1 00:00:24,635 --> 00:00:29,555 The heavens. The great bowl of the heavens, of our sky. 2 00:00:30,835 --> 00:00:33,195 Just so beautiful! 3 00:00:33,195 --> 00:00:37,755 I love the sky because, wherever I am in the world, if I can find 4 00:00:37,755 --> 00:00:41,195 some space, I can look up at this 5 00:00:41,195 --> 00:00:45,075 big, blue, pristine space. 6 00:00:48,995 --> 00:00:54,435 And I like the apparent permanence - the fact that I can stare into 7 00:00:54,435 --> 00:00:59,155 a sky that the dinosaurs stared into, that Neanderthals stared into. 8 00:01:01,595 --> 00:01:06,075 The atmosphere is essential for the Earth to be habitable at all. 9 00:01:07,435 --> 00:01:11,835 This thin layer of gas that clings to our planet, 10 00:01:11,835 --> 00:01:15,595 keeps liquid water on the Earth's surface 11 00:01:15,595 --> 00:01:19,955 and shields life from the most harmful of the sun's rays. 12 00:01:22,875 --> 00:01:26,555 As far as we know, our thin blue line is unique 13 00:01:26,555 --> 00:01:28,915 in the vast void of space... 14 00:01:31,755 --> 00:01:35,155 ..and today, scientists are beginning to piece 15 00:01:35,155 --> 00:01:38,795 together just how our planet got its special blue bubble. 16 00:01:47,555 --> 00:01:51,075 By going back to the Earth's earliest origins, 17 00:01:51,075 --> 00:01:56,515 we can now tell the almost implausible story of our atmosphere. 18 00:02:01,115 --> 00:02:05,115 How it emerged from a toxic orange hell... 19 00:02:07,195 --> 00:02:11,115 ..and transformed the planet from an exposed ball of rock... 20 00:02:14,155 --> 00:02:16,355 ..to a beautiful, living world... 21 00:02:17,915 --> 00:02:21,995 ..capable of nurturing a staggering abundance of life. 22 00:02:25,755 --> 00:02:30,515 This atmosphere has been the planet's great protector 23 00:02:30,515 --> 00:02:33,435 for 2.5 billion years, 24 00:02:33,435 --> 00:02:37,275 soaking up everything that our planet has thrown at it. 25 00:02:38,795 --> 00:02:43,635 It's a thin, delicate, fragile cloak that shields 26 00:02:43,635 --> 00:02:47,755 and protects all life on Earth. 27 00:03:23,475 --> 00:03:27,915 Our atmosphere is a unique mix of gasses not found anywhere 28 00:03:27,915 --> 00:03:30,195 else in the solar system, 29 00:03:30,195 --> 00:03:34,315 gasses that allow Earth to be a living, breathing world. 30 00:03:41,315 --> 00:03:46,515 78% of our atmosphere is nitrogen, which can be taken up by 31 00:03:46,515 --> 00:03:51,475 bacteria in the soil and plants, and it's an integral part of DNA. 32 00:03:51,475 --> 00:03:54,755 21% of our atmosphere is oxygen. 33 00:03:54,755 --> 00:03:58,395 It's there for animals to breathe, but also for many living things 34 00:03:58,395 --> 00:04:01,035 to use to convert their food into energy. 35 00:04:03,155 --> 00:04:06,795 Even less abundant gasses are crucial for sustaining life. 36 00:04:08,875 --> 00:04:13,035 A fraction of a percent is water vapour, which condenses 37 00:04:13,035 --> 00:04:14,755 and falls as rain, 38 00:04:14,755 --> 00:04:18,035 and a tiny amount is carbon dioxide, 39 00:04:18,035 --> 00:04:21,795 which might be a waste product to us but it's absolutely 40 00:04:21,795 --> 00:04:25,555 essential for plants when it comes to photosynthesis. 41 00:04:25,555 --> 00:04:30,475 It almost appears that this unique cocktail of gasses 42 00:04:30,475 --> 00:04:33,915 is here as a sort of life-support system. 43 00:04:36,875 --> 00:04:40,435 So, where did this beautiful atmosphere come from 44 00:04:40,435 --> 00:04:43,715 and how did it lead to the origins of life here? 45 00:04:47,835 --> 00:04:51,035 Well, to answer that, we need to go back to the very beginning... 46 00:04:58,235 --> 00:05:01,075 ..4.6 billion years ago. 47 00:05:09,115 --> 00:05:13,515 Our Earth began as nothing more than dust and gas. 48 00:05:16,515 --> 00:05:21,715 A nebulous cloud containing every element our new world would need. 49 00:05:25,755 --> 00:05:30,995 Over tens of millions of years, the cloud begins to clump together, 50 00:05:30,995 --> 00:05:33,275 forming rocks. 51 00:05:33,275 --> 00:05:35,515 Pulled together by gravity... 52 00:05:36,995 --> 00:05:39,715 ..they grow bigger and bigger... 53 00:05:44,795 --> 00:05:48,395 ..until, finally, a new world is formed. 54 00:05:58,915 --> 00:06:02,715 Asteroids rain down on the young Earth 55 00:06:02,715 --> 00:06:05,835 for hundreds of millions of years... 56 00:06:08,595 --> 00:06:13,195 ..its molten surface still searing from the heat of its creation. 57 00:06:25,515 --> 00:06:27,595 But something is missing. 58 00:06:30,155 --> 00:06:31,875 The colour blue. 59 00:06:38,075 --> 00:06:41,395 You see, the Earth has no atmosphere. 60 00:06:43,315 --> 00:06:48,875 The sun and the newly formed moon sit in a jet-black sky. 61 00:06:56,395 --> 00:06:59,035 This is how the Earth could have remained... 62 00:07:04,955 --> 00:07:09,835 ..a lifeless ball of rock, floating in the void of space. 63 00:07:24,075 --> 00:07:26,515 This is what the surface of the Earth may have 64 00:07:26,515 --> 00:07:29,635 looked like 4 billion years ago. 65 00:07:31,075 --> 00:07:33,355 Stark, brutal and yet, 66 00:07:33,355 --> 00:07:36,915 in some ways, beautiful landscape. 67 00:07:39,515 --> 00:07:44,635 The early Earth was little more than a ball of cooling rock, 68 00:07:44,635 --> 00:07:47,915 so where did the planet's first atmosphere come from? 69 00:07:50,075 --> 00:07:54,315 Now it might surprise you, but I've got some clues to the answer 70 00:07:54,315 --> 00:07:57,955 to that question in my pocket, 71 00:07:57,955 --> 00:08:00,955 in the form of this tiny, 72 00:08:00,955 --> 00:08:07,195 but extremely rare and valuable, granular piece of rock. 73 00:08:07,195 --> 00:08:13,355 This, you see, is a carbonaceous chondrite meteorite, 74 00:08:13,355 --> 00:08:19,275 and it was formed at the same time our solar system was formed - 75 00:08:19,275 --> 00:08:21,435 and I've got it in my hand! 76 00:08:21,435 --> 00:08:25,955 I am holding the history of our solar system 77 00:08:25,955 --> 00:08:27,995 and the Earth in my hand. 78 00:08:29,715 --> 00:08:34,955 4.5 billion years ago, trillions of tonnes of this 79 00:08:34,955 --> 00:08:40,235 type of material came together to form our planet. 80 00:08:41,875 --> 00:08:45,995 These meteorites are leftovers from the Earth's creation. 81 00:08:47,035 --> 00:08:49,475 So, through chemical analysis, 82 00:08:49,475 --> 00:08:54,395 scientists can discover the raw ingredients that made our world. 83 00:08:57,355 --> 00:09:01,075 These meteorites contain heavy elements, like iron, 84 00:09:01,075 --> 00:09:05,035 and the rocky constituents that formed the planet itself. 85 00:09:06,995 --> 00:09:10,915 But chondrite meteorites contain lighter elements too. 86 00:09:12,795 --> 00:09:17,635 Chemical analysis reveals that these rocks contain carbon, 87 00:09:17,635 --> 00:09:19,555 hydrogen and sulphur, 88 00:09:19,555 --> 00:09:23,075 and we can still see them belching as gasses 89 00:09:23,075 --> 00:09:25,715 from volcanic vents around the world today. 90 00:09:28,395 --> 00:09:33,595 When combined, these elements form new compounds like methane, 91 00:09:33,595 --> 00:09:38,115 carbon dioxide and hydrogen sulphide, 92 00:09:38,115 --> 00:09:42,075 which are light enough to exist as gasses 93 00:09:42,075 --> 00:09:45,395 but not so light they drift off into space. 94 00:09:47,395 --> 00:09:50,675 So, meteorites like this weren't just the 95 00:09:50,675 --> 00:09:52,315 building blocks of our planet - 96 00:09:52,315 --> 00:09:57,235 they contained the essential ingredients for its atmosphere. 97 00:09:57,235 --> 00:09:59,995 And 4.5 billion years ago, 98 00:09:59,995 --> 00:10:03,355 that had begun to change everything. 99 00:10:19,995 --> 00:10:22,715 The ancient Earth holds within it 100 00:10:22,715 --> 00:10:26,075 everything it needs to create the first atmosphere. 101 00:10:30,235 --> 00:10:34,035 Those ingredients just have to make it to the surface. 102 00:10:41,355 --> 00:10:45,755 But deep within the young Earth, something is stirring. 103 00:11:04,555 --> 00:11:09,875 Across the globe, molten magma races up from within... 104 00:11:14,355 --> 00:11:18,435 ..and these rivers of liquid fire unleash gasses that will 105 00:11:18,435 --> 00:11:20,715 transform our planet. 106 00:11:37,195 --> 00:11:41,795 The world is smothered by a thick toxic fog. 107 00:11:59,635 --> 00:12:03,435 As the sun creeps above the horizon, 108 00:12:03,435 --> 00:12:05,995 gas scatters the light. 109 00:12:09,795 --> 00:12:13,715 Earth gets its first colour-filled sunrise. 110 00:12:17,155 --> 00:12:21,675 This new world now has an atmosphere... 111 00:12:27,475 --> 00:12:30,115 ..but one like nothing we've ever seen. 112 00:12:42,555 --> 00:12:47,195 We're all familiar with the colours in the early-morning sky, 113 00:12:47,195 --> 00:12:51,875 but a sunrise 4 billion years ago would have been very different. 114 00:12:51,875 --> 00:12:56,355 Sunlight passing through that churning mixture of methane 115 00:12:56,355 --> 00:13:00,955 and carbon dioxide would have given the whole planet an orange hue. 116 00:13:02,235 --> 00:13:05,115 But this toxic atmosphere was very important. 117 00:13:05,115 --> 00:13:08,155 It was the first time that our planet had 118 00:13:08,155 --> 00:13:11,195 a protective shield from space. 119 00:13:11,195 --> 00:13:14,315 But, of course, it was still a very alien world - 120 00:13:14,315 --> 00:13:18,235 would have been to us - and not just because of that noxious 121 00:13:18,235 --> 00:13:23,315 orange fog, or the searing, hot, black, bare volcanic rocks 122 00:13:23,315 --> 00:13:24,555 beneath our feet. 123 00:13:24,555 --> 00:13:27,275 It was because something fundamental, 124 00:13:27,275 --> 00:13:30,675 something that we take for granted every day, was missing. 125 00:13:33,595 --> 00:13:34,755 Water. 126 00:13:46,555 --> 00:13:50,835 Today, 70% of the Earth's surface is covered in water. 127 00:13:53,435 --> 00:13:56,315 A planet of almost limitless blue... 128 00:13:59,435 --> 00:14:00,995 ..with endless rivers... 129 00:14:02,715 --> 00:14:04,035 ..freezing ice caps... 130 00:14:05,755 --> 00:14:07,875 ..and turquoise tropical paradises. 131 00:14:24,035 --> 00:14:26,155 But 4.5 billion years ago... 132 00:14:28,515 --> 00:14:32,515 ..there wasn't a single drop of liquid water 133 00:14:32,515 --> 00:14:34,475 on the ancient Earth's surface. 134 00:14:44,115 --> 00:14:47,195 However, the planet wasn't totally dry. 135 00:14:50,355 --> 00:14:53,715 The young atmosphere did contain water. 136 00:14:55,555 --> 00:14:59,515 Asteroids and volcanic eruptions have released a vast 137 00:14:59,515 --> 00:15:01,235 ocean of water vapour. 138 00:15:10,955 --> 00:15:13,955 Trillions of droplets were floating in the sky... 139 00:15:24,915 --> 00:15:28,675 ..so small they soar on moving air. 140 00:15:37,035 --> 00:15:41,275 Colliding and merging with each other, they slowly grow... 141 00:15:44,715 --> 00:15:49,355 ..until they can no longer fight Earth's gravity. 142 00:15:58,035 --> 00:16:01,595 En masse, they are pulled downwards, towards the ground. 143 00:16:12,635 --> 00:16:16,315 But with the atmosphere still scorchingly hot from heat 144 00:16:16,315 --> 00:16:17,915 trapped by Earth's formation... 145 00:16:20,115 --> 00:16:22,395 ..not a single drop of rain... 146 00:16:26,395 --> 00:16:29,075 ..has ever made it to the surface. 147 00:16:32,395 --> 00:16:38,355 And it's been the same story every day for tens of millions of years. 148 00:16:40,435 --> 00:16:44,515 The Earth is stuck - a barren desert world 149 00:16:44,515 --> 00:16:48,115 totally incapable of supporting life. 150 00:16:55,035 --> 00:16:58,075 Water today is on a continual journey. 151 00:17:00,475 --> 00:17:04,755 It emerges from the leaves of green plants as vapour, 152 00:17:04,755 --> 00:17:07,995 rises up to the sky, where it forms clouds, 153 00:17:07,995 --> 00:17:10,275 which then condense into rain, 154 00:17:10,275 --> 00:17:13,475 which falls onto the ground, which drains into the rivers, 155 00:17:13,475 --> 00:17:17,875 which eventually flow into our vast oceans. 156 00:17:17,875 --> 00:17:22,795 And we're very used to seeing water appear out of our atmosphere. 157 00:17:22,795 --> 00:17:27,195 What about those lovely soft layers of mist that we see over rivers, 158 00:17:27,195 --> 00:17:31,315 or the dew on your toes if you scuff across a summer lawn, 159 00:17:31,315 --> 00:17:34,075 or when it falls as rain or snow? 160 00:17:41,995 --> 00:17:45,515 The only reason our planet is a water world is because it's the 161 00:17:45,515 --> 00:17:50,115 right temperature and pressure for water to form out of the atmosphere. 162 00:17:52,955 --> 00:17:57,235 4.4 billion years ago, Earth needed to cool down. 163 00:18:00,635 --> 00:18:04,915 Slowly, heat has been radiating out into space... 164 00:18:09,475 --> 00:18:11,835 ..over millions and millions of years. 165 00:18:27,955 --> 00:18:29,155 Until... 166 00:18:32,075 --> 00:18:34,875 ..a tipping point is reached. 167 00:18:53,235 --> 00:18:56,955 What starts with just a few drops 168 00:18:56,955 --> 00:18:59,475 becomes the greatest deluge 169 00:18:59,475 --> 00:19:01,675 the solar system has ever seen. 170 00:19:28,155 --> 00:19:30,995 Huge weather systems sweep across the planet 171 00:19:30,995 --> 00:19:35,995 and storms which last centuries dump oceans of water from the skies. 172 00:19:44,675 --> 00:19:49,275 A key element in the equation of life had been 173 00:19:49,275 --> 00:19:50,955 well and truly unleashed. 174 00:20:01,675 --> 00:20:05,035 Our planet is transformed. 175 00:20:17,235 --> 00:20:21,075 As the Earth continued to cool, the rains that fell from its thick, 176 00:20:21,075 --> 00:20:23,795 dense atmosphere created a new water world. 177 00:20:23,795 --> 00:20:26,515 And for the first time in its history, 178 00:20:26,515 --> 00:20:29,995 it would have looked a little bit like this. 179 00:20:29,995 --> 00:20:33,075 If you gazed into the sky, you would have seen clouds, 180 00:20:33,075 --> 00:20:35,795 you would have felt the wind and the rain on your face. 181 00:20:35,795 --> 00:20:37,715 And if you listened, 182 00:20:37,715 --> 00:20:40,875 you'd have heard waves carving a new coastline. 183 00:20:42,075 --> 00:20:44,875 But that's where the similarities would have ended, 184 00:20:44,875 --> 00:20:49,835 because this rocky, wet world was devoid of life. 185 00:20:49,835 --> 00:20:52,955 But it was a world where life could begin. 186 00:21:12,395 --> 00:21:15,515 Water was the crucial ingredient. 187 00:21:20,995 --> 00:21:26,195 Not long after Earth's oceans rained from the sky, 188 00:21:26,195 --> 00:21:31,675 a shallow pool was about to play host to the most important 189 00:21:31,675 --> 00:21:34,755 moment in the history of the Earth. 190 00:21:50,195 --> 00:21:53,595 So much of how life began is still a mystery. 191 00:21:57,675 --> 00:22:02,955 It's not known exactly when, where or how it happened. 192 00:22:05,355 --> 00:22:09,795 But we do know that, one day on Earth, 193 00:22:09,795 --> 00:22:13,435 a living thing came into existence. 194 00:22:17,275 --> 00:22:20,555 The first microscopic organism. 195 00:22:26,955 --> 00:22:31,795 And in that instant of pure chance, everything changed. 196 00:22:33,795 --> 00:22:37,235 The Earth became a living world. 197 00:22:42,675 --> 00:22:47,435 All trace of the first life has vanished, lost to history. 198 00:22:50,075 --> 00:22:51,755 But even today, 199 00:22:51,755 --> 00:22:56,035 we can get clues as to what early life might have been like. 200 00:23:00,795 --> 00:23:05,315 High in the Andes is one of the largest geyser fields in the world. 201 00:23:10,635 --> 00:23:15,075 The water in this vent is boiling at 85 degrees Centigrade 202 00:23:15,075 --> 00:23:18,755 and NASA scientists have looked into this water and found 203 00:23:18,755 --> 00:23:21,795 that it contains one of the highest concentrations of arsenic, 204 00:23:21,795 --> 00:23:24,435 a serious toxin, anywhere in the world. 205 00:23:26,515 --> 00:23:29,915 And these toxic conditions are similar to those 206 00:23:29,915 --> 00:23:32,195 found on the early Earth. 207 00:23:32,195 --> 00:23:35,075 But amongst the poison and boiling water, 208 00:23:35,075 --> 00:23:37,595 something ancient is flourishing. 209 00:23:39,355 --> 00:23:41,955 Just look at all of these beautiful colours here. 210 00:23:45,675 --> 00:23:52,195 That's life - a primordial mat of billions of thriving bacteria. 211 00:23:56,195 --> 00:24:00,555 These hardy bacteria are called extremophiles and, just 212 00:24:00,555 --> 00:24:04,955 like their predecessors, they've adapted to live in this hot water. 213 00:24:04,955 --> 00:24:08,635 In fact, they've carved out a niche where they can proliferate. 214 00:24:08,635 --> 00:24:11,355 There are a great range of species here and an enormous 215 00:24:11,355 --> 00:24:13,875 number of individual organisms. 216 00:24:16,955 --> 00:24:21,155 Which just goes to show that even the simplest life is inherently 217 00:24:21,155 --> 00:24:24,715 flexible, adaptable and tough. 218 00:24:24,715 --> 00:24:28,715 So, perhaps it's not surprising that that early life grabbed 219 00:24:28,715 --> 00:24:32,755 an opportunity to try and live in an environment which, for us, 220 00:24:32,755 --> 00:24:35,235 is incredibly harsh and hostile, 221 00:24:35,235 --> 00:24:37,395 but where they could prosper. 222 00:24:44,115 --> 00:24:46,475 Today, life is prolific. 223 00:24:46,475 --> 00:24:50,675 It thrives in the most unlikely of places across the world. 224 00:24:50,675 --> 00:24:54,395 But living in these extreme environments comes 225 00:24:54,395 --> 00:24:55,915 with severe limitations. 226 00:24:57,795 --> 00:25:00,715 The extremophile bacteria living around these 227 00:25:00,715 --> 00:25:03,195 hot springs are essentially locked in, 228 00:25:03,195 --> 00:25:06,475 defined by the very precise requirements in terms of the 229 00:25:06,475 --> 00:25:10,315 heat of the water and the nutrients in it. And if we were to remove 230 00:25:10,315 --> 00:25:14,995 them from this highly specialised environment, they would likely die. 231 00:25:14,995 --> 00:25:18,715 And things were pretty much the same for early life on Earth. 232 00:25:18,715 --> 00:25:23,075 It was essentially stuck, trapped in the niches that it evolved to 233 00:25:23,075 --> 00:25:27,035 survive in. And because all of the nutrients were in the water, 234 00:25:27,035 --> 00:25:31,035 the option for life on land simply wasn't there. 235 00:25:31,035 --> 00:25:35,315 Early life wasn't prolific, widespread, or even visible. 236 00:25:55,875 --> 00:25:59,275 The ancient Earth is harsh and unforgiving... 237 00:26:04,435 --> 00:26:05,955 ..with barren black land... 238 00:26:11,515 --> 00:26:13,355 ..and acidic green oceans. 239 00:26:17,715 --> 00:26:22,475 But the biggest barrier to life's flourishing is the atmosphere, 240 00:26:22,475 --> 00:26:24,595 toxic and orange. 241 00:26:25,795 --> 00:26:29,315 An atmosphere in constant turmoil. 242 00:26:40,195 --> 00:26:45,195 Tectonic movements in the Earth's crust drives land formation, 243 00:26:45,195 --> 00:26:49,435 which in turn creates massive atmospheric instability. 244 00:26:54,995 --> 00:26:57,795 Vicious winds sweep dust high up into the air... 245 00:27:01,315 --> 00:27:04,155 ..and these dust particles create more clouds. 246 00:27:08,315 --> 00:27:13,835 Storms rage across the planet, laced with poisonous gasses... 247 00:27:15,875 --> 00:27:19,235 ..deadly to the vast majority of life we know today. 248 00:27:27,275 --> 00:27:32,275 But whilst chaos rages above the waves, deep underwater 249 00:27:32,275 --> 00:27:36,395 our ancestors are simply existing, 250 00:27:36,395 --> 00:27:37,995 seemingly trapped... 251 00:27:40,315 --> 00:27:41,835 ..with no means of escape... 252 00:27:46,155 --> 00:27:51,075 ..day after day, for nearly a billion years 253 00:27:51,075 --> 00:27:53,355 where nothing appears to happen. 254 00:28:08,235 --> 00:28:11,675 Today, life is no longer confined to the water. 255 00:28:12,955 --> 00:28:15,115 Oh, yes, what a view! 256 00:28:16,155 --> 00:28:20,355 Both life and the atmosphere that supports it have undergone 257 00:28:20,355 --> 00:28:22,195 an astonishing transformation. 258 00:28:36,075 --> 00:28:37,355 It's a male. 259 00:28:37,355 --> 00:28:40,475 It's got the comb on top of its head and its feathers are all silvery, 260 00:28:40,475 --> 00:28:44,475 rippling in the wind as it glides along the edge of this escarpment. 261 00:28:46,395 --> 00:28:49,075 With a wingspan of more than 3m, 262 00:28:49,075 --> 00:28:53,035 the giant Andean condor is one of the largest birds on Earth. 263 00:28:54,195 --> 00:28:57,035 Oh, goodness me! Look at that! 264 00:29:00,595 --> 00:29:03,555 Absolutely sensational. Now I can see its eye. 265 00:29:03,555 --> 00:29:07,435 I'm looking into the eye of an Andean condor. 266 00:29:07,435 --> 00:29:08,755 Oh! 267 00:29:08,755 --> 00:29:10,515 It's ornithological nirvana! 268 00:29:13,595 --> 00:29:17,555 Watching these giant birds soaring here 269 00:29:17,555 --> 00:29:22,755 just reveals how their life is completely intertwined with 270 00:29:22,755 --> 00:29:26,595 that thin cloak of air that's wrapped around our planet. 271 00:29:26,595 --> 00:29:31,035 But then, when you think about it, everything - every plant, 272 00:29:31,035 --> 00:29:35,395 fungi, every bacteria, every tiny insect, every giant reptile, 273 00:29:35,395 --> 00:29:40,355 even us - are completely dependent on this atmosphere. 274 00:29:46,195 --> 00:29:50,595 So, how DID the atmosphere go from a toxic orange haze to the 275 00:29:50,595 --> 00:29:53,515 nurturing cocktail of gasses we know today? 276 00:29:57,635 --> 00:30:02,915 Well, it was life itself that would make the difference... 277 00:30:05,035 --> 00:30:07,955 ..thanks to a giant evolutionary leap. 278 00:30:11,155 --> 00:30:14,675 The development of complex life was far from inevitable. 279 00:30:14,675 --> 00:30:15,795 When you think about it, 280 00:30:15,795 --> 00:30:18,115 there are plenty of forks in the road of evolution, 281 00:30:18,115 --> 00:30:19,835 trillions of dead ends 282 00:30:19,835 --> 00:30:22,675 and there is no definitive end point. 283 00:30:22,675 --> 00:30:27,115 But the very fact that we exist proves that whatever card 284 00:30:27,115 --> 00:30:30,555 is thrown at life, it plays it and it survives. 285 00:30:35,635 --> 00:30:37,275 And that's precisely 286 00:30:37,275 --> 00:30:40,835 what was happening 3.5 billion years ago. 287 00:30:40,835 --> 00:30:46,795 Life was playing its card - slowly evolving, gently proliferating - 288 00:30:46,795 --> 00:30:50,795 and it wasn't quite as stuck as we might have thought it was. 289 00:30:50,795 --> 00:30:55,555 In fact, a significant development in a single cell was about to 290 00:30:55,555 --> 00:30:59,035 change the way that life could exist. 291 00:30:59,035 --> 00:31:03,395 Life was about to take a quantum leap forward. 292 00:31:06,715 --> 00:31:10,875 A leap, that would change our atmosphere forever. 293 00:31:20,755 --> 00:31:25,475 It started with a mutation that altered the fundamental 294 00:31:25,475 --> 00:31:28,155 chemistry of the cells... 295 00:31:29,475 --> 00:31:32,555 ..giving them the ability to capture the sun's rays... 296 00:31:35,195 --> 00:31:38,715 ..and store the energy as glucose, 297 00:31:38,715 --> 00:31:43,515 energy the cells can then use to grow and reproduce. 298 00:31:48,955 --> 00:31:52,075 This was photosynthesis... 299 00:31:53,595 --> 00:31:57,435 ..an evolutionary innovation that will change 300 00:31:57,435 --> 00:32:00,875 the course of Earth's history forever. 301 00:32:14,875 --> 00:32:18,715 The ancestors of this cell are still around today. 302 00:32:22,555 --> 00:32:25,555 They can be found in almost every puddle, lake, 303 00:32:25,555 --> 00:32:27,555 sea or ocean across our planet. 304 00:32:31,475 --> 00:32:35,435 Peering down through this microscope is like taking a look 305 00:32:35,435 --> 00:32:41,235 back at life on Earth almost 3.5 billion years ago. 306 00:32:41,235 --> 00:32:47,475 You see, these rod-shaped structures here are cyanobacteria, 307 00:32:47,475 --> 00:32:50,475 and we think they're pretty similar to those that existed 308 00:32:50,475 --> 00:32:55,955 trillions of generations ago, when our atmosphere was very different. 309 00:32:55,955 --> 00:32:59,075 Now, they may not look impressive, but I've got to tell you, 310 00:32:59,075 --> 00:33:03,835 they're probably one of the most successful organisms to ever live. 311 00:33:03,835 --> 00:33:09,115 A little over 3 billion years ago, these tiny flecks, 312 00:33:09,115 --> 00:33:11,235 these microscopic organisms 313 00:33:11,235 --> 00:33:15,435 just a fraction of a millimetre across, started to build 314 00:33:15,435 --> 00:33:20,555 an atmosphere which humans could live and breathe in. 315 00:33:25,875 --> 00:33:29,955 Thanks to energy from the sun, these cells are able to steal 316 00:33:29,955 --> 00:33:35,515 hydrogen from water molecules and combine it with the carbon dioxide 317 00:33:35,515 --> 00:33:40,995 dissolved in the oceans, fabricating essential tools for life. 318 00:33:48,315 --> 00:33:52,235 Individually, these revolutionary cells, 319 00:33:52,235 --> 00:33:55,275 which you can still find in water bodies like this all across 320 00:33:55,275 --> 00:33:58,275 the planet, produced a negligible, 321 00:33:58,275 --> 00:34:01,555 unremarkable, nonexistent effect. 322 00:34:03,035 --> 00:34:05,755 But when they combined in their trillions, 323 00:34:05,755 --> 00:34:09,675 when they combined en masse, they were about to demonstrate, 324 00:34:09,675 --> 00:34:15,555 for the very first time, the awesome power of life on Earth, 325 00:34:15,555 --> 00:34:19,835 and that would have a profound, long-lasting 326 00:34:19,835 --> 00:34:22,955 physical resonance on our planet. 327 00:34:27,155 --> 00:34:30,435 Life powered by photosynthesis thrived. 328 00:34:34,955 --> 00:34:38,755 Cells with this new ability to harness energy from the sun 329 00:34:38,755 --> 00:34:41,515 out-competed those that couldn't. 330 00:34:43,075 --> 00:34:45,315 So, they began to multiply. 331 00:34:48,995 --> 00:34:50,715 One becomes two. 332 00:34:51,995 --> 00:34:53,315 Two become four. 333 00:35:05,595 --> 00:35:08,995 Until there are literally trillions of offspring. 334 00:35:11,715 --> 00:35:17,595 Enough to fundamentally change the chemistry of our world. 335 00:35:25,795 --> 00:35:31,035 Photosynthesis was a game-changer for life because the 336 00:35:31,035 --> 00:35:35,715 ingredients that it required were so readily available and abundant. 337 00:35:35,715 --> 00:35:41,675 But the by-products of many types of photosynthesis include a very 338 00:35:41,675 --> 00:35:44,515 reactive and dangerous gas. 339 00:35:44,515 --> 00:35:48,475 Now, for these revolutionary early organisms, 340 00:35:48,475 --> 00:35:51,755 this was just a waste product, something to be thrown away. 341 00:35:51,755 --> 00:35:54,115 But for the likes of you and I, 342 00:35:54,115 --> 00:35:59,595 and the rest of complex life on Earth, it's absolutely essential. 343 00:35:59,595 --> 00:36:02,755 I'm talking, of course, about oxygen. 344 00:36:08,395 --> 00:36:12,275 Trillions of bacteria are spread across the ancient oceans... 345 00:36:17,235 --> 00:36:21,715 ..and the waste oxygen they throw away is enough to build a new 346 00:36:21,715 --> 00:36:24,155 atmosphere for our planet. 347 00:36:29,235 --> 00:36:32,395 Bubbles of oxygen race upwards, towards the surface. 348 00:36:37,035 --> 00:36:38,355 But they can't escape. 349 00:36:42,795 --> 00:36:45,835 The bubbles are absorbed and vanish. 350 00:36:54,635 --> 00:36:59,795 Earth seems trapped, with a toxic atmosphere of methane 351 00:36:59,795 --> 00:37:01,475 and carbon dioxide. 352 00:37:15,715 --> 00:37:19,355 The Earth was essentially in stasis. 353 00:37:19,355 --> 00:37:23,275 You see, that toxic orange atmosphere still enveloped 354 00:37:23,275 --> 00:37:24,675 the planet. 355 00:37:24,675 --> 00:37:28,995 Life was still microscopic and could only exist in the oceans, 356 00:37:28,995 --> 00:37:33,075 and there was no oxygen in the atmosphere. 357 00:37:33,075 --> 00:37:37,035 To all intents and purposes, you could say, well, 358 00:37:37,035 --> 00:37:39,155 that the planet was stuck. 359 00:37:41,915 --> 00:37:44,475 But that was about to change. 360 00:37:48,875 --> 00:37:52,875 Because it wasn't just oxygen dissolved in the water - 361 00:37:52,875 --> 00:37:54,635 there were metals, too... 362 00:37:57,555 --> 00:38:00,115 ..including iron. 363 00:38:05,195 --> 00:38:08,595 The iron, like oxygen, is invisible 364 00:38:08,595 --> 00:38:11,595 to us when it's dissolved in water. 365 00:38:11,595 --> 00:38:14,635 But we all know what happens when iron, 366 00:38:14,635 --> 00:38:16,635 oxygen and water come together... 367 00:38:19,555 --> 00:38:23,475 ..and there's plenty of evidence of that on this old bus. 368 00:38:26,315 --> 00:38:30,035 Just look here - this lovely brown, 369 00:38:30,035 --> 00:38:31,875 orange and red. 370 00:38:33,155 --> 00:38:34,435 Rust. 371 00:38:34,435 --> 00:38:38,355 The iron is being oxidised - aggressively attacked 372 00:38:38,355 --> 00:38:42,155 by the oxygen in the presence of water, or water vapour. 373 00:38:42,155 --> 00:38:45,475 But what's interesting is that, whilst the iron 374 00:38:45,475 --> 00:38:49,835 and whilst the oxygen are soluble in water, 375 00:38:49,835 --> 00:38:51,835 the rust is not. 376 00:39:09,355 --> 00:39:11,715 The newly released oxygen reacts 377 00:39:11,715 --> 00:39:14,275 with the dissolved iron already present 378 00:39:14,275 --> 00:39:17,035 in the oceans, 379 00:39:17,035 --> 00:39:21,155 and that causes something extraordinary to happen. 380 00:39:22,995 --> 00:39:25,715 Rust pours onto the ocean floor. 381 00:39:35,795 --> 00:39:37,955 The world's oceans turn red. 382 00:39:50,195 --> 00:39:52,315 And if you know where to look, you can 383 00:39:52,315 --> 00:39:55,395 still find evidence for this bizarre effect. 384 00:39:57,715 --> 00:39:59,595 I'm armed with a rock hammer. 385 00:39:59,595 --> 00:40:02,675 If I have a little tap at this stone, there we are. 386 00:40:02,675 --> 00:40:04,435 Let's have a look at what's inside. 387 00:40:05,715 --> 00:40:09,075 This rock once formed part of an ancient seafloor. 388 00:40:09,075 --> 00:40:11,795 Hm, look at that. 389 00:40:11,795 --> 00:40:14,515 You see that there, that red? 390 00:40:14,515 --> 00:40:16,515 That's iron 391 00:40:16,515 --> 00:40:19,915 laid down billions of years ago, 392 00:40:19,915 --> 00:40:23,715 a volatile memory of oxygen reacting 393 00:40:23,715 --> 00:40:26,595 with iron in the early seas. 394 00:40:27,675 --> 00:40:30,395 A sort of geological tattoo. 395 00:40:30,395 --> 00:40:31,595 I love that. 396 00:40:34,115 --> 00:40:36,755 This rust was to have a profound effect 397 00:40:36,755 --> 00:40:39,395 on our Earth's young atmosphere. 398 00:40:46,475 --> 00:40:51,595 For half a billion years, oxygen has been trapped in the oceans. 399 00:40:53,955 --> 00:40:58,515 But now, iron has almost been totally flushed from the seas. 400 00:41:03,995 --> 00:41:09,315 At last, the oxygen in the water has nothing else to react with. 401 00:41:11,235 --> 00:41:13,715 It can break free. 402 00:41:39,035 --> 00:41:43,835 Over millions years, oxygen flooded from the oceans... 403 00:41:47,955 --> 00:41:50,795 ..and our atmosphere was transformed. 404 00:42:11,155 --> 00:42:14,355 When those bubbles first breached the surface of the ocean, 405 00:42:14,355 --> 00:42:17,195 you might have thought that the atmosphere was getting 406 00:42:17,195 --> 00:42:20,435 a breath of fresh air, and to some extent it was. 407 00:42:20,435 --> 00:42:25,035 But this wasn't the moment when life suddenly flourished, 408 00:42:25,035 --> 00:42:29,715 or when it developed that complete and utter dependence that 409 00:42:29,715 --> 00:42:32,635 contemporary complex life has upon oxygen. 410 00:42:34,195 --> 00:42:39,115 But that's not to say that when those bubbles first fizzed 411 00:42:39,115 --> 00:42:41,955 out there that this wasn't a momentous moment. 412 00:42:41,955 --> 00:42:43,475 It was. 413 00:42:43,475 --> 00:42:46,595 The planet was about to be re-calibrated, 414 00:42:46,595 --> 00:42:49,715 and the relationship between the ocean, 415 00:42:49,715 --> 00:42:54,115 the land and the atmosphere was going to change forever. 416 00:42:54,115 --> 00:42:59,635 And as this volatile, reactive gas flooded into the atmosphere, the 417 00:42:59,635 --> 00:43:04,875 full destructive force of oxygen was felt across the planet's surface. 418 00:43:27,435 --> 00:43:29,755 Oxygen attacks the Earth. 419 00:43:38,835 --> 00:43:44,355 Any rocks containing iron and aluminium rust and crumble, 420 00:43:44,355 --> 00:43:47,275 driving vast dust storms. 421 00:43:51,115 --> 00:43:54,515 The world is being torn apart by its own atmosphere... 422 00:43:57,355 --> 00:44:00,875 ..and this has a startling side-effect - 423 00:44:00,875 --> 00:44:04,235 the entire Earth turns a vivid red. 424 00:44:12,115 --> 00:44:16,035 Scientists find evidence for this red Earth in 425 00:44:16,035 --> 00:44:19,435 rock formations in landscapes all over the world. 426 00:44:19,435 --> 00:44:23,755 Direct evidence of the action of all of those 427 00:44:23,755 --> 00:44:27,915 trillions of cyanobacteria churning out oxygen. 428 00:44:27,915 --> 00:44:34,115 And before oxygen, the planet was barren, grey and black. 429 00:44:34,115 --> 00:44:39,795 You see, it's oxidation that gives us this wonderful red hue. 430 00:44:56,595 --> 00:44:59,515 But oxygen's effect on the land went further. 431 00:45:02,395 --> 00:45:05,915 You see, oxygen doesn't just react with iron - 432 00:45:05,915 --> 00:45:08,235 it reacts with pretty much anything. 433 00:45:09,315 --> 00:45:12,515 It attacks minerals within the Earth's crust... 434 00:45:16,395 --> 00:45:20,795 ..creating as many as 3,000 exotic new minerals, 435 00:45:20,795 --> 00:45:23,915 all previously unknown to the solar system. 436 00:45:30,275 --> 00:45:34,355 Minerals that led to an explosion of colour right across the planet. 437 00:45:42,915 --> 00:45:45,275 Minerals that, to this day, 438 00:45:45,275 --> 00:45:49,795 play a vital role in sustaining the rich complexity of life we know. 439 00:45:55,155 --> 00:46:01,435 Now, one of the colours unleashed by oxygen is this rather 440 00:46:01,435 --> 00:46:04,395 wonderful sea green here. 441 00:46:05,515 --> 00:46:07,995 You see, when copper, the metal, 442 00:46:07,995 --> 00:46:12,195 comes into contact with oxygen in the air, it oxidises, 443 00:46:12,195 --> 00:46:15,035 producing this - copper oxide. 444 00:46:15,035 --> 00:46:18,275 And it turns out that this compound 445 00:46:18,275 --> 00:46:22,915 was fundamentally important in the development of more complex 446 00:46:22,915 --> 00:46:28,715 life. And what's more, it retains its biological importance today. 447 00:46:28,715 --> 00:46:33,915 It's necessary for the synthesis of neurotransmitters in our brains, 448 00:46:33,915 --> 00:46:35,835 and the brains of other animals, 449 00:46:35,835 --> 00:46:39,355 and also for the production of hormones and pigments. 450 00:46:39,355 --> 00:46:42,355 So, even in today's world, 451 00:46:42,355 --> 00:46:47,635 life is dependent on that chemical complexity that was unlocked 452 00:46:47,635 --> 00:46:53,195 so long ago, when our atmosphere became richer in oxygen. 453 00:47:05,155 --> 00:47:08,955 Thanks to oxygen, we live in a world of extraordinary colour 454 00:47:08,955 --> 00:47:10,475 and diversity. 455 00:47:13,915 --> 00:47:17,635 A myriad of minerals colours the Earth's surface... 456 00:47:21,235 --> 00:47:23,515 ..and the biological world has continued 457 00:47:23,515 --> 00:47:25,755 to make use of this ever-increasing 458 00:47:25,755 --> 00:47:29,835 chemical complexity to transform the planet. 459 00:47:29,835 --> 00:47:33,115 From the rich green carpet of plant life... 460 00:47:35,355 --> 00:47:36,475 SHUTTER CLICKS 461 00:47:37,875 --> 00:47:41,995 ..to the fluorescent pink feathers of flamingos. 462 00:47:55,435 --> 00:48:00,155 Oxygen has allowed life to flourish in ways unimaginable 463 00:48:00,155 --> 00:48:01,715 3 billion years ago. 464 00:48:03,195 --> 00:48:07,995 But this volatile gas had one more gift to bestow. 465 00:48:11,835 --> 00:48:16,755 As oxygen enriches the atmosphere, it reacts with methane, 466 00:48:16,755 --> 00:48:18,555 stripping it away. 467 00:48:21,715 --> 00:48:27,395 And as methane levels drop, the orange haze lifts. 468 00:48:30,555 --> 00:48:33,675 Nitrogen and oxygen in the atmosphere are left 469 00:48:33,675 --> 00:48:35,235 to scatter the light. 470 00:48:36,875 --> 00:48:39,155 The colour begins to change. 471 00:48:43,395 --> 00:48:48,115 For the first time in Earth's history, the sky 472 00:48:48,115 --> 00:48:50,795 is an oxygen-rich, brilliant blue. 473 00:49:05,955 --> 00:49:11,315 Today, this lovely thin blue line marks our Earth as unique 474 00:49:11,315 --> 00:49:14,275 in the entire known universe. 475 00:49:14,275 --> 00:49:18,515 It's a spectacular demonstration of a 4 billion-year 476 00:49:18,515 --> 00:49:22,275 dance between our atmosphere and life - 477 00:49:22,275 --> 00:49:24,675 an atmosphere that was 478 00:49:24,675 --> 00:49:29,235 created, shaped and calibrated by life itself. 479 00:49:32,995 --> 00:49:39,155 Our planet went from volatile, fiery and dead to the beautiful 480 00:49:39,155 --> 00:49:41,635 living and breathing blue bubble 481 00:49:41,635 --> 00:49:44,315 floating in the darkness of space. 482 00:50:05,715 --> 00:50:10,075 How do scientists unravel billions of years of our planet's history? 483 00:50:13,915 --> 00:50:19,235 In this episode, we saw how meteorites - 484 00:50:19,235 --> 00:50:21,795 rocks that have fallen from space - 485 00:50:21,795 --> 00:50:25,515 can tell us what Earth's early atmosphere was made from. 486 00:50:26,675 --> 00:50:29,155 This is a chondrite meteorite. 487 00:50:29,155 --> 00:50:32,995 4.567 billion years old - 488 00:50:32,995 --> 00:50:35,315 the oldest thing you could hold in your hand - 489 00:50:35,315 --> 00:50:37,355 and it's made of all these tiny droplets 490 00:50:37,355 --> 00:50:40,875 that were part of the earliest solar nebula, including 491 00:50:40,875 --> 00:50:44,595 all the gasses that eventually would wind up in the atmosphere. 492 00:50:48,675 --> 00:50:52,475 Meteorites are so valuable to science 493 00:50:52,475 --> 00:50:55,675 that researchers go to great lengths to track them down. 494 00:50:59,035 --> 00:51:04,075 In 2020, scientists from the University of Manchester set out 495 00:51:04,075 --> 00:51:08,995 on a nine-week expedition to one of the most remote areas of Antarctica. 496 00:51:11,475 --> 00:51:14,595 Meteorite hunters go into the depths of Antarctica, 497 00:51:14,595 --> 00:51:18,595 into the extremes of the cold, near the South Pole, because 498 00:51:18,595 --> 00:51:21,875 they can find so many meteorites in one expedition, because the 499 00:51:21,875 --> 00:51:26,435 meteorites show up so well on the white ice... 500 00:51:26,435 --> 00:51:30,315 ..compared to, say, other places where the meteorites are 501 00:51:30,315 --> 00:51:32,675 very hard to spot from normal rocks. 502 00:51:35,595 --> 00:51:38,075 Studying meteorites has helped answer some of the most 503 00:51:38,075 --> 00:51:41,155 fundamental questions about our planet. 504 00:51:42,795 --> 00:51:46,155 So, the question of where the water on Earth came from 505 00:51:46,155 --> 00:51:49,835 and when it arrived is really central to everything. 506 00:51:51,035 --> 00:51:56,115 Some water was present in the material that formed our planet, 507 00:51:56,115 --> 00:51:58,275 but that's not the whole story. 508 00:51:59,995 --> 00:52:03,755 We think that one of the other ways that the Earth got its water 509 00:52:03,755 --> 00:52:05,755 is through meteorites. 510 00:52:05,755 --> 00:52:10,075 So, these meteorites would have had water locked into their rocks, 511 00:52:10,075 --> 00:52:13,795 or perhaps even on their surface, as frozen, in outer space. 512 00:52:15,435 --> 00:52:17,635 And then, the water would have been degassed 513 00:52:17,635 --> 00:52:19,875 into our atmosphere as water vapour. 514 00:52:19,875 --> 00:52:22,555 Later on, when the Earth cooled even further, 515 00:52:22,555 --> 00:52:24,555 that atmosphere would have condensed 516 00:52:24,555 --> 00:52:28,395 and the water vapour would have then formed liquid water on our surface. 517 00:52:31,955 --> 00:52:36,795 Scientists think it's only after the arrival of water that life 518 00:52:36,795 --> 00:52:38,715 was able to get started. 519 00:52:40,915 --> 00:52:45,115 The origin of life is one of the greatest questions in science and 520 00:52:45,115 --> 00:52:49,475 it's fair to say that we don't know when, where or how life started. 521 00:52:51,395 --> 00:52:54,715 A shallow rock pool is one of the leading theories. 522 00:52:55,835 --> 00:52:58,715 People think that shallow pools would have been a potentially 523 00:52:58,715 --> 00:53:01,355 important site for the origin of life because they can get 524 00:53:01,355 --> 00:53:03,355 wet and dry over and over again. 525 00:53:06,275 --> 00:53:09,515 Through this repeated cycling of wetting and drying, 526 00:53:09,515 --> 00:53:12,715 re-flooding and evaporating, maybe through a tide, maybe through 527 00:53:12,715 --> 00:53:16,715 seasonal variation, more and more complex molecules can form. 528 00:53:18,915 --> 00:53:22,675 And that process could have been the precursors for things like DNA, 529 00:53:22,675 --> 00:53:25,595 which is what makes up the information in our cells today. 530 00:53:29,475 --> 00:53:31,515 But there are other theories. 531 00:53:36,955 --> 00:53:41,555 Some scientists think life began in a deep-sea hydrothermal vent. 532 00:53:45,155 --> 00:53:48,795 Hydrothermal vents are sources of gases, 533 00:53:48,795 --> 00:53:51,355 like hydrogen sulphide for example, and provide 534 00:53:51,355 --> 00:53:54,715 the kind of reactive conditions to make the building blocks of life. 535 00:53:56,835 --> 00:54:01,075 Others think that life originated somewhere completely else - 536 00:54:01,075 --> 00:54:04,875 not on the Earth at all - and landed here on a meteorite. 537 00:54:09,875 --> 00:54:13,355 All of these different theories have sort of different details, 538 00:54:13,355 --> 00:54:16,715 but the punch line is that life needed water 539 00:54:16,715 --> 00:54:19,195 and it needed a way to harness energy. 540 00:54:23,235 --> 00:54:26,155 Although life's origins are still debated, 541 00:54:26,155 --> 00:54:29,675 scientists have some idea when it happened. 542 00:54:31,835 --> 00:54:36,555 This is one of the clear-cut examples that life was living 543 00:54:36,555 --> 00:54:38,155 even 3 billion years ago. 544 00:54:38,155 --> 00:54:40,275 This is a formation called a stromatolite. 545 00:54:40,275 --> 00:54:42,715 What you're looking at shows a structure 546 00:54:42,715 --> 00:54:46,635 created by a lot of microorganisms, single-celled organisms. 547 00:54:46,635 --> 00:54:52,115 And as they grow and they reach for the light, they secrete various 548 00:54:52,115 --> 00:54:57,915 gluey substances that glue together bits of sand in the environment, 549 00:54:57,915 --> 00:55:01,795 and that actually helps keep it from dispersing and blowing away. 550 00:55:01,795 --> 00:55:05,355 They are astounding in that they have the ability to adapt to 551 00:55:05,355 --> 00:55:08,195 environmental change and to change the environment 552 00:55:08,195 --> 00:55:10,035 because they can be so abundant. 553 00:55:12,195 --> 00:55:17,475 These fossilised structures were created by cyanobacteria 554 00:55:17,475 --> 00:55:20,515 and millions of them can still be found along the coast 555 00:55:20,515 --> 00:55:22,155 of Western Australia. 556 00:55:23,875 --> 00:55:27,035 Cyanobacteria might not seem so impressive, 557 00:55:27,035 --> 00:55:29,795 but they're probably one of the most influential 558 00:55:29,795 --> 00:55:33,155 and successful organisms ever to appear on planet Earth. 559 00:55:34,595 --> 00:55:39,075 They were the organisms that invented this ability to 560 00:55:39,075 --> 00:55:43,475 break water into oxygen and hydrogen 561 00:55:43,475 --> 00:55:45,995 and spit out that oxygen. 562 00:55:47,635 --> 00:55:50,795 That oxygen was able to get released into our atmosphere. 563 00:55:53,075 --> 00:55:56,715 They completely transformed the world. 564 00:55:59,995 --> 00:56:03,755 There are these moments in the history of life that seem to 565 00:56:03,755 --> 00:56:05,875 have only happened once. 566 00:56:05,875 --> 00:56:09,355 Oxygen producing photosynthesis is one of them. 567 00:56:09,355 --> 00:56:11,875 Was it a freak accident? We just don't know. 568 00:56:14,595 --> 00:56:17,515 The evolution of our atmosphere is, in many respects, 569 00:56:17,515 --> 00:56:20,875 the story of the evolution of life on our planet. 570 00:56:20,875 --> 00:56:23,435 Life can change a planet fundamentally. 571 00:56:26,875 --> 00:56:30,315 But it's always this cause-and-effect kind of dance 572 00:56:30,315 --> 00:56:32,795 between the environment changing life 573 00:56:32,795 --> 00:56:34,675 and life changing the environment. 574 00:56:38,355 --> 00:56:42,355 The story of our changing atmosphere is not over. 575 00:56:42,355 --> 00:56:45,355 It will continue to evolve both naturally 576 00:56:45,355 --> 00:56:48,115 and under the influence of human activity. 577 00:56:50,515 --> 00:56:53,595 If we don't understand the history of the atmosphere, 578 00:56:53,595 --> 00:56:57,435 how can we possibly be the stewards of the atmosphere moving forward? 579 00:57:01,355 --> 00:57:03,195 By understanding the huge 580 00:57:03,195 --> 00:57:07,155 and complex steps it took to develop our atmosphere, hopefully 581 00:57:07,155 --> 00:57:10,515 we can develop approaches to take care of it for generations to come. 582 00:57:19,115 --> 00:57:20,275 Next time... 583 00:57:24,675 --> 00:57:26,955 ..the making of the modern world. 584 00:57:28,355 --> 00:57:30,555 How the end of the dinosaurs... 585 00:57:33,075 --> 00:57:36,475 ..through cataclysm and chaos, 586 00:57:36,475 --> 00:57:39,555 set the stage for a human planet... 587 00:57:41,155 --> 00:57:42,795 ..to take its place. 588 00:57:48,995 --> 00:57:51,715 If the Earth could talk, what would it tell us? 589 00:57:51,715 --> 00:57:54,195 Well, the Open University imagine how it might answer 590 00:57:54,195 --> 00:57:56,115 some of our questions. 591 00:57:56,115 --> 00:57:58,915 To experience this interactive presentation, go to the 592 00:57:58,915 --> 00:58:02,675 website on the screen and follow the links to the Open University.