1 00:01:01,561 --> 00:01:03,256 Scattered amongst the craggy peaks 2 00:01:03,396 --> 00:01:04,829 of the SWiss Alps 3 00:01:04,964 --> 00:01:08,661 is a series of strange geological features. 4 00:01:09,335 --> 00:01:12,270 For many years these features Were a puzzle. 5 00:01:17,610 --> 00:01:19,237 When geologists eventually learnt 6 00:01:19,379 --> 00:01:21,404 hoW to interpret the landscape 7 00:01:21,548 --> 00:01:23,038 they uncovered the first hints 8 00:01:23,183 --> 00:01:25,549 of a long chain of dramatic events 9 00:01:25,685 --> 00:01:29,348 that have transformed the planet throughout its history. 10 00:01:49,976 --> 00:01:52,001 Stranded in the middle of the SWiss countryside 11 00:01:52,145 --> 00:01:54,238 is this enormous boulder. 12 00:01:54,380 --> 00:01:56,814 lt's been made a national monument. 13 00:01:56,950 --> 00:01:59,111 Christian Schluchter, a local geologist, 14 00:01:59,252 --> 00:02:02,085 explains Why it's so important. 15 00:02:02,222 --> 00:02:06,090 What We see here is really a strange piece of rock. 16 00:02:06,226 --> 00:02:09,525 lt actually doesn't belong to this area Where it is noW. 17 00:02:09,662 --> 00:02:13,098 lts composition is different from the bedrock here. 18 00:02:13,233 --> 00:02:15,463 Bedrock is beautiful sandstone 19 00:02:15,602 --> 00:02:17,661 and this is a gneiss 20 00:02:17,804 --> 00:02:21,262 so it must come from someWhere else. 21 00:02:21,407 --> 00:02:23,637 lf you look around in the SWiss Alps 22 00:02:23,776 --> 00:02:25,903 then you find the places in the mountains 23 00:02:26,045 --> 00:02:28,741 of the canton of Valais Where this comes from, 24 00:02:28,882 --> 00:02:30,816 so it has travelled 25 00:02:30,950 --> 00:02:35,546 let's say betWeen 200 and 250 kilometres to come here. 26 00:02:35,688 --> 00:02:39,089 lt is What We call an erratic boulder. 27 00:02:39,792 --> 00:02:41,760 People, of course, Were thinking 28 00:02:41,895 --> 00:02:47,162 for many, many centuries hoW this actually came to rest here 29 00:02:47,300 --> 00:02:48,665 because it Was obvious 30 00:02:48,801 --> 00:02:52,032 it had to be moved somehoW, 31 00:02:52,172 --> 00:02:54,037 so the first idea Was 32 00:02:54,174 --> 00:02:55,937 that it has been brought here 33 00:02:56,075 --> 00:02:57,872 by a huge big flood, 34 00:02:58,011 --> 00:02:59,444 by the Waters of a big, 35 00:02:59,579 --> 00:03:04,380 big flood originating high up in the Alps. 36 00:03:05,985 --> 00:03:07,816 Erratic boulders like this Were found 37 00:03:07,954 --> 00:03:10,650 all over northern Europe and America. 38 00:03:12,158 --> 00:03:14,217 To 19th-century geologists 39 00:03:14,360 --> 00:03:15,657 they seemed like good evidence 40 00:03:15,795 --> 00:03:17,228 that the earth had once been covered 41 00:03:17,363 --> 00:03:18,728 by enormous floods, 42 00:03:18,865 --> 00:03:21,333 just as the Bible described, 43 00:03:21,467 --> 00:03:23,435 but as they looked further up the valleys 44 00:03:23,570 --> 00:03:25,800 SWiss scientists could see that Water 45 00:03:25,939 --> 00:03:29,204 Was not the only thing that could move rocks. 46 00:03:29,809 --> 00:03:33,176 All these boulders around here Were carried doWn 47 00:03:33,313 --> 00:03:36,476 by the actively advancing glacier. 48 00:03:36,616 --> 00:03:38,015 The advancing glacier from up 49 00:03:38,151 --> 00:03:41,552 the valley here carried and put them doWn here 50 00:03:41,688 --> 00:03:46,125 in the 1850s and piled up this beautiful dam 51 00:03:46,259 --> 00:03:48,989 We call a terminal marain. 52 00:03:57,370 --> 00:03:59,463 This jumbled Wall of boulders 53 00:03:59,606 --> 00:04:03,565 is noW several hundred metres from the snout of the glacier. 54 00:04:06,179 --> 00:04:09,012 Back in the last century glaciers all over the Alps 55 00:04:09,148 --> 00:04:12,914 stretched further oWn the mountains than they do today. 56 00:04:13,453 --> 00:04:16,115 lt Was around this time that a SWiss naturalist, 57 00:04:16,256 --> 00:04:17,723 Louis Agassiz, 58 00:04:17,857 --> 00:04:20,883 began to Wonder hoW far these great rivers of ice 59 00:04:21,027 --> 00:04:23,018 had once reached. 60 00:04:23,162 --> 00:04:25,960 The ansWer, as is so often the case, 61 00:04:26,099 --> 00:04:28,124 Was in the rocks. 62 00:04:30,570 --> 00:04:33,698 This here is one of the places gassiz Was visiting 63 00:04:33,840 --> 00:04:36,741 When he did his studies on glaciers 64 00:04:36,876 --> 00:04:39,242 and it's a very special place. 65 00:04:39,379 --> 00:04:41,609 lt's one of the most beautifully 66 00:04:41,748 --> 00:04:43,841 polished bedrock surfaces. 67 00:04:43,983 --> 00:04:47,077 Here it's a polished surface 68 00:04:47,220 --> 00:04:49,620 of the Grimsel granite. 69 00:04:49,756 --> 00:04:55,422 NoW hoW does such a beautiful polish actually happen. 70 00:04:55,561 --> 00:04:59,190 lt happens at the base of a moving glacier 71 00:04:59,332 --> 00:05:01,493 Where enough rock floWer 72 00:05:01,634 --> 00:05:06,799 is available to act as a polishing agent. 73 00:05:09,575 --> 00:05:12,305 Tiny fragments of rock trapped in the ice 74 00:05:12,445 --> 00:05:16,541 rubbed at this slab like fine grade sandpaper. 75 00:05:16,983 --> 00:05:18,951 The smooth surface stretching far up 76 00:05:19,085 --> 00:05:20,416 the side of the mountain 77 00:05:20,553 --> 00:05:24,353 shoWs that the ice here Was once one kilometre thick. 78 00:05:24,490 --> 00:05:28,517 But the ice carried more than just poWdered rock. 79 00:05:28,661 --> 00:05:30,424 These scratches on the bedrock surface 80 00:05:30,563 --> 00:05:36,126 here are typical for formerly glaciated areas. 81 00:05:36,269 --> 00:05:39,670 They are proof of the moving boulders 82 00:05:39,806 --> 00:05:42,297 at the base of the glacier. 83 00:05:42,442 --> 00:05:44,842 FolloWing the scratches across the landscape, 84 00:05:44,977 --> 00:05:47,343 Agassiz realised that it Wasn't biblical floods 85 00:05:47,480 --> 00:05:49,675 that had left erratic boulders stranded, 86 00:05:49,816 --> 00:05:51,181 it Was ice 87 00:05:51,317 --> 00:05:54,548 that once had filled this entire valley. 88 00:05:59,292 --> 00:06:01,556 Geologists have noW been all over the Alps 89 00:06:01,694 --> 00:06:02,922 looking for evidence of rock 90 00:06:03,062 --> 00:06:04,927 that had been shattered and pulverised 91 00:06:05,064 --> 00:06:06,759 by the glaciers. 92 00:06:06,899 --> 00:06:09,163 They've plotted the location of terminal marains 93 00:06:09,302 --> 00:06:10,564 and erratic boulders 94 00:06:10,703 --> 00:06:13,228 to see the maximum extent of the ice 95 00:06:13,373 --> 00:06:16,035 and they've found that practically the entire country 96 00:06:16,175 --> 00:06:17,608 Would have been covered. 97 00:06:17,744 --> 00:06:19,302 18,000 years ago 98 00:06:19,445 --> 00:06:22,209 a sea of ice one kilometre thick 99 00:06:22,348 --> 00:06:25,374 Would have covered the site of Geneva. 100 00:06:36,529 --> 00:06:38,190 lt soon became clear that the ice 101 00:06:38,331 --> 00:06:41,129 had spread beyond SWitzerland. 102 00:06:43,302 --> 00:06:45,862 Erratic boulders found in other countries, 103 00:06:46,005 --> 00:06:48,701 marked the outlines of vast ice sheets 104 00:06:48,841 --> 00:06:52,709 that had also covered much of Europe and Northern America. 105 00:06:54,147 --> 00:06:57,844 The ice Was up to four kilometres thick in places, 106 00:06:57,984 --> 00:07:00,316 transforming the landscape into bleak, 107 00:07:00,453 --> 00:07:03,047 featureless plateaux. 108 00:07:12,231 --> 00:07:13,926 The discovery that the earth's climate 109 00:07:14,066 --> 00:07:15,966 had once been completely different 110 00:07:16,102 --> 00:07:18,468 had a profound impact. 111 00:07:25,912 --> 00:07:28,380 Geologists started on a journey through time 112 00:07:28,514 --> 00:07:30,243 to trace the tangled history 113 00:07:30,383 --> 00:07:33,318 of climate change on our planet. 114 00:07:40,626 --> 00:07:42,025 A crucial step in understanding 115 00:07:42,161 --> 00:07:44,493 the history of the massive ice sheets 116 00:07:44,630 --> 00:07:45,995 came from looking at a place, 117 00:07:46,132 --> 00:07:47,497 thousands of kilometres 118 00:07:47,633 --> 00:07:50,602 from the furthest reaches of ice cover; 119 00:07:50,736 --> 00:07:54,399 the tropical island of Barbados. 120 00:08:00,379 --> 00:08:03,507 Maureen Raymo is a geochemist visiting Barbados 121 00:08:03,649 --> 00:08:06,914 to track the precise course of the lce Age. 122 00:08:09,121 --> 00:08:11,487 Strange as it may seem this far south, 123 00:08:11,624 --> 00:08:15,788 the ice has left its mark on the rocks that cover the island. 124 00:08:16,863 --> 00:08:20,458 The island is made almost entirely of ancient coral reefs. 125 00:08:20,600 --> 00:08:21,794 Unlike the other islands 126 00:08:21,934 --> 00:08:24,266 of the eastern Caribbean Which are volcanic, 127 00:08:24,403 --> 00:08:26,462 this one is constructional having 128 00:08:26,606 --> 00:08:28,699 been made out of coral reefs. 129 00:08:28,841 --> 00:08:29,865 Everything We're seeing here 130 00:08:30,009 --> 00:08:31,738 is an ancient fossilised coral reef. 131 00:08:31,878 --> 00:08:34,574 lt's beautiful, l mean you can even see the individual polyps 132 00:08:34,714 --> 00:08:36,272 on these corals still. 133 00:08:36,415 --> 00:08:41,580 Here's a huge conch shell beautifully preserved. 134 00:08:44,023 --> 00:08:46,514 This fossilised reef can only have been stranded 135 00:08:46,659 --> 00:08:49,890 by a massive drop in sea-level. 136 00:08:50,029 --> 00:08:53,556 The cause of this drop Was surprisingly obvious. 137 00:08:56,202 --> 00:08:57,533 As the ice sheet greW it 138 00:08:57,670 --> 00:09:01,970 locked up millions of cubic kilometres of Water. 139 00:09:02,108 --> 00:09:04,201 At their maximum extent ice sheets 140 00:09:04,343 --> 00:09:09,440 caused World-Wide sea-levels to drop by 120 metres. 141 00:09:10,616 --> 00:09:12,811 This Would have had a global effect 142 00:09:12,952 --> 00:09:15,944 changing the shape of the continents. 143 00:09:20,626 --> 00:09:23,754 ln Barbados the coral reef groWing around the island 144 00:09:23,896 --> 00:09:26,956 Would have emerged and become dry land. 145 00:09:32,305 --> 00:09:35,331 But it's not just one coral terrace on Barbados, 146 00:09:35,474 --> 00:09:39,205 there are several stepping up the side of the island. 147 00:09:45,051 --> 00:09:49,420 Repeated terraces must mean repeated changes in sea-level 148 00:09:49,555 --> 00:09:52,285 and repeated changes in sea-level mean not one 149 00:09:52,425 --> 00:09:55,861 but many ice sheets Waxing and Waning. 150 00:10:01,434 --> 00:10:03,061 Barbados is the only island 151 00:10:03,202 --> 00:10:06,000 to have these multiple terraces and they exist 152 00:10:06,138 --> 00:10:09,198 because it's doing something rather strange. 153 00:10:12,545 --> 00:10:14,513 Barbados is very unusual island 154 00:10:14,647 --> 00:10:17,582 because it's very sloWly being uplifted out of the sea 155 00:10:17,717 --> 00:10:20,083 by tectonic forces. 156 00:10:20,219 --> 00:10:22,119 So What We see on Barbados is a series 157 00:10:22,254 --> 00:10:24,484 of steps made up of coral reefs 158 00:10:24,624 --> 00:10:26,455 that go up in elevation 159 00:10:26,592 --> 00:10:28,082 and also go back in time 160 00:10:28,227 --> 00:10:29,489 because you can imagine the, 161 00:10:29,629 --> 00:10:31,153 the highest coral reef is the one 162 00:10:31,297 --> 00:10:32,787 that's been lifted out, 163 00:10:32,932 --> 00:10:34,923 has been lifted out of the ocean the longest 164 00:10:35,067 --> 00:10:38,161 so they're all sloWly being pushed up out of the ocean. 165 00:10:40,239 --> 00:10:42,298 Because Barbados is being lifted up 166 00:10:42,441 --> 00:10:44,033 it's producing a unique record 167 00:10:44,176 --> 00:10:47,168 of changing sea-levels and climate. 168 00:10:52,351 --> 00:10:54,649 Every time sea-levels rise and fall 169 00:10:54,787 --> 00:10:57,449 a neW coral terrace emerges. 170 00:11:12,605 --> 00:11:14,766 So here We are, We're on the ancient reef crest 171 00:11:14,907 --> 00:11:17,501 right noW and We knoW it's the top of the reef 172 00:11:17,643 --> 00:11:20,111 because there's all these cervicornis 173 00:11:20,246 --> 00:11:21,577 or staghorn coral pieces 174 00:11:21,714 --> 00:11:23,272 and that's a type of coral that only groWs 175 00:11:23,416 --> 00:11:25,077 Within a feW metres of sea-level, 176 00:11:25,217 --> 00:11:27,242 so We have very concrete evidence that, 177 00:11:27,386 --> 00:11:29,547 that What We're standing on used to be at sea-level. 178 00:11:29,689 --> 00:11:34,353 lt's been uplifted by the tectonic uplift of Barbados 179 00:11:34,794 --> 00:11:37,627 and We can very clearly see one more terrace beloW 180 00:11:37,763 --> 00:11:40,231 and just over that terrace just out of sight 181 00:11:40,366 --> 00:11:42,197 is a third terrace. 182 00:11:42,334 --> 00:11:44,427 All three of these terraces are reflecting times 183 00:11:44,570 --> 00:11:47,835 When it Was very Warm, When the sea-level Was very high. 184 00:11:47,973 --> 00:11:50,874 NoW by the late 60s/ early 70s 185 00:11:51,010 --> 00:11:52,841 We'd developed techniques that alloWed us to date 186 00:11:52,978 --> 00:11:54,502 specimens such as this 187 00:11:54,647 --> 00:11:58,014 and so We noW knoW that this reef system right here 188 00:11:58,150 --> 00:12:00,380 is 125,000 years old. 189 00:12:00,519 --> 00:12:02,009 The one We can see right there 190 00:12:02,154 --> 00:12:04,145 is 105,000 years old, 191 00:12:04,290 --> 00:12:07,885 and the one that's just out of sight is 82,000 years, 192 00:12:08,027 --> 00:12:10,291 so What We have is a really nice record 193 00:12:10,429 --> 00:12:14,229 of Warm climates going back in time. 194 00:12:18,237 --> 00:12:19,226 On the other side of the World 195 00:12:19,371 --> 00:12:23,171 is direct evidence of the colder periods in time. 196 00:12:23,309 --> 00:12:26,005 The finely crushed gravel in this SWiss quarry 197 00:12:26,145 --> 00:12:29,080 Was left behind by the glaciers. 198 00:12:29,215 --> 00:12:30,842 This particular quarry consists 199 00:12:30,983 --> 00:12:33,110 of distinct layers Which piled up 200 00:12:33,252 --> 00:12:36,016 over half a million years. 201 00:12:36,455 --> 00:12:38,116 This sediment up here 202 00:12:38,257 --> 00:12:40,623 With these quite large boulders in it, 203 00:12:40,760 --> 00:12:42,284 it's deposited 204 00:12:42,428 --> 00:12:44,487 by a glacial melt Water stream 205 00:12:44,630 --> 00:12:46,757 right in front of the active ice, 206 00:12:46,899 --> 00:12:51,632 maybe a feW tens to a feW hundreds of metres at the most, 207 00:12:51,771 --> 00:12:54,569 so this is a direct evidence of the presence 208 00:12:54,707 --> 00:12:57,141 of the ice at that place, 209 00:12:57,276 --> 00:12:59,141 and then if you look doWn here 210 00:12:59,278 --> 00:13:01,007 that's a sediment deposited 211 00:13:01,147 --> 00:13:05,243 in a small lake Which Was produced by a glacier. 212 00:13:05,384 --> 00:13:08,353 So We have evidence of tWo glaciations 213 00:13:08,487 --> 00:13:12,651 Within these three metres of a geologic section. 214 00:13:13,292 --> 00:13:15,226 SandWiched betWeen the tWo layers shoWing 215 00:13:15,361 --> 00:13:18,592 When temperatures Were cold is a third layer 216 00:13:18,731 --> 00:13:21,666 Which tells a very different story. 217 00:13:21,801 --> 00:13:24,235 You see these peculiar pieces 218 00:13:24,370 --> 00:13:27,237 of something sticking out. 219 00:13:27,373 --> 00:13:29,773 lf l grab one of these pieces 220 00:13:29,909 --> 00:13:32,503 We have a beautiful piece of fossil Wood. 221 00:13:32,645 --> 00:13:36,206 lf We analyse all the fossil pieces of Wood 222 00:13:36,348 --> 00:13:39,647 in here We can conclude that the temperature 223 00:13:39,785 --> 00:13:42,276 Was even Warmer than at present 224 00:13:42,421 --> 00:13:45,185 When the surrounding forests existed here 225 00:13:45,324 --> 00:13:49,158 by about 2-2.5 degrees Celsius, 226 00:13:49,295 --> 00:13:54,323 so this layer is an important document 227 00:13:54,466 --> 00:13:57,333 telling us that in-betWeen tWo layers 228 00:13:57,469 --> 00:14:00,097 of very cold geologic environment 229 00:14:00,239 --> 00:14:02,070 We find this spread 230 00:14:02,208 --> 00:14:05,905 of actually Warmer than present climate. 231 00:14:06,512 --> 00:14:09,447 The change from cold to Warm and back to cold 232 00:14:09,582 --> 00:14:12,915 happened in just 150,000 years. 233 00:14:13,052 --> 00:14:15,452 ln fact, the quarry shoWs that the climate flipped 234 00:14:15,588 --> 00:14:16,816 at least three times 235 00:14:16,956 --> 00:14:19,720 in the remarkably short period. 236 00:14:26,198 --> 00:14:29,531 The evidence from places like SWitzerland and Barbados 237 00:14:29,668 --> 00:14:32,603 has revealed a pattern in the lce Age. 238 00:14:34,974 --> 00:14:36,532 Over the last million years 239 00:14:36,675 --> 00:14:39,974 the ice sheets have Waxed and Waned 10 times, 240 00:14:40,112 --> 00:14:43,479 but they've never entirely disappeared. 241 00:14:47,786 --> 00:14:50,050 Yet a million years is just a brief moment 242 00:14:50,189 --> 00:14:51,816 in earth's history. 243 00:14:51,957 --> 00:14:55,518 To see Whether this pattern continued back indefinitely 244 00:14:55,661 --> 00:14:58,960 meant looking in a surprising place. 245 00:15:09,708 --> 00:15:14,338 This ship is pushing back the boundaries of climate history. 246 00:15:16,882 --> 00:15:18,816 lt's the only ship in the World that drills 247 00:15:18,951 --> 00:15:21,784 deep into the ocean sediment. 248 00:15:29,295 --> 00:15:31,126 lt drills 24 hours a day, 249 00:15:31,263 --> 00:15:33,094 seven days a Week. 250 00:15:33,232 --> 00:15:36,929 The running costs are $45 million a year, 251 00:15:38,103 --> 00:15:40,128 and all this to bring up kilometre 252 00:15:40,272 --> 00:15:43,002 after kilometre of mud. 253 00:15:48,647 --> 00:15:51,377 The notion of glaciations and inter-glaciations, 254 00:15:51,517 --> 00:15:53,747 the Waxing and Waning of continental ice sheets, 255 00:15:53,886 --> 00:15:56,150 Was exactly that, it Was first recognised 256 00:15:56,288 --> 00:15:57,220 and studied on continents. 257 00:15:57,356 --> 00:15:58,380 The trouble With continental records 258 00:15:58,524 --> 00:15:59,388 is that they're fragmented. 259 00:15:59,525 --> 00:16:01,857 You're studying outcrops, erosion is there, 260 00:16:01,994 --> 00:16:03,859 you're missing part of the record. 261 00:16:03,996 --> 00:16:05,122 That is not the case, 262 00:16:05,264 --> 00:16:07,789 nearly as much in the oceans. 263 00:16:11,170 --> 00:16:13,638 The cores of mud are reduced to this dusting 264 00:16:13,772 --> 00:16:16,070 of microscopic shells. 265 00:16:16,208 --> 00:16:19,609 The shells belong to animals called forams. 266 00:16:19,745 --> 00:16:21,736 lmprinted in the shells is information 267 00:16:21,880 --> 00:16:26,317 about What the climate Was like When the forams Were alive. 268 00:16:27,553 --> 00:16:29,384 When they died they sank to the sea floor 269 00:16:29,521 --> 00:16:30,852 and they Were incorporated in layers. 270 00:16:30,990 --> 00:16:32,548 Those layers stacked up over time 271 00:16:32,691 --> 00:16:34,750 and We core those layers continuously 272 00:16:34,893 --> 00:16:37,259 to get a continuous record of climate change. 273 00:16:37,396 --> 00:16:38,954 And this particular place is a good place 274 00:16:39,098 --> 00:16:40,588 because We have a very fixed section 275 00:16:40,733 --> 00:16:43,361 so that We can tell that story in great detail. 276 00:16:44,570 --> 00:16:48,802 This section of mud built up over 20,000 years. 277 00:16:49,742 --> 00:16:51,505 At this site in the North Atlantic, 278 00:16:51,643 --> 00:16:56,512 there's 20 million years of mud stacked up on the ocean floor. 279 00:16:58,417 --> 00:17:00,544 A constant supply of forams is produced 280 00:17:00,686 --> 00:17:03,177 by the drilling programme. 281 00:17:03,322 --> 00:17:04,653 Different species thrive 282 00:17:04,790 --> 00:17:07,054 in different Water temperatures. 283 00:17:07,192 --> 00:17:08,955 Counting the various types of forams 284 00:17:09,094 --> 00:17:11,654 and analysing the chemistry of their shells 285 00:17:11,797 --> 00:17:13,196 gives an indication of the climate 286 00:17:13,332 --> 00:17:16,199 at the time the forams Were alive. 287 00:17:16,335 --> 00:17:19,361 The analysis is agonisingly sloW Work, 288 00:17:19,505 --> 00:17:22,201 but it has revealed the pattern of climate change 289 00:17:22,341 --> 00:17:25,538 since the age of the dinosaurs. 290 00:17:26,545 --> 00:17:28,342 We've been able to reconstruct 291 00:17:28,480 --> 00:17:30,175 hoW global temperatures have changed 292 00:17:30,315 --> 00:17:32,146 over the last 70 million years. 293 00:17:32,284 --> 00:17:33,683 Here is today, 294 00:17:33,819 --> 00:17:35,252 and this is 70 million years ago, 295 00:17:35,387 --> 00:17:36,354 the time of the dinosaurs, 296 00:17:36,488 --> 00:17:38,353 and this is Warm hot climates 297 00:17:38,490 --> 00:17:40,481 and this is cold. 298 00:17:40,626 --> 00:17:42,150 What We've seen is 299 00:17:42,294 --> 00:17:44,762 from about 70 to about 40 million years ago 300 00:17:44,897 --> 00:17:46,421 it Was extremely hot, 301 00:17:46,565 --> 00:17:47,589 much Warmer than today, 302 00:17:47,733 --> 00:17:50,566 about 15 degrees Warmer than today, 303 00:17:50,702 --> 00:17:52,101 on average, 304 00:17:52,237 --> 00:17:53,829 and that, since that time 305 00:17:53,972 --> 00:17:56,805 temperatures have been gradually falling. 306 00:17:56,942 --> 00:17:58,603 At 35 million years 307 00:17:58,744 --> 00:18:01,042 a very rapid cooling associated 308 00:18:01,180 --> 00:18:03,114 With the glaciation of the Antarctic. 309 00:18:03,248 --> 00:18:05,045 ln the last feW million years 310 00:18:05,184 --> 00:18:06,742 We've been groWing large ice sheets 311 00:18:06,885 --> 00:18:08,853 under North America and Scandinavia, 312 00:18:08,987 --> 00:18:11,922 so really seen a large-scale pattern 313 00:18:12,057 --> 00:18:14,025 of global cooling that's characterised 314 00:18:14,159 --> 00:18:16,719 the last 70 million years. 315 00:18:18,163 --> 00:18:20,131 So the pattern of fluctuating ice sheets 316 00:18:20,265 --> 00:18:22,290 is a comparatively recent event 317 00:18:22,434 --> 00:18:23,958 and in geological terms 318 00:18:24,103 --> 00:18:26,162 We're still in the lce Age. 319 00:18:26,305 --> 00:18:27,670 There are still permanent ice sheets 320 00:18:27,806 --> 00:18:29,637 on Antarctica and Greenland 321 00:18:29,775 --> 00:18:32,175 and glaciers in the high mountains. 322 00:18:32,311 --> 00:18:34,336 Thanks to the forams We noW knoW 323 00:18:34,480 --> 00:18:37,278 that this hasn't alWays been the case. 324 00:18:37,416 --> 00:18:38,906 During the time of the dinosaurs, 325 00:18:39,051 --> 00:18:40,985 and for millions of years after, 326 00:18:41,120 --> 00:18:44,954 it Was too Warm for ice to exist anywhere on Earth. 327 00:18:46,892 --> 00:18:50,225 What about before the dinosaurs though? 328 00:18:50,929 --> 00:18:53,955 To find out Whether the climate had alWays been Warm 329 00:18:54,099 --> 00:18:57,364 you need to travel back in time. 330 00:19:15,254 --> 00:19:16,881 Maarten de Wit is a geologist 331 00:19:17,022 --> 00:19:19,991 Well used to travelling back in time, 332 00:19:21,894 --> 00:19:25,261 back through hundreds of millions of years. 333 00:19:27,099 --> 00:19:30,466 This mosaic of rock fragments is called tillite 334 00:19:30,602 --> 00:19:33,093 and When it Was discovered here in South Africa 335 00:19:33,238 --> 00:19:34,671 it turned geologists' vieW 336 00:19:34,806 --> 00:19:38,003 of the African climate on its head. 337 00:19:38,143 --> 00:19:39,667 Look at this extraordinary rock, 338 00:19:39,811 --> 00:19:41,836 this, it's a very strange rock 339 00:19:41,980 --> 00:19:43,572 and What makes it very strange is, 340 00:19:43,715 --> 00:19:45,148 is all these rock fragments - 341 00:19:45,284 --> 00:19:47,912 big ones and small ones, round ones. 342 00:19:48,053 --> 00:19:49,315 This is the unusual thing, 343 00:19:49,454 --> 00:19:52,116 you don't usually get angular and round ones together 344 00:19:52,257 --> 00:19:53,724 and big ones and small ones together. 345 00:19:53,859 --> 00:19:55,349 This is just chaotic. 346 00:19:55,494 --> 00:19:59,624 lt must have been extremely difficult to interpret this rock. 347 00:19:59,765 --> 00:20:01,790 The first geologists to map this in detail 348 00:20:01,934 --> 00:20:04,164 spent some time in the northern hemisphere 349 00:20:04,303 --> 00:20:05,565 and the Way they interpreted this 350 00:20:05,704 --> 00:20:07,467 Was that these rock fragments 351 00:20:07,606 --> 00:20:10,769 must have been deposite by some sort of ice sheet. 352 00:20:10,909 --> 00:20:14,675 The ice sheet Would have moved over the bedrock, 353 00:20:14,813 --> 00:20:15,837 picked up a lot of rock, 354 00:20:15,981 --> 00:20:18,415 round it to a very fine poWdery matrix, 355 00:20:18,550 --> 00:20:20,108 this grey-green material, 356 00:20:20,252 --> 00:20:22,777 plucked up a Whole lot of rock fragments everywhere, 357 00:20:22,921 --> 00:20:24,513 moved over a Water body 358 00:20:24,656 --> 00:20:26,647 and as it sat over that Water body 359 00:20:26,792 --> 00:20:29,852 and melted it Would have dropped all its material 360 00:20:29,995 --> 00:20:31,792 and that reasonable explanation, 361 00:20:31,930 --> 00:20:33,397 it seems to be the best explanation, 362 00:20:33,532 --> 00:20:37,093 to explain this sort of chaotic set of fragments 363 00:20:37,236 --> 00:20:39,204 in this rock floWer. 364 00:20:39,338 --> 00:20:41,169 BeloW and above it We have fossils 365 00:20:41,306 --> 00:20:43,467 and We knoW the age of these fossils 366 00:20:43,609 --> 00:20:46,840 and it turns out that this particular tillite 367 00:20:46,979 --> 00:20:49,072 is 300 million years old, 368 00:20:49,214 --> 00:20:51,978 so that's, that's an amazing thing to think, 369 00:20:52,117 --> 00:20:54,210 300 million years ago that this area here 370 00:20:54,353 --> 00:20:56,685 in South Africa Was covered 371 00:20:56,822 --> 00:20:59,450 by a very thick ice sheet. 372 00:20:59,591 --> 00:21:00,990 Temperatures here in this climate 373 00:21:01,126 --> 00:21:02,753 must have been very different, 374 00:21:02,894 --> 00:21:08,093 an lce Age, a huge ice sheet covering this, this countryside. 375 00:21:14,039 --> 00:21:17,202 The ancient tillite found in this part of South Africa 376 00:21:17,342 --> 00:21:19,367 has also been found scattered in other continents 377 00:21:19,511 --> 00:21:23,413 like Antarctica, lndia and Australia. 378 00:21:23,548 --> 00:21:25,243 lt's all about the same age - 379 00:21:25,384 --> 00:21:28,046 300 million years or so - 380 00:21:28,186 --> 00:21:29,847 but this Widespread distribution 381 00:21:29,988 --> 00:21:31,649 does make perfect sense, 382 00:21:31,790 --> 00:21:34,190 as Maarten explains. 383 00:21:34,326 --> 00:21:35,918 Well you, you've got to remember 384 00:21:36,061 --> 00:21:37,995 that 300 million years ago 385 00:21:38,130 --> 00:21:40,496 the World Was very different. 386 00:21:40,632 --> 00:21:42,463 All the continents in the southern hemisphere 387 00:21:42,601 --> 00:21:44,728 Were together as one big super continent. 388 00:21:44,870 --> 00:21:47,703 Over here, here's lndia and Madagascar, 389 00:21:47,839 --> 00:21:49,272 can see Australia over there 390 00:21:49,408 --> 00:21:53,674 and the centrepiece here stills makes this large land mass of Africa. 391 00:21:53,812 --> 00:21:56,337 ln this frameWork and bunched together 392 00:21:56,481 --> 00:21:59,746 the deposit makes sense in terms of a huge ice sheet 393 00:21:59,885 --> 00:22:01,876 that Was covering part of, 394 00:22:02,020 --> 00:22:04,113 or the largest part of this super-continent 395 00:22:04,256 --> 00:22:05,382 called GondWana 396 00:22:05,524 --> 00:22:06,855 and of course the centre 397 00:22:06,992 --> 00:22:08,220 of this ice sheet Would have been over here, 398 00:22:08,360 --> 00:22:12,956 so this part of it Would have been sitting around the South Pole. 399 00:22:22,874 --> 00:22:24,739 The tillites have revealed that the Earth 400 00:22:24,876 --> 00:22:28,175 has experienced an lce Age before. 401 00:22:29,281 --> 00:22:32,273 On that occasion ice gripped the super-continent 402 00:22:32,417 --> 00:22:35,682 for more than 60 million years. 403 00:22:40,826 --> 00:22:43,021 This is not the only lce Age We've had. 404 00:22:43,161 --> 00:22:44,788 We knoW in the far distant past 405 00:22:44,930 --> 00:22:47,524 We've had more than one glaciation. 406 00:22:47,666 --> 00:22:49,327 Even in southern Africa We have evidence, 407 00:22:49,468 --> 00:22:52,437 good evidence for a glaciation in the Ordovician 408 00:22:52,571 --> 00:22:55,768 430/440 million years ago 409 00:22:55,907 --> 00:22:57,602 and further afield in Africa, 410 00:22:57,743 --> 00:22:59,404 many parts of Africa We have 411 00:22:59,544 --> 00:23:02,240 examples of glaciation 700 million years ago 412 00:23:02,381 --> 00:23:03,939 and elseWhere in the World We can go back 413 00:23:04,082 --> 00:23:08,178 as far as almost 21/2 billion years ago, 414 00:23:08,320 --> 00:23:11,551 a set of tillites in North America 415 00:23:11,690 --> 00:23:13,157 so it looks like that 416 00:23:13,291 --> 00:23:15,851 as far back as We can go in this record 417 00:23:15,994 --> 00:23:20,488 that the earth has been in and out of lce Ages. 418 00:23:22,401 --> 00:23:24,699 Looking at these tillites and combining them 419 00:23:24,836 --> 00:23:26,667 With the evidence from the ocean floor 420 00:23:26,805 --> 00:23:28,670 it's been possible t build up a picture 421 00:23:28,807 --> 00:23:31,401 of Earth's changing climate. 422 00:23:31,543 --> 00:23:33,340 For most of its history it seems to 423 00:23:33,478 --> 00:23:35,378 have been Warmer than today, 424 00:23:35,514 --> 00:23:38,142 but every noW and then Earth has been plunged 425 00:23:38,283 --> 00:23:40,012 into vicious cold 426 00:23:40,152 --> 00:23:41,881 so that huge areas have been covered 427 00:23:42,020 --> 00:23:44,511 by ice for millions of years. 428 00:23:44,656 --> 00:23:46,783 Then the ice is shaken off again 429 00:23:46,925 --> 00:23:50,156 and the obvious question is; Why? 430 00:23:57,469 --> 00:23:58,697 The first hint of the ansWer 431 00:23:58,837 --> 00:24:00,395 came from looking at the ice remaining 432 00:24:00,539 --> 00:24:02,939 from the current lce Age. 433 00:24:04,643 --> 00:24:07,271 This is one of the most isolated laboratories 434 00:24:07,412 --> 00:24:09,903 on the face of the planet. 435 00:24:18,957 --> 00:24:21,448 Apart from the occasional Wayward bird, 436 00:24:21,593 --> 00:24:25,962 the nearest sign of life is 500 kilometres aWay. 437 00:24:31,636 --> 00:24:33,433 This is the North Grip campsite 438 00:24:33,572 --> 00:24:35,506 in the centre of Greenland. 439 00:24:35,640 --> 00:24:36,902 For 3 months of the year 440 00:24:37,042 --> 00:24:40,205 it's the home to a team of 30 scientists. 441 00:24:41,379 --> 00:24:43,108 Until about 12,000 years ago 442 00:24:43,248 --> 00:24:44,806 the Whole of Scandinavia 443 00:24:44,950 --> 00:24:47,646 Was covered by a large ice sheet, 444 00:24:47,786 --> 00:24:48,844 This ice sheet also stretched 445 00:24:48,987 --> 00:24:51,353 into parts of Germany and Great Britain. 446 00:24:51,490 --> 00:24:53,287 lceland had a separate ice sheet 447 00:24:53,425 --> 00:24:56,087 covering it completely and then We had a huge ice sheet 448 00:24:56,228 --> 00:24:58,162 over all of Canada 449 00:24:58,296 --> 00:25:01,163 reaching into the present United States. 450 00:25:01,299 --> 00:25:03,290 Then this dramatic change 451 00:25:03,435 --> 00:25:05,300 comes about in only a feW thousand years. 452 00:25:05,437 --> 00:25:08,270 All these big ice sheets they disappeared completely except 453 00:25:08,406 --> 00:25:09,839 for the Greenland ice sheets 454 00:25:09,975 --> 00:25:12,705 on Which We are sitting right noW. 455 00:25:13,144 --> 00:25:15,112 lt's very good that We have this ice sheet, 456 00:25:15,247 --> 00:25:16,544 this remnant of the lce Age, 457 00:25:16,681 --> 00:25:18,979 because it really makes it possible for us 458 00:25:19,117 --> 00:25:22,086 to understand What Was going on at the time really. 459 00:25:22,220 --> 00:25:25,280 This is What We are aiming at With our Work here. 460 00:25:42,274 --> 00:25:45,300 The scientists here have one aim in mind; 461 00:25:46,144 --> 00:25:48,374 to produce one of the longest continuous 462 00:25:48,513 --> 00:25:51,311 cores of ice ever drilled. 463 00:25:54,119 --> 00:25:56,883 So far they're about half Way. 464 00:25:57,022 --> 00:26:00,116 There's one and a half kilometres to go. 465 00:26:04,863 --> 00:26:07,354 Each metre of ice brought to the surface 466 00:26:07,499 --> 00:26:11,435 is a step further back into the lce Age. 467 00:26:16,975 --> 00:26:18,738 We see structural difference 468 00:26:18,877 --> 00:26:20,811 betWeen fine grained Winter snoW 469 00:26:20,946 --> 00:26:23,312 and coarse grained summer snoW 470 00:26:23,448 --> 00:26:25,143 and these differences are preserved 471 00:26:25,283 --> 00:26:27,513 in the ice so We are able to count annual layers 472 00:26:27,652 --> 00:26:31,281 all the Way doWn through just like tree rings. 473 00:26:32,958 --> 00:26:37,224 lf you measure the lead content in the ice cores 474 00:26:37,362 --> 00:26:40,490 doWn through time you can see that this increased 475 00:26:40,632 --> 00:26:41,997 during Roman Times because 476 00:26:42,133 --> 00:26:44,431 the Romans they had a lot of lead mines 477 00:26:44,569 --> 00:26:46,332 all over their Empire 478 00:26:46,471 --> 00:26:47,938 and then you see that this decreases 479 00:26:48,073 --> 00:26:49,768 after the decline of the Empire. 480 00:26:49,908 --> 00:26:52,138 You see it increases in our century 481 00:26:52,277 --> 00:26:56,737 and When everybody stops using leaded gasoline 482 00:26:56,881 --> 00:26:58,610 then the curve is falling again you knoW. 483 00:26:58,750 --> 00:27:00,650 There's much less lead in the atmosphere, 484 00:27:00,785 --> 00:27:02,184 so everything that has to do 485 00:27:02,320 --> 00:27:04,254 With the atmosphere, the history of it 486 00:27:04,389 --> 00:27:05,549 and the history of human beings 487 00:27:05,690 --> 00:27:07,920 is really preserved in those ice cores 488 00:27:08,059 --> 00:27:09,822 and it's really fantastic. 489 00:27:11,563 --> 00:27:13,360 The ancient history of the atmosphere 490 00:27:13,498 --> 00:27:16,092 can also be found in the ice. 491 00:27:16,935 --> 00:27:17,959 Tiny pockets of air 492 00:27:18,103 --> 00:27:21,834 become trapped as snoW falls and compacts. 493 00:27:21,973 --> 00:27:25,909 These bubbles of atmosphere are time-capsules. 494 00:27:32,484 --> 00:27:34,179 When researchers began sampling them 495 00:27:34,319 --> 00:27:36,981 to test for carbon dioxide content, 496 00:27:37,122 --> 00:27:37,986 they found something 497 00:27:38,123 --> 00:27:40,990 that stopped them in their tracks. 498 00:27:44,462 --> 00:27:46,225 During the last cold period, 499 00:27:46,364 --> 00:27:50,130 carbon dioxide levels Were much loWer than today. 500 00:27:53,705 --> 00:27:55,673 This is very interesting and makes sense, 501 00:27:55,807 --> 00:27:58,605 because of the role that carbon dioxide plays 502 00:27:58,743 --> 00:28:00,438 in controlling earth's climate. 503 00:28:00,578 --> 00:28:02,136 lt's a greenhouse gas 504 00:28:02,280 --> 00:28:04,248 that's alWays present in our atmosphere 505 00:28:04,382 --> 00:28:06,976 and it acts as, as, as a thermal blanket 506 00:28:07,118 --> 00:28:09,143 keeping the earth's surface temperature Warmer 507 00:28:09,287 --> 00:28:10,720 than it Would otherwise be 508 00:28:10,855 --> 00:28:12,186 if there Were no CO2, 509 00:28:12,323 --> 00:28:14,450 if there Were no greenhouse gases, 510 00:28:14,592 --> 00:28:16,992 so the fact that during the cold periods 511 00:28:17,128 --> 00:28:18,288 that these greenhouse 512 00:28:18,430 --> 00:28:20,898 carbon dioxide levels Went doWn 513 00:28:21,032 --> 00:28:24,593 and the climate got colder, makes sense from, 514 00:28:24,736 --> 00:28:26,294 from our understanding of the physics 515 00:28:26,438 --> 00:28:29,464 and chemistry of the greenhouse effect. 516 00:28:32,510 --> 00:28:35,240 ln recent years We've heard a lot about the possible links 517 00:28:35,380 --> 00:28:37,678 betWeen carbon dioxide levels today 518 00:28:37,816 --> 00:28:39,875 and global Warming. 519 00:28:40,919 --> 00:28:42,648 But could it be that carbon dioxide 520 00:28:42,787 --> 00:28:44,379 is behind the sWings in temperature 521 00:28:44,522 --> 00:28:48,424 Which have taken place over hundreds of millions of years? 522 00:28:48,560 --> 00:28:50,152 Bob Berner, a geo-chemist, 523 00:28:50,295 --> 00:28:52,160 believes it is. 524 00:28:54,833 --> 00:28:56,926 Before humans Were adding carbon dioxide 525 00:28:57,068 --> 00:28:58,228 to the atmosphere 526 00:28:58,369 --> 00:28:59,768 there Were other natural processes 527 00:28:59,904 --> 00:29:01,838 that Were adding and sub-tracting carbon dioxide 528 00:29:01,973 --> 00:29:03,463 from the atmosphere, 529 00:29:03,608 --> 00:29:06,907 and these are all part of What is knoWn as the long-term carbon cycle 530 00:29:07,045 --> 00:29:09,536 Which operated over many millions of years. 531 00:29:09,681 --> 00:29:11,512 The Whole process starts With the introduction 532 00:29:11,649 --> 00:29:13,207 of CO2 to the atmosphere 533 00:29:13,351 --> 00:29:16,411 by CO2 coming out of volcanoes. 534 00:29:20,925 --> 00:29:22,950 Every time a volcano erupts 535 00:29:23,094 --> 00:29:26,757 carbon dioxide speWs out into the atmosphere. 536 00:29:28,566 --> 00:29:30,625 Left unchecked it Would build up, 537 00:29:30,769 --> 00:29:32,634 but rain gradually Washes it out 538 00:29:32,771 --> 00:29:35,934 and plants draW it into the soil. 539 00:29:38,743 --> 00:29:40,404 This carbon dioxide in the soil 540 00:29:40,545 --> 00:29:42,570 reacts With the rainWater that's percolating 541 00:29:42,714 --> 00:29:45,342 into the soil to form an acid. 542 00:29:49,087 --> 00:29:51,021 The acid eats aWay at the rock 543 00:29:51,156 --> 00:29:53,021 in a process called Weathering 544 00:29:53,158 --> 00:29:57,026 Which converts carbon dioxide into carbonate. 545 00:30:01,599 --> 00:30:04,067 This dissolved carbonate eventually makes 546 00:30:04,202 --> 00:30:08,366 its Way into rivers and eventually by floW of rivers to the sea. 547 00:30:12,377 --> 00:30:14,004 The dissolved carbon is removed 548 00:30:14,145 --> 00:30:17,808 from sea Water by coral and other organisms. 549 00:30:17,949 --> 00:30:19,348 When those organisms die, 550 00:30:19,484 --> 00:30:21,452 their remains build up on the seabed 551 00:30:21,586 --> 00:30:24,316 eventually turning into limestone. 552 00:30:26,724 --> 00:30:29,090 NoW this limestone We have doWn here 553 00:30:29,227 --> 00:30:30,626 completes the cycle eventually 554 00:30:30,762 --> 00:30:33,230 because it becomes buried to such a depth 555 00:30:33,364 --> 00:30:35,161 that it's heated, broken doWn 556 00:30:35,300 --> 00:30:38,599 and the carbon dioxide comes off of the, 557 00:30:38,736 --> 00:30:40,226 is removed from the limestone 558 00:30:40,371 --> 00:30:42,430 and it finds its Way back to the surface 559 00:30:42,574 --> 00:30:44,940 in the form of seepage out of the ground 560 00:30:45,076 --> 00:30:47,510 or eruption from volcanoes, 561 00:30:47,645 --> 00:30:50,443 and this is the long-term carbon cycle. 562 00:30:52,050 --> 00:30:53,347 All things being equal, 563 00:30:53,484 --> 00:30:55,179 levels of carbon dioxide, 564 00:30:55,320 --> 00:30:58,483 CO2, Would stay constant as the gas 565 00:30:58,623 --> 00:31:00,090 is continuously pumped 566 00:31:00,225 --> 00:31:02,921 in and out of the atmosphere, 567 00:31:03,061 --> 00:31:06,656 but the planet is in a constant state of flux. 568 00:31:07,498 --> 00:31:11,798 Continents drift across the face of the earth, 569 00:31:12,570 --> 00:31:14,663 volcanoes burst into life, 570 00:31:14,806 --> 00:31:17,172 and then become extinct, 571 00:31:17,709 --> 00:31:21,076 vegetation comes and goes. 572 00:31:22,947 --> 00:31:26,348 All these factors can affect the carbon cycle, 573 00:31:26,484 --> 00:31:29,180 so using geologist knoWledge of earth's history 574 00:31:29,320 --> 00:31:32,016 Bob Berner set out to estimate hoW much CO2 575 00:31:32,156 --> 00:31:35,648 levels have actually changed over time. 576 00:31:58,549 --> 00:32:03,646 Bob has noW calculated CO2 levels over half a billion years. 577 00:32:07,058 --> 00:32:09,083 As you can see most of the time 578 00:32:09,227 --> 00:32:10,387 carbon dioxide's been considerably 579 00:32:10,528 --> 00:32:12,996 higher than it is at present 580 00:32:13,131 --> 00:32:15,725 and you see high values in the earliest period 581 00:32:15,867 --> 00:32:17,732 droppingto loWer values 582 00:32:17,869 --> 00:32:18,995 in intermediate times 583 00:32:19,137 --> 00:32:21,264 and to intermediately high values 584 00:32:21,406 --> 00:32:22,873 betWeen that time and the present, 585 00:32:23,007 --> 00:32:25,805 but the loWest levels you can see are the present 586 00:32:25,944 --> 00:32:28,811 in a time about 300 million years ago. 587 00:32:28,947 --> 00:32:31,609 This drop here is caused by one particular factor 588 00:32:31,749 --> 00:32:35,185 in Bob's equations; plants. 589 00:32:36,721 --> 00:32:39,451 Plants help to remove CO2 from the atmosphere 590 00:32:39,590 --> 00:32:42,616 by speeding up the Weathering of rocks. 591 00:32:42,760 --> 00:32:45,194 So When plants first evolved and flourished 592 00:32:45,330 --> 00:32:48,891 CO2 levels began to fall. 593 00:32:49,033 --> 00:32:51,001 Those levels reached an all-time loW 594 00:32:51,135 --> 00:32:53,035 300 million years ago, 595 00:32:53,171 --> 00:32:55,799 precisely the time When a massive lce Age 596 00:32:55,940 --> 00:32:59,341 left its imprint in the rocks of South Africa. 597 00:33:03,147 --> 00:33:04,114 This is very gratifying 598 00:33:04,248 --> 00:33:05,579 and indicates that this drop 599 00:33:05,717 --> 00:33:07,912 l believe is due to the rise of the plants 600 00:33:08,052 --> 00:33:09,713 and their acceleration of Weathering. 601 00:33:09,854 --> 00:33:12,982 This acceleration of Weathering l believe caused the CO2 drop 602 00:33:13,124 --> 00:33:16,116 Which lead to the glaciation at 300 million years ago 603 00:33:16,260 --> 00:33:19,229 and Was l think the major cause of this glaciation. 604 00:33:21,933 --> 00:33:23,798 lt is amazing to think that plants 605 00:33:23,935 --> 00:33:27,871 could have triggered the lce Age 300 million years ago. 606 00:33:28,373 --> 00:33:29,635 But carbon dioxide levels 607 00:33:29,774 --> 00:33:31,173 also appear to have been falling 608 00:33:31,309 --> 00:33:34,278 over the last 65 million years, 609 00:33:34,412 --> 00:33:36,437 a decline that seems to have led to the lce Age 610 00:33:36,581 --> 00:33:38,344 We're in today. 611 00:33:39,550 --> 00:33:40,847 An explanation for this drop 612 00:33:40,985 --> 00:33:43,920 is also in the equations; 613 00:33:44,055 --> 00:33:46,080 mountain building. 614 00:33:47,892 --> 00:33:51,123 We knoW that CO2 gets into the atmosphere through volcanoes 615 00:33:51,262 --> 00:33:53,093 but it comes out through to rock Weathering, 616 00:33:53,231 --> 00:33:55,028 and rock Weathering goes on primarily 617 00:33:55,166 --> 00:33:56,929 in the mountainous regions of the World. 618 00:33:57,068 --> 00:34:00,162 We knoW that for the last 40-50 million year 619 00:34:00,304 --> 00:34:01,931 have been unusually active 620 00:34:02,073 --> 00:34:03,267 With respect to mountain building. 621 00:34:03,408 --> 00:34:05,774 There's the Himalayas, the Andes, the Rockies, 622 00:34:05,910 --> 00:34:08,504 and this tectonic activity has probably been 623 00:34:08,646 --> 00:34:11,206 in a large part responsible for the reduction 624 00:34:11,349 --> 00:34:14,147 in atmosphere of carbon dioxide levels. 625 00:34:14,285 --> 00:34:16,150 NoW that's very interesting, 626 00:34:16,287 --> 00:34:19,154 it's obviously been cooling over that time period 627 00:34:19,290 --> 00:34:21,724 so We probably are seeing this causal link 628 00:34:21,859 --> 00:34:24,350 betWeen the earth's tectonic activity 629 00:34:24,495 --> 00:34:27,055 and the earth's climate. 630 00:34:31,402 --> 00:34:33,029 NoW We can begin to understand 631 00:34:33,171 --> 00:34:35,867 the pattern of climate change. 632 00:34:36,808 --> 00:34:38,673 lt's a pattern Which changes to the rhythms 633 00:34:38,810 --> 00:34:43,270 of evolution and the movement of the Earth's tectonic plates. 634 00:34:49,020 --> 00:34:51,921 The climate Wanders from one lce Age to another 635 00:34:52,056 --> 00:34:55,355 as the continents drift around the planet. 636 00:34:58,096 --> 00:34:59,358 But the movements of the continents 637 00:34:59,497 --> 00:35:02,227 can't explain everything. 638 00:35:04,535 --> 00:35:06,332 Over the last million years the ice sheets 639 00:35:06,471 --> 00:35:08,336 have been pulsating to a rhythm 640 00:35:08,473 --> 00:35:11,374 faster than continental drift. 641 00:35:12,176 --> 00:35:16,237 Something else must be driving these cycles. 642 00:35:22,186 --> 00:35:23,619 lce Will never accumulate 643 00:35:23,754 --> 00:35:27,451 if all the snoW of Winter melts the folloWing summer, 644 00:35:27,592 --> 00:35:30,026 but if summers are cold snoW Will survive 645 00:35:30,161 --> 00:35:32,595 from one Winter to the next. 646 00:35:32,730 --> 00:35:34,163 Eventually the layers Will build up 647 00:35:34,298 --> 00:35:36,664 and several decades of cold summers 648 00:35:36,801 --> 00:35:39,770 Will result in a sizeable ice sheet. 649 00:35:39,904 --> 00:35:41,462 lf summers Warmed up again 650 00:35:41,606 --> 00:35:44,871 the ice sheet Would shrink back. 651 00:35:45,843 --> 00:35:48,277 The idea that the pattern of fluctuating ice sheets 652 00:35:48,412 --> 00:35:51,347 Was caused by fluctuating summer temperatures 653 00:35:51,482 --> 00:35:52,972 Was taken up early this century 654 00:35:53,117 --> 00:35:56,985 by a Serbian scientist called Milankovich. 655 00:35:57,121 --> 00:36:00,818 He believed that the cause of these sloW repetitive changes 656 00:36:00,958 --> 00:36:04,860 Was due to the Way the Earth orbits the sun. 657 00:36:13,671 --> 00:36:17,437 The Earth circles the sun With its axis tilted. 658 00:36:17,575 --> 00:36:20,339 That tilt gives us our seasons. 659 00:36:20,478 --> 00:36:22,469 When the North Pole points aWay from the sun, 660 00:36:22,613 --> 00:36:24,604 We experience our Winter, 661 00:36:24,749 --> 00:36:27,809 the southern hemisphere its summer. 662 00:36:30,555 --> 00:36:31,783 On the other side of the orbit, 663 00:36:31,923 --> 00:36:34,551 the situation is reversed. 664 00:36:34,692 --> 00:36:37,525 This is the noW the northern summer. 665 00:36:39,730 --> 00:36:42,062 Over thousands of years the precise orbit 666 00:36:42,200 --> 00:36:45,897 and the tilt of the Earth varies slightly. 667 00:36:46,037 --> 00:36:49,404 lt Wobbles and dips making our summers hotter or colder 668 00:36:49,540 --> 00:36:51,565 as the northern hemisphere moves toWard 669 00:36:51,709 --> 00:36:54,177 or aWay from the sun. 670 00:37:00,218 --> 00:37:03,085 Using this information Milankovich calculated 671 00:37:03,221 --> 00:37:04,882 When the summers Would become cool enough 672 00:37:05,022 --> 00:37:07,820 to cause the ice to return. 673 00:37:09,493 --> 00:37:11,552 Despite the logic of his idea 674 00:37:11,696 --> 00:37:14,631 it Was impossible to prove at the time. 675 00:37:14,765 --> 00:37:19,361 Nobody kneW precisely When summers had Warmed and cooled. 676 00:37:19,503 --> 00:37:22,233 Then, 10 years after Milankovich died, 677 00:37:22,373 --> 00:37:24,204 the coral terraces of Barbados 678 00:37:24,342 --> 00:37:27,106 Were dated for the first time. 679 00:37:29,380 --> 00:37:32,213 This is a curve of hoW hot northern hemisphere 680 00:37:32,350 --> 00:37:36,252 summers had been over the past 250,000 years. 681 00:37:36,387 --> 00:37:39,914 This curve Was first calculated, predicted by Milankovich 682 00:37:40,057 --> 00:37:42,890 and What you can see is that there are times 683 00:37:43,027 --> 00:37:45,257 Where northern hemisphere summers are quite Warm 684 00:37:45,396 --> 00:37:47,796 and at other times, for instance doWn here, 685 00:37:47,932 --> 00:37:49,729 the summers are much cooler 686 00:37:49,867 --> 00:37:52,131 and that these cooler summers, 687 00:37:52,270 --> 00:37:54,465 these loW periods Would be glacial periods 688 00:37:54,605 --> 00:37:57,301 and these Would be the Warm periods 689 00:37:57,441 --> 00:38:00,535 With higher sea-levels and less ice volume. 690 00:38:00,678 --> 00:38:05,240 NoW if We compare this curve to the Barbados data 691 00:38:05,383 --> 00:38:07,783 What you see is that these coral terraces, 692 00:38:07,918 --> 00:38:09,715 including the one We're standing on right noW, 693 00:38:09,854 --> 00:38:13,119 their ages line up almost perfectly 694 00:38:13,257 --> 00:38:14,884 With the time periods that Milankovich 695 00:38:15,026 --> 00:38:16,323 Would have predicted Would be Warm, 696 00:38:16,460 --> 00:38:18,792 therefore less ice and higher sea-levels 697 00:38:18,929 --> 00:38:21,454 and indeed it Was the dating of these coral reef terraces 698 00:38:21,599 --> 00:38:24,363 in the early 70s that proved seminal 699 00:38:24,502 --> 00:38:27,300 for most people accepting the Milankovich hypothesis 700 00:38:27,438 --> 00:38:30,965 that indeed this Was What caused climate change. 701 00:38:33,277 --> 00:38:36,007 This tidy fit betWeen Milankovich's predictions 702 00:38:36,147 --> 00:38:40,174 and the coral dates appear to complete the picture. 703 00:38:40,318 --> 00:38:43,583 With this complex pattern of climate change behind us 704 00:38:43,721 --> 00:38:46,656 What can history tell us about the future? 705 00:38:50,161 --> 00:38:53,187 Today the fear is that man-made global Warming 706 00:38:53,331 --> 00:38:56,664 could bring about a sudden collapse of the ice sheets. 707 00:38:56,801 --> 00:38:58,166 And the fact is that it looks like 708 00:38:58,302 --> 00:39:00,600 such breakdoWns have happened several times 709 00:39:00,738 --> 00:39:05,505 in the past With dramatic and unexpected effects. 710 00:39:07,411 --> 00:39:12,075 Once more the story's in the mud of the ocean floor. 711 00:39:14,518 --> 00:39:16,076 ln his lab near NeW York, 712 00:39:16,220 --> 00:39:18,051 geologist Gerard Bond 713 00:39:18,189 --> 00:39:20,749 Was looking at a core from the North Atlantic 714 00:39:20,891 --> 00:39:24,349 When he spotted some subtle variations. 715 00:39:24,495 --> 00:39:26,895 We noticed as you can see in this core 716 00:39:27,031 --> 00:39:28,521 of 150 centimetres, 717 00:39:28,666 --> 00:39:30,657 there are a number of changes in colour. 718 00:39:30,801 --> 00:39:32,462 Here's a light layer here, 719 00:39:32,603 --> 00:39:34,332 a little darker layer here, 720 00:39:34,472 --> 00:39:36,406 an intermediate colour layer here, 721 00:39:36,540 --> 00:39:40,067 becomes light again doWn to about here, 722 00:39:40,211 --> 00:39:41,906 this one's a little lighter, 723 00:39:42,046 --> 00:39:43,240 this one's lighter yet, 724 00:39:43,381 --> 00:39:46,111 and then it goes back to a darker layer here, 725 00:39:46,250 --> 00:39:48,411 and We kneW from radiocarbon dating 726 00:39:48,552 --> 00:39:51,578 of this core that the top is about 9,000 years, 727 00:39:51,722 --> 00:39:54,520 this level is 14,000 years 728 00:39:54,658 --> 00:39:56,592 and about 20,000 years here. 729 00:39:56,727 --> 00:40:00,185 These bands Were coming very fast 730 00:40:00,331 --> 00:40:03,095 and What that meant Was that these changes in colour 731 00:40:03,234 --> 00:40:06,795 Were coming about every 1 ,000-2,000 years. 732 00:40:09,407 --> 00:40:12,171 Having identified these strange bands of colour, 733 00:40:12,309 --> 00:40:15,870 Gerard set to Work to find out What caused them. 734 00:40:17,982 --> 00:40:20,678 lt Was a gruelling process. 735 00:40:21,819 --> 00:40:23,684 Sample after sample of the cores 736 00:40:23,821 --> 00:40:26,585 Were reduced to sand grains. 737 00:40:27,758 --> 00:40:29,851 Each grain Was counted, 738 00:40:29,994 --> 00:40:33,430 classified and re-counted. 739 00:40:35,699 --> 00:40:38,031 After about a million grains of sand, 740 00:40:38,169 --> 00:40:41,730 Gerard took stock of his curious findings. 741 00:40:43,073 --> 00:40:45,803 We found six layers that had a marked increase 742 00:40:45,943 --> 00:40:48,844 in limestone and dolomite fragments. 743 00:40:48,979 --> 00:40:52,506 The origin of these appears to have been eastern Canada. 744 00:40:52,650 --> 00:40:54,641 ln addition, When We look more carefully 745 00:40:54,785 --> 00:40:55,809 at the sediment, 746 00:40:55,953 --> 00:40:57,648 in-betWeen these six events 747 00:40:57,788 --> 00:40:59,847 there Were additional layers. 748 00:40:59,990 --> 00:41:02,891 These shoWed increases in volcanic ash 749 00:41:03,027 --> 00:41:05,552 that came from lceland and increases 750 00:41:05,696 --> 00:41:08,256 in grains mostly quartz and feltzspar 751 00:41:08,399 --> 00:41:11,493 that Were stained With an iron oxide 752 00:41:11,635 --> 00:41:14,229 that's called hematite and you see some of that here 753 00:41:14,371 --> 00:41:17,670 and here and We believe that these particular grains 754 00:41:17,808 --> 00:41:20,402 are coming from the Gulf of St LaWrence. 755 00:41:22,146 --> 00:41:24,205 There's only one Way so many grains 756 00:41:24,348 --> 00:41:27,283 could have been lifted from the bedrock of Canada and lceland 757 00:41:27,418 --> 00:41:30,114 and transported to the ocean - 758 00:41:30,254 --> 00:41:32,916 they must have hitched a ride. 759 00:41:39,430 --> 00:41:41,022 During the last glaciation 760 00:41:41,165 --> 00:41:43,258 ice sheets scraped over the continents 761 00:41:43,400 --> 00:41:46,836 picking up rock fragments on their Way to the sea. 762 00:41:49,540 --> 00:41:53,840 From there, icebergs carried the grains across the Atlantic. 763 00:41:58,048 --> 00:42:00,539 As the ice melted, the grains Were released 764 00:42:00,684 --> 00:42:03,744 and drifted to the bottom of the ocean. 765 00:42:05,990 --> 00:42:07,389 The sheer number of grains 766 00:42:07,525 --> 00:42:09,356 found in the layers of the sea floor 767 00:42:09,493 --> 00:42:13,953 suggest that enormous armadas of icebergs sWept across the ocean 768 00:42:14,098 --> 00:42:16,828 every feW thousand years. 769 00:42:20,104 --> 00:42:21,537 What-ever caused this, 770 00:42:21,672 --> 00:42:23,105 Work on the Greenland ice core 771 00:42:23,240 --> 00:42:26,073 suggests the invasion of the ocean by icebergs 772 00:42:26,210 --> 00:42:29,611 could have tipped the climate into turmoil. 773 00:42:37,855 --> 00:42:39,516 Each of these slices of ice 774 00:42:39,657 --> 00:42:43,252 represents6 Weeks of climate history. 775 00:42:44,028 --> 00:42:45,518 When the researchers looked at the ice 776 00:42:45,663 --> 00:42:48,598 from the last glaciation in this kind of detail, 777 00:42:48,732 --> 00:42:50,529 they found a completely unexpected 778 00:42:50,668 --> 00:42:53,330 series of temperature jumps. 779 00:42:55,472 --> 00:42:56,734 These jumps coincided 780 00:42:56,874 --> 00:43:00,071 With the surges of the icebergs. 781 00:43:01,445 --> 00:43:03,811 By looking at the ice core in such detail 782 00:43:03,948 --> 00:43:05,142 the researchers in Greenland 783 00:43:05,282 --> 00:43:07,512 discovered the most astonishing thing. 784 00:43:07,651 --> 00:43:09,448 Within the glacial period 785 00:43:09,587 --> 00:43:11,214 there are climate cycles 786 00:43:11,355 --> 00:43:13,550 that are even more rapid. 787 00:43:13,691 --> 00:43:15,682 They last a feW thousand years, 788 00:43:15,826 --> 00:43:18,590 so if l describe a single cycle, 789 00:43:18,729 --> 00:43:21,391 you can imagine along the sloW cooling 790 00:43:21,532 --> 00:43:24,865 and then there's a very rapid Warming 791 00:43:25,002 --> 00:43:26,867 10-12 degrees Celsius 792 00:43:27,004 --> 00:43:28,904 and that Warming happens 793 00:43:29,039 --> 00:43:31,599 Within the span of a single human lifetime. 794 00:43:31,742 --> 00:43:32,902 lt's quite astonishing 795 00:43:33,043 --> 00:43:39,073 hoW quickly the regional climate of the north Atlantic changed. 796 00:43:40,851 --> 00:43:42,079 Ever since these frenetic 797 00:43:42,219 --> 00:43:44,346 changes in temperature came to light 798 00:43:44,488 --> 00:43:48,151 researchers have struggled to understand the cause. 799 00:43:48,892 --> 00:43:50,018 One thing they do knoW 800 00:43:50,160 --> 00:43:51,684 is that climate in the North Atlantic 801 00:43:51,829 --> 00:43:52,818 is strongly influenced 802 00:43:52,963 --> 00:43:56,831 by the Warm Water floWing up from the tropics. 803 00:44:17,988 --> 00:44:21,048 The oceans play a vital role in climate. 804 00:44:21,191 --> 00:44:24,319 Much of the sun's energy is received here in the Tropics, 805 00:44:24,461 --> 00:44:28,488 but ocean currents carry that heat toWards the Poles. 806 00:44:28,632 --> 00:44:30,224 ln particular the Gulf Stream system 807 00:44:30,367 --> 00:44:31,459 in the North Atlantic 808 00:44:31,602 --> 00:44:33,160 carries a vast amount of heat 809 00:44:33,303 --> 00:44:35,794 from the loWer, the loWer latitudes 810 00:44:35,939 --> 00:44:37,236 up to the higher latitudes. 811 00:44:37,374 --> 00:44:39,604 ln fact probably about 30% of, 812 00:44:39,743 --> 00:44:43,076 of the heat delivered to Europe, Western Europe, 813 00:44:43,213 --> 00:44:45,443 Great Britain is, is brought 814 00:44:45,582 --> 00:44:47,777 by the Gulf Stream system. 815 00:44:49,486 --> 00:44:51,977 This Warm Water is draWn up from the tropics 816 00:44:52,122 --> 00:44:56,252 because of sinking cold Water in the North Atlantic. 817 00:44:57,628 --> 00:45:01,029 ln the tropics, evaporation caused by the sun's heat 818 00:45:01,165 --> 00:45:03,895 creates surface Waters that are particularly salty 819 00:45:04,034 --> 00:45:06,161 as Well as Warm. 820 00:45:08,439 --> 00:45:11,374 As the Gulf Stream carries this Warm Water northWards 821 00:45:11,508 --> 00:45:12,736 it gives up its heat, 822 00:45:12,876 --> 00:45:15,868 becoming cold and dense. 823 00:45:17,981 --> 00:45:20,313 Near Greenland it's dense enough to plummet 824 00:45:20,451 --> 00:45:21,679 to the ocean floor, 825 00:45:21,819 --> 00:45:25,277 draWing up more tropical Waters behind. 826 00:45:26,323 --> 00:45:28,985 lt's the sinking of this cold, salty Water 827 00:45:29,126 --> 00:45:31,754 Which is the engine behind a conveyor belt 828 00:45:31,895 --> 00:45:35,331 that's bringing Warmth to the northern latitudes. 829 00:45:35,466 --> 00:45:37,457 Stop this Water from sinking 830 00:45:37,601 --> 00:45:40,866 and you stop this heat supply to the north. 831 00:45:42,406 --> 00:45:44,271 And that's exactly What scientists believe 832 00:45:44,408 --> 00:45:47,673 the armadas of icebergs may have done. 833 00:45:50,981 --> 00:45:53,040 NoW of course if you have 834 00:45:53,183 --> 00:45:56,243 the North Atlantic choke full of icebergs, 835 00:45:56,386 --> 00:45:57,717 all those icebergs are going to melt 836 00:45:57,855 --> 00:45:59,823 and deliver a huge amount of fresh Water 837 00:45:59,957 --> 00:46:00,889 to the surface Waters 838 00:46:01,024 --> 00:46:03,356 and this fresh Water Would have loWered 839 00:46:03,494 --> 00:46:05,985 the solidity of the surface Water, loWered the density 840 00:46:06,130 --> 00:46:09,065 and shut doWn the conveyor belt. 841 00:46:12,169 --> 00:46:14,137 By shutting doWn the conveyor belt 842 00:46:14,271 --> 00:46:15,568 the heat supply to the north 843 00:46:15,706 --> 00:46:16,798 Would have been cut off 844 00:46:16,940 --> 00:46:20,376 and temperatures on land Would have plummeted. 845 00:46:22,713 --> 00:46:24,203 So perhaps here's the explanation 846 00:46:24,348 --> 00:46:25,872 of the rapid flips in climate 847 00:46:26,016 --> 00:46:28,450 during the last glaciation. 848 00:46:30,354 --> 00:46:33,152 Enough icebergs surging out into the Atlantic 849 00:46:33,290 --> 00:46:35,724 Would have sWitched off the conveyor. 850 00:46:35,859 --> 00:46:37,383 After the ice had melted 851 00:46:37,528 --> 00:46:39,758 the conveyor Would suddenly sWitch back on 852 00:46:39,897 --> 00:46:42,832 leading to rapid Warming in the north. 853 00:46:43,500 --> 00:46:45,263 These sudden sWings happened 854 00:46:45,402 --> 00:46:49,532 at least 20 times in 60,000 years 855 00:46:49,673 --> 00:46:52,540 but eventually the icebergs stopped coming 856 00:46:52,676 --> 00:46:55,577 and the climate calmed doWn. 857 00:46:55,712 --> 00:46:58,374 This is a time that agriculture's developed, 858 00:46:58,515 --> 00:46:59,880 cultures have flourished, 859 00:47:00,017 --> 00:47:02,986 but this is also a very unusual time for climate. 860 00:47:03,120 --> 00:47:05,645 lt's been very calm, very stable. 861 00:47:05,789 --> 00:47:07,347 We knoW from the geologic record 862 00:47:07,491 --> 00:47:11,052 that in fact usually climate is much more dynamic. 863 00:47:11,195 --> 00:47:12,719 We're going very quickly 864 00:47:12,863 --> 00:47:15,354 betWeen colder periods and Warmer periods. 865 00:47:15,499 --> 00:47:18,127 lndeed some climate changes can happen 866 00:47:18,268 --> 00:47:20,065 in the course of a single human lifetime 867 00:47:20,204 --> 00:47:22,399 as We knoW from the end of the last glacial 868 00:47:22,539 --> 00:47:24,905 to the present Warm period. 869 00:47:26,410 --> 00:47:28,844 Perhaps human civilisation only emerged 870 00:47:28,979 --> 00:47:32,176 because this rapid change came to an end. 871 00:47:32,749 --> 00:47:36,014 Today We may be reaping the benefit of a feW thousand years 872 00:47:36,153 --> 00:47:37,848 of stable temperatures 873 00:47:37,988 --> 00:47:42,049 but no-one knoWs hoW long this benign lull Will last. 874 00:47:42,626 --> 00:47:44,389 All the factors that influence climate 875 00:47:44,528 --> 00:47:45,790 in the past Will continue 876 00:47:45,929 --> 00:47:48,591 to have an effect in the future. 877 00:47:48,732 --> 00:47:50,359 NoW there is the additional concern 878 00:47:50,500 --> 00:47:53,731 that mankind Will prematurely tip the balance 879 00:47:53,871 --> 00:47:56,840 back into more turbulent times. 880 00:47:59,076 --> 00:48:01,067 As they've travelled back in time, 881 00:48:01,211 --> 00:48:02,769 geologists have uncovered a history 882 00:48:02,913 --> 00:48:05,177 of climate change far more profound 883 00:48:05,315 --> 00:48:09,411 than anything the SWiss pioneers could have suspected. 884 00:48:11,521 --> 00:48:14,456 Everything they've found shoWs that climate change 885 00:48:14,591 --> 00:48:18,527 is a natural result of the Way the Earth Works. 886 00:48:18,662 --> 00:48:21,358 Climate has been changing one Way or another 887 00:48:21,498 --> 00:48:23,693 throughout Earth's history 888 00:48:23,834 --> 00:48:25,301 and there's no reason to believe 889 00:48:25,435 --> 00:48:28,461 that it Will ever stop changing.