1 00:00:06,680 --> 00:00:08,680 [thunder crashing] 2 00:00:11,800 --> 00:00:13,040 [rainfall] 3 00:00:13,120 --> 00:00:14,000 [dog barking] 4 00:00:14,080 --> 00:00:15,480 [birds calling] 5 00:00:16,960 --> 00:00:19,040 [varied bird calls] 6 00:00:22,600 --> 00:00:24,600 [wings fluttering] 7 00:00:25,600 --> 00:00:30,080 [narrator] The Earth, home to millions of species. 8 00:00:30,160 --> 00:00:31,360 [man talking on radio] 9 00:00:31,440 --> 00:00:33,720 [woman singing] 10 00:00:34,720 --> 00:00:37,960 But what might live... beyond? 11 00:00:43,400 --> 00:00:46,800 Astronomers have discovered  thousands of planets 12 00:00:46,880 --> 00:00:48,880 outside our solar system. 13 00:00:51,800 --> 00:00:54,640 They believe there are trillions more. 14 00:00:59,440 --> 00:01:02,920 If life exists on only a fraction of them, 15 00:01:04,120 --> 00:01:08,800 then the universe must be... alive. 16 00:01:09,560 --> 00:01:11,560 [cawing] 17 00:01:15,560 --> 00:01:17,600 [chattering] 18 00:01:18,880 --> 00:01:22,200 All living things have the same needs. 19 00:01:25,040 --> 00:01:26,200 To feed... 20 00:01:32,920 --> 00:01:34,200 reproduce... 21 00:01:38,560 --> 00:01:39,680 and evolve. 22 00:01:43,480 --> 00:01:46,320 By applying the laws of life on Earth 23 00:01:46,920 --> 00:01:48,720 to the rest of the universe... 24 00:01:50,680 --> 00:01:52,480 it's possible to imagine 25 00:01:53,040 --> 00:01:54,600 what could live... 26 00:01:55,920 --> 00:01:57,920 on alien worlds. 27 00:02:26,920 --> 00:02:30,360 Most planets we know of are so hellish, 28 00:02:31,920 --> 00:02:35,200 it seems impossible  that anything could live. 29 00:02:37,320 --> 00:02:41,120 But it's amazing where life can take hold. 30 00:02:42,440 --> 00:02:44,040 [squelching] 31 00:02:44,720 --> 00:02:48,880 [woman] For as long as I can remember, my mom always told me I was an alien, 32 00:02:50,760 --> 00:02:54,680 because I just had my mind on outer space from the beginning. 33 00:02:57,840 --> 00:03:01,920 I just had always known that I wanted to get out there and explore the universe. 34 00:03:16,000 --> 00:03:17,360 Oh, my God. 35 00:03:18,040 --> 00:03:20,440 -[sighs] -[bleeping] 36 00:03:23,160 --> 00:03:26,040 This is the most incredible place I think I've ever seen. 37 00:03:27,440 --> 00:03:30,680 This is what I dream other planets looking like. 38 00:03:31,360 --> 00:03:33,440 It's... it's incredible. [laughs] 39 00:03:34,360 --> 00:03:35,480 So, yeah. 40 00:03:36,240 --> 00:03:37,440 [sobs] 41 00:03:40,440 --> 00:03:45,000 The Danakil Depression is known locally as "The Gateway to Hell." 42 00:03:48,800 --> 00:03:52,520 120 meters below sea level and volcanic... 43 00:03:54,840 --> 00:03:57,240 it's the hottest place on Earth. 44 00:04:00,920 --> 00:04:04,240 We're at 79C. 82C. 45 00:04:04,960 --> 00:04:07,400 This one's topping out at 87. 46 00:04:12,920 --> 00:04:14,920 If life can exist here... 47 00:04:16,640 --> 00:04:20,640 it could exist on any number of worlds  in the universe. 48 00:04:24,440 --> 00:04:26,880 Life on other planets,  they're gonna have, uh, chemistry. 49 00:04:26,960 --> 00:04:29,760 Whether it looks exactly like ours, we don't know, 50 00:04:29,840 --> 00:04:32,200 but they're gonna have chemistry that helps them live. 51 00:04:32,640 --> 00:04:35,640 And that chemistry  is going to be subject to limits. 52 00:04:37,120 --> 00:04:39,560 For example, all life is made up  of cells. 53 00:04:39,640 --> 00:04:41,880 Inside these cells they have biomolecules 54 00:04:41,960 --> 00:04:44,520 that allow the cells to function and live and work. 55 00:04:44,600 --> 00:04:48,000 That's our machinery that runs and makes this chemistry happen, 56 00:04:48,080 --> 00:04:49,800 that keeps life living. [laughs] 57 00:04:49,880 --> 00:04:53,560 And so we really wanna understand how that machinery works 58 00:04:54,280 --> 00:04:56,920 and what's gonna make that machinery break down. 59 00:05:01,880 --> 00:05:04,320 Until recently, it was assumed 60 00:05:04,400 --> 00:05:07,440 that Danakil was too extreme to support life. 61 00:05:10,400 --> 00:05:16,400 But astrobiologists come here to look  for simple single-celled microbes... 62 00:05:18,560 --> 00:05:20,840 known as extremophiles. 63 00:05:34,560 --> 00:05:36,760 [Kennda] Microbes are too small to see with the naked eye, 64 00:05:36,840 --> 00:05:39,880 so it's not going to be as simple as taking a little bit of water out of a lake 65 00:05:39,960 --> 00:05:42,840 and putting it under a microscope  and seeing lots of teeming bugs. 66 00:05:50,120 --> 00:05:53,320 The only way to detect the presence of extremophiles 67 00:05:54,840 --> 00:05:58,440 is to find traces of their DNA, 68 00:06:00,120 --> 00:06:03,080 using a portable genetic sequencer. 69 00:06:05,640 --> 00:06:09,000 This is a very small device  and it's very sensitive to temperature, 70 00:06:09,120 --> 00:06:12,280 and we're in one of the hottest places  on the planet Earth. 71 00:06:13,440 --> 00:06:15,640 So, here in the field right now, we do... a cool block, 72 00:06:15,720 --> 00:06:18,920 to kind of keep it cool, and we have our channels running. 73 00:06:19,000 --> 00:06:20,640 [static crackling] 74 00:06:20,720 --> 00:06:24,000 -[bleeping] -And we have... [laughs] 75 00:06:24,360 --> 00:06:26,880 We have sequencing! 76 00:06:27,480 --> 00:06:29,920 We actually have sequencing happening. 77 00:06:30,640 --> 00:06:32,600 We have DNA in here.  78 00:06:34,720 --> 00:06:35,560 Excellent. 79 00:06:38,200 --> 00:06:41,240 Sequencing of DNA is proof 80 00:06:41,320 --> 00:06:46,120 that extremophiles can survive  in the acidic waters of Danakil. 81 00:06:48,800 --> 00:06:53,320 These guys are like the superheroes  of microbes, and it's just amazing, 82 00:06:53,400 --> 00:06:57,840 as we learn more and more about the different strategies and mechanisms 83 00:06:57,920 --> 00:07:01,040 that they come up with to survive  these kinds of environments. 84 00:07:04,640 --> 00:07:09,480 Finding things alive here opens up an intriguing possibility. 85 00:07:10,640 --> 00:07:15,560 But some life forms are tough enough  to survive anywhere... 86 00:07:19,000 --> 00:07:22,440 even in the deepest reaches of space. 87 00:07:31,760 --> 00:07:33,600 A red dwarf star. 88 00:07:39,440 --> 00:07:42,440 The most common type of star  in our galaxy. 89 00:07:56,240 --> 00:08:00,120 Imagine a planet in such a close orbit, 90 00:08:00,200 --> 00:08:03,360 its rotation is locked by the star's gravity, 91 00:08:06,080 --> 00:08:09,440 so it always shows the same face to its sun. 92 00:08:18,840 --> 00:08:20,880 This is Janus. 93 00:08:29,640 --> 00:08:33,360 How would life adapt on such an extreme world? 94 00:08:40,200 --> 00:08:44,040 On one side of the planet, it's always daytime, 95 00:08:44,120 --> 00:08:46,080 a searing desert. 96 00:08:48,000 --> 00:08:50,000 [wind whistling] 97 00:08:51,040 --> 00:08:54,320 On the other side, it's forever night, 98 00:08:54,400 --> 00:08:56,400 a frozen shadowland. 99 00:09:03,760 --> 00:09:09,240 Squeezed between the two, a sliver of perpetual twilight. 100 00:09:18,240 --> 00:09:22,120 Freezing meltwater flows from the cold side, 101 00:09:22,880 --> 00:09:25,600 carving canyons through the landscape. 102 00:09:28,480 --> 00:09:32,360 Even here, where the planet's  most hospitable, 103 00:09:32,440 --> 00:09:34,280 there's little vegetation. 104 00:09:39,920 --> 00:09:42,160 But deep in these canyons 105 00:09:42,240 --> 00:09:45,080 lives an extraordinary five-legged creature... 106 00:09:46,880 --> 00:09:48,320 a pentapod. 107 00:09:52,920 --> 00:09:54,840 No bigger than a cat, 108 00:09:54,920 --> 00:09:57,800 it's the dominant life form on Janus, 109 00:09:59,840 --> 00:10:02,800 capable of adapting to any conditions. 110 00:10:10,440 --> 00:10:12,240 On the cold side, 111 00:10:12,320 --> 00:10:14,760 it's stocky and hairy. 112 00:10:20,640 --> 00:10:25,640 On the hot side, it's shiny, slender and skittish. 113 00:10:27,680 --> 00:10:30,800 Pentapods can become whatever they need to be 114 00:10:31,360 --> 00:10:33,280 in order to survive. 115 00:10:34,160 --> 00:10:35,920 [grunting] 116 00:10:42,240 --> 00:10:46,920 On Earth, all animals adapt  to fit their environment. 117 00:10:48,200 --> 00:10:49,880 [birdsong] 118 00:10:51,040 --> 00:10:54,080 But some are more adaptable than others. 119 00:11:00,840 --> 00:11:02,840 [birds cawing] 120 00:11:08,320 --> 00:11:10,920 [woman] This trail that I just came across here, 121 00:11:11,000 --> 00:11:13,080 it's a beautifully manicured trail, 122 00:11:13,160 --> 00:11:16,920 and you would think it was made by some bigger animal or maybe even a human. 123 00:11:17,640 --> 00:11:19,520 But it's actually made by ants. 124 00:11:22,200 --> 00:11:24,000 The leaf-cutter ant, in particular. 125 00:11:27,160 --> 00:11:28,960 All looks quiet right now, 126 00:11:29,040 --> 00:11:32,680 but if we come back at night, this will actually turn into an ant super-highway, 127 00:11:32,760 --> 00:11:36,320 with leaves just streaming up, like, towards their nest. 128 00:11:40,160 --> 00:11:42,160 [cicadas chirping] 129 00:11:48,720 --> 00:11:49,680 Oh, wow. 130 00:11:50,480 --> 00:11:51,720 Look at that. 131 00:11:54,440 --> 00:11:56,480 This is the ant nest. 132 00:11:58,840 --> 00:12:02,000 You can really see  into the heart of this colony. 133 00:12:02,080 --> 00:12:03,760 There's a lot going on. 134 00:12:07,520 --> 00:12:11,360 There's actually, for leaf-cutter ants, there's different castes. 135 00:12:12,960 --> 00:12:16,880 There is the soldiers, there are different workers. 136 00:12:17,640 --> 00:12:18,920 There's also the queen. 137 00:12:19,000 --> 00:12:22,360 She's the only one who's laying eggs, and there's only a single queen. 138 00:12:22,440 --> 00:12:24,560 Without her, none of this would be here. 139 00:12:27,240 --> 00:12:30,880 An ant colony depends on the division of labor. 140 00:12:33,280 --> 00:12:39,080 Different castes have different jobs, and they come in all shapes and sizes. 141 00:12:43,520 --> 00:12:45,840 [Magdalena] I just grabbed one of the soldiers, 142 00:12:45,920 --> 00:12:48,600 and I also grabbed the really, really small worker. 143 00:12:48,680 --> 00:12:51,400 And it's not the smallest worker in this colony, 144 00:12:51,480 --> 00:12:53,000 but it's-- it's pretty close. 145 00:12:53,080 --> 00:12:56,000 And I mean, the soldiers, I barely can hold her. 146 00:12:56,120 --> 00:12:57,840 It's really hard. I can feel her power. 147 00:12:57,920 --> 00:13:01,440 I can feel she's trying to get out.   Her jaws are wide open. 148 00:13:02,120 --> 00:13:04,240 But, I mean, the difference is incredible. 149 00:13:04,320 --> 00:13:08,720 And to think that they all started  from the same-- the same larva. 150 00:13:12,120 --> 00:13:15,400 All ants in a colony are closely related. 151 00:13:17,440 --> 00:13:19,800 They share most of the same genes. 152 00:13:21,720 --> 00:13:27,280 But as they grow up, some genes are switched on, others switched off, 153 00:13:28,280 --> 00:13:30,360 depending on the food they are fed. 154 00:13:32,440 --> 00:13:37,480 Any of them can become workers, foragers or soldiers. 155 00:13:41,640 --> 00:13:46,280 So, this ability to create such different shapes and forms from the same blueprint, 156 00:13:47,040 --> 00:13:49,240 this is actually called polyphenism. 157 00:13:49,320 --> 00:13:52,840 And "poly" just means "many," and "phenism" would be "shapes." 158 00:14:01,080 --> 00:14:05,640 Oh, the spider just did exactly  what I was trying to avoid all night. 159 00:14:05,720 --> 00:14:10,080 She walked exactly into one of these  trails of these leaf-cutters here. 160 00:14:10,520 --> 00:14:12,800 And that's not good news. 161 00:14:13,840 --> 00:14:17,800 So here, you really see the power of these soldiers and their jaws. 162 00:14:18,920 --> 00:14:21,200 If something disturbs the colony, 163 00:14:22,640 --> 00:14:26,480 it's their job to come in and get it, and that's exactly what they did. 164 00:14:34,520 --> 00:14:35,720 But wow. 165 00:14:41,080 --> 00:14:42,640 Aaah! [laughs] 166 00:14:42,720 --> 00:14:45,240 All right, I'm already being attacked. [chuckles] 167 00:14:45,320 --> 00:14:46,400 Ooh, that's gonna hurt. 168 00:14:46,480 --> 00:14:48,440 They are now coming for me. 169 00:14:54,240 --> 00:14:57,720 So, any creature that has this ability to morph 170 00:14:57,800 --> 00:15:01,200 and react to changes in its environment as quickly as ants can do, 171 00:15:01,280 --> 00:15:04,320 has an amazing advantage to not just survive, 172 00:15:04,400 --> 00:15:06,400 but actually dominate its world. 173 00:15:21,840 --> 00:15:26,280 On Janus, pentapods are masters of polyphenism. 174 00:15:29,920 --> 00:15:33,680 Like ants, they're able to develop  into different forms. 175 00:15:37,120 --> 00:15:40,160 But they all begin life in the same place... 176 00:15:42,840 --> 00:15:44,880 the Twilight Zone. 177 00:15:47,000 --> 00:15:49,320 [wind whistling] 178 00:15:52,600 --> 00:15:55,400 A pair of adults is ready to breed. 179 00:15:56,480 --> 00:15:58,120 [chattering] 180 00:15:58,200 --> 00:16:01,160 They're both male and female. 181 00:16:02,720 --> 00:16:04,080 Hermaphrodites. 182 00:16:06,120 --> 00:16:08,360 Each can produce offspring, 183 00:16:09,800 --> 00:16:12,440 doubling their chances of success. 184 00:16:21,960 --> 00:16:24,000 [clicking and chattering] 185 00:16:27,880 --> 00:16:32,680 Having mated, a pentapod leaves the shelter of the canyon. 186 00:16:36,320 --> 00:16:39,240 It climbs to high ground, 187 00:16:41,400 --> 00:16:43,200 ready to spawn. 188 00:16:49,440 --> 00:16:51,160 [wind whistling] 189 00:16:51,240 --> 00:16:57,400 At the top, a constant wind blows between  the cold and hot sides of the planet. 190 00:17:09,520 --> 00:17:14,600 But the wind provides an opportunity to scatter their larvae. 191 00:17:19,240 --> 00:17:22,680 This way, they can colonize the planet. 192 00:17:23,440 --> 00:17:25,440 [fluttering] 193 00:17:35,320 --> 00:17:39,000 On the hot side, water is scarce... 194 00:17:42,280 --> 00:17:45,880 condensing only in shaded areas. 195 00:17:55,920 --> 00:17:59,000 If there's nothing to eat, they move on. 196 00:18:10,240 --> 00:18:14,520 With five legs,  they can skitter in any direction. 197 00:18:17,320 --> 00:18:18,920 And with ten eyes, 198 00:18:19,360 --> 00:18:21,800 not much escapes their attention. 199 00:18:30,240 --> 00:18:32,040 If they sense a meal,  200 00:18:32,800 --> 00:18:35,320 they use feelers to root it out. 201 00:18:37,080 --> 00:18:39,080 [squeaking] 202 00:18:41,400 --> 00:18:44,680 They need to make the most of every opportunity. 203 00:19:02,840 --> 00:19:05,600 Life in any desert is an ordeal. 204 00:19:06,640 --> 00:19:08,920 Only the tough survive. 205 00:19:10,840 --> 00:19:12,680 And in the natural world, 206 00:19:12,760 --> 00:19:14,600 there's nothing much tougher... 207 00:19:15,840 --> 00:19:17,480 than a scorpion. 208 00:19:23,280 --> 00:19:25,000 -Oh. Anything? -Here? 209 00:19:25,080 --> 00:19:26,320 I don't think so. 210 00:19:32,040 --> 00:19:34,840 [man] My first childhood memory of the scorpion, 211 00:19:34,920 --> 00:19:39,760 I was, uh, ten years old  and I see this big scorpion. 212 00:19:41,240 --> 00:19:42,720 I screamed "Mom!" 213 00:19:42,800 --> 00:19:45,520 Uh, so she came to my aid 214 00:19:45,600 --> 00:19:47,880 and she was like, "What? What happened?" 215 00:19:47,960 --> 00:19:50,840 And I point to the scorpion, uh, on the ceiling, 216 00:19:50,920 --> 00:19:52,600 I said, "That's gonna eat me." 217 00:19:53,280 --> 00:19:57,360 And she was just like, "No, come on. Be cool. This is just a scorpion." 218 00:19:58,600 --> 00:20:01,760 So, as a cute Mexican mother, 219 00:20:01,840 --> 00:20:04,240 she took, uh... her sandal 220 00:20:04,320 --> 00:20:08,040 and just smashed the, uh, little bastard on the ceiling. 221 00:20:17,440 --> 00:20:23,000 Carlos Santibáñez-López is now an expert on scorpions, 222 00:20:24,120 --> 00:20:26,800 specializing in the study of their venom. 223 00:20:28,720 --> 00:20:32,640 [Carlos] I go at night and I use the UV light, 224 00:20:32,720 --> 00:20:35,960 because UV light makes scorpions glow. 225 00:20:36,520 --> 00:20:39,280 They have a special protein in their shell. 226 00:20:40,720 --> 00:20:43,320 Yeah, let's-- Let's take a look at this one. 227 00:20:47,960 --> 00:20:50,720 -Oh, look at this! -[man] There's a lot of them. 228 00:20:51,240 --> 00:20:52,360 [Carlos] Yeah, this is great. 229 00:20:56,000 --> 00:21:00,560 Scorpions have barely changed in 400 million years. 230 00:21:01,760 --> 00:21:04,720 Perfectly adapted for life in the desert. 231 00:21:06,360 --> 00:21:10,640 Scorpions have a very slow metabolism. 232 00:21:11,400 --> 00:21:15,560 They can spend long periods without food or water. 233 00:21:16,920 --> 00:21:20,600 We have records of some species  lasting one year 234 00:21:21,360 --> 00:21:22,920 without eating anything. 235 00:21:24,160 --> 00:21:27,000 And they have just enough energy 236 00:21:27,080 --> 00:21:30,720 to sustain essential functions to keep them alive. 237 00:21:32,320 --> 00:21:36,920 They need to ensure  that the next time food is available, 238 00:21:37,000 --> 00:21:38,280 they catch it. 239 00:21:40,200 --> 00:21:45,680 So, scorpions have developed a lot  of weapons that they can use to hunt prey, 240 00:21:47,000 --> 00:21:49,520 including the most important weapon... 241 00:21:51,360 --> 00:21:52,280 venom. 242 00:22:09,720 --> 00:22:11,800 To study scorpion venom, 243 00:22:12,680 --> 00:22:16,200 Carlos needs to extract it  from glands in the tail. 244 00:22:18,720 --> 00:22:25,240 Venom is a powerful cocktail that contains minerals, salts 245 00:22:25,320 --> 00:22:29,120 and hundreds of proteins with a different function. 246 00:22:30,240 --> 00:22:32,400 Try to be as fast as you can. 247 00:22:33,200 --> 00:22:34,640 [whispers] There you go. 248 00:22:34,720 --> 00:22:38,200 We use electricity to stimulate the muscles. 249 00:22:40,920 --> 00:22:44,280 We're only gonna get small... very small amounts, 250 00:22:44,360 --> 00:22:46,160 a teeny, tiny drop of it. 251 00:22:46,240 --> 00:22:50,040 But this drop is so valuable  that we don't wanna lose it. 252 00:22:52,320 --> 00:22:54,280 Give him a nice massage. 253 00:22:54,360 --> 00:22:57,040 Yeah. There's a tiny droplet. 254 00:22:58,320 --> 00:23:00,440 -[man] There. -Oh, yes, it's-- Okay, so it's working. 255 00:23:00,520 --> 00:23:02,000 Uh, we have venom. 256 00:23:02,560 --> 00:23:05,760 It is right there, but it's a teeny, tiny drop. 257 00:23:06,400 --> 00:23:08,560 -Uh... do you see it? -[man] That's right. Yeah. 258 00:23:08,640 --> 00:23:11,360 [Carlos] I mean, it's--  it's like a-- a drop of water. 259 00:23:21,480 --> 00:23:24,040 Venom is such an effective weapon, 260 00:23:24,640 --> 00:23:28,480 it's used by reptiles, insects and fish. 261 00:23:30,320 --> 00:23:34,600 It has evolved, separately, at least 30 times. 262 00:23:38,840 --> 00:23:42,560 The more often a trait like venom  has evolved on Earth, 263 00:23:44,240 --> 00:23:47,640 the more likely it is to exist  on other planets. 264 00:24:01,440 --> 00:24:03,400 On the hot side of Janus, 265 00:24:03,840 --> 00:24:06,920 pentapods use venom to catch their prey. 266 00:24:08,040 --> 00:24:09,280 [squeaking] 267 00:24:09,360 --> 00:24:10,760 [munching] 268 00:24:13,880 --> 00:24:15,560 [crunching] 269 00:24:16,640 --> 00:24:19,080 But hunting alone is risky. 270 00:24:20,400 --> 00:24:21,920 [squeaking] 271 00:24:23,160 --> 00:24:24,760 [skittering] 272 00:24:27,760 --> 00:24:29,400 [whimpering] 273 00:24:31,320 --> 00:24:35,040 Even a venomous predator is powerless 274 00:24:35,120 --> 00:24:36,920 against a swarm. 275 00:24:39,600 --> 00:24:41,600 [screeching] 276 00:24:44,920 --> 00:24:46,920 [wailing] 277 00:24:49,360 --> 00:24:51,400 [creatures chattering] 278 00:24:54,520 --> 00:24:58,640 On the cold side of the planet, things are just as tough. 279 00:25:02,920 --> 00:25:07,720 In perpetual darkness and with no energy from the sun... 280 00:25:09,920 --> 00:25:12,000 how can anything survive? 281 00:25:22,320 --> 00:25:26,520 On Earth, nearly all life depends on sunlight. 282 00:25:28,440 --> 00:25:29,600 [birdsong] 283 00:25:29,680 --> 00:25:32,760 Plants convert solar energy into food, 284 00:25:34,120 --> 00:25:36,280 which feeds other life forms. 285 00:25:39,520 --> 00:25:42,400 But there are some extraordinary places on Earth 286 00:25:42,480 --> 00:25:46,120 where life has evolved without any light. 287 00:25:55,000 --> 00:25:56,320 [bleeping] 288 00:25:57,040 --> 00:25:59,760 [woman] When I contemplate going in a cave like this, 289 00:25:59,840 --> 00:26:03,200 one of the things I know is it's an alien environment. 290 00:26:03,280 --> 00:26:05,360 -[woman] It's fogging up a little bit. -[man] Yeah. 291 00:26:05,440 --> 00:26:08,000 [woman] It is full of good ways to die. 292 00:26:09,160 --> 00:26:14,760 One of the big risks in this cave is there is a lot of hydrogen sulfide. 293 00:26:15,960 --> 00:26:17,920 Hydrogen sulfide can kill you. 294 00:26:18,000 --> 00:26:19,640 -[Diana] Okay. You ready? -[man] Yeah. 295 00:26:19,720 --> 00:26:24,080 [Diana] And so my husband comes along to act as a safety officer. 296 00:26:26,080 --> 00:26:30,760 He's not afraid to pull us out and say, "Time to go, you've had enough." 297 00:26:49,040 --> 00:26:53,400 Cueva de Villa Luz is a maze of limestone chambers. 298 00:26:57,680 --> 00:27:01,920 Hydrogen sulfide bubbles up  from the Earth's crust. 299 00:27:04,160 --> 00:27:10,400 Mixing with oxygen, it forms sulfuric acid and turns the water milky white. 300 00:27:13,720 --> 00:27:16,960 And yet, some life forms survive, 301 00:27:17,520 --> 00:27:20,080 and even thrive in these conditions. 302 00:27:25,600 --> 00:27:26,840 Snottites... 303 00:27:30,280 --> 00:27:32,800 dripping colonies of bacteria. 304 00:27:38,040 --> 00:27:42,040 [Diana] There are a lot of organisms  in one snottite. 305 00:27:44,080 --> 00:27:46,880 Instead of relying on photosynthesis, 306 00:27:47,520 --> 00:27:50,960 they are eating hydrogen sulfide 307 00:27:52,160 --> 00:27:55,680 and are using it as their energy source. 308 00:28:01,000 --> 00:28:03,280 -[Diana] Okay, ready to flame? -[husband] Yep. 309 00:28:04,280 --> 00:28:06,200 [Diana] So, make it nice and sterile. 310 00:28:07,480 --> 00:28:09,560 Okay, cap that, please. 311 00:28:13,800 --> 00:28:15,640 Okay, let's go for this one. 312 00:28:16,400 --> 00:28:17,360 Okay. 313 00:28:18,400 --> 00:28:20,680 Okay. One snottite. 314 00:28:23,520 --> 00:28:26,240 These are some of the best snottites in the world. 315 00:28:27,200 --> 00:28:28,280 So acidic. 316 00:28:29,080 --> 00:28:31,720 More acidic than car battery acid. 317 00:28:36,400 --> 00:28:39,280 An entire ecosystem has evolved 318 00:28:40,040 --> 00:28:42,200 to feed off the snottites. 319 00:28:44,440 --> 00:28:47,240 Creatures that have never seen daylight. 320 00:28:55,160 --> 00:28:56,160 [Diana] Can you see those? 321 00:28:58,120 --> 00:28:59,360 [husband] Yes, I do. 322 00:29:00,360 --> 00:29:03,560 [Diana] So, there's some really big ones over here to the right. 323 00:29:05,040 --> 00:29:09,600 So, whenever you see one  of those white streamers of bacteria, 324 00:29:10,320 --> 00:29:12,200 you'll see a fish go after it. 325 00:29:13,840 --> 00:29:17,680 Okay, here comes some more over there. See? Here comes a big one, see? 326 00:29:18,360 --> 00:29:20,920 It's coming. There, it got it! 327 00:29:24,960 --> 00:29:28,080 [Diana] Studying life in total darkness 328 00:29:28,160 --> 00:29:33,920 has expanded how we look for life in other places in the universe. 329 00:29:34,440 --> 00:29:36,600 It's made us think about the fact 330 00:29:36,680 --> 00:29:40,640 that we could find life in places we never considered. 331 00:29:42,680 --> 00:29:44,320 -[husband] Yep, there we go. -[Diana] 25. 332 00:29:44,400 --> 00:29:47,200 -[bleeping] -[husband] 25. It's getting pretty high. 333 00:29:47,280 --> 00:29:48,240 [Diana] All right. 334 00:29:48,320 --> 00:29:50,240 You think we ought to get out of here? 335 00:29:50,320 --> 00:29:51,280 [husband] Yeah. 336 00:30:04,880 --> 00:30:07,800 All life needs some form of energy. 337 00:30:10,040 --> 00:30:13,920 On the hot face of Janus, it comes from starlight. 338 00:30:17,680 --> 00:30:21,920 On the cold face,  it comes from deep within. 339 00:30:29,000 --> 00:30:31,320 Geothermal activity. 340 00:30:35,720 --> 00:30:39,560 When volcanic pressure  forces water to the surface, 341 00:30:40,520 --> 00:30:42,760 there's a flurry of new life... 342 00:30:45,120 --> 00:30:47,800 which stirs pentapods into action. 343 00:31:01,560 --> 00:31:05,800 They're after grubs  that emerge around geothermal pools. 344 00:31:10,240 --> 00:31:11,640 But it's not so easy. 345 00:31:17,800 --> 00:31:20,200 The grubs have evolved a defense. 346 00:31:21,240 --> 00:31:24,640 They jump and flash a warning signal  to others... 347 00:31:27,320 --> 00:31:29,880 acting as one to stay alive. 348 00:31:30,000 --> 00:31:32,000 [loud buzzing] 349 00:31:46,120 --> 00:31:50,360 On Earth, some animals  use light in the same way... 350 00:31:51,120 --> 00:31:53,040 to send signals. 351 00:31:54,440 --> 00:31:56,440 [cicadas chirping] 352 00:32:01,520 --> 00:32:05,080 [woman] Every single point of light that you see out there is a firefly. 353 00:32:07,160 --> 00:32:10,080 Right as the sun sets, you'll start to see them come up, 354 00:32:11,240 --> 00:32:13,120 like little sparks rising from a fire. 355 00:32:13,200 --> 00:32:16,760 It's just spectacular, and it only gets better as the night gets darker. 356 00:32:26,080 --> 00:32:28,680 Fireflies flash as a form  of communication. 357 00:32:29,720 --> 00:32:32,760 They are among the only land animals 358 00:32:32,840 --> 00:32:35,440 that communicate with light  of their own making. 359 00:32:39,280 --> 00:32:42,760 Bioluminescence evolved among fireflies 360 00:32:42,840 --> 00:32:44,600 as a warning to predators 361 00:32:45,320 --> 00:32:50,240 that they're packed with toxins  and should be given a wide berth. 362 00:32:53,840 --> 00:32:55,200 Now the same mechanism 363 00:32:55,840 --> 00:32:58,000 is used for finding a mate. 364 00:33:01,720 --> 00:33:07,480 So, the firefly produces light from an  organ on its abdomen called the lantern. 365 00:33:08,280 --> 00:33:11,000 And this organ has an enzyme 366 00:33:11,080 --> 00:33:13,160 that produces one photon of light. 367 00:33:13,240 --> 00:33:15,000 This chemical reaction involves oxygen. 368 00:33:15,080 --> 00:33:18,400 So, by controlling the flow of oxygen  to their lantern, 369 00:33:18,480 --> 00:33:20,760 they can produce, uh, flashes. 370 00:33:20,840 --> 00:33:22,920 They can turn  the chemical reaction on and off, 371 00:33:23,000 --> 00:33:27,000 and use these flashes to communicate with each other. 372 00:33:35,520 --> 00:33:39,720 The males are flying around, and they're doing little advertisements, 373 00:33:39,800 --> 00:33:43,160 little flashes that say,  "Here I am. This is me, check me out." 374 00:33:46,040 --> 00:33:49,360 And then the females are waiting on  the ground below and they're looking up. 375 00:33:51,520 --> 00:33:54,720 And when they see a guy that they like, they flash back. 376 00:33:57,840 --> 00:34:00,400 And then the male will come over, he'll flash again. 377 00:34:00,480 --> 00:34:03,080 She flashes back  and they come together and mate. 378 00:34:04,160 --> 00:34:08,400 So, this is actually one big flirtatious dance 379 00:34:08,480 --> 00:34:10,600 that we're seeing right here behind us. 380 00:34:13,440 --> 00:34:16,000 Each species creates its own  little language 381 00:34:16,080 --> 00:34:18,080 that they can use to find each other in the dark. 382 00:34:20,320 --> 00:34:24,440 But using light to communicate is inherently risky. 383 00:34:26,440 --> 00:34:31,200 Some species have evolved  to emit fake signals. 384 00:34:34,920 --> 00:34:39,720 What we have here  is a predatory Photuris female, 385 00:34:39,800 --> 00:34:43,040 also called femmes fatales, because they have a reputation 386 00:34:43,120 --> 00:34:46,800 for luring in males of other species  to eat them. 387 00:34:47,720 --> 00:34:52,560 They can hack in to the communication  between a male and a female 388 00:34:52,640 --> 00:34:54,600 and use that to her advantage. 389 00:34:56,320 --> 00:34:59,120 So, you can tell  this is a predatory firefly 390 00:34:59,200 --> 00:35:02,600 because her lantern  has a different shape to it. 391 00:35:03,640 --> 00:35:07,800 Only two-- two little lines light up,  almost like an equals sign. 392 00:35:08,520 --> 00:35:12,160 So, basically, a male will be  flying around looking for a mate 393 00:35:12,240 --> 00:35:15,120 and then when the males flash, they flash back, 394 00:35:15,200 --> 00:35:17,920 just as if  they were a female of that species. 395 00:35:18,000 --> 00:35:20,520 So, they're imitating the females of that other species 396 00:35:20,600 --> 00:35:22,240 to get the male to come over, 397 00:35:22,320 --> 00:35:24,280 but they don't wanna mate with that male... 398 00:35:25,400 --> 00:35:27,800 she wants to eat that male. 399 00:35:30,400 --> 00:35:34,480 And she proceeds to do so  in an extremely violent way. 400 00:35:36,360 --> 00:35:38,360 [munching] 401 00:35:39,360 --> 00:35:43,880 This is a classic example of a predator using mimicry. 402 00:35:48,120 --> 00:35:51,480 One species  copying the behavior of another... 403 00:35:52,840 --> 00:35:54,720 in order to kill it. 404 00:35:58,960 --> 00:36:00,480 [Avalon] Lying and deceit is... 405 00:36:00,560 --> 00:36:03,520 is pretty widespread in the animal kingdom, I would say. 406 00:36:04,720 --> 00:36:07,720 And I think it would be on any planet. 407 00:36:17,400 --> 00:36:20,920 [fountains hissing] 408 00:36:23,080 --> 00:36:27,000 On Janus, the grubs use light to stay alive. 409 00:36:32,040 --> 00:36:35,240 But their system is about to be hacked. 410 00:36:47,040 --> 00:36:52,600 By catching a few grubs, the pentapods absorb their bioluminescence... 411 00:36:56,120 --> 00:36:58,400 and mimic their warning signals. 412 00:37:04,640 --> 00:37:08,680 The grubs instinctively jump away  from flashing lights. 413 00:37:10,520 --> 00:37:12,600 But this time, it's a trap. 414 00:37:15,840 --> 00:37:19,000 The pentapods have them  where they want them. 415 00:37:24,120 --> 00:37:29,200 Again, adaptability is the secret  to their survival. 416 00:37:42,440 --> 00:37:44,600 But for all creatures on Janus, 417 00:37:45,400 --> 00:37:49,200 existence depends on one key ingredient... 418 00:37:53,000 --> 00:37:56,840 whether in the hot, cold or twilight worlds. 419 00:37:59,920 --> 00:38:01,080 Water. 420 00:38:20,240 --> 00:38:23,640 [man] Everybody knows the story of Goldilocks and the Three Bears. 421 00:38:26,440 --> 00:38:29,880 She sneaks into their house  and tries to eat their porridge. 422 00:38:33,640 --> 00:38:35,480 The first bowl is too hot. 423 00:38:39,680 --> 00:38:41,840 The second bowl is freezing cold. 424 00:38:46,440 --> 00:38:49,720 It's only when she tries the third bowl that she's happy. 425 00:38:54,840 --> 00:38:58,480 "This one," Goldilocks says, "is just right." 426 00:39:01,160 --> 00:39:04,120 When we look around the universe in the search for life,  427 00:39:04,200 --> 00:39:07,360 we are looking for conditions  that are "just right." 428 00:39:13,640 --> 00:39:15,760 And "just right," in this case, 429 00:39:16,600 --> 00:39:19,080 is defined by the presence of this stuff. 430 00:39:20,280 --> 00:39:21,400 Water. 431 00:39:27,680 --> 00:39:32,120 Water transports the essentials for life around the planet 432 00:39:34,760 --> 00:39:37,000 and around every living body. 433 00:39:41,440 --> 00:39:45,120 It's the most important substance  in the universe. 434 00:39:52,960 --> 00:39:54,800 [man] Because water is so familiar to us, 435 00:39:54,880 --> 00:40:00,360 it's not until you really stop and think  about it that you realize how weird it is. 436 00:40:00,440 --> 00:40:03,320 Water is made up  by one oxygen atom... 437 00:40:05,440 --> 00:40:07,320 and two hydrogen atoms. 438 00:40:08,160 --> 00:40:11,600 And because of the nature of the elements and the way they're bound, 439 00:40:11,680 --> 00:40:15,000 we have a net negative charge  at the oxygen side 440 00:40:15,080 --> 00:40:16,960 and positive on the two hydrogens. 441 00:40:17,040 --> 00:40:19,440 This means that every hydrogen  in a molecule 442 00:40:19,520 --> 00:40:22,880 can interact with the oxygen  on the other molecules neighboring. 443 00:40:23,680 --> 00:40:27,400 Replicate this attraction for billions of neighboring molecules 444 00:40:27,480 --> 00:40:29,400 and you get  a substance that is very sticky. 445 00:40:31,800 --> 00:40:34,640 And water molecules don't just attract each other, 446 00:40:34,720 --> 00:40:38,200 they attract almost any other molecule they come in contact with. 447 00:40:41,040 --> 00:40:43,280 They pull other substances apart, 448 00:40:43,960 --> 00:40:46,480 break them down, and dissolve them. 449 00:40:59,520 --> 00:41:02,320 Water is the universal solvent 450 00:41:03,440 --> 00:41:07,600 because of its unique ability to dissolve nutrients and chemicals. 451 00:41:15,840 --> 00:41:21,680 It seems certain the first spark  of life on Earth happened not on land... 452 00:41:24,040 --> 00:41:25,560 but in water. 453 00:41:31,640 --> 00:41:34,200 [Donato] Deep underwater, in the primordial oceans, 454 00:41:34,280 --> 00:41:37,560 the chemical ingredients for life were swirling around. 455 00:41:40,400 --> 00:41:43,840 What was needed was a place  to concentrate these ingredients... 456 00:41:45,920 --> 00:41:49,560 to allow the chemical reaction that would eventually lead to life. 457 00:41:52,440 --> 00:41:55,880 That place could have been  a hydrothermal vent. 458 00:41:59,800 --> 00:42:03,120 Water interacts with hot rocks  deep underground. 459 00:42:04,120 --> 00:42:07,200 It comes gushing back up  into the freezing seawater 460 00:42:07,280 --> 00:42:09,280 carrying nutrients and chemicals... 461 00:42:11,360 --> 00:42:13,320 little bubbles of life. 462 00:42:17,440 --> 00:42:21,000 The link between water and life is so strong, 463 00:42:21,920 --> 00:42:26,320 it's hard to imagine any life anywhere in the universe 464 00:42:26,400 --> 00:42:28,400 existing without it. 465 00:42:37,520 --> 00:42:39,040 [Donato] It's mind-boggling to think, 466 00:42:39,120 --> 00:42:42,520 you know, how life can find a way  in very extreme places. 467 00:42:42,600 --> 00:42:43,800 Very hot, very cold. 468 00:42:44,200 --> 00:42:46,480 And at the end, it's all about the water. 469 00:42:46,560 --> 00:42:49,000 If there's liquid water, you'll find life. 470 00:43:00,120 --> 00:43:02,880 Water on Janus is scarce. 471 00:43:05,840 --> 00:43:08,160 It either freezes as ice... 472 00:43:11,240 --> 00:43:13,480 or evaporates into the wind. 473 00:43:18,240 --> 00:43:20,760 But there's just enough liquid water 474 00:43:21,320 --> 00:43:23,120 for life to take hold... 475 00:43:26,320 --> 00:43:28,840 and for the toughest of creatures 476 00:43:29,440 --> 00:43:31,760 to adapt and survive. 477 00:43:33,000 --> 00:43:34,760 [wind howling] 478 00:43:36,280 --> 00:43:38,280 [fluttering] 479 00:43:42,640 --> 00:43:44,920 At NASA, they have a saying. 480 00:43:46,240 --> 00:43:48,240 "If you want to find life... 481 00:43:48,880 --> 00:43:50,600 follow the water." 482 00:43:59,760 --> 00:44:03,080 How might life adapt on a different world? 483 00:44:04,520 --> 00:44:06,440 One with two stars, 484 00:44:09,480 --> 00:44:12,200 where there's more energy than on Earth. 485 00:44:12,880 --> 00:44:14,280 [creatures calling] 486 00:44:15,800 --> 00:44:19,400 A planet perfect for life.