1 00:00:24,834 --> 00:00:29,234 The heavens. The great bowl of the heavens, of our sky. 2 00:00:29,274 --> 00:00:29,714 The heavens. The great bowl of the heavens, of our sky. 3 00:00:31,034 --> 00:00:33,354 Just so beautiful! 4 00:00:33,394 --> 00:00:37,914 I love the sky because, wherever I am in the world, if I can find 5 00:00:37,954 --> 00:00:41,354 some space, I can look up at this 6 00:00:41,394 --> 00:00:45,234 big, blue, pristine space. 7 00:00:49,194 --> 00:00:53,834 And I like the apparent permanence - the fact that I can stare into 8 00:00:53,874 --> 00:00:54,594 And I like the apparent permanence - the fact that I can stare into 9 00:00:54,634 --> 00:00:58,954 a sky that the dinosaurs stared into, that Neanderthals stared into. 10 00:00:58,994 --> 00:00:59,314 a sky that the dinosaurs stared into, that Neanderthals stared into. 11 00:01:01,794 --> 00:01:06,154 The atmosphere is essential for the Earth to be habitable at all. 12 00:01:06,194 --> 00:01:06,234 The atmosphere is essential for the Earth to be habitable at all. 13 00:01:07,634 --> 00:01:11,994 This thin layer of gas that clings to our planet, 14 00:01:12,034 --> 00:01:15,754 keeps liquid water on the Earth's surface 15 00:01:15,794 --> 00:01:20,114 and shields life from the most harmful of the sun's rays. 16 00:01:23,074 --> 00:01:26,714 As far as we know, our thin blue line is unique 17 00:01:26,754 --> 00:01:29,074 in the vast void of space... 18 00:01:31,954 --> 00:01:35,314 ..and today, scientists are beginning to piece 19 00:01:35,354 --> 00:01:38,954 together just how our planet got its special blue bubble. 20 00:01:47,754 --> 00:01:51,234 By going back to the Earth's earliest origins, 21 00:01:51,274 --> 00:01:55,354 we can now tell the almost implausible story of our atmosphere. 22 00:01:55,394 --> 00:01:56,674 we can now tell the almost implausible story of our atmosphere. 23 00:02:01,314 --> 00:02:05,274 How it emerged from a toxic orange hell... 24 00:02:07,394 --> 00:02:11,274 ..and transformed the planet from an exposed ball of rock... 25 00:02:14,354 --> 00:02:16,514 ..to a beautiful, living world... 26 00:02:18,114 --> 00:02:22,154 ..capable of nurturing a staggering abundance of life. 27 00:02:25,954 --> 00:02:30,234 {\an8}This atmosphere has been the planet's great protector 28 00:02:30,274 --> 00:02:30,674 {\an8}This atmosphere has been the planet's great protector 29 00:02:30,714 --> 00:02:33,594 for 2.5 billion years, 30 00:02:33,634 --> 00:02:37,434 soaking up everything that our planet has thrown at it. 31 00:02:38,994 --> 00:02:43,554 It's a thin, delicate, fragile cloak that shields 32 00:02:43,594 --> 00:02:43,794 It's a thin, delicate, fragile cloak that shields 33 00:02:43,834 --> 00:02:47,914 and protects all life on Earth. 34 00:03:23,674 --> 00:03:28,074 Our atmosphere is a unique mix of gasses not found anywhere 35 00:03:28,114 --> 00:03:30,354 else in the solar system, 36 00:03:30,394 --> 00:03:34,474 gasses that allow Earth to be a living, breathing world. 37 00:03:41,514 --> 00:03:46,074 78% of our atmosphere is nitrogen, which can be taken up by 38 00:03:46,114 --> 00:03:46,674 78% of our atmosphere is nitrogen, which can be taken up by 39 00:03:46,714 --> 00:03:51,234 bacteria in the soil and plants, and it's an integral part of DNA. 40 00:03:51,274 --> 00:03:51,634 bacteria in the soil and plants, and it's an integral part of DNA. 41 00:03:51,674 --> 00:03:54,914 21% of our atmosphere is oxygen. 42 00:03:54,954 --> 00:03:58,554 It's there for animals to breathe, but also for many living things 43 00:03:58,594 --> 00:04:01,194 to use to convert their food into energy. 44 00:04:03,354 --> 00:04:06,954 Even less abundant gasses are crucial for sustaining life. 45 00:04:09,074 --> 00:04:13,194 A fraction of a percent is water vapour, which condenses 46 00:04:13,234 --> 00:04:14,914 and falls as rain, 47 00:04:14,954 --> 00:04:18,194 and a tiny amount is carbon dioxide, 48 00:04:18,234 --> 00:04:21,954 which might be a waste product to us but it's absolutely 49 00:04:21,994 --> 00:04:25,714 essential for plants when it comes to photosynthesis. 50 00:04:25,754 --> 00:04:30,194 It almost appears that this unique cocktail of gasses 51 00:04:30,234 --> 00:04:30,634 It almost appears that this unique cocktail of gasses 52 00:04:30,674 --> 00:04:34,074 is here as a sort of life-support system. 53 00:04:37,074 --> 00:04:40,594 So, where did this beautiful atmosphere come from 54 00:04:40,634 --> 00:04:43,874 and how did it lead to the origins of life here? 55 00:04:48,034 --> 00:04:51,194 Well, to answer that, we need to go back to the very beginning... 56 00:04:58,434 --> 00:05:01,234 ..4.6 billion years ago. 57 00:05:09,314 --> 00:05:13,674 Our Earth began as nothing more than dust and gas. 58 00:05:16,714 --> 00:05:21,474 A nebulous cloud containing every element our new world would need. 59 00:05:21,514 --> 00:05:21,874 A nebulous cloud containing every element our new world would need. 60 00:05:25,954 --> 00:05:30,674 Over tens of millions of years, the cloud begins to clump together, 61 00:05:30,714 --> 00:05:31,154 Over tens of millions of years, the cloud begins to clump together, 62 00:05:31,194 --> 00:05:33,434 forming rocks. 63 00:05:33,474 --> 00:05:35,674 Pulled together by gravity... 64 00:05:37,194 --> 00:05:39,874 ..they grow bigger and bigger... 65 00:05:44,994 --> 00:05:48,554 ..until, finally, a new world is formed. 66 00:05:59,114 --> 00:06:02,874 Asteroids rain down on the young Earth 67 00:06:02,914 --> 00:06:05,994 for hundreds of millions of years... 68 00:06:08,794 --> 00:06:13,354 ..its molten surface still searing from the heat of its creation. 69 00:06:25,714 --> 00:06:27,754 But something is missing. 70 00:06:30,354 --> 00:06:32,034 The colour blue. 71 00:06:38,274 --> 00:06:41,554 You see, the Earth has no atmosphere. 72 00:06:43,514 --> 00:06:47,594 The sun and the newly formed moon sit in a jet-black sky. 73 00:06:47,634 --> 00:06:49,034 The sun and the newly formed moon sit in a jet-black sky. 74 00:06:56,594 --> 00:06:59,194 This is how the Earth could have remained... 75 00:07:05,154 --> 00:07:09,994 ..a lifeless ball of rock, floating in the void of space. 76 00:07:24,274 --> 00:07:26,674 This is what the surface of the Earth may have 77 00:07:26,714 --> 00:07:29,794 looked like 4 billion years ago. 78 00:07:31,274 --> 00:07:33,514 Stark, brutal and yet, 79 00:07:33,554 --> 00:07:37,074 in some ways, beautiful landscape. 80 00:07:39,714 --> 00:07:43,994 The early Earth was little more than a ball of cooling rock, 81 00:07:44,034 --> 00:07:44,794 The early Earth was little more than a ball of cooling rock, 82 00:07:44,834 --> 00:07:48,074 so where did the planet's first atmosphere come from? 83 00:07:50,274 --> 00:07:54,474 Now it might surprise you, but I've got some clues to the answer 84 00:07:54,514 --> 00:07:58,114 to that question in my pocket, 85 00:07:58,154 --> 00:08:01,114 in the form of this tiny, 86 00:08:01,154 --> 00:08:05,554 but extremely rare and valuable, granular piece of rock. 87 00:08:05,594 --> 00:08:07,354 but extremely rare and valuable, granular piece of rock. 88 00:08:07,394 --> 00:08:11,714 This, you see, is a carbonaceous chondrite meteorite, 89 00:08:11,754 --> 00:08:13,514 This, you see, is a carbonaceous chondrite meteorite, 90 00:08:13,554 --> 00:08:17,834 and it was formed at the same time our solar system was formed - 91 00:08:17,874 --> 00:08:19,434 and it was formed at the same time our solar system was formed - 92 00:08:19,474 --> 00:08:21,594 and I've got it in my hand! 93 00:08:21,634 --> 00:08:26,074 I am holding the history of our solar system 94 00:08:26,154 --> 00:08:28,154 and the Earth in my hand. 95 00:08:29,914 --> 00:08:34,274 4.5 billion years ago, trillions of tonnes of this 96 00:08:34,314 --> 00:08:35,114 4.5 billion years ago, trillions of tonnes of this 97 00:08:35,154 --> 00:08:39,394 type of material came together to form our planet. 98 00:08:39,434 --> 00:08:40,394 type of material came together to form our planet. 99 00:08:42,074 --> 00:08:46,154 These meteorites are leftovers from the Earth's creation. 100 00:08:47,234 --> 00:08:49,634 So, through chemical analysis, 101 00:08:49,674 --> 00:08:54,554 scientists can discover the raw ingredients that made our world. 102 00:08:57,554 --> 00:09:01,234 These meteorites contain heavy elements, like iron, 103 00:09:01,274 --> 00:09:05,194 and the rocky constituents that formed the planet itself. 104 00:09:07,194 --> 00:09:11,074 But chondrite meteorites contain lighter elements too. 105 00:09:12,994 --> 00:09:17,314 Chemical analysis reveals that these rocks contain carbon, 106 00:09:17,354 --> 00:09:17,794 Chemical analysis reveals that these rocks contain carbon, 107 00:09:17,834 --> 00:09:19,714 hydrogen and sulphur, 108 00:09:19,754 --> 00:09:23,234 and we can still see them belching as gasses 109 00:09:23,274 --> 00:09:25,874 from volcanic vents around the world today. 110 00:09:28,594 --> 00:09:32,714 When combined, these elements form new compounds like methane, 111 00:09:32,754 --> 00:09:33,754 When combined, these elements form new compounds like methane, 112 00:09:33,794 --> 00:09:38,274 carbon dioxide and hydrogen sulphide, 113 00:09:38,314 --> 00:09:42,234 which are light enough to exist as gasses 114 00:09:42,274 --> 00:09:45,554 but not so light they drift off into space. 115 00:09:47,594 --> 00:09:50,834 So, meteorites like this weren't just the 116 00:09:50,874 --> 00:09:52,474 building blocks of our planet - 117 00:09:52,514 --> 00:09:57,354 they contained the essential ingredients for its atmosphere. 118 00:09:57,434 --> 00:10:00,154 And 4.5 billion years ago, 119 00:10:00,194 --> 00:10:03,514 that had begun to change everything. 120 00:10:20,194 --> 00:10:22,874 The ancient Earth holds within it 121 00:10:22,914 --> 00:10:26,234 everything it needs to create the first atmosphere. 122 00:10:30,434 --> 00:10:34,194 Those ingredients just have to make it to the surface. 123 00:10:41,554 --> 00:10:45,914 But deep within the young Earth, something is stirring. 124 00:11:04,754 --> 00:11:09,114 Across the globe, molten magma races up from within... 125 00:11:09,154 --> 00:11:10,034 Across the globe, molten magma races up from within... 126 00:11:14,554 --> 00:11:18,594 ..and these rivers of liquid fire unleash gasses that will 127 00:11:18,634 --> 00:11:20,874 transform our planet. 128 00:11:37,394 --> 00:11:41,914 The world is smothered by a thick toxic fog. 129 00:11:59,834 --> 00:12:03,594 As the sun creeps above the horizon, 130 00:12:03,634 --> 00:12:06,154 gas scatters the light. 131 00:12:09,994 --> 00:12:13,874 Earth gets its first colour-filled sunrise. 132 00:12:17,354 --> 00:12:21,834 This new world now has an atmosphere... 133 00:12:27,674 --> 00:12:30,274 ..but one like nothing we've ever seen. 134 00:12:42,754 --> 00:12:47,354 We're all familiar with the colours in the early-morning sky, 135 00:12:47,394 --> 00:12:51,634 but a sunrise 4 billion years ago would have been very different. 136 00:12:51,674 --> 00:12:52,034 but a sunrise 4 billion years ago would have been very different. 137 00:12:52,074 --> 00:12:56,514 Sunlight passing through that churning mixture of methane 138 00:12:56,554 --> 00:13:00,914 and carbon dioxide would have given the whole planet an orange hue. 139 00:13:00,954 --> 00:13:01,114 and carbon dioxide would have given the whole planet an orange hue. 140 00:13:02,434 --> 00:13:05,274 But this toxic atmosphere was very important. 141 00:13:05,314 --> 00:13:08,314 It was the first time that our planet had 142 00:13:08,354 --> 00:13:11,354 a protective shield from space. 143 00:13:11,394 --> 00:13:14,474 But, of course, it was still a very alien world - 144 00:13:14,514 --> 00:13:18,394 would have been to us - and not just because of that noxious 145 00:13:18,434 --> 00:13:23,434 orange fog, or the searing, hot, black, bare volcanic rocks 146 00:13:23,514 --> 00:13:24,714 beneath our feet. 147 00:13:24,754 --> 00:13:27,434 It was because something fundamental, 148 00:13:27,474 --> 00:13:30,834 something that we take for granted every day, was missing. 149 00:13:33,794 --> 00:13:34,914 Water. 150 00:13:46,754 --> 00:13:50,994 Today, 70% of the Earth's surface is covered in water. 151 00:13:53,634 --> 00:13:56,474 A planet of almost limitless blue... 152 00:13:59,634 --> 00:14:01,154 ..with endless rivers... 153 00:14:02,914 --> 00:14:04,194 ..freezing ice caps... 154 00:14:05,954 --> 00:14:08,034 ..and turquoise tropical paradises. 155 00:14:24,234 --> 00:14:26,314 But 4.5 billion years ago... 156 00:14:28,714 --> 00:14:32,674 ..there wasn't a single drop of liquid water 157 00:14:32,714 --> 00:14:34,634 on the ancient Earth's surface. 158 00:14:44,314 --> 00:14:47,354 However, the planet wasn't totally dry. 159 00:14:50,554 --> 00:14:53,874 The young atmosphere did contain water. 160 00:14:55,754 --> 00:14:59,674 Asteroids and volcanic eruptions have released a vast 161 00:14:59,714 --> 00:15:01,394 ocean of water vapour. 162 00:15:11,154 --> 00:15:14,114 Trillions of droplets were floating in the sky... 163 00:15:25,114 --> 00:15:28,834 ..so small they soar on moving air. 164 00:15:37,234 --> 00:15:41,434 Colliding and merging with each other, they slowly grow... 165 00:15:44,914 --> 00:15:49,074 ..until they can no longer fight Earth's gravity. 166 00:15:49,114 --> 00:15:49,514 ..until they can no longer fight Earth's gravity. 167 00:15:58,234 --> 00:16:01,754 En masse, they are pulled downwards, towards the ground. 168 00:16:12,834 --> 00:16:16,474 But with the atmosphere still scorchingly hot from heat 169 00:16:16,514 --> 00:16:18,074 trapped by Earth's formation... 170 00:16:20,314 --> 00:16:22,554 ..not a single drop of rain... 171 00:16:26,594 --> 00:16:29,234 ..has ever made it to the surface. 172 00:16:32,594 --> 00:16:37,274 And it's been the same story every day for tens of millions of years. 173 00:16:37,314 --> 00:16:38,514 And it's been the same story every day for tens of millions of years. 174 00:16:40,634 --> 00:16:44,674 The Earth is stuck - a barren desert world 175 00:16:44,714 --> 00:16:48,274 totally incapable of supporting life. 176 00:16:55,234 --> 00:16:58,234 Water today is on a continual journey. 177 00:17:00,674 --> 00:17:04,914 It emerges from the leaves of green plants as vapour, 178 00:17:04,954 --> 00:17:08,154 rises up to the sky, where it forms clouds, 179 00:17:08,194 --> 00:17:10,434 which then condense into rain, 180 00:17:10,474 --> 00:17:13,634 which falls onto the ground, which drains into the rivers, 181 00:17:13,674 --> 00:17:18,034 which eventually flow into our vast oceans. 182 00:17:18,074 --> 00:17:22,394 And we're very used to seeing water appear out of our atmosphere. 183 00:17:22,434 --> 00:17:22,954 And we're very used to seeing water appear out of our atmosphere. 184 00:17:22,994 --> 00:17:27,354 What about those lovely soft layers of mist that we see over rivers, 185 00:17:27,394 --> 00:17:31,474 or the dew on your toes if you scuff across a summer lawn, 186 00:17:31,514 --> 00:17:34,234 or when it falls as rain or snow? 187 00:17:42,194 --> 00:17:45,674 The only reason our planet is a water world is because it's the 188 00:17:45,714 --> 00:17:50,074 right temperature and pressure for water to form out of the atmosphere. 189 00:17:50,114 --> 00:17:50,274 right temperature and pressure for water to form out of the atmosphere. 190 00:17:53,154 --> 00:17:57,274 {\an8}4.4 billion years ago, Earth needed to cool down. 191 00:17:57,314 --> 00:17:57,394 {\an8}4.4 billion years ago, Earth needed to cool down. 192 00:18:00,834 --> 00:18:05,074 Slowly, heat has been radiating out into space... 193 00:18:09,674 --> 00:18:11,994 ..over millions and millions of years. 194 00:18:28,154 --> 00:18:29,314 Until... 195 00:18:32,274 --> 00:18:35,034 ..a tipping point is reached. 196 00:18:53,434 --> 00:18:57,114 What starts with just a few drops 197 00:18:57,154 --> 00:18:59,634 becomes the greatest deluge 198 00:18:59,674 --> 00:19:01,834 the solar system has ever seen. 199 00:19:28,354 --> 00:19:31,154 Huge weather systems sweep across the planet 200 00:19:31,194 --> 00:19:35,674 and storms which last centuries dump oceans of water from the skies. 201 00:19:35,714 --> 00:19:36,154 and storms which last centuries dump oceans of water from the skies. 202 00:19:44,874 --> 00:19:49,034 A key element in the equation of life had been 203 00:19:49,074 --> 00:19:49,434 A key element in the equation of life had been 204 00:19:49,474 --> 00:19:51,114 well and truly unleashed. 205 00:20:01,874 --> 00:20:05,194 Our planet is transformed. 206 00:20:17,434 --> 00:20:21,234 As the Earth continued to cool, the rains that fell from its thick, 207 00:20:21,274 --> 00:20:23,954 dense atmosphere created a new water world. 208 00:20:23,994 --> 00:20:26,674 And for the first time in its history, 209 00:20:26,714 --> 00:20:30,154 it would have looked a little bit like this. 210 00:20:30,194 --> 00:20:33,234 If you gazed into the sky, you would have seen clouds, 211 00:20:33,274 --> 00:20:35,954 you would have felt the wind and the rain on your face. 212 00:20:35,994 --> 00:20:37,874 And if you listened, 213 00:20:37,914 --> 00:20:41,034 you'd have heard waves carving a new coastline. 214 00:20:42,274 --> 00:20:45,034 But that's where the similarities would have ended, 215 00:20:45,074 --> 00:20:49,554 because this rocky, wet world was devoid of life. 216 00:20:49,594 --> 00:20:49,994 because this rocky, wet world was devoid of life. 217 00:20:50,034 --> 00:20:53,114 But it was a world where life could begin. 218 00:21:12,594 --> 00:21:15,674 Water was the crucial ingredient. 219 00:21:21,194 --> 00:21:25,394 Not long after Earth's oceans rained from the sky, 220 00:21:25,434 --> 00:21:26,354 Not long after Earth's oceans rained from the sky, 221 00:21:26,394 --> 00:21:30,554 a shallow pool was about to play host to the most important 222 00:21:30,594 --> 00:21:31,834 a shallow pool was about to play host to the most important 223 00:21:31,874 --> 00:21:34,914 moment in the history of the Earth. 224 00:21:50,394 --> 00:21:53,754 So much of how life began is still a mystery. 225 00:21:57,874 --> 00:22:02,354 It's not known exactly when, where or how it happened. 226 00:22:02,394 --> 00:22:03,114 It's not known exactly when, where or how it happened. 227 00:22:05,554 --> 00:22:09,954 But we do know that, one day on Earth, 228 00:22:09,994 --> 00:22:13,594 a living thing came into existence. 229 00:22:17,474 --> 00:22:20,714 The first microscopic organism. 230 00:22:27,154 --> 00:22:31,954 And in that instant of pure chance, everything changed. 231 00:22:33,994 --> 00:22:37,394 The Earth became a living world. 232 00:22:42,874 --> 00:22:47,434 All trace of the first life has vanished, lost to history. 233 00:22:47,474 --> 00:22:47,594 All trace of the first life has vanished, lost to history. 234 00:22:50,274 --> 00:22:51,914 But even today, 235 00:22:51,954 --> 00:22:56,194 we can get clues as to what early life might have been like. 236 00:23:00,994 --> 00:23:05,474 High in the Andes is one of the largest geyser fields in the world. 237 00:23:10,834 --> 00:23:15,114 The water in this vent is boiling at 85 degrees Centigrade 238 00:23:15,154 --> 00:23:15,234 The water in this vent is boiling at 85 degrees Centigrade 239 00:23:15,274 --> 00:23:18,914 and NASA scientists have looked into this water and found 240 00:23:18,954 --> 00:23:21,954 that it contains one of the highest concentrations of arsenic, 241 00:23:21,994 --> 00:23:24,594 a serious toxin, anywhere in the world. 242 00:23:26,714 --> 00:23:30,074 And these toxic conditions are similar to those 243 00:23:30,114 --> 00:23:32,354 found on the early Earth. 244 00:23:32,394 --> 00:23:35,234 But amongst the poison and boiling water, 245 00:23:35,274 --> 00:23:37,754 something ancient is flourishing. 246 00:23:39,554 --> 00:23:42,114 Just look at all of these beautiful colours here. 247 00:23:45,874 --> 00:23:49,994 That's life - a primordial mat of billions of thriving bacteria. 248 00:23:50,034 --> 00:23:52,354 That's life - a primordial mat of billions of thriving bacteria. 249 00:23:56,394 --> 00:24:00,714 These hardy bacteria are called extremophiles and, just 250 00:24:00,754 --> 00:24:05,114 like their predecessors, they've adapted to live in this hot water. 251 00:24:05,154 --> 00:24:08,794 In fact, they've carved out a niche where they can proliferate. 252 00:24:08,834 --> 00:24:11,514 There are a great range of species here and an enormous 253 00:24:11,554 --> 00:24:14,034 number of individual organisms. 254 00:24:17,154 --> 00:24:21,314 Which just goes to show that even the simplest life is inherently 255 00:24:21,354 --> 00:24:24,874 flexible, adaptable and tough. 256 00:24:24,914 --> 00:24:28,874 So, perhaps it's not surprising that that early life grabbed 257 00:24:28,914 --> 00:24:32,914 an opportunity to try and live in an environment which, for us, 258 00:24:32,954 --> 00:24:35,394 is incredibly harsh and hostile, 259 00:24:35,434 --> 00:24:37,554 but where they could prosper. 260 00:24:44,314 --> 00:24:46,634 Today, life is prolific. 261 00:24:46,674 --> 00:24:50,834 It thrives in the most unlikely of places across the world. 262 00:24:50,874 --> 00:24:54,554 But living in these extreme environments comes 263 00:24:54,594 --> 00:24:56,074 with severe limitations. 264 00:24:57,994 --> 00:25:00,874 The extremophile bacteria living around these 265 00:25:00,914 --> 00:25:03,354 hot springs are essentially locked in, 266 00:25:03,394 --> 00:25:06,634 defined by the very precise requirements in terms of the 267 00:25:06,674 --> 00:25:10,474 heat of the water and the nutrients in it. And if we were to remove 268 00:25:10,514 --> 00:25:15,114 them from this highly specialised environment, they would likely die. 269 00:25:15,194 --> 00:25:18,874 And things were pretty much the same for early life on Earth. 270 00:25:18,914 --> 00:25:23,234 It was essentially stuck, trapped in the niches that it evolved to 271 00:25:23,274 --> 00:25:27,194 survive in. And because all of the nutrients were in the water, 272 00:25:27,234 --> 00:25:31,194 the option for life on land simply wasn't there. 273 00:25:31,234 --> 00:25:35,474 Early life wasn't prolific, widespread, or even visible. 274 00:25:56,074 --> 00:25:59,434 The ancient Earth is harsh and unforgiving... 275 00:26:04,634 --> 00:26:06,114 ..with barren black land... 276 00:26:11,714 --> 00:26:13,514 ..and acidic green oceans. 277 00:26:17,914 --> 00:26:22,634 But the biggest barrier to life's flourishing is the atmosphere, 278 00:26:22,674 --> 00:26:24,754 toxic and orange. 279 00:26:25,994 --> 00:26:29,474 An atmosphere in constant turmoil. 280 00:26:40,394 --> 00:26:45,354 Tectonic movements in the Earth's crust drives land formation, 281 00:26:45,394 --> 00:26:49,434 which in turn creates massive atmospheric instability. 282 00:26:49,474 --> 00:26:49,594 which in turn creates massive atmospheric instability. 283 00:26:55,194 --> 00:26:57,954 Vicious winds sweep dust high up into the air... 284 00:27:01,514 --> 00:27:04,314 ..and these dust particles create more clouds. 285 00:27:08,514 --> 00:27:13,034 Storms rage across the planet, laced with poisonous gasses... 286 00:27:13,074 --> 00:27:13,994 Storms rage across the planet, laced with poisonous gasses... 287 00:27:16,074 --> 00:27:19,394 ..deadly to the vast majority of life we know today. 288 00:27:27,474 --> 00:27:32,434 But whilst chaos rages above the waves, deep underwater 289 00:27:32,474 --> 00:27:36,554 our ancestors are simply existing, 290 00:27:36,594 --> 00:27:38,154 seemingly trapped... 291 00:27:40,514 --> 00:27:41,994 ..with no means of escape... 292 00:27:46,354 --> 00:27:50,954 ..day after day, for nearly a billion years 293 00:27:50,994 --> 00:27:51,234 ..day after day, for nearly a billion years 294 00:27:51,274 --> 00:27:53,514 where nothing appears to happen. 295 00:28:08,434 --> 00:28:11,834 Today, life is no longer confined to the water. 296 00:28:13,154 --> 00:28:15,274 Oh, yes, what a view! 297 00:28:16,354 --> 00:28:20,514 Both life and the atmosphere that supports it have undergone 298 00:28:20,554 --> 00:28:22,354 an astonishing transformation. 299 00:28:36,274 --> 00:28:37,514 It's a male. 300 00:28:37,554 --> 00:28:40,634 It's got the comb on top of its head and its feathers are all silvery, 301 00:28:40,674 --> 00:28:44,634 rippling in the wind as it glides along the edge of this escarpment. 302 00:28:46,594 --> 00:28:49,234 With a wingspan of more than 3m, 303 00:28:49,274 --> 00:28:53,194 the giant Andean condor is one of the largest birds on Earth. 304 00:28:54,394 --> 00:28:57,194 Oh, goodness me! Look at that! 305 00:29:00,794 --> 00:29:03,714 Absolutely sensational. Now I can see its eye. 306 00:29:03,754 --> 00:29:07,594 I'm looking into the eye of an Andean condor. 307 00:29:07,634 --> 00:29:08,914 Oh! 308 00:29:08,954 --> 00:29:10,674 It's ornithological nirvana! 309 00:29:13,794 --> 00:29:17,714 Watching these giant birds soaring here 310 00:29:17,754 --> 00:29:22,234 just reveals how their life is completely intertwined with 311 00:29:22,274 --> 00:29:22,914 just reveals how their life is completely intertwined with 312 00:29:22,954 --> 00:29:26,754 that thin cloak of air that's wrapped around our planet. 313 00:29:26,794 --> 00:29:31,194 But then, when you think about it, everything - every plant, 314 00:29:31,234 --> 00:29:35,554 fungi, every bacteria, every tiny insect, every giant reptile, 315 00:29:35,594 --> 00:29:39,674 even us - are completely dependent on this atmosphere. 316 00:29:39,714 --> 00:29:40,514 even us - are completely dependent on this atmosphere. 317 00:29:46,394 --> 00:29:50,754 So, how DID the atmosphere go from a toxic orange haze to the 318 00:29:50,794 --> 00:29:53,674 nurturing cocktail of gasses we know today? 319 00:29:57,834 --> 00:30:02,234 Well, it was life itself that would make the difference... 320 00:30:02,274 --> 00:30:03,074 Well, it was life itself that would make the difference... 321 00:30:05,234 --> 00:30:08,114 ..thanks to a giant evolutionary leap. 322 00:30:11,354 --> 00:30:14,834 {\an8}The development of complex life was far from inevitable. 323 00:30:14,874 --> 00:30:15,954 When you think about it, 324 00:30:15,994 --> 00:30:18,274 there are plenty of forks in the road of evolution, 325 00:30:18,314 --> 00:30:19,994 trillions of dead ends 326 00:30:20,034 --> 00:30:22,834 and there is no definitive end point. 327 00:30:22,874 --> 00:30:27,274 But the very fact that we exist proves that whatever card 328 00:30:27,314 --> 00:30:30,714 is thrown at life, it plays it and it survives. 329 00:30:35,834 --> 00:30:37,434 And that's precisely 330 00:30:37,474 --> 00:30:40,994 what was happening 3.5 billion years ago. 331 00:30:41,034 --> 00:30:45,314 Life was playing its card - slowly evolving, gently proliferating - 332 00:30:45,354 --> 00:30:46,954 Life was playing its card - slowly evolving, gently proliferating - 333 00:30:46,994 --> 00:30:50,954 and it wasn't quite as stuck as we might have thought it was. 334 00:30:50,994 --> 00:30:55,554 In fact, a significant development in a single cell was about to 335 00:30:55,594 --> 00:30:55,714 In fact, a significant development in a single cell was about to 336 00:30:55,754 --> 00:30:59,194 change the way that life could exist. 337 00:30:59,234 --> 00:31:03,554 Life was about to take a quantum leap forward. 338 00:31:06,914 --> 00:31:11,034 A leap, that would change our atmosphere forever. 339 00:31:20,954 --> 00:31:25,274 It started with a mutation that altered the fundamental 340 00:31:25,314 --> 00:31:25,634 It started with a mutation that altered the fundamental 341 00:31:25,674 --> 00:31:28,314 chemistry of the cells... 342 00:31:29,674 --> 00:31:32,714 ..giving them the ability to capture the sun's rays... 343 00:31:35,394 --> 00:31:38,874 ..and store the energy as glucose, 344 00:31:38,914 --> 00:31:43,674 energy the cells can then use to grow and reproduce. 345 00:31:49,154 --> 00:31:52,234 This was photosynthesis... 346 00:31:53,794 --> 00:31:57,594 ..an evolutionary innovation that will change 347 00:31:57,634 --> 00:32:01,034 the course of Earth's history forever. 348 00:32:15,074 --> 00:32:18,874 The ancestors of this cell are still around today. 349 00:32:22,754 --> 00:32:25,714 They can be found in almost every puddle, lake, 350 00:32:25,754 --> 00:32:27,714 sea or ocean across our planet. 351 00:32:31,674 --> 00:32:35,594 Peering down through this microscope is like taking a look 352 00:32:35,634 --> 00:32:40,154 back at life on Earth almost 3.5 billion years ago. 353 00:32:40,194 --> 00:32:41,394 back at life on Earth almost 3.5 billion years ago. 354 00:32:41,434 --> 00:32:46,274 You see, these rod-shaped structures here are cyanobacteria, 355 00:32:46,314 --> 00:32:47,634 You see, these rod-shaped structures here are cyanobacteria, 356 00:32:47,674 --> 00:32:50,634 and we think they're pretty similar to those that existed 357 00:32:50,674 --> 00:32:55,514 trillions of generations ago, when our atmosphere was very different. 358 00:32:55,554 --> 00:32:56,114 trillions of generations ago, when our atmosphere was very different. 359 00:32:56,154 --> 00:32:59,234 Now, they may not look impressive, but I've got to tell you, 360 00:32:59,274 --> 00:33:03,754 they're probably one of the most successful organisms to ever live. 361 00:33:03,794 --> 00:33:03,994 they're probably one of the most successful organisms to ever live. 362 00:33:04,034 --> 00:33:08,834 A little over 3 billion years ago, these tiny flecks, 363 00:33:08,874 --> 00:33:09,274 A little over 3 billion years ago, these tiny flecks, 364 00:33:09,314 --> 00:33:11,394 these microscopic organisms 365 00:33:11,434 --> 00:33:15,594 just a fraction of a millimetre across, started to build 366 00:33:15,634 --> 00:33:20,154 an atmosphere which humans could live and breathe in. 367 00:33:20,194 --> 00:33:20,714 an atmosphere which humans could live and breathe in. 368 00:33:26,074 --> 00:33:30,114 Thanks to energy from the sun, these cells are able to steal 369 00:33:30,154 --> 00:33:34,474 hydrogen from water molecules and combine it with the carbon dioxide 370 00:33:34,514 --> 00:33:35,674 hydrogen from water molecules and combine it with the carbon dioxide 371 00:33:35,714 --> 00:33:40,634 dissolved in the oceans, fabricating essential tools for life. 372 00:33:40,674 --> 00:33:41,154 dissolved in the oceans, fabricating essential tools for life. 373 00:33:48,514 --> 00:33:52,394 Individually, these revolutionary cells, 374 00:33:52,434 --> 00:33:55,434 which you can still find in water bodies like this all across 375 00:33:55,474 --> 00:33:58,434 the planet, produced a negligible, 376 00:33:58,474 --> 00:34:01,714 unremarkable, nonexistent effect. 377 00:34:03,234 --> 00:34:05,914 But when they combined in their trillions, 378 00:34:05,954 --> 00:34:09,834 when they combined en masse, they were about to demonstrate, 379 00:34:09,874 --> 00:34:14,474 for the very first time, the awesome power of life on Earth, 380 00:34:14,514 --> 00:34:15,714 for the very first time, the awesome power of life on Earth, 381 00:34:15,754 --> 00:34:19,994 and that would have a profound, long-lasting 382 00:34:20,034 --> 00:34:23,114 physical resonance on our planet. 383 00:34:27,354 --> 00:34:30,594 Life powered by photosynthesis thrived. 384 00:34:35,154 --> 00:34:38,914 Cells with this new ability to harness energy from the sun 385 00:34:38,954 --> 00:34:41,674 out-competed those that couldn't. 386 00:34:43,274 --> 00:34:45,474 So, they began to multiply. 387 00:34:49,194 --> 00:34:50,874 One becomes two. 388 00:34:52,194 --> 00:34:53,474 Two become four. 389 00:35:05,794 --> 00:35:09,154 Until there are literally trillions of offspring. 390 00:35:11,914 --> 00:35:16,034 Enough to fundamentally change the chemistry of our world. 391 00:35:16,074 --> 00:35:17,754 Enough to fundamentally change the chemistry of our world. 392 00:35:25,994 --> 00:35:30,354 Photosynthesis was a game-changer for life because the 393 00:35:30,394 --> 00:35:31,194 Photosynthesis was a game-changer for life because the 394 00:35:31,234 --> 00:35:35,514 ingredients that it required were so readily available and abundant. 395 00:35:35,554 --> 00:35:35,874 ingredients that it required were so readily available and abundant. 396 00:35:35,914 --> 00:35:40,634 But the by-products of many types of photosynthesis include a very 397 00:35:40,674 --> 00:35:41,834 But the by-products of many types of photosynthesis include a very 398 00:35:41,874 --> 00:35:44,674 reactive and dangerous gas. 399 00:35:44,714 --> 00:35:48,634 Now, for these revolutionary early organisms, 400 00:35:48,674 --> 00:35:51,914 this was just a waste product, something to be thrown away. 401 00:35:51,954 --> 00:35:54,274 But for the likes of you and I, 402 00:35:54,314 --> 00:35:59,074 and the rest of complex life on Earth, it's absolutely essential. 403 00:35:59,114 --> 00:35:59,754 and the rest of complex life on Earth, it's absolutely essential. 404 00:35:59,794 --> 00:36:02,914 I'm talking, of course, about oxygen. 405 00:36:08,594 --> 00:36:12,434 {\an8}Trillions of bacteria are spread across the ancient oceans... 406 00:36:17,434 --> 00:36:21,634 ..and the waste oxygen they throw away is enough to build a new 407 00:36:21,674 --> 00:36:21,874 ..and the waste oxygen they throw away is enough to build a new 408 00:36:21,914 --> 00:36:24,314 atmosphere for our planet. 409 00:36:29,434 --> 00:36:32,554 Bubbles of oxygen race upwards, towards the surface. 410 00:36:37,234 --> 00:36:38,514 But they can't escape. 411 00:36:42,994 --> 00:36:45,994 The bubbles are absorbed and vanish. 412 00:36:54,834 --> 00:36:59,594 Earth seems trapped, with a toxic atmosphere of methane 413 00:36:59,634 --> 00:36:59,954 Earth seems trapped, with a toxic atmosphere of methane 414 00:36:59,994 --> 00:37:01,634 and carbon dioxide. 415 00:37:15,914 --> 00:37:19,514 The Earth was essentially in stasis. 416 00:37:19,554 --> 00:37:23,434 You see, that toxic orange atmosphere still enveloped 417 00:37:23,474 --> 00:37:24,834 the planet. 418 00:37:24,874 --> 00:37:29,154 Life was still microscopic and could only exist in the oceans, 419 00:37:29,194 --> 00:37:33,234 and there was no oxygen in the atmosphere. 420 00:37:33,274 --> 00:37:37,194 To all intents and purposes, you could say, well, 421 00:37:37,234 --> 00:37:39,314 that the planet was stuck. 422 00:37:42,114 --> 00:37:44,634 But that was about to change. 423 00:37:49,074 --> 00:37:53,034 Because it wasn't just oxygen dissolved in the water - 424 00:37:53,074 --> 00:37:54,794 there were metals, too... 425 00:37:57,754 --> 00:38:00,274 ..including iron. 426 00:38:05,394 --> 00:38:08,754 {\an8}The iron, like oxygen, is invisible 427 00:38:08,794 --> 00:38:11,754 to us when it's dissolved in water. 428 00:38:11,794 --> 00:38:14,794 But we all know what happens when iron, 429 00:38:14,834 --> 00:38:16,794 oxygen and water come together... 430 00:38:19,754 --> 00:38:23,634 ..and there's plenty of evidence of that on this old bus. 431 00:38:26,514 --> 00:38:30,194 {\an8}Just look here - this lovely brown, 432 00:38:30,234 --> 00:38:32,034 {\an8}orange and red. 433 00:38:33,354 --> 00:38:34,594 Rust. 434 00:38:34,634 --> 00:38:38,514 The iron is being oxidised - aggressively attacked 435 00:38:38,554 --> 00:38:42,314 by the oxygen in the presence of water, or water vapour. 436 00:38:42,354 --> 00:38:45,634 But what's interesting is that, whilst the iron 437 00:38:45,674 --> 00:38:49,994 and whilst the oxygen are soluble in water, 438 00:38:50,034 --> 00:38:51,994 the rust is not. 439 00:39:09,554 --> 00:39:11,874 The newly released oxygen reacts 440 00:39:11,914 --> 00:39:14,434 with the dissolved iron already present 441 00:39:14,474 --> 00:39:17,194 in the oceans, 442 00:39:17,234 --> 00:39:21,314 and that causes something extraordinary to happen. 443 00:39:23,194 --> 00:39:25,874 Rust pours onto the ocean floor. 444 00:39:35,994 --> 00:39:38,114 The world's oceans turn red. 445 00:39:50,394 --> 00:39:52,474 And if you know where to look, you can 446 00:39:52,514 --> 00:39:55,554 still find evidence for this bizarre effect. 447 00:39:57,914 --> 00:39:59,754 {\an8}I'm armed with a rock hammer. 448 00:39:59,794 --> 00:40:02,834 {\an8}If I have a little tap at this stone, there we are. 449 00:40:02,874 --> 00:40:04,594 Let's have a look at what's inside. 450 00:40:05,914 --> 00:40:09,234 This rock once formed part of an ancient seafloor. 451 00:40:09,274 --> 00:40:11,954 Hm, look at that. 452 00:40:11,994 --> 00:40:14,674 You see that there, that red? 453 00:40:14,714 --> 00:40:16,674 That's iron 454 00:40:16,714 --> 00:40:20,074 laid down billions of years ago, 455 00:40:20,114 --> 00:40:23,874 a volatile memory of oxygen reacting 456 00:40:23,914 --> 00:40:26,754 with iron in the early seas. 457 00:40:27,874 --> 00:40:30,554 A sort of geological tattoo. 458 00:40:30,594 --> 00:40:31,754 I love that. 459 00:40:34,314 --> 00:40:36,914 This rust was to have a profound effect 460 00:40:36,954 --> 00:40:39,554 on our Earth's young atmosphere. 461 00:40:46,674 --> 00:40:51,354 For half a billion years, oxygen has been trapped in the oceans. 462 00:40:51,394 --> 00:40:51,754 For half a billion years, oxygen has been trapped in the oceans. 463 00:40:54,154 --> 00:40:58,514 But now, iron has almost been totally flushed from the seas. 464 00:40:58,554 --> 00:40:58,674 But now, iron has almost been totally flushed from the seas. 465 00:41:04,194 --> 00:41:08,794 At last, the oxygen in the water has nothing else to react with. 466 00:41:08,834 --> 00:41:09,474 At last, the oxygen in the water has nothing else to react with. 467 00:41:11,434 --> 00:41:13,874 It can break free. 468 00:41:39,234 --> 00:41:43,634 Over millions years, oxygen flooded from the oceans... 469 00:41:43,674 --> 00:41:43,994 Over millions years, oxygen flooded from the oceans... 470 00:41:48,154 --> 00:41:50,954 ..and our atmosphere was transformed. 471 00:42:11,354 --> 00:42:14,514 When those bubbles first breached the surface of the ocean, 472 00:42:14,554 --> 00:42:17,354 you might have thought that the atmosphere was getting 473 00:42:17,394 --> 00:42:20,594 a breath of fresh air, and to some extent it was. 474 00:42:20,634 --> 00:42:25,194 But this wasn't the moment when life suddenly flourished, 475 00:42:25,234 --> 00:42:29,794 or when it developed that complete and utter dependence that 476 00:42:29,834 --> 00:42:29,874 or when it developed that complete and utter dependence that 477 00:42:29,914 --> 00:42:32,794 contemporary complex life has upon oxygen. 478 00:42:34,394 --> 00:42:38,994 But that's not to say that when those bubbles first fizzed 479 00:42:39,034 --> 00:42:39,274 But that's not to say that when those bubbles first fizzed 480 00:42:39,314 --> 00:42:42,114 out there that this wasn't a momentous moment. 481 00:42:42,154 --> 00:42:43,634 It was. 482 00:42:43,674 --> 00:42:46,754 The planet was about to be re-calibrated, 483 00:42:46,794 --> 00:42:49,874 and the relationship between the ocean, 484 00:42:49,914 --> 00:42:54,274 the land and the atmosphere was going to change forever. 485 00:42:54,314 --> 00:42:58,514 And as this volatile, reactive gas flooded into the atmosphere, the 486 00:42:58,554 --> 00:42:59,794 And as this volatile, reactive gas flooded into the atmosphere, the 487 00:42:59,834 --> 00:43:04,634 full destructive force of oxygen was felt across the planet's surface. 488 00:43:04,674 --> 00:43:05,034 full destructive force of oxygen was felt across the planet's surface. 489 00:43:27,634 --> 00:43:29,914 Oxygen attacks the Earth. 490 00:43:39,034 --> 00:43:43,634 Any rocks containing iron and aluminium rust and crumble, 491 00:43:43,674 --> 00:43:44,514 Any rocks containing iron and aluminium rust and crumble, 492 00:43:44,554 --> 00:43:47,434 driving vast dust storms. 493 00:43:51,314 --> 00:43:54,674 The world is being torn apart by its own atmosphere... 494 00:43:57,554 --> 00:44:01,034 ..and this has a startling side-effect - 495 00:44:01,074 --> 00:44:04,394 the entire Earth turns a vivid red. 496 00:44:12,314 --> 00:44:16,194 Scientists find evidence for this red Earth in 497 00:44:16,234 --> 00:44:19,594 rock formations in landscapes all over the world. 498 00:44:19,634 --> 00:44:23,914 Direct evidence of the action of all of those 499 00:44:23,954 --> 00:44:28,074 trillions of cyanobacteria churning out oxygen. 500 00:44:28,114 --> 00:44:32,834 And before oxygen, the planet was barren, grey and black. 501 00:44:32,874 --> 00:44:34,274 And before oxygen, the planet was barren, grey and black. 502 00:44:34,314 --> 00:44:38,954 You see, it's oxidation that gives us this wonderful red hue. 503 00:44:38,994 --> 00:44:39,954 You see, it's oxidation that gives us this wonderful red hue. 504 00:44:56,794 --> 00:44:59,674 But oxygen's effect on the land went further. 505 00:45:02,594 --> 00:45:06,074 You see, oxygen doesn't just react with iron - 506 00:45:06,114 --> 00:45:08,394 it reacts with pretty much anything. 507 00:45:09,514 --> 00:45:12,674 It attacks minerals within the Earth's crust... 508 00:45:16,594 --> 00:45:20,954 ..creating as many as 3,000 exotic new minerals, 509 00:45:20,994 --> 00:45:24,074 all previously unknown to the solar system. 510 00:45:30,474 --> 00:45:34,514 Minerals that led to an explosion of colour right across the planet. 511 00:45:43,114 --> 00:45:45,434 Minerals that, to this day, 512 00:45:45,474 --> 00:45:49,754 play a vital role in sustaining the rich complexity of life we know. 513 00:45:49,794 --> 00:45:49,954 play a vital role in sustaining the rich complexity of life we know. 514 00:45:55,354 --> 00:45:59,994 Now, one of the colours unleashed by oxygen is this rather 515 00:46:00,034 --> 00:46:01,594 Now, one of the colours unleashed by oxygen is this rather 516 00:46:01,634 --> 00:46:04,554 wonderful sea green here. 517 00:46:05,714 --> 00:46:08,154 You see, when copper, the metal, 518 00:46:08,194 --> 00:46:12,314 comes into contact with oxygen in the air, it oxidises, 519 00:46:12,394 --> 00:46:15,194 producing this - copper oxide. 520 00:46:15,234 --> 00:46:18,434 And it turns out that this compound 521 00:46:18,474 --> 00:46:22,554 was fundamentally important in the development of more complex 522 00:46:22,594 --> 00:46:23,074 was fundamentally important in the development of more complex 523 00:46:23,114 --> 00:46:27,674 life. And what's more, it retains its biological importance today. 524 00:46:27,714 --> 00:46:28,874 life. And what's more, it retains its biological importance today. 525 00:46:28,914 --> 00:46:33,834 It's necessary for the synthesis of neurotransmitters in our brains, 526 00:46:33,874 --> 00:46:34,074 It's necessary for the synthesis of neurotransmitters in our brains, 527 00:46:34,114 --> 00:46:35,994 and the brains of other animals, 528 00:46:36,034 --> 00:46:39,514 and also for the production of hormones and pigments. 529 00:46:39,554 --> 00:46:42,514 So, even in today's world, 530 00:46:42,554 --> 00:46:47,154 life is dependent on that chemical complexity that was unlocked 531 00:46:47,194 --> 00:46:47,794 life is dependent on that chemical complexity that was unlocked 532 00:46:47,834 --> 00:46:52,274 so long ago, when our atmosphere became richer in oxygen. 533 00:46:52,314 --> 00:46:53,354 so long ago, when our atmosphere became richer in oxygen. 534 00:47:05,354 --> 00:47:09,114 Thanks to oxygen, we live in a world of extraordinary colour 535 00:47:09,154 --> 00:47:10,634 and diversity. 536 00:47:14,114 --> 00:47:17,794 A myriad of minerals colours the Earth's surface... 537 00:47:21,434 --> 00:47:23,674 ..and the biological world has continued 538 00:47:23,714 --> 00:47:25,914 to make use of this ever-increasing 539 00:47:25,954 --> 00:47:29,994 chemical complexity to transform the planet. 540 00:47:30,034 --> 00:47:33,274 From the rich green carpet of plant life... 541 00:47:35,554 --> 00:47:36,634 SHUTTER CLICKS 542 00:47:38,074 --> 00:47:42,154 {\an8}..to the fluorescent pink feathers of flamingos. 543 00:47:55,634 --> 00:47:59,954 Oxygen has allowed life to flourish in ways unimaginable 544 00:47:59,994 --> 00:48:00,314 Oxygen has allowed life to flourish in ways unimaginable 545 00:48:00,354 --> 00:48:01,874 3 billion years ago. 546 00:48:03,394 --> 00:48:08,154 But this volatile gas had one more gift to bestow. 547 00:48:12,034 --> 00:48:16,354 As oxygen enriches the atmosphere, it reacts with methane, 548 00:48:16,394 --> 00:48:16,914 As oxygen enriches the atmosphere, it reacts with methane, 549 00:48:16,954 --> 00:48:18,714 stripping it away. 550 00:48:21,914 --> 00:48:26,634 And as methane levels drop, the orange haze lifts. 551 00:48:26,674 --> 00:48:27,554 And as methane levels drop, the orange haze lifts. 552 00:48:30,754 --> 00:48:33,834 Nitrogen and oxygen in the atmosphere are left 553 00:48:33,874 --> 00:48:35,394 to scatter the light. 554 00:48:37,074 --> 00:48:39,314 The colour begins to change. 555 00:48:43,594 --> 00:48:48,154 For the first time in Earth's history, the sky 556 00:48:48,194 --> 00:48:48,274 For the first time in Earth's history, the sky 557 00:48:48,314 --> 00:48:50,954 is an oxygen-rich, brilliant blue. 558 00:49:06,154 --> 00:49:10,714 Today, this lovely thin blue line marks our Earth as unique 559 00:49:10,754 --> 00:49:11,474 Today, this lovely thin blue line marks our Earth as unique 560 00:49:11,514 --> 00:49:14,434 in the entire known universe. 561 00:49:14,474 --> 00:49:18,674 It's a spectacular demonstration of a 4 billion-year 562 00:49:18,714 --> 00:49:22,434 dance between our atmosphere and life - 563 00:49:22,474 --> 00:49:24,834 an atmosphere that was 564 00:49:24,874 --> 00:49:29,194 created, shaped and calibrated by life itself. 565 00:49:29,234 --> 00:49:29,394 created, shaped and calibrated by life itself. 566 00:49:33,194 --> 00:49:37,394 Our planet went from volatile, fiery and dead to the beautiful 567 00:49:37,434 --> 00:49:39,314 Our planet went from volatile, fiery and dead to the beautiful 568 00:49:39,354 --> 00:49:41,794 living and breathing blue bubble 569 00:49:41,834 --> 00:49:44,474 floating in the darkness of space. 570 00:50:05,914 --> 00:50:10,194 How do scientists unravel billions of years of our planet's history? 571 00:50:14,114 --> 00:50:18,394 In this episode, we saw how meteorites - 572 00:50:18,434 --> 00:50:19,394 In this episode, we saw how meteorites - 573 00:50:19,434 --> 00:50:21,954 rocks that have fallen from space - 574 00:50:21,994 --> 00:50:25,674 can tell us what Earth's early atmosphere was made from. 575 00:50:26,874 --> 00:50:29,314 This is a chondrite meteorite. 576 00:50:29,354 --> 00:50:33,154 4.567 billion years old - 577 00:50:33,194 --> 00:50:35,474 the oldest thing you could hold in your hand - 578 00:50:35,514 --> 00:50:37,514 and it's made of all these tiny droplets 579 00:50:37,554 --> 00:50:41,034 that were part of the earliest solar nebula, including 580 00:50:41,074 --> 00:50:44,754 all the gasses that eventually would wind up in the atmosphere. 581 00:50:48,874 --> 00:50:52,634 Meteorites are so valuable to science 582 00:50:52,674 --> 00:50:55,834 that researchers go to great lengths to track them down. 583 00:50:59,234 --> 00:51:03,514 In 2020, scientists from the University of Manchester set out 584 00:51:03,554 --> 00:51:04,234 In 2020, scientists from the University of Manchester set out 585 00:51:04,274 --> 00:51:08,634 on a nine-week expedition to one of the most remote areas of Antarctica. 586 00:51:08,674 --> 00:51:09,154 on a nine-week expedition to one of the most remote areas of Antarctica. 587 00:51:11,674 --> 00:51:14,754 Meteorite hunters go into the depths of Antarctica, 588 00:51:14,794 --> 00:51:18,754 into the extremes of the cold, near the South Pole, because 589 00:51:18,794 --> 00:51:22,034 they can find so many meteorites in one expedition, because the 590 00:51:22,074 --> 00:51:26,594 meteorites show up so well on the white ice... 591 00:51:26,634 --> 00:51:30,474 ..compared to, say, other places where the meteorites are 592 00:51:30,514 --> 00:51:32,834 very hard to spot from normal rocks. 593 00:51:35,794 --> 00:51:38,234 Studying meteorites has helped answer some of the most 594 00:51:38,274 --> 00:51:41,314 fundamental questions about our planet. 595 00:51:42,994 --> 00:51:46,314 So, the question of where the water on Earth came from 596 00:51:46,354 --> 00:51:49,994 and when it arrived is really central to everything. 597 00:51:51,234 --> 00:51:55,834 Some water was present in the material that formed our planet, 598 00:51:55,874 --> 00:51:56,274 Some water was present in the material that formed our planet, 599 00:51:56,314 --> 00:51:58,434 but that's not the whole story. 600 00:52:00,194 --> 00:52:03,914 We think that one of the other ways that the Earth got its water 601 00:52:03,954 --> 00:52:05,914 is through meteorites. 602 00:52:05,954 --> 00:52:10,154 So, these meteorites would have had water locked into their rocks, 603 00:52:10,194 --> 00:52:10,234 So, these meteorites would have had water locked into their rocks, 604 00:52:10,274 --> 00:52:13,954 or perhaps even on their surface, as frozen, in outer space. 605 00:52:15,634 --> 00:52:17,794 And then, the water would have been degassed 606 00:52:17,834 --> 00:52:20,034 into our atmosphere as water vapour. 607 00:52:20,074 --> 00:52:22,714 Later on, when the Earth cooled even further, 608 00:52:22,754 --> 00:52:24,714 that atmosphere would have condensed 609 00:52:24,754 --> 00:52:28,554 and the water vapour would have then formed liquid water on our surface. 610 00:52:32,154 --> 00:52:36,834 Scientists think it's only after the arrival of water that life 611 00:52:36,874 --> 00:52:36,954 Scientists think it's only after the arrival of water that life 612 00:52:36,994 --> 00:52:38,874 was able to get started. 613 00:52:41,114 --> 00:52:45,274 The origin of life is one of the greatest questions in science and 614 00:52:45,314 --> 00:52:49,634 it's fair to say that we don't know when, where or how life started. 615 00:52:51,594 --> 00:52:54,874 A shallow rock pool is one of the leading theories. 616 00:52:56,034 --> 00:52:58,874 People think that shallow pools would have been a potentially 617 00:52:58,914 --> 00:53:01,514 important site for the origin of life because they can get 618 00:53:01,554 --> 00:53:03,514 wet and dry over and over again. 619 00:53:06,474 --> 00:53:09,674 Through this repeated cycling of wetting and drying, 620 00:53:09,714 --> 00:53:12,874 re-flooding and evaporating, maybe through a tide, maybe through 621 00:53:12,914 --> 00:53:16,874 seasonal variation, more and more complex molecules can form. 622 00:53:19,114 --> 00:53:22,834 And that process could have been the precursors for things like DNA, 623 00:53:22,874 --> 00:53:25,754 which is what makes up the information in our cells today. 624 00:53:29,674 --> 00:53:31,674 But there are other theories. 625 00:53:37,154 --> 00:53:41,434 Some scientists think life began in a deep-sea hydrothermal vent. 626 00:53:41,474 --> 00:53:41,714 Some scientists think life began in a deep-sea hydrothermal vent. 627 00:53:45,354 --> 00:53:48,954 Hydrothermal vents are sources of gases, 628 00:53:48,994 --> 00:53:51,514 like hydrogen sulphide for example, and provide 629 00:53:51,554 --> 00:53:54,874 the kind of reactive conditions to make the building blocks of life. 630 00:53:57,034 --> 00:54:01,234 Others think that life originated somewhere completely else - 631 00:54:01,274 --> 00:54:05,034 not on the Earth at all - and landed here on a meteorite. 632 00:54:10,074 --> 00:54:13,514 All of these different theories have sort of different details, 633 00:54:13,554 --> 00:54:16,874 but the punch line is that life needed water 634 00:54:16,914 --> 00:54:19,354 and it needed a way to harness energy. 635 00:54:23,434 --> 00:54:26,314 Although life's origins are still debated, 636 00:54:26,354 --> 00:54:29,834 scientists have some idea when it happened. 637 00:54:32,034 --> 00:54:36,714 This is one of the clear-cut examples that life was living 638 00:54:36,754 --> 00:54:38,314 even 3 billion years ago. 639 00:54:38,354 --> 00:54:40,434 This is a formation called a stromatolite. 640 00:54:40,474 --> 00:54:42,874 What you're looking at shows a structure 641 00:54:42,914 --> 00:54:46,794 created by a lot of microorganisms, single-celled organisms. 642 00:54:46,834 --> 00:54:51,154 And as they grow and they reach for the light, they secrete various 643 00:54:51,194 --> 00:54:52,274 And as they grow and they reach for the light, they secrete various 644 00:54:52,314 --> 00:54:57,314 gluey substances that glue together bits of sand in the environment, 645 00:54:57,354 --> 00:54:58,074 gluey substances that glue together bits of sand in the environment, 646 00:54:58,114 --> 00:55:01,954 and that actually helps keep it from dispersing and blowing away. 647 00:55:01,994 --> 00:55:05,514 They are astounding in that they have the ability to adapt to 648 00:55:05,554 --> 00:55:08,354 environmental change and to change the environment 649 00:55:08,394 --> 00:55:10,194 because they can be so abundant. 650 00:55:12,394 --> 00:55:16,794 These fossilised structures were created by cyanobacteria 651 00:55:16,834 --> 00:55:17,634 These fossilised structures were created by cyanobacteria 652 00:55:17,674 --> 00:55:20,674 and millions of them can still be found along the coast 653 00:55:20,714 --> 00:55:22,314 of Western Australia. 654 00:55:24,074 --> 00:55:27,194 Cyanobacteria might not seem so impressive, 655 00:55:27,234 --> 00:55:29,954 but they're probably one of the most influential 656 00:55:29,994 --> 00:55:33,314 and successful organisms ever to appear on planet Earth. 657 00:55:34,794 --> 00:55:39,234 They were the organisms that invented this ability to 658 00:55:39,274 --> 00:55:43,474 break water into oxygen and hydrogen 659 00:55:43,514 --> 00:55:43,634 break water into oxygen and hydrogen 660 00:55:43,674 --> 00:55:46,154 and spit out that oxygen. 661 00:55:47,834 --> 00:55:50,954 That oxygen was able to get released into our atmosphere. 662 00:55:53,274 --> 00:55:56,874 They completely transformed the world. 663 00:56:00,194 --> 00:56:03,914 There are these moments in the history of life that seem to 664 00:56:03,954 --> 00:56:06,034 have only happened once. 665 00:56:06,074 --> 00:56:09,514 Oxygen producing photosynthesis is one of them. 666 00:56:09,554 --> 00:56:12,034 Was it a freak accident? We just don't know. 667 00:56:14,794 --> 00:56:17,674 The evolution of our atmosphere is, in many respects, 668 00:56:17,714 --> 00:56:21,034 the story of the evolution of life on our planet. 669 00:56:21,074 --> 00:56:23,594 Life can change a planet fundamentally. 670 00:56:27,074 --> 00:56:30,474 But it's always this cause-and-effect kind of dance 671 00:56:30,514 --> 00:56:32,954 between the environment changing life 672 00:56:32,994 --> 00:56:34,834 and life changing the environment. 673 00:56:38,554 --> 00:56:42,514 The story of our changing atmosphere is not over. 674 00:56:42,554 --> 00:56:45,514 It will continue to evolve both naturally 675 00:56:45,554 --> 00:56:48,274 and under the influence of human activity. 676 00:56:50,714 --> 00:56:53,754 If we don't understand the history of the atmosphere, 677 00:56:53,794 --> 00:56:57,594 how can we possibly be the stewards of the atmosphere moving forward? 678 00:57:01,554 --> 00:57:03,354 By understanding the huge 679 00:57:03,394 --> 00:57:07,314 and complex steps it took to develop our atmosphere, hopefully 680 00:57:07,354 --> 00:57:10,674 we can develop approaches to take care of it for generations to come. 681 00:57:19,314 --> 00:57:20,434 Next time... 682 00:57:24,874 --> 00:57:27,114 ..the making of the modern world. 683 00:57:28,554 --> 00:57:30,714 How the end of the dinosaurs... 684 00:57:33,274 --> 00:57:36,634 ..through cataclysm and chaos, 685 00:57:36,674 --> 00:57:39,714 set the stage for a human planet... 686 00:57:41,354 --> 00:57:42,954 ..to take its place. 687 00:57:49,194 --> 00:57:51,874 If the Earth could talk, what would it tell us? 688 00:57:51,914 --> 00:57:54,354 Well, the Open University imagine how it might answer 689 00:57:54,394 --> 00:57:56,274 some of our questions. 690 00:57:56,314 --> 00:57:59,074 To experience this interactive presentation, go to the 691 00:57:59,114 --> 00:58:02,834 website on the screen and follow the links to the Open University.