1 00:00:09,968 --> 00:00:13,838 Yes, this is home. 2 00:00:13,872 --> 00:00:16,140 This is Earth. 3 00:00:16,175 --> 00:00:19,077 Having trouble finding a familiar continent? 4 00:00:19,111 --> 00:00:22,013 The past is another planet. 5 00:00:22,047 --> 00:00:24,015 Actually, many. 6 00:00:24,049 --> 00:00:27,452 I'm standing on the great expanse of time that has elapsed 7 00:00:27,486 --> 00:00:30,588 since the Big Bang. In order to think about it, 8 00:00:30,622 --> 00:00:33,424 we've compressed it all into a single year. 9 00:00:33,459 --> 00:00:36,594 It's the early morning of December 23 10 00:00:36,628 --> 00:00:38,262 on this Cosmic Calendar of ours, 11 00:00:38,297 --> 00:00:41,599 or about 350 million years ago, 12 00:00:41,633 --> 00:00:45,002 when our world was a mere four billion years old. 13 00:00:45,037 --> 00:00:46,671 Earth looks so different. 14 00:00:46,705 --> 00:00:48,606 You might not even know the place. 15 00:00:48,640 --> 00:00:50,441 The stars wouldn't help you. 16 00:00:50,476 --> 00:00:53,244 Even the constellations would have been different back then. 17 00:00:59,752 --> 00:01:01,519 The dinosaurs were still 18 00:01:01,553 --> 00:01:04,655 more than 100 million years in the future. 19 00:01:04,690 --> 00:01:07,558 There were no birds, no flowers. 20 00:01:07,593 --> 00:01:10,428 And the air was different, too. 21 00:01:12,097 --> 00:01:15,833 The atmosphere had more oxygen than at any other time 22 00:01:15,868 --> 00:01:18,736 in Earth's history, before or since. 23 00:01:18,771 --> 00:01:23,041 This allowed insects to grow much larger than they do today. 24 00:01:24,943 --> 00:01:26,911 How? 25 00:01:26,945 --> 00:01:28,579 Insects don't have lungs. 26 00:01:28,614 --> 00:01:31,249 Life-giving oxygen is taken in through openings 27 00:01:31,283 --> 00:01:33,084 in the outside of their bodies 28 00:01:33,118 --> 00:01:35,586 and transported through a network of tubes. 29 00:01:35,621 --> 00:01:37,588 If an insect were too large, 30 00:01:37,623 --> 00:01:41,025 the outer reaches of these tubes would absorb all the oxygen 31 00:01:41,060 --> 00:01:43,928 before it could ever get to its internal organs. 32 00:01:46,098 --> 00:01:47,665 But during the Carboniferous Period, 33 00:01:47,700 --> 00:01:50,668 the atmosphere had almost twice the oxygen as today. 34 00:01:50,703 --> 00:01:53,071 Insects could then grow much bigger 35 00:01:53,105 --> 00:01:55,740 and still get enough oxygen in their bodies. 36 00:01:55,774 --> 00:01:59,377 That's why the dragonflies here are as big as eagles 37 00:01:59,411 --> 00:02:02,447 and the millipedes the size of alligators. 38 00:02:02,481 --> 00:02:05,583 So why was there so much oxygen back then? 39 00:02:05,617 --> 00:02:08,753 It was produced by a new kind of life. 40 00:03:39,930 --> 00:03:41,430 "The Lost Worlds of Planet Earth" 41 00:03:42,769 --> 00:03:44,436 What kind of life could've changed 42 00:03:44,470 --> 00:03:46,972 the Earth's atmosphere so dramatically? 43 00:03:51,411 --> 00:03:55,380 Plants that could reach for the sky-- 44 00:03:55,415 --> 00:03:57,115 trees. 45 00:03:57,150 --> 00:03:58,784 In their competition for sunlight, 46 00:03:58,818 --> 00:04:01,720 trees evolved a way to defy gravity. 47 00:04:01,754 --> 00:04:04,456 Before trees, the tallest vegetation was 48 00:04:04,490 --> 00:04:06,458 only about waist-high. 49 00:04:06,492 --> 00:04:09,828 And then something wonderful happened. 50 00:04:13,466 --> 00:04:17,602 A plant molecule evolved that was both strong and flexible, 51 00:04:17,637 --> 00:04:19,805 a material that could support a lot of weight, 52 00:04:19,839 --> 00:04:23,075 yet bend in the wind without breaking. 53 00:04:23,109 --> 00:04:25,477 Lignin made trees possible. 54 00:04:25,511 --> 00:04:27,913 Now life could build upward. 55 00:04:27,947 --> 00:04:30,115 And this opened a whole new territory, 56 00:04:30,149 --> 00:04:31,683 a three-dimensional matrix 57 00:04:31,718 --> 00:04:34,119 for communities far above the ground. 58 00:04:34,153 --> 00:04:37,856 Earth became the Planet of the Trees. 59 00:04:37,890 --> 00:04:40,025 But lignin had a downside: 60 00:04:40,059 --> 00:04:42,461 it was hard to swallow. 61 00:04:42,495 --> 00:04:46,198 When nature's demolition crew, the fungi and bacteria, 62 00:04:46,232 --> 00:04:48,533 tried to eat anything with lignin in it, 63 00:04:48,568 --> 00:04:51,136 they got a really bad case of indigestion. 64 00:04:51,170 --> 00:04:52,704 And termites wouldn't evolve 65 00:04:52,739 --> 00:04:55,207 for at least another 100 million years. 66 00:04:55,241 --> 00:04:58,543 What to do with all those dead trees? 67 00:04:58,578 --> 00:05:01,313 It took the fungi and bacteria millions of years 68 00:05:01,347 --> 00:05:04,549 to evolve the biochemical means to consume them. 69 00:05:04,584 --> 00:05:07,552 Meanwhile, the trees just kept springing up, 70 00:05:07,587 --> 00:05:09,554 dying, falling over 71 00:05:09,589 --> 00:05:13,024 and getting buried by the mud that built up over eons. 72 00:05:13,059 --> 00:05:15,861 Eventually, there were hundreds of billions of trees 73 00:05:15,895 --> 00:05:17,963 entombed in the Earth, 74 00:05:17,997 --> 00:05:21,166 buried forests all over the Earth. 75 00:05:21,200 --> 00:05:24,603 What possible harm could come from that? 76 00:05:34,347 --> 00:05:38,817 This cliff in Nova Scotia is another kind of calendar. 77 00:05:38,851 --> 00:05:42,054 It tells the story of that other world 78 00:05:42,088 --> 00:05:44,656 that once flourished right here. 79 00:05:44,691 --> 00:05:47,559 And this is the death mask 80 00:05:47,593 --> 00:05:49,561 of that 300 million-year-old tree. 81 00:05:49,595 --> 00:05:53,065 It was cast by minerals that replaced the original wood 82 00:05:53,099 --> 00:05:56,668 cell by cell-- in other words, a fossil. 83 00:05:56,703 --> 00:05:59,337 The tree surrendered its organic molecules 84 00:05:59,372 --> 00:06:00,872 to the environment long ago, 85 00:06:00,907 --> 00:06:04,509 its carbon and water. Only its shape remains. 86 00:06:04,544 --> 00:06:07,512 When this tree was alive, it took in carbon dioxide 87 00:06:07,547 --> 00:06:09,514 and water and used sunlight 88 00:06:09,549 --> 00:06:12,350 to turn them into energy-rich organic matter. 89 00:06:12,385 --> 00:06:15,353 The tree gave off oxygen as a waste product. 90 00:06:15,388 --> 00:06:18,724 That's what trees and other plants still do. 91 00:06:18,758 --> 00:06:23,095 When plants die, they decay, 92 00:06:23,129 --> 00:06:25,263 and this reverses the transaction. 93 00:06:25,298 --> 00:06:27,899 Their organic matter combines with oxygen 94 00:06:27,934 --> 00:06:30,068 and decomposes, 95 00:06:30,103 --> 00:06:32,471 putting carbon dioxide back into the air. 96 00:06:32,505 --> 00:06:34,473 This balances the books 97 00:06:34,507 --> 00:06:36,808 for the chemistry of Earth's atmosphere. 98 00:06:36,843 --> 00:06:40,245 But if the trees are buried before they can decay, 99 00:06:40,279 --> 00:06:42,080 two things happen... they take the carbon 100 00:06:42,115 --> 00:06:45,150 and stored solar energy with them 101 00:06:45,184 --> 00:06:46,218 and leave the oxygen behind 102 00:06:46,252 --> 00:06:48,153 to build up in the atmosphere. 103 00:06:48,187 --> 00:06:51,056 That's what happened around 300 million years ago. 104 00:06:51,090 --> 00:06:52,991 There was an oxygen surplus. 105 00:06:53,026 --> 00:06:56,061 That's how the bugs got so big. 106 00:06:56,095 --> 00:06:59,064 And what became of all that buried carbon? 107 00:06:59,098 --> 00:07:03,135 It lay there for eons before dealing life on Earth 108 00:07:03,169 --> 00:07:08,106 its most devastating blow of all time. 109 00:07:10,009 --> 00:07:13,111 There are places on this planet where you can walk through time 110 00:07:13,146 --> 00:07:16,748 and read the history written in the rocks. 111 00:07:16,783 --> 00:07:19,618 This beach in Nova Scotia is one of them. 112 00:07:19,652 --> 00:07:21,186 Every layer is a page. 113 00:07:21,220 --> 00:07:23,455 Each one tells the story of a flood, 114 00:07:23,489 --> 00:07:27,192 one after another, over millions of years. 115 00:07:27,226 --> 00:07:29,961 The layer cake of flood deposits was slowly buried 116 00:07:29,996 --> 00:07:33,131 and turned into rock by heat and pressure. 117 00:07:33,166 --> 00:07:35,967 The same forces that built mountains 118 00:07:36,002 --> 00:07:37,636 then tilted and uplifted them, 119 00:07:37,670 --> 00:07:40,272 along with the entombed fossil forest. 120 00:07:40,306 --> 00:07:41,840 The newer layers were always 121 00:07:41,874 --> 00:07:43,942 deposited on top of the older ones. 122 00:07:43,976 --> 00:07:46,645 All the pages are in the correct order, 123 00:07:46,679 --> 00:07:49,481 bearing witness to what happened here 124 00:07:49,515 --> 00:07:51,516 over millions of years. 125 00:07:51,551 --> 00:07:53,452 Back that way 126 00:07:53,486 --> 00:07:55,320 lies the more distant past. 127 00:07:55,355 --> 00:07:57,289 And with every step I take, 128 00:07:57,323 --> 00:08:00,492 I move about 1,000 years closer to the present 129 00:08:00,526 --> 00:08:03,862 and away from the world of 300 million years ago. 130 00:08:03,896 --> 00:08:07,432 50 million years later lies that way. 131 00:08:15,341 --> 00:08:19,077 This was the beginning of the end of the Permian world, 132 00:08:19,112 --> 00:08:22,080 an event of unequalled carnage. 133 00:08:22,115 --> 00:08:24,916 The Permian is the darkest corridor 134 00:08:24,951 --> 00:08:28,587 in this memorial to the broken branches on the Tree of Life-- 135 00:08:28,621 --> 00:08:30,822 the Halls of Extinction. 136 00:08:30,857 --> 00:08:32,891 Death has never come so close 137 00:08:32,925 --> 00:08:34,726 to reigning supreme on this world 138 00:08:34,761 --> 00:08:37,162 in the quarter billion years since. 139 00:08:37,196 --> 00:08:39,998 The eruptions, in what is now Siberia, 140 00:08:40,033 --> 00:08:43,001 lasted for hundreds of thousands of years. 141 00:08:43,036 --> 00:08:47,406 The lava flooded and buried more than a million square miles. 142 00:08:47,440 --> 00:08:51,243 This event dwarfs any volcanic eruption 143 00:08:51,277 --> 00:08:53,111 in historical times. 144 00:09:02,581 --> 00:09:06,512 _ 145 00:09:13,066 --> 00:09:16,535 Huge quantities of carbon dioxide came pouring 146 00:09:16,569 --> 00:09:18,203 out of the volcanic fissures. 147 00:09:18,237 --> 00:09:21,206 This greenhouse gas warmed the climate. 148 00:09:21,240 --> 00:09:23,608 And this is where the long-buried forests 149 00:09:23,643 --> 00:09:27,979 of the earlier Carboniferous Period reenter the story. 150 00:09:28,014 --> 00:09:30,482 During the intervening 50 million years, 151 00:09:30,516 --> 00:09:34,152 those trees had turned into immense deposits of coal, 152 00:09:34,187 --> 00:09:35,487 and as it happened, 153 00:09:35,521 --> 00:09:36,488 one of the world's largest 154 00:09:36,522 --> 00:09:37,889 accumulations of coal 155 00:09:37,924 --> 00:09:40,492 was buried right there in Siberia. 156 00:09:40,526 --> 00:09:43,161 The heat from the lava baked the coal, 157 00:09:43,196 --> 00:09:46,465 driving methane and sulfur-rich gases out of the ground. 158 00:09:46,499 --> 00:09:48,333 They were laden 159 00:09:48,368 --> 00:09:51,770 with toxic and radioactive ash particles-- 160 00:09:51,804 --> 00:09:54,239 coal smoke. 161 00:09:54,273 --> 00:09:58,010 This witch's brew polluted the atmosphere 162 00:09:58,044 --> 00:10:00,278 and radically destabilized Earth's climate. 163 00:10:00,313 --> 00:10:03,915 A sulfuric acid haze blocked incoming sunlight 164 00:10:03,950 --> 00:10:05,917 and darkened the planet. 165 00:10:05,952 --> 00:10:09,287 Global temperatures plummeted to subfreezing. 166 00:10:12,358 --> 00:10:14,926 During lulls in the eruptions, 167 00:10:14,961 --> 00:10:17,429 the acid haze fell back to the surface. 168 00:10:17,463 --> 00:10:19,498 But the carbon dioxide remained 169 00:10:19,532 --> 00:10:22,501 and built up in the atmosphere to cause global warming. 170 00:10:22,535 --> 00:10:24,002 Years of frigid cold 171 00:10:24,037 --> 00:10:27,272 alternating with millennia of stifling heat 172 00:10:27,306 --> 00:10:29,941 battered a dwindling population of plants and animals. 173 00:10:29,976 --> 00:10:31,443 They had no chance 174 00:10:31,477 --> 00:10:35,881 to adapt to the drastic swings in climate. 175 00:10:38,384 --> 00:10:40,352 As the global warming 176 00:10:40,386 --> 00:10:42,988 continued, the surface and the bottom waters 177 00:10:43,022 --> 00:10:45,524 slowly mixed, raising the temperature 178 00:10:45,558 --> 00:10:47,993 of the once-frigid depths of the sea floor. 179 00:10:48,027 --> 00:10:49,695 Methane-rich ices 180 00:10:49,729 --> 00:10:53,665 that had been frozen in the sediments began to melt. 181 00:10:57,837 --> 00:11:00,572 Newly liberated methane gas made its way to the surface 182 00:11:00,606 --> 00:11:02,407 and into the atmosphere. 183 00:11:02,442 --> 00:11:05,377 Methane traps heat far more efficiently 184 00:11:05,411 --> 00:11:07,846 than carbon dioxide, so the climate 185 00:11:07,880 --> 00:11:09,915 got even hotter. 186 00:11:09,949 --> 00:11:11,917 And the methane also destroyed 187 00:11:11,951 --> 00:11:14,052 the ozone layer in the stratosphere. 188 00:11:14,087 --> 00:11:16,221 The natural sunscreen that protects life 189 00:11:16,255 --> 00:11:19,624 from deadly ultraviolet rays was eaten away. 190 00:11:21,794 --> 00:11:25,163 The circulatory system of the world ocean shut down. 191 00:11:25,198 --> 00:11:28,667 These stagnant waters became oxygen-starved, 192 00:11:28,701 --> 00:11:31,069 killing almost all the fish in the sea. 193 00:11:31,104 --> 00:11:34,406 But one kind of life flourished in this brutal environment... 194 00:11:34,440 --> 00:11:38,043 bacteria that produced deadly hydrogen sulfide gas 195 00:11:38,077 --> 00:11:40,278 as a waste product. 196 00:11:40,313 --> 00:11:43,181 That was the last straw. 197 00:11:43,216 --> 00:11:46,618 The poison gas killed almost all the remaining plants 198 00:11:46,652 --> 00:11:49,087 and animals on the land. 199 00:11:49,122 --> 00:11:52,257 This was the Great Dying. 200 00:11:52,291 --> 00:11:56,261 The closest life on Earth has ever come to annihilation. 201 00:11:56,295 --> 00:11:59,965 Nine in ten of all species perished. 202 00:11:59,999 --> 00:12:02,567 It took a long time for life to bounce back. 203 00:12:02,602 --> 00:12:06,104 For a few million years, Earth could have been called 204 00:12:06,139 --> 00:12:08,073 the Planet of the Dead. 205 00:12:08,107 --> 00:12:11,710 We are descended from one of the few species 206 00:12:11,744 --> 00:12:13,612 that managed to squeak by. 207 00:12:16,282 --> 00:12:19,751 You are human and alive at this very moment 208 00:12:19,786 --> 00:12:22,421 because they managed to endure, conveying 209 00:12:22,455 --> 00:12:25,557 their DNA through one of the most treacherous periods 210 00:12:25,591 --> 00:12:27,759 in the history of life. 211 00:12:43,780 --> 00:12:47,382 This mountain was made entirely by life. 212 00:12:47,417 --> 00:12:49,618 The life that flourished back in the glory days 213 00:12:49,652 --> 00:12:53,054 of the Permian, before all hell broke loose. 214 00:12:53,089 --> 00:12:55,023 This is part of the 400 mile-long 215 00:12:55,058 --> 00:12:57,125 Guadalupe Mountain chain that runs through 216 00:12:57,160 --> 00:12:58,960 Texas and New Mexico. 217 00:12:58,995 --> 00:13:02,364 It's the world's largest fossil reef. 218 00:13:02,398 --> 00:13:05,400 All this was once a great inland sea. 219 00:13:05,435 --> 00:13:09,771 The reef flourished and grew for millions of years, 220 00:13:09,806 --> 00:13:13,141 and was home to multitudes of sponges, green algae, 221 00:13:13,176 --> 00:13:15,744 and animals too small to see. 222 00:13:15,778 --> 00:13:17,746 When these creatures died, 223 00:13:17,780 --> 00:13:20,882 they sank to the bottom and were buried in the silt. 224 00:13:20,917 --> 00:13:23,085 Over millions of years, 225 00:13:23,119 --> 00:13:26,088 their remains were converted into oil and gas. 226 00:13:26,122 --> 00:13:28,090 Eventually, the basin 227 00:13:28,124 --> 00:13:30,492 silted in and the reef died. 228 00:13:30,526 --> 00:13:33,261 This marine ghost town was then buried 229 00:13:33,296 --> 00:13:34,996 a mile beneath the surface. 230 00:13:35,031 --> 00:13:38,066 Later, tectonic forces lifted the skeletal reef 231 00:13:38,101 --> 00:13:41,236 high above sea level, where it was eroded and sculpted 232 00:13:41,270 --> 00:13:43,438 over eons by wind and rain. 233 00:13:43,473 --> 00:13:45,741 Just imagine what this place looked like 234 00:13:45,775 --> 00:13:48,243 275 million years ago, 235 00:13:48,277 --> 00:13:50,312 when it was a vibrant, tropical inland sea, 236 00:13:50,346 --> 00:13:52,314 dotted with islands 237 00:13:52,348 --> 00:13:55,183 and brimming with life. 238 00:13:58,621 --> 00:14:01,189 Until about 220 million years ago, 239 00:14:01,224 --> 00:14:05,260 New England and North Africa were next-door neighbors. 240 00:14:05,294 --> 00:14:07,295 There was no such thing as the Atlantic Ocean. 241 00:14:07,330 --> 00:14:11,633 Those thin blue fingers at the center-- they were lakes. 242 00:14:11,667 --> 00:14:14,603 They were the first outward signs that the supercontinent 243 00:14:14,637 --> 00:14:16,171 was splitting apart and that 244 00:14:16,205 --> 00:14:19,374 life on Earth was due for another big shake-up. 245 00:14:19,409 --> 00:14:22,677 A million years later, the lakes became a long bay, 246 00:14:22,712 --> 00:14:25,614 which would grow into the Atlantic Ocean. 247 00:14:25,648 --> 00:14:28,216 These profound changes at the surface 248 00:14:28,251 --> 00:14:32,354 were merely symptoms of a drama that was unfolding far beneath, 249 00:14:32,388 --> 00:14:33,688 in the depths of the Earth. 250 00:14:36,092 --> 00:14:38,960 By the time we got here, the telltale traces 251 00:14:38,995 --> 00:14:40,729 of global upheaval were buried 252 00:14:40,763 --> 00:14:42,964 at the bottom of the deep blue sea. 253 00:14:42,999 --> 00:14:45,500 We were completely cut off from the great story 254 00:14:45,535 --> 00:14:47,135 of Earth's violent past-- 255 00:14:47,170 --> 00:14:50,906 a species of amnesiacs trying to find out 256 00:14:50,940 --> 00:14:53,809 who we were and what happened 257 00:14:53,843 --> 00:14:55,877 before we awakened. 258 00:14:55,912 --> 00:14:59,681 In 1570, Abraham Ortelius created the first 259 00:14:59,716 --> 00:15:03,185 modern world atlas, reflecting on the discoveries 260 00:15:03,219 --> 00:15:04,986 of the previous 80 years-- 261 00:15:05,021 --> 00:15:08,223 the Golden Age of Exploration. 262 00:15:08,257 --> 00:15:10,025 Before the ink was dry, 263 00:15:10,059 --> 00:15:12,494 Ortelius stepped back from his masterpiece 264 00:15:12,528 --> 00:15:15,864 and became the first of many to notice the striking 265 00:15:15,898 --> 00:15:18,166 puzzle-piece fit between the continents 266 00:15:18,201 --> 00:15:20,569 on either side of the Atlantic. 267 00:15:20,603 --> 00:15:23,839 He later wrote that the Americas were torn away 268 00:15:23,873 --> 00:15:26,908 from Europe and Africa by earthquakes and floods. 269 00:15:26,943 --> 00:15:28,710 But Ortelius's observation 270 00:15:28,745 --> 00:15:30,545 remained nothing more than a hunch 271 00:15:30,580 --> 00:15:32,547 for the next couple of centuries... 272 00:15:33,950 --> 00:15:36,418 until an early 20th century 273 00:15:36,452 --> 00:15:38,420 German astronomer and meteorologist 274 00:15:38,454 --> 00:15:39,955 amassed the evidence 275 00:15:39,989 --> 00:15:42,424 to build the scientific case for it. 276 00:15:42,458 --> 00:15:45,594 Alfred Wegener had been drafted during the First World War, 277 00:15:45,628 --> 00:15:48,063 but was wounded soon after. 278 00:15:48,097 --> 00:15:50,399 As he recovered in a field hospital, 279 00:15:50,433 --> 00:15:52,534 he scoured scientific literature 280 00:15:52,568 --> 00:15:55,270 for clues to the Earth's past. 281 00:15:55,304 --> 00:15:56,972 Years before, 282 00:15:57,006 --> 00:15:59,408 Wegener had happened upon an intriguing paper 283 00:15:59,442 --> 00:16:00,976 in the stacks of his university library. 284 00:16:01,010 --> 00:16:03,745 It puzzled Wegener 285 00:16:03,780 --> 00:16:07,215 that fossils of the same species of a now-extinct fern 286 00:16:07,250 --> 00:16:11,887 were reported to be found on both sides of the Atlantic. 287 00:16:11,921 --> 00:16:14,623 Even more curious were the discoveries of fossils 288 00:16:14,657 --> 00:16:17,826 of the same dinosaurs on both continents. 289 00:16:17,860 --> 00:16:19,761 In the early 20th century, 290 00:16:19,796 --> 00:16:22,330 geologists explained how life crossed the oceans 291 00:16:22,365 --> 00:16:27,169 by imagining that land bridges had once existed between them. 292 00:16:27,203 --> 00:16:30,639 It was thought that these land bridges gradually disintegrated 293 00:16:30,673 --> 00:16:33,942 and vanished beneath the waves long ago. 294 00:16:33,976 --> 00:16:36,478 But there was one piece of evidence that convinced Wegener 295 00:16:36,512 --> 00:16:39,781 that the prevailing scientific view must be wrong... 296 00:16:39,816 --> 00:16:42,417 the Earth itself. 297 00:16:42,452 --> 00:16:45,987 Why would a mountain range cross the oceanic divide 298 00:16:46,022 --> 00:16:48,190 to continue on another continent? 299 00:16:48,224 --> 00:16:50,325 And why would you find the same unique pattern 300 00:16:50,359 --> 00:16:53,995 in the layers of rocks in both Brazil and South Africa? 301 00:16:54,030 --> 00:16:55,997 And another thing... 302 00:16:56,032 --> 00:16:59,267 under what circumstances could tropical plants have flourished 303 00:16:59,302 --> 00:17:02,671 in the frozen wastes of the Arctic? 304 00:17:02,705 --> 00:17:04,806 Wegener concluded that there was only 305 00:17:04,841 --> 00:17:07,542 one logical solution to this puzzle... 306 00:17:07,577 --> 00:17:11,012 There had once been a single supercontinent on Earth. 307 00:17:11,047 --> 00:17:14,449 He named it Pangaea. 308 00:17:14,484 --> 00:17:18,320 So Wegener becomes the toast of the scientific world, right? 309 00:17:18,354 --> 00:17:20,288 Not exactly. 310 00:17:20,323 --> 00:17:22,691 Most geologists ridiculed Wegener's hypothesis 311 00:17:22,725 --> 00:17:24,693 of continental drift. 312 00:17:24,727 --> 00:17:28,663 They preferred their imaginary natural land bridges 313 00:17:28,698 --> 00:17:30,699 to explain away Wegener's evidence. 314 00:17:32,602 --> 00:17:35,837 How, they asked, could a continent plow through 315 00:17:35,872 --> 00:17:38,673 the solid rock of the ocean floor? 316 00:17:38,708 --> 00:17:41,576 Wegener had no convincing answer. 317 00:17:41,611 --> 00:17:43,712 He became the laughingstock of the field; 318 00:17:43,746 --> 00:17:46,815 a pariah at scientific conferences. 319 00:17:48,584 --> 00:17:51,319 Despite this, Wegener continued to fight for his ideas, 320 00:17:51,354 --> 00:17:54,689 conducting daring research expeditions to gather evidence. 321 00:17:54,724 --> 00:17:58,527 On one of these, he learned that colleagues were 322 00:17:58,561 --> 00:18:01,396 trapped on an ice cap without food. 323 00:18:01,431 --> 00:18:03,598 On his way back from the mission, 324 00:18:03,633 --> 00:18:05,567 he became lost in a blizzard. 325 00:18:05,601 --> 00:18:08,403 A day or two after his 50th birthday, 326 00:18:08,438 --> 00:18:09,738 he disappeared, 327 00:18:09,772 --> 00:18:11,907 never knowing that, in time, 328 00:18:11,941 --> 00:18:14,342 he would be vindicated and come to be viewed 329 00:18:14,377 --> 00:18:17,946 as one of the greatest geologists in history. 330 00:18:23,052 --> 00:18:25,253 Scientists are human. 331 00:18:25,288 --> 00:18:27,055 We have our blind spots and prejudices. 332 00:18:27,090 --> 00:18:29,958 Science is a mechanism 333 00:18:29,992 --> 00:18:31,960 designed to ferret them out. 334 00:18:31,994 --> 00:18:34,363 Problem is, we aren't always faithful 335 00:18:34,397 --> 00:18:36,198 to the core values of science. 336 00:18:36,232 --> 00:18:40,602 Few people knew this better than Marie Tharp. 337 00:18:46,509 --> 00:18:50,545 It's 1952, and Marie is patiently enduring the slights 338 00:18:50,580 --> 00:18:53,215 of her fellow members of the geology department. 339 00:18:53,249 --> 00:18:55,384 Her degrees in geology and mathematics 340 00:18:55,418 --> 00:18:57,085 count for little with them. 341 00:18:57,120 --> 00:19:00,255 Bruce Heezen, a graduate student from Iowa, 342 00:19:00,289 --> 00:19:02,491 has just returned from a lengthy expedition 343 00:19:02,525 --> 00:19:05,293 to map the ocean floor using sonar. 344 00:19:08,197 --> 00:19:10,198 Will you do something with these? 345 00:19:15,271 --> 00:19:17,973 Bruce, look. 346 00:19:18,007 --> 00:19:19,107 It's-- it's all come together. 347 00:19:19,142 --> 00:19:20,942 There's this giant rift valley 348 00:19:20,977 --> 00:19:22,978 that runs through the bottom of the Atlantic. 349 00:19:23,012 --> 00:19:24,179 Aw, geez, Marie, come on. 350 00:19:24,213 --> 00:19:25,981 This is just more girl talk. 351 00:19:26,015 --> 00:19:28,650 You're not in enough trouble with everyone here already? 352 00:19:28,685 --> 00:19:30,619 This sounds too much like continental drift. 353 00:19:30,653 --> 00:19:32,621 You want to end up like Wegener? 354 00:19:34,957 --> 00:19:38,860 But Marie would not be dissuaded. 355 00:19:38,895 --> 00:19:42,764 Years later, when Marie and Bruce placed a map of oceanic 356 00:19:42,799 --> 00:19:45,200 earthquake epicenters on a light table 357 00:19:45,234 --> 00:19:46,702 over her seafloor map, 358 00:19:46,736 --> 00:19:48,537 the earthquakes fell right along 359 00:19:48,571 --> 00:19:49,771 the rift valley. 360 00:19:49,806 --> 00:19:52,441 This was the smoking gun 361 00:19:52,475 --> 00:19:54,309 for Wegener's moving continents. 362 00:19:54,343 --> 00:19:56,211 Heezen now knew 363 00:19:56,245 --> 00:19:59,514 that Marie had been right all along. 364 00:19:59,549 --> 00:20:02,384 Together, they created the first true map of the Earth, 365 00:20:02,418 --> 00:20:05,220 including the ocean floor. 366 00:20:08,257 --> 00:20:10,525 We were at last ready to read 367 00:20:10,560 --> 00:20:12,561 the autobiography of the Earth. 368 00:20:18,435 --> 00:20:22,071 Let's take the Ship of the Imagination... 369 00:20:22,105 --> 00:20:24,807 to a part of the world that has been off-limits 370 00:20:24,841 --> 00:20:26,942 to all but a few of us. 371 00:20:40,257 --> 00:20:41,757 Two-thirds of the Earth 372 00:20:41,791 --> 00:20:45,394 lies beneath more than 1,000 feet of water. 373 00:20:45,428 --> 00:20:48,731 It's a vast and largely unexplored frontier. 374 00:20:48,765 --> 00:20:51,300 Everybody knows the Alps and the Rockies, 375 00:20:51,334 --> 00:20:53,902 but some of the world's most amazing mountain ranges 376 00:20:53,937 --> 00:20:55,504 are hidden from view. 377 00:20:57,807 --> 00:21:01,310 Below 1,000 meters, we enter a world 378 00:21:01,344 --> 00:21:03,112 where there is no sunlight. 379 00:21:04,681 --> 00:21:08,350 Hidden in the darkness, a world of wonders. 380 00:21:10,954 --> 00:21:14,256 This is the longest submarine mountain range in the world, 381 00:21:14,291 --> 00:21:17,493 the Atlantic Mid-Ocean Ridge. 382 00:21:17,527 --> 00:21:21,530 It wraps around our globe like the seam on a baseball. 383 00:21:24,734 --> 00:21:28,537 The past is another planet, 384 00:21:28,572 --> 00:21:31,807 but most of us don't really know this one. 385 00:21:31,841 --> 00:21:35,477 We don't see the mountains for the water. 386 00:21:35,512 --> 00:21:39,048 This is the world that Marie Tharp was the first to imagine. 387 00:21:39,082 --> 00:21:41,050 The highest peaks of the ridge 388 00:21:41,084 --> 00:21:43,619 rise over four kilometers above 389 00:21:43,653 --> 00:21:45,454 the ocean floor. 390 00:21:45,488 --> 00:21:48,390 There are sprawling mountain ranges and canyons, too. 391 00:21:48,425 --> 00:21:51,060 We've now entered the Marianas Trench, 392 00:21:51,094 --> 00:21:52,828 the deepest canyon on Earth, 393 00:21:52,862 --> 00:21:55,731 more than ten kilometers deep. 394 00:21:55,765 --> 00:21:58,701 It formed when tectonic forces pushed the seabed 395 00:21:58,735 --> 00:22:00,703 under the adjoining continental plate. 396 00:22:00,737 --> 00:22:03,138 More people have walked on the Moon 397 00:22:03,173 --> 00:22:05,741 than have ever been down here. 398 00:22:05,775 --> 00:22:10,012 The pressure here is a crushing eight tons per square inch. 399 00:22:10,046 --> 00:22:12,214 Being this deep in the ocean 400 00:22:12,249 --> 00:22:15,918 is like having 50 jumbo jets stacked on top of you. 401 00:22:15,952 --> 00:22:19,755 Yet even here, life has taken hold. 402 00:22:22,425 --> 00:22:25,828 The fact that sunlight can't penetrate the deep ocean 403 00:22:25,862 --> 00:22:28,430 doesn't mean there isn't light down here. 404 00:22:28,465 --> 00:22:31,433 Many underwater species glow in the dark, 405 00:22:31,468 --> 00:22:34,503 through a process called bioluminescence. 406 00:22:34,537 --> 00:22:37,406 Our long history as land mammals, 407 00:22:37,440 --> 00:22:40,576 denizens of the sunlit world, hasn't prepared us 408 00:22:40,610 --> 00:22:43,345 for the amazing variety of life that evolution 409 00:22:43,380 --> 00:22:45,948 has crafted in the deep oceans. 410 00:22:48,285 --> 00:22:50,619 Since there's no sunlight down here, 411 00:22:50,654 --> 00:22:53,088 there's no photosynthesis. 412 00:22:53,123 --> 00:22:57,193 That means there are no plants to feed on, 413 00:22:57,227 --> 00:23:00,596 and yet, even here, in a world of permanent midnight, 414 00:23:00,630 --> 00:23:02,598 there's a thriving food chain. 415 00:23:02,632 --> 00:23:03,933 It begins 416 00:23:03,967 --> 00:23:06,402 with a process called chemosynthesis. 417 00:23:06,436 --> 00:23:09,371 These microscopic creatures have learned to eat 418 00:23:09,406 --> 00:23:13,075 what's pouring out of that vent... 419 00:23:13,109 --> 00:23:16,145 a noxious compound called hydrogen sulfide. 420 00:23:16,179 --> 00:23:17,580 That thick 421 00:23:17,614 --> 00:23:20,249 black smoke provides the chemical energy 422 00:23:20,283 --> 00:23:22,418 that makes life possible here. 423 00:23:22,452 --> 00:23:25,421 Tiny crustaceans eat the bacteria, 424 00:23:25,455 --> 00:23:28,857 and the larger animals eat the crustaceans. 425 00:23:32,329 --> 00:23:34,797 One day, on some future Earth, 426 00:23:34,831 --> 00:23:36,398 these mountains could very well 427 00:23:36,433 --> 00:23:38,801 end up above the water. 428 00:23:38,835 --> 00:23:42,004 Tectonic forces continue to shape our planet. 429 00:23:42,038 --> 00:23:45,975 The future is also another planet. 430 00:23:46,009 --> 00:23:48,177 It was a volcano like this one 431 00:23:48,211 --> 00:23:52,815 that created the Hawaiian islands millions of years ago. 432 00:24:12,469 --> 00:24:15,938 We live on the crust of a seething cauldron. 433 00:24:15,972 --> 00:24:19,008 At the center of our planet, there's an iron core. 434 00:24:19,042 --> 00:24:22,845 It's nested inside of a larger, liquid iron shell. 435 00:24:22,879 --> 00:24:26,682 Wrapped over this is the part called the mantle. 436 00:24:26,716 --> 00:24:29,618 It's rocky but hot and viscous. 437 00:24:29,653 --> 00:24:33,122 Like a pot of soup cooking on a stove, the mantle 438 00:24:33,156 --> 00:24:34,356 is churning. 439 00:24:34,391 --> 00:24:36,392 What keeps it moving? 440 00:24:36,426 --> 00:24:40,296 Two things... the heat left over from Earth's formation, 441 00:24:40,330 --> 00:24:43,966 and the decay of radioactive elements in the core. 442 00:24:44,000 --> 00:24:46,569 And this outer layer-- the crust, 443 00:24:46,603 --> 00:24:49,638 where you and me and everyone we know lives-- 444 00:24:49,673 --> 00:24:52,041 is only as thick as the skin on an apple. 445 00:24:52,075 --> 00:24:53,742 The mantle 446 00:24:53,777 --> 00:24:56,979 drags the solid overlying crust along with it. 447 00:24:57,013 --> 00:25:00,349 The crust resists because it's cool and rigid. 448 00:25:00,383 --> 00:25:04,153 From time to time, it reaches the breaking point. 449 00:25:04,187 --> 00:25:07,489 When that happens, the Earth quakes. 450 00:25:07,524 --> 00:25:10,092 It's not because somebody misbehaved 451 00:25:10,126 --> 00:25:11,860 and is being punished. 452 00:25:11,895 --> 00:25:13,696 It's due to random forces 453 00:25:13,730 --> 00:25:16,165 that are governed by the laws of nature. 454 00:25:16,199 --> 00:25:19,501 Our sense of the stability of the Earth is an illusion 455 00:25:19,536 --> 00:25:21,704 due to the shortness of our lives. 456 00:25:21,738 --> 00:25:25,608 If we could watch our planet on its own timescale, 457 00:25:25,642 --> 00:25:30,246 in which big changes take millions of years to play out, 458 00:25:30,280 --> 00:25:34,917 we would see it as the dynamic organism it really is. 459 00:25:40,156 --> 00:25:43,626 This is the world of the late Triassic period 460 00:25:43,660 --> 00:25:46,795 about 200 million years ago. 461 00:25:46,830 --> 00:25:48,931 That little guy? 462 00:25:48,965 --> 00:25:51,400 It's one of our distant ancestors. 463 00:25:51,434 --> 00:25:54,336 He lived in Newark, New Jersey. 464 00:25:56,640 --> 00:26:00,809 Wherever you walk on Earth... 465 00:26:00,844 --> 00:26:03,812 lost worlds lie buried beneath your feet. 466 00:26:03,847 --> 00:26:06,048 50 or 100 million years ago, 467 00:26:06,082 --> 00:26:08,550 even the most seemingly ordinary places 468 00:26:08,585 --> 00:26:11,253 have been the scene of epic change. 469 00:26:11,288 --> 00:26:13,656 These Palisades are a monument 470 00:26:13,690 --> 00:26:16,892 to the breakup of the supercontinent Pangaea. 471 00:26:16,927 --> 00:26:19,061 The sequence of volcanic eruptions 472 00:26:19,095 --> 00:26:23,432 that made these cliffs also led to the next mass extinction-- 473 00:26:23,466 --> 00:26:26,569 the one that ended the Triassic world. 474 00:26:26,603 --> 00:26:27,903 But a catastrophic 475 00:26:27,938 --> 00:26:30,239 extinction event for one species 476 00:26:30,273 --> 00:26:32,308 is a golden opportunity for another. 477 00:26:36,680 --> 00:26:39,081 The Triassic extinctions offered one group 478 00:26:39,115 --> 00:26:41,016 that had been around for a while 479 00:26:41,051 --> 00:26:42,818 the chance to take center stage. 480 00:26:46,723 --> 00:26:48,991 The dinosaurs had a good, long run 481 00:26:49,025 --> 00:26:52,127 for 170 million years. 482 00:26:52,162 --> 00:26:55,965 Back then, India was an island. 483 00:26:55,999 --> 00:26:59,668 It crept northward at the pace of a few inches per year 484 00:26:59,703 --> 00:27:03,505 on its slow but inexorable rendezvous with Asia. 485 00:27:03,540 --> 00:27:05,608 Then, once again, 486 00:27:05,642 --> 00:27:08,110 the molten rock beneath Earth's surface 487 00:27:08,144 --> 00:27:12,181 burst forth and flooded a huge area of western India. 488 00:27:18,722 --> 00:27:20,823 The knockout punch 489 00:27:20,857 --> 00:27:23,726 literally came out of the blue. 490 00:28:00,260 --> 00:28:03,596 Few animals larger than a hundred pounds 491 00:28:03,630 --> 00:28:06,665 survived the catastrophes of the late Cretaceous. 492 00:28:07,471 --> 00:28:11,774 The dust cloud brought night and cold to the surface for months. 493 00:28:11,808 --> 00:28:14,043 The dinosaurs froze and starved to death. 494 00:28:14,077 --> 00:28:16,045 But there were small creatures 495 00:28:16,079 --> 00:28:18,047 who took shelter in the Earth. 496 00:28:18,081 --> 00:28:19,982 And when they emerged... 497 00:28:20,017 --> 00:28:22,018 they found that the monsters who had hunted 498 00:28:22,052 --> 00:28:24,520 and terrorized them were gone. 499 00:28:24,554 --> 00:28:28,324 The Earth was becoming the Planet of the Mammals. 500 00:28:28,358 --> 00:28:32,328 And the Earth continued its ceaseless changing. 501 00:28:34,264 --> 00:28:37,400 This was once a desert where nothing could grow. 502 00:28:37,434 --> 00:28:41,137 It was a million square miles of sand and salt, 503 00:28:41,171 --> 00:28:44,507 far more hostile than any environment on Earth today. 504 00:28:44,541 --> 00:28:48,077 Daytime temperatures were hot enough to bake bread. 505 00:28:48,111 --> 00:28:50,746 And it was more than a mile below sea level, 506 00:28:50,781 --> 00:28:52,548 so the atmospheric pressure 507 00:28:52,582 --> 00:28:55,151 was about 50% higher than what we're used to. 508 00:28:55,185 --> 00:28:56,919 It would be hard to think 509 00:28:56,953 --> 00:28:59,722 of a more unpromising environment on this planet. 510 00:28:59,756 --> 00:29:02,525 Yet this was the basin of the Mediterranean 511 00:29:02,559 --> 00:29:05,027 five and a half million years ago, 512 00:29:05,062 --> 00:29:07,229 before it became a sea. 513 00:29:07,264 --> 00:29:10,199 The Earth never stops moving for long. 514 00:29:10,233 --> 00:29:12,702 The natural dam at the western end 515 00:29:12,736 --> 00:29:14,337 of the deep basin 516 00:29:14,371 --> 00:29:17,006 gave way, probably due to earthquakes. 517 00:29:17,040 --> 00:29:20,543 And the deluge began. 518 00:29:20,577 --> 00:29:24,280 The torrential waters rushed in at a rate 40,000 times greater 519 00:29:24,314 --> 00:29:26,749 than Niagara Falls, turning a vast desert 520 00:29:26,783 --> 00:29:29,151 into the Mediterranean Sea... 521 00:29:30,320 --> 00:29:33,189 in less than a year. 522 00:29:33,223 --> 00:29:35,358 There were as yet no humans 523 00:29:35,392 --> 00:29:37,593 to witness this enormous flood, 524 00:29:37,627 --> 00:29:40,396 nor to admire the beauty it created. 525 00:29:40,430 --> 00:29:42,798 Meanwhile, half a world away, 526 00:29:42,833 --> 00:29:46,569 a broad channel separated North and South America... 527 00:29:46,603 --> 00:29:48,771 allowing ocean currents to flow 528 00:29:48,805 --> 00:29:51,440 from the Atlantic into the Pacific Ocean. 529 00:29:51,475 --> 00:29:53,643 Tectonic forces gradually brought 530 00:29:53,677 --> 00:29:56,312 these two continents together, closing the channel 531 00:29:56,346 --> 00:29:59,649 and creating the Isthmus of Panama. 532 00:29:59,683 --> 00:30:02,918 This reorganized the worldwide pattern of ocean currents, 533 00:30:02,953 --> 00:30:05,688 which, in turn, affected the global climate. 534 00:30:08,458 --> 00:30:11,327 In Africa, the lush green forest canopy 535 00:30:11,361 --> 00:30:13,729 gave way to a sparser landscape. 536 00:30:13,764 --> 00:30:15,564 Some species 537 00:30:15,599 --> 00:30:18,267 that were highly specialized for life in the trees 538 00:30:18,302 --> 00:30:20,136 became extinct. 539 00:30:20,170 --> 00:30:23,072 But the generalists, the ones that could find a way 540 00:30:23,106 --> 00:30:25,408 to make a living no matter what life threw at them, 541 00:30:25,442 --> 00:30:28,177 endured and evolved. 542 00:30:31,214 --> 00:30:34,784 Our ancestors had once burrowed deep in the ground 543 00:30:34,818 --> 00:30:37,153 to avoid predators who stalked the surface. 544 00:30:37,187 --> 00:30:39,455 But when the dinosaurs perished, 545 00:30:39,489 --> 00:30:41,290 they emerged into the daylight, 546 00:30:41,325 --> 00:30:43,192 and over the eons, made new lives 547 00:30:43,226 --> 00:30:45,261 in the branches of the trees. 548 00:30:45,295 --> 00:30:47,830 They developed opposable thumbs and toes 549 00:30:47,864 --> 00:30:49,298 for swinging from branch to branch, 550 00:30:49,333 --> 00:30:51,334 across the broad canopy of treetops, 551 00:30:51,368 --> 00:30:53,602 where all their needs were fulfilled. 552 00:30:53,637 --> 00:30:57,373 They could also walk upright, but only for short distances. 553 00:30:57,407 --> 00:31:01,010 With so many trees around, they didn't have to go very far. 554 00:31:01,044 --> 00:31:03,012 But then it got colder, 555 00:31:03,046 --> 00:31:04,814 and the trees thinned out, 556 00:31:04,848 --> 00:31:07,483 broad grasslands sprang up, and our ancestors 557 00:31:07,517 --> 00:31:10,286 were forced to traverse them in search of food. 558 00:31:10,320 --> 00:31:12,321 You needed a totally different skill set 559 00:31:12,356 --> 00:31:14,156 to make it on the savanna. 560 00:31:14,191 --> 00:31:15,658 In the old days, 561 00:31:15,692 --> 00:31:17,660 you could sit perched on your tree branch 562 00:31:17,694 --> 00:31:20,129 and watch the big cats from a safe distance. 563 00:31:20,163 --> 00:31:23,733 Now you were playing on the same dangerous field. 564 00:31:27,237 --> 00:31:29,872 The survivors were those who evolved the ability 565 00:31:29,906 --> 00:31:32,508 to walk great distances on their hind legs 566 00:31:32,542 --> 00:31:33,809 and to run when necessary. 567 00:31:34,945 --> 00:31:36,345 This changed the way 568 00:31:36,380 --> 00:31:38,080 they looked at the world. 569 00:31:38,115 --> 00:31:41,350 Hands and arms were no longer tied up with walking. 570 00:31:41,352 --> 00:31:45,521 They were free to gather food and pick up sticks and bones. 571 00:31:45,555 --> 00:31:48,090 These could be used as weapons and tools. 572 00:31:48,125 --> 00:31:49,925 Think of it... 573 00:31:49,960 --> 00:31:53,529 A change in the topography of a small piece of land 574 00:31:53,563 --> 00:31:56,832 half a world away reroutes ocean currents. 575 00:31:56,867 --> 00:31:59,201 Africa grows colder and drier. 576 00:31:59,236 --> 00:32:02,104 Most of the trees can't withstand the new climate. 577 00:32:02,139 --> 00:32:04,206 The primates who lived in them 578 00:32:04,241 --> 00:32:07,376 have to seek other homes, and before you know it, 579 00:32:07,411 --> 00:32:10,413 they're using tools to remake the planet. 580 00:32:10,447 --> 00:32:14,283 The Earth has shaped the course of human destiny, 581 00:32:14,318 --> 00:32:19,088 but so has the invisible pull of distant worlds. 582 00:32:46,384 --> 00:32:48,218 The planets have influenced 583 00:32:48,253 --> 00:32:51,555 our lives, but not in the way you think. 584 00:32:51,589 --> 00:32:53,590 The gravitational pull of Venus-- 585 00:32:53,625 --> 00:32:56,126 small but close-- 586 00:32:56,160 --> 00:32:59,763 and that of Jupiter-- distant but massive-- 587 00:32:59,797 --> 00:33:04,268 tilted the Earth's axis this way and that... 588 00:33:06,571 --> 00:33:09,973 and ever so slightly tweaked the shape of its orbit. 589 00:33:12,577 --> 00:33:14,111 This periodically altered 590 00:33:14,145 --> 00:33:15,546 the amount of sunlight 591 00:33:15,580 --> 00:33:17,681 falling on the edge of the northern ice cap. 592 00:33:20,985 --> 00:33:23,387 Sometimes it made the summers there colder, 593 00:33:23,421 --> 00:33:25,155 and the glaciers advanced southward 594 00:33:25,190 --> 00:33:26,957 from one year to the next, 595 00:33:26,991 --> 00:33:28,425 grinding and scraping, 596 00:33:28,459 --> 00:33:31,261 and crushing everything in their path. 597 00:33:33,097 --> 00:33:35,232 That's what we call an ice age. 598 00:33:35,266 --> 00:33:38,468 At other times, changes in Earth's axis and orbit 599 00:33:38,503 --> 00:33:40,370 made the Arctic summers warmer. 600 00:33:42,040 --> 00:33:44,641 And the melting glaciers began to retreat. 601 00:33:46,044 --> 00:33:48,745 Imagine how resourceful our ancestors had to be 602 00:33:48,780 --> 00:33:51,849 in order to survive these radical changes in climate. 603 00:33:51,883 --> 00:33:53,784 With each glacial period, 604 00:33:53,818 --> 00:33:56,854 the ice sheets grow at the expense of the oceans; 605 00:33:56,888 --> 00:34:00,257 the world sea level falls by more than 400 feet, 606 00:34:00,291 --> 00:34:02,292 uncovering wide areas of land 607 00:34:02,327 --> 00:34:04,361 along the edges of the continents. 608 00:34:04,395 --> 00:34:07,698 15 to 25,000 years ago, 609 00:34:07,732 --> 00:34:10,000 there was a period when the ice receded, 610 00:34:10,034 --> 00:34:12,469 exposing a temporary land bridge. 611 00:34:12,504 --> 00:34:15,873 The gateway to the other half of the planet swings open. 612 00:34:15,907 --> 00:34:18,609 Bands of wanderers crossed the land bridge 613 00:34:18,643 --> 00:34:21,345 to North America and parts south. 614 00:34:21,379 --> 00:34:24,715 About 10,000 years ago, the manic swings 615 00:34:24,749 --> 00:34:28,118 of the climate and sea levels came to a stop. 616 00:34:28,153 --> 00:34:31,822 A new and gentler climate age began. 617 00:34:31,856 --> 00:34:34,892 It's the one we live in now. 618 00:34:34,926 --> 00:34:36,793 When the great ice sheets melted, 619 00:34:36,828 --> 00:34:38,962 the sea rose to its present height 620 00:34:38,997 --> 00:34:42,366 and the rivers carried silt from the highlands 621 00:34:42,400 --> 00:34:45,869 to build great delta plains where they met the sea. 622 00:34:45,904 --> 00:34:49,706 On those fertile plains, we learned a new way of life... 623 00:34:49,741 --> 00:34:53,744 how to grow things, to feed ourselves and more. 624 00:34:53,778 --> 00:34:56,246 For most of us, this meant an end 625 00:34:56,281 --> 00:34:58,615 to a million years of wandering. 626 00:35:00,451 --> 00:35:02,553 The way the planets tug at each other, 627 00:35:02,587 --> 00:35:04,822 the way the skin of the Earth moves, 628 00:35:04,856 --> 00:35:07,191 the way those motions affect climate 629 00:35:07,225 --> 00:35:10,027 and the evolution of life and intelligence-- 630 00:35:10,061 --> 00:35:12,763 they all combined to give us the means 631 00:35:12,797 --> 00:35:15,032 to turn the mud of those river deltas 632 00:35:15,066 --> 00:35:18,602 into the first civilizations. 633 00:35:18,636 --> 00:35:21,939 There's nothing like an interglacial period, 634 00:35:21,973 --> 00:35:24,908 one of those balmy intermissions in an ice age. 635 00:35:24,943 --> 00:35:28,378 And the great news is that this one is due to last 636 00:35:28,413 --> 00:35:31,949 for another 50,000 years. 637 00:35:33,585 --> 00:35:36,787 What a break for our kind. 638 00:35:36,821 --> 00:35:39,289 Just one problem. 639 00:35:39,324 --> 00:35:41,258 We can't seem to stop burning up all those 640 00:35:41,292 --> 00:35:44,795 buried trees from way back in the Carboniferous Age, 641 00:35:44,829 --> 00:35:46,263 in the form of coal; 642 00:35:46,297 --> 00:35:48,732 and the remains of ancient plankton, 643 00:35:48,766 --> 00:35:51,802 in the form of oil and gas. 644 00:35:53,571 --> 00:35:56,540 If we could, we'd be home free, climate-wise. 645 00:35:56,574 --> 00:36:00,143 Instead, we're dumping carbon dioxide into the atmosphere 646 00:36:00,178 --> 00:36:02,146 at a rate the Earth hasn't seen 647 00:36:02,180 --> 00:36:04,481 since the great climate catastrophes of the past, 648 00:36:04,516 --> 00:36:08,218 the ones that led to mass extinctions. 649 00:36:08,253 --> 00:36:11,822 We just can't seem to break our addiction to the kinds of fuel 650 00:36:11,856 --> 00:36:15,559 that'll bring back a climate last seen by the dinosaurs; 651 00:36:15,593 --> 00:36:18,929 a climate that will drown our coastal cities and wreak havoc 652 00:36:18,963 --> 00:36:23,901 on the environment and our ability to feed ourselves. 653 00:36:23,935 --> 00:36:26,804 All the while, the glorious sun 654 00:36:26,838 --> 00:36:29,840 pours immaculate, free energy down upon us; 655 00:36:29,874 --> 00:36:32,676 more than we will ever need. 656 00:36:32,710 --> 00:36:35,445 Why can't we summon the ingenuity and courage 657 00:36:35,480 --> 00:36:37,748 of the generations that came before us? 658 00:36:37,782 --> 00:36:41,618 The dinosaurs never saw that asteroid coming. 659 00:36:41,653 --> 00:36:43,987 What's our excuse? 660 00:36:53,898 --> 00:36:55,599 There's a corridor 661 00:36:55,633 --> 00:36:57,868 in the Halls of Extinction that is, right now, 662 00:36:57,902 --> 00:37:00,137 empty and unmarked. 663 00:37:00,171 --> 00:37:04,875 The autobiography of the Earth is still being written. 664 00:37:04,909 --> 00:37:09,513 There's a chance that the end of our story lies in there. 665 00:37:18,490 --> 00:37:20,424 Congratulations. 666 00:37:20,426 --> 00:37:23,627 You're alive. 667 00:37:23,629 --> 00:37:26,430 There's an unbroken thread that stretches across 668 00:37:26,432 --> 00:37:28,832 more than three billion years 669 00:37:28,834 --> 00:37:31,802 that connects us to the first life 670 00:37:31,804 --> 00:37:35,005 that ever touched this world. 671 00:37:35,007 --> 00:37:38,408 Think of how tough, resourceful and lucky 672 00:37:38,410 --> 00:37:40,677 all of our countless ancestors must have been 673 00:37:40,679 --> 00:37:42,546 to survive long enough 674 00:37:42,548 --> 00:37:45,782 to pass on the message of life to the next 675 00:37:45,784 --> 00:37:49,186 and the next... 676 00:37:49,188 --> 00:37:51,722 and the next generation, 677 00:37:51,724 --> 00:37:54,624 hundreds of millions of times... 678 00:38:00,031 --> 00:38:01,698 before it came to us. 679 00:38:05,703 --> 00:38:08,038 There were so many rivers to cross, 680 00:38:08,040 --> 00:38:09,639 so many hazards along the way. 681 00:38:09,641 --> 00:38:12,776 Predators, starvation, disease, 682 00:38:12,778 --> 00:38:15,945 miscalculation, long winters, 683 00:38:15,947 --> 00:38:18,348 drought, flood and violence. 684 00:38:18,350 --> 00:38:20,717 Not to mention the occasional upheavals that 685 00:38:20,719 --> 00:38:23,887 erupted from within our planet and the apocalyptic bolts 686 00:38:23,889 --> 00:38:27,090 that come from the blue. No matter where we hail from 687 00:38:27,092 --> 00:38:30,226 or who our parents were, we are descended 688 00:38:30,228 --> 00:38:33,396 from the hearty survivors of unimaginable catastrophes. 689 00:38:33,398 --> 00:38:37,367 Each of us is a runner in the longest and most dangerous 690 00:38:37,369 --> 00:38:39,803 relay race there ever was, 691 00:38:39,805 --> 00:38:43,673 and at this moment, we hold the baton in our hands. 692 00:38:48,679 --> 00:38:53,016 The past is another planet. 693 00:38:53,018 --> 00:38:55,552 And so is the future. 694 00:38:55,554 --> 00:38:59,089 Some 250 million years from now, 695 00:38:59,091 --> 00:39:01,291 many geologists think that the lands of the Earth 696 00:39:01,293 --> 00:39:03,994 will be united once again. 697 00:39:18,409 --> 00:39:20,543 All this beauty will have vanished 698 00:39:20,545 --> 00:39:22,679 and the Earth of our moment in time 699 00:39:22,681 --> 00:39:26,750 will take its place among the lost worlds. 700 00:39:26,752 --> 00:39:29,419 The great internal engine of plate tectonics 701 00:39:29,421 --> 00:39:31,454 is indifferent to life, 702 00:39:31,456 --> 00:39:34,391 as are the small changes in the Earth's orbit and tilt 703 00:39:34,393 --> 00:39:36,292 and the occasional collisions 704 00:39:36,294 --> 00:39:39,429 with little worlds on rogue orbits. 705 00:39:39,431 --> 00:39:42,399 These processes have no notion of what has been going on 706 00:39:42,401 --> 00:39:44,934 over billions of years on our planet's surface. 707 00:39:44,936 --> 00:39:47,971 They do not care. 708 00:39:47,973 --> 00:39:51,141 Each of us is a tiny being 709 00:39:51,143 --> 00:39:53,910 riding on the outermost skin of one of the smaller planets 710 00:39:53,912 --> 00:39:57,147 for a few dozen trips around the local star. 711 00:39:59,950 --> 00:40:02,585 The things that live the longest on Earth 712 00:40:02,587 --> 00:40:04,387 endure for only about a millionth 713 00:40:04,389 --> 00:40:06,656 of the age of our planet. 714 00:40:06,658 --> 00:40:08,725 So, of course, the individual organisms 715 00:40:08,727 --> 00:40:11,261 see nothing of the overall pattern. 716 00:40:11,263 --> 00:40:14,297 Of changing continents... 717 00:40:14,299 --> 00:40:16,800 climate... 718 00:40:16,802 --> 00:40:18,835 evolution. 719 00:40:18,837 --> 00:40:21,805 That we understand even a little of our origins 720 00:40:21,807 --> 00:40:26,076 is one of the great triumphs of human insight and courage. 721 00:40:26,078 --> 00:40:29,846 Who we are and why we are here can only be glimpsed 722 00:40:29,848 --> 00:40:32,782 by piecing together something of the full picture, 723 00:40:32,784 --> 00:40:36,786 which must encompass eons of time... 724 00:40:36,788 --> 00:40:39,522 millions of species... 725 00:40:42,693 --> 00:40:45,261 and a multitude of worlds. 726 00:40:52,269 --> 00:40:55,171 In this perspective, it's not surprising 727 00:40:55,173 --> 00:40:57,273 that we're a mystery to ourselves and that, 728 00:40:57,275 --> 00:40:59,709 despite our manifest pretension, 729 00:40:59,711 --> 00:41:02,779 we are far from being masters of our own little house. 730 00:41:08,686 --> 00:41:11,655 This new corridor has no name above the entrance 731 00:41:11,657 --> 00:41:14,591 to designate its epoch, and we don't yet know 732 00:41:14,593 --> 00:41:18,962 which failed species will be memorialized within its walls. 733 00:41:18,964 --> 00:41:23,667 What happens here, in countless ways, both large and small, 734 00:41:23,669 --> 00:41:26,036 is being written by us. 735 00:41:26,038 --> 00:41:28,338 Right now.