1 00:00:02,933 --> 00:00:07,800 NARRATOR: From a fiery hellscape 2 00:00:07,800 --> 00:00:12,466 to a thriving oasis 3 00:00:12,466 --> 00:00:14,833 filled with life, 4 00:00:14,833 --> 00:00:19,066 our planet has played host to a vast array of creatures. 5 00:00:19,066 --> 00:00:22,400 STEVE BRUSATTE: It is one unfolding story 6 00:00:22,400 --> 00:00:25,100 with so many twists and turns 7 00:00:25,100 --> 00:00:26,400 and new characters coming in, 8 00:00:26,400 --> 00:00:27,933 and old characters going extinct. 9 00:00:27,933 --> 00:00:31,100 It's like the longest-running television show of all time. 10 00:00:31,100 --> 00:00:33,233 ♪ ♪ 11 00:00:33,233 --> 00:00:35,000 NARRATOR: Throughout Earth's history... 12 00:00:35,000 --> 00:00:37,533 (eruption roars) 13 00:00:37,533 --> 00:00:40,366 ...powerful geological forces shape the course of evolution. 14 00:00:40,366 --> 00:00:43,733 And 66 million years ago... 15 00:00:43,733 --> 00:00:46,500 (explosion roars) 16 00:00:46,500 --> 00:00:49,166 ...one catastrophe sparks the beginning of a new era. 17 00:00:49,166 --> 00:00:50,766 AISHA MORRIS: One major event 18 00:00:50,766 --> 00:00:53,566 can have these ripple effects throughout the rest of history, 19 00:00:53,566 --> 00:00:57,400 and this event is almost unmatched. 20 00:00:57,400 --> 00:01:00,266 NARRATOR: An era in which a species emerges 21 00:01:00,266 --> 00:01:04,666 that changes the planet faster than any before it. 22 00:01:04,666 --> 00:01:08,700 AMELIA VILLASEÑOR: Humans have modified the planet in a geological blink of an eye. 23 00:01:08,700 --> 00:01:13,033 We have basically altered every part that there is to alter. 24 00:01:13,033 --> 00:01:15,766 ♪ ♪ 25 00:01:15,766 --> 00:01:20,966 NARRATOR: What extraordinary series of events gave rise to us? 26 00:01:20,966 --> 00:01:23,266 MÓNICA CARVALHO: This is one of those scenarios 27 00:01:23,266 --> 00:01:26,800 in which we see geology driving the evolution of life. 28 00:01:28,000 --> 00:01:31,266 NARRATOR: And can lessons from our planet's past 29 00:01:31,266 --> 00:01:33,533 help secure our future? 30 00:01:35,033 --> 00:01:37,766 ZERAY ALEMSEGED: Our survival as a species 31 00:01:37,766 --> 00:01:41,766 is intricately linked to the future of the planet. 32 00:01:41,766 --> 00:01:45,033 NARRATOR: "Ancient Earth: Humans." 33 00:01:45,033 --> 00:01:46,700 ♪ ♪ 34 00:01:46,700 --> 00:01:49,533 Right now, on "NOVA." 35 00:01:52,366 --> 00:01:57,366 ♪ ♪ 36 00:02:08,766 --> 00:02:13,800 ♪ ♪ 37 00:02:22,133 --> 00:02:27,166 ♪ ♪ 38 00:02:28,400 --> 00:02:30,400 NARRATOR: Over the course of Earth's 39 00:02:30,400 --> 00:02:34,266 four-and-a-half-billion-year history, 40 00:02:34,266 --> 00:02:37,933 countless species have come and gone. 41 00:02:44,266 --> 00:02:49,866 But for over 160 million years, it was dominated by creatures 42 00:02:49,866 --> 00:02:53,100 amongst the largest to have ever evolved. 43 00:02:54,933 --> 00:02:59,433 This is the age of dinosaurs. 44 00:02:59,433 --> 00:03:03,933 MORRIS: I think it would interesting, humbling, and a bit terrifying 45 00:03:03,933 --> 00:03:06,400 to be walking amongst 46 00:03:06,400 --> 00:03:08,266 some of these massive creatures 47 00:03:08,266 --> 00:03:10,133 that were roaming around 48 00:03:10,133 --> 00:03:11,933 and munching on these huge plants 49 00:03:11,933 --> 00:03:14,733 that were growing at the time. 50 00:03:14,733 --> 00:03:16,866 (dinosaurs bellowing in distance) 51 00:03:16,866 --> 00:03:18,866 JANE FRANCIS: The sounds, I think, 52 00:03:18,866 --> 00:03:21,900 would have been really interesting. 53 00:03:21,900 --> 00:03:24,533 Bird-like chattering. 54 00:03:24,533 --> 00:03:26,366 Definitely a lot of loud and hoarse noises. 55 00:03:26,366 --> 00:03:27,966 (dinosaurs lowing) 56 00:03:27,966 --> 00:03:30,100 BRUSATTE: The whole fantastic variety 57 00:03:30,100 --> 00:03:32,333 of meat-eating dinosaurs, plant-eating dinosaurs, 58 00:03:32,333 --> 00:03:33,900 long-necked dinosaurs, 59 00:03:33,900 --> 00:03:36,600 dinosaurs with horns and spikes, 60 00:03:36,600 --> 00:03:39,000 and dinosaurs with feathers and wings. 61 00:03:39,000 --> 00:03:44,233 (dinosaur screeching) 62 00:03:44,233 --> 00:03:47,766 NARRATOR: But the reign of the dinosaurs nears its end, 63 00:03:47,766 --> 00:03:53,733 as a looming disaster will set the stage for our own evolution. 64 00:03:53,733 --> 00:03:58,466 ♪ ♪ 65 00:03:58,466 --> 00:04:00,533 ("Never Close Enough" by SIPHO. playing) 66 00:04:00,533 --> 00:04:05,433 ♪ Oh, we won't ever hear the silence ♪ 67 00:04:05,433 --> 00:04:08,466 ♪ Or ever see the colors ♪ 68 00:04:08,466 --> 00:04:09,800 (exploding) 69 00:04:09,800 --> 00:04:13,766 ♪ That never lived in our minds ♪ 70 00:04:13,766 --> 00:04:16,466 ♪ ♪ 71 00:04:16,466 --> 00:04:17,800 ♪ Just a moment ♪ 72 00:04:17,800 --> 00:04:21,100 ♪ Never too far out ♪ 73 00:04:21,100 --> 00:04:25,266 ♪ Never close enough ♪ 74 00:04:29,900 --> 00:04:33,300 ♪ ♪ 75 00:04:41,366 --> 00:04:44,733 NARRATOR: An asteroid the size of Mount Everest 76 00:04:44,733 --> 00:04:48,600 is on a direct collision course with Earth. 77 00:04:51,100 --> 00:04:56,166 ♪ ♪ 78 00:04:57,666 --> 00:05:02,733 (dinosaurs calling) 79 00:05:02,733 --> 00:05:05,766 (explosion rumbling) 80 00:05:12,200 --> 00:05:14,200 NARRATOR: The blast from the impact 81 00:05:14,200 --> 00:05:17,300 annihilates everything in its path. 82 00:05:17,300 --> 00:05:20,433 (shock wave rushing) 83 00:05:24,733 --> 00:05:27,133 MORRIS: The energy released when this asteroid struck 84 00:05:27,133 --> 00:05:31,066 was the equivalent of ten billion nuclear bombs. 85 00:05:35,900 --> 00:05:39,333 MARK MASLIN: It caused earthquakes 100 times more powerful 86 00:05:39,333 --> 00:05:41,166 than any earthquake 87 00:05:41,166 --> 00:05:43,566 that humans have ever encountered. 88 00:05:43,566 --> 00:05:46,033   GARETH COLLINS: It would have looked like 89 00:05:46,033 --> 00:05:49,000 a second sun on the horizon, a huge ball of fire. 90 00:05:49,000 --> 00:05:51,966 It certainly wouldn't have been possible 91 00:05:51,966 --> 00:05:53,733 to bathe in its beauty, 92 00:05:53,733 --> 00:05:55,200 because if you were unfortunate enough 93 00:05:55,200 --> 00:05:57,433 to be able to see it, you were toast. 94 00:05:57,433 --> 00:05:59,500 (shock wave rushing) 95 00:05:59,500 --> 00:06:01,900 JESSICA WATKINS: It is difficult to imagine 96 00:06:01,900 --> 00:06:03,600 what it would have been like to be a dinosaur 97 00:06:03,600 --> 00:06:05,000 on the surface that day. 98 00:06:05,000 --> 00:06:07,933 Um, not a great day to be a dinosaur. (laughs) 99 00:06:07,933 --> 00:06:10,466 This was probably the biggest asteroid 100 00:06:10,466 --> 00:06:15,300 that's hit the Earth in at least the last half a billion years. 101 00:06:15,300 --> 00:06:18,033 And the dinosaurs had no idea what was coming. 102 00:06:18,033 --> 00:06:19,800 ♪ ♪ 103 00:06:19,800 --> 00:06:21,200 (thunder rumbling) 104 00:06:21,200 --> 00:06:24,033 NARRATOR: After billions upon billions of tons 105 00:06:24,033 --> 00:06:26,400 of super-heated debris are thrown up 106 00:06:26,400 --> 00:06:30,633 into the atmosphere, it begins to rain. 107 00:06:31,966 --> 00:06:33,700 Not water, 108 00:06:33,700 --> 00:06:38,366 but bullets of rock known as spherules. 109 00:06:38,366 --> 00:06:42,600 ♪ ♪ 110 00:06:42,600 --> 00:06:44,466 In an asteroid impact, 111 00:06:44,466 --> 00:06:48,366 the molten rock vaporizes to form a gas. 112 00:06:48,366 --> 00:06:52,200 That gas expands to form a plume, and inside the plume, 113 00:06:52,200 --> 00:06:57,466 that gas condenses, solidifies, and cools, 114 00:06:57,466 --> 00:07:00,100 and becomes these rounded droplets 115 00:07:00,100 --> 00:07:03,166 that then rain down on the surrounding environment. 116 00:07:04,466 --> 00:07:06,500 COLLINS: These particular spherules were found 117 00:07:06,500 --> 00:07:10,066 about 300 miles away from the impact site. 118 00:07:10,066 --> 00:07:12,966 It's amazing to think that these tiny spherules 119 00:07:12,966 --> 00:07:16,200 were produced in this intense fireball. 120 00:07:16,200 --> 00:07:19,833 ♪ ♪ 121 00:07:24,700 --> 00:07:26,966 NARRATOR: The impact formed a vast crater 122 00:07:26,966 --> 00:07:30,666 over 110 miles wide. 123 00:07:30,666 --> 00:07:34,066 (wind blowing, birds chirping) 124 00:07:34,066 --> 00:07:35,700 But, over time, 125 00:07:35,700 --> 00:07:41,033 this was buried under more than 1,600 feet of rock. 126 00:07:50,133 --> 00:07:53,200 Today, at ground zero of the impact, 127 00:07:53,200 --> 00:07:56,566 the jungles burst with biodiversity. 128 00:08:01,833 --> 00:08:04,166 It's hard to imagine the devastation 129 00:08:04,166 --> 00:08:07,733 inflicted 66 million years ago. 130 00:08:09,000 --> 00:08:15,100 ♪ ♪ 131 00:08:15,100 --> 00:08:18,233 To uncover the true extent of the catastrophe... 132 00:08:20,000 --> 00:08:25,333 ...scientists study geological clues it left behind. 133 00:08:25,333 --> 00:08:29,700 ♪ ♪ 134 00:08:29,700 --> 00:08:33,433 CHRIS LOWERY: I'm standing in this beautiful geological formation 135 00:08:33,433 --> 00:08:34,933 called a cenote. 136 00:08:36,133 --> 00:08:37,633 Cenote is a Mayan word 137 00:08:37,633 --> 00:08:39,300 which means "a hole filled with water." 138 00:08:41,966 --> 00:08:43,900 These cenotes form 139 00:08:43,900 --> 00:08:46,166 as rainwater trickles through cracks in the rock, 140 00:08:46,166 --> 00:08:47,666 slowly eroding those cracks, 141 00:08:47,666 --> 00:08:49,833 and they get wider and wider until they collapse, 142 00:08:49,833 --> 00:08:51,066 and a big sinkhole forms. 143 00:08:56,933 --> 00:09:00,266 NARRATOR: Taking a satellite image of the Yucatán Peninsula 144 00:09:00,266 --> 00:09:03,533 and overlaying a map of the cenotes on top of it 145 00:09:03,533 --> 00:09:05,466 reveals a subtle pattern. 146 00:09:05,466 --> 00:09:09,700 LOWERY: Each of these yellow dots is a cenote. 147 00:09:09,700 --> 00:09:10,833 You can see thousands of cenotes. 148 00:09:10,833 --> 00:09:12,466 There's as many as 10,000. 149 00:09:12,466 --> 00:09:13,900 And if we look at the northwestern part 150 00:09:13,900 --> 00:09:14,966 of the Yucatán over here, 151 00:09:14,966 --> 00:09:17,233 we see about 400 of these cenotes 152 00:09:17,233 --> 00:09:18,833 that form this cluster. 153 00:09:20,433 --> 00:09:24,900 NARRATOR: Scientists call this cluster the Ring of Cenotes, 154 00:09:24,900 --> 00:09:28,500 because if the arc it forms is extended into the ocean, 155 00:09:28,500 --> 00:09:32,133 it creates a circle. 156 00:09:32,133 --> 00:09:34,033 LOWERY: This cluster of cenotes actually corresponds 157 00:09:34,033 --> 00:09:36,333 very closely to the inner rim of the crater itself. 158 00:09:36,333 --> 00:09:38,533 Almost like a bull's eye of the impact crater. 159 00:09:40,800 --> 00:09:43,333 NARRATOR: The asteroid impact weakened the rock 160 00:09:43,333 --> 00:09:44,900 around the crater's rim. 161 00:09:44,900 --> 00:09:47,233 (birds chirping) 162 00:09:47,233 --> 00:09:49,966 So, over millions of years, 163 00:09:49,966 --> 00:09:52,533 rainwater eroded the weakened layers, 164 00:09:52,533 --> 00:09:57,733 creating caves, which collapsed to form the Ring of Cenotes. 165 00:10:00,166 --> 00:10:02,233 LOWERY: So, these amazing natural features 166 00:10:02,233 --> 00:10:04,066 are some of the only visual reminders 167 00:10:04,066 --> 00:10:05,566 we have left of the impact. 168 00:10:05,566 --> 00:10:10,000 ♪ ♪ 169 00:10:10,000 --> 00:10:13,766 NARRATOR: But how could an impact on one side of the planet 170 00:10:13,766 --> 00:10:18,966 wipe out species on the other side? 171 00:10:18,966 --> 00:10:22,500 To solve this mystery, scientists need to understand 172 00:10:22,500 --> 00:10:27,500 what happened in the days and months that followed. 173 00:10:38,600 --> 00:10:42,633 In the hours after the chaos of the initial impact, 174 00:10:42,633 --> 00:10:46,100 debris and dust thrown up by the collision 175 00:10:46,100 --> 00:10:50,033 combine with soot and ash from wildfires, 176 00:10:50,033 --> 00:10:53,533 forming a vast, gray cloud, 177 00:10:53,533 --> 00:10:57,200 which engulfs the entire planet 178 00:10:57,200 --> 00:10:59,933 and causes death and destruction 179 00:10:59,933 --> 00:11:03,333 on a global scale. 180 00:11:03,333 --> 00:11:04,666 One of the big mysteries is 181 00:11:04,666 --> 00:11:06,033 that the heavier particles rained out 182 00:11:06,033 --> 00:11:08,166 of the atmosphere within a few months, 183 00:11:08,166 --> 00:11:09,733 maybe a year, tops, 184 00:11:09,733 --> 00:11:11,566 but that doesn't really explain 185 00:11:11,566 --> 00:11:13,733 the extent of the extinction that followed. 186 00:11:13,733 --> 00:11:17,366 So, there has been this global detective chase 187 00:11:17,366 --> 00:11:21,300 to understand how the extinction unfolded. 188 00:11:21,300 --> 00:11:22,966 ♪ ♪ 189 00:11:22,966 --> 00:11:24,866 NARRATOR: But it wasn't in the atmosphere 190 00:11:24,866 --> 00:11:28,033 that scientists found the smoking gun. 191 00:11:29,866 --> 00:11:32,600 It was deep underground. 192 00:11:37,700 --> 00:11:39,833 LOWERY: So, beneath our feet is the Earth's crust. 193 00:11:40,933 --> 00:11:42,700 The Earth's crust is layers of rock, 194 00:11:42,700 --> 00:11:44,833 20 miles thick in most places, 195 00:11:44,833 --> 00:11:47,300 and these layers of rock, uh, can be read 196 00:11:47,300 --> 00:11:49,733 like a story of the Earth's history. 197 00:11:49,733 --> 00:11:51,600 We can drill into these layers, and we can 198 00:11:51,600 --> 00:11:53,600 recover samples, and we can use that to understand 199 00:11:53,600 --> 00:11:55,800 how things have changed through the past. 200 00:11:58,033 --> 00:12:00,433 NARRATOR: In the 1950s and '60s, 201 00:12:00,433 --> 00:12:02,700 oil drilling in the Yucatán Peninsula 202 00:12:02,700 --> 00:12:06,233 unearthed samples that were rich in a particular type of rock. 203 00:12:09,300 --> 00:12:11,366 LOWERY: So, this is a rock called anhydrite. 204 00:12:11,366 --> 00:12:12,866 It might look very boring, 205 00:12:12,866 --> 00:12:15,733 but it's actually very rich in an element called sulfur. 206 00:12:15,733 --> 00:12:18,766 And the sulfur is what's really important about this story. 207 00:12:24,166 --> 00:12:27,633 ♪ ♪ 208 00:12:32,733 --> 00:12:37,366 NARRATOR: In 2016, Chris Lowery and a team of scientists 209 00:12:37,366 --> 00:12:40,266 drilled through the seafloor into the impact crater. 210 00:12:41,633 --> 00:12:44,033 LOWERY: When we drilled into the crater, 211 00:12:44,033 --> 00:12:46,100 we got the cores back from the layers of rock 212 00:12:46,100 --> 00:12:47,133 where the asteroid actually hit. 213 00:12:49,766 --> 00:12:51,733 We found that there was no anhydrite. 214 00:12:56,066 --> 00:12:58,000 What we think this means is all this anhydrite 215 00:12:58,000 --> 00:13:01,200 was vaporized by the force of the impact. 216 00:13:01,200 --> 00:13:04,200 This would have put, we think, about 325 billion tons of sulfur 217 00:13:04,200 --> 00:13:06,433 into the upper atmosphere, and this is where this impact 218 00:13:06,433 --> 00:13:08,266 really had its devastating effect. 219 00:13:12,333 --> 00:13:14,666 MORRIS: So, we end up with a lot of sulfur 220 00:13:14,666 --> 00:13:15,900 in the upper atmosphere, 221 00:13:15,900 --> 00:13:17,400 and the atmospheric circulation 222 00:13:17,400 --> 00:13:19,433 moves this material around the planet. 223 00:13:21,233 --> 00:13:23,300 CARVALHO: Unlike carbon dioxide, 224 00:13:23,300 --> 00:13:26,300 that traps the heat from the sun, 225 00:13:26,300 --> 00:13:28,100 sulfur does the opposite, 226 00:13:28,100 --> 00:13:30,733 and it actually reflects a lot of the radiation 227 00:13:30,733 --> 00:13:32,566 that's coming in from the sun. 228 00:13:34,333 --> 00:13:40,033 (wind blowing) 229 00:13:40,033 --> 00:13:42,966 NARRATOR: With less sunlight reaching the surface, 230 00:13:42,966 --> 00:13:46,033 it becomes dark and cold, 231 00:13:46,033 --> 00:13:51,366 plunging the planet into a global impact winter. 232 00:13:51,366 --> 00:13:52,700 CARVALHO: With very little light, 233 00:13:52,700 --> 00:13:55,500 there's barely no photosynthesis. 234 00:13:55,500 --> 00:13:57,433 And photosynthesis is the main process 235 00:13:57,433 --> 00:14:01,066 by which plants are able to produce the food 236 00:14:01,066 --> 00:14:06,066 that's feeding all the animals that live in ecosystems. 237 00:14:07,366 --> 00:14:10,466 BRUSATTE: What I have here is a replica of a skull. 238 00:14:10,466 --> 00:14:13,400 It's a type of dinosaur called an ornithomimid, 239 00:14:13,400 --> 00:14:14,800 and it was thriving 240 00:14:14,800 --> 00:14:17,833 during those last glory days before the asteroid hit. 241 00:14:17,833 --> 00:14:20,533 And it probably ate a lot of plants. 242 00:14:20,533 --> 00:14:22,633 The dinosaurs and other animals that ate plants, 243 00:14:22,633 --> 00:14:24,700 they didn't have any food, so they died. 244 00:14:24,700 --> 00:14:26,500 And the meat-eaters then died, and so on. 245 00:14:26,500 --> 00:14:29,800 Ecosystems collapsed like houses of cards. 246 00:14:31,000 --> 00:14:34,133 So it was really that global impact winter 247 00:14:34,133 --> 00:14:39,500 that sealed the fate of most of the dinosaurs. 248 00:14:39,500 --> 00:14:43,800 NARRATOR: But it isn't just the dinosaurs that are wiped out. 249 00:14:43,800 --> 00:14:45,366 AMMIE KALAN: We have an estimate that about 250 00:14:45,366 --> 00:14:49,166 75% of all living plants and animals 251 00:14:49,166 --> 00:14:51,033 at that time went extinct 252 00:14:51,033 --> 00:14:53,133 as a result of the asteroid's impact. 253 00:14:53,133 --> 00:14:55,633 This was one of the worst 254 00:14:55,633 --> 00:14:58,133 mass extinctions in Earth history. 255 00:14:58,133 --> 00:15:02,566 ♪ ♪ 256 00:15:02,566 --> 00:15:06,300 NARRATOR: The asteroid impact wipes out all of the dinosaurs 257 00:15:06,300 --> 00:15:10,900 except for some smaller ones that are the ancestors of birds. 258 00:15:10,900 --> 00:15:16,300 And, crucially, some mammals also survive. 259 00:15:18,600 --> 00:15:22,500 FRANCIS: Extinctions are really important because they change things. 260 00:15:22,500 --> 00:15:24,466 They give us a change 261 00:15:24,466 --> 00:15:26,433 in the direction of evolution, 262 00:15:26,433 --> 00:15:28,133 and it gives an opportunity 263 00:15:28,133 --> 00:15:30,266 for new species of animal and plants 264 00:15:30,266 --> 00:15:34,100 to evolve into the landscape. 265 00:15:34,100 --> 00:15:38,600 (birds calling) 266 00:15:38,600 --> 00:15:41,700 NARRATOR: You don't have to look into the past to find examples 267 00:15:41,700 --> 00:15:46,333 of the types of animals that survived that long winter, 268 00:15:46,333 --> 00:15:51,133 because areas of ecological destruction on Earth today 269 00:15:51,133 --> 00:15:54,533 demonstrate that with a depleted habitat, 270 00:15:54,533 --> 00:15:57,566 but just enough opportunity, 271 00:15:57,566 --> 00:16:00,533 there is always a chance that some species 272 00:16:00,533 --> 00:16:05,000 will find a way to exploit the devastation that is left. 273 00:16:07,833 --> 00:16:09,933 BRUSATTE: There are some types of organisms, 274 00:16:09,933 --> 00:16:13,233 because they're adaptable, because they can grow fast, 275 00:16:13,233 --> 00:16:14,966 because they can eat lots of different things, 276 00:16:14,966 --> 00:16:18,466 they are well suited for living in conditions 277 00:16:18,466 --> 00:16:21,300 that other animals and plants just can't handle. 278 00:16:21,300 --> 00:16:25,466 This was a huge catastrophe for mammals, 279 00:16:25,466 --> 00:16:29,766 but just enough survived that they were able to 280 00:16:29,766 --> 00:16:34,333 inherit a planet that was barren of dinosaurs. 281 00:16:34,333 --> 00:16:38,133 So, these are replica fossils 282 00:16:38,133 --> 00:16:41,666 of a tiny early mammal called Purgatorius. 283 00:16:41,666 --> 00:16:44,800 Purgatorius is one of these early mammals 284 00:16:44,800 --> 00:16:47,733 that thrived once the dinosaurs went extinct. 285 00:16:47,733 --> 00:16:50,200 So, here is Purgatorius's jaw, 286 00:16:50,200 --> 00:16:52,066 and you can even see the teeth there, 287 00:16:52,066 --> 00:16:55,700 and the tiny little heel bone, which is minute, 288 00:16:55,700 --> 00:16:58,500 and its ankle bone here. 289 00:16:58,500 --> 00:17:00,000 And it's really on the backs 290 00:17:00,000 --> 00:17:02,800 of these really tiny small mammals 291 00:17:02,800 --> 00:17:06,100 that the evolution of the rest of mammals really lies on. 292 00:17:09,966 --> 00:17:14,366 ♪ ♪ 293 00:17:14,366 --> 00:17:17,800 NARRATOR: It is thought that the cold, dark conditions 294 00:17:17,800 --> 00:17:22,900 last for over a decade. 295 00:17:22,900 --> 00:17:25,466 But as the skies clear 296 00:17:25,466 --> 00:17:28,433 and the sunlight returns to full strength, 297 00:17:28,433 --> 00:17:30,866 temperatures rise again, 298 00:17:30,866 --> 00:17:34,900 creating a climate warmer than the one we have today. 299 00:17:34,900 --> 00:17:37,566 ♪ ♪ 300 00:17:37,566 --> 00:17:40,600 And mammals, which have lived in the shadows 301 00:17:40,600 --> 00:17:46,000 of the dinosaurs for around 140 million years, 302 00:17:46,000 --> 00:17:50,200 find a way to gain a foothold. 303 00:17:50,200 --> 00:17:53,600 BRUSATTE: And this new world was a world of prime opportunity 304 00:17:53,600 --> 00:17:55,000 for the mammals that survived. 305 00:17:55,000 --> 00:17:58,833 It was their springboard to an entirely new future. 306 00:18:01,733 --> 00:18:06,233 NARRATOR: A new chapter for life is beginning: 307 00:18:06,233 --> 00:18:10,433 the age of mammals. 308 00:18:10,433 --> 00:18:13,400 But it's not an asteroid from space 309 00:18:13,400 --> 00:18:15,700 that will spur the next big change 310 00:18:15,700 --> 00:18:17,833 in the course of evolution. 311 00:18:17,833 --> 00:18:22,366 It's powerful forces within Earth itself. 312 00:18:22,366 --> 00:18:26,400 ♪ ♪ 313 00:18:30,533 --> 00:18:33,933 Deep beneath the North Atlantic Ocean, 314 00:18:33,933 --> 00:18:37,866 volcanic activity starts to bake organic matter 315 00:18:37,866 --> 00:18:40,666 within the seafloor. 316 00:18:40,666 --> 00:18:44,033 As this carbon-rich material is heated, 317 00:18:44,033 --> 00:18:48,400 bubbles of the greenhouse gases carbon dioxide and methane 318 00:18:48,400 --> 00:18:52,700 stream out and warm the atmosphere. 319 00:18:52,700 --> 00:18:56,233 FRANCIS: Methane acts much faster and much more strongly 320 00:18:56,233 --> 00:18:57,633 than carbon dioxide. 321 00:18:57,633 --> 00:19:00,733 So, if we're releasing methane from the seafloor, 322 00:19:00,733 --> 00:19:06,066 it would have caused rapid warming. 323 00:19:07,433 --> 00:19:10,900 NARRATOR: As this warming releases other reserves of methane, 324 00:19:10,900 --> 00:19:16,633 it nudges the climate past a tipping point. 325 00:19:16,633 --> 00:19:19,133 We had what we think was a runaway effect. 326 00:19:21,100 --> 00:19:22,866 LOWERY: The rate of things really matters 327 00:19:22,866 --> 00:19:24,533 when you're talking about warming, 328 00:19:24,533 --> 00:19:27,966 and this global temperature spike 56 million years ago 329 00:19:27,966 --> 00:19:30,033 is a example of that sort of runaway effect 330 00:19:30,033 --> 00:19:31,400 and the devastating consequences of that 331 00:19:31,400 --> 00:19:33,566 in terms of climate. 332 00:19:33,566 --> 00:19:35,900 (thunder clapping) 333 00:19:39,900 --> 00:19:42,633 NARRATOR: On an already warm planet, 334 00:19:42,633 --> 00:19:47,333 global temperatures rise by at least nine degrees Fahrenheit, 335 00:19:47,333 --> 00:19:48,733 a dramatic spike... 336 00:19:48,733 --> 00:19:51,066 (thunder claps) 337 00:19:51,066 --> 00:19:55,600 ...that triggers chaos in Earth's climate. 338 00:19:55,600 --> 00:19:58,466 Violent storms batter the planet 339 00:19:58,466 --> 00:20:01,733 with flash floods... 340 00:20:03,700 --> 00:20:07,300 ...prolonged droughts, 341 00:20:07,300 --> 00:20:09,666 and destructive hurricanes. 342 00:20:12,400 --> 00:20:13,766 JAMES ZACHOS: The warming event 343 00:20:13,766 --> 00:20:15,800 had impacts on virtually 344 00:20:15,800 --> 00:20:17,766 every environment on Earth. 345 00:20:18,766 --> 00:20:22,133 With the combination of warming and ocean acidification, 346 00:20:22,133 --> 00:20:24,133 there was one of the largest 347 00:20:24,133 --> 00:20:27,800 deep sea mass extinctions in recent Earth history. 348 00:20:32,400 --> 00:20:36,166 NARRATOR: Alongside catastrophic impacts in the deep oceans 349 00:20:36,166 --> 00:20:41,233 are surprising changes in life near the poles, 350 00:20:41,233 --> 00:20:45,533 where temperatures now rise above 70 degrees Fahrenheit. 351 00:20:47,966 --> 00:20:51,533 BRUSATTE: There were alligators above the Arctic Circle, 352 00:20:51,533 --> 00:20:54,966 trying to take shade underneath palm trees. 353 00:20:54,966 --> 00:20:56,800 So, I've been to the Arctic 354 00:20:56,800 --> 00:20:58,666 and collected fossil plants, 355 00:20:58,666 --> 00:21:00,966 and I have a leaf about 45 million years old 356 00:21:00,966 --> 00:21:04,733 from the forest that once grew close to the North Pole. 357 00:21:04,733 --> 00:21:07,700 Here we are, standing among banks of snow, 358 00:21:07,700 --> 00:21:09,333 and my hands are freezing cold, 359 00:21:09,333 --> 00:21:11,566 and yet here is a leaf that's telling me 360 00:21:11,566 --> 00:21:13,333 that millions of years ago, 361 00:21:13,333 --> 00:21:17,566 there was warmth and lush life in the polar regions. 362 00:21:17,566 --> 00:21:20,633 It's incredibly exciting to find fossils 363 00:21:20,633 --> 00:21:22,333 from this time period, 364 00:21:22,333 --> 00:21:25,500 because it's an unimaginable thing. 365 00:21:25,500 --> 00:21:29,866   It's the warmest the planet has been in 180 million years. 366 00:21:29,866 --> 00:21:33,433 And for the first time, you are looking at these plants 367 00:21:33,433 --> 00:21:36,633 that were actually thriving in these ecosystems. 368 00:21:40,200 --> 00:21:43,400 NARRATOR: This warmer world brings new opportunities 369 00:21:43,400 --> 00:21:45,500 for mammals on land, 370 00:21:45,500 --> 00:21:48,966 because now, for the first time, 371 00:21:48,966 --> 00:21:53,533 across vast areas of North America, Europe, and Asia, 372 00:21:53,533 --> 00:21:59,500 one habitat starts to flourish and spread out from the Equator. 373 00:21:59,500 --> 00:22:02,533 CARVALHO: Tropical rain forests, as we know them today, 374 00:22:02,533 --> 00:22:05,600 started spreading north and south. 375 00:22:05,600 --> 00:22:09,600 And from the pollen record, we see many new types of pollen 376 00:22:09,600 --> 00:22:11,733 showing up during this time period, 377 00:22:11,733 --> 00:22:15,833 which is reflecting many new species of plants. 378 00:22:15,833 --> 00:22:19,733 ♪ ♪ 379 00:22:19,733 --> 00:22:22,900 NARRATOR: This rich environment would play a vital role 380 00:22:22,900 --> 00:22:27,266 in the emergence of a new type of mammal. 381 00:22:27,266 --> 00:22:30,433 One that is more like us. 382 00:22:30,433 --> 00:22:34,566 (birds chirping) 383 00:22:40,466 --> 00:22:42,533 Tropical forests evolved 384 00:22:42,533 --> 00:22:48,433 into some of the most biodiverse habitats on Earth. 385 00:22:51,800 --> 00:22:54,500 (birds chirping) 386 00:22:54,500 --> 00:22:58,366 Home to countless species of animals and plants. 387 00:23:01,966 --> 00:23:06,833 ♪ ♪ 388 00:23:06,833 --> 00:23:10,200 And 56 million years ago, 389 00:23:10,200 --> 00:23:14,400 many of these plants were providing a crucial ingredient. 390 00:23:16,700 --> 00:23:19,400 In my hand, I have a fossilized flower, 391 00:23:19,400 --> 00:23:20,766 and it's pretty incredible. 392 00:23:20,766 --> 00:23:22,233 It's really tiny. 393 00:23:22,233 --> 00:23:24,400 (chuckling): It's only about the size of my fingernail. 394 00:23:24,400 --> 00:23:27,433 And it was found in Utah, in North America, 395 00:23:27,433 --> 00:23:31,533 and it's been dated to around 51 million years old. 396 00:23:33,600 --> 00:23:35,133 So, flowering plants 397 00:23:35,133 --> 00:23:37,966 have been on Earth for over 130 million years. 398 00:23:37,966 --> 00:23:40,433 But during this period of time on Earth, 399 00:23:40,433 --> 00:23:42,100 which was really hot and humid, 400 00:23:42,100 --> 00:23:44,400 the tropical forests were spreading, 401 00:23:44,400 --> 00:23:46,200 and at that time, we think the flowering plants 402 00:23:46,200 --> 00:23:48,433 also continued to evolve and diversify. 403 00:23:48,433 --> 00:23:53,433 ♪ ♪ 404 00:23:53,433 --> 00:23:54,833 NARRATOR: Flowering plants 405 00:23:54,833 --> 00:23:57,933 are one of the great drivers of biodiversity, 406 00:23:57,933 --> 00:24:01,733 and, following the spike in global temperature, 407 00:24:01,733 --> 00:24:06,066 Earth's blossoming forests were full of them. 408 00:24:06,066 --> 00:24:09,033 ♪ ♪ 409 00:24:18,200 --> 00:24:20,100 KALAN: As flowering plants flourished, 410 00:24:20,100 --> 00:24:22,900   so did the species that relied on them, 411 00:24:22,900 --> 00:24:26,233 such as insects, but also birds and mammals. 412 00:24:26,233 --> 00:24:28,500 And that's really significant, because flowering plants 413 00:24:28,500 --> 00:24:31,133 also produce fruit. 414 00:24:31,133 --> 00:24:32,766 And we think fruit 415 00:24:32,766 --> 00:24:35,700 was one of the factors that drove the evolution 416 00:24:35,700 --> 00:24:38,433 of our mammal ancestors. 417 00:24:40,266 --> 00:24:46,033 NARRATOR: Against a thriving backdrop of opportunity and reward, 418 00:24:46,033 --> 00:24:49,600 a new branch of mammals is evolving, 419 00:24:49,600 --> 00:24:54,366 which takes full advantage of this rich food source. 420 00:24:57,900 --> 00:25:02,400 They are known as the first true primates. 421 00:25:02,400 --> 00:25:04,866 ♪ ♪ 422 00:25:04,866 --> 00:25:07,900 KALAN: So, I have in my bag an illustration 423 00:25:07,900 --> 00:25:13,433 of one of the first true primates, called Teilhardina. 424 00:25:13,433 --> 00:25:16,400 And it would have evolved around 56 million years ago, 425 00:25:16,400 --> 00:25:19,366 during this period of climate change, 426 00:25:19,366 --> 00:25:21,666 where there was a lot of warming. 427 00:25:21,666 --> 00:25:24,066 And we know from the fossils 428 00:25:24,066 --> 00:25:25,933 that this primate would have been very small, 429 00:25:25,933 --> 00:25:28,966 only around maybe two ounces or so. 430 00:25:28,966 --> 00:25:33,766 And you can see here they had very big, forward-facing eyes 431 00:25:33,766 --> 00:25:36,366 and these grasping hands and feet, 432 00:25:36,366 --> 00:25:37,533 very much in line 433 00:25:37,533 --> 00:25:40,466 with modern-day primate characteristics. 434 00:25:41,666 --> 00:25:44,400 NARRATOR: It took millions of years of evolution, 435 00:25:44,400 --> 00:25:48,433 but this was the first time a species had evolved 436 00:25:48,433 --> 00:25:50,666 that truly resembled the primates 437 00:25:50,666 --> 00:25:52,800 we see around the world today. 438 00:25:56,000 --> 00:25:57,200 KALAN: They're climbing 439 00:25:57,200 --> 00:26:01,633 and leaping through the canopy. 440 00:26:01,633 --> 00:26:04,400 And right now they're watching us. 441 00:26:05,966 --> 00:26:08,000 I have one looking right at me right now. 442 00:26:08,000 --> 00:26:09,000 (chuckles) 443 00:26:09,000 --> 00:26:13,066 Showing their curiosity. 444 00:26:14,800 --> 00:26:18,000 And their acrobatic skills. (chuckles) 445 00:26:18,000 --> 00:26:20,800 (animals calling in background) 446 00:26:20,800 --> 00:26:23,400 These are the black howler monkeys, 447 00:26:23,400 --> 00:26:27,966 and they are basically a tree canopy-adapted species. 448 00:26:27,966 --> 00:26:30,266 They use their grasping hands and feet 449 00:26:30,266 --> 00:26:32,666 and this amazing prehensile tail 450 00:26:32,666 --> 00:26:35,066 to make their way through the canopy. 451 00:26:35,066 --> 00:26:38,233 (animals calling in background) 452 00:26:38,233 --> 00:26:40,500 So, the first true primates, 453 00:26:40,500 --> 00:26:43,666 like Teilhardina, would have had traits 454 00:26:43,666 --> 00:26:47,300 very similar to the howler monkeys that we see here today. 455 00:26:47,300 --> 00:26:49,933 ♪ ♪ 456 00:26:49,933 --> 00:26:53,966 NARRATOR: Abundant fruit may have helped these true primates 457 00:26:53,966 --> 00:26:58,533 evolve some of their distinctive characteristics. 458 00:27:00,733 --> 00:27:04,466 KALAN: Fruit is essentially a wonderful source of energy for them 459 00:27:04,466 --> 00:27:06,133 that's packed with calories, 460 00:27:06,133 --> 00:27:10,333 and it can be really hard to find these small fruits 461 00:27:10,333 --> 00:27:13,733 in this large, dense, green canopy, 462 00:27:13,733 --> 00:27:17,000 and that's where their big eyes and their hands 463 00:27:17,000 --> 00:27:20,500 help them to be able to find and pick out ripe fruits. 464 00:27:22,700 --> 00:27:24,933 And this would have been essential for them 465 00:27:24,933 --> 00:27:27,833 to be able to adapt to a life in the trees. 466 00:27:27,833 --> 00:27:33,866 ♪ ♪ 467 00:27:38,866 --> 00:27:44,666 ♪ ♪ 468 00:27:44,666 --> 00:27:48,033 So, with this global temperature spike, 469 00:27:48,033 --> 00:27:50,433 forests started to spread further and further, 470 00:27:50,433 --> 00:27:53,466 even up into the northern hemispheres, 471 00:27:53,466 --> 00:27:56,333 and, with that, primates were then able to expand 472 00:27:56,333 --> 00:27:59,733 into Europe, North America, Asia, and Africa. 473 00:27:59,733 --> 00:28:02,566 MASLIN: We enter the golden age of primates. 474 00:28:02,566 --> 00:28:04,033 We have them evolving 475 00:28:04,033 --> 00:28:05,733 into lots of different species. 476 00:28:05,733 --> 00:28:08,900 This was perhaps, at that moment in time, 477 00:28:08,900 --> 00:28:11,500 the pinnacle of primate diversity. 478 00:28:11,500 --> 00:28:13,700 At this time, it really was 479 00:28:13,700 --> 00:28:15,400 not really "Planet of the Apes," 480 00:28:15,400 --> 00:28:18,400 but it definitely was "Planet of the Primates." 481 00:28:18,400 --> 00:28:20,466 ♪ ♪ 482 00:28:20,466 --> 00:28:23,000 NARRATOR: But the global spread of primates 483 00:28:23,000 --> 00:28:26,200 is about to come to an end. 484 00:28:26,200 --> 00:28:29,833 They have thrived for over 20 million years 485 00:28:29,833 --> 00:28:32,400 on a warm Earth. 486 00:28:32,400 --> 00:28:38,000 But now, the planet's climate is cooling dramatically. 487 00:28:38,000 --> 00:28:44,033 ♪ ♪ 488 00:28:45,833 --> 00:28:48,333 FRANCIS: The mechanism is still debated, 489 00:28:48,333 --> 00:28:50,600 but we think natural cycles 490 00:28:50,600 --> 00:28:53,933 reduced carbon dioxide levels in the atmosphere. 491 00:28:53,933 --> 00:28:55,566 And there were other impacts, as well, 492 00:28:55,566 --> 00:28:58,600 such as the movement of the tectonic plates 493 00:28:58,600 --> 00:29:00,700 that changed ocean circulation, 494 00:29:00,700 --> 00:29:03,100 that had an impact on the atmosphere, 495 00:29:03,100 --> 00:29:05,866 and gradually, the polar regions began to, 496 00:29:05,866 --> 00:29:07,833 to cool, particularly Antarctica. 497 00:29:10,233 --> 00:29:14,333 NARRATOR: Across the northern continents, cooler, drier conditions 498 00:29:14,333 --> 00:29:18,666 decimate the lush forest ecosystems, 499 00:29:18,666 --> 00:29:22,366 and the habitats where the first true primates emerged 500 00:29:22,366 --> 00:29:25,600 begin to disappear. 501 00:29:25,600 --> 00:29:27,500 KALAN: This was really bad for primates, 502 00:29:27,500 --> 00:29:30,800 because it meant that their habitat was shrinking. 503 00:29:30,800 --> 00:29:33,000 Along with that comes the fact, then, 504 00:29:33,000 --> 00:29:34,733 that they cannot get access 505 00:29:34,733 --> 00:29:36,233 to all the food resources that they need. 506 00:29:39,566 --> 00:29:43,433 NARRATOR: Primate populations plummet in Europe 507 00:29:43,433 --> 00:29:47,033 and disappear completely from North America. 508 00:29:48,400 --> 00:29:50,966 But around Earth's warm Equator, 509 00:29:50,966 --> 00:29:55,700 their habitat continues to thrive. 510 00:29:55,700 --> 00:30:00,033 The critical thing about those primates in Africa 511 00:30:00,033 --> 00:30:03,333 is that we can trace our evolutionary lineage 512 00:30:03,333 --> 00:30:05,866 all the way back to them. 513 00:30:05,866 --> 00:30:11,900 ♪ ♪ 514 00:30:16,633 --> 00:30:21,766 NARRATOR: As primates prosper in the warmth of East Africa... 515 00:30:21,766 --> 00:30:24,400 ♪ ♪ 516 00:30:24,400 --> 00:30:29,866 ...tectonic forces deep within the Earth's crust 517 00:30:29,866 --> 00:30:33,133 begin to tear the continent apart. 518 00:30:35,933 --> 00:30:38,133 ♪ ♪ 519 00:30:38,133 --> 00:30:41,866 Hot magma wells up, 520 00:30:41,866 --> 00:30:45,933 driving the creation of a new environment. 521 00:30:45,933 --> 00:30:48,566 ♪ ♪ 522 00:30:48,566 --> 00:30:50,800 Over millions of years, 523 00:30:50,800 --> 00:30:56,066 deep valleys are forged and mountain ranges rise. 524 00:30:56,066 --> 00:31:02,066 ♪ ♪ 525 00:31:03,333 --> 00:31:04,733 Until, 526 00:31:04,733 --> 00:31:06,733 running thousands of miles 527 00:31:06,733 --> 00:31:09,466 through present-day Ethiopia in the north 528 00:31:09,466 --> 00:31:12,000 to Mozambique in the south, 529 00:31:12,000 --> 00:31:16,466 the East African Rift Valley is formed. 530 00:31:16,466 --> 00:31:22,500 ♪ ♪ 531 00:31:31,566 --> 00:31:34,466 APRIL NOWELL: The Rift Valley system created 532 00:31:34,466 --> 00:31:37,000 both these deep valleys and, of course, 533 00:31:37,000 --> 00:31:39,400 these really high mountain ranges, 534 00:31:39,400 --> 00:31:42,500   and that would have created this rain shadow, 535 00:31:42,500 --> 00:31:45,066 so it blocked the monsoon rains from coming across, 536 00:31:45,066 --> 00:31:48,466 and that created a whole new landscape. 537 00:31:48,466 --> 00:31:50,733 CARVALHO: So, this is one of the perfect scenarios 538 00:31:50,733 --> 00:31:53,133 in which we see geology and tectonics 539 00:31:53,133 --> 00:31:56,433 actually driving the evolution of life. 540 00:31:56,433 --> 00:32:00,000 With this drier climate, all the vegetation changes. 541 00:32:00,000 --> 00:32:03,400 You go from a complete cover of forest 542 00:32:03,400 --> 00:32:05,700 to having a mosaic of environments. 543 00:32:05,700 --> 00:32:10,533 Patches of forests connected by grasslands. 544 00:32:10,533 --> 00:32:12,600 NARRATOR: This shifting landscape 545 00:32:12,600 --> 00:32:17,633 presents these primates with new challenges. 546 00:32:17,633 --> 00:32:21,166 KALAN: This was really an evolutionary fork in the road for primates. 547 00:32:21,166 --> 00:32:23,300 Food resources became more dispersed, 548 00:32:23,300 --> 00:32:25,733 which meant that primates had to travel further 549 00:32:25,733 --> 00:32:28,900 in order to find enough food to survive. 550 00:32:28,900 --> 00:32:32,033 And what we see is that that likely led to 551 00:32:32,033 --> 00:32:35,633   evolving more efficient ways of moving through the landscape. 552 00:32:42,833 --> 00:32:46,400 ALEMSEGED: Africa is fundamental to our origin story 553 00:32:46,400 --> 00:32:50,933 because most of our development happened in Africa. 554 00:32:50,933 --> 00:32:52,233 The conditions were unique 555 00:32:52,233 --> 00:32:54,800 not only for the flourishment of our species 556 00:32:54,800 --> 00:32:56,700 and our lineage in general, 557 00:32:56,700 --> 00:32:59,266 but for the preservation of their remains. 558 00:32:59,266 --> 00:33:03,600 (talking indistinctly) 559 00:33:03,600 --> 00:33:05,466 NARRATOR: The fossils discovered here 560 00:33:05,466 --> 00:33:08,466 help paleontologists like Zeray Alemseged 561 00:33:08,466 --> 00:33:13,300 retrace the complex story of our evolution. 562 00:33:13,300 --> 00:33:15,266 VILLASEÑOR: There is evidence 563 00:33:15,266 --> 00:33:18,100 in the fossil record that there's a mix of 564 00:33:18,100 --> 00:33:19,933 walking and climbing traits, 565 00:33:19,933 --> 00:33:22,800 and so our ancestors were experimenting with 566 00:33:22,800 --> 00:33:25,900 walking on two legs. 567 00:33:30,000 --> 00:33:34,100 NARRATOR: They were still spending time in the trees, but a specimen 568 00:33:34,100 --> 00:33:37,133 almost three-and-a-half-million years old, 569 00:33:37,133 --> 00:33:41,000 which Zeray named Selam, adds to evidence 570 00:33:41,000 --> 00:33:44,633 that our ancestors were regularly walking upright. 571 00:33:47,066 --> 00:33:49,266 What I'm holding here is 572 00:33:49,266 --> 00:33:51,666 a replica of a skull of Selam, 573 00:33:51,666 --> 00:33:53,433 which is earliest child ever discovered. 574 00:33:53,433 --> 00:33:57,400 This hole here, which is where the spine 575 00:33:57,400 --> 00:33:59,700 would insert and connect to the brain, 576 00:33:59,700 --> 00:34:03,433 is more centralized, and that is what happens 577 00:34:03,433 --> 00:34:08,433 when you have a upright, walking individual. 578 00:34:08,433 --> 00:34:09,933 By studying the skull in general, 579 00:34:09,933 --> 00:34:11,600 we were able to comprehend 580 00:34:11,600 --> 00:34:13,900 that the species to which she belonged 581 00:34:13,900 --> 00:34:16,300 was at the cusp of being human. 582 00:34:16,300 --> 00:34:18,500 The ability to walk upright 583 00:34:18,500 --> 00:34:20,866 changed everything for our ancestors. 584 00:34:20,866 --> 00:34:22,866 It allowed us to run, 585 00:34:22,866 --> 00:34:24,266 it allowed us to have shoulders 586 00:34:24,266 --> 00:34:26,666 that we could actually throw things, so we could hunt. 587 00:34:26,666 --> 00:34:30,400 Over time, tool use becomes much more complex. 588 00:34:30,400 --> 00:34:34,200 So, for example, I have here something called a hand axe. 589 00:34:34,200 --> 00:34:35,700 This one here 590 00:34:35,700 --> 00:34:37,700 was used to butcher a horse, 591 00:34:37,700 --> 00:34:39,233 and we know that because 592 00:34:39,233 --> 00:34:43,133 we were able to extract blood residue from the edge. 593 00:34:43,133 --> 00:34:46,666 These stone tools tell us that our ancient ancestors 594 00:34:46,666 --> 00:34:50,466 were much more cognitively, socially, 595 00:34:50,466 --> 00:34:52,266 technologically sophisticated 596 00:34:52,266 --> 00:34:56,033 than we ever thought before. 597 00:34:56,033 --> 00:34:59,100 Every time we find a new fossil or a new artifact, 598 00:34:59,100 --> 00:35:03,000 it's like adding a new page to that human story. 599 00:35:03,000 --> 00:35:09,433 ♪ ♪ 600 00:35:12,900 --> 00:35:14,833 (animal trumpeting) 601 00:35:14,833 --> 00:35:19,133 NARRATOR: The fossil record reveals that around 300,000 years ago, 602 00:35:19,133 --> 00:35:23,533 a number of human-like species are thriving. 603 00:35:26,833 --> 00:35:28,500 And it's in Africa 604 00:35:28,500 --> 00:35:33,333 that our own ancestors eventually emerge-- 605 00:35:33,333 --> 00:35:35,333 Homo sapiens. 606 00:35:38,533 --> 00:35:42,000 But the world humans encounter as they leave Africa 607 00:35:42,000 --> 00:35:46,333 is vastly different from the one their predecessors inhabited. 608 00:35:46,333 --> 00:35:52,366 ♪ ♪ 609 00:36:02,700 --> 00:36:05,900 Over millions of years, 610 00:36:05,900 --> 00:36:09,200 Earth has continued to cool... 611 00:36:15,566 --> 00:36:20,266 ...and is now in the thick of the Ice Age. 612 00:36:20,266 --> 00:36:23,400 ♪ ♪ 613 00:36:23,400 --> 00:36:27,066 FRANCIS: There were times when about 25% of the land surface 614 00:36:27,066 --> 00:36:29,900 would have been covered by ice. 615 00:36:29,900 --> 00:36:31,933 Particularly in the Northern Hemisphere, 616 00:36:31,933 --> 00:36:33,700 glaciers and glacial landscapes 617 00:36:33,700 --> 00:36:37,066 extended as far as New York and London. 618 00:36:41,300 --> 00:36:43,033 So much water was locked up as ice 619 00:36:43,033 --> 00:36:46,300 that the oceans dropped by hundreds of feet. 620 00:36:46,300 --> 00:36:50,466 ♪ ♪ 621 00:36:50,466 --> 00:36:55,033 ALEMSEGED: As Homo sapiens moved from one place to another, 622 00:36:55,033 --> 00:36:56,933 they would be facing many challenging conditions. 623 00:36:56,933 --> 00:36:59,066 Remember, we are a tropical species. 624 00:37:00,766 --> 00:37:02,766 But at the same time, there seem to have been 625 00:37:02,766 --> 00:37:06,833 some type of shift in terms of our behavior. 626 00:37:06,833 --> 00:37:09,166 Humans were doing all sorts of things 627 00:37:09,166 --> 00:37:11,533 that you wouldn't have imagined to have happened 628 00:37:11,533 --> 00:37:12,900 during the Ice Age. 629 00:37:12,900 --> 00:37:18,933 (birds chirping) 630 00:37:20,366 --> 00:37:26,400 ♪ ♪ 631 00:37:32,066 --> 00:37:37,766 NARRATOR: Today, we uncover hidden evidence of these behaviors. 632 00:37:46,866 --> 00:37:52,533 ♪ ♪ 633 00:37:53,666 --> 00:37:55,866 Clues that our ancestors 634 00:37:55,866 --> 00:37:58,200 had evolved impressive powers of creativity. 635 00:38:07,466 --> 00:38:09,733 Wow! 636 00:38:12,200 --> 00:38:15,233 The panel of the spotted horses 637 00:38:15,233 --> 00:38:18,700 is one of my absolute favorite in all of cave art, 638 00:38:18,700 --> 00:38:21,100 and I've seen it reproduced a thousand times 639 00:38:21,100 --> 00:38:23,133 in books and so on, 640 00:38:23,133 --> 00:38:26,600 but nothing compares to standing right in front of it. 641 00:38:26,600 --> 00:38:28,400 You see the colors, you see the textures. 642 00:38:30,933 --> 00:38:33,866 In some ways, it looks deceptively simple, 643 00:38:33,866 --> 00:38:36,466 but these lines are so carefully placed 644 00:38:36,466 --> 00:38:39,066 that you immediately know that this is a horse, 645 00:38:39,066 --> 00:38:41,100 just from looking at its contour. 646 00:38:42,700 --> 00:38:45,166 It's a real combination of 647 00:38:45,166 --> 00:38:46,666 what they're seeing in their environment, 648 00:38:46,666 --> 00:38:50,000 as well as maybe some symbolic meaning 649 00:38:50,000 --> 00:38:53,100 through the placement of the dots around them. 650 00:38:53,100 --> 00:38:55,966 And then with the hand prints around it. 651 00:38:55,966 --> 00:38:57,700 I look at those hands, 652 00:38:57,700 --> 00:38:59,666 and you know that's us, you know that's a human. 653 00:38:59,666 --> 00:39:02,866 That's what connects us to 654 00:39:02,866 --> 00:39:05,866 the people who made these 25,000 years ago. 655 00:39:05,866 --> 00:39:10,766 ♪ ♪ 656 00:39:12,700 --> 00:39:14,666 NARRATOR: Ancient art like this 657 00:39:14,666 --> 00:39:17,533 has been found all over the world. 658 00:39:27,133 --> 00:39:30,433 Within the caves of Indonesia 659 00:39:30,433 --> 00:39:35,166 are paintings dated to around 45,000 years ago-- 660 00:39:35,166 --> 00:39:39,300 the world's oldest known images of animals. 661 00:39:41,633 --> 00:39:45,733 Studying this expanding footprint of creativity 662 00:39:45,733 --> 00:39:47,866 helps scientists piece together 663 00:39:47,866 --> 00:39:53,266 the puzzle of what makes us human. 664 00:39:53,266 --> 00:39:57,066 ♪ ♪ 665 00:40:00,166 --> 00:40:02,366 NOWELL: Prehistoric people around the world 666 00:40:02,366 --> 00:40:07,400 chose to recreate nature through their art. 667 00:40:07,400 --> 00:40:10,700 And, of course, the big question is, why? 668 00:40:10,700 --> 00:40:14,200 For me, the most compelling explanation 669 00:40:14,200 --> 00:40:17,933 is that these images were probably part of 670 00:40:17,933 --> 00:40:20,166 an oral storytelling tradition. 671 00:40:20,166 --> 00:40:21,633 That they were the illustrations 672 00:40:21,633 --> 00:40:23,166 that went along with their stories. 673 00:40:25,100 --> 00:40:28,100 And they're not just for entertainment value, 674 00:40:28,100 --> 00:40:30,500 but they actually also communicate a lot of 675 00:40:30,500 --> 00:40:34,033 really important information. 676 00:40:34,033 --> 00:40:37,733 In order to be able to survive in a particular environment, 677 00:40:37,733 --> 00:40:39,600 one person's knowledge isn't enough. 678 00:40:39,600 --> 00:40:41,366 ♪ ♪ 679 00:40:41,366 --> 00:40:43,433 But humans live in communities, 680 00:40:43,433 --> 00:40:46,300 and we share our knowledge. 681 00:40:46,300 --> 00:40:49,700 It's not one mind, but many minds working together. 682 00:40:49,700 --> 00:40:54,733 It's this grand total, this sum of all the knowledge 683 00:40:54,733 --> 00:40:56,833 that we have that we then pass on 684 00:40:56,833 --> 00:40:59,200 from generation to generation over time, 685 00:40:59,200 --> 00:41:02,900 and that's what archaeologists call cumulative culture. 686 00:41:02,900 --> 00:41:06,400 For me, this is key. 687 00:41:06,400 --> 00:41:09,600 This is what makes humans unique, 688 00:41:09,600 --> 00:41:11,233 and it's really what has allowed us 689 00:41:11,233 --> 00:41:14,200 to move out into all different kinds of environments 690 00:41:14,200 --> 00:41:15,700 and essentially live in 691 00:41:15,700 --> 00:41:17,766 basically every corner of this planet. 692 00:41:17,766 --> 00:41:22,000 ♪ ♪ 693 00:41:22,000 --> 00:41:25,000 NARRATOR: The most extreme cold and dry conditions 694 00:41:25,000 --> 00:41:27,366 of the Ice Age don't last. 695 00:41:30,800 --> 00:41:33,333 Because subtle changes in Earth's orbit 696 00:41:33,333 --> 00:41:38,833 alter the amount of sunlight reaching its surface. 697 00:41:38,833 --> 00:41:42,533 This, along with increasing carbon dioxide 698 00:41:42,533 --> 00:41:46,700 in the atmosphere, drives temperatures up 699 00:41:46,700 --> 00:41:49,166 and causes much of the ice to melt. 700 00:41:49,166 --> 00:41:52,133 ♪ ♪ 701 00:41:52,133 --> 00:41:53,600 And as it retreats, 702 00:41:53,600 --> 00:41:57,933 humans apply their skills in a revolutionary new way. 703 00:42:06,466 --> 00:42:09,600 They begin to farm. 704 00:42:09,600 --> 00:42:16,100 ♪ ♪ 705 00:42:16,100 --> 00:42:18,733 VILLASEÑOR: Farming was a major turning point for humans. 706 00:42:18,733 --> 00:42:21,066 We started to modify the landscape 707 00:42:21,066 --> 00:42:22,933 in a way that we'd never done before. 708 00:42:22,933 --> 00:42:25,533 With farming, we transitioned 709 00:42:25,533 --> 00:42:28,166 from using the environment 710 00:42:28,166 --> 00:42:29,533 to owning the environment 711 00:42:29,533 --> 00:42:31,800 through domesticating animals, 712 00:42:31,800 --> 00:42:36,500 but also having a permanent landscape that we control. 713 00:42:38,400 --> 00:42:43,533 NARRATOR: Within a few thousand years of those first seeds being sown, 714 00:42:43,533 --> 00:42:46,866 humans are farming across the planet 715 00:42:46,866 --> 00:42:49,833 on an ever-increasing scale. 716 00:42:49,833 --> 00:42:55,866 ♪ ♪ 717 00:42:59,266 --> 00:43:03,700 Today, about half of the habitable land on Earth 718 00:43:03,700 --> 00:43:05,400 is used for agriculture, 719 00:43:05,400 --> 00:43:09,100 and our takeover of the natural world 720 00:43:09,100 --> 00:43:12,200 has had an unprecedented impact. 721 00:43:12,200 --> 00:43:17,666 ♪ ♪ 722 00:43:17,666 --> 00:43:20,266 We have cut down three trillion trees-- 723 00:43:20,266 --> 00:43:22,433 that's half the trees on the planet-- 724 00:43:22,433 --> 00:43:26,333 to make way for agriculture and our cities. 725 00:43:26,333 --> 00:43:30,333 ♪ ♪ 726 00:43:30,333 --> 00:43:35,000 NARRATOR: Humans now have a greater effect on shaping Earth's surface 727 00:43:35,000 --> 00:43:37,900 than many of its natural processes, 728 00:43:37,900 --> 00:43:42,200 and human-made materials like concrete and plastic 729 00:43:42,200 --> 00:43:45,800 outweigh the combined biomass of all life on the planet. 730 00:43:45,800 --> 00:43:49,500 ♪ ♪ 731 00:43:49,500 --> 00:43:53,133 MORRIS: Humans have done a lot to create a place where 732 00:43:53,133 --> 00:43:55,233 they can thrive in relative comfort. 733 00:43:55,233 --> 00:43:59,266   We have buildings, we have very tall buildings. 734 00:43:59,266 --> 00:44:01,166 We have cars, buses, trains. 735 00:44:01,166 --> 00:44:03,600 We've conquered the sky. 736 00:44:03,600 --> 00:44:05,666 ♪ ♪ 737 00:44:05,666 --> 00:44:07,266 NARRATOR: And the engine of this progress 738 00:44:07,266 --> 00:44:09,833 is powered by materials deposited 739 00:44:09,833 --> 00:44:11,800 over the course of Earth's history. 740 00:44:14,266 --> 00:44:17,433 MASLIN: Modern human society 741 00:44:17,433 --> 00:44:20,200 is built on the use of fossil fuels. 742 00:44:21,633 --> 00:44:24,866 Coal, oil, and natural gas, 743 00:44:24,866 --> 00:44:28,266 you can see them as fossilized sunlight. 744 00:44:28,266 --> 00:44:31,666 ♪ ♪ 745 00:44:31,666 --> 00:44:35,566 Plants and animals have trapped energy from the sun, 746 00:44:35,566 --> 00:44:37,066 stored it in their carbon, 747 00:44:37,066 --> 00:44:40,000 and then been laid down in geological strata. 748 00:44:41,533 --> 00:44:46,333 VILLASEÑOR: Humans have basically mined the geological record to fuel 749 00:44:46,333 --> 00:44:48,400 many of the technologies that we depend on today. 750 00:44:49,666 --> 00:44:53,766 NARRATOR: Humanity is acting as a geological force, 751 00:44:53,766 --> 00:44:56,900 adding greenhouse gases to the atmosphere 752 00:44:56,900 --> 00:45:00,366 around ten times faster than the volcanic activity 753 00:45:00,366 --> 00:45:04,766 that caused global warming 56 million years ago. 754 00:45:07,133 --> 00:45:09,500 We've driven 20,000 years' worth of climate change 755 00:45:09,500 --> 00:45:11,600 in only 170 years. 756 00:45:11,600 --> 00:45:14,200 As someone who studies natural events, 757 00:45:14,200 --> 00:45:17,100 it's remarkable, the change that we have made. 758 00:45:19,433 --> 00:45:21,100 We're changing every aspect of the planet. 759 00:45:21,100 --> 00:45:26,066 The oceans, the land, the atmosphere, the ice. 760 00:45:26,066 --> 00:45:31,733 ♪ ♪ 761 00:45:31,733 --> 00:45:33,433 MORRIS: I think this would be 762 00:45:33,433 --> 00:45:35,166 an unrecognizable planet to our ancestors. 763 00:45:38,600 --> 00:45:41,733 NARRATOR: The planet we have transformed 764 00:45:41,733 --> 00:45:45,566 now supports more than eight billion people. 765 00:45:45,566 --> 00:45:48,066 A remarkable milestone for a species 766 00:45:48,066 --> 00:45:52,133 that was unlikely to have evolved at all. 767 00:45:52,133 --> 00:45:56,000 MASLIN: Every single one of your ancestors 768 00:45:56,000 --> 00:45:59,400 must have survived and reproduced to produce you. 769 00:45:59,400 --> 00:46:03,700 The chances that any one of us actually exists, 770 00:46:03,700 --> 00:46:08,766 the chances of our own species existing, are so, so small, 771 00:46:08,766 --> 00:46:12,633 it must make us realize how lucky we are. 772 00:46:12,633 --> 00:46:14,666 ♪ ♪ 773 00:46:23,433 --> 00:46:24,900 NARRATOR: Since Earth formed 774 00:46:24,900 --> 00:46:29,433 four-and-a-half billion years ago, 775 00:46:29,433 --> 00:46:34,833 the evolution of humanity has been far from inevitable. 776 00:46:34,833 --> 00:46:38,466 Life has been threatened by asteroids. 777 00:46:38,466 --> 00:46:42,566 (explosions roar) 778 00:46:42,566 --> 00:46:45,366 ♪ ♪ 779 00:46:45,366 --> 00:46:48,066 Catastrophic volcanic eruptions. 780 00:46:48,066 --> 00:46:49,833 ♪ ♪ 781 00:46:49,833 --> 00:46:54,533 And the almost complete glaciation of Earth's surface. 782 00:46:54,533 --> 00:46:57,633 BRUSATTE: In the history of the Earth, the history of life, 783 00:46:57,633 --> 00:47:00,533 it is one unfolding story 784 00:47:00,533 --> 00:47:03,133 with so many twists and turns and plot lines 785 00:47:03,133 --> 00:47:05,133 and new characters coming in, 786 00:47:05,133 --> 00:47:06,833 and old characters going extinct. 787 00:47:06,833 --> 00:47:09,266 It's like the longest-running television show of all time. 788 00:47:09,266 --> 00:47:12,800 ♪ ♪ 789 00:47:12,800 --> 00:47:16,800 NARRATOR: But from a barren environment once devoid of an atmosphere... 790 00:47:16,800 --> 00:47:20,900 ♪ ♪ 791 00:47:20,900 --> 00:47:22,633 ...to thriving ecosystems 792 00:47:22,633 --> 00:47:26,133 bursting with plants and animals, 793 00:47:26,133 --> 00:47:28,833 our planet's geology and climate 794 00:47:28,833 --> 00:47:33,700 shaped a world where Homo sapiens could evolve, 795 00:47:33,700 --> 00:47:36,600 the first species 796 00:47:36,600 --> 00:47:40,766 able to look not only into Earth's past... 797 00:47:43,000 --> 00:47:47,500 ...but also toward its future. 798 00:47:47,500 --> 00:47:51,133 ♪ ♪ 799 00:47:51,133 --> 00:47:53,533 MISSION CONTROL: T minus 15. 800 00:47:53,533 --> 00:47:58,633 NARRATOR: In 2021, NASA launched a rocket... 801 00:47:58,633 --> 00:47:59,833 MISSION CONTROL: Ten... 802 00:47:59,833 --> 00:48:02,166 ANNOUNCER: Nine, eight, seven... 803 00:48:02,166 --> 00:48:05,633 NARRATOR: ...toward an asteroid seven million miles from Earth. 804 00:48:05,633 --> 00:48:11,700 ANNOUNCER: Three, two, one... 805 00:48:11,700 --> 00:48:13,866 And lift-off of the Falcon 9 and DART, 806 00:48:13,866 --> 00:48:17,433 on NASA's first planetary defense test 807 00:48:17,433 --> 00:48:20,500 to intentionally crash into an asteroid. 808 00:48:20,500 --> 00:48:23,866 ♪ ♪ 809 00:48:25,533 --> 00:48:28,433 NARRATOR: Even though this asteroid was a fraction of the size 810 00:48:28,433 --> 00:48:31,466 of the one that wiped out the dinosaurs, 811 00:48:31,466 --> 00:48:34,766 humanity was about to make history. 812 00:48:34,766 --> 00:48:36,866 Oh, my goodness! (applauding) 813 00:48:36,866 --> 00:48:40,800 (applause continues) 814 00:48:40,800 --> 00:48:42,833 (cheering and applauding) 815 00:48:42,833 --> 00:48:45,633 We have impact! 816 00:48:45,633 --> 00:48:47,966 (cheering and applauding) 817 00:48:47,966 --> 00:48:51,033 COLLINS: As someone that studies asteroid impacts and knows 818 00:48:51,033 --> 00:48:52,400 how disastrous 819 00:48:52,400 --> 00:48:54,233 their consequences can be, 820 00:48:54,233 --> 00:48:56,500 it was really exciting 821 00:48:56,500 --> 00:48:59,233 to watch the NASA DART spacecraft 822 00:48:59,233 --> 00:49:03,200   slam into the asteroid and successfully deflect it. 823 00:49:03,200 --> 00:49:06,300 (cheering and applauding) 824 00:49:08,000 --> 00:49:13,033 ♪ ♪ 825 00:49:15,833 --> 00:49:20,000 NARRATOR: Our technology allows us to consider a future free from 826 00:49:20,000 --> 00:49:22,833 the threat of a cataclysmic asteroid impact. 827 00:49:24,500 --> 00:49:26,900 But it also gives us a perspective 828 00:49:26,900 --> 00:49:29,433 never experienced by our ancestors. 829 00:49:31,100 --> 00:49:36,300 One that brings into sharp focus threats far closer to home. 830 00:49:36,300 --> 00:49:42,333 ♪ ♪ 831 00:49:50,933 --> 00:49:54,466 WATKINS: It takes 90 minutes to orbit the Earth on the I.S.S. 832 00:49:56,233 --> 00:50:01,266 So, we see 16 sunrises and sunsets every day. 833 00:50:01,266 --> 00:50:03,266 It is hard to pull yourself away 834 00:50:03,266 --> 00:50:04,866 from watching the world go by. 835 00:50:08,066 --> 00:50:09,866 ♪ ♪ 836 00:50:09,866 --> 00:50:11,700 We're up in... 837 00:50:13,766 --> 00:50:16,900 ...the Canadian plains now. 838 00:50:16,900 --> 00:50:18,500 (interview): Seeing the Earth for the first time 839 00:50:18,500 --> 00:50:19,733 from the cupola windows 840 00:50:19,733 --> 00:50:22,066 was just absolutely breathtaking. 841 00:50:22,066 --> 00:50:23,500 It's difficult to describe. 842 00:50:24,733 --> 00:50:28,800 Just really seeing the planet as one body. 843 00:50:28,800 --> 00:50:31,000 Getting to see how 844 00:50:31,000 --> 00:50:33,800 all of the different climates and environments of the Earth 845 00:50:33,800 --> 00:50:36,000 are really connected. 846 00:50:36,000 --> 00:50:39,300 And also, how fragile that ecosystem is. 847 00:50:39,300 --> 00:50:40,966 It really drives home 848 00:50:40,966 --> 00:50:43,666 the importance of taking care of this planet 849 00:50:43,666 --> 00:50:45,700 and the responsibility we've been given to do so. 850 00:50:45,700 --> 00:50:50,700 ♪ ♪ 851 00:50:52,966 --> 00:50:55,333 I think oftentimes we as a species 852 00:50:55,333 --> 00:50:57,766 focus too much on the bombastic. 853 00:50:57,766 --> 00:51:00,300 On the big, bold, brash things. 854 00:51:00,300 --> 00:51:02,000 When it comes down to it, 855 00:51:02,000 --> 00:51:04,866 the risk of an asteroid hitting us is tiny, 856 00:51:04,866 --> 00:51:08,433 but the risk that climate and environmental change 857 00:51:08,433 --> 00:51:12,466 pose to us right now, every day, day in and day out, 858 00:51:12,466 --> 00:51:15,633 that risk is so much higher, it's so much more real. 859 00:51:15,633 --> 00:51:19,400 We do have a responsibility to look in the past 860 00:51:19,400 --> 00:51:22,733 and use that information wisely to make decisions 861 00:51:22,733 --> 00:51:25,600 about our future and the future of this planet. 862 00:51:25,600 --> 00:51:27,966 It is our responsibility. 863 00:51:27,966 --> 00:51:30,866 We are the only species that understands 864 00:51:30,866 --> 00:51:32,900 the consequence of our actions. 865 00:51:34,600 --> 00:51:37,900 WATKINS: I think, as human beings, we've been given a gift, 866 00:51:37,900 --> 00:51:40,000 and that is our intelligence 867 00:51:40,000 --> 00:51:42,133 and capability to investigate 868 00:51:42,133 --> 00:51:45,500 our impact on the environment around us, 869 00:51:45,500 --> 00:51:48,833 and I think using that gift 870 00:51:48,833 --> 00:51:51,166 to understand how we can affect our future 871 00:51:51,166 --> 00:51:53,466 is really imperative. 872 00:51:53,466 --> 00:51:56,700 ♪ ♪ 873 00:52:16,833 --> 00:52:24,366 ♪ ♪ 874 00:52:28,200 --> 00:52:35,733 ♪ ♪ 875 00:52:37,366 --> 00:52:44,900 ♪ ♪ 876 00:52:46,533 --> 00:52:54,066 ♪ ♪ 877 00:52:59,800 --> 00:53:07,033 ♪ ♪