1 00:00:23,200 --> 00:00:28,300 The heavens. The great bowl of the heavens, of our sky. 2 00:00:29,400 --> 00:00:32,000 Just so beautiful! 3 00:00:32,000 --> 00:00:36,460 I love the sky because, wherever I am in the world, if I can find 4 00:00:36,460 --> 00:00:39,860 some space, I can look up at this 5 00:00:39,860 --> 00:00:43,780 big, blue, pristine space. 6 00:00:47,700 --> 00:00:53,140 And I like the apparent permanence - the fact that I can stare into 7 00:00:53,140 --> 00:00:57,900 a sky that the dinosaurs stared into, that Neanderthals stared into. 8 00:01:00,260 --> 00:01:04,820 The atmosphere is essential for the Earth to be habitable at all. 9 00:01:06,140 --> 00:01:10,500 This thin layer of gas that clings to our planet, 10 00:01:10,500 --> 00:01:14,300 keeps liquid water on the Earth's surface 11 00:01:14,300 --> 00:01:18,620 and shields life from the most harmful of the sun's rays. 12 00:01:21,540 --> 00:01:25,300 As far as we know, our thin blue line is unique 13 00:01:25,300 --> 00:01:27,660 in the vast void of space... 14 00:01:30,460 --> 00:01:33,860 ..and today, scientists are beginning to piece 15 00:01:33,860 --> 00:01:37,540 together just how our planet got its special blue bubble. 16 00:01:46,260 --> 00:01:49,780 By going back to the Earth's earliest origins, 17 00:01:49,780 --> 00:01:55,220 we can now tell the almost implausible story of our atmosphere. 18 00:01:59,860 --> 00:02:03,860 How it emerged from a toxic orange hell... 19 00:02:05,860 --> 00:02:09,820 ..and transformed the planet from an exposed ball of rock... 20 00:02:12,900 --> 00:02:15,060 ..to a beautiful, living world... 21 00:02:16,620 --> 00:02:20,700 ..capable of nurturing a staggering abundance of life. 22 00:02:24,420 --> 00:02:29,260 This atmosphere has been the planet's great protector 23 00:02:29,260 --> 00:02:32,140 for 2.5 billion years, 24 00:02:32,140 --> 00:02:36,020 soaking up everything that our planet has thrown at it. 25 00:02:37,500 --> 00:02:42,380 It's a thin, delicate, fragile cloak that shields 26 00:02:42,380 --> 00:02:46,420 and protects all life on Earth. 27 00:03:22,180 --> 00:03:26,660 Our atmosphere is a unique mix of gasses not found anywhere 28 00:03:26,660 --> 00:03:28,900 else in the solar system, 29 00:03:28,900 --> 00:03:33,100 gasses that allow Earth to be a living, breathing world. 30 00:03:40,020 --> 00:03:45,180 78% of our atmosphere is nitrogen, which can be taken up by 31 00:03:45,180 --> 00:03:50,220 bacteria in the soil and plants, and it's an integral part of DNA. 32 00:03:50,220 --> 00:03:53,460 21% of our atmosphere is oxygen. 33 00:03:53,460 --> 00:03:57,100 It's there for animals to breathe, but also for many living things 34 00:03:57,100 --> 00:03:59,780 to use to convert their food into energy. 35 00:04:01,860 --> 00:04:05,500 Even less abundant gasses are crucial for sustaining life. 36 00:04:07,540 --> 00:04:11,780 A fraction of a percent is water vapour, which condenses 37 00:04:11,780 --> 00:04:13,460 and falls as rain, 38 00:04:13,460 --> 00:04:16,740 and a tiny amount is carbon dioxide, 39 00:04:16,740 --> 00:04:20,460 which might be a waste product to us but it's absolutely 40 00:04:20,460 --> 00:04:24,260 essential for plants when it comes to photosynthesis. 41 00:04:24,260 --> 00:04:29,180 It almost appears that this unique cocktail of gasses 42 00:04:29,180 --> 00:04:32,620 is here as a sort of life-support system. 43 00:04:35,540 --> 00:04:39,100 So, where did this beautiful atmosphere come from 44 00:04:39,100 --> 00:04:42,460 and how did it lead to the origins of life here? 45 00:04:46,540 --> 00:04:49,740 Well, to answer that, we need to go back to the very beginning... 46 00:04:56,940 --> 00:04:59,820 ..4.6 billion years ago. 47 00:05:07,780 --> 00:05:12,260 Our Earth began as nothing more than dust and gas. 48 00:05:15,220 --> 00:05:20,460 A nebulous cloud containing every element our new world would need. 49 00:05:24,460 --> 00:05:29,740 Over tens of millions of years, the cloud begins to clump together, 50 00:05:29,740 --> 00:05:31,980 forming rocks. 51 00:05:31,980 --> 00:05:34,220 Pulled together by gravity... 52 00:05:35,700 --> 00:05:38,420 ..they grow bigger and bigger... 53 00:05:43,420 --> 00:05:47,140 ..until, finally, a new world is formed. 54 00:05:57,620 --> 00:06:01,340 Asteroids rain down on the young Earth 55 00:06:01,340 --> 00:06:04,540 for hundreds of millions of years... 56 00:06:07,300 --> 00:06:11,940 ..its molten surface still searing from the heat of its creation. 57 00:06:24,220 --> 00:06:26,340 But something is missing. 58 00:06:28,900 --> 00:06:30,620 The colour blue. 59 00:06:36,780 --> 00:06:40,140 You see, the Earth has no atmosphere. 60 00:06:41,980 --> 00:06:47,620 The sun and the newly formed moon sit in a jet-black sky. 61 00:06:55,100 --> 00:06:57,780 This is how the Earth could have remained... 62 00:07:03,660 --> 00:07:08,620 ..a lifeless ball of rock, floating in the void of space. 63 00:07:22,740 --> 00:07:25,260 This is what the surface of the Earth may have 64 00:07:25,260 --> 00:07:28,380 looked like 4 billion years ago. 65 00:07:29,820 --> 00:07:32,060 Stark, brutal and yet, 66 00:07:32,060 --> 00:07:35,620 in some ways, beautiful landscape. 67 00:07:38,180 --> 00:07:43,340 The early Earth was little more than a ball of cooling rock, 68 00:07:43,340 --> 00:07:46,700 so where did the planet's first atmosphere come from? 69 00:07:48,780 --> 00:07:53,020 Now it might surprise you, but I've got some clues to the answer 70 00:07:53,020 --> 00:07:56,700 to that question in my pocket, 71 00:07:56,700 --> 00:07:59,660 in the form of this tiny, 72 00:07:59,660 --> 00:08:05,860 but extremely rare and valuable, granular piece of rock. 73 00:08:05,860 --> 00:08:12,020 This, you see, is a carbonaceous chondrite meteorite, 74 00:08:12,020 --> 00:08:17,940 and it was formed at the same time our solar system was formed - 75 00:08:17,940 --> 00:08:20,140 and I've got it in my hand! 76 00:08:20,140 --> 00:08:24,660 I am holding the history of our solar system 77 00:08:24,660 --> 00:08:26,700 and the Earth in my hand. 78 00:08:28,420 --> 00:08:33,620 4.5 billion years ago, trillions of tonnes of this 79 00:08:33,620 --> 00:08:38,940 type of material came together to form our planet. 80 00:08:40,580 --> 00:08:44,700 These meteorites are leftovers from the Earth's creation. 81 00:08:45,780 --> 00:08:48,140 So, through chemical analysis, 82 00:08:48,140 --> 00:08:53,140 scientists can discover the raw ingredients that made our world. 83 00:08:56,060 --> 00:08:59,780 These meteorites contain heavy elements, like iron, 84 00:08:59,780 --> 00:09:03,780 and the rocky constituents that formed the planet itself. 85 00:09:05,700 --> 00:09:09,620 But chondrite meteorites contain lighter elements too. 86 00:09:11,460 --> 00:09:16,380 Chemical analysis reveals that these rocks contain carbon, 87 00:09:16,380 --> 00:09:18,260 hydrogen and sulphur, 88 00:09:18,260 --> 00:09:21,780 and we can still see them belching as gasses 89 00:09:21,780 --> 00:09:24,420 from volcanic vents around the world today. 90 00:09:27,060 --> 00:09:32,300 When combined, these elements form new compounds like methane, 91 00:09:32,300 --> 00:09:36,820 carbon dioxide and hydrogen sulphide, 92 00:09:36,820 --> 00:09:40,740 which are light enough to exist as gasses 93 00:09:40,740 --> 00:09:44,140 but not so light they drift off into space. 94 00:09:46,060 --> 00:09:49,380 So, meteorites like this weren't just the 95 00:09:49,380 --> 00:09:50,980 building blocks of our planet - 96 00:09:50,980 --> 00:09:55,940 they contained the essential ingredients for its atmosphere. 97 00:09:55,940 --> 00:09:58,700 And 4.5 billion years ago, 98 00:09:58,700 --> 00:10:02,100 that had begun to change everything. 99 00:10:18,700 --> 00:10:21,340 The ancient Earth holds within it 100 00:10:21,340 --> 00:10:24,820 everything it needs to create the first atmosphere. 101 00:10:28,940 --> 00:10:32,740 Those ingredients just have to make it to the surface. 102 00:10:40,020 --> 00:10:44,460 But deep within the young Earth, something is stirring. 103 00:11:03,220 --> 00:11:08,580 Across the globe, molten magma races up from within... 104 00:11:13,020 --> 00:11:17,180 ..and these rivers of liquid fire unleash gasses that will 105 00:11:17,180 --> 00:11:19,380 transform our planet. 106 00:11:35,900 --> 00:11:40,500 The world is smothered by a thick toxic fog. 107 00:11:58,420 --> 00:12:02,180 As the sun creeps above the horizon, 108 00:12:02,180 --> 00:12:04,700 gas scatters the light. 109 00:12:08,500 --> 00:12:12,420 Earth gets its first colour-filled sunrise. 110 00:12:15,820 --> 00:12:20,420 This new world now has an atmosphere... 111 00:12:26,180 --> 00:12:28,820 ..but one like nothing we've ever seen. 112 00:12:41,260 --> 00:12:45,860 We're all familiar with the colours in the early-morning sky, 113 00:12:45,860 --> 00:12:50,540 but a sunrise 4 billion years ago would have been very different. 114 00:12:50,540 --> 00:12:55,060 Sunlight passing through that churning mixture of methane 115 00:12:55,060 --> 00:12:59,620 and carbon dioxide would have given the whole planet an orange hue. 116 00:13:00,940 --> 00:13:03,820 But this toxic atmosphere was very important. 117 00:13:03,820 --> 00:13:06,900 It was the first time that our planet had 118 00:13:06,900 --> 00:13:09,860 a protective shield from space. 119 00:13:09,860 --> 00:13:12,980 But, of course, it was still a very alien world - 120 00:13:12,980 --> 00:13:16,900 would have been to us - and not just because of that noxious 121 00:13:16,900 --> 00:13:22,020 orange fog, or the searing, hot, black, bare volcanic rocks 122 00:13:22,020 --> 00:13:23,260 beneath our feet. 123 00:13:23,260 --> 00:13:25,940 It was because something fundamental, 124 00:13:25,940 --> 00:13:29,380 something that we take for granted every day, was missing. 125 00:13:32,340 --> 00:13:33,500 Water. 126 00:13:45,220 --> 00:13:49,540 Today, 70% of the Earth's surface is covered in water. 127 00:13:52,140 --> 00:13:55,020 A planet of almost limitless blue... 128 00:13:58,180 --> 00:13:59,740 ..with endless rivers... 129 00:14:01,420 --> 00:14:02,780 ..freezing ice caps... 130 00:14:04,460 --> 00:14:06,580 ..and turquoise tropical paradises. 131 00:14:22,780 --> 00:14:24,900 But 4.5 billion years ago... 132 00:14:27,220 --> 00:14:31,220 ..there wasn't a single drop of liquid water 133 00:14:31,220 --> 00:14:33,220 on the ancient Earth's surface. 134 00:14:42,820 --> 00:14:45,900 However, the planet wasn't totally dry. 135 00:14:49,060 --> 00:14:52,460 The young atmosphere did contain water. 136 00:14:54,260 --> 00:14:58,220 Asteroids and volcanic eruptions have released a vast 137 00:14:58,220 --> 00:14:59,940 ocean of water vapour. 138 00:15:09,660 --> 00:15:12,620 Trillions of droplets were floating in the sky... 139 00:15:23,660 --> 00:15:27,340 ..so small they soar on moving air. 140 00:15:35,700 --> 00:15:39,980 Colliding and merging with each other, they slowly grow... 141 00:15:43,380 --> 00:15:48,100 ..until they can no longer fight Earth's gravity. 142 00:15:56,740 --> 00:16:00,340 En masse, they are pulled downwards, towards the ground. 143 00:16:11,260 --> 00:16:15,060 But with the atmosphere still scorchingly hot from heat 144 00:16:15,060 --> 00:16:16,700 trapped by Earth's formation... 145 00:16:18,820 --> 00:16:21,140 ..not a single drop of rain... 146 00:16:25,140 --> 00:16:27,820 ..has ever made it to the surface. 147 00:16:31,060 --> 00:16:37,100 And it's been the same story every day for tens of millions of years. 148 00:16:39,100 --> 00:16:43,180 The Earth is stuck - a barren desert world 149 00:16:43,180 --> 00:16:46,860 totally incapable of supporting life. 150 00:16:53,700 --> 00:16:56,780 Water today is on a continual journey. 151 00:16:59,180 --> 00:17:03,420 It emerges from the leaves of green plants as vapour, 152 00:17:03,420 --> 00:17:06,660 rises up to the sky, where it forms clouds, 153 00:17:06,660 --> 00:17:08,980 which then condense into rain, 154 00:17:08,980 --> 00:17:12,140 which falls onto the ground, which drains into the rivers, 155 00:17:12,140 --> 00:17:16,580 which eventually flow into our vast oceans. 156 00:17:16,580 --> 00:17:21,420 And we're very used to seeing water appear out of our atmosphere. 157 00:17:21,420 --> 00:17:25,900 What about those lovely soft layers of mist that we see over rivers, 158 00:17:25,900 --> 00:17:30,020 or the dew on your toes if you scuff across a summer lawn, 159 00:17:30,020 --> 00:17:32,820 or when it falls as rain or snow? 160 00:17:40,700 --> 00:17:44,220 The only reason our planet is a water world is because it's the 161 00:17:44,220 --> 00:17:48,820 right temperature and pressure for water to form out of the atmosphere. 162 00:17:51,660 --> 00:17:55,980 4.4 billion years ago, Earth needed to cool down. 163 00:17:59,340 --> 00:18:03,620 Slowly, heat has been radiating out into space... 164 00:18:08,140 --> 00:18:10,580 ..over millions and millions of years. 165 00:18:26,660 --> 00:18:27,900 Until... 166 00:18:30,820 --> 00:18:33,580 ..a tipping point is reached. 167 00:18:51,980 --> 00:18:55,700 What starts with just a few drops 168 00:18:55,700 --> 00:18:58,220 becomes the greatest deluge 169 00:18:58,220 --> 00:19:00,420 the solar system has ever seen. 170 00:19:26,820 --> 00:19:29,700 Huge weather systems sweep across the planet 171 00:19:29,700 --> 00:19:34,660 and storms which last centuries dump oceans of water from the skies. 172 00:19:43,340 --> 00:19:48,020 A key element in the equation of life had been 173 00:19:48,020 --> 00:19:49,620 well and truly unleashed. 174 00:20:00,420 --> 00:20:03,700 Our planet is transformed. 175 00:20:15,940 --> 00:20:19,780 As the Earth continued to cool, the rains that fell from its thick, 176 00:20:19,780 --> 00:20:22,500 dense atmosphere created a new water world. 177 00:20:22,500 --> 00:20:25,220 And for the first time in its history, 178 00:20:25,220 --> 00:20:28,660 it would have looked a little bit like this. 179 00:20:28,660 --> 00:20:31,820 If you gazed into the sky, you would have seen clouds, 180 00:20:31,820 --> 00:20:34,540 you would have felt the wind and the rain on your face. 181 00:20:34,540 --> 00:20:36,420 And if you listened, 182 00:20:36,420 --> 00:20:39,580 you'd have heard waves carving a new coastline. 183 00:20:40,740 --> 00:20:43,540 But that's where the similarities would have ended, 184 00:20:43,540 --> 00:20:48,540 because this rocky, wet world was devoid of life. 185 00:20:48,540 --> 00:20:51,660 But it was a world where life could begin. 186 00:21:11,100 --> 00:21:14,260 Water was the crucial ingredient. 187 00:21:19,700 --> 00:21:24,900 Not long after Earth's oceans rained from the sky, 188 00:21:24,900 --> 00:21:30,380 a shallow pool was about to play host to the most important 189 00:21:30,380 --> 00:21:33,460 moment in the history of the Earth. 190 00:21:48,860 --> 00:21:52,340 So much of how life began is still a mystery. 191 00:21:56,380 --> 00:22:01,700 It's not known exactly when, where or how it happened. 192 00:22:04,020 --> 00:22:08,460 But we do know that, one day on Earth, 193 00:22:08,460 --> 00:22:12,140 a living thing came into existence. 194 00:22:16,020 --> 00:22:19,260 The first microscopic organism. 195 00:22:25,620 --> 00:22:30,540 And in that instant of pure chance, everything changed. 196 00:22:32,540 --> 00:22:35,900 The Earth became a living world. 197 00:22:41,380 --> 00:22:46,180 All trace of the first life has vanished, lost to history. 198 00:22:48,820 --> 00:22:50,460 But even today, 199 00:22:50,460 --> 00:22:54,780 we can get clues as to what early life might have been like. 200 00:22:59,540 --> 00:23:04,020 High in the Andes is one of the largest geyser fields in the world. 201 00:23:09,300 --> 00:23:13,700 The water in this vent is boiling at 85 degrees Centigrade 202 00:23:13,700 --> 00:23:17,460 and NASA scientists have looked into this water and found 203 00:23:17,460 --> 00:23:20,460 that it contains one of the highest concentrations of arsenic, 204 00:23:20,460 --> 00:23:23,140 a serious toxin, anywhere in the world. 205 00:23:25,220 --> 00:23:28,620 And these toxic conditions are similar to those 206 00:23:28,620 --> 00:23:30,860 found on the early Earth. 207 00:23:30,860 --> 00:23:33,740 But amongst the poison and boiling water, 208 00:23:33,740 --> 00:23:36,340 something ancient is flourishing. 209 00:23:38,060 --> 00:23:40,700 Just look at all of these beautiful colours here. 210 00:23:44,300 --> 00:23:50,900 That's life - a primordial mat of billions of thriving bacteria. 211 00:23:54,900 --> 00:23:59,260 These hardy bacteria are called extremophiles and, just 212 00:23:59,260 --> 00:24:03,620 like their predecessors, they've adapted to live in this hot water. 213 00:24:03,620 --> 00:24:07,340 In fact, they've carved out a niche where they can proliferate. 214 00:24:07,340 --> 00:24:10,140 There are a great range of species here and an enormous 215 00:24:10,140 --> 00:24:12,620 number of individual organisms. 216 00:24:15,660 --> 00:24:19,860 Which just goes to show that even the simplest life is inherently 217 00:24:19,860 --> 00:24:23,420 flexible, adaptable and tough. 218 00:24:23,420 --> 00:24:27,380 So, perhaps it's not surprising that that early life grabbed 219 00:24:27,380 --> 00:24:31,500 an opportunity to try and live in an environment which, for us, 220 00:24:31,500 --> 00:24:33,940 is incredibly harsh and hostile, 221 00:24:33,940 --> 00:24:36,140 but where they could prosper. 222 00:24:42,820 --> 00:24:45,180 Today, life is prolific. 223 00:24:45,180 --> 00:24:49,380 It thrives in the most unlikely of places across the world. 224 00:24:49,380 --> 00:24:53,140 But living in these extreme environments comes 225 00:24:53,140 --> 00:24:54,660 with severe limitations. 226 00:24:56,460 --> 00:24:59,420 The extremophile bacteria living around these 227 00:24:59,420 --> 00:25:01,860 hot springs are essentially locked in, 228 00:25:01,860 --> 00:25:05,140 defined by the very precise requirements in terms of the 229 00:25:05,140 --> 00:25:09,020 heat of the water and the nutrients in it. And if we were to remove 230 00:25:09,020 --> 00:25:13,660 them from this highly specialised environment, they would likely die. 231 00:25:13,660 --> 00:25:17,420 And things were pretty much the same for early life on Earth. 232 00:25:17,420 --> 00:25:21,740 It was essentially stuck, trapped in the niches that it evolved to 233 00:25:21,740 --> 00:25:25,700 survive in. And because all of the nutrients were in the water, 234 00:25:25,700 --> 00:25:29,700 the option for life on land simply wasn't there. 235 00:25:29,700 --> 00:25:34,020 Early life wasn't prolific, widespread, or even visible. 236 00:25:54,580 --> 00:25:58,020 The ancient Earth is harsh and unforgiving... 237 00:26:03,180 --> 00:26:04,700 ..with barren black land... 238 00:26:10,260 --> 00:26:12,060 ..and acidic green oceans. 239 00:26:16,380 --> 00:26:21,220 But the biggest barrier to life's flourishing is the atmosphere, 240 00:26:21,220 --> 00:26:23,300 toxic and orange. 241 00:26:24,540 --> 00:26:28,020 An atmosphere in constant turmoil. 242 00:26:38,900 --> 00:26:43,900 Tectonic movements in the Earth's crust drives land formation, 243 00:26:43,900 --> 00:26:48,180 which in turn creates massive atmospheric instability. 244 00:26:53,700 --> 00:26:56,540 Vicious winds sweep dust high up into the air... 245 00:27:00,020 --> 00:27:02,860 ..and these dust particles create more clouds. 246 00:27:07,020 --> 00:27:12,540 Storms rage across the planet, laced with poisonous gasses... 247 00:27:14,620 --> 00:27:17,940 ..deadly to the vast majority of life we know today. 248 00:27:25,940 --> 00:27:30,980 But whilst chaos rages above the waves, deep underwater 249 00:27:30,980 --> 00:27:35,140 our ancestors are simply existing, 250 00:27:35,140 --> 00:27:36,780 seemingly trapped... 251 00:27:39,060 --> 00:27:40,540 ..with no means of escape... 252 00:27:44,820 --> 00:27:49,780 ..day after day, for nearly a billion years 253 00:27:49,780 --> 00:27:52,100 where nothing appears to happen. 254 00:28:06,900 --> 00:28:10,420 Today, life is no longer confined to the water. 255 00:28:11,700 --> 00:28:13,820 Oh, yes, what a view! 256 00:28:14,820 --> 00:28:19,140 Both life and the atmosphere that supports it have undergone 257 00:28:19,140 --> 00:28:20,900 an astonishing transformation. 258 00:28:34,860 --> 00:28:36,020 It's a male. 259 00:28:36,020 --> 00:28:39,180 It's got the comb on top of its head and its feathers are all silvery, 260 00:28:39,180 --> 00:28:43,220 rippling in the wind as it glides along the edge of this escarpment. 261 00:28:45,140 --> 00:28:47,780 With a wingspan of more than 3m, 262 00:28:47,780 --> 00:28:51,740 the giant Andean condor is one of the largest birds on Earth. 263 00:28:52,900 --> 00:28:55,780 Oh, goodness me! Look at that! 264 00:28:59,260 --> 00:29:02,220 Absolutely sensational. Now I can see its eye. 265 00:29:02,220 --> 00:29:06,140 I'm looking into the eye of an Andean condor. 266 00:29:06,140 --> 00:29:07,460 Oh! 267 00:29:07,460 --> 00:29:09,260 It's ornithological nirvana! 268 00:29:12,300 --> 00:29:16,260 Watching these giant birds soaring here 269 00:29:16,260 --> 00:29:21,460 just reveals how their life is completely intertwined with 270 00:29:21,460 --> 00:29:25,300 that thin cloak of air that's wrapped around our planet. 271 00:29:25,300 --> 00:29:29,740 But then, when you think about it, everything - every plant, 272 00:29:29,740 --> 00:29:34,060 fungi, every bacteria, every tiny insect, every giant reptile, 273 00:29:34,060 --> 00:29:39,100 even us - are completely dependent on this atmosphere. 274 00:29:44,860 --> 00:29:49,260 So, how DID the atmosphere go from a toxic orange haze to the 275 00:29:49,260 --> 00:29:52,260 nurturing cocktail of gasses we know today? 276 00:29:56,340 --> 00:30:01,620 Well, it was life itself that would make the difference... 277 00:30:03,700 --> 00:30:06,660 ..thanks to a giant evolutionary leap. 278 00:30:09,860 --> 00:30:13,340 The development of complex life was far from inevitable. 279 00:30:13,340 --> 00:30:14,460 When you think about it, 280 00:30:14,460 --> 00:30:16,820 there are plenty of forks in the road of evolution, 281 00:30:16,820 --> 00:30:18,540 trillions of dead ends 282 00:30:18,540 --> 00:30:21,380 and there is no definitive end point. 283 00:30:21,380 --> 00:30:25,820 But the very fact that we exist proves that whatever card 284 00:30:25,820 --> 00:30:29,260 is thrown at life, it plays it and it survives. 285 00:30:34,340 --> 00:30:35,940 And that's precisely 286 00:30:35,940 --> 00:30:39,500 what was happening 3.5 billion years ago. 287 00:30:39,500 --> 00:30:45,460 Life was playing its card - slowly evolving, gently proliferating - 288 00:30:45,460 --> 00:30:49,500 and it wasn't quite as stuck as we might have thought it was. 289 00:30:49,500 --> 00:30:54,260 In fact, a significant development in a single cell was about to 290 00:30:54,260 --> 00:30:57,700 change the way that life could exist. 291 00:30:57,700 --> 00:31:02,140 Life was about to take a quantum leap forward. 292 00:31:05,420 --> 00:31:09,540 A leap, that would change our atmosphere forever. 293 00:31:19,460 --> 00:31:24,220 It started with a mutation that altered the fundamental 294 00:31:24,220 --> 00:31:26,900 chemistry of the cells... 295 00:31:28,180 --> 00:31:31,300 ..giving them the ability to capture the sun's rays... 296 00:31:33,900 --> 00:31:37,420 ..and store the energy as glucose, 297 00:31:37,420 --> 00:31:42,220 energy the cells can then use to grow and reproduce. 298 00:31:47,620 --> 00:31:50,820 This was photosynthesis... 299 00:31:52,300 --> 00:31:56,140 ..an evolutionary innovation that will change 300 00:31:56,140 --> 00:31:59,580 the course of Earth's history forever. 301 00:32:13,620 --> 00:32:17,420 The ancestors of this cell are still around today. 302 00:32:21,260 --> 00:32:24,300 They can be found in almost every puddle, lake, 303 00:32:24,300 --> 00:32:26,300 sea or ocean across our planet. 304 00:32:30,180 --> 00:32:34,140 Peering down through this microscope is like taking a look 305 00:32:34,140 --> 00:32:39,940 back at life on Earth almost 3.5 billion years ago. 306 00:32:39,940 --> 00:32:46,180 You see, these rod-shaped structures here are cyanobacteria, 307 00:32:46,180 --> 00:32:49,140 and we think they're pretty similar to those that existed 308 00:32:49,140 --> 00:32:54,620 trillions of generations ago, when our atmosphere was very different. 309 00:32:54,620 --> 00:32:57,780 Now, they may not look impressive, but I've got to tell you, 310 00:32:57,780 --> 00:33:02,540 they're probably one of the most successful organisms to ever live. 311 00:33:02,540 --> 00:33:07,820 A little over 3 billion years ago, these tiny flecks, 312 00:33:07,820 --> 00:33:09,940 these microscopic organisms 313 00:33:09,940 --> 00:33:14,140 just a fraction of a millimetre across, started to build 314 00:33:14,140 --> 00:33:19,260 an atmosphere which humans could live and breathe in. 315 00:33:24,620 --> 00:33:28,620 Thanks to energy from the sun, these cells are able to steal 316 00:33:28,620 --> 00:33:34,220 hydrogen from water molecules and combine it with the carbon dioxide 317 00:33:34,220 --> 00:33:39,700 dissolved in the oceans, fabricating essential tools for life. 318 00:33:46,980 --> 00:33:50,940 Individually, these revolutionary cells, 319 00:33:50,940 --> 00:33:53,980 which you can still find in water bodies like this all across 320 00:33:53,980 --> 00:33:57,020 the planet, produced a negligible, 321 00:33:57,020 --> 00:34:00,260 unremarkable, nonexistent effect. 322 00:34:01,700 --> 00:34:04,460 But when they combined in their trillions, 323 00:34:04,460 --> 00:34:08,340 when they combined en masse, they were about to demonstrate, 324 00:34:08,340 --> 00:34:14,260 for the very first time, the awesome power of life on Earth, 325 00:34:14,260 --> 00:34:18,580 and that would have a profound, long-lasting 326 00:34:18,580 --> 00:34:21,700 physical resonance on our planet. 327 00:34:25,820 --> 00:34:29,180 Life powered by photosynthesis thrived. 328 00:34:33,660 --> 00:34:37,460 Cells with this new ability to harness energy from the sun 329 00:34:37,460 --> 00:34:40,260 out-competed those that couldn't. 330 00:34:41,820 --> 00:34:44,020 So, they began to multiply. 331 00:34:47,740 --> 00:34:49,420 One becomes two. 332 00:34:50,740 --> 00:34:52,060 Two become four. 333 00:35:04,260 --> 00:35:07,700 Until there are literally trillions of offspring. 334 00:35:10,420 --> 00:35:16,340 Enough to fundamentally change the chemistry of our world. 335 00:35:24,460 --> 00:35:29,740 Photosynthesis was a game-changer for life because the 336 00:35:29,740 --> 00:35:34,340 ingredients that it required were so readily available and abundant. 337 00:35:34,340 --> 00:35:40,420 But the by-products of many types of photosynthesis include a very 338 00:35:40,420 --> 00:35:43,220 reactive and dangerous gas. 339 00:35:43,220 --> 00:35:47,180 Now, for these revolutionary early organisms, 340 00:35:47,180 --> 00:35:50,460 this was just a waste product, something to be thrown away. 341 00:35:50,460 --> 00:35:52,780 But for the likes of you and I, 342 00:35:52,780 --> 00:35:58,260 and the rest of complex life on Earth, it's absolutely essential. 343 00:35:58,260 --> 00:36:01,420 I'm talking, of course, about oxygen. 344 00:36:07,100 --> 00:36:11,020 Trillions of bacteria are spread across the ancient oceans... 345 00:36:15,940 --> 00:36:20,420 ..and the waste oxygen they throw away is enough to build a new 346 00:36:20,420 --> 00:36:22,860 atmosphere for our planet. 347 00:36:27,860 --> 00:36:31,100 Bubbles of oxygen race upwards, towards the surface. 348 00:36:35,780 --> 00:36:37,100 But they can't escape. 349 00:36:41,500 --> 00:36:44,540 The bubbles are absorbed and vanish. 350 00:36:53,340 --> 00:36:58,540 Earth seems trapped, with a toxic atmosphere of methane 351 00:36:58,540 --> 00:37:00,220 and carbon dioxide. 352 00:37:14,460 --> 00:37:18,060 The Earth was essentially in stasis. 353 00:37:18,060 --> 00:37:21,980 You see, that toxic orange atmosphere still enveloped 354 00:37:21,980 --> 00:37:23,340 the planet. 355 00:37:23,340 --> 00:37:27,700 Life was still microscopic and could only exist in the oceans, 356 00:37:27,700 --> 00:37:31,740 and there was no oxygen in the atmosphere. 357 00:37:31,740 --> 00:37:35,780 To all intents and purposes, you could say, well, 358 00:37:35,780 --> 00:37:37,900 that the planet was stuck. 359 00:37:40,660 --> 00:37:43,180 But that was about to change. 360 00:37:47,540 --> 00:37:51,580 Because it wasn't just oxygen dissolved in the water - 361 00:37:51,580 --> 00:37:53,380 there were metals, too... 362 00:37:56,300 --> 00:37:58,860 ..including iron. 363 00:38:03,860 --> 00:38:07,340 The iron, like oxygen, is invisible 364 00:38:07,340 --> 00:38:10,300 to us when it's dissolved in water. 365 00:38:10,300 --> 00:38:13,340 But we all know what happens when iron, 366 00:38:13,340 --> 00:38:15,380 oxygen and water come together... 367 00:38:18,260 --> 00:38:22,140 ..and there's plenty of evidence of that on this old bus. 368 00:38:25,060 --> 00:38:28,820 Just look here - this lovely brown, 369 00:38:28,820 --> 00:38:30,580 orange and red. 370 00:38:31,900 --> 00:38:33,100 Rust. 371 00:38:33,100 --> 00:38:36,980 The iron is being oxidised - aggressively attacked 372 00:38:36,980 --> 00:38:40,860 by the oxygen in the presence of water, or water vapour. 373 00:38:40,860 --> 00:38:44,180 But what's interesting is that, whilst the iron 374 00:38:44,180 --> 00:38:48,580 and whilst the oxygen are soluble in water, 375 00:38:48,580 --> 00:38:50,540 the rust is not. 376 00:39:08,060 --> 00:39:10,420 The newly released oxygen reacts 377 00:39:10,420 --> 00:39:13,020 with the dissolved iron already present 378 00:39:13,020 --> 00:39:15,700 in the oceans, 379 00:39:15,700 --> 00:39:19,860 and that causes something extraordinary to happen. 380 00:39:21,740 --> 00:39:24,460 Rust pours onto the ocean floor. 381 00:39:34,500 --> 00:39:36,660 The world's oceans turn red. 382 00:39:48,900 --> 00:39:51,060 And if you know where to look, you can 383 00:39:51,060 --> 00:39:54,100 still find evidence for this bizarre effect. 384 00:39:56,420 --> 00:39:58,300 I'm armed with a rock hammer. 385 00:39:58,300 --> 00:40:01,420 If I have a little tap at this stone, there we are. 386 00:40:01,420 --> 00:40:03,180 Let's have a look at what's inside. 387 00:40:04,380 --> 00:40:07,780 This rock once formed part of an ancient seafloor. 388 00:40:07,780 --> 00:40:10,500 Hm, look at that. 389 00:40:10,500 --> 00:40:13,260 You see that there, that red? 390 00:40:13,260 --> 00:40:15,260 That's iron 391 00:40:15,260 --> 00:40:18,660 laid down billions of years ago, 392 00:40:18,660 --> 00:40:22,420 a volatile memory of oxygen reacting 393 00:40:22,420 --> 00:40:25,260 with iron in the early seas. 394 00:40:26,380 --> 00:40:29,100 A sort of geological tattoo. 395 00:40:29,100 --> 00:40:30,340 I love that. 396 00:40:32,820 --> 00:40:35,460 This rust was to have a profound effect 397 00:40:35,460 --> 00:40:38,060 on our Earth's young atmosphere. 398 00:40:45,180 --> 00:40:50,340 For half a billion years, oxygen has been trapped in the oceans. 399 00:40:52,620 --> 00:40:57,260 But now, iron has almost been totally flushed from the seas. 400 00:41:02,660 --> 00:41:08,060 At last, the oxygen in the water has nothing else to react with. 401 00:41:09,980 --> 00:41:12,460 It can break free. 402 00:41:37,740 --> 00:41:42,540 Over millions years, oxygen flooded from the oceans... 403 00:41:46,620 --> 00:41:49,500 ..and our atmosphere was transformed. 404 00:42:09,820 --> 00:42:13,060 When those bubbles first breached the surface of the ocean, 405 00:42:13,060 --> 00:42:15,900 you might have thought that the atmosphere was getting 406 00:42:15,900 --> 00:42:19,060 a breath of fresh air, and to some extent it was. 407 00:42:19,060 --> 00:42:23,740 But this wasn't the moment when life suddenly flourished, 408 00:42:23,740 --> 00:42:28,420 or when it developed that complete and utter dependence that 409 00:42:28,420 --> 00:42:31,380 contemporary complex life has upon oxygen. 410 00:42:32,860 --> 00:42:37,820 But that's not to say that when those bubbles first fizzed 411 00:42:37,820 --> 00:42:40,660 out there that this wasn't a momentous moment. 412 00:42:40,660 --> 00:42:42,140 It was. 413 00:42:42,140 --> 00:42:45,300 The planet was about to be re-calibrated, 414 00:42:45,300 --> 00:42:48,420 and the relationship between the ocean, 415 00:42:48,420 --> 00:42:52,820 the land and the atmosphere was going to change forever. 416 00:42:52,820 --> 00:42:58,260 And as this volatile, reactive gas flooded into the atmosphere, the 417 00:42:58,260 --> 00:43:03,580 full destructive force of oxygen was felt across the planet's surface. 418 00:43:26,140 --> 00:43:28,500 Oxygen attacks the Earth. 419 00:43:37,540 --> 00:43:43,100 Any rocks containing iron and aluminium rust and crumble, 420 00:43:43,100 --> 00:43:46,020 driving vast dust storms. 421 00:43:49,780 --> 00:43:53,220 The world is being torn apart by its own atmosphere... 422 00:43:56,020 --> 00:43:59,580 ..and this has a startling side-effect - 423 00:43:59,580 --> 00:44:02,980 the entire Earth turns a vivid red. 424 00:44:10,820 --> 00:44:14,700 Scientists find evidence for this red Earth in 425 00:44:14,700 --> 00:44:18,140 rock formations in landscapes all over the world. 426 00:44:18,140 --> 00:44:22,420 Direct evidence of the action of all of those 427 00:44:22,420 --> 00:44:26,580 trillions of cyanobacteria churning out oxygen. 428 00:44:26,580 --> 00:44:32,780 And before oxygen, the planet was barren, grey and black. 429 00:44:32,780 --> 00:44:38,500 You see, it's oxidation that gives us this wonderful red hue. 430 00:44:55,300 --> 00:44:58,220 But oxygen's effect on the land went further. 431 00:45:01,060 --> 00:45:04,580 You see, oxygen doesn't just react with iron - 432 00:45:04,580 --> 00:45:06,940 it reacts with pretty much anything. 433 00:45:07,980 --> 00:45:11,220 It attacks minerals within the Earth's crust... 434 00:45:15,100 --> 00:45:19,420 ..creating as many as 3,000 exotic new minerals, 435 00:45:19,420 --> 00:45:22,620 all previously unknown to the solar system. 436 00:45:29,020 --> 00:45:33,060 Minerals that led to an explosion of colour right across the planet. 437 00:45:41,620 --> 00:45:43,980 Minerals that, to this day, 438 00:45:43,980 --> 00:45:48,500 play a vital role in sustaining the rich complexity of life we know. 439 00:45:53,820 --> 00:46:00,140 Now, one of the colours unleashed by oxygen is this rather 440 00:46:00,140 --> 00:46:03,100 wonderful sea green here. 441 00:46:04,220 --> 00:46:06,700 You see, when copper, the metal, 442 00:46:06,700 --> 00:46:10,900 comes into contact with oxygen in the air, it oxidises, 443 00:46:10,900 --> 00:46:13,740 producing this - copper oxide. 444 00:46:13,740 --> 00:46:16,940 And it turns out that this compound 445 00:46:16,940 --> 00:46:21,660 was fundamentally important in the development of more complex 446 00:46:21,660 --> 00:46:27,420 life. And what's more, it retains its biological importance today. 447 00:46:27,420 --> 00:46:32,620 It's necessary for the synthesis of neurotransmitters in our brains, 448 00:46:32,620 --> 00:46:34,540 and the brains of other animals, 449 00:46:34,540 --> 00:46:38,060 and also for the production of hormones and pigments. 450 00:46:38,060 --> 00:46:41,060 So, even in today's world, 451 00:46:41,060 --> 00:46:46,340 life is dependent on that chemical complexity that was unlocked 452 00:46:46,340 --> 00:46:51,940 so long ago, when our atmosphere became richer in oxygen. 453 00:47:03,820 --> 00:47:07,620 Thanks to oxygen, we live in a world of extraordinary colour 454 00:47:07,620 --> 00:47:09,220 and diversity. 455 00:47:12,620 --> 00:47:16,340 A myriad of minerals colours the Earth's surface... 456 00:47:19,940 --> 00:47:22,180 ..and the biological world has continued 457 00:47:22,180 --> 00:47:24,460 to make use of this ever-increasing 458 00:47:24,460 --> 00:47:28,500 chemical complexity to transform the planet. 459 00:47:28,500 --> 00:47:31,820 From the rich green carpet of plant life... 460 00:47:34,140 --> 00:47:35,180 SHUTTER CLICKS 461 00:47:36,540 --> 00:47:40,740 ..to the fluorescent pink feathers of flamingos. 462 00:47:54,140 --> 00:47:58,900 Oxygen has allowed life to flourish in ways unimaginable 463 00:47:58,900 --> 00:48:00,460 3 billion years ago. 464 00:48:01,900 --> 00:48:06,740 But this volatile gas had one more gift to bestow. 465 00:48:10,540 --> 00:48:15,500 As oxygen enriches the atmosphere, it reacts with methane, 466 00:48:15,500 --> 00:48:17,300 stripping it away. 467 00:48:20,420 --> 00:48:26,140 And as methane levels drop, the orange haze lifts. 468 00:48:29,220 --> 00:48:32,380 Nitrogen and oxygen in the atmosphere are left 469 00:48:32,380 --> 00:48:33,980 to scatter the light. 470 00:48:35,580 --> 00:48:37,860 The colour begins to change. 471 00:48:42,100 --> 00:48:46,860 For the first time in Earth's history, the sky 472 00:48:46,860 --> 00:48:49,540 is an oxygen-rich, brilliant blue. 473 00:49:04,660 --> 00:49:10,060 Today, this lovely thin blue line marks our Earth as unique 474 00:49:10,060 --> 00:49:12,940 in the entire known universe. 475 00:49:12,940 --> 00:49:17,220 It's a spectacular demonstration of a 4 billion-year 476 00:49:17,220 --> 00:49:21,020 dance between our atmosphere and life - 477 00:49:21,020 --> 00:49:23,380 an atmosphere that was 478 00:49:23,380 --> 00:49:27,940 created, shaped and calibrated by life itself. 479 00:49:31,660 --> 00:49:37,820 Our planet went from volatile, fiery and dead to the beautiful 480 00:49:37,820 --> 00:49:40,340 living and breathing blue bubble 481 00:49:40,340 --> 00:49:43,020 floating in the darkness of space. 482 00:50:04,420 --> 00:50:08,820 How do scientists unravel billions of years of our planet's history? 483 00:50:12,620 --> 00:50:17,980 In this episode, we saw how meteorites - 484 00:50:17,980 --> 00:50:20,500 rocks that have fallen from space - 485 00:50:20,500 --> 00:50:24,260 can tell us what Earth's early atmosphere was made from. 486 00:50:25,380 --> 00:50:27,900 - This is a chondrite meteorite. 487 00:50:27,900 --> 00:50:31,700 4.567 billion years old - 488 00:50:31,700 --> 00:50:33,980 the oldest thing you could hold in your hand - 489 00:50:33,980 --> 00:50:36,020 and it's made of all these tiny droplets 490 00:50:36,020 --> 00:50:39,540 that were part of the earliest solar nebula, including 491 00:50:39,540 --> 00:50:43,340 all the gasses that eventually would wind up in the atmosphere. 492 00:50:47,340 --> 00:50:51,140 - Meteorites are so valuable to science 493 00:50:51,140 --> 00:50:54,420 that researchers go to great lengths to track them down. 494 00:50:57,740 --> 00:51:02,740 In 2020, scientists from the University of Manchester set out 495 00:51:02,740 --> 00:51:07,700 on a nine-week expedition to one of the most remote areas of Antarctica. 496 00:51:10,180 --> 00:51:13,260 - Meteorite hunters go into the depths of Antarctica, 497 00:51:13,260 --> 00:51:17,260 into the extremes of the cold, near the South Pole, because 498 00:51:17,260 --> 00:51:20,580 they can find so many meteorites in one expedition, because the 499 00:51:20,580 --> 00:51:25,140 meteorites show up so well on the white ice... 500 00:51:25,140 --> 00:51:29,020 ..compared to, say, other places where the meteorites are 501 00:51:29,020 --> 00:51:31,380 very hard to spot from normal rocks. 502 00:51:34,260 --> 00:51:36,780 - Studying meteorites has helped answer some of the most 503 00:51:36,780 --> 00:51:39,860 fundamental questions about our planet. 504 00:51:41,500 --> 00:51:44,820 - So, the question of where the water on Earth came from 505 00:51:44,820 --> 00:51:48,540 and when it arrived is really central to everything. 506 00:51:49,740 --> 00:51:54,860 - Some water was present in the material that formed our planet, 507 00:51:54,860 --> 00:51:57,060 but that's not the whole story. 508 00:51:58,700 --> 00:52:02,500 - We think that one of the other ways that the Earth got its water 509 00:52:02,500 --> 00:52:04,460 is through meteorites. 510 00:52:04,460 --> 00:52:08,700 So, these meteorites would have had water locked into their rocks, 511 00:52:08,700 --> 00:52:12,540 or perhaps even on their surface, as frozen, in outer space. 512 00:52:14,100 --> 00:52:16,300 And then, the water would have been degassed 513 00:52:16,300 --> 00:52:18,540 into our atmosphere as water vapour. 514 00:52:18,540 --> 00:52:21,300 Later on, when the Earth cooled even further, 515 00:52:21,300 --> 00:52:23,260 that atmosphere would have condensed 516 00:52:23,260 --> 00:52:27,140 and the water vapour would have then formed liquid water on our surface. 517 00:52:30,660 --> 00:52:35,540 - Scientists think it's only after the arrival of water that life 518 00:52:35,540 --> 00:52:37,420 was able to get started. 519 00:52:39,580 --> 00:52:43,780 - The origin of life is one of the greatest questions in science and 520 00:52:43,780 --> 00:52:48,180 it's fair to say that we don't know when, where or how life started. 521 00:52:50,060 --> 00:52:53,460 - A shallow rock pool is one of the leading theories. 522 00:52:54,540 --> 00:52:57,380 - People think that shallow pools would have been a potentially 523 00:52:57,380 --> 00:53:00,100 important site for the origin of life because they can get 524 00:53:00,100 --> 00:53:02,100 wet and dry over and over again. 525 00:53:04,900 --> 00:53:08,220 - Through this repeated cycling of wetting and drying, 526 00:53:08,220 --> 00:53:11,420 re-flooding and evaporating, maybe through a tide, maybe through 527 00:53:11,420 --> 00:53:15,460 seasonal variation, more and more complex molecules can form. 528 00:53:17,620 --> 00:53:21,380 - And that process could have been the precursors for things like DNA, 529 00:53:21,380 --> 00:53:24,300 which is what makes up the information in our cells today. 530 00:53:28,220 --> 00:53:30,220 - But there are other theories. 531 00:53:35,620 --> 00:53:40,300 - Some scientists think life began in a deep-sea hydrothermal vent. 532 00:53:43,860 --> 00:53:47,500 - Hydrothermal vents are sources of gases, 533 00:53:47,500 --> 00:53:50,020 like hydrogen sulphide for example, and provide 534 00:53:50,020 --> 00:53:53,460 the kind of reactive conditions to make the building blocks of life. 535 00:53:55,540 --> 00:53:59,780 - Others think that life originated somewhere completely else - 536 00:53:59,780 --> 00:54:03,620 not on the Earth at all - and landed here on a meteorite. 537 00:54:08,540 --> 00:54:12,020 - All of these different theories have sort of different details, 538 00:54:12,020 --> 00:54:15,340 but the punch line is that life needed water 539 00:54:15,340 --> 00:54:17,940 and it needed a way to harness energy. 540 00:54:21,900 --> 00:54:24,860 - Although life's origins are still debated, 541 00:54:24,860 --> 00:54:28,420 scientists have some idea when it happened. 542 00:54:30,540 --> 00:54:35,300 - This is one of the clear-cut examples that life was living 543 00:54:35,300 --> 00:54:36,860 even 3 billion years ago. 544 00:54:36,860 --> 00:54:39,020 This is a formation called a stromatolite. 545 00:54:39,020 --> 00:54:41,460 What you're looking at shows a structure 546 00:54:41,460 --> 00:54:45,340 created by a lot of microorganisms, single-celled organisms. 547 00:54:45,340 --> 00:54:50,780 And as they grow and they reach for the light, they secrete various 548 00:54:50,780 --> 00:54:56,580 gluey substances that glue together bits of sand in the environment, 549 00:54:56,580 --> 00:55:00,460 and that actually helps keep it from dispersing and blowing away. 550 00:55:00,460 --> 00:55:04,020 - They are astounding in that they have the ability to adapt to 551 00:55:04,020 --> 00:55:06,940 environmental change and to change the environment 552 00:55:06,940 --> 00:55:08,780 because they can be so abundant. 553 00:55:10,860 --> 00:55:16,220 - These fossilised structures were created by cyanobacteria 554 00:55:16,220 --> 00:55:19,260 and millions of them can still be found along the coast 555 00:55:19,260 --> 00:55:20,900 of Western Australia. 556 00:55:22,580 --> 00:55:25,740 - Cyanobacteria might not seem so impressive, 557 00:55:25,740 --> 00:55:28,500 but they're probably one of the most influential 558 00:55:28,500 --> 00:55:31,900 and successful organisms ever to appear on planet Earth. 559 00:55:33,300 --> 00:55:37,820 - They were the organisms that invented this ability to 560 00:55:37,820 --> 00:55:42,220 break water into oxygen and hydrogen 561 00:55:42,220 --> 00:55:44,740 and spit out that oxygen. 562 00:55:46,300 --> 00:55:49,540 - That oxygen was able to get released into our atmosphere. 563 00:55:51,780 --> 00:55:55,420 - They completely transformed the world. 564 00:55:58,700 --> 00:56:02,500 - There are these moments in the history of life that seem to 565 00:56:02,500 --> 00:56:04,620 have only happened once. 566 00:56:04,620 --> 00:56:08,020 Oxygen producing photosynthesis is one of them. 567 00:56:08,020 --> 00:56:10,580 Was it a freak accident? We just don't know. 568 00:56:13,260 --> 00:56:16,220 - The evolution of our atmosphere is, in many respects, 569 00:56:16,220 --> 00:56:19,500 the story of the evolution of life on our planet. 570 00:56:19,500 --> 00:56:22,100 Life can change a planet fundamentally. 571 00:56:25,540 --> 00:56:29,020 But it's always this cause-and-effect kind of dance 572 00:56:29,020 --> 00:56:31,540 between the environment changing life 573 00:56:31,540 --> 00:56:33,420 and life changing the environment. 574 00:56:37,020 --> 00:56:41,060 - The story of our changing atmosphere is not over. 575 00:56:41,060 --> 00:56:44,100 It will continue to evolve both naturally 576 00:56:44,100 --> 00:56:46,860 and under the influence of human activity. 577 00:56:49,180 --> 00:56:52,220 - If we don't understand the history of the atmosphere, 578 00:56:52,220 --> 00:56:56,180 how can we possibly be the stewards of the atmosphere moving forward? 579 00:57:00,060 --> 00:57:01,900 - By understanding the huge 580 00:57:01,900 --> 00:57:05,820 and complex steps it took to develop our atmosphere, hopefully 581 00:57:05,820 --> 00:57:09,260 we can develop approaches to take care of it for generations to come. 582 00:57:17,860 --> 00:57:19,020 - Next time... 583 00:57:23,380 --> 00:57:25,700 ..the making of the modern world. 584 00:57:27,140 --> 00:57:29,300 How the end of the dinosaurs... 585 00:57:31,780 --> 00:57:35,220 ..through cataclysm and chaos, 586 00:57:35,220 --> 00:57:38,260 set the stage for a human planet... 587 00:57:39,900 --> 00:57:41,540 ..to take its place. 588 00:57:47,660 --> 00:57:50,420 If the Earth could talk, what would it tell us? 589 00:57:50,420 --> 00:57:52,940 Well, the Open University imagine how it might answer 590 00:57:52,940 --> 00:57:54,780 some of our questions. 591 00:57:54,780 --> 00:57:57,620 To experience this interactive presentation, go to the 592 00:57:57,620 --> 00:58:01,380 website on the screen and follow the links to the Open University.