1 00:00:00,140 --> 00:00:03,555 (instrumental music) 2 00:00:08,340 --> 00:00:10,515 I've spent most of my life trying to understand 3 00:00:10,515 --> 00:00:12,805 the forces that shaped our planet. 4 00:00:13,105 --> 00:00:14,730 And as a geologist, it always seemed to me 5 00:00:14,730 --> 00:00:17,605 that rocks were right at the heart of things. 6 00:00:18,115 --> 00:00:19,940 (explosion) 7 00:00:23,035 --> 00:00:26,110 But now, I'm discovering it's not only volcanoes 8 00:00:26,110 --> 00:00:28,585 and colliding continents that have driven 9 00:00:28,585 --> 00:00:30,625 the Earth's greatest changes, 10 00:00:31,660 --> 00:00:34,615 because at crucial moments in its history, 11 00:00:34,615 --> 00:00:38,045 another force has helped create the planet we live on: 12 00:00:39,445 --> 00:00:40,755 plants. 13 00:00:41,840 --> 00:00:43,555 Just look at this seed. 14 00:00:43,555 --> 00:00:46,390 It's small, it's brown, it weighs hardly anything. 15 00:00:46,390 --> 00:00:48,220 Looks pretty ordinary, 16 00:00:48,220 --> 00:00:50,230 but actually nothing can be further from the truth 17 00:00:50,230 --> 00:00:51,565 because what it will become 18 00:00:51,565 --> 00:00:53,765 is truly extraordinary. 19 00:00:53,765 --> 00:00:57,945 (majestic music) 20 00:01:02,900 --> 00:01:05,025 These are giant sequoias. 21 00:01:05,435 --> 00:01:08,290 Some are over 3,000 years old. 22 00:01:11,490 --> 00:01:14,830 And sequoias are the largest single life form on Earth. 23 00:01:16,710 --> 00:01:19,165 All from a tiny seed. 24 00:01:21,255 --> 00:01:23,890 Yet even that pales into insignificance when compared 25 00:01:23,890 --> 00:01:26,005 to what the whole of the plant kingdom has done 26 00:01:26,005 --> 00:01:28,160 throughout the history of our planet. 27 00:01:30,020 --> 00:01:31,980 They harness light from a star, 28 00:01:31,980 --> 00:01:34,515 bringing energy to our world. 29 00:01:34,515 --> 00:01:35,395 (explosion) 30 00:01:35,395 --> 00:01:39,065 They and their ancestors created our life-giving atmosphere. 31 00:01:40,645 --> 00:01:43,115 I'm breathing oxygen that was made two and a half 32 00:01:43,115 --> 00:01:44,610 billion years ago. 33 00:01:44,610 --> 00:01:46,860 (majestic music) 34 00:01:48,245 --> 00:01:51,185 They sculpted the very surface of the Earth 35 00:01:52,155 --> 00:01:55,125 and they drove the evolution of all animals, 36 00:01:55,125 --> 00:01:56,460 (monkeys screeching) 37 00:01:56,460 --> 00:01:58,455 including our own ancestors. 38 00:01:58,455 --> 00:02:01,375 (majestic music) 39 00:02:02,595 --> 00:02:05,220 It's a whole new story about our Earth 40 00:02:08,675 --> 00:02:11,160 told through remarkable images, 41 00:02:11,520 --> 00:02:13,940 captured for the very first time, 42 00:02:16,180 --> 00:02:18,770 and the latest scientific discoveries. 43 00:02:18,770 --> 00:02:20,475 Wish me luck. 44 00:02:27,575 --> 00:02:29,445 This is the start of that story, 45 00:02:29,445 --> 00:02:33,825 how plants took a barren alien rock, our planet, 46 00:02:33,825 --> 00:02:37,200 and transformed it into the home we know today. 47 00:02:47,465 --> 00:02:50,715 (suspenseful music) 48 00:02:52,470 --> 00:02:54,055 Ooh! 49 00:02:54,055 --> 00:02:55,730 It's a long way down. 50 00:02:57,970 --> 00:02:59,930 I'm in Central Vietnam, 51 00:03:00,775 --> 00:03:03,235 and I'm descending into one of the largest caves 52 00:03:03,235 --> 00:03:04,595 in the world. 53 00:03:04,595 --> 00:03:07,235 The structure's absolutely fantastic. 54 00:03:07,235 --> 00:03:08,280 Ugh! 55 00:03:12,275 --> 00:03:14,285 At seven kilometers long, 56 00:03:14,285 --> 00:03:16,525 this is known as Hang Son Doong. 57 00:03:16,525 --> 00:03:19,700 (eerie suspenseful music) 58 00:03:20,785 --> 00:03:22,865 It's a dark, alien world. 59 00:03:24,175 --> 00:03:26,510 Down here, very little is alive. 60 00:03:31,345 --> 00:03:33,380 But I'm not here for the cave. 61 00:03:35,800 --> 00:03:38,555 Oh, look at that! 62 00:03:39,475 --> 00:03:41,510 (majestic music) 63 00:03:41,510 --> 00:03:43,260 For goodness' sake! 64 00:03:44,060 --> 00:03:45,905 It looks like the roof has collapsed 65 00:03:45,905 --> 00:03:48,540 and the rainforest just invaded. 66 00:03:48,540 --> 00:03:51,695 It's a rainforest inside a cave. 67 00:03:52,825 --> 00:03:54,705 After being in the darkness and the black for ages, 68 00:03:54,705 --> 00:03:57,535 look at that, you just suddenly see brilliant green. 69 00:03:59,700 --> 00:04:01,210 This isn't the entrance. 70 00:04:02,490 --> 00:04:05,860 We're three kilometers into the heart of the cave system. 71 00:04:10,345 --> 00:04:14,840 It's a thriving lost world with towering Polyalthia trees. 72 00:04:17,230 --> 00:04:19,140 And home to strange creatures like this 73 00:04:19,140 --> 00:04:21,890 Vietnamese flat-backed millipede. 74 00:04:24,600 --> 00:04:26,375 Isn't that incredible? 75 00:04:26,375 --> 00:04:27,865 It's got antlers. 76 00:04:27,865 --> 00:04:30,695 (majestic music) 77 00:04:30,695 --> 00:04:33,785 You really feel as if you've left the confines of that cave 78 00:04:33,785 --> 00:04:37,860 and just escaped really into this fantastic forest. 79 00:04:37,860 --> 00:04:39,775 It's a wonderland, really. 80 00:04:40,785 --> 00:04:44,665 This rainforest exists because of one thing above all. 81 00:04:45,525 --> 00:04:47,835 Something which has enabled plants to colonize 82 00:04:47,835 --> 00:04:49,795 almost everywhere on Earth. 83 00:04:52,200 --> 00:04:53,380 Light. 84 00:04:55,635 --> 00:04:59,685 Light, which has traveled 150 million kilometers 85 00:04:59,685 --> 00:05:01,270 from the sun. 86 00:05:04,240 --> 00:05:07,060 Plants have this truly remarkable ability 87 00:05:07,060 --> 00:05:10,820 to harness energy from outer space to produce food. 88 00:05:11,575 --> 00:05:13,615 It's this ability to eat the sun, 89 00:05:13,615 --> 00:05:16,945 to manufacture life from light, 90 00:05:16,945 --> 00:05:19,205 that's allowed plants to dominate our planet. 91 00:05:23,410 --> 00:05:26,960 This is the most important natural process on Earth. 92 00:05:29,425 --> 00:05:31,930 It's how the plant kingdom has transformed 93 00:05:31,930 --> 00:05:35,625 a lifeless planet into a living world. 94 00:05:35,625 --> 00:05:40,050 (majestic music) 95 00:05:42,470 --> 00:05:44,225 But it wasn't always like this. 96 00:05:46,480 --> 00:05:48,090 (suspenseful music) 97 00:05:48,090 --> 00:05:50,860 And to see how it started, we need to go back 98 00:05:50,860 --> 00:05:52,850 three billion years. 99 00:05:58,810 --> 00:06:02,450 To begin with, our planet was like an alien world. 100 00:06:02,450 --> 00:06:04,500 (footsteps) 101 00:06:05,085 --> 00:06:07,375 There was very little oxygen. 102 00:06:09,630 --> 00:06:12,540 The atmosphere was a cocktail of toxic gases, 103 00:06:13,880 --> 00:06:16,550 like methane and sulphur dioxide. 104 00:06:17,965 --> 00:06:20,210 The land was lifeless. 105 00:06:25,410 --> 00:06:27,230 This barren saltpan in southern Kenya 106 00:06:27,230 --> 00:06:29,105 is about as close as you can get in the modern day Earth 107 00:06:29,105 --> 00:06:31,985 to that ancient world three billion years ago. 108 00:06:32,595 --> 00:06:34,900 But the one crucial difference between the planet then 109 00:06:34,900 --> 00:06:37,690 and the planet now is that back then, 110 00:06:37,690 --> 00:06:39,740 I'd have been burnt to a crisp. 111 00:06:41,650 --> 00:06:44,120 (suspenseful music) 112 00:06:44,120 --> 00:06:46,955 That's because the primitive atmosphere couldn't screen out 113 00:06:46,955 --> 00:06:50,415 the sun's powerful ultraviolet rays. 114 00:06:53,340 --> 00:06:57,345 Back then, these UV rays were hundreds of times stronger 115 00:06:57,345 --> 00:06:58,630 than they are now. 116 00:07:02,220 --> 00:07:04,600 Nothing could survive on land. 117 00:07:09,435 --> 00:07:12,100 Yet all this was about to change. 118 00:07:14,905 --> 00:07:17,860 A momentous event that would create the planet's first 119 00:07:17,860 --> 00:07:20,270 life-supporting atmosphere. 120 00:07:23,930 --> 00:07:26,750 This event, between three and two and a half 121 00:07:26,750 --> 00:07:28,490 billion years ago, 122 00:07:28,490 --> 00:07:30,665 was the single greatest turning point 123 00:07:30,665 --> 00:07:32,835 in the history of life on Earth. 124 00:07:34,790 --> 00:07:38,000 And it was all brought about by the earliest ancestors 125 00:07:38,000 --> 00:07:39,555 of plants. 126 00:07:41,795 --> 00:07:45,645 (epic music) 127 00:07:48,140 --> 00:07:51,140 Here at the Sishen iron mine in South Africa, 128 00:07:51,140 --> 00:07:54,605 evidence of that epic event can still be unearthed today. 129 00:07:54,605 --> 00:07:57,070 (truck engine noise) 130 00:07:58,320 --> 00:08:01,185 But to get to it, you need a bit of help. 131 00:08:01,185 --> 00:08:02,985 (siren wailing) 132 00:08:02,985 --> 00:08:05,035 (muffled radio chatter) 133 00:08:05,035 --> 00:08:06,030 Thirty seconds. 134 00:08:06,830 --> 00:08:07,875 Ten. 135 00:08:08,915 --> 00:08:12,870 (multiple explosions) 136 00:08:12,870 --> 00:08:17,050 (epic music) 137 00:08:22,850 --> 00:08:25,640 That is 200,000 tonnes of iron ore 138 00:08:25,640 --> 00:08:27,560 just being blasted apart. 139 00:08:30,765 --> 00:08:34,570 These explosions open a cross section back in time 140 00:08:34,570 --> 00:08:37,640 to the distant origins of the plant kingdom. 141 00:08:43,150 --> 00:08:44,785 This is iron ore. 142 00:08:44,785 --> 00:08:46,070 It's so heavy. 143 00:08:46,415 --> 00:08:50,735 Now pure iron's got this metallic glint, it's shiny, 144 00:08:50,735 --> 00:08:54,125 but you can see that this has got loads of red in it. 145 00:08:54,125 --> 00:08:57,170 And it's red for a really simple reason. 146 00:08:57,170 --> 00:08:58,250 It's rusted. 147 00:08:58,250 --> 00:09:01,370 It's rusted because it's come into contact with oxygen. 148 00:09:01,370 --> 00:09:04,755 Oxygen produced by the very first burst of life. 149 00:09:04,755 --> 00:09:08,625 (dramatic music) 150 00:09:09,480 --> 00:09:12,765 The miners want the ore for its iron content. 151 00:09:13,555 --> 00:09:15,145 But I'm going to use this iron oxide 152 00:09:15,145 --> 00:09:17,350 for a very different reason, something I don't think 153 00:09:17,350 --> 00:09:18,900 has ever been done before, 154 00:09:19,685 --> 00:09:21,270 which is why I'm a wee bit excited. 155 00:09:23,360 --> 00:09:25,970 I've taken a chunk of the iron oxide rock 156 00:09:25,970 --> 00:09:28,860 and had it ground up into fine powder. 157 00:09:31,935 --> 00:09:34,330 It's then been turned into a solution, 158 00:09:36,090 --> 00:09:38,670 one I'm hoping will allow me to take a breath 159 00:09:38,670 --> 00:09:41,625 from the planet's earliest oxygen. 160 00:09:41,625 --> 00:09:44,915 Oxygen made by the ancient ancestors of plants. 161 00:09:45,890 --> 00:09:46,890 And now, what I'm going to do 162 00:09:46,890 --> 00:09:50,125 is kind of jump start it, really, with this battery. 163 00:09:50,125 --> 00:09:52,060 I'm going to attach a lead 164 00:09:52,060 --> 00:09:54,350 and pass an electric current through it. 165 00:09:54,350 --> 00:09:57,390 And we should see a simple reaction. 166 00:09:59,435 --> 00:10:00,570 Oh yeah, yeah. 167 00:10:00,570 --> 00:10:02,590 Yeah, there's some bubbles coming off. 168 00:10:03,855 --> 00:10:05,985 (majestic music) 169 00:10:05,985 --> 00:10:08,535 These bubbles are the gas oxygen. 170 00:10:08,535 --> 00:10:10,880 It's being released for the first time 171 00:10:10,880 --> 00:10:13,655 in over two and a half billion years, 172 00:10:13,655 --> 00:10:15,945 when it was locked away in the rock. 173 00:10:17,540 --> 00:10:18,660 There's a lovely little train of them 174 00:10:18,660 --> 00:10:20,715 just rising up to the top of the test tube 175 00:10:20,715 --> 00:10:22,675 and forming a little pocket of gas. 176 00:10:25,260 --> 00:10:26,515 You're never sure with these experiments 177 00:10:26,515 --> 00:10:28,180 whether you're really going to get it or not, 178 00:10:28,180 --> 00:10:29,975 but that's exactly what I was hoping to see. 179 00:10:33,220 --> 00:10:35,260 In just one hour, I've collected enough 180 00:10:35,260 --> 00:10:37,775 to fill the whole test tube. 181 00:10:38,980 --> 00:10:42,530 (majestic music) 182 00:10:43,645 --> 00:10:45,865 The thing is, this isn't any old oxygen. 183 00:10:45,865 --> 00:10:49,120 This is oxygen that's come from those iron bands. 184 00:10:49,120 --> 00:10:52,475 The very oxygen that changed our planet. 185 00:10:53,425 --> 00:10:54,665 In fact, I can't resist it. 186 00:10:54,665 --> 00:10:56,445 I'm going to have to... (pop) 187 00:10:56,445 --> 00:11:00,210 (inhales) 188 00:11:00,210 --> 00:11:01,525 Ah! 189 00:11:01,525 --> 00:11:03,080 I can't believe it. 190 00:11:04,255 --> 00:11:06,085 I'm breathing oxygen that was made 191 00:11:06,085 --> 00:11:08,210 two and a half billion years ago. 192 00:11:09,180 --> 00:11:10,140 It's all gone. 193 00:11:10,140 --> 00:11:11,850 Liberated from the rocks now. 194 00:11:11,850 --> 00:11:13,180 It's up there somewhere. 195 00:11:15,810 --> 00:11:19,390 These iron bands tell a remarkable story. 196 00:11:20,145 --> 00:11:23,685 Oxygen was now flooding the Earth's atmosphere. 197 00:11:23,685 --> 00:11:27,565 (majestic music) 198 00:11:29,535 --> 00:11:32,610 It cleaned out the planet's toxic gases, 199 00:11:33,700 --> 00:11:37,910 leaving the sky a clear blue for the first time. 200 00:11:43,000 --> 00:11:45,790 Geologists call it the Great Oxidation Event, 201 00:11:45,790 --> 00:11:47,335 and it certainly was an event. 202 00:11:47,335 --> 00:11:49,930 This was an irreversible change between two 203 00:11:49,930 --> 00:11:51,430 very different worlds, 204 00:11:51,430 --> 00:11:54,475 a planet with virtually no free oxygen 205 00:11:54,475 --> 00:11:56,600 and a planet full of oxygen. 206 00:11:57,475 --> 00:12:00,025 This was the greatest change in the history of life 207 00:12:00,025 --> 00:12:01,190 on Earth. 208 00:12:03,725 --> 00:12:06,315 So how did this great event happen? 209 00:12:07,940 --> 00:12:11,030 The answer lies with the first burst of life, 210 00:12:11,030 --> 00:12:15,330 which emerged not on the hostile land but under water. 211 00:12:17,330 --> 00:12:20,495 Back then, water acted as a liquid sunscreen 212 00:12:20,495 --> 00:12:22,620 to the dangerous UV rays. 213 00:12:24,005 --> 00:12:25,715 Under the protection of water, 214 00:12:25,715 --> 00:12:28,460 the earliest organisms on Earth evolved 215 00:12:28,460 --> 00:12:30,960 in the form of tiny bacteria. 216 00:12:32,765 --> 00:12:36,035 And here, in East Africa, is a rare chance to see 217 00:12:36,035 --> 00:12:37,720 what it would have been like. 218 00:12:39,180 --> 00:12:40,770 This is Lake Magadi. 219 00:12:40,770 --> 00:12:43,060 The waters here are just super salty. 220 00:12:43,390 --> 00:12:44,270 Agh! 221 00:12:44,270 --> 00:12:46,395 I can feel it nipping away at my feet. 222 00:12:48,275 --> 00:12:51,440 But the bacteria I'm wading through are close descendants 223 00:12:51,440 --> 00:12:54,035 of the very first microorganisms that lived 224 00:12:54,035 --> 00:12:56,070 three billion years ago. 225 00:12:56,990 --> 00:12:59,825 It's fantastic to think that swimming in the top layer here 226 00:12:59,825 --> 00:13:03,325 are some of the most primitive life forms on Earth. 227 00:13:04,155 --> 00:13:07,410 And those bacteria, just like the ones all that time ago, 228 00:13:07,410 --> 00:13:09,580 have got something surprising about them. 229 00:13:10,590 --> 00:13:11,920 They're purple. 230 00:13:18,135 --> 00:13:19,765 These are hallow bacteria, 231 00:13:20,340 --> 00:13:23,050 and they didn't just occupy the occasional lake. 232 00:13:23,860 --> 00:13:26,810 Much of the world's oceans were purple too. 233 00:13:26,810 --> 00:13:30,525 (epic music) 234 00:13:30,525 --> 00:13:33,280 Imagine that from outer space. 235 00:13:34,515 --> 00:13:36,235 A purple Earth. 236 00:13:41,995 --> 00:13:46,460 The purple bacteria live by harnessing energy from the sun, 237 00:13:48,130 --> 00:13:50,000 but they only use part of the light. 238 00:13:51,250 --> 00:13:53,960 Some rays pass deeper into the water. 239 00:13:55,675 --> 00:13:57,925 And over time, down there, 240 00:13:57,925 --> 00:14:00,350 a different type of bacteria evolved. 241 00:14:01,765 --> 00:14:04,520 They had to live off the colors of light left over. 242 00:14:05,680 --> 00:14:07,475 This made them appear green. 243 00:14:08,440 --> 00:14:10,730 These were the green bacteria. 244 00:14:12,610 --> 00:14:14,605 This seemingly arbitrary event, 245 00:14:14,605 --> 00:14:18,130 bacteria absorbing one color of light rather than another, 246 00:14:18,130 --> 00:14:20,910 would have colossal repercussions for the planet. 247 00:14:24,785 --> 00:14:29,585 Over time, these green bacteria, a type of Cyanobacteria, 248 00:14:29,585 --> 00:14:32,205 came to dominate the waters of the world. 249 00:14:34,040 --> 00:14:37,130 Eventually, as we'll see, these green microorganisms 250 00:14:37,130 --> 00:14:40,055 became the ancestor of all plants on Earth. 251 00:14:40,055 --> 00:14:41,810 Because right from the start, 252 00:14:41,810 --> 00:14:43,520 they were reflecting green light, 253 00:14:43,520 --> 00:14:46,400 the stalks of the plants became green 254 00:14:46,400 --> 00:14:48,515 and the leaves were green. 255 00:14:48,515 --> 00:14:51,255 In fact, that's why all plants on Earth became green, 256 00:14:51,255 --> 00:14:52,815 from the grasses to the forests, 257 00:14:52,815 --> 00:14:55,530 and it's also why today, 258 00:14:55,530 --> 00:14:57,700 instead of living on a purple planet, 259 00:14:57,700 --> 00:14:59,240 we've got a green one. 260 00:15:01,075 --> 00:15:05,000 (soft dramatic music) 261 00:15:08,285 --> 00:15:10,590 But it wasn't just about color 262 00:15:11,190 --> 00:15:13,995 because the green bacteria did something 263 00:15:13,995 --> 00:15:16,095 their purple cousins couldn't. 264 00:15:17,045 --> 00:15:18,960 They produced oxygen. 265 00:15:22,970 --> 00:15:25,890 They would breathe life into the lifeless land. 266 00:15:26,930 --> 00:15:29,435 Without them, the story of our planet 267 00:15:29,435 --> 00:15:31,260 would be more like that of Mars. 268 00:15:33,965 --> 00:15:37,115 How the green bacteria did this is so complex 269 00:15:37,115 --> 00:15:40,065 that scientists still grapple with the details. 270 00:15:43,655 --> 00:15:46,115 I've come to the Eden Project in Cornwall 271 00:15:46,115 --> 00:15:47,910 to try to understand it. 272 00:15:50,415 --> 00:15:52,440 I'm to be the subject of an experiment 273 00:15:52,440 --> 00:15:54,955 that's never been attempted before. 274 00:15:55,675 --> 00:15:56,455 Hi. 275 00:15:56,455 --> 00:15:57,280 Hello there. 276 00:15:57,280 --> 00:15:58,130 I'm the guinea pig. 277 00:15:58,130 --> 00:15:59,330 Doctor, I presume? 278 00:15:59,330 --> 00:16:01,130 Indeed, Dan Martin. Hi. 279 00:16:01,130 --> 00:16:03,265 Hi, Katrina Hope. Nice to meet you. 280 00:16:03,265 --> 00:16:05,020 Look at this, this is fantastic. 281 00:16:05,600 --> 00:16:06,895 Incredible, isn't it? 282 00:16:06,895 --> 00:16:08,455 I'm about to be locked inside 283 00:16:08,455 --> 00:16:10,310 this airtight chamber. 284 00:16:10,310 --> 00:16:12,770 I hope to experience first-hand 285 00:16:12,770 --> 00:16:15,480 my very own Great Oxidation Event. 286 00:16:15,480 --> 00:16:16,980 (suspenseful music) 287 00:16:16,980 --> 00:16:18,520 Okay, everyone, I'm going to start reducing 288 00:16:18,520 --> 00:16:20,945 the oxygen concentration in here now. 289 00:16:22,150 --> 00:16:23,555 (beeping) 290 00:16:23,555 --> 00:16:25,950 The first step is to lower oxygen levels 291 00:16:25,950 --> 00:16:27,830 closer to those of the early Earth. 292 00:16:27,830 --> 00:16:29,825 (suspenseful music) 293 00:16:29,825 --> 00:16:32,070 So first of all, this is going to monitor 294 00:16:32,070 --> 00:16:34,245 your heart rate and your oxygen levels, 295 00:16:34,245 --> 00:16:36,590 so if we pop that on we can just have a look here. 296 00:16:36,590 --> 00:16:37,845 (beeping) 297 00:16:37,845 --> 00:16:40,795 It's a lack of oxygen that complex life like us 298 00:16:40,795 --> 00:16:42,850 can't operate at for long. 299 00:16:43,725 --> 00:16:45,675 So at the top is your heart rate. 300 00:16:45,675 --> 00:16:46,390 (beeping) 301 00:16:46,390 --> 00:16:47,845 How's that? Is that really high? 302 00:16:48,565 --> 00:16:50,680 I think you might be a little bit anxious 303 00:16:50,680 --> 00:16:51,805 about going in there. 304 00:16:51,805 --> 00:16:52,892 I am a little bit. 305 00:16:52,892 --> 00:16:55,185 I'm sure your resting heart rate's not normally 95. 306 00:16:55,185 --> 00:16:56,820 No, I have been thinking a lot about it. 307 00:16:58,270 --> 00:17:00,565 My vital signs are being monitored, 308 00:17:00,565 --> 00:17:02,945 along with the oxygen levels in my blood. 309 00:17:04,150 --> 00:17:06,910 Now it's time to be sealed inside the chamber 310 00:17:06,910 --> 00:17:09,080 for the next 48 hours. 311 00:17:09,080 --> 00:17:11,285 (suspenseful music) 312 00:17:11,285 --> 00:17:12,575 I'm as ready as I'll ever be, guys, 313 00:17:12,575 --> 00:17:14,670 so can we open this door? 314 00:17:16,040 --> 00:17:17,040 Wish me luck. 315 00:17:21,875 --> 00:17:23,715 It's small, isn't it? 316 00:17:24,975 --> 00:17:26,885 (locks clicking) 317 00:17:28,675 --> 00:17:31,930 Oxygen levels in the air are normally 21%. 318 00:17:31,930 --> 00:17:33,230 (beeping) 319 00:17:33,230 --> 00:17:36,020 Inside the chamber, they're far lower. 320 00:17:36,690 --> 00:17:38,905 Just over 12%. 321 00:17:40,980 --> 00:17:42,660 At these concentrations, 322 00:17:42,660 --> 00:17:45,315 the cellular activity in my body and brain 323 00:17:45,315 --> 00:17:47,080 is starting to slow down. 324 00:17:47,080 --> 00:17:48,415 Go. 325 00:17:48,415 --> 00:17:50,320 Green, yellow, 326 00:17:50,320 --> 00:17:53,830 red, green, kind of orange. 327 00:17:54,405 --> 00:17:57,535 Er, purple, blue. 328 00:17:58,215 --> 00:18:01,215 You'll find that thinking becomes a little bit slower. 329 00:18:02,470 --> 00:18:05,630 My hand-to-eye coordination is being impaired. 330 00:18:07,455 --> 00:18:09,225 You can put them in any order you like. 331 00:18:09,225 --> 00:18:10,640 That's the way. 332 00:18:11,605 --> 00:18:13,720 Can you just tell us how exactly are you feeling? 333 00:18:13,720 --> 00:18:16,355 Yeah, it's funny, I felt very slow, yeah. 334 00:18:16,355 --> 00:18:18,935 That slowness is there, definitely. 335 00:18:18,935 --> 00:18:20,990 (beeping) 336 00:18:23,145 --> 00:18:26,785 The doctors calculate that at the rate I use up oxygen, 337 00:18:26,785 --> 00:18:29,695 if it carried on like this, I'd be unconscious 338 00:18:29,695 --> 00:18:31,640 in just 24 hours. 339 00:18:32,240 --> 00:18:36,170 Your oxygen saturation is sort of 88%. 340 00:18:36,170 --> 00:18:37,670 If that was your level in a hospital, 341 00:18:37,670 --> 00:18:39,705 we'd be pretty worried about you right now. 342 00:18:39,705 --> 00:18:42,700 (suspenseful music) 343 00:18:42,700 --> 00:18:45,880 The next crucial step is to see if the 300 plants 344 00:18:45,880 --> 00:18:49,850 in here with me can produce enough oxygen to keep me alive. 345 00:18:51,805 --> 00:18:54,595 It's all to do with the wondrous ability they inherited 346 00:18:54,595 --> 00:18:56,375 from those green bacteria. 347 00:18:57,640 --> 00:18:59,720 It's photosynthesis, of course. 348 00:19:00,185 --> 00:19:02,715 I think we can have the lights on, please. 349 00:19:04,605 --> 00:19:07,450 To kick start it, you need light. 350 00:19:08,680 --> 00:19:10,025 Wow! 351 00:19:10,025 --> 00:19:11,865 Suddenly the light's hit. 352 00:19:13,655 --> 00:19:18,030 (suspenseful music) 353 00:19:18,030 --> 00:19:21,315 Plants use photosynthesis to live and grow, 354 00:19:21,315 --> 00:19:23,250 and most importantly, for me, 355 00:19:24,680 --> 00:19:26,045 to make oxygen. 356 00:19:26,045 --> 00:19:28,710 (suspenseful music) 357 00:19:28,710 --> 00:19:31,545 Photosynthesis is an intricate process 358 00:19:31,545 --> 00:19:33,970 that science is still trying to unlock. 359 00:19:36,015 --> 00:19:37,980 But the production of oxygen 360 00:19:37,980 --> 00:19:40,345 is one of its key features. 361 00:19:41,805 --> 00:19:43,770 To understand what's happening, 362 00:19:43,770 --> 00:19:47,655 you need to enter a complex and microscopic world. 363 00:19:47,655 --> 00:19:50,395 (majestic music) 364 00:19:50,395 --> 00:19:54,580 Inside every leaf of every plant on the planet 365 00:19:54,580 --> 00:19:58,085 are the direct descendants of those first green bacteria. 366 00:19:59,665 --> 00:20:03,145 Magnify a leaf 1,000 times and you can see them. 367 00:20:03,145 --> 00:20:05,130 They're known as chloroplasts. 368 00:20:05,915 --> 00:20:08,010 Packed into every cell. 369 00:20:11,255 --> 00:20:13,755 They still behave a bit like bacteria. 370 00:20:14,595 --> 00:20:16,430 This is real footage of them moving 371 00:20:16,430 --> 00:20:18,330 towards a flash of light. 372 00:20:23,810 --> 00:20:27,195 They're just 5,000ths of a millimeter across. 373 00:20:28,280 --> 00:20:32,190 And it's inside chloroplasts that photosynthesis happens. 374 00:20:36,320 --> 00:20:39,080 Light rays from the sun are made of photons. 375 00:20:40,710 --> 00:20:42,750 They're tiny, fast-moving particles 376 00:20:42,750 --> 00:20:45,040 of electromagnetic energy. 377 00:20:46,191 --> 00:20:47,290 (zapping noise) 378 00:20:47,290 --> 00:20:50,125 When they hit the surface, the energy of the photons 379 00:20:50,125 --> 00:20:54,590 is captured by a ring called the light-harvesting complex. 380 00:20:59,395 --> 00:21:00,715 Inside this structure, 381 00:21:00,715 --> 00:21:04,600 the energy of two photons is used to split a water molecule. 382 00:21:04,600 --> 00:21:08,240 (epic music) 383 00:21:10,570 --> 00:21:12,985 It's ripped into its two elements, 384 00:21:12,985 --> 00:21:15,155 hydrogen and oxygen. 385 00:21:18,865 --> 00:21:21,545 The plant uses the hydrogen to live and grow. 386 00:21:25,210 --> 00:21:28,205 But right now I'm interested in the other part of the water. 387 00:21:28,580 --> 00:21:31,170 The part plants pump out as a waste product, 388 00:21:32,555 --> 00:21:34,170 the oxygen. 389 00:21:35,510 --> 00:21:39,390 (suspenseful music) 390 00:21:47,850 --> 00:21:50,760 Scientists have calculated that the 300 plants 391 00:21:50,760 --> 00:21:54,525 in here with me should raise oxygen levels in this chamber 392 00:21:54,525 --> 00:21:58,360 from 12% to 21% within 48 hours. 393 00:22:02,145 --> 00:22:05,280 I'm finding out how reliable the process of photosynthesis 394 00:22:05,280 --> 00:22:06,880 really is. 395 00:22:11,085 --> 00:22:12,345 It is quite concerning. 396 00:22:12,345 --> 00:22:15,180 You've been very busy this afternoon, a lot of activity, 397 00:22:15,180 --> 00:22:18,180 so we need to restrict the amount that you're talking 398 00:22:18,180 --> 00:22:21,720 and really get you resting as much as possible, 399 00:22:21,720 --> 00:22:23,890 not dashing around the chamber any more. 400 00:22:23,890 --> 00:22:25,970 This is doctor's orders, bed rest. 401 00:22:25,970 --> 00:22:27,225 Night-night! 402 00:22:34,355 --> 00:22:36,440 As I drift off to sleep, 403 00:22:36,440 --> 00:22:38,820 the 11,000 leaves go to work. 404 00:22:42,830 --> 00:22:45,825 They have 30 cubic meters of the box to fill. 405 00:22:48,285 --> 00:22:50,715 Some plants, like this maize, 406 00:22:50,715 --> 00:22:53,505 and the banana plant are particularly efficient 407 00:22:53,505 --> 00:22:55,755 at pumping out oxygen. 408 00:22:56,675 --> 00:23:00,755 (suspenseful music) 409 00:23:01,930 --> 00:23:04,105 So we can see the increase every hour here. 410 00:23:04,105 --> 00:23:05,515 That's incredible really. 411 00:23:05,515 --> 00:23:08,395 They're really pushing out a lot of oxygen, as you can see. 412 00:23:08,395 --> 00:23:11,480 (suspenseful music) 413 00:23:13,150 --> 00:23:15,655 Every hour, my plants are producing 414 00:23:15,655 --> 00:23:18,185 over 40 liters of oxygen. 415 00:23:18,185 --> 00:23:19,860 Hi, Iain. It's Katrina. 416 00:23:19,860 --> 00:23:21,160 We're now 41 hours in. 417 00:23:21,160 --> 00:23:23,620 Really? 41 hours in? 418 00:23:23,620 --> 00:23:25,750 Yeah, so the oxygen levels are still climbing 419 00:23:25,750 --> 00:23:28,450 gradually every hour, so it's going really well. 420 00:23:29,540 --> 00:23:31,870 With my vital signs returning to normal, 421 00:23:31,870 --> 00:23:33,000 (camera shutter clicks) 422 00:23:33,000 --> 00:23:35,625 I'm now a top attraction at the Eden Project. 423 00:23:35,625 --> 00:23:37,455 Hello! Hello! 424 00:23:37,455 --> 00:23:38,470 Can you see him? 425 00:23:38,470 --> 00:23:39,880 What's he doing in that box? 426 00:23:39,880 --> 00:23:41,305 He looks very happy in there. 427 00:23:41,305 --> 00:23:42,255 What's that on his finger? 428 00:23:42,255 --> 00:23:43,715 It's measuring his oxygen levels. 429 00:23:45,095 --> 00:23:47,345 Eat your heart out, David Blaine! 430 00:23:50,515 --> 00:23:53,155 Finally, after 48 long hours, 431 00:23:53,155 --> 00:23:56,150 oxygen levels are almost back to normal. 432 00:23:57,100 --> 00:23:58,655 The plants have triumphed. 433 00:23:58,655 --> 00:24:01,245 (suspenseful music intensifies) 434 00:24:05,375 --> 00:24:06,330 Yay! 435 00:24:07,280 --> 00:24:08,295 Oh, I'm out! 436 00:24:08,295 --> 00:24:09,460 Ah! 437 00:24:09,960 --> 00:24:12,165 Survived it, fantastic! 438 00:24:12,865 --> 00:24:15,500 It's amazing just thinking that I've survived, 439 00:24:15,500 --> 00:24:19,670 but actually, I guess I've really survived because of them, 440 00:24:19,670 --> 00:24:20,915 because of the plants. 441 00:24:20,915 --> 00:24:23,300 I leave here thinking that I needed those plants 442 00:24:23,300 --> 00:24:25,215 way more than they needed me. 443 00:24:26,555 --> 00:24:29,180 It's easy to think of this as just an experiment but to me, 444 00:24:29,180 --> 00:24:31,775 when you're lying in there, you realize that this place 445 00:24:31,775 --> 00:24:34,070 is a metaphor for something much bigger, 446 00:24:34,070 --> 00:24:35,270 for the planet, really, 447 00:24:35,270 --> 00:24:39,150 and for our relationship with plants through photosynthesis 448 00:24:39,150 --> 00:24:41,235 to keep life going. 449 00:24:41,235 --> 00:24:44,140 (soft dramatic music) 450 00:24:44,140 --> 00:24:46,780 The early Earth was like my chamber. 451 00:24:46,780 --> 00:24:50,185 It was transformed from a world with very little oxygen 452 00:24:50,185 --> 00:24:52,535 to a world rich in oxygen. 453 00:24:54,085 --> 00:24:57,245 And all that oxygen began to do something else. 454 00:24:58,300 --> 00:25:01,385 High in the stratosphere, it created ozone. 455 00:25:05,115 --> 00:25:07,175 This was a protective blanket, 456 00:25:07,175 --> 00:25:10,145 which enveloped the Earth and blocked most of the sun's 457 00:25:10,145 --> 00:25:12,150 dangerous UV rays. 458 00:25:14,765 --> 00:25:18,005 It meant that for the first time in the planet's history, 459 00:25:18,005 --> 00:25:20,235 plants could move on to the land. 460 00:25:21,575 --> 00:25:23,745 But it was no small step. 461 00:25:23,745 --> 00:25:27,365 (epic music) 462 00:25:35,205 --> 00:25:37,205 The thing is, if you'd been protected by water 463 00:25:37,205 --> 00:25:39,665 for billions of years, then the move to the land 464 00:25:39,665 --> 00:25:42,330 was going to be a rude shock. 465 00:25:43,640 --> 00:25:45,755 Yet over 400 million years ago, 466 00:25:45,755 --> 00:25:48,715 plants finally made that leap. (car engine noise) 467 00:25:51,555 --> 00:25:54,810 Surprisingly, the best evidence for these pioneers 468 00:25:54,810 --> 00:25:57,985 doesn't come from some exotic corner of our planet, 469 00:25:59,595 --> 00:26:00,940 but from Britain. 470 00:26:04,560 --> 00:26:06,900 I've come to just outside the village of Rhynie 471 00:26:06,900 --> 00:26:08,950 in northeast Scotland to see this, 472 00:26:08,950 --> 00:26:10,580 a stone wall. 473 00:26:11,155 --> 00:26:12,905 But not just any stone wall, of course. 474 00:26:12,905 --> 00:26:16,295 For me, this is the most important stone wall 475 00:26:16,295 --> 00:26:18,300 in the history of science. 476 00:26:22,290 --> 00:26:25,675 (suspenseful music) 477 00:26:26,570 --> 00:26:29,715 Back 410 million years ago, 478 00:26:29,715 --> 00:26:33,135 Scotland was located well south of the equator 479 00:26:33,135 --> 00:26:35,260 and looked like another world. 480 00:26:39,970 --> 00:26:42,895 Hot springs and geysers boiled out across a rocky 481 00:26:42,895 --> 00:26:45,020 and barren landscape. 482 00:26:46,360 --> 00:26:48,525 (water splashing noise) 483 00:26:50,855 --> 00:26:52,955 But something else was happening 484 00:26:52,955 --> 00:26:54,500 as scientists discovered 485 00:26:54,500 --> 00:26:57,665 when they came across some curious markings in this wall. 486 00:26:58,620 --> 00:27:00,175 This is one of them. 487 00:27:00,175 --> 00:27:02,000 Look at this, you see these really strange 488 00:27:02,000 --> 00:27:04,830 elongated kind of shapes here. 489 00:27:05,445 --> 00:27:07,965 The first people just didn't really know what they were. 490 00:27:07,965 --> 00:27:10,005 They thought maybe at first it was some kind of lava, 491 00:27:10,005 --> 00:27:12,225 but when they looked really closely, 492 00:27:12,225 --> 00:27:14,310 especially when they got it cut and polished, 493 00:27:14,310 --> 00:27:16,605 this rock literally came alive. 494 00:27:16,605 --> 00:27:19,690 (suspenseful music) 495 00:27:23,565 --> 00:27:26,775 Because you can see these dark features here, 496 00:27:27,610 --> 00:27:30,860 they realized that this was something that was once living. 497 00:27:33,745 --> 00:27:36,920 And when they were alive, this is what they looked like. 498 00:27:38,365 --> 00:27:40,580 (eerie music) 499 00:27:40,580 --> 00:27:42,875 Just a few centimeters tall, 500 00:27:42,875 --> 00:27:44,955 they're called Aglaophyton. 501 00:27:47,090 --> 00:27:50,165 Bulbous shapes on the end of naked stems, 502 00:27:53,645 --> 00:27:55,605 a time before leaves or roots. 503 00:27:56,135 --> 00:27:58,980 Yet somehow, these bizarre life forms survived 504 00:27:58,980 --> 00:28:00,475 along the water's edge. 505 00:28:02,520 --> 00:28:05,490 What geologists had found right here in Scotland 506 00:28:05,490 --> 00:28:07,815 were some of the earliest pioneering plants 507 00:28:07,815 --> 00:28:09,985 to make that giant leap, 508 00:28:10,740 --> 00:28:12,115 to colonize the land. 509 00:28:13,650 --> 00:28:16,765 (dramatic music) 510 00:28:16,765 --> 00:28:19,325 And around this time, all along the margins 511 00:28:19,325 --> 00:28:23,290 of lakes and rivers, primitive plants were coming ashore. 512 00:28:27,795 --> 00:28:30,255 For the first time, when viewed from space, 513 00:28:30,255 --> 00:28:32,800 the land began to look alive. 514 00:28:34,470 --> 00:28:37,635 The beginning of a transformation from hostile world 515 00:28:37,635 --> 00:28:39,565 to fertile Earth. 516 00:28:43,230 --> 00:28:45,775 Yet this wasn't a full-scale invasion. 517 00:28:46,660 --> 00:28:48,100 Just a toehold. 518 00:28:49,770 --> 00:28:52,150 Plants were still tied to the water's edge, 519 00:28:52,150 --> 00:28:55,690 unable to head inland and penetrate the harsh, 520 00:28:55,690 --> 00:28:57,020 rocky surface. 521 00:28:58,705 --> 00:29:01,415 But all this was about to change. 522 00:29:04,000 --> 00:29:07,375 Plants evolved an inspired solution to the problem, 523 00:29:07,375 --> 00:29:10,345 a brilliant device for collecting water and nutrients 524 00:29:10,345 --> 00:29:13,300 and something that they never really had before. 525 00:29:13,300 --> 00:29:14,720 Roots. 526 00:29:16,760 --> 00:29:19,845 (percussion music) 527 00:29:24,230 --> 00:29:25,350 Cambodia. 528 00:29:25,890 --> 00:29:28,275 The 12th-century temple here at Ta Prohm 529 00:29:28,275 --> 00:29:30,700 is a wonder of civilization, 530 00:29:32,070 --> 00:29:34,645 but it's also a wonder of the natural world. 531 00:29:35,745 --> 00:29:37,860 Although the roots of these strangler figs 532 00:29:37,860 --> 00:29:40,530 are very different from the first ones to evolve, 533 00:29:41,365 --> 00:29:43,630 it's a superb place to reveal how roots 534 00:29:43,630 --> 00:29:46,340 allowed plants to invade inland. 535 00:29:50,710 --> 00:29:52,465 Roots are hugely powerful. 536 00:29:52,465 --> 00:29:53,890 I mean, I love this one. 537 00:29:53,890 --> 00:29:56,050 Look at it prising its way into that roof, 538 00:29:56,050 --> 00:29:58,675 just lifting that whole structure up 539 00:29:58,675 --> 00:30:00,550 and then boring down here 540 00:30:01,020 --> 00:30:03,315 through these stone blocks and then disappearing. 541 00:30:04,810 --> 00:30:09,305 Just tiny pressures exerted over decades of centuries. 542 00:30:12,340 --> 00:30:14,825 Add these up and you get phenomenal strength. 543 00:30:15,610 --> 00:30:18,740 A pressure of up to 10 kilograms per square centimeter. 544 00:30:20,455 --> 00:30:24,095 Around 400 million years ago, the first roots appeared. 545 00:30:24,095 --> 00:30:26,500 (suspenseful music) 546 00:30:26,500 --> 00:30:30,110 and gave plants the ability to smash up the rocky planet. 547 00:30:32,710 --> 00:30:36,380 And this created a vital ingredient for life on land. 548 00:30:39,250 --> 00:30:42,460 When the tiny, broken-up fragments of rock 549 00:30:42,460 --> 00:30:45,100 get mixed up with dead plant material, 550 00:30:45,100 --> 00:30:48,815 it ends up as this ideal environment for storing water. 551 00:30:50,350 --> 00:30:53,360 An environment that we call soil. 552 00:30:56,155 --> 00:30:59,705 Today, soil covers 40% of the planet's land. 553 00:31:00,700 --> 00:31:02,970 It takes a long time to form, 554 00:31:02,970 --> 00:31:06,540 1,000 years to make just 2cm of soil. 555 00:31:07,080 --> 00:31:11,245 But it's essential for plant life, just as it was back then. 556 00:31:14,520 --> 00:31:17,215 Because the primitive leafless plant 557 00:31:17,215 --> 00:31:19,760 could now break free from the water's edge. 558 00:31:22,720 --> 00:31:25,270 Roots, and the soil they created, 559 00:31:25,270 --> 00:31:27,105 made plants unstoppable. 560 00:31:27,105 --> 00:31:28,875 (orchestra music) 561 00:31:28,875 --> 00:31:32,230 allowing them to colonize inland for the first time. 562 00:31:33,810 --> 00:31:36,145 An invasion that would have a dramatic influence 563 00:31:36,145 --> 00:31:38,230 on all life on Earth. 564 00:31:40,535 --> 00:31:43,530 (water splashing) 565 00:31:46,580 --> 00:31:48,035 For millions of years, 566 00:31:48,035 --> 00:31:51,205 animals had been confined to the rivers and oceans. 567 00:31:52,330 --> 00:31:55,295 Now they could finally emerge from the water. 568 00:31:58,720 --> 00:32:01,510 We get an idea of those first tentative steps 569 00:32:02,345 --> 00:32:04,385 by traveling back in time with a creature 570 00:32:04,385 --> 00:32:08,565 that's barely changed for 500 million years. 571 00:32:10,940 --> 00:32:13,395 (bubbling noise) 572 00:32:18,855 --> 00:32:21,345 I've come to the east coast of America, 573 00:32:21,345 --> 00:32:23,695 where these ancient creatures still come ashore 574 00:32:23,695 --> 00:32:25,535 at dusk to mate. 575 00:32:28,460 --> 00:32:29,790 Here they are. 576 00:32:30,500 --> 00:32:31,785 Horseshoe crabs. 577 00:32:34,080 --> 00:32:36,415 Looks like something from another planet. 578 00:32:37,710 --> 00:32:39,840 He sees with two main eyes here, 579 00:32:39,840 --> 00:32:42,375 but they've got something like ten eyes 580 00:32:42,375 --> 00:32:44,095 scattered across their body. 581 00:32:44,470 --> 00:32:46,385 And the really weird bit 582 00:32:46,385 --> 00:32:48,300 is if you lift them up. 583 00:32:49,310 --> 00:32:50,630 I mean, look at that. 584 00:32:50,630 --> 00:32:52,940 For a start, they've got five pairs of legs. 585 00:32:52,940 --> 00:32:54,435 Look, one, two, three, four, five, 586 00:32:54,435 --> 00:32:56,605 whereas normal crabs just have four. 587 00:32:57,105 --> 00:32:59,065 They're actually more related to the scorpion 588 00:32:59,065 --> 00:33:00,850 than to normal crabs, look at that. 589 00:33:01,390 --> 00:33:04,570 But the really interesting bit is tucked under here. 590 00:33:04,570 --> 00:33:07,030 You get these things called book gills. 591 00:33:07,030 --> 00:33:08,620 Look at that there. 592 00:33:08,620 --> 00:33:10,285 It's like sheaves of a book. 593 00:33:10,285 --> 00:33:12,910 And that allows them to extract oxygen, 594 00:33:12,910 --> 00:33:15,800 not just from the water but also from the air. 595 00:33:16,175 --> 00:33:18,750 It's an amazing breathing apparatus. 596 00:33:20,130 --> 00:33:21,720 Better put her back now. 597 00:33:21,720 --> 00:33:24,005 Come on, dear, there you go. 598 00:33:30,055 --> 00:33:31,855 As long as they're kept moist, 599 00:33:31,855 --> 00:33:35,260 these lung-like gills enable the crabs to stay out of water 600 00:33:35,260 --> 00:33:36,770 for days at a time. 601 00:33:38,815 --> 00:33:41,605 Fossils show that horseshoe crabs appeared on land 602 00:33:41,605 --> 00:33:43,775 at least 400 million years ago. 603 00:33:45,535 --> 00:33:48,830 They're some of the first animals ever to come ashore. 604 00:33:48,830 --> 00:33:52,170 (waves breaking) 605 00:33:55,355 --> 00:33:58,125 Amphibians and insects soon followed. 606 00:34:00,125 --> 00:34:02,835 Oxygen allowed them to move on to land. 607 00:34:03,620 --> 00:34:05,865 But something else was also enticing them. 608 00:34:08,465 --> 00:34:11,555 It's funny, plants create oxygen as a waste product 609 00:34:11,555 --> 00:34:14,300 and it's that waste product that has transformed 610 00:34:14,300 --> 00:34:16,025 our atmosphere. 611 00:34:16,025 --> 00:34:18,725 But of course, the main reason that plants photosynthesize 612 00:34:18,725 --> 00:34:20,280 is to create sugars. 613 00:34:20,735 --> 00:34:23,780 Sugars that are vital for plants to live and to grow 614 00:34:23,780 --> 00:34:28,025 and also provide a source of food for all animals. 615 00:34:28,025 --> 00:34:32,040 (dramatic music) 616 00:34:33,540 --> 00:34:36,075 Plants make this sugar from water, 617 00:34:37,630 --> 00:34:40,205 carbon dioxide from the air 618 00:34:41,915 --> 00:34:43,875 and energy from the sun. 619 00:34:47,165 --> 00:34:50,220 And again, it all happens in those tiny chloroplasts. 620 00:34:50,220 --> 00:34:53,260 (zapping) 621 00:34:53,755 --> 00:34:57,485 We've seen how light splits water into oxygen and hydrogen. 622 00:34:57,485 --> 00:34:59,600 (dramatic music) 623 00:35:00,690 --> 00:35:02,530 Well, the plant takes that hydrogen 624 00:35:02,530 --> 00:35:06,485 and combines it with carbon dioxide to make sugar. 625 00:35:10,025 --> 00:35:12,650 By exposing a plant to carbon dioxide 626 00:35:12,650 --> 00:35:14,825 tagged with a radioactive marker, 627 00:35:14,825 --> 00:35:17,625 you can see the sugar being created. 628 00:35:18,980 --> 00:35:21,875 For the first time, scientists have imaged its creation 629 00:35:21,875 --> 00:35:23,845 and movement through a plant. 630 00:35:23,845 --> 00:35:25,705 In this case, maize. 631 00:35:28,965 --> 00:35:32,625 As soon as carbon dioxide is sucked into the plant's cells, 632 00:35:32,625 --> 00:35:34,300 they begin to glow. 633 00:35:36,345 --> 00:35:38,940 This is the actual moment that photosynthesis 634 00:35:38,940 --> 00:35:41,890 turns the carbon dioxide into sugar. 635 00:35:44,985 --> 00:35:47,985 In just 15 minutes, the newly-formed sugar 636 00:35:47,985 --> 00:35:50,245 is sent to the roots for storage. 637 00:35:52,785 --> 00:35:56,210 The plant can then use this sugar to grow and thrive. 638 00:35:59,795 --> 00:36:01,745 That's why photosynthesis is nature's 639 00:36:01,745 --> 00:36:03,675 most astonishing achievement. 640 00:36:04,415 --> 00:36:07,085 The ability of plants to be powered by light 641 00:36:07,085 --> 00:36:11,340 from beyond our planet sets them apart from all other life. 642 00:36:12,020 --> 00:36:15,720 And that connection with that star, our sun, 643 00:36:15,720 --> 00:36:19,525 makes plants a foundation stone for all living things. 644 00:36:20,265 --> 00:36:22,270 It's just such a wonderful thought. 645 00:36:23,085 --> 00:36:25,690 (majestic instrumental music) 646 00:36:27,730 --> 00:36:29,950 400 million years ago, 647 00:36:29,950 --> 00:36:32,780 leafless plants were flourishing like never before. 648 00:36:37,120 --> 00:36:40,000 But a dramatic transformation of the atmosphere 649 00:36:40,000 --> 00:36:43,255 was about to throw plants into a global crisis. 650 00:36:43,255 --> 00:36:44,705 (suspenseful music) 651 00:36:44,705 --> 00:36:46,955 Not only would it change their shape, 652 00:36:47,625 --> 00:36:50,425 it would change all life on our planet. 653 00:36:53,010 --> 00:36:55,555 (chanting) 654 00:37:09,815 --> 00:37:12,950 This is Lake Tarawera in New Zealand. 655 00:37:16,580 --> 00:37:19,235 This ancient landscape is home to a plant 656 00:37:19,235 --> 00:37:23,670 that 360 million years ago confronted that crisis. 657 00:37:24,545 --> 00:37:26,580 It came up with an inspired solution. 658 00:37:30,050 --> 00:37:32,595 Looks like the land that time forgot, doesn't it? 659 00:37:32,595 --> 00:37:34,920 Just that strange mixture of different shapes 660 00:37:34,920 --> 00:37:36,340 of plants and trees. 661 00:37:36,340 --> 00:37:38,765 Really unfamiliar and alien. 662 00:37:39,430 --> 00:37:40,970 It's almost primeval. 663 00:37:45,355 --> 00:37:48,440 The early plants had become victims of their own success. 664 00:37:49,690 --> 00:37:52,315 They were gorging on so much carbon dioxide 665 00:37:52,315 --> 00:37:55,160 in the atmosphere, that they were using it up. 666 00:37:56,320 --> 00:37:59,075 Levels plummeted by 90%. 667 00:38:01,405 --> 00:38:05,495 Without enough of this vital gas, plants began struggling. 668 00:38:06,625 --> 00:38:08,455 If they couldn't find a way to breathe in 669 00:38:08,455 --> 00:38:11,750 more carbon dioxide, they'd suffocate. 670 00:38:11,750 --> 00:38:15,545 (eerie suspenseful music) 671 00:38:15,545 --> 00:38:18,785 The early plants, plants like these gorgeous ferns here, 672 00:38:18,785 --> 00:38:21,885 came up with a remarkable new structure. 673 00:38:21,885 --> 00:38:24,525 Large, flat surfaces that house within them 674 00:38:24,525 --> 00:38:26,920 a complex breathing apparatus. 675 00:38:28,305 --> 00:38:29,770 We call them leaves. 676 00:38:31,155 --> 00:38:34,300 (dramatic music) 677 00:38:35,035 --> 00:38:38,150 Leaves were the answer to all plants' breathing problems. 678 00:38:40,495 --> 00:38:42,865 They massively increased their surface area 679 00:38:42,865 --> 00:38:44,420 by over a hundredfold, 680 00:38:45,415 --> 00:38:48,290 allowing them to absorb far more carbon dioxide. 681 00:38:51,760 --> 00:38:53,380 Now, for the first time, 682 00:38:53,380 --> 00:38:56,960 shade was cast by a beautiful and delicate canopy, 683 00:38:57,715 --> 00:38:59,090 like these Dicksonia. 684 00:39:00,550 --> 00:39:02,470 These ferns are incredible. 685 00:39:03,020 --> 00:39:04,890 They're like giant umbrellas. 686 00:39:08,060 --> 00:39:10,820 The key to this advanced breathing apparatus 687 00:39:10,820 --> 00:39:13,560 is on the underside of each fern leaf. 688 00:39:14,600 --> 00:39:17,940 They're microscopic holes called stomata. 689 00:39:20,660 --> 00:39:23,570 Filmed in action with an electron microscope, 690 00:39:23,570 --> 00:39:26,158 this is them opening and closing. 691 00:39:26,998 --> 00:39:29,710 Speeded up 140 times. 692 00:39:29,710 --> 00:39:33,500 (eerie music) 693 00:39:38,800 --> 00:39:42,005 There are thousands of stomata on every leaf on Earth. 694 00:39:44,755 --> 00:39:47,980 They allow a single fern to breathe in five liters 695 00:39:47,980 --> 00:39:50,315 of carbon dioxide a day. 696 00:39:50,315 --> 00:39:54,435 (majestic music) 697 00:39:59,700 --> 00:40:03,285 The evolution of leaves, rich in stomata, 698 00:40:03,285 --> 00:40:05,320 saved plants from suffocation. 699 00:40:07,335 --> 00:40:10,540 But leaves also allow plants to capture more light. 700 00:40:12,880 --> 00:40:15,375 This in turn fueled fierce competition, 701 00:40:16,375 --> 00:40:18,930 each plant desperate for the sun's rays. 702 00:40:22,385 --> 00:40:26,220 This family squabble would lead to a new type of plant. 703 00:40:27,305 --> 00:40:30,525 One that would have surprising repercussions for the planet. 704 00:40:31,595 --> 00:40:34,140 (waves crashing) 705 00:40:34,140 --> 00:40:35,545 How do we know? 706 00:40:35,545 --> 00:40:38,155 Well, it's all thanks to some rare evidence here 707 00:40:38,155 --> 00:40:40,355 in Nova Scotia in Canada. 708 00:40:43,720 --> 00:40:46,445 To reach it, you have to abseil to the bottom 709 00:40:46,445 --> 00:40:48,225 of this 30 meter cliff. 710 00:40:50,045 --> 00:40:52,730 Here, scientists discovered the remains 711 00:40:52,730 --> 00:40:54,450 of a mysterious world. 712 00:40:55,955 --> 00:40:58,535 You know, this is just the best way to see rocks. 713 00:40:58,535 --> 00:41:01,340 You really feel as if you're a time traveler, 714 00:41:01,340 --> 00:41:03,390 peeling back the layers of history one by one 715 00:41:03,390 --> 00:41:04,345 as you go down. 716 00:41:04,965 --> 00:41:09,015 I mean, these rocks are over 300 million years old. 717 00:41:10,765 --> 00:41:13,015 But it's what's locked inside the rocks 718 00:41:13,015 --> 00:41:16,655 at the base of this cliff that took scientists' breath away. 719 00:41:20,185 --> 00:41:21,200 Ah. 720 00:41:22,660 --> 00:41:25,495 These fossilized remains are just spectacular! 721 00:41:25,495 --> 00:41:27,040 I mean, look at the texture. 722 00:41:27,040 --> 00:41:28,960 You can tell it's a plant but 723 00:41:28,960 --> 00:41:32,695 this isn't some big shrub or overgrown fern. 724 00:41:32,695 --> 00:41:36,460 You can see here, look, you can get traces of bark. 725 00:41:36,460 --> 00:41:39,385 And down here, you can see there are some roots coming off. 726 00:41:40,125 --> 00:41:42,720 This is completely extinct, you don't get this any more, 727 00:41:42,720 --> 00:41:44,550 but what I'm actually crouching beside 728 00:41:44,550 --> 00:41:47,560 is one of the planet's very early tree trunks. 729 00:41:47,965 --> 00:41:49,890 And not just one tree, because look here, 730 00:41:50,510 --> 00:41:52,230 there's another one here. 731 00:41:53,855 --> 00:41:55,065 There's another there. 732 00:41:57,020 --> 00:41:59,060 This is a fossil forest. 733 00:41:59,060 --> 00:42:01,325 (mysterious music) 734 00:42:02,155 --> 00:42:06,365 These Lepidodendron trees had strange diamond-shaped bark. 735 00:42:08,485 --> 00:42:11,240 Each diamond sprouting a needle-like leaf. 736 00:42:14,060 --> 00:42:17,715 Over 300 million years ago, they made up the planet's 737 00:42:17,715 --> 00:42:20,050 first tropical forests. 738 00:42:24,185 --> 00:42:28,870 (majestic music) 739 00:42:31,270 --> 00:42:33,970 Found in swamps throughout the Earth's tropics, 740 00:42:33,970 --> 00:42:36,565 these first forests were so extensive 741 00:42:36,565 --> 00:42:40,280 you'd have seen a band of dark green from space. 742 00:42:43,600 --> 00:42:47,570 And all those new leaves were pumping out oxygen, 743 00:42:48,490 --> 00:42:51,820 so much that levels of oxygen increased 744 00:42:51,820 --> 00:42:54,545 to not far off double what they are today. 745 00:42:58,255 --> 00:43:00,710 It was having a very odd effect on animals. 746 00:43:02,545 --> 00:43:05,420 In particular, insects and their cousins. 747 00:43:05,420 --> 00:43:08,350 (suspenseful music) 748 00:43:08,350 --> 00:43:12,220 Instead of lungs, invertebrates have simple breathing tubes 749 00:43:12,220 --> 00:43:14,480 that rely on diffusion for oxygen 750 00:43:14,480 --> 00:43:16,350 to reach their internal organs. 751 00:43:17,885 --> 00:43:20,180 The size of these animals is therefore limited 752 00:43:20,180 --> 00:43:22,860 by the concentration of oxygen in the air. 753 00:43:25,280 --> 00:43:28,700 Increase the oxygen, just as the first forest did, 754 00:43:28,700 --> 00:43:30,690 and things get interesting. 755 00:43:34,850 --> 00:43:37,205 Do you see these markings on the rock here? 756 00:43:37,205 --> 00:43:40,940 There's two lines of little dents, one here and one here. 757 00:43:41,505 --> 00:43:43,380 They are fossilized footprints 758 00:43:43,380 --> 00:43:45,930 that date back to the very early forests. 759 00:43:45,930 --> 00:43:47,305 When scientists first studied them 760 00:43:47,305 --> 00:43:48,335 they realized they weren't made 761 00:43:48,335 --> 00:43:50,720 by some reptile or amphibian. 762 00:43:50,720 --> 00:43:52,770 They were made by a millipede. 763 00:43:53,340 --> 00:43:58,330 Now, here is one of the biggest millipede species 764 00:43:58,330 --> 00:44:00,235 alive on Earth today. 765 00:44:01,100 --> 00:44:02,430 That's pretty big. 766 00:44:08,135 --> 00:44:10,025 Using the tracks for scale, 767 00:44:10,025 --> 00:44:12,665 it's clear the ancestors of this little fellow 768 00:44:12,665 --> 00:44:14,235 were massive. 769 00:44:15,515 --> 00:44:18,120 (eerie music) 770 00:44:22,250 --> 00:44:25,960 Called Arthropleuridea, it was over 2 meters long. 771 00:44:29,140 --> 00:44:31,845 The forests would have been terrifying 772 00:44:33,260 --> 00:44:36,600 with giant scorpions and giant spiders. 773 00:44:40,925 --> 00:44:42,315 And not just on the land. 774 00:44:43,685 --> 00:44:46,815 I think the most impressive of all were the dragonflies. 775 00:44:47,735 --> 00:44:49,775 I mean, most modern dragonflies have wing spans 776 00:44:49,775 --> 00:44:52,785 up to 10 centimeters across, but back then, 777 00:44:52,785 --> 00:44:54,325 they were way larger. 778 00:44:54,610 --> 00:44:57,125 Some were up to a meter across. 779 00:45:05,640 --> 00:45:07,205 These Meganeura 780 00:45:07,205 --> 00:45:11,040 were the largest insects ever to take to the skies. 781 00:45:11,040 --> 00:45:12,760 (insect wings fluttering) 782 00:45:14,130 --> 00:45:17,770 But in this oversize world pumped with oxygen, 783 00:45:17,770 --> 00:45:21,020 the plant kingdom still reigned supreme. 784 00:45:21,020 --> 00:45:23,210 (waves crashing) 785 00:45:23,210 --> 00:45:26,315 Then, 230 million years ago, 786 00:45:26,315 --> 00:45:28,820 a new group of animals emerged from the shadows 787 00:45:28,820 --> 00:45:30,480 of the swampy forests. 788 00:45:30,980 --> 00:45:34,115 They would become the largest creatures to roam the Earth, 789 00:45:34,115 --> 00:45:35,870 and they were ready to do battle 790 00:45:35,870 --> 00:45:37,785 with the kingdom of the plants. 791 00:45:38,330 --> 00:45:41,040 I'm talking, of course, of dinosaurs. 792 00:45:41,870 --> 00:45:44,285 (dinosaur roaring) 793 00:45:44,285 --> 00:45:45,875 (suspenseful music) 794 00:45:45,875 --> 00:45:48,165 It's the meat-eaters that get all the press. 795 00:45:48,165 --> 00:45:51,175 (dinosaur roaring) 796 00:45:51,175 --> 00:45:52,960 But recent research has revealed 797 00:45:52,960 --> 00:45:56,185 that out of the 700 species discovered, 798 00:45:56,185 --> 00:45:58,895 over two-thirds were herbivores. 799 00:45:58,895 --> 00:46:00,935 (epic music) 800 00:46:00,935 --> 00:46:02,550 Vegetarians ruled, 801 00:46:03,815 --> 00:46:06,545 led by the biggest herbivores in history, 802 00:46:06,545 --> 00:46:08,475 the sauropods. 803 00:46:08,475 --> 00:46:10,615 (growling) 804 00:46:12,660 --> 00:46:15,240 To discover the impact of these huge dinosaurs 805 00:46:15,240 --> 00:46:16,650 on the plant kingdom, 806 00:46:16,650 --> 00:46:20,150 I've come to an animal sanctuary to see it in the flesh. 807 00:46:20,150 --> 00:46:23,285 (rustling noise) 808 00:46:23,835 --> 00:46:27,090 Unfortunately, this place doesn't have a living sauropod, 809 00:46:27,090 --> 00:46:29,955 but what it does have is the biggest herbivore 810 00:46:29,955 --> 00:46:31,795 that the planet's got to offer. 811 00:46:32,250 --> 00:46:33,625 the African elephant. 812 00:46:34,000 --> 00:46:35,510 Come and meet Butch. 813 00:46:37,075 --> 00:46:39,010 This beautiful four-tonne elephant 814 00:46:39,010 --> 00:46:42,265 can help me truly appreciate the staggering size 815 00:46:42,265 --> 00:46:43,640 of the dinosaurs. 816 00:46:48,835 --> 00:46:50,560 (engine purring) 817 00:46:50,560 --> 00:46:51,860 Can we go up? 818 00:46:53,110 --> 00:46:55,775 (engine reving) 819 00:46:55,775 --> 00:46:59,900 Now Butch here is about as big as a big African bull gets, 820 00:46:59,900 --> 00:47:04,575 and that's already four meters high, 821 00:47:05,960 --> 00:47:08,040 but if we want to get to the height of a sauropod, 822 00:47:08,040 --> 00:47:09,745 we have to go much higher. 823 00:47:10,385 --> 00:47:11,625 Six meters. 824 00:47:11,625 --> 00:47:12,970 We've got to be higher than that. 825 00:47:13,885 --> 00:47:15,500 We're now at eight meters. 826 00:47:15,500 --> 00:47:17,177 We've still got to go higher. 827 00:47:18,170 --> 00:47:20,225 Where are we at, ten meters now? 828 00:47:20,225 --> 00:47:21,660 A bit higher than that. 829 00:47:21,660 --> 00:47:23,920 We're still not at the height of a sauropod yet. 830 00:47:24,720 --> 00:47:26,470 Okay, we're getting there, nearly. 831 00:47:27,600 --> 00:47:29,260 Okay, fine. 832 00:47:29,260 --> 00:47:30,475 (engine sputtering) 833 00:47:30,475 --> 00:47:32,055 (elephant growling) 834 00:47:32,055 --> 00:47:34,765 So my head's now about 12 meters, 835 00:47:34,765 --> 00:47:37,730 which is about the height of a four-storey building 836 00:47:37,730 --> 00:47:41,200 and then also the height of a sauropod. 837 00:47:41,200 --> 00:47:44,040 The thing is, on the end of a nine-meter neck, 838 00:47:44,785 --> 00:47:47,405 this is the skull of a sauropod. 839 00:47:49,465 --> 00:47:51,295 It seems quite small. 840 00:47:51,295 --> 00:47:53,465 But the point was that this had to be 841 00:47:53,465 --> 00:47:55,970 maneuverable and nimble to get right up at that 842 00:47:55,970 --> 00:47:57,585 high-level foliage. 843 00:48:00,470 --> 00:48:03,435 Sauropods were like nothing else the planet had ever seen. 844 00:48:05,130 --> 00:48:07,810 They weighed more than 10 times an African elephant. 845 00:48:10,305 --> 00:48:12,805 Now, Butch here eats about 90 kilograms 846 00:48:12,805 --> 00:48:14,605 of foliage every day, 847 00:48:14,605 --> 00:48:16,900 which is roughly about that much hay. 848 00:48:16,900 --> 00:48:19,570 But scientists have estimated that sauropods 849 00:48:19,570 --> 00:48:23,780 ate about 1,500 kilograms of hay every day. 850 00:48:23,780 --> 00:48:27,030 In other words, about 20 times that daily diet. 851 00:48:27,740 --> 00:48:30,150 Or 50 bales of hay. 852 00:48:30,830 --> 00:48:34,610 Now if you imagine you've got herds of about 30 sauropods, 853 00:48:34,610 --> 00:48:37,220 much bigger than these beasts here, 854 00:48:37,220 --> 00:48:38,930 and you realize that the plant kingdom 855 00:48:38,930 --> 00:48:42,045 was up against the ultimate salad predator. 856 00:48:42,965 --> 00:48:45,490 (suspenseful music) 857 00:48:45,490 --> 00:48:48,095 150 million years ago, 858 00:48:48,095 --> 00:48:50,060 dinosaurs were stripping the land 859 00:48:50,060 --> 00:48:52,310 of vast swathes of foliage. 860 00:48:52,310 --> 00:48:54,105 (cracking noise) 861 00:48:54,105 --> 00:48:56,355 For the first time, the plant kingdom 862 00:48:56,355 --> 00:48:59,605 was under serious attack from another dynasty. 863 00:49:02,610 --> 00:49:05,070 To fight back, plants began to evolve 864 00:49:05,070 --> 00:49:08,250 a whole arsenal of defenses for their precious leaves. 865 00:49:08,250 --> 00:49:11,545 (suspenseful orchestra music) 866 00:49:11,545 --> 00:49:14,755 Here in California, we can see just how intense 867 00:49:14,755 --> 00:49:16,420 this arms race was 868 00:49:16,420 --> 00:49:19,415 in one of the world's most unusual gardens. 869 00:49:21,505 --> 00:49:24,925 It's full of a group of bizarre and extremely rare plants 870 00:49:24,925 --> 00:49:26,435 called cycads. 871 00:49:27,290 --> 00:49:30,635 But once, they made up a quarter of all plants on Earth. 872 00:49:30,635 --> 00:49:35,145 (suspenseful orchestra music) 873 00:49:36,185 --> 00:49:37,695 This is incredible. 874 00:49:39,405 --> 00:49:41,940 Exactly the kind of place you'd expect a dinosaur 875 00:49:41,940 --> 00:49:43,285 just to pop out. 876 00:49:46,905 --> 00:49:49,350 To stave off attack from those ravenous dinosaurs, 877 00:49:49,350 --> 00:49:52,200 cycads developed some clever lines of defense, 878 00:49:52,200 --> 00:49:55,035 and the most obvious being physical weapons 879 00:49:55,035 --> 00:49:57,245 like needles and spikes and, agh! 880 00:49:58,585 --> 00:49:59,960 These are vicious. 881 00:50:00,245 --> 00:50:01,970 The main point was to make leaves 882 00:50:01,970 --> 00:50:04,805 as painful as possible to eat. 883 00:50:04,805 --> 00:50:08,055 (electric guitar riff) 884 00:50:08,870 --> 00:50:11,550 (epic rock music) 885 00:50:12,645 --> 00:50:16,045 These defenses came in all shapes and sizes. 886 00:50:20,025 --> 00:50:24,235 And some plants also spiced things up with chemical weapons. 887 00:50:29,445 --> 00:50:32,400 This is a Trapps Valley cycad from South Africa, 888 00:50:32,400 --> 00:50:34,785 but it's pretty typical in that the leaves contain 889 00:50:34,785 --> 00:50:36,705 a nerve agent that if you ingest it, 890 00:50:36,705 --> 00:50:39,960 it causes vomiting, diarrhea, paralysis of the limbs 891 00:50:39,960 --> 00:50:42,215 and then, of course, death. 892 00:50:42,760 --> 00:50:45,160 Obviously, I'm not going to eat one of the leaves, 893 00:50:45,160 --> 00:50:47,800 but I can eat a plant whose ancestors emerged 894 00:50:47,800 --> 00:50:49,465 around the time of the dinosaurs, 895 00:50:49,465 --> 00:50:52,345 and who also have a chemical weapon, and that is 896 00:50:53,880 --> 00:50:55,015 a chili. 897 00:50:56,190 --> 00:50:58,480 In particular, a habaneros chili, 898 00:50:59,815 --> 00:51:01,895 which is supposed to be one of the most 899 00:51:01,895 --> 00:51:03,105 powerful in the world. 900 00:51:05,280 --> 00:51:07,575 There's a chemical in here called capsicum 901 00:51:08,860 --> 00:51:11,440 that is contained in the fruit. 902 00:51:13,655 --> 00:51:15,855 And that essentially is a toxin. 903 00:51:17,120 --> 00:51:18,375 (chuckles) 904 00:51:19,460 --> 00:51:20,670 Ah! 905 00:51:24,290 --> 00:51:27,335 Which is, at this precise moment, 906 00:51:27,335 --> 00:51:31,050 burning and inflaming all of my mouth. 907 00:51:32,225 --> 00:51:33,305 Oh, my gosh! 908 00:51:37,730 --> 00:51:40,355 The thing is, the toxins in the cycads, right, 909 00:51:40,355 --> 00:51:43,730 they were far more powerful even than the chilis. 910 00:51:44,730 --> 00:51:45,820 Oh, my gosh! 911 00:51:47,175 --> 00:51:48,930 So you can imagine what 912 00:51:48,930 --> 00:51:50,780 the dinosaurs would have had to endure. 913 00:51:50,780 --> 00:51:51,860 Oh, my. 914 00:51:52,485 --> 00:51:53,655 I'm going to have to... 915 00:51:59,525 --> 00:52:00,900 Ah! 916 00:52:02,430 --> 00:52:04,165 Can't even say how sore that is! 917 00:52:05,760 --> 00:52:06,880 Ahhh! 918 00:52:08,295 --> 00:52:09,460 Mmmm. 919 00:52:11,680 --> 00:52:12,965 Eat a chili, they said. 920 00:52:14,725 --> 00:52:16,175 It'll be funny, they said. 921 00:52:17,105 --> 00:52:18,390 Mmmm. 922 00:52:19,100 --> 00:52:20,565 You know what, forget about cycads. 923 00:52:20,565 --> 00:52:23,020 That could have brought down a 70-tonne sauropod. 924 00:52:28,030 --> 00:52:30,245 And the arms race didn't stop there. 925 00:52:31,370 --> 00:52:33,320 Plants evolved a new tactic. 926 00:52:35,250 --> 00:52:37,575 Not so much a line of defense 927 00:52:38,365 --> 00:52:40,280 as a line of communication. 928 00:52:45,760 --> 00:52:47,965 We know that when some plants are attacked 929 00:52:47,965 --> 00:52:51,755 they activate a quick-acting toxin that deters herbivores. 930 00:52:53,725 --> 00:52:57,290 Now we're discovering that this defense goes even further, 931 00:52:58,645 --> 00:53:01,225 because plants can actually warn other plants 932 00:53:01,225 --> 00:53:03,020 that a herbivore is eating them. 933 00:53:08,320 --> 00:53:11,860 And at last, scientists here at Exeter University 934 00:53:11,860 --> 00:53:14,945 are beginning to listen in to this hidden conversation. 935 00:53:19,795 --> 00:53:22,165 They're finding that when plants are attacked, 936 00:53:22,165 --> 00:53:25,340 they also release an unseen gas from their leaves. 937 00:53:27,415 --> 00:53:29,090 What it does is extraordinary. 938 00:53:31,885 --> 00:53:35,035 And this will be the first time it's been captured on film 939 00:53:35,035 --> 00:53:36,645 using specialist imagery. 940 00:53:38,390 --> 00:53:40,850 These two Arabidopsis plants are being put 941 00:53:40,850 --> 00:53:42,255 inside a chamber. 942 00:53:44,935 --> 00:53:47,890 A third plant is then cut to mimic an attack. 943 00:53:47,890 --> 00:53:50,780 (suspenseful music) 944 00:53:55,240 --> 00:53:57,200 It's added to the undamaged plants. 945 00:54:01,900 --> 00:54:03,500 The chamber is sealed. 946 00:54:14,055 --> 00:54:16,300 The plant leaves are now releasing the gas. 947 00:54:19,260 --> 00:54:21,765 As they do so, their biological activity 948 00:54:21,765 --> 00:54:23,305 can be seen changing. 949 00:54:29,395 --> 00:54:32,030 Something remarkable happens. 950 00:54:33,355 --> 00:54:36,430 The gas triggers a change in the biological activity 951 00:54:36,430 --> 00:54:38,495 in the two neighboring plants. 952 00:54:44,455 --> 00:54:46,415 They have detected the message warning them 953 00:54:46,415 --> 00:54:48,090 to protect themselves. 954 00:54:49,490 --> 00:54:52,545 (buzzing) 955 00:54:57,975 --> 00:54:59,715 Scientists don't know all the details 956 00:54:59,715 --> 00:55:01,215 of this plant language, 957 00:55:01,215 --> 00:55:04,095 but increasingly, they believe there's a chatter 958 00:55:04,095 --> 00:55:06,025 between plants all around us. 959 00:55:09,570 --> 00:55:11,190 I think most people assume that plants 960 00:55:11,190 --> 00:55:13,230 lead a rather passive life, 961 00:55:13,230 --> 00:55:15,900 that they're static and unresponsive. 962 00:55:15,900 --> 00:55:17,445 But that's just not true. 963 00:55:17,445 --> 00:55:21,430 In reality, they move, they sense, they communicate. 964 00:55:22,360 --> 00:55:24,530 It's almost as if they show a kind of intelligence. 965 00:55:25,870 --> 00:55:30,040 (rock music) 966 00:55:30,040 --> 00:55:34,415 For 200 million years, the dinosaurs and the plants 967 00:55:34,415 --> 00:55:37,835 were locked in a titanic evolutionary battle, 968 00:55:38,640 --> 00:55:41,215 each trying to gain the upper hand. 969 00:55:41,215 --> 00:55:43,040 (dinosaurs roaring) 970 00:55:44,350 --> 00:55:48,000 But it was now that some plants played their trump card. 971 00:55:50,900 --> 00:55:52,800 (gear clicking) 972 00:55:57,440 --> 00:56:00,570 They used wood to grow taller and taller. 973 00:56:03,695 --> 00:56:06,405 And in California's Sierra Nevada, 974 00:56:06,405 --> 00:56:08,830 I'm about to find out just how tall. 975 00:56:12,120 --> 00:56:15,970 To do that, I need the help of biologist Jim Spickler. 976 00:56:19,515 --> 00:56:21,175 I'm as ready as I'll ever be. 977 00:56:21,175 --> 00:56:23,590 Take your time, I mean, we've got some time. 978 00:56:23,590 --> 00:56:25,055 Absolutely. 979 00:56:26,260 --> 00:56:29,270 (eerie music) 980 00:56:32,855 --> 00:56:35,820 This is the grandest example of them all. 981 00:56:36,650 --> 00:56:38,175 The giant sequoia. 982 00:56:40,400 --> 00:56:41,780 What you see is just impossible 983 00:56:41,780 --> 00:56:43,020 for your mind to process. 984 00:56:43,020 --> 00:56:44,400 The scale is so large. 985 00:56:45,080 --> 00:56:46,595 It's extraordinary. 986 00:56:47,445 --> 00:56:49,290 I feel as if I'm in Lord of the Rings. 987 00:56:50,375 --> 00:56:51,870 (grunting) 988 00:56:53,165 --> 00:56:56,415 (eerie music) 989 00:57:10,770 --> 00:57:12,310 Ah, what a great tree! 990 00:57:15,435 --> 00:57:17,565 70 million years ago, 991 00:57:17,565 --> 00:57:21,150 the ancestors of this type of tree, the conifers, 992 00:57:21,150 --> 00:57:22,735 got ever taller. 993 00:57:24,910 --> 00:57:27,950 This was the ultimate in plant construction. 994 00:57:29,740 --> 00:57:31,450 Conifers like the giant sequoias 995 00:57:31,450 --> 00:57:34,535 raised their precious leaves out of reach. 996 00:57:37,120 --> 00:57:40,615 The dinosaurs were no longer the biggest organisms on Earth. 997 00:57:41,885 --> 00:57:45,260 That title had been well and truly won back 998 00:57:45,260 --> 00:57:47,640 by these giants of the plant kingdom. 999 00:57:50,840 --> 00:57:53,840 This is so tall, but I've still got... 1000 00:57:53,840 --> 00:57:56,025 I don't know, another third to go. 1001 00:57:56,025 --> 00:57:59,405 The thing is, by using wood to grow really tall like this, 1002 00:57:59,405 --> 00:58:02,525 it gave trees another advantage over plants 1003 00:58:02,525 --> 00:58:04,110 because it allowed them first pick of the sun's 1004 00:58:04,110 --> 00:58:05,485 strongest rays. 1005 00:58:05,485 --> 00:58:07,690 The thing is, of course, for plants, 1006 00:58:07,690 --> 00:58:09,785 light means success. 1007 00:58:11,035 --> 00:58:14,960 (majestic music) 1008 00:58:14,960 --> 00:58:17,795 If you had a satellite image of the dinosaur era 1009 00:58:17,795 --> 00:58:19,925 70 million years ago, 1010 00:58:19,925 --> 00:58:22,800 you'd see the Earth like it had never been before, 1011 00:58:23,330 --> 00:58:24,795 and never would be again. 1012 00:58:27,215 --> 00:58:30,675 The climate was so warm, the poles had no ice. 1013 00:58:32,180 --> 00:58:34,350 Instead, they were covered with conifers, 1014 00:58:34,940 --> 00:58:37,015 a vast polar forest. 1015 00:58:39,525 --> 00:58:42,300 And the mighty sequoia trees were not just found 1016 00:58:42,300 --> 00:58:45,820 in small areas of the Sierra Nevada, as they are today. 1017 00:58:46,830 --> 00:58:48,115 They were global, 1018 00:58:48,735 --> 00:58:52,210 stretching along the Pacific coast and as far south 1019 00:58:52,210 --> 00:58:53,530 as Australia. 1020 00:58:53,530 --> 00:58:55,785 (majestic music) 1021 00:58:55,785 --> 00:58:58,840 How far are we from the top, then? 1022 00:58:58,840 --> 00:59:00,080 We're getting close. 1023 00:59:00,080 --> 00:59:01,335 (grunting) 1024 00:59:03,635 --> 00:59:05,280 Ah, it's extraordinary. 1025 00:59:09,345 --> 00:59:10,965 This is it. 1026 00:59:10,965 --> 00:59:12,895 This is the top of the tree. 1027 00:59:12,895 --> 00:59:14,095 Wooh! 1028 00:59:14,095 --> 00:59:15,890 (epic orchestra music) 1029 00:59:15,890 --> 00:59:17,640 Unbelievable! 1030 00:59:17,640 --> 00:59:20,725 (epic orchestra music) 1031 00:59:23,185 --> 00:59:26,865 It's staggering to think that using just a gas, 1032 00:59:26,865 --> 00:59:28,395 carbon dioxide; 1033 00:59:28,395 --> 00:59:30,690 and a liquid, water, 1034 00:59:30,690 --> 00:59:34,000 together with light energy from beyond our world, 1035 00:59:34,540 --> 00:59:39,215 you can construct a cathedral of wood 90 meters tall. 1036 00:59:47,710 --> 00:59:49,515 Since they first appeared, 1037 00:59:49,515 --> 00:59:53,290 plants and their ancestors have revolutionized our planet. 1038 00:59:53,290 --> 00:59:55,550 (explosion) 1039 00:59:56,225 --> 00:59:58,880 They created oxygen for the atmosphere, 1040 00:59:58,880 --> 01:00:02,135 (epic orchestra music) 1041 01:00:02,135 --> 01:00:04,280 which would allow them to conquer the land 1042 01:00:04,280 --> 01:00:06,900 and transform rock into soil, 1043 01:00:09,065 --> 01:00:12,205 in turn, fueling the explosion of all life. 1044 01:00:14,040 --> 01:00:16,330 From a barren, alien planet, 1045 01:00:17,040 --> 01:00:18,955 plants have made a living Earth. 1046 01:00:20,130 --> 01:00:21,660 And left on its own, 1047 01:00:21,660 --> 01:00:24,165 the world would have continued like this, 1048 01:00:24,165 --> 01:00:28,545 dominated by large dinosaurs and endless forests. 1049 01:00:29,585 --> 01:00:31,080 But 65 million years ago, 1050 01:00:31,080 --> 01:00:33,130 something happened that would change everything. 1051 01:00:33,130 --> 01:00:36,010 A chance event that would have dramatic consequences 1052 01:00:36,010 --> 01:00:38,095 not just for plants but for all life, 1053 01:00:38,815 --> 01:00:42,860 and it would originate not on Earth, but in outer space. 1054 01:00:42,860 --> 01:00:45,065 (wooshing rumbling noise) 1055 01:00:45,065 --> 01:00:46,935 (explosion) 1056 01:00:52,145 --> 01:00:54,860 The asteroid would kill off the dinosaurs, 1057 01:00:54,860 --> 01:00:58,325 and the next chapter would see the triumph of a whole new 1058 01:00:58,325 --> 01:00:59,820 group of plants. 1059 01:01:03,410 --> 01:01:06,920 Flowers transform the bond between animal and plant, 1060 01:01:07,875 --> 01:01:11,140 even sculpting the very planet itself. 1061 01:01:12,465 --> 01:01:16,425 Above all, plants would drive our human story. 1062 01:01:16,425 --> 01:01:19,015 But all that was still to come. 1063 01:01:19,015 --> 01:01:21,680 (uplifting music)