1 00:00:00,000 --> 00:00:25,000 © anoXmous @ http://thepiratebay.sx/user/Zen_Bud 1 00:00:43,950 --> 00:00:48,380 This is our planet's final frontier, 2 00:00:50,590 --> 00:00:56,680 an inner world where only the most adventurous dare to go. 3 00:01:49,640 --> 00:01:51,150 Beneath our feet 4 00:01:51,230 --> 00:01:56,400 are countless miles of cave shafts and passages. 5 00:02:12,750 --> 00:02:15,300 The Cave of Swallows in Mexico, 6 00:02:15,380 --> 00:02:17,550 400 metres to the bottom, 7 00:02:17,630 --> 00:02:21,720 deep enough to engulf the Empire State Building. 8 00:02:28,850 --> 00:02:32,400 This is the biggest cave shaft in the world. 9 00:02:32,440 --> 00:02:35,270 Yet these depths were first explored 10 00:02:35,320 --> 00:02:39,150 only two years before man landed on the moon. 11 00:02:42,530 --> 00:02:48,040 Today caves remain the least explored places on Earth. 12 00:02:48,200 --> 00:02:51,750 However, human beings are seldom the first 13 00:02:51,830 --> 00:02:55,540 to reach these black, damp places. 14 00:02:59,970 --> 00:03:06,680 Here, live some of the strangest and least-known animals on the planet. 15 00:03:39,960 --> 00:03:46,970 This galaxy of little lights is created by thousands of living creatures. 16 00:03:51,350 --> 00:03:56,520 Any animal that lives in a cave has to cope with complete blackness, 17 00:03:56,560 --> 00:04:02,150 but in New Zealand some have turned this darkness to their advantage. 18 00:04:14,960 --> 00:04:18,960 A silicon strand is lowered from the ceiling, 19 00:04:19,040 --> 00:04:21,880 alongside hundreds of others. 20 00:04:29,390 --> 00:04:31,720 Beautiful though these threads are, 21 00:04:31,850 --> 00:04:34,980 they have a sinister purpose. 22 00:04:36,440 --> 00:04:39,980 This is a cave glow worm. 23 00:04:40,190 --> 00:04:45,240 To trap its prey it goes fishing with a line of silk. 24 00:04:52,080 --> 00:04:56,370 The silk comes from glands in the glow worm's mouth 25 00:04:56,460 --> 00:04:59,790 and is loaded with droplets of mucus. 26 00:05:14,180 --> 00:05:18,900 Each glow worm produces dozens of these threads. 27 00:05:21,400 --> 00:05:23,360 Once its lines are set, 28 00:05:23,440 --> 00:05:26,610 the glow worm hangs from a mucus hammock 29 00:05:26,700 --> 00:05:30,320 and waits, like a patient angler. 30 00:05:34,700 --> 00:05:37,910 But the glow worm doesn't leave everything to chance. 31 00:05:38,080 --> 00:05:42,290 That ghostly blue light is the result of a chemical reaction 32 00:05:42,380 --> 00:05:46,970 taking place inside a special capsule in its tail. 33 00:05:47,760 --> 00:05:50,970 The light literally shines out of its backside. 34 00:05:51,050 --> 00:05:54,430 It's a lure for attracting prey. 35 00:06:22,210 --> 00:06:26,760 Insects seem irresistibly drawn towards the source 36 00:06:26,840 --> 00:06:30,800 and then get trapped by the sticky lines. 37 00:06:40,020 --> 00:06:41,520 Once stuck, 38 00:06:41,600 --> 00:06:43,440 there is no escape. 39 00:06:48,900 --> 00:06:52,990 Now it's just a matter of reeling in the line 40 00:06:53,240 --> 00:06:57,240 and slowly consuming the catch - alive. 41 00:07:13,050 --> 00:07:16,180 By ensnaring the insects that hatch in this cave, 42 00:07:16,260 --> 00:07:19,390 these glow worms have solved the biggest challenge 43 00:07:19,470 --> 00:07:21,810 that permanent cave dwellers face - 44 00:07:21,890 --> 00:07:25,520 finding a regular and reliable source of food. 45 00:07:32,950 --> 00:07:37,700 One kind of rock makes this whole underground world possible - 46 00:07:37,780 --> 00:07:39,330 limestone. 47 00:07:39,660 --> 00:07:42,620 Most of the world's caves are found within it 48 00:07:42,710 --> 00:07:46,460 and it covers nearly 10 percent of the earth's surface. 49 00:07:52,670 --> 00:07:58,470 Limestone is composed of minerals derived from marine shells and corals, 50 00:07:58,510 --> 00:08:02,020 so although this rocky escarpment in the United States 51 00:08:02,060 --> 00:08:05,060 is now hundreds of metres above sea level 52 00:08:05,150 --> 00:08:08,270 it was actually formed under water. 53 00:08:15,530 --> 00:08:19,280 The limestone towers of Vietnam's Ha Long Bay 54 00:08:19,370 --> 00:08:22,370 are a reminder of this link with the sea. 55 00:08:22,450 --> 00:08:27,080 Originally, this whole area would have been one solid block of limestone, 56 00:08:27,130 --> 00:08:29,500 the base of a coral reef. 57 00:08:40,260 --> 00:08:47,650 In Borneo, rain has sculptured the limestone into extremely sharp-sided pinnacles. 58 00:09:01,120 --> 00:09:04,450 But the dissolving power of rainwater 59 00:09:04,500 --> 00:09:09,040 has other, much more dramatic effects underground. 60 00:09:20,050 --> 00:09:25,390 Rivers that flow over limestone often seem to completely disappear. 61 00:09:39,780 --> 00:09:43,240 When the water reaches the more resistant bed of limestone 62 00:09:43,330 --> 00:09:45,660 its course is altered. 63 00:09:50,000 --> 00:09:51,500 Once underground, 64 00:09:51,590 --> 00:09:55,840 the water takes on a new, more erosive power. 65 00:10:01,550 --> 00:10:03,930 During its journey from the surface 66 00:10:04,010 --> 00:10:07,390 the water absorbed carbon dioxide from the soil 67 00:10:07,430 --> 00:10:09,600 making it mildly acidic. 68 00:10:09,810 --> 00:10:14,230 And over millions of years this acid eats away the limestone 69 00:10:14,320 --> 00:10:17,900 creating a maze of caverns and passages 70 00:10:17,990 --> 00:10:20,700 that sometimes go on for miles. 71 00:11:00,900 --> 00:11:06,240 This is the biggest underground river passage in the world, 72 00:11:06,280 --> 00:11:10,540 so big a jumbo jet could fly through it. 73 00:11:10,620 --> 00:11:13,750 It's Deer Cave, in Borneo. 74 00:11:26,220 --> 00:11:28,390 The sheer size of Deer Cave 75 00:11:28,430 --> 00:11:32,770 allows some animals to gather there in huge numbers. 76 00:11:40,280 --> 00:11:45,620 A staggering 3 million wrinkle-lipped bats live here. 77 00:11:49,160 --> 00:11:52,120 The bats roost high on the walls and ceilings 78 00:11:52,160 --> 00:11:54,710 where they're well protected from the outside elements 79 00:11:54,750 --> 00:11:56,880 and safe from predators. 80 00:12:05,180 --> 00:12:06,930 And while they're up here 81 00:12:07,010 --> 00:12:10,640 the bats produce something very important. 82 00:12:15,230 --> 00:12:20,780 This hundred metre high mound is made entirely of bat droppings - 83 00:12:20,860 --> 00:12:22,030 guano. 84 00:12:44,840 --> 00:12:50,640 Its surface is covered by a thick carpet of cockroaches, 85 00:12:50,890 --> 00:12:53,310 hundreds of thousands of them. 86 00:12:58,810 --> 00:13:05,110 Caves are one of the few habitats on Earth not directly powered by sunlight. 87 00:13:05,200 --> 00:13:13,870 In the absence of plants this food chain is based on a continuous supply of bat droppings. 88 00:13:26,090 --> 00:13:28,970 The cockroaches feed on the guano 89 00:13:29,430 --> 00:13:32,140 and anything that falls into it. 90 00:13:59,710 --> 00:14:03,550 The droppings also support other types of cockroaches 91 00:14:03,630 --> 00:14:07,550 which spend part of their day resting on cave walls. 92 00:14:11,800 --> 00:14:16,600 These in turn become food for giant cave centipedes, 93 00:14:16,640 --> 00:14:19,640 some more than 20 centimetres long. 94 00:14:23,360 --> 00:14:25,980 Bizarrely, there are crabs here, too, 95 00:14:26,030 --> 00:14:29,200 sifting through the droppings for nutrients. 96 00:14:36,410 --> 00:14:40,670 All these animals spend their entire lives within the cave. 97 00:14:40,710 --> 00:14:44,790 They're totally dependant on the digested remains of food 98 00:14:44,840 --> 00:14:47,170 that's brought here from outside. 99 00:15:14,570 --> 00:15:17,290 Each evening in just two hours 100 00:15:17,370 --> 00:15:21,080 three million bats leave the safety of the cave 101 00:15:21,160 --> 00:15:24,580 to hunt for insects in the forest outside. 102 00:15:27,170 --> 00:15:29,800 But not all will return. 103 00:15:51,740 --> 00:15:53,360 As they leave the cave 104 00:15:53,450 --> 00:15:57,700 the stream of bats form a doughnut-shaped ring. 105 00:16:00,870 --> 00:16:05,460 The wheeling bats seem to confuse a rufus-bellied eagle, 106 00:16:05,540 --> 00:16:11,340 but they must still survive the attacks of other, more specialised, birds of prey. 107 00:16:22,390 --> 00:16:28,360 Peregrine falcons and bat hawks are the jetfighters of the bird world. 108 00:17:00,260 --> 00:17:03,140 Good hunting will end as the light fades 109 00:17:03,230 --> 00:17:07,150 so the bat hawks bolt their catches on the wing 110 00:17:08,400 --> 00:17:10,820 and fly straight back for more. 111 00:17:13,240 --> 00:17:15,530 Any bat separated from the group 112 00:17:15,610 --> 00:17:20,240 becomes a clear and obvious target and is asking for trouble. 113 00:17:31,630 --> 00:17:35,880 Yet the nightly onslaught has little impact on bat numbers - 114 00:17:35,970 --> 00:17:41,510 by the morning the vast majority will be back in the safety of the cave. 115 00:17:51,480 --> 00:17:56,110 Bats are not the only commuters in these Bornean caves. 116 00:17:56,190 --> 00:17:58,410 There's a day shift as well. 117 00:18:04,620 --> 00:18:07,000 Returning from hunting in the sunlight 118 00:18:07,040 --> 00:18:09,620 these commuters rely on their loud clicks 119 00:18:09,670 --> 00:18:14,210 to find their way through the cave passages in total darkness. 120 00:18:20,510 --> 00:18:22,760 They're cave swiftlets. 121 00:18:23,100 --> 00:18:27,060 Like bats they use echolocation to navigate. 122 00:18:27,140 --> 00:18:29,770 We need lights to see what's going on, 123 00:18:29,810 --> 00:18:35,860 but in the pitch black the swiftlets manage unerringly to locate their individual nesting sites, 124 00:18:35,940 --> 00:18:38,860 which are only a few centimetres across. 125 00:18:43,740 --> 00:18:49,620 It's a remarkable skill and one we still do not fully understand. 126 00:18:53,380 --> 00:18:56,420 These birds are unusual for another reason. 127 00:18:56,500 --> 00:19:02,260 Their little cup-like nests are made entirely from threads of saliva. 128 00:19:07,390 --> 00:19:11,020 It takes more than 30 days to complete one. 129 00:19:12,230 --> 00:19:15,230 The nests are very precious objects, 130 00:19:15,190 --> 00:19:17,980 and not only for the birds. 131 00:19:35,920 --> 00:19:42,130 For 500 years people have been harvesting the nests of cave swiftlets. 132 00:19:55,060 --> 00:19:57,690 It's a very risky business. 133 00:19:57,730 --> 00:20:00,070 with virtually no safety equipment 134 00:20:00,110 --> 00:20:03,200 and using ladders made from forest vines 135 00:20:03,240 --> 00:20:06,780 the gatherers climb into the highest reaches of the cave 136 00:20:06,830 --> 00:20:10,000 often more than 60 metres from the floor. 137 00:20:19,090 --> 00:20:21,840 The work may be hazardous in the extreme, 138 00:20:21,920 --> 00:20:24,430 but the rewards are great. 139 00:20:34,310 --> 00:20:37,110 The pure white nests of cave swiftlets 140 00:20:37,190 --> 00:20:40,690 are the main ingredient of birds' nest soup 141 00:20:40,780 --> 00:20:44,780 and gram for gram are worth as much as silver. 142 00:20:46,870 --> 00:20:51,870 As soon as its nest is removed a bird will immediately build another. 143 00:20:51,950 --> 00:20:56,210 So, as long as this valuable harvest is properly controlled, 144 00:20:56,250 --> 00:20:59,210 the colonies will continue to flourish. 145 00:21:11,810 --> 00:21:15,270 These Bornean caves are among the biggest in the world 146 00:21:15,310 --> 00:21:16,810 and they're still getting bigger 147 00:21:16,850 --> 00:21:22,280 as each year rainwater eats away a little more limestone. 148 00:21:32,950 --> 00:21:36,670 But water in caves doesn't only erode. 149 00:21:36,750 --> 00:21:38,960 It also builds. 150 00:21:45,920 --> 00:21:49,760 This water is loaded with dissolved limestone 151 00:21:49,840 --> 00:21:52,140 and when it meets the air in the cave 152 00:21:52,220 --> 00:21:55,430 some of that is deposited as a mineral - 153 00:21:55,600 --> 00:21:56,980 calcite. 154 00:21:59,310 --> 00:22:00,560 As it builds up 155 00:22:00,610 --> 00:22:04,900 so the calcite forms decorations that hang from the ceiling - 156 00:22:04,940 --> 00:22:06,650 stalactites. 157 00:22:14,450 --> 00:22:18,870 Each drop leaves behind only a miniscule amount of calcite, 158 00:22:18,960 --> 00:22:24,090 but over time the process can produce some spectacular results. 159 00:22:55,040 --> 00:22:57,910 If the water seeps though the ceiling quickly, 160 00:22:57,950 --> 00:23:01,460 then the calcite is deposited on the floor of the cave 161 00:23:01,540 --> 00:23:04,590 and that creates stalagmites. 162 00:23:14,140 --> 00:23:17,470 Variations in water flow and the air currents 163 00:23:17,520 --> 00:23:23,610 produce an infinite variety of forms, but all are created by the same process - 164 00:23:23,900 --> 00:23:27,980 the slow deposition of dissolved limestone. 165 00:23:31,400 --> 00:23:34,450 And when stalactite meets stalagmite 166 00:23:34,530 --> 00:23:36,870 a column is born. 167 00:24:00,980 --> 00:24:05,020 Structures like these in North America's Carlsbad Cavern 168 00:24:05,060 --> 00:24:08,440 can take many thousands of years to develop. 169 00:24:08,530 --> 00:24:13,820 But sometimes the formations in a cave stop growing altogether. 170 00:24:42,270 --> 00:24:49,480 These flooded caves in Mexico have remained virtually unchanged for thousands of years. 171 00:24:49,520 --> 00:24:54,320 Since the last Ice Age they've become cut off from the outside world. 172 00:24:54,400 --> 00:24:59,280 Yet their impact on life on the surface has been huge. 173 00:25:04,710 --> 00:25:10,670 500 years ago they supported one of the world's great civilisations 174 00:25:10,750 --> 00:25:11,960 the Maya. 175 00:25:17,300 --> 00:25:22,890 Mexico's Yucatan Peninsula has no rivers, lakes or streams 176 00:25:22,930 --> 00:25:29,900 so the Maya relied on the cenotes - the flooded entrances to the water-filled caves. 177 00:25:32,940 --> 00:25:39,120 These flooded shafts are the region's only source of open fresh water. 178 00:25:41,280 --> 00:25:47,040 The cenotes are, in effect, gigantic fresh water wells. 179 00:26:12,190 --> 00:26:15,320 Away from the life-giving rays of sunshine 180 00:26:15,530 --> 00:26:19,030 one might not expect to find plants. 181 00:26:27,710 --> 00:26:30,330 But in the darkness of the cave tunnels 182 00:26:30,380 --> 00:26:35,920 roots of giant tropical trees have pushed their way through cracks in the limestone 183 00:26:35,960 --> 00:26:38,300 to reach the flooded caverns. 184 00:26:40,010 --> 00:26:41,390 Without this water 185 00:26:41,470 --> 00:26:45,850 the Yucatan's forest could not grow so luxuriantly. 186 00:27:05,990 --> 00:27:10,000 The Maya knew that their lives depended on this water, 187 00:27:10,040 --> 00:27:13,040 but it's only with the help of today's technology 188 00:27:13,080 --> 00:27:20,130 that we've come to appreciate the full significance and scale of these flooded passageways. 189 00:27:23,640 --> 00:27:31,060 So far, more than 350 miles of underwater galleries in the Yucatan have been mapped, 190 00:27:31,140 --> 00:27:37,980 but still nobody yet knows the true extend of this subterranean waterworld. 191 00:27:38,150 --> 00:27:40,450 And with good reason. 192 00:27:42,820 --> 00:27:47,200 Underwater caving is notoriously dangerous. 193 00:27:47,240 --> 00:27:51,000 When the nearest exit may be hundreds of metres or more away, 194 00:27:51,040 --> 00:27:54,830 running out of air down here would be fatal. 195 00:27:58,380 --> 00:28:00,010 To avoid getting lost 196 00:28:00,050 --> 00:28:02,930 divers carry with them a spool of string. 197 00:28:02,970 --> 00:28:04,930 It becomes their lifeline - 198 00:28:04,970 --> 00:28:06,050 literally. 199 00:28:20,110 --> 00:28:23,410 The string also doubles as a measuring tape - 200 00:28:23,450 --> 00:28:26,410 a technique that has been used here, in Mexico, 201 00:28:26,450 --> 00:28:30,040 to chart the largest underwater cave in the world - 202 00:28:30,080 --> 00:28:32,830 all 100 miles of it. 203 00:28:41,050 --> 00:28:47,220 Cave exploration often requires you to push yourself through narrow gaps in the rock. 204 00:28:47,430 --> 00:28:51,270 Cavers call such places 'squeezes.' 205 00:29:00,400 --> 00:29:01,990 The tighter the squeeze, 206 00:29:02,070 --> 00:29:07,320 the greater the chance of damaging some vital life-support system. 207 00:29:33,680 --> 00:29:38,860 In these conditions a diver could easily become disorientated 208 00:29:38,940 --> 00:29:41,070 and that could be fatal. 209 00:29:55,250 --> 00:30:00,380 The flooded caverns can play tricks on you in other ways. 210 00:30:08,470 --> 00:30:10,140 What seems like air, 211 00:30:10,220 --> 00:30:11,470 isn't. 212 00:30:12,220 --> 00:30:15,310 It's just another kind of water. 213 00:30:22,940 --> 00:30:25,070 This is a halocline - 214 00:30:25,110 --> 00:30:28,570 a meeting of fresh and salt water. 215 00:30:31,200 --> 00:30:37,330 Fresh water from the jungle flows over the heavier salt water from the sea. 216 00:30:38,330 --> 00:30:41,960 The saltwater layer is extremely low in oxygen 217 00:30:42,000 --> 00:30:46,130 making it a particularly difficult place for animals to live. 218 00:30:46,380 --> 00:30:48,470 Yet some have managed it, 219 00:30:48,590 --> 00:30:53,850 like the remiped, one of the most ancient of all living crustaceans. 220 00:31:02,400 --> 00:31:06,360 The Maya understood the importance of the cenotes, 221 00:31:06,440 --> 00:31:09,950 but they could never have known that these flooded passageways 222 00:31:10,030 --> 00:31:13,830 were actually the beginning of subterranean rivers, 223 00:31:14,120 --> 00:31:17,660 all of which eventually flow out to the sea. 224 00:31:27,510 --> 00:31:32,050 Salt water, unlike fresh water, does not erode limestone, 225 00:31:32,140 --> 00:31:38,140 so most sea caves are created by the mechanical pounding of the waves. 226 00:31:44,650 --> 00:31:50,900 The rocky outcrops of New Zealand's Poor Knight Islands are riddled with sea caves 227 00:31:50,950 --> 00:31:52,860 and just like those in Borneo 228 00:31:52,910 --> 00:31:56,620 they have become important shelters for many species. 229 00:32:01,250 --> 00:32:04,000 After a day feeding in the open water 230 00:32:04,040 --> 00:32:08,300 vast shoals of demoiselle fish return to the caves, 231 00:32:08,340 --> 00:32:11,680 which they use as a refuge from predators. 232 00:32:14,220 --> 00:32:18,140 For these fish the caves are a night time retreat, 233 00:32:18,220 --> 00:32:21,230 but they're not the only commuters in here. 234 00:32:21,270 --> 00:32:25,060 There are other fish working to a different schedule. 235 00:32:32,450 --> 00:32:35,910 The bigeyes are the equivalent of bats. 236 00:32:35,990 --> 00:32:39,290 Night feeders leave the cave each evening. 237 00:32:43,620 --> 00:32:46,250 And like all cave commuters 238 00:32:46,290 --> 00:32:50,670 they are most vulnerable at the scheduled time of departure. 239 00:33:01,890 --> 00:33:08,060 A bottleneck funnels these exiting bats into dense concentrations 240 00:33:08,110 --> 00:33:10,650 attracting the attention of others. 241 00:33:38,470 --> 00:33:42,810 The bats can detect the snakes using echolocation, 242 00:33:43,020 --> 00:33:45,730 but the snakes are literally in the dark - 243 00:33:45,770 --> 00:33:47,690 they can see nothing. 244 00:34:01,370 --> 00:34:05,160 The strikes seem to be largely hit-and-miss, 245 00:34:07,040 --> 00:34:10,290 but the snakes have a secret weapon. 246 00:34:10,630 --> 00:34:14,300 They can actually sense each bat flying past. 247 00:34:14,380 --> 00:34:20,010 Receptors in the snake's head pick up the heat given off by the flying bats, 248 00:34:20,220 --> 00:34:22,760 as this thermal image shows. 249 00:34:29,400 --> 00:34:33,230 To the snakes the bats are apparently glowing 250 00:34:33,280 --> 00:34:36,280 and this gives them something to aim at. 251 00:34:58,680 --> 00:35:02,800 This is the price that these cave commuters must pay 252 00:35:02,890 --> 00:35:06,140 for their daytime sanctuary on the ground. 253 00:35:06,310 --> 00:35:11,730 Small wonder then that there are other cave dwellers that stay put. 254 00:35:19,280 --> 00:35:21,780 Many caves are like islands - 255 00:35:21,820 --> 00:35:26,330 cut off from the outside world and from other caves. 256 00:35:34,250 --> 00:35:41,300 This isolation has resulted in the evolution of some various strange creatures. 257 00:35:43,090 --> 00:35:45,930 They are the cave specialists - 258 00:35:45,970 --> 00:35:52,020 troglodytes, animals that never emerge from the caves or see daylight. 259 00:36:04,910 --> 00:36:07,660 These troglodytes from Thailand 260 00:36:07,700 --> 00:36:11,540 are possibly the most specialised creatures on Earth 261 00:36:11,620 --> 00:36:15,290 for they live only in cave waterfalls. 262 00:36:16,090 --> 00:36:19,550 The entire population of these cave angel fish 263 00:36:19,630 --> 00:36:24,050 seems to be restricted to just two small caves. 264 00:36:27,970 --> 00:36:30,680 It's the same story with other troglodytes. 265 00:36:30,730 --> 00:36:36,270 There may well be less than a hundred Texas cave salamanders in the wild. 266 00:36:52,910 --> 00:36:56,960 And the Belizean white crab is another creature 267 00:36:57,040 --> 00:37:00,710 that is unique to just one cave system. 268 00:37:05,550 --> 00:37:07,720 Living in perpetual darkness 269 00:37:07,800 --> 00:37:10,970 they have all not only lost the pigment in their skin, 270 00:37:11,100 --> 00:37:13,100 but also their eyes. 271 00:37:15,150 --> 00:37:19,020 It takes thousands of generations for eyes to be lost, 272 00:37:19,070 --> 00:37:24,240 so these species must have been isolated for a very long time. 273 00:37:29,080 --> 00:37:34,710 But the blind salamander has other highly developed sensory organs. 274 00:37:37,250 --> 00:37:43,510 Receptors in their skin detect minute movements in the water made by its prey. 275 00:37:49,930 --> 00:37:55,940 External gills help it to breathe in water that is particularly low in oxygen. 276 00:38:07,660 --> 00:38:12,830 The cave angel fish feed on bacteria in the fast flowing water 277 00:38:12,870 --> 00:38:17,420 keeping their grip with microscopic hooks on their fins. 278 00:38:28,010 --> 00:38:30,600 Food is often in short supply 279 00:38:30,720 --> 00:38:33,100 and troglodytes like the crab 280 00:38:33,180 --> 00:38:37,310 have to survive on whatever washes into the cave from outside. 281 00:38:41,730 --> 00:38:45,610 The salamander might not encounter food for several months, 282 00:38:45,690 --> 00:38:47,700 so when something does come along 283 00:38:47,820 --> 00:38:49,860 it can't afford to miss it. 284 00:38:56,870 --> 00:39:03,340 It's astonishing that these extraordinary cave dwellers manage to survive at all. 285 00:39:03,750 --> 00:39:06,340 But one cave is so inhospitable 286 00:39:06,420 --> 00:39:10,390 that one would not expect it to contain any life whatsoever. 287 00:39:16,350 --> 00:39:20,520 The water flowing out of the Villa Luz cave in Mexico 288 00:39:20,600 --> 00:39:24,730 is actually coloured white with sulphuric acid. 289 00:39:39,660 --> 00:39:42,630 Explorers entering this dangerous cave 290 00:39:42,710 --> 00:39:46,550 must wear respirators and carry monitors. 291 00:39:46,590 --> 00:39:50,090 Poisonous gases rise to fatal levels so quickly 292 00:39:50,180 --> 00:39:53,260 that an early warning system is essential. 293 00:39:58,060 --> 00:40:01,900 Bats survive by staying close to the skylights, 294 00:40:01,980 --> 00:40:06,860 but venturing deep into the cave is very dangerous indeed. 295 00:40:16,330 --> 00:40:22,080 The source of these toxic fumes lies several miles below. 296 00:40:22,250 --> 00:40:27,630 Hydrogen sulphide gas bubbles up from oil deposits in the earth's crust. 297 00:40:27,710 --> 00:40:30,170 It mixes with oxygen and the water, 298 00:40:30,260 --> 00:40:32,970 and forms sulphuric acid. 299 00:40:44,270 --> 00:40:48,730 These are not the sort of conditions in which you would expect to find fish, 300 00:40:48,820 --> 00:40:51,900 yet these cave mollies seem to thrive 301 00:40:51,990 --> 00:40:55,490 despite the acid and the low levels of oxygen. 302 00:40:58,080 --> 00:41:02,210 There is, in fact, more life here than anyone would think possible, 303 00:41:02,290 --> 00:41:07,500 but the biggest surprise is something altogether more bizarre. 304 00:41:17,720 --> 00:41:26,440 These strange stalactite-like formations are known, rather appropriately, as snotites, 305 00:41:26,520 --> 00:41:30,980 the drops dripping from the ends are sulphuric acid, 306 00:41:31,070 --> 00:41:33,610 strong enough to burn skin. 307 00:41:37,160 --> 00:41:41,450 The snotites are, in fact, vast colonies of bacteria, 308 00:41:41,540 --> 00:41:45,040 capable of going a centimetre a day. 309 00:41:49,420 --> 00:41:51,500 In this world without sunlight 310 00:41:51,590 --> 00:41:56,890 these bacteria extract energy from the hydrogen sulphide gas. 311 00:42:01,430 --> 00:42:05,520 Bacteria like these are known as extremofile 312 00:42:05,600 --> 00:42:10,360 because of their ability to survive in such extreme conditions. 313 00:42:12,780 --> 00:42:17,820 And these extremofiles play another important role in this cave. 314 00:42:17,910 --> 00:42:21,580 Surprisingly, they are the basis of a food chain 315 00:42:21,620 --> 00:42:26,460 which supports, amongst other creatures, the larvae of these midges. 316 00:42:36,220 --> 00:42:39,970 Villa Luz's ecosystem was certainly very remarkable, 317 00:42:40,100 --> 00:42:45,680 but cave explorers were soon to make an even more astonishing discovery. 318 00:42:58,360 --> 00:43:03,830 Beneath this arid landscape lies a subterranean wonderland. 319 00:43:09,790 --> 00:43:13,550 Without water one might not expect to find any caves, 320 00:43:13,630 --> 00:43:18,050 but beneath these rolling desert slopes in the United States 321 00:43:18,130 --> 00:43:25,140 lies one of the longest, deepest and most surprising caves in the world. 322 00:43:29,060 --> 00:43:33,360 Its secrets remained unknown until 1986, 323 00:43:33,440 --> 00:43:37,030 when cavers dug through several metres of loose rock 324 00:43:37,070 --> 00:43:39,200 to the bottom of this pit. 325 00:43:42,620 --> 00:43:45,580 They named the cave 'Lechuguilla' 326 00:43:45,700 --> 00:43:53,040 and since this discovery more than 120 miles of passageways have been mapped. 327 00:43:58,170 --> 00:44:00,380 When the first explorers descended, 328 00:44:00,470 --> 00:44:03,970 no-one guessed at the sheer size of this cave. 329 00:44:04,050 --> 00:44:08,180 But even that was not going to be the biggest surprise. 330 00:44:08,310 --> 00:44:10,730 Little did they realise that Lechuguilla 331 00:44:10,810 --> 00:44:13,860 would soon be regarded by cavers the world over 332 00:44:13,940 --> 00:44:17,610 as the most beautiful of all caves. 333 00:44:17,860 --> 00:44:19,280 They were about to discover 334 00:44:19,360 --> 00:44:24,700 some of the most exquisite formations ever seen underground. 335 00:44:38,960 --> 00:44:44,550 The walls were covered with the most delicate and fragile crystals. 336 00:44:59,730 --> 00:45:03,110 Many of these crystals were made of gypsum, 337 00:45:03,200 --> 00:45:05,870 a mineral that comes from limestone. 338 00:45:06,120 --> 00:45:09,450 And there was mile after mile of them. 339 00:45:26,850 --> 00:45:30,310 Water is the creator of most caves, 340 00:45:30,350 --> 00:45:33,180 but, unlike all other limestone caves, 341 00:45:33,270 --> 00:45:38,610 Lechuguilla's rock had not been eaten away by running rainwater. 342 00:45:39,980 --> 00:45:42,490 Something else was responsible. 343 00:45:50,870 --> 00:45:57,830 The only water Lechuguilla has are these wonderfully still clear pools. 344 00:46:02,630 --> 00:46:05,380 As the explorers went deeper into the cave, 345 00:46:05,470 --> 00:46:10,430 they came across whole galleries filled with the most unusual formations, 346 00:46:10,510 --> 00:46:16,100 like these 5-metre cones, frosted with the most delicate crystals. 347 00:46:45,920 --> 00:46:48,800 It was Lechuguilla's gypsum crystals 348 00:46:48,890 --> 00:46:53,220 that made scientists question how these caverns were formed. 349 00:46:55,520 --> 00:47:02,770 They discovered that Lechuguilla's limestone had actually been eaten away by sulphuric acid, 350 00:47:02,860 --> 00:47:06,650 cutting through literally miles of limestone. 351 00:47:24,210 --> 00:47:27,420 And when sulphuric acid dissolves limestone 352 00:47:27,510 --> 00:47:29,800 it leaves behind gypsum, 353 00:47:29,890 --> 00:47:33,720 the basis of Lechuguilla's remarkable formations. 354 00:47:33,810 --> 00:47:35,350 And there was one set, 355 00:47:35,430 --> 00:47:37,890 more than a mile from the surface, 356 00:47:37,930 --> 00:47:40,600 that almost defied belief. 357 00:47:57,540 --> 00:48:02,040 The Chandelier Ballroom was the ultimate discovery. 358 00:48:02,130 --> 00:48:04,630 With its six-metre long crystals 359 00:48:04,710 --> 00:48:10,510 it's surely the most bizarre cave chamber in the world. 360 00:48:51,880 --> 00:48:56,890 And the walls had one further surprise. 361 00:48:58,430 --> 00:49:04,730 Extremofile bacteria were found to be feeding on the rock itself. 362 00:49:10,610 --> 00:49:16,240 The discovery of life that exists without drawing any of its energy from the sun 363 00:49:16,320 --> 00:49:23,160 shows us once again how complex and surprising the underground world can be. 364 00:49:26,840 --> 00:49:32,970 Each year explorers chart over a hundred miles of new cave passages. 365 00:49:34,800 --> 00:49:38,930 But with half the world's limestone still to be explored, 366 00:49:39,010 --> 00:49:45,060 who knows how many Lechuguillas are still waiting to be discovered? 270 00:49:59,631 --> 00:50:24,631 © anoXmous @ http://thepiratebay.sx/user/Zen_Bud