1 00:00:06,480 --> 00:00:08,440 [thunder crashing] 2 00:00:08,520 --> 00:00:10,120 [rainfall] 3 00:00:12,120 --> 00:00:13,720 [dog barking] 4 00:00:13,800 --> 00:00:15,360 [birds calling] 5 00:00:16,280 --> 00:00:18,280 [varied bird calls] 6 00:00:21,600 --> 00:00:23,600 [wings fluttering] 7 00:00:24,480 --> 00:00:28,960 [narrator] The Earth, home to millions of species. 8 00:00:29,040 --> 00:00:30,280 [man talking on radio] 9 00:00:30,360 --> 00:00:32,360 [woman singing] 10 00:00:33,520 --> 00:00:36,800 But what might live... beyond? 11 00:00:42,320 --> 00:00:45,680 Astronomers have discovered  thousands of planets 12 00:00:45,760 --> 00:00:47,760 outside our solar system. 13 00:00:50,640 --> 00:00:53,840 They believe there are trillions more. 14 00:00:56,920 --> 00:01:00,280 If life exists on only a fraction of them, 15 00:01:01,520 --> 00:01:06,120 then the universe must be... alive. 16 00:01:06,880 --> 00:01:08,880 [creatures calling] 17 00:01:16,280 --> 00:01:19,560 All living things have the same needs. 18 00:01:22,320 --> 00:01:23,800 To feed... 19 00:01:30,200 --> 00:01:31,560 reproduce... 20 00:01:35,920 --> 00:01:37,560 and evolve. 21 00:01:41,040 --> 00:01:43,680 By applying the laws of life on Earth 22 00:01:44,240 --> 00:01:46,520 to the rest of the universe... 23 00:01:48,040 --> 00:01:51,680 it's possible to imagine what could live... 24 00:01:53,240 --> 00:01:55,280 on alien worlds. 25 00:02:27,520 --> 00:02:29,480 [cicadas chirping] 26 00:02:29,560 --> 00:02:35,680 Planets beyond our solar system  are known to astronomers as exoplanets. 27 00:02:38,440 --> 00:02:41,960 They are all  trillions of miles from Earth. 28 00:02:45,640 --> 00:02:50,760 And yet, it might be possible to detect a faint signature of life, 29 00:02:52,240 --> 00:02:54,760 from the light of the stars they orbit. 30 00:02:57,400 --> 00:03:02,040 Every star is sending to us  light of all different colors. 31 00:03:02,120 --> 00:03:04,760 So, if we can catch that light  in our telescope 32 00:03:04,840 --> 00:03:08,680 and put it through an instrument that spreads the light out into a rainbow, 33 00:03:09,240 --> 00:03:11,600 and we look in great detail  at that rainbow, 34 00:03:11,680 --> 00:03:13,840 we will find the chemical fingerprints 35 00:03:13,920 --> 00:03:17,360 of the elements in the atmosphere  of that star. 36 00:03:19,040 --> 00:03:23,320 This is one of those rainbows captured  by the telescope of a distant star 37 00:03:23,400 --> 00:03:26,400 about 12 light-years away, the star Tau Ceti. 38 00:03:27,040 --> 00:03:31,720 We can see these dark lines, like  from hydrogen in the star's atmosphere. 39 00:03:32,240 --> 00:03:36,280 Down here, we see these  three characteristic lines of magnesium. 40 00:03:37,040 --> 00:03:39,200 So, this is the atmosphere of the star, 41 00:03:39,760 --> 00:03:41,960 but what we wanna do is catch light 42 00:03:42,040 --> 00:03:45,080 that passes through  the atmosphere of an exoplanet, 43 00:03:45,160 --> 00:03:49,240 to capture the chemical fingerprint of  that atmosphere in exactly the same way. 44 00:03:52,440 --> 00:03:56,120 In 2012, this sort of fingerprint 45 00:03:56,200 --> 00:03:58,400 was visible in our own solar system. 46 00:04:03,320 --> 00:04:05,840 When Venus passed in front of the sun, 47 00:04:06,400 --> 00:04:08,520 it was silhouetted against it. 48 00:04:13,120 --> 00:04:18,600 For a moment, a tiny halo appeared, the atmosphere of Venus. 49 00:04:21,640 --> 00:04:25,240 It's this sliver of light astronomers are looking for. 50 00:04:30,440 --> 00:04:34,680 If they can analyze the atmosphere of distant exoplanets 51 00:04:36,240 --> 00:04:38,880 silhouetted against distant stars, 52 00:04:40,080 --> 00:04:42,960 they might find proof of life. 53 00:04:45,080 --> 00:04:47,080 [seabirds calling] 54 00:04:49,640 --> 00:04:51,800 [bird calls slowing] 55 00:04:56,040 --> 00:05:00,920 [Natalie] We've thought very carefully about what the signs of life will be. 56 00:05:01,880 --> 00:05:05,120 So we look around and we look at what's in the atmosphere 57 00:05:05,200 --> 00:05:08,720 that could be remotely detectable  from light-years away. 58 00:05:11,040 --> 00:05:13,800 And it always leads us back  to the same gas. 59 00:05:16,240 --> 00:05:17,600 Oxygen. 60 00:05:23,880 --> 00:05:26,560 50 to 70 percent of oxygen in our atmosphere 61 00:05:26,640 --> 00:05:29,000 is actually coming from the ocean... 62 00:05:30,640 --> 00:05:32,800 which is the lungs of planet Earth. 63 00:05:38,280 --> 00:05:42,440 The process that drives the growth  of the giant kelp in the oceans, 64 00:05:42,520 --> 00:05:45,560 and, in fact, all the forests  that we see on the land, 65 00:05:46,440 --> 00:05:48,400 is photosynthesis. 66 00:05:52,520 --> 00:05:55,440 What interests me most  about photosynthesis 67 00:05:55,520 --> 00:05:57,920 is the waste product  that gets tossed away, 68 00:05:58,000 --> 00:06:00,720 and that's the oxygen that goes into the atmosphere. 69 00:06:07,920 --> 00:06:11,240 We think that almost all of the oxygen in our atmosphere 70 00:06:11,320 --> 00:06:13,920 is produced by photosynthesis, 71 00:06:14,000 --> 00:06:16,280 by life here on planet Earth. 72 00:06:19,840 --> 00:06:22,560 If you see it in abundance, 73 00:06:22,640 --> 00:06:25,080 you know that the planet is a living world. 74 00:06:35,760 --> 00:06:38,280 Among trillions of worlds out there, 75 00:06:39,640 --> 00:06:44,120 those with more oxygen are more likely to sustain life. 76 00:06:51,480 --> 00:06:55,240 Imagine... a planet like Earth 77 00:06:55,320 --> 00:06:57,200 orbiting not one star... 78 00:06:58,240 --> 00:06:59,720 but two. 79 00:07:07,120 --> 00:07:09,120 This is Eden. 80 00:07:16,080 --> 00:07:18,080 [creatures singing and calling] 81 00:07:19,440 --> 00:07:24,880 The light from its twin stars powers photosynthesis... 82 00:07:29,240 --> 00:07:31,840 pumping oxygen into the atmosphere... 83 00:07:34,400 --> 00:07:36,920 allowing life to thrive. 84 00:07:41,080 --> 00:07:42,680 [cooing] 85 00:07:42,760 --> 00:07:44,360 [sniffing] 86 00:07:45,880 --> 00:07:49,000 Grazers feed on low-lying fungus... 87 00:07:49,080 --> 00:07:50,280 [twig snaps] 88 00:07:51,120 --> 00:07:54,120 ...but they're constantly alert to danger. 89 00:08:00,840 --> 00:08:04,000 The canopy is home to predators... 90 00:08:05,040 --> 00:08:06,400 [chattering] 91 00:08:07,160 --> 00:08:10,280 ...perfectly evolved to live among the trees... 92 00:08:11,560 --> 00:08:13,040 [snuffling] 93 00:08:17,920 --> 00:08:19,720 [chattering] 94 00:08:19,800 --> 00:08:22,400 ...waiting for their moment to strike. 95 00:08:23,000 --> 00:08:24,200 [chattering] 96 00:08:25,440 --> 00:08:27,440 -[rustling] -[purring] 97 00:08:30,600 --> 00:08:32,080 [screeching] 98 00:08:34,200 --> 00:08:36,960 On the ground, the grazer has the edge. 99 00:08:37,640 --> 00:08:39,640 It's faster in a chase. 100 00:08:44,160 --> 00:08:45,000 [squawking] 101 00:08:45,840 --> 00:08:49,000 But the predator has evolved  a special weapon. 102 00:09:02,440 --> 00:09:05,040 This time, the grazer escapes... 103 00:09:06,120 --> 00:09:09,560 and the predator conserves its energy. 104 00:09:14,560 --> 00:09:16,560 [birdsong] 105 00:09:21,440 --> 00:09:24,960 On any planet, energy is precious. 106 00:09:29,000 --> 00:09:32,440 Starlight is a virtually infinite source. 107 00:09:33,520 --> 00:09:37,560 But the trick is to turn that light into life. 108 00:09:43,720 --> 00:09:46,120 [man] We are in the tropical rainforest. 109 00:09:49,240 --> 00:09:54,000 There are more types of plants and animals here than anywhere else on Earth. 110 00:10:08,640 --> 00:10:11,360 The trees and plants  are soaking up the sun's energy. 111 00:10:11,440 --> 00:10:16,040 By the magic of photosynthesis, they convert sunlight into glucose energy, 112 00:10:16,120 --> 00:10:17,560 in other words, sugar. 113 00:10:17,640 --> 00:10:21,320 You can see it and even taste it. 114 00:10:28,320 --> 00:10:30,680 You can actually taste  the energy from the sun. 115 00:10:34,440 --> 00:10:36,760 Plants act like batteries, 116 00:10:38,240 --> 00:10:41,480 capturing the sun's energy as glucose. 117 00:10:43,640 --> 00:10:46,000 Herbivores eat plants. 118 00:10:46,960 --> 00:10:49,320 Carnivores eat herbivores. 119 00:10:52,000 --> 00:10:54,280 Every link in the food chain 120 00:10:55,040 --> 00:10:58,440 depends on the transfer  of this glucose energy. 121 00:11:02,240 --> 00:11:03,880 And in this forest, 122 00:11:03,960 --> 00:11:07,080 one animal can't get enough of the stuff. 123 00:11:08,280 --> 00:11:10,360 [humming] 124 00:11:10,440 --> 00:11:12,280 The hummingbird. 125 00:11:13,960 --> 00:11:17,760 [Alejandro] Hummingbirds can move their wings over a hundred times a second. 126 00:11:17,840 --> 00:11:19,840 [chirping] 127 00:11:21,800 --> 00:11:23,160 [humming] 128 00:11:23,240 --> 00:11:27,360 You can feel how much energy  they are spending just by being there. 129 00:11:34,320 --> 00:11:36,160 This frenzy of activity 130 00:11:37,520 --> 00:11:40,400 is fueled by glucose-rich nectar. 131 00:11:43,800 --> 00:11:48,400 [Alejandro] This is a device that from the front, it looks like a flower, 132 00:11:48,480 --> 00:11:51,400 so a hummingbird comes and it feeds from it. 133 00:11:58,720 --> 00:12:00,360 And there is one. 134 00:12:01,400 --> 00:12:03,880 It's going back and forth. Come on, you can do it. 135 00:12:06,400 --> 00:12:08,800 Uh... Okay, so now, he's drinking. 136 00:12:12,120 --> 00:12:15,840 The device measures the nectar the bird is drinking 137 00:12:16,280 --> 00:12:18,600 and the oxygen it is breathing. 138 00:12:21,120 --> 00:12:23,960 We calculate the energy intake  from the nectar 139 00:12:24,040 --> 00:12:26,280 and the energy output from the oxygen 140 00:12:26,360 --> 00:12:30,440 and we can calculate very accurately how much energy the bird is using. 141 00:12:33,920 --> 00:12:39,320 A hovering hummingbird consumes oxygen at an incredible rate. 142 00:12:40,520 --> 00:12:43,720 Ten times faster than an Olympic sprinter. 143 00:12:47,840 --> 00:12:53,240 The more oxygen it can get into its cells, the faster it can burn glucose, 144 00:12:54,920 --> 00:12:57,280 which unlocks the energy within. 145 00:13:05,240 --> 00:13:10,200 On Earth, 21 percent of the atmosphere is oxygen... 146 00:13:12,400 --> 00:13:15,680 fueling the diversity of life around us. 147 00:13:30,640 --> 00:13:35,160 On Eden, there's ten percent more oxygen  than on Earth... 148 00:13:38,920 --> 00:13:41,880 so life here can be more diverse... 149 00:13:45,080 --> 00:13:46,920 more energetic... 150 00:13:49,720 --> 00:13:51,720 more competitive. 151 00:13:56,440 --> 00:13:58,560 [panting] 152 00:14:01,240 --> 00:14:03,240 [animals and birds calling] 153 00:14:05,520 --> 00:14:08,760 Summer is breeding season for grazers. 154 00:14:16,400 --> 00:14:20,920 Always fearful of predators, they don't spend time finding a mate. 155 00:14:23,040 --> 00:14:26,400 Instead, they produce worm-like spawn. 156 00:14:29,240 --> 00:14:31,400 Each needs to fuse with another 157 00:14:32,360 --> 00:14:34,400 to create an embryo. 158 00:14:40,240 --> 00:14:43,600 For protection, they form a cocoon. 159 00:14:56,560 --> 00:15:00,400 Suspended above the ground,  the embryos can grow, 160 00:15:01,720 --> 00:15:03,800 away from predators. 161 00:15:19,680 --> 00:15:24,160 Here on Earth, the threat of death is a huge factor 162 00:15:24,720 --> 00:15:26,840 in the evolution of life. 163 00:15:30,720 --> 00:15:32,200 [David] Predation is everywhere. 164 00:15:32,280 --> 00:15:33,920 There's not an organism out there 165 00:15:34,000 --> 00:15:37,120 that doesn't run the risk of being eaten by another organism. 166 00:15:39,200 --> 00:15:43,680 The aspect that I'm interested in  is how predation shapes reproduction. 167 00:15:54,320 --> 00:15:56,480 They're gonna be comin' in here. 168 00:15:59,040 --> 00:16:02,760 This river is perfect for studying guppy fish... 169 00:16:04,120 --> 00:16:06,200 and their patterns of reproduction. 170 00:16:07,920 --> 00:16:10,120 -[man] Here. Here's another male. -[David] Yeah, yeah. 171 00:16:12,520 --> 00:16:14,560 This is an easy neighborhood. 172 00:16:14,640 --> 00:16:17,680 Here, guppies live with only one other species of fish, 173 00:16:17,760 --> 00:16:21,920 and it's a fish that rarely eats guppies  or harasses guppies. 174 00:16:22,400 --> 00:16:26,680 They can swim wherever they want without any risk of somebody trying to eat them. 175 00:16:28,720 --> 00:16:31,200 -Oh, right. There you go. All right. -[man] Here we go. 176 00:16:32,680 --> 00:16:35,840 Here we have some babies that  we just caught. We have five of them here. 177 00:16:36,720 --> 00:16:40,440 They may look small to you, but that's really big for a newborn baby guppy. 178 00:16:43,720 --> 00:16:46,440 The guppies here invest a lot of effort 179 00:16:46,520 --> 00:16:48,400 in relatively few offspring. 180 00:16:51,880 --> 00:16:54,640 Downstream, it's a different story. 181 00:16:57,600 --> 00:16:58,520 [David] Okay! 182 00:17:00,160 --> 00:17:01,360 Wow. 183 00:17:06,360 --> 00:17:10,840 This boulder is a natural barrier, dividing the river. 184 00:17:15,560 --> 00:17:18,080 Below it lurks danger. 185 00:17:21,120 --> 00:17:25,160 A guppy life down here is pretty much like the life of a fugitive. 186 00:17:25,240 --> 00:17:27,280 You're always on the run from predators. 187 00:17:27,360 --> 00:17:29,320 If a guppy were to swim out here... 188 00:17:31,240 --> 00:17:33,080 it wouldn't last a second. 189 00:17:36,000 --> 00:17:38,160 The only defense the guppies have 190 00:17:38,240 --> 00:17:40,800 is to produce lots of offspring, 191 00:17:42,120 --> 00:17:45,640 in the hope that some will survive  to adulthood. 192 00:17:49,560 --> 00:17:54,160 Okay, I've two babies from up there,  where guppies live without predators, 193 00:17:54,240 --> 00:17:57,640 and four from down here, where guppies live with predators. 194 00:17:57,720 --> 00:17:59,520 There's a dramatic difference in size. 195 00:17:59,600 --> 00:18:02,160 Those that are from here are much, much smaller 196 00:18:02,240 --> 00:18:04,560 than the ones that I caught  above the barrier. 197 00:18:07,520 --> 00:18:11,600 Moms don't have a big prospect of living to the future, no matter what they do. 198 00:18:12,160 --> 00:18:15,680 So the best strategy down here is to make many small babies. 199 00:18:16,280 --> 00:18:18,280 -[birds calling] -[animal barking] 200 00:18:19,560 --> 00:18:23,240 The guppies have evolved two different ways of breeding. 201 00:18:25,200 --> 00:18:27,240 Having a few large babies... 202 00:18:28,920 --> 00:18:31,000 or lots of small ones. 203 00:18:34,520 --> 00:18:38,640 The deciding factor is the threat from predators. 204 00:18:45,240 --> 00:18:48,000 [David] If you're one of the prey items,  you're gonna die young, 205 00:18:48,080 --> 00:18:49,840 so you better live fast. 206 00:18:50,320 --> 00:18:54,600 You better put a lot into having babies, because if you don't, you'll go extinct. 207 00:19:01,520 --> 00:19:04,800 Such a strategy would apply on any planet 208 00:19:05,280 --> 00:19:08,800 wherever one species preys on another. 209 00:19:18,040 --> 00:19:21,760 On Eden, the grazers have evolved  to breed fast. 210 00:19:25,720 --> 00:19:29,880 They produce as many offspring  as quickly as possible... 211 00:19:32,720 --> 00:19:36,000 to ensure the survival of the species. 212 00:19:42,760 --> 00:19:44,800 [birds squawking] 213 00:19:47,440 --> 00:19:50,920 But in the forest,  they're never truly safe. 214 00:19:56,360 --> 00:20:00,680 As summer ends, the fungi grow orange-colored fruit... 215 00:20:02,840 --> 00:20:04,880 which attract grazers. 216 00:20:04,960 --> 00:20:06,240 -[whoosh] -[squeaking] 217 00:20:10,280 --> 00:20:14,200 Spores within the fruit spread an infection. 218 00:20:21,760 --> 00:20:23,360 [growling] 219 00:20:27,960 --> 00:20:28,840 [chatters] 220 00:20:28,920 --> 00:20:30,720 Now, when predators attack, 221 00:20:32,120 --> 00:20:34,720 infected grazers don't run. 222 00:20:35,520 --> 00:20:37,680 They've lost their fear instinct. 223 00:20:40,680 --> 00:20:41,920 [grazer squeals] 224 00:20:42,000 --> 00:20:43,640 [predator chattering] 225 00:20:44,800 --> 00:20:45,920 [squeals] 226 00:20:46,000 --> 00:20:47,320 [growling] 227 00:20:52,320 --> 00:20:54,000 It's an easy meal... 228 00:20:55,840 --> 00:20:57,680 but a poisonous one. 229 00:21:00,960 --> 00:21:02,440 [wails] 230 00:21:05,040 --> 00:21:11,160 The fungi have used the grazers  to infect and kill the predators. 231 00:21:28,640 --> 00:21:34,000 Such complex relationships  between species exist on Earth... 232 00:21:36,920 --> 00:21:39,120 but not all are so lethal. 233 00:21:44,120 --> 00:21:48,680 The Hadza are hunter-gatherers, living off the land. 234 00:21:50,840 --> 00:21:53,080 [man, speaking Hadza] My name is Palango. 235 00:21:56,200 --> 00:22:01,160 As a man, my job is to hunt. 236 00:22:03,200 --> 00:22:07,360 I always carry a bow and arrow 237 00:22:08,400 --> 00:22:11,120 for protection... 238 00:22:15,240 --> 00:22:16,640 because the bush 239 00:22:17,480 --> 00:22:21,120 has many dangerous animals. 240 00:22:24,240 --> 00:22:28,440 One high-calorie food is prized  above all else. 241 00:22:30,040 --> 00:22:31,040 Honey. 242 00:22:33,520 --> 00:22:36,200 But finding fresh honey is difficult. 243 00:22:40,640 --> 00:22:44,360 The bees move their nests  from season to season. 244 00:22:47,920 --> 00:22:50,360 So the Hadza call on help. 245 00:22:50,880 --> 00:22:52,280 [whistling] 246 00:22:55,760 --> 00:22:57,080 [continues whistling] 247 00:22:57,680 --> 00:23:01,160 [Palango, in Hadza] Honeyguides are very clever birds. 248 00:23:01,240 --> 00:23:02,240 [whistles] 249 00:23:02,320 --> 00:23:07,040 They know where honey is, and they will take you there. 250 00:23:11,960 --> 00:23:13,800 [honeyguide chirping] 251 00:23:14,760 --> 00:23:16,400 She makes a special cry... 252 00:23:17,000 --> 00:23:18,800 [whistling] 253 00:23:19,280 --> 00:23:20,800 ...and I whistle back. 254 00:23:22,120 --> 00:23:24,120 [honeyguide chirping] 255 00:23:28,080 --> 00:23:29,640 [whistling] 256 00:23:29,720 --> 00:23:34,400 If I follow her, she will lead me directly to the honey. 257 00:23:39,320 --> 00:23:40,800 [whistling] 258 00:23:44,520 --> 00:23:46,680 -[honeyguide chirping] -[Palango whistling] 259 00:23:50,840 --> 00:23:53,480 The honeyguide has lived up to its name. 260 00:23:54,480 --> 00:23:58,080 It's led them to a bees' nest  in a baobab tree. 261 00:24:03,480 --> 00:24:06,880 The hunters need the bird  to find the bees. 262 00:24:08,640 --> 00:24:12,160 And the bird needs the hunters  to access the honey. 263 00:24:13,920 --> 00:24:17,400 [Palango] The honeyguides take us to the bees. 264 00:24:20,560 --> 00:24:23,440 But the bees are aggressive. 265 00:24:24,160 --> 00:24:25,920 So she needs our help. 266 00:24:26,360 --> 00:24:30,280 Climbing up a baobab tree... 267 00:24:33,720 --> 00:24:39,480 is very hard and dangerous. 268 00:24:44,120 --> 00:24:46,840 One day I fell. 269 00:24:52,480 --> 00:24:58,400 We use smoke to get the bees drunk 270 00:24:59,640 --> 00:25:02,840 and chase them out of the nest. 271 00:25:35,320 --> 00:25:37,480 The risk is worth it. 272 00:25:40,040 --> 00:25:42,400 Fresh, rich, honey. 273 00:25:54,080 --> 00:25:56,480 Palango makes sure the bird gets its share. 274 00:26:00,000 --> 00:26:02,000 It's a win-win situation. 275 00:26:08,520 --> 00:26:11,840 A complex relationship between species 276 00:26:12,440 --> 00:26:14,800 is known as symbiosis. 277 00:26:21,320 --> 00:26:25,680 The richer the ecosystem, the more complex the relationship. 278 00:26:37,840 --> 00:26:42,800 On Eden, a deadly three-way symbiosis  has evolved... 279 00:26:44,640 --> 00:26:46,720 centered around the fungi. 280 00:26:50,120 --> 00:26:51,480 -[twig snaps] -[chattering] 281 00:26:53,440 --> 00:26:55,960 First, they feed the grazers. 282 00:26:57,160 --> 00:26:58,360 -[whoosh] -[squeaks] 283 00:26:59,400 --> 00:27:01,400 Then, they infect them... 284 00:27:05,240 --> 00:27:07,600 to poison the predators. 285 00:27:15,000 --> 00:27:16,640 [wails] 286 00:27:24,520 --> 00:27:29,400 And the fungi do all this to grow their next generation... 287 00:27:36,240 --> 00:27:40,400 which feeds on the bodies  of the dead predators. 288 00:27:41,360 --> 00:27:43,360 [bird calls echoing] 289 00:27:50,080 --> 00:27:54,480 On Earth, fungi play a crucial, but invisible role 290 00:27:54,560 --> 00:27:56,680 in the life of any forest, 291 00:27:59,400 --> 00:28:01,280 behind the scenes. 292 00:28:14,040 --> 00:28:17,840 [man] So, I think most people think the first complex life on our planet 293 00:28:17,920 --> 00:28:20,720 was something like insects, or maybe even the dinosaurs. 294 00:28:21,440 --> 00:28:24,760 But, actually,  hundreds of millions of years before that, 295 00:28:25,320 --> 00:28:30,600 really the first complex  multicellular organisms were these things. 296 00:28:31,320 --> 00:28:32,360 Fungi. 297 00:28:36,720 --> 00:28:40,600 We know of at least 140,000 species, 298 00:28:41,440 --> 00:28:45,000 but that's likely to be less than ten percent of the real total. 299 00:28:49,320 --> 00:28:52,240 There's probably thousands  of different fungal species 300 00:28:52,840 --> 00:28:54,720 just in this forest alone. 301 00:29:06,680 --> 00:29:10,000 Okay, so we've actually got three mushrooms here 302 00:29:10,680 --> 00:29:13,920 and you can actually see these dotted  all throughout the forest. 303 00:29:14,640 --> 00:29:16,800 But what's amazing is that these mushrooms 304 00:29:16,880 --> 00:29:19,120 are really just the tip of the iceberg. 305 00:29:19,680 --> 00:29:21,280 When we look below the surface, 306 00:29:21,720 --> 00:29:25,800 most of the fungus is actually  in these little... tiny little threads, 307 00:29:25,880 --> 00:29:28,200 that go all throughout the soil. 308 00:29:28,280 --> 00:29:29,840 And this is called the mycelium, 309 00:29:29,920 --> 00:29:32,720 and it connects all of the other mushrooms in this area. 310 00:29:35,120 --> 00:29:40,000 There can be tens of kilometers  of these tiny microscopic fungi 311 00:29:40,080 --> 00:29:42,280 spreading throughout the entire soil. 312 00:29:43,720 --> 00:29:47,400 The tree needs those fibers to survive, 313 00:29:48,000 --> 00:29:51,240 because the tree can capture  carbon from the atmosphere, 314 00:29:51,320 --> 00:29:53,720 and it provides that carbon to the fungus. 315 00:29:54,200 --> 00:29:58,480 In contrast, the fungi access  nitrogen and phosphorus from the soil, 316 00:29:58,560 --> 00:30:00,720 which they give in exchange for that carbon. 317 00:30:01,240 --> 00:30:05,080 So, really, it's a mutualism that benefits both of the organisms. 318 00:30:11,720 --> 00:30:14,080 Possibly the most extraordinary thing 319 00:30:14,520 --> 00:30:16,520 about this mycelial system 320 00:30:16,920 --> 00:30:18,800 is just how connected it is. 321 00:30:20,520 --> 00:30:23,560 So, the fungi that are attached to the roots of this tree 322 00:30:23,640 --> 00:30:26,120 will also be attached to the roots of that tree, 323 00:30:26,640 --> 00:30:28,560 and that tree over there, 324 00:30:28,640 --> 00:30:31,800 and they will also be connected  to their neighbors 325 00:30:31,880 --> 00:30:34,760 via the same mycelial system 326 00:30:34,840 --> 00:30:38,080 that is really going tree to tree to tree. 327 00:30:44,160 --> 00:30:49,160 The mycelial network is like a circuit of wires and nodes 328 00:30:49,840 --> 00:30:52,280 through which information can flow. 329 00:30:54,920 --> 00:30:59,280 And with it, fungi can maintain the forest. 330 00:31:02,720 --> 00:31:05,360 So, if we have one tree over there that's dying, 331 00:31:05,440 --> 00:31:08,640 it might reallocate more nutrients towards that tree, 332 00:31:08,720 --> 00:31:10,560 so that the tree can do better 333 00:31:10,640 --> 00:31:13,480 and, as a result, the fungal system does better. 334 00:31:14,120 --> 00:31:18,080 Similarly, if there's disturbance  at some part of the fungal network, 335 00:31:18,160 --> 00:31:20,120 it will remove nutrients away 336 00:31:20,200 --> 00:31:23,360 so that it can minimize the impact of that disturbance. 337 00:31:25,320 --> 00:31:28,480 It's these invisible ecosystem engineers 338 00:31:28,560 --> 00:31:33,280 that are keeping the entire system  functioning in a really healthy way. 339 00:31:41,320 --> 00:31:44,680 This system has become known  as the Wood Wide Web, 340 00:31:44,760 --> 00:31:46,560 and it sounds like a bit of a joke, 341 00:31:46,640 --> 00:31:51,720 but, really, it doesn't function  so differently from the internet, 342 00:31:51,800 --> 00:31:55,240 keeping all of the organisms  connected in the forest system. 343 00:31:55,320 --> 00:31:57,320 [whirring sound effects] 344 00:32:02,720 --> 00:32:05,960 This process is happening all across the planet, 345 00:32:06,040 --> 00:32:08,160 in every ecosystem we can imagine. 346 00:32:12,840 --> 00:32:17,800 So, if we're gonna get a lush ecosystem on some alien planet out there, 347 00:32:17,880 --> 00:32:20,000 I bet you that it's underpinned 348 00:32:20,080 --> 00:32:23,160 by something like this massive mycelial system. 349 00:32:26,480 --> 00:32:28,480 [birds calling] 350 00:32:28,560 --> 00:32:30,560 [insects chirping] 351 00:32:34,120 --> 00:32:35,440 -[squeaks] -[whoosh] 352 00:32:36,520 --> 00:32:39,920 Life in the forests of Eden is a trade-off 353 00:32:40,680 --> 00:32:44,600 between fungi, grazers and predators. 354 00:32:44,680 --> 00:32:46,160 [growling] 355 00:32:47,520 --> 00:32:49,160 [wails] 356 00:32:55,520 --> 00:32:59,160 But there are greater celestial forces at play. 357 00:33:05,760 --> 00:33:09,280 Eden has stronger seasons than on Earth, 358 00:33:12,480 --> 00:33:17,080 greater fluctuations of light and warmth from its twin stars. 359 00:33:21,480 --> 00:33:23,080 [sniffing] 360 00:33:23,840 --> 00:33:25,480 [chattering] 361 00:33:27,520 --> 00:33:29,680 As winter approaches, 362 00:33:29,760 --> 00:33:32,000 the remaining predators migrate... 363 00:33:34,320 --> 00:33:35,880 chasing the light. 364 00:33:35,960 --> 00:33:37,120 [chattering] 365 00:33:41,440 --> 00:33:43,960 The remaining grazers die. 366 00:33:46,920 --> 00:33:49,040 It's the same every winter. 367 00:33:50,240 --> 00:33:52,960 Nothing grows in the dark forest... 368 00:33:53,040 --> 00:33:54,720 [rustling] 369 00:33:54,800 --> 00:33:56,520 [creaking sounds] 370 00:33:56,600 --> 00:34:00,400 ...except the embryos in their cocoons. 371 00:34:01,280 --> 00:34:03,080 [crunching sounds] 372 00:34:03,160 --> 00:34:04,680 [rumbling sounds] 373 00:34:07,240 --> 00:34:09,840 Just as the season starts to change... 374 00:34:13,320 --> 00:34:15,320 the grazers hatch... 375 00:34:18,760 --> 00:34:22,880 taking their cue  from the return of the twin stars. 376 00:34:27,720 --> 00:34:29,720 [birdsong] 377 00:34:31,720 --> 00:34:35,240 On Earth, life does the same thing, 378 00:34:35,320 --> 00:34:37,480 using the seasons as a clock. 379 00:34:44,880 --> 00:34:46,360 It's midsummer, 380 00:34:47,200 --> 00:34:49,200 the longest day of the year. 381 00:34:59,000 --> 00:35:01,320 [woman] There's a lot of fly fishermen  out this time of year 382 00:35:01,400 --> 00:35:04,560 because this is the time of year that the fish are biting, 383 00:35:05,760 --> 00:35:08,760 because there is an abundant food source in the river, 384 00:35:08,840 --> 00:35:12,400 and that food source are all these guys, the mayfly nymph. 385 00:35:13,240 --> 00:35:17,520 So, we think of mayflies as flying around on the land with us, 386 00:35:18,440 --> 00:35:21,680 but they spend the vast majority  of their life cycle living down 387 00:35:21,760 --> 00:35:24,680 on the bottom of the river, developing, growing, 388 00:35:25,240 --> 00:35:28,560 and it's all really building up  to this one time in the year 389 00:35:28,640 --> 00:35:29,960 where they're all going to emerge. 390 00:35:36,920 --> 00:35:38,800 Yellow Breeches River 391 00:35:39,880 --> 00:35:42,120 feeds the Susquehanna. 392 00:35:47,200 --> 00:35:48,640 Beneath these waters, 393 00:35:49,360 --> 00:35:53,840 millions of mayflies  are primed and ready to go. 394 00:35:59,040 --> 00:36:02,040 And when the sun sets, they emerge... 395 00:36:02,120 --> 00:36:03,720 [crowd cheering and applauding] 396 00:36:06,040 --> 00:36:07,320 en masse. 397 00:36:13,320 --> 00:36:17,120 [Allison] There are just so many insects that seemingly came out of nowhere. 398 00:36:20,520 --> 00:36:22,840 It really almost feels like an alien invasion. 399 00:36:30,080 --> 00:36:33,800 Mayflies live, at most, for two days. 400 00:36:35,520 --> 00:36:40,080 In that time, they must find a mate  to pass on their genes. 401 00:36:44,320 --> 00:36:47,120 [Allison] They have one shot, they have one chance, and if they miss it, 402 00:36:47,200 --> 00:36:48,960 it's game over for that mayfly. 403 00:36:50,760 --> 00:36:52,760 [cheering and applause] 404 00:37:00,720 --> 00:37:02,160 Once they've mated, 405 00:37:02,600 --> 00:37:06,360 the females return to the river  to lay their eggs, 406 00:37:06,440 --> 00:37:08,000 and then die. 407 00:37:10,920 --> 00:37:13,080 [Allison] Each of these little white dots is a mayfly 408 00:37:13,160 --> 00:37:16,320 that successfully made it back  to the water and has laid eggs. 409 00:37:17,920 --> 00:37:21,880 They are floating down by the thousands, by the hundreds of thousands. 410 00:37:22,520 --> 00:37:24,480 They have started the next generation 411 00:37:25,480 --> 00:37:27,800 that will continue on  and do this again next year 412 00:37:27,880 --> 00:37:30,120 in this really precisely timed event. 413 00:37:36,240 --> 00:37:40,080 The rhythm of the seasons  is always dictated 414 00:37:40,160 --> 00:37:43,480 by the tilt of a planet towards its star. 415 00:37:49,400 --> 00:37:54,080 Earth is tilted at an angle  of 23-and-a-half degrees. 416 00:38:00,520 --> 00:38:04,120 On Eden, that angle is 40 degrees, 417 00:38:06,840 --> 00:38:10,800 so more light spreads across more of the planet's surface. 418 00:38:14,640 --> 00:38:18,040 And more light means more life. 419 00:38:24,800 --> 00:38:27,680 It's spring, and there's food to eat... 420 00:38:30,120 --> 00:38:34,400 but the new grazers need to grow  as fast as possible... 421 00:38:35,400 --> 00:38:37,120 [distant roaring] 422 00:38:39,440 --> 00:38:40,600 [roaring and chattering] 423 00:38:40,680 --> 00:38:42,800 ...before the predators return... 424 00:38:49,320 --> 00:38:52,080 and the life cycle repeats. 425 00:39:03,720 --> 00:39:05,720 Wondrous creatures... 426 00:39:08,480 --> 00:39:10,480 fed by glucose... 427 00:39:17,960 --> 00:39:19,960 powered by oxygen... 428 00:39:22,480 --> 00:39:24,640 nourished by starlight. 429 00:39:35,440 --> 00:39:40,680 What is true on Eden may be true throughout the universe... 430 00:39:43,360 --> 00:39:47,640 that all life depends on the flow of energy. 431 00:40:00,120 --> 00:40:03,400 How might life adapt  on a different world, 432 00:40:05,520 --> 00:40:08,240 inhabited by intelligent beings, 433 00:40:10,360 --> 00:40:13,200 intelligent enough to make a new home... 434 00:40:14,480 --> 00:40:16,840 among the stars?