> 00:13:44,365 it would have been over our heads, and the bottom of it was all getting crushed along. 148 00:13:44,400 --> 00:13:50,400 Yeah. The old rock started out underneath, so it's been brought up and over and across. Thrust over. 149 00:13:50,435 --> 00:13:54,560 Murchison had believed the landscape was made up of sedimentary layers 150 00:13:54,595 --> 00:13:58,440 that got progressively younger the further east you went. 151 00:13:58,475 --> 00:14:00,565 But Lapworth had discovered evidence 152 00:14:00,600 --> 00:14:06,880 that the formation of Scotland's mountains must have been much more violent. 153 00:14:06,915 --> 00:14:11,125 It is a truly revolutionary way of looking at rocks 154 00:14:11,160 --> 00:14:15,580 and the idea that they involve big motions and grinding processes, 155 00:14:15,615 --> 00:14:20,000 it does change fundamentally the way in which you view mountains. 156 00:14:25,600 --> 00:14:30,565 Lapworth saw that mountains could be built in a whole new way. 157 00:14:30,600 --> 00:14:34,720 The layers of rock didn't follow a simple sequence of youngest rocks 158 00:14:34,755 --> 00:14:37,885 on one side of the country and oldest on the other. 159 00:14:37,920 --> 00:14:44,600 They could also be thrust up and over each other by massive sideways movements of the Earth. 160 00:14:55,160 --> 00:15:00,400 This box is a replica of a model that the Victorians used to explain 161 00:15:00,435 --> 00:15:03,480 how sideways movements built mountains. 162 00:15:06,960 --> 00:15:10,400 I'm just putting a layer of black sand along the base of the box here, 163 00:15:10,435 --> 00:15:14,080 and that's going to be our first geological layer. 164 00:15:15,600 --> 00:15:18,565 I'm going to have to get a move on! 165 00:15:18,600 --> 00:15:23,240 These sand layers represent the mountainside behind me. 166 00:15:23,275 --> 00:15:25,960 I'm just going to put the lid on. 167 00:15:29,200 --> 00:15:33,280 I'm going to turn this wooden handle which is going to turn this screw 168 00:15:33,315 --> 00:15:36,737 and send these wooden blocks into the layers 169 00:15:36,772 --> 00:15:40,160 as if a great sideways force is crashing in. 170 00:15:40,195 --> 00:15:42,000 Going do it really slowly though. 171 00:15:47,920 --> 00:15:50,320 There we go. 172 00:15:52,760 --> 00:15:57,565 There she goes! Look at that, it actually works! 173 00:15:57,600 --> 00:16:02,640 You can see that this slab of rock strata has been thrust up and over 174 00:16:02,675 --> 00:16:04,725 the top of this slab of rock strata, 175 00:16:04,760 --> 00:16:08,680 which is exactly what Lapworth was saying. 176 00:16:09,680 --> 00:16:12,205 Look at it go! 177 00:16:12,240 --> 00:16:16,440 Look at it! It's like a bulldozer, that's exactly what it's like. 178 00:16:18,360 --> 00:16:22,000 It's beautiful. I never thought it would be this good. 179 00:16:22,035 --> 00:16:24,485 A whole series of zig zags are forming 180 00:16:24,520 --> 00:16:29,960 and what we are doing, look behind, we're building mountains. 181 00:16:33,440 --> 00:16:36,240 And the point is that is exactly what's going on over there. 182 00:16:41,120 --> 00:16:42,640 Get out of here! 183 00:16:51,560 --> 00:16:55,240 What the amateur Lapworth had spotted in the Highlands 184 00:16:55,275 --> 00:16:58,920 made a total mockery of Murchison's grand orderly scheme. 185 00:17:01,440 --> 00:17:08,880 But for Lapworth, the revelation that vast slabs of rock could move so dramatically left him overwhelmed. 186 00:17:15,680 --> 00:17:17,325 Whether it's the excitement of his discovery 187 00:17:17,360 --> 00:17:22,120 or the relentless pace of the work, it all proves too much of a strain. 188 00:17:22,155 --> 00:17:24,525 Nightmares plagued Lapworth. 189 00:17:24,560 --> 00:17:30,040 He tosses and turns at night, imagining the weight of great sheets of rock grinding above him. 190 00:17:30,075 --> 00:17:33,720 Some say he suffered a nervous breakdown. 191 00:17:49,040 --> 00:17:54,640 Lapworth did recover and he published his findings in 1885, 192 00:17:54,675 --> 00:17:58,240 but he was fearful of how his ideas would be received. 193 00:17:59,760 --> 00:18:02,005 And for good reason. 194 00:18:02,040 --> 00:18:08,640 The geological establishment did not want to be upstaged by a mere amateur. 195 00:18:10,680 --> 00:18:13,720 There's a final ironic twist to this story. 196 00:18:13,755 --> 00:18:16,285 Recognising that trouble was afoot, 197 00:18:16,320 --> 00:18:21,325 the Murchison camp sent in their crack team - Ben Peach and John Horne, 198 00:18:21,360 --> 00:18:27,880 two of the top geologists that were so good and so inseparable, they were dubbed the Heavenly Twins. 199 00:18:31,160 --> 00:18:35,045 Peach and Horne were a perfect scientific partnership. 200 00:18:35,080 --> 00:18:41,000 John Horne was analytical, but Ben Peach was as much an artist as a geologist. 201 00:18:41,035 --> 00:18:45,680 His paintings capture brilliantly the structure of rocks and mountains. 202 00:18:49,480 --> 00:18:55,080 The Heavenly Twins set off into the Highlands with a very particular mission. 203 00:18:55,115 --> 00:18:59,757 Their job was to kill off the Lapworth idea, once and for all. 204 00:18:59,792 --> 00:19:04,400 But to their surprise, instead of demonstrating that he was wrong, 205 00:19:04,435 --> 00:19:07,480 they proved that Lapworth was dead right. 206 00:19:11,960 --> 00:19:18,320 Peach and Horne found a whole range of mountains in the West Highlands thrust up by big sideways movements. 207 00:19:22,080 --> 00:19:24,520 Lapworth was completely vindicated. 208 00:19:26,400 --> 00:19:33,200 Although in his lifetime, sadly, he never received the credit his brilliant discovery deserved. 209 00:19:40,200 --> 00:19:43,205 The mountains of Scotland had revealed 210 00:19:43,240 --> 00:19:47,640 that the world was now more violent than had previously been thought. 211 00:19:49,840 --> 00:19:53,240 Rather than a simple build up of layer upon layer of rock, 212 00:19:53,275 --> 00:19:56,685 landscapes were also clearly formed by huge forces 213 00:19:56,720 --> 00:20:01,040 that could thrust billions of tonnes of rock up and over itself. 214 00:20:03,240 --> 00:20:07,960 This realisation only created fresh puzzles for the men of rock. 215 00:20:09,920 --> 00:20:13,340 Where did these massive movements in the earth come from? 216 00:20:13,375 --> 00:20:16,760 What could cause solid rock to move sideways so powerfully? 217 00:20:29,440 --> 00:20:35,360 The early geologists didn't realise it, but one of the biggest clues was right under their feet. 218 00:20:43,120 --> 00:20:46,805 It was lying deep underground, 219 00:20:46,840 --> 00:20:50,760 in the very same corner of the Scottish Highlands. 220 00:20:59,840 --> 00:21:06,160 Just a few miles away from the mountains Lapworth conquered, is this dramatic cavern. 221 00:21:07,120 --> 00:21:09,920 The mysterious Smoo Caves. 222 00:21:12,560 --> 00:21:14,285 I love exploring caves. 223 00:21:14,320 --> 00:21:18,965 You always feel as if you're entering a kind of lost world. 224 00:21:19,000 --> 00:21:24,320 For geologists, they're brilliant because they can let you in, you can see the rock in all its glory. 225 00:21:24,355 --> 00:21:28,165 This rock's made of limestone and rocks like limestone 226 00:21:28,200 --> 00:21:33,000 can take you to a time and a place where Scotland was very different. 227 00:21:38,440 --> 00:21:44,000 There's a whole swathe of these types of rocks running up and down the West Highlands. 228 00:21:46,560 --> 00:21:49,600 What's special about them is something they contain. 229 00:21:53,680 --> 00:21:57,000 As Peach and Horne investigated Lapworth's theory, 230 00:21:57,035 --> 00:22:00,320 they made an extraordinary discovery of their own. 231 00:22:08,240 --> 00:22:11,925 I know this must look like an overgrown woodlouse, 232 00:22:11,960 --> 00:22:15,165 but this is actually a really special fossil - a trilobite. 233 00:22:15,200 --> 00:22:21,080 500 million years or so ago, you'd have found them swimming around in the warm shallows. 234 00:22:21,115 --> 00:22:23,925 You get thousands of them all over Scotland, 235 00:22:23,960 --> 00:22:28,060 but the ones from this area were beautifully drawn by Ben Peach. 236 00:22:28,095 --> 00:22:32,160 You can see his sketches here - look at that! Fantastic artist. 237 00:22:32,195 --> 00:22:35,437 He's got this exquisite attention to detail, 238 00:22:35,472 --> 00:22:38,680 but even more amazing is the story they tell. 239 00:22:41,640 --> 00:22:47,720 These seemingly insignificant little fossils date back 500 million years. 240 00:22:49,440 --> 00:22:52,205 But they're far more than just ancient creatures. 241 00:22:52,240 --> 00:22:58,600 They were part of a jigsaw of evidence that would help to explain the movement of mountains. 242 00:23:12,480 --> 00:23:17,160 I'm drawing a map to show something intriguing about the trilobites. 243 00:23:19,480 --> 00:23:24,640 Something that utterly confused Peach and Horne and the other early geologists. 244 00:23:31,640 --> 00:23:35,740 It's not the trilobites themselves that were important, 245 00:23:35,775 --> 00:23:39,840 it was the type of trilobites and where they were found. 246 00:23:39,875 --> 00:23:44,085 The trilobites that were found in England and Wales 247 00:23:44,120 --> 00:23:49,640 were the same type they found right across continental Europe. 248 00:23:51,040 --> 00:23:55,440 But they were completely different to the trilobites that we find in Scotland. 249 00:23:57,680 --> 00:24:02,680 The Scottish ones were the same as those that were found 250 00:24:02,715 --> 00:24:07,117 in places like Greenland and Newfoundland down here. 251 00:24:07,152 --> 00:24:11,520 In other words, similar to those in North America. 252 00:24:11,555 --> 00:24:14,960 The big question was why? 253 00:24:23,360 --> 00:24:25,685 It was a complete mystery. 254 00:24:25,720 --> 00:24:29,400 The Victorians came up with all kinds of explanations. 255 00:24:32,880 --> 00:24:38,680 One idea was the trilobites had crossed over on a bridge of land between Scotland and North America 256 00:24:38,715 --> 00:24:42,120 which was washed away during the Biblical flood. 257 00:24:44,560 --> 00:24:48,685 Seems outlandish today, but for Victorian geologists, 258 00:24:48,720 --> 00:24:53,120 it was the most plausible explanation they could come up with. 259 00:24:53,155 --> 00:24:57,520 But then, another strange piece of the puzzle began to emerge. 260 00:25:11,000 --> 00:25:16,280 On December 23rd 1872, a ship set sail for an epic voyage. 261 00:25:18,120 --> 00:25:21,640 A three-year journey, covering 70,000 miles. 262 00:25:25,600 --> 00:25:30,480 The HMS Challenger was the first to carry out a survey of the ocean bed. 263 00:25:34,800 --> 00:25:41,840 On board was a Scottish scientist, Charles Wyville Thomson, a pioneer of ocean floor exploration. 264 00:25:46,360 --> 00:25:51,840 Sailors and scientists knew very little nothing about the depths beneath the waves. 265 00:25:56,480 --> 00:25:58,245 Thomson's survey laid the way 266 00:25:58,280 --> 00:26:03,640 for the first network of deep-sea telegraph cables and a new era in communications. 267 00:26:05,560 --> 00:26:09,245 To survey the sea bed, Wyville Thompson's ship had 268 00:26:09,280 --> 00:26:14,420 miles and miles of rough hemp rope at the end of which was a lead weight. 269 00:26:14,455 --> 00:26:19,560 They would hang this over the edge and just chuck it overboard really. 270 00:26:22,400 --> 00:26:24,640 The lead weight would plunge to the bottom. 271 00:26:26,160 --> 00:26:31,720 That was the easy bit. The hard work starts when you're hauling this thing back in. 272 00:26:31,755 --> 00:26:33,205 It must have been absolutely hell. 273 00:26:33,240 --> 00:26:38,280 You can imagine doing it when the boat's pitching and tossing. 274 00:26:38,315 --> 00:26:41,485 The rope's just slicing through your fingers. 275 00:26:41,520 --> 00:26:46,805 It's cold, it's wet, you're miserable, you're exhausted 276 00:26:46,840 --> 00:26:52,560 and all the time you're trying to count the number of fathoms you're hauling up. 277 00:26:56,160 --> 00:27:00,880 And at the end of it all, you've got a single measurement of the depth 278 00:27:00,915 --> 00:27:04,440 and you've got to do that thousands more times. 279 00:27:09,040 --> 00:27:12,685 After years of painstaking measurements, 280 00:27:12,720 --> 00:27:16,800 Wyville Thomson and his crew located something strange on the Atlantic seabed. 281 00:27:19,520 --> 00:27:23,960 Roughly half way to America, the ocean floor rose sharply. 282 00:27:26,160 --> 00:27:32,440 Instead of five miles to the bottom of the sea, they discovered it was suddenly less than two. 283 00:27:32,475 --> 00:27:35,240 Wyville Thomson was mystified. 284 00:27:36,280 --> 00:27:40,485 At first, he thinks he's stumbled upon a submerged mountain, 285 00:27:40,520 --> 00:27:44,845 but as the survey progresses, it becomes clear this is much bigger. 286 00:27:44,880 --> 00:27:52,080 A colossal ridge running from one pole to the other, right down the middle of the Atlantic Ocean. 287 00:27:53,080 --> 00:27:57,500 Wyville Thomson had discovered, not an ancient land bridge 288 00:27:57,535 --> 00:28:01,920 between Britain and America, but something even more curious. 289 00:28:03,520 --> 00:28:07,880 A chain of underwater mountains that rises from the ocean floor 290 00:28:07,915 --> 00:28:12,525 and runs 10,000 miles from the Arctic Sea in the north, 291 00:28:12,560 --> 00:28:15,800 down the middle of the Atlantic almost as far as Antarctica. 292 00:28:21,200 --> 00:28:25,920 The origins of this Mid-Atlantic Ridge were a complete mystery. 293 00:28:29,280 --> 00:28:34,840 It was the 20th century before geologists came up with a possible explanation 294 00:28:34,875 --> 00:28:37,445 for Lapworth's sideways movements of the Earth, 295 00:28:37,480 --> 00:28:43,960 Peach and Horne's isolated trilobites and Wyville Thomson's Mid-Atlantic Ridge. 296 00:28:46,320 --> 00:28:52,840 The explanation was based on an idea people had spotted as far back as the 1500s 297 00:28:52,875 --> 00:28:55,800 when the first atlases of the globe were drawn. 298 00:28:57,320 --> 00:29:01,200 Take a map of the world and cut out the landmasses. There we go. 299 00:29:01,235 --> 00:29:03,685 There's South America. 300 00:29:03,720 --> 00:29:07,160 And I'm really not going to do all these islands, just do that. 301 00:29:07,195 --> 00:29:11,320 I'm sorry to the northern islands of Canada. 302 00:29:11,355 --> 00:29:13,760 They've got to go. 303 00:29:15,560 --> 00:29:21,000 When you've cut out all the landmasses, you can do this trick of fitting them together. 304 00:29:21,035 --> 00:29:26,120 Here's South America and Africa and we can move them close together. 305 00:29:26,155 --> 00:29:29,040 Look at this join here. 306 00:29:29,075 --> 00:29:30,565 It's so snug. 307 00:29:30,600 --> 00:29:33,580 And then here's little Madagascar... 308 00:29:33,615 --> 00:29:36,427 just tuck it in there. Here's India. 309 00:29:36,462 --> 00:29:39,851 Move India up, it tucks in here. 310 00:29:39,886 --> 00:29:43,240 North America, just bring it down... 311 00:29:43,275 --> 00:29:44,840 and it fits snugly into there. 312 00:29:49,480 --> 00:29:53,205 This trick of the maps led some geologists to think 313 00:29:53,240 --> 00:29:56,800 that all the world's landmasses were once joined together... 314 00:29:56,835 --> 00:30:00,217 and that they'd slowly drifted apart 315 00:30:00,252 --> 00:30:03,600 and re-arranged themselves over time. 316 00:30:05,760 --> 00:30:10,160 An idea they began to call continental drift. 317 00:30:18,960 --> 00:30:24,400 Perhaps Wyville Thomson's Mid-Atlantic Ridge was a giant scar... 318 00:30:24,435 --> 00:30:29,840 the crack where this ancient super-continent had split apart. 319 00:30:31,840 --> 00:30:35,800 Continental drift was a very clever theory, 320 00:30:35,835 --> 00:30:38,880 but what could cause it to happen? 321 00:30:42,120 --> 00:30:45,085 Huge forces were clearly at work. 322 00:30:45,120 --> 00:30:49,120 But the men of rock struggled to make sense of their discoveries. 323 00:30:53,280 --> 00:30:57,480 Then, early in the 20th century, a gung-ho geologist - 324 00:30:57,515 --> 00:30:59,805 again, working in Scotland - 325 00:30:59,840 --> 00:31:02,640 found another part of the puzzle. 326 00:31:20,800 --> 00:31:23,885 The Highlands near Glencoe. 327 00:31:23,920 --> 00:31:28,240 For many, a wet and sometimes miserable experience. 328 00:31:31,600 --> 00:31:33,960 Back in the early 1900s... 329 00:31:33,995 --> 00:31:35,965 Ohh...! 330 00:31:36,000 --> 00:31:42,280 .. an intrepid young geologist, Edward Bailey, had a bracing daily routine out here. 331 00:31:45,440 --> 00:31:48,040 Oh! Oh! 332 00:31:55,040 --> 00:32:00,360 You think, "It's going to be cold, it's going to be cold!" 333 00:32:00,395 --> 00:32:02,885 But, boy, it's cold! 334 00:32:02,920 --> 00:32:06,000 Agh, I knew it was going to be cold! 335 00:32:10,320 --> 00:32:14,645 Bailey spent years training himself to be tough. 336 00:32:14,680 --> 00:32:18,400 As a boy, he invited classmates to slap him in the face 337 00:32:18,435 --> 00:32:21,165 to test his endurance. 338 00:32:21,200 --> 00:32:23,605 He became a boxing champion 339 00:32:23,640 --> 00:32:27,880 and slept with windows wide open in winter. 340 00:32:30,120 --> 00:32:35,000 And nothing pleased him more than his daily, naked swim. 341 00:32:35,035 --> 00:32:36,485 Ah... 342 00:32:36,520 --> 00:32:39,245 When I think about Bailey, 343 00:32:39,280 --> 00:32:43,800 I'm torn between thinking he's an absolute hero and an absolute nutter. 344 00:32:44,920 --> 00:32:47,540 I mean, he used to do this every day. 345 00:32:47,575 --> 00:32:50,125 Just dive into some loch or some river. 346 00:32:50,160 --> 00:32:54,840 And then he'd, kind of, put on his clothes still wet 347 00:32:54,875 --> 00:32:57,360 and head off into the mountains. 348 00:33:01,960 --> 00:33:04,445 Here's me with all the gear. 349 00:33:04,480 --> 00:33:07,725 That wasn't the style for our Bailey. Look at him. 350 00:33:07,760 --> 00:33:12,120 He's got these all-weather shorts. Look at him, in the snow! 351 00:33:12,155 --> 00:33:16,480 And when the survey told him that wasn't professional enough, 352 00:33:16,515 --> 00:33:19,760 he told them to stuff the job and resigned. 353 00:33:23,000 --> 00:33:26,120 No-one could ever argue with Bailey. 354 00:33:26,155 --> 00:33:28,680 The shorts stayed on. 355 00:33:38,800 --> 00:33:43,005 In 1905, Bailey, came to the peaks of Glencoe 356 00:33:43,040 --> 00:33:47,960 to join the British Geological Survey team who were mapping the Highlands. 357 00:33:51,800 --> 00:33:57,840 What they found was evidence of an explosive era in Scotland's ancient history. 358 00:34:10,200 --> 00:34:13,740 When geologists first started investigating Glencoe... 359 00:34:13,775 --> 00:34:17,245 they realised there were lots of volcanic rocks here. 360 00:34:17,280 --> 00:34:21,320 The whole place is stuffed full of them. But they didn't know why. 361 00:34:21,355 --> 00:34:25,320 What were they doing here in the heart of the highlands? 362 00:34:25,355 --> 00:34:28,845 Bailey and his team set off to find out. 363 00:34:28,880 --> 00:34:34,760 Inch by inch, they set out to carefully map and survey the landscape. 364 00:34:37,560 --> 00:34:41,045 Bailey was often frowned upon 365 00:34:41,080 --> 00:34:44,440 since he took official maps and completely redrew them as he saw fit. 366 00:34:44,475 --> 00:34:49,000 He was devoted to his fieldwork in the mountains. 367 00:34:54,160 --> 00:34:59,280 He famously used to eat his lunch straight after breakfast so he didn't have to carry it 368 00:34:59,315 --> 00:35:03,960 and if his feet got wet while crossing rivers or fords, no matter, 369 00:35:03,995 --> 00:35:08,080 the holes in his boots let the water drain out. What a guy! 370 00:35:11,680 --> 00:35:14,325 As Bailey climbed through Glencoe, 371 00:35:14,360 --> 00:35:20,120 he began to follow a dramatic crack up the side of the mountain. 372 00:35:20,155 --> 00:35:24,960 He and his team traced the line across the landscape. 373 00:35:27,200 --> 00:35:31,360 And when they drew up their map, it revealed a giant circle. 374 00:35:36,560 --> 00:35:42,600 Bailey realised this was no ordinary geological feature. 375 00:35:46,680 --> 00:35:51,120 He wondered if it was the mouth of a massive volcano. 376 00:35:54,200 --> 00:35:59,520 Then he looked more closely at the rocks themselves. 377 00:36:01,280 --> 00:36:05,885 Now as Bailey and his team were going along rivers like this, 378 00:36:05,920 --> 00:36:11,160 they kept finding two types of rock that started out as molten magma. 379 00:36:11,195 --> 00:36:16,097 One of them is this, it's a granite. It's got really big crystals. 380 00:36:16,132 --> 00:36:21,000 The other one has got really fine crystals. You can't really see them. 381 00:36:23,000 --> 00:36:26,360 Molten rock deep underground cools very slowly 382 00:36:26,395 --> 00:36:29,245 and large crystals have time to grow. 383 00:36:29,280 --> 00:36:35,000 But molten rock that has exploded out into open air cools rapidly 384 00:36:35,035 --> 00:36:38,565 so crystals don't have time to form. 385 00:36:38,600 --> 00:36:42,480 We've got one rock that's down deep and the other rock near the surface, 386 00:36:42,515 --> 00:36:46,360 yet, here, they're found side by side. 387 00:36:46,395 --> 00:36:49,000 Bailey wants to know why. 388 00:36:53,160 --> 00:36:55,480 Then Bailey made a connection. 389 00:36:57,320 --> 00:37:01,365 The two rocks and the huge circular crack in the landscape 390 00:37:01,400 --> 00:37:05,925 told him he was stood on the remains of a very special kind of volcano, 391 00:37:05,960 --> 00:37:12,520 one that would reveal the enormity of the forces that had shaped the continents. 392 00:37:15,760 --> 00:37:18,480 I'm going to build a model of how he saw it working. 393 00:37:21,120 --> 00:37:26,520 I know this looks crazy, but I'm making my own wee miniature version of Glencoe. 394 00:37:26,555 --> 00:37:30,285 I know this barrel has just got mud and water in it 395 00:37:30,320 --> 00:37:34,800 but, to me, this is a subterranean pool of molten rock - magma. 396 00:37:36,800 --> 00:37:38,480 Should be red hot really. 397 00:37:40,600 --> 00:37:45,460 The thing is that this magma is erupting up 398 00:37:45,495 --> 00:37:49,447 and spewing out at the surface of a volcano. 399 00:37:49,482 --> 00:37:53,365 I'm going to build the top of that volcano. 400 00:37:53,400 --> 00:37:57,605 When volcanoes erupt, the lava and ash builds up... 401 00:37:57,640 --> 00:38:02,800 higher and higher, forming a huge heavy cone at the top. 402 00:38:02,835 --> 00:38:05,937 What Bailey realises is that, eventually, 403 00:38:05,972 --> 00:38:09,005 the top of the volcano would get so heavy 404 00:38:09,040 --> 00:38:13,280 that the weight of it would sink into the magma below. 405 00:38:17,560 --> 00:38:19,885 I'm covered in magma. 406 00:38:19,920 --> 00:38:24,680 I'm covered! What would happen is the magma would come rushing out. 407 00:38:31,080 --> 00:38:35,600 Bailey realises the volcano has broken along that circular faultline 408 00:38:35,635 --> 00:38:38,377 and collapsed violently in on itself, 409 00:38:38,412 --> 00:38:41,085 creating the most almighty explosion 410 00:38:41,120 --> 00:38:43,925 and that explains why those two rock types - 411 00:38:43,960 --> 00:38:47,560 one at the top of the volcano and the other deep in its roots - 412 00:38:47,595 --> 00:38:49,125 are now lying side by side. 413 00:38:49,160 --> 00:38:55,440 What Bailey had discovered was a colossal new type of volcano - a caldera. 414 00:39:00,400 --> 00:39:04,320 Calderas produce the most explosive eruptions on Earth. 415 00:39:07,800 --> 00:39:10,325 They're a type of mega-eruption 416 00:39:10,360 --> 00:39:14,160 caused when a volcano collapses in on itself. 417 00:39:16,520 --> 00:39:23,240 As the Glencoe volcano erupted, the magma chamber below began to empty... 418 00:39:23,275 --> 00:39:27,657 the base could no longer support the top. 419 00:39:27,692 --> 00:39:32,040 The heavy upper cone collapsed inwards... 420 00:39:32,075 --> 00:39:35,280 and caused a catastrophic explosion. 421 00:39:46,400 --> 00:39:51,120 Bailey had identified one of the biggest supervolcanoes in Earth's history. 422 00:39:55,120 --> 00:40:01,200 For 45 years, he mapped monuments to Scotland's violent volcanic past. 423 00:40:08,960 --> 00:40:13,480 He discovered the country was covered in volcanoes. 424 00:40:21,480 --> 00:40:25,320 Bailey and his fellow geologists surveyed a great line of them, 425 00:40:25,355 --> 00:40:29,160 stretching along the islands of the west coast of Scotland. 426 00:40:33,360 --> 00:40:37,160 Ardnamurchan - with its perfect ring structure. 427 00:40:39,480 --> 00:40:41,205 The cliffs on Eigg, 428 00:40:41,240 --> 00:40:43,840 solidified sheets of molten rock. 429 00:40:46,480 --> 00:40:49,760 And the mighty Cuillin Ridge of Skye. 430 00:40:52,840 --> 00:40:58,920 But did Bailey's discoveries have anything to do with trilobites and the Mid-Atlantic Ridge? 431 00:41:00,800 --> 00:41:05,320 Could his discoveries help explain the theory of continental drift? 432 00:41:12,720 --> 00:41:16,045 The men of rock now had several pieces of a jigsaw. 433 00:41:16,080 --> 00:41:22,805 Lapworth had discovered solid rock had been pushed sideways to form mountain ranges. 434 00:41:22,840 --> 00:41:30,240 Peach and Horne had found fossils in Scotland that appeared to match those from far side of the globe. 435 00:41:31,320 --> 00:41:35,440 Bailey had revealed the immeasurable power inside the Earth. 436 00:41:38,000 --> 00:41:42,640 And Wyville Thomson had uncovered a giant ridge on the seabed. 437 00:41:42,675 --> 00:41:45,925 But no-one could understand how they were linked. 438 00:41:45,960 --> 00:41:50,640 They had observations but nothing to tie them together. 439 00:41:51,400 --> 00:41:57,160 It would take a geological genius to solve the puzzle. 440 00:42:07,120 --> 00:42:10,960 I'm at the biggest balloon festival in Britain... 441 00:42:14,560 --> 00:42:18,520 .. because the theory that united the men of rock's observations 442 00:42:18,555 --> 00:42:20,805 came not from studying mountains... 443 00:42:20,840 --> 00:42:26,840 but from something much more familiar to us all. 444 00:42:29,800 --> 00:42:31,440 Heat. 445 00:42:33,880 --> 00:42:37,720 I love watching this - the effort to get these things off the ground, 446 00:42:37,755 --> 00:42:40,525 all the noise and the action, the heat when you get close. 447 00:42:40,560 --> 00:42:44,885 And it's a real battle. You can see them fighting with the balloons 448 00:42:44,920 --> 00:42:50,920 as if the balloon doesn't want to go up but that hot air just keeps piling in there 449 00:42:50,955 --> 00:42:55,400 until eventually it accepts the inevitable and just rears up. 450 00:42:55,435 --> 00:42:58,440 And that's really what's driving it there, just hot air. 451 00:42:58,475 --> 00:43:00,680 It's pure physics in action. 452 00:43:07,040 --> 00:43:09,880 We all know warm air rises. 453 00:43:11,200 --> 00:43:13,840 That's what makes these balloons lift off. 454 00:43:27,960 --> 00:43:34,360 It's a simple but fundamental principle of physics. It's called convection. 455 00:43:34,395 --> 00:43:40,760 Heat from the burners warms the huge bubble of trapped air inside the balloon. 456 00:43:40,795 --> 00:43:44,400 It becomes less dense than the colder air outside... 457 00:43:46,240 --> 00:43:49,320 .. so up it goes. 458 00:43:53,240 --> 00:44:00,480 And it's this principle that would turn another man of rock into the unsung hero of geology. 459 00:44:07,000 --> 00:44:12,960 Arthur Holmes was one of the most brilliant minds of the 20th century. 460 00:44:13,840 --> 00:44:18,960 He was a professor at Edinburgh University, a geologist and a physicist. 461 00:44:24,120 --> 00:44:29,280 He was fascinated with the heat deep inside the Earth. 462 00:44:32,400 --> 00:44:37,280 In 1928, he put forward an extraordinary and controversial idea - 463 00:44:37,315 --> 00:44:41,725 that molten rock could behave just like hot air 464 00:44:41,760 --> 00:44:45,800 and perhaps heat, convection, could be driving the movement 465 00:44:45,835 --> 00:44:50,477 of the entire surface of the planet over millions of years. 466 00:44:50,512 --> 00:44:55,120 I'm meeting geologist John Underhill who's going to show me 467 00:44:55,155 --> 00:44:57,765 how Holmes's ideas work in the lab. 468 00:44:57,800 --> 00:45:01,760 First, ice goes under one end of this fish tank. 469 00:45:01,795 --> 00:45:05,480 Just put a couple more in. 470 00:45:07,600 --> 00:45:14,120 At the other end of the tank, John creates a much hotter temperature. 471 00:45:14,155 --> 00:45:18,617 I'm going to slip this heater, a hot plate, underneath this end. 472 00:45:18,652 --> 00:45:23,080 And he's using coloured dyes to track the movement of the water. 473 00:45:25,080 --> 00:45:31,280 I now need to roll my sleeves up and put the dye into the fish-tank. 474 00:45:31,315 --> 00:45:34,160 First, he puts blue dye in the cold end. 475 00:45:37,480 --> 00:45:39,320 That's fantastic. 476 00:45:44,240 --> 00:45:47,360 In the hot end, he puts red dye. 477 00:45:48,960 --> 00:45:53,360 It'll show how heat can create different types of movement. 478 00:45:54,360 --> 00:45:56,720 It's quite hypnotic watching it. 479 00:45:56,755 --> 00:45:59,045 Now we see it starting to spread. 480 00:45:59,080 --> 00:46:02,840 You can see it starting to go up there. This is convection. 481 00:46:02,875 --> 00:46:05,885 It's beautiful, isn't it? 482 00:46:05,920 --> 00:46:09,920 The hot plate makes the warm, red water rise, 483 00:46:09,955 --> 00:46:12,605 just like the hot air balloons. 484 00:46:12,640 --> 00:46:17,160 On the other side, the cold water is denser, so it sinks. 485 00:46:17,195 --> 00:46:20,677 This rise and fall makes something crucial happen. 486 00:46:20,712 --> 00:46:24,125 This is where it's going to get really interesting 487 00:46:24,160 --> 00:46:29,320 because it hits the top surface, nowhere to go, so it starts to go horizontally. 488 00:46:29,355 --> 00:46:30,685 That is gorgeous. 489 00:46:30,720 --> 00:46:36,480 And we can see it moving sideways and actually starting to come down. 490 00:46:36,515 --> 00:46:38,685 This is the crucial thing. 491 00:46:38,720 --> 00:46:42,165 We've got horizontal motion of the water column, 492 00:46:42,200 --> 00:46:45,320 so a conveyor belt is set up, this convection is set up. 493 00:46:46,920 --> 00:46:49,725 This was Holmes's big breakthrough. 494 00:46:49,760 --> 00:46:54,400 The rise and fall of heat drives sideways motion. 495 00:46:54,435 --> 00:46:59,005 He realised that if this was molten rock, not water, 496 00:46:59,040 --> 00:47:05,160 you'd have a conveyor belt that powered massive movements of the Earth's crust. 497 00:47:05,195 --> 00:47:08,165 We're replicating it in a liquid - water - 498 00:47:08,200 --> 00:47:11,800 but what Holmes is getting at is that solid earth actually behaves like a liquid. 499 00:47:11,835 --> 00:47:16,525 Absolutely. I think the key insight that he could bring to all this 500 00:47:16,560 --> 00:47:19,805 was he could imagine that what we are seeing here happens within the earth 501 00:47:19,840 --> 00:47:25,320 and, thereby, he was able to recognise the engine that drives continental drift. 502 00:47:25,355 --> 00:47:29,925 Now that was revolutionary. That was different and it was out of kilter. 503 00:47:29,960 --> 00:47:35,480 He was considered a maverick for even saying that continental drift was possible. 504 00:47:40,320 --> 00:47:47,360 Holmes proposed that heat from the Earth's core drives semi-molten rock to the surface. 505 00:47:47,395 --> 00:47:51,040 It splits apart the crust at the Mid-Atlantic Ridge. 506 00:47:53,520 --> 00:47:57,640 Where it cools, it's forced back into the inner Earth. 507 00:47:57,675 --> 00:48:01,120 And a cycle of convection is produced. 508 00:48:04,120 --> 00:48:06,880 This was Holmes's great insight. 509 00:48:11,440 --> 00:48:14,405 Holmes sees it clearly. 510 00:48:14,440 --> 00:48:18,685 Heat from the inner Earth producing a huge convection cycle. 511 00:48:18,720 --> 00:48:24,040 It's that cycle that moves the continents sideways on the surface of the globe. 512 00:48:28,400 --> 00:48:32,560 Now, at last, the jigsaw puzzle was complete. 513 00:48:35,840 --> 00:48:42,760 Lapworth's mountains showed how these sideways movements thrust old rocks on top of young. 514 00:48:44,760 --> 00:48:51,480 The Glencoe caldera showed where these movements forced the Earth's crust down into the inner earth. 515 00:48:53,800 --> 00:49:00,040 One part of the crust was forced under the other, melting to form a deep pool of molten rock... 516 00:49:00,075 --> 00:49:04,240 which burst violently back to the surface. 517 00:49:08,280 --> 00:49:11,325 And Wyville Thomson's Mid-Atlantic Ridge 518 00:49:11,360 --> 00:49:14,840 showed where convection pushed the Earth's crust apart 519 00:49:14,875 --> 00:49:17,920 and new rock was forced upwards from beneath. 520 00:49:28,760 --> 00:49:32,400 In World War Two, Holmes spent many hours on fire-watch duty. 521 00:49:34,960 --> 00:49:41,600 He had the time to write down everything he knew about geology and, also, his most radical ideas. 522 00:49:41,635 --> 00:49:45,320 And in 1944, he published his work. 523 00:49:48,240 --> 00:49:51,280 The Principles of Physical Geology. 524 00:49:52,320 --> 00:49:58,440 It went on to become the single most important geology book of the 20th century. 525 00:49:59,840 --> 00:50:02,485 This is actually a big deal for me 526 00:50:02,520 --> 00:50:06,840 because this is the original version of Holmes's book. 527 00:50:07,840 --> 00:50:10,840 It's fantastic leafing through it. 528 00:50:10,875 --> 00:50:13,805 Great stuff. This, when it came out, 529 00:50:13,840 --> 00:50:18,040 almost immediately made the geologists' best-sellers list... 530 00:50:18,075 --> 00:50:20,965 and I guess it became our bible, really. 531 00:50:21,000 --> 00:50:28,520 I had, I think, the fifth edition which got me through university. So it's dear to me. The thing is, 532 00:50:28,555 --> 00:50:34,777 Holmes really wrestled with the idea of whether to put his theory of convection into this book 533 00:50:34,812 --> 00:50:41,000 and he kind of slides it in at the last minute, the very last diagram in the book. There it is. 534 00:50:41,035 --> 00:50:45,160 This is the first time that convection as a mechanism for moving continents was laid out. 535 00:50:45,195 --> 00:50:49,080 You can see here the hot magma rising up as currents, 536 00:50:49,115 --> 00:50:52,597 moving sideways and descending back down again. 537 00:50:52,632 --> 00:50:56,045 It's interesting here, I just noticed, he says, 538 00:50:56,080 --> 00:51:02,120 "This is to illustrate a purely hypothetical mechanism for engineering continental drift. " 539 00:51:02,155 --> 00:51:04,725 He's hedging his bets here, covering his back. 540 00:51:04,760 --> 00:51:10,520 He knows it's controversial so he's going, "If it did happen, this is one way it might happen. " 541 00:51:10,555 --> 00:51:15,360 But you get the impression, the very fact he's got it in there, 542 00:51:15,395 --> 00:51:18,377 he knows, he really believes in it. 543 00:51:18,412 --> 00:51:21,526 It seemed like the perfect theory. 544 00:51:21,561 --> 00:51:24,640 Now all it needed was the proof. 545 00:51:27,920 --> 00:51:31,000 It came from a horrifying source. 546 00:51:36,040 --> 00:51:39,160 The Cold War brought an unexpected revelation. 547 00:51:45,440 --> 00:51:50,160 When a worldwide treaty banned nuclear tests in the atmosphere, 548 00:51:50,195 --> 00:51:53,880 bombs were then detonated underground. 549 00:51:54,720 --> 00:51:58,880 The Americans needed a method of surveillance 550 00:51:58,915 --> 00:52:01,240 to monitor tests around the world. 551 00:52:03,720 --> 00:52:09,280 They set up a global network of seismometers to listen in on the tremors in the ground. 552 00:52:13,320 --> 00:52:18,000 Then, as they look for telltale vibrations from enemy nuclear tests, 553 00:52:19,280 --> 00:52:25,080 they found something completely unexpected about the structure of the Earth. 554 00:52:31,000 --> 00:52:35,120 The seismometers detected, not just nuclear tests, 555 00:52:35,155 --> 00:52:38,240 but geological events across the world... 556 00:52:39,920 --> 00:52:42,480 .. volcanic eruptions and earthquakes... 557 00:52:45,200 --> 00:52:48,480 .. each tremor a pinpoint on a map... 558 00:52:52,480 --> 00:52:54,680 .. until a pattern emerged. 559 00:52:55,960 --> 00:52:58,085 This all looks a bit psychedelic 560 00:52:58,120 --> 00:53:03,040 but this is the most important recent development in the history of geology. 561 00:53:03,075 --> 00:53:05,445 The world map of tectonic plates. 562 00:53:05,480 --> 00:53:09,085 It explains how the planet's most devastating events - 563 00:53:09,120 --> 00:53:13,120 earthquakes and volcanoes - all lie along plate boundaries. 564 00:53:13,155 --> 00:53:17,085 What it really shows is where the geological action is. 565 00:53:17,120 --> 00:53:22,440 Like over here in the middle of the Atlantic where two vast slabs of crust are spreading apart. 566 00:53:22,475 --> 00:53:27,760 Or over here along the edge of the Pacific where two slabs are colliding together. 567 00:53:27,795 --> 00:53:32,837 You can see right around the Pacific, the so-called Ring of Fire. 568 00:53:32,872 --> 00:53:37,880 All these surface motions are powered by convection from below. 569 00:53:37,915 --> 00:53:40,400 Just as predicted by Holmes. 570 00:53:44,840 --> 00:53:49,200 Heat deep in the Earth has driven our entire geological history. 571 00:53:51,640 --> 00:53:54,525 For millions of years, 572 00:53:54,560 --> 00:53:58,760 the tectonic plates have moved back and forth the surface of the planet 573 00:53:58,795 --> 00:54:02,240 to create the globe we recognise today. 574 00:54:09,560 --> 00:54:14,920 The movement of continents explains the mystery of why fossils from Scotland 575 00:54:14,955 --> 00:54:20,280 are so similar to those found thousands of miles away across the ocean. 576 00:54:24,000 --> 00:54:27,160 The fossils of Scotland match North America 577 00:54:27,195 --> 00:54:29,685 because they were very close together. 578 00:54:29,720 --> 00:54:33,165 Scotland was once part of an arc of islands strung out 579 00:54:33,200 --> 00:54:38,160 along the edge of a vast continent, Laurentia, with America at its heart. 580 00:54:40,160 --> 00:54:43,960 500 million years ago, Scotland was on the Equator 581 00:54:43,995 --> 00:54:47,760 and part of an ancient North American continent. 582 00:54:53,000 --> 00:54:56,160 Thousands of miles away, separated by a vast ocean, 583 00:54:56,195 --> 00:54:59,525 England was part of a different continent too. 584 00:54:59,560 --> 00:55:05,160 Over millions of years, those two ancient continents collided... 585 00:55:07,560 --> 00:55:11,925 .. and Scotland finally came together with England 586 00:55:11,960 --> 00:55:15,800 in an incredibly slow but immensely powerful act of union. 587 00:55:23,320 --> 00:55:28,080 Today, you can still see the results of this great geological clash. 588 00:55:31,080 --> 00:55:35,920 These cliffs became crumpled when the two continents collided. 589 00:55:35,955 --> 00:55:40,760 They sit on the border between England and Scotland at St Abbs. 590 00:55:40,795 --> 00:55:45,360 Layers of rock that were laid down flat on the ocean floor 591 00:55:45,395 --> 00:55:49,360 have been thrust up vertically out of the ground. 592 00:55:57,080 --> 00:56:03,160 For geologists, it's one of the most remarkable places in the British Isles. 593 00:56:10,600 --> 00:56:14,325 These rocks are so crumbly! 594 00:56:14,360 --> 00:56:18,600 This whole thing just feels... really precarious! 595 00:56:23,080 --> 00:56:26,565 These buckled rocks look like they've been in some kind of giant pile-up. 596 00:56:26,600 --> 00:56:32,520 These ones are angled in one direction. Just down there, they're angled in the opposite direction. 597 00:56:32,555 --> 00:56:37,240 It's because this whole coastline is the site of a giant collision, 598 00:56:37,275 --> 00:56:41,240 albeit a very slow one, between England and Scotland. 599 00:56:44,160 --> 00:56:47,925 This clash between the ancient continents 600 00:56:47,960 --> 00:56:53,160 forced the rock layers into striking shapes and angles. 601 00:56:59,800 --> 00:57:05,560 It's this collision with England that forced up the mountains of the Scotland, 602 00:57:05,595 --> 00:57:08,680 fuelled volcanic eruptions and shaped the landscape. 603 00:57:14,840 --> 00:57:18,925 Finally, I'm returning to the Scottish mountain 604 00:57:18,960 --> 00:57:23,880 where I was inspired to become a geologist, a man of rock. 605 00:57:26,120 --> 00:57:30,400 Dun Caan on the Isle of Raasay near Skye. 606 00:57:36,480 --> 00:57:38,965 This mountain top is so important to me 607 00:57:39,000 --> 00:57:43,845 because this is where I first learned to read the rocks, read the landscape. 608 00:57:43,880 --> 00:57:49,960 The fact that we can do that today is all down to countless pioneers - amateurs and professionals. 609 00:57:49,995 --> 00:57:51,965 People like Lapworth, people like Bailey. 610 00:57:52,000 --> 00:57:59,640 It was because of them that we understand Scotland, and through it the world. 611 00:58:02,120 --> 00:58:05,125 Next time, I'll look at the daredevil scientist 612 00:58:05,160 --> 00:58:09,680 who revealed that our land had been gripped by a great and ancient ice age. 613 00:58:09,715 --> 00:58:11,205 I'm getting squeezed! 614 00:58:11,240 --> 00:58:17,600 And the humble janitor who wondered if the causes of the Ice Age lay in the heavens. 615 00:58:19,120 --> 00:58:23,360 Oh. The sound of the Ice Age.