1 00:00:01,067 --> 00:00:03,233 Viewers like you make this program possible. 2 00:00:03,233 --> 00:00:05,333 Support your local PBS station. 3 00:00:12,667 --> 00:00:13,833 ♪ 4 00:00:13,833 --> 00:00:16,533 NARRATOR: Earth, our home. 5 00:00:18,400 --> 00:00:20,500 A rocky world 6 00:00:20,500 --> 00:00:24,167 enveloped by a thin blue layer 7 00:00:24,167 --> 00:00:27,500 clinging to the surface. 8 00:00:27,500 --> 00:00:29,200 Our atmosphere. 9 00:00:29,200 --> 00:00:32,933 ROBERT HAZEN: The atmosphere is the only thing 10 00:00:32,933 --> 00:00:37,267 that stands between us and that cold, dark void of space. 11 00:00:38,667 --> 00:00:41,867 (rumbling) 12 00:00:41,867 --> 00:00:45,100 NARRATOR: The story of the air that surrounds us 13 00:00:45,100 --> 00:00:47,467 is the story of Earth itself. 14 00:00:47,467 --> 00:00:49,000 ♪ 15 00:00:49,000 --> 00:00:50,333 SONIA TIKOO: It is incredible to think that 16 00:00:50,333 --> 00:00:54,133 this 4.5 billion-year-old rock could hold clues 17 00:00:54,133 --> 00:00:56,500 as to how our early atmosphere formed. 18 00:00:56,500 --> 00:00:59,100 (lightning crackling, rain falling) 19 00:00:59,100 --> 00:01:01,500 NARRATOR: Clues that reveal colossal transformations. 20 00:01:02,700 --> 00:01:06,700 MIKE WONG: It is absolutely mind-blowing that a tiny bacteria 21 00:01:06,700 --> 00:01:09,133 could affect a planetary-scale phenomenon 22 00:01:09,133 --> 00:01:10,333 like our atmosphere. 23 00:01:10,333 --> 00:01:12,100 ♪ 24 00:01:12,100 --> 00:01:17,833 NARRATOR: How did our atmosphere make Earth a unique place, 25 00:01:17,833 --> 00:01:21,067 the only home to life as we know it? 26 00:01:21,067 --> 00:01:23,933 We have never found another planet that has 27 00:01:23,933 --> 00:01:26,467 an atmosphere like ours. 28 00:01:26,467 --> 00:01:28,600 PETER GIRGUIS: And understanding how Earth got its atmosphere 29 00:01:28,600 --> 00:01:32,900 is the first step in understanding how to protect it. 30 00:01:32,900 --> 00:01:37,067 NARRATOR: "Ancient Earth: Birth of the Sky," 31 00:01:37,067 --> 00:01:40,333 right now, on "NOVA." 32 00:01:40,333 --> 00:01:46,600 ♪ 33 00:01:50,133 --> 00:01:52,867 (rumbling) 34 00:01:55,600 --> 00:01:58,367 NARRATOR: In the depths of space 35 00:01:58,367 --> 00:02:02,233 lies a young, unrecognizable planet. 36 00:02:02,233 --> 00:02:07,167 ♪ 37 00:02:07,167 --> 00:02:11,900 Bombarded by asteroids, 38 00:02:11,900 --> 00:02:16,900 this battered world is our Earth. 39 00:02:16,900 --> 00:02:22,900 ♪ 40 00:02:22,900 --> 00:02:27,067 A desolate and volatile globe 41 00:02:27,067 --> 00:02:32,633 overlooked by a new-born moon that dominates the sky. 42 00:02:33,933 --> 00:02:38,533 With no recognizable atmosphere, the void of space 43 00:02:38,533 --> 00:02:43,333 nearly touches the surface of slowly cooling lava. 44 00:02:43,333 --> 00:02:47,700 ♪ 45 00:02:47,700 --> 00:02:52,133 There's little protection from the young sun's harsh radiation. 46 00:02:55,167 --> 00:02:59,800 This world looks nothing like the Earth we know today. 47 00:03:03,167 --> 00:03:05,300 Around four and a half billion years ago, 48 00:03:05,300 --> 00:03:08,267 Earth was inhospitable for life. 49 00:03:08,267 --> 00:03:11,333 (rumbling) 50 00:03:11,333 --> 00:03:14,700 HAZEN: There were meteors and asteroids bombarding the surface. 51 00:03:14,700 --> 00:03:15,733 It was too hot. 52 00:03:15,733 --> 00:03:16,967 It was a terrible place to be. 53 00:03:16,967 --> 00:03:19,767 ♪ 54 00:03:19,767 --> 00:03:22,400 LINGAPPA: The question is, 55 00:03:22,400 --> 00:03:25,267 how did our planet transform from this barren rock, 56 00:03:25,267 --> 00:03:28,100 into somewhere capable of supporting life? 57 00:03:28,100 --> 00:03:30,167 ♪ 58 00:03:30,167 --> 00:03:33,733 WONG: This is the story of how our planet became a living world, 59 00:03:33,733 --> 00:03:37,200 and the dance, the co-evolution 60 00:03:37,200 --> 00:03:39,000 between life and our atmosphere. 61 00:03:39,000 --> 00:03:45,067 ♪ 62 00:03:47,900 --> 00:03:49,433 ("Never Close Enough" by SIPHO. playing) 63 00:03:49,433 --> 00:03:54,333 ♪ Oh, we won't ever hear the silence ♪ 64 00:03:54,333 --> 00:03:57,367 ♪ Or ever see the colors 65 00:03:57,367 --> 00:03:59,667 (exploding) 66 00:03:59,667 --> 00:04:02,667 ♪ That never lived in our minds ♪ 67 00:04:02,667 --> 00:04:06,700 ♪ Just a moment 68 00:04:06,700 --> 00:04:10,067 ♪ Never too far out 69 00:04:10,067 --> 00:04:13,767 ♪ Never close enough 70 00:04:17,933 --> 00:04:21,800 ♪ 71 00:04:25,133 --> 00:04:29,433 NARRATOR: Today, our planet is an oasis for life, 72 00:04:29,433 --> 00:04:31,533 enveloped by a layer of 73 00:04:31,533 --> 00:04:35,433 nourishing and protective gases-- 74 00:04:35,433 --> 00:04:38,833 the atmosphere. 75 00:04:38,833 --> 00:04:40,867 It's extremely thin, it's almost 76 00:04:40,867 --> 00:04:42,733 like the skin on apple, 77 00:04:42,733 --> 00:04:45,200 if you pretended the apple was planet Earth. 78 00:04:45,200 --> 00:04:46,867 TIKOO: The diameter of the earth 79 00:04:46,867 --> 00:04:50,367 is about 8,000 miles across, 80 00:04:50,367 --> 00:04:51,933 and the atmosphere adds 81 00:04:51,933 --> 00:04:55,333 just another 60 or so miles on top of that. 82 00:04:55,333 --> 00:04:57,533 (laughing): We wouldn't... we wouldn't be 83 00:04:57,533 --> 00:04:59,100 on planet Earth if it weren't for the atmosphere. 84 00:04:59,100 --> 00:05:00,467 And when I say we, 85 00:05:00,467 --> 00:05:04,533 not just you and me sitting here, but any life. 86 00:05:04,533 --> 00:05:06,833 GIRGUIS: Everything from fungi to bacteria, 87 00:05:06,833 --> 00:05:09,033 to tiny insects, to giant reptiles, 88 00:05:09,033 --> 00:05:10,800 are entirely dependent 89 00:05:10,800 --> 00:05:12,333 on this atmosphere of ours. 90 00:05:12,333 --> 00:05:15,533 ♪ 91 00:05:15,533 --> 00:05:17,067 It does many things for us, 92 00:05:17,067 --> 00:05:19,167 and we can think of the simple answer that we, 93 00:05:19,167 --> 00:05:22,800 as human beings, use the oxygen to live. 94 00:05:22,800 --> 00:05:26,100 NARRATOR: Besides oxygen, other important gases 95 00:05:26,100 --> 00:05:29,433 make up the atmosphere. 96 00:05:29,433 --> 00:05:32,833 LYONS: Perhaps the single most critical aspect 97 00:05:32,833 --> 00:05:35,833 of our atmosphere is the fact that carbon dioxide 98 00:05:35,833 --> 00:05:39,067 is one of the greenhouse gases that keeps our planet habitable. 99 00:05:40,067 --> 00:05:41,800 PIERREHUMBERT: Nitrogen is an essential 100 00:05:41,800 --> 00:05:44,233 component of the atmosphere, 101 00:05:44,233 --> 00:05:45,367 because all life as we know it-- 102 00:05:45,367 --> 00:05:47,667 amino acids, DNA, 103 00:05:47,667 --> 00:05:49,200 all of the things that are essential to us-- 104 00:05:49,200 --> 00:05:52,800 rely on nitrogen. 105 00:05:52,800 --> 00:05:54,233 The atmosphere protects us 106 00:05:54,233 --> 00:05:55,367 from ultraviolet radiation 107 00:05:55,367 --> 00:05:56,767 because it has a small amount 108 00:05:56,767 --> 00:05:58,633 of a molecule called ozone. 109 00:06:01,333 --> 00:06:03,267 LINGAPPA: It controls our climate, 110 00:06:03,267 --> 00:06:05,600 which makes this planet, like, 111 00:06:05,600 --> 00:06:07,167 a livable temperature for us at all. 112 00:06:07,167 --> 00:06:12,033 It sort of insulates us from the cold of space. 113 00:06:13,933 --> 00:06:16,233 NARRATOR: But the journey to today's atmosphere 114 00:06:16,233 --> 00:06:20,400 has been full of drama. 115 00:06:20,400 --> 00:06:23,000 WONG: It's a long, winding road 116 00:06:23,000 --> 00:06:25,467 between the initial atmosphere that Earth had 117 00:06:25,467 --> 00:06:28,733 through all of the various different kinds of atmospheres 118 00:06:28,733 --> 00:06:30,700 in the middle of its history, 119 00:06:30,700 --> 00:06:33,133 and finally arriving at the atmosphere that we have now. 120 00:06:44,000 --> 00:06:50,033 ♪ 121 00:06:55,800 --> 00:06:59,833 NARRATOR: Millions of years after the birth of the planet, 122 00:06:59,833 --> 00:07:04,900 there's still no atmosphere as we know it. 123 00:07:09,267 --> 00:07:13,133 But that is going to change. 124 00:07:14,233 --> 00:07:15,700 Four and a half billion years ago, 125 00:07:15,700 --> 00:07:17,333 the Earth would have been a very violent place. 126 00:07:17,333 --> 00:07:19,067 (rumbling) 127 00:07:19,067 --> 00:07:22,567 LYONS: Such that it's called the Hadean, which comes from 128 00:07:22,567 --> 00:07:25,600 the god Hades, the Greek god of the underworld, 129 00:07:25,600 --> 00:07:27,467 because it was imagined to be 130 00:07:27,467 --> 00:07:29,767 a hellish kind of place. 131 00:07:29,767 --> 00:07:35,667 (thundering, rumbling) 132 00:07:35,667 --> 00:07:37,833 (bursting) 133 00:07:37,833 --> 00:07:42,300 (magma rushing) 134 00:07:44,067 --> 00:07:45,633 NARRATOR: Across the globe, 135 00:07:45,633 --> 00:07:48,267 molten magma surges up from within. 136 00:07:48,267 --> 00:07:50,600 (splashing) 137 00:07:50,600 --> 00:07:55,767 Rivers of fire unleash a cocktail of gases. 138 00:07:55,767 --> 00:07:58,967 (booming) 139 00:07:58,967 --> 00:08:02,100 ♪ 140 00:08:02,100 --> 00:08:05,100 Carbon dioxide, nitrogen, and methane 141 00:08:05,100 --> 00:08:09,333 explode out of volcanoes in thick plumes. 142 00:08:09,333 --> 00:08:12,833 ♪ 143 00:08:12,833 --> 00:08:15,100 These are the building blocks 144 00:08:15,100 --> 00:08:16,833 of our early atmosphere. 145 00:08:16,833 --> 00:08:19,800 ♪ 146 00:08:27,267 --> 00:08:31,833 And we can see echoes of this young planet 147 00:08:31,833 --> 00:08:34,133 still on Earth today. 148 00:08:34,133 --> 00:08:38,800 ♪ 149 00:08:49,967 --> 00:08:51,533 The volcanoes that we have here in Iceland look 150 00:08:51,533 --> 00:08:52,967 very similar to those that we had 151 00:08:52,967 --> 00:08:54,400 four and a half billion years ago. 152 00:08:54,400 --> 00:08:59,000 The early Earth was dominated by volcanic activity, 153 00:08:59,000 --> 00:09:00,633 and this lasted for millions of years. 154 00:09:00,633 --> 00:09:04,167 ♪ 155 00:09:04,167 --> 00:09:06,600 Those volcanoes acted as pathways 156 00:09:06,600 --> 00:09:09,300 for the gases that are trapped inside the magma 157 00:09:09,300 --> 00:09:12,933 to escape into our atmosphere. 158 00:09:12,933 --> 00:09:15,033 NARRATOR: But how do scientists know 159 00:09:15,033 --> 00:09:19,767 what the atmosphere was like in the past? 160 00:09:19,767 --> 00:09:21,700 Surprisingly, clues are hidden 161 00:09:21,700 --> 00:09:26,400 in some of the rocks we find today. 162 00:09:26,400 --> 00:09:28,667 Throughout Earth's history and evolution, 163 00:09:28,667 --> 00:09:32,100 there's been a dynamic interplay between the Earth's surface 164 00:09:32,100 --> 00:09:33,533 and the Earth's atmosphere. 165 00:09:33,533 --> 00:09:35,100 And because of this interplay, 166 00:09:35,100 --> 00:09:39,333 there are chemical fingerprints that are trapped in rocks. 167 00:09:41,767 --> 00:09:43,233 The rock I'm holding in my hand 168 00:09:43,233 --> 00:09:46,267 is 3.4 billion years old. 169 00:09:46,267 --> 00:09:48,467 And there are tiny bubbles 170 00:09:48,467 --> 00:09:50,167 trapped in this rock 171 00:09:50,167 --> 00:09:52,367 that are samples 172 00:09:52,367 --> 00:09:53,967 of Earth's ancient atmosphere. 173 00:09:53,967 --> 00:09:56,733 So we can measure the gases 174 00:09:56,733 --> 00:09:58,767 and piece together evidence 175 00:09:58,767 --> 00:10:01,733 of what the atmosphere was like in the past. 176 00:10:01,733 --> 00:10:03,733 ♪ 177 00:10:03,733 --> 00:10:05,167 NARRATOR: However, 178 00:10:05,167 --> 00:10:07,967 to understand the very earliest atmosphere, 179 00:10:07,967 --> 00:10:10,400 scientists have to go back to a time 180 00:10:10,400 --> 00:10:13,267 before Earth was formed. 181 00:10:15,400 --> 00:10:19,600 The planet is made up of rock that started as debris 182 00:10:19,600 --> 00:10:22,800 floating in the early solar system. 183 00:10:23,800 --> 00:10:29,567 But this debris is also falling to Earth today as meteorites. 184 00:10:29,567 --> 00:10:31,000 WILLIAMS: In my pocket here, 185 00:10:31,000 --> 00:10:32,300 I've got the most incredible rock. 186 00:10:32,300 --> 00:10:34,333 This is a chondrite meteorite. 187 00:10:34,333 --> 00:10:37,567 These chondrite meteorites 188 00:10:37,567 --> 00:10:39,667 formed when rock dust came together 189 00:10:39,667 --> 00:10:42,233 to form small chunks of rock like this. 190 00:10:42,233 --> 00:10:44,000 They eventually smashed together, 191 00:10:44,000 --> 00:10:45,800 forming our planet Earth. 192 00:10:45,800 --> 00:10:48,833 And so these are really the building blocks of our planet. 193 00:10:51,300 --> 00:10:52,867 And so it's so humbling, 194 00:10:52,867 --> 00:10:54,567 because it's not only older than all of the life 195 00:10:54,567 --> 00:10:56,133 that we know on Earth, 196 00:10:56,133 --> 00:10:57,800 but even the planet itself, 197 00:10:57,800 --> 00:11:00,000 right back to 4.6 billion years ago. 198 00:11:01,333 --> 00:11:05,067 NARRATOR: These rocks are not just the building blocks of our planet, 199 00:11:05,067 --> 00:11:08,100 but of our early atmosphere as well. 200 00:11:08,100 --> 00:11:09,600 WILLIAMS: Thanks to these space rocks, 201 00:11:09,600 --> 00:11:13,033 the ingredients for our early atmosphere were there. 202 00:11:13,033 --> 00:11:15,600 It's just that they were locked inside the planet. 203 00:11:18,033 --> 00:11:22,133 NARRATOR: Chondrite meteorites are like time machines, 204 00:11:22,133 --> 00:11:25,333 allowing scientists to travel back billions of years 205 00:11:25,333 --> 00:11:28,233 to when the atmosphere first developed. 206 00:11:29,900 --> 00:11:32,867 WILLIAMS: Experts can study these chondrites in great detail. 207 00:11:32,867 --> 00:11:35,733 They can analyze them in the laboratory 208 00:11:35,733 --> 00:11:37,333 to understand their chemical signatures, 209 00:11:37,333 --> 00:11:39,133 and that's going to tell them about the gases 210 00:11:39,133 --> 00:11:41,900 that they would have contributed to 211 00:11:41,900 --> 00:11:44,067 our early Earth's atmosphere, 212 00:11:44,067 --> 00:11:46,333 such as water vapor, carbon dioxide, 213 00:11:46,333 --> 00:11:50,233 sulfur dioxide, hydrogen, methane, and nitrogen. 214 00:11:52,267 --> 00:11:54,200 HAZEN: It's remarkable that you can learn 215 00:11:54,200 --> 00:11:56,700 about the history of the atmosphere 216 00:11:56,700 --> 00:11:59,000 going back billions and billions of years 217 00:11:59,000 --> 00:12:00,867 just by studying rocks. 218 00:12:03,700 --> 00:12:06,667 WONG: When I learn about this, I feel simultaneously 219 00:12:06,667 --> 00:12:09,600 like a time traveler and a detective, 220 00:12:09,600 --> 00:12:12,833 being able to piece together the story of our ancient Earth. 221 00:12:14,400 --> 00:12:17,600 LYONS: Each year, techniques become more and more powerful 222 00:12:17,600 --> 00:12:21,100 at deciphering bits of information of what the Earth 223 00:12:21,100 --> 00:12:22,300 may have been like 224 00:12:22,300 --> 00:12:23,933 four and a half billion years ago, 225 00:12:23,933 --> 00:12:27,500 that even a short time ago would have been completely a mystery. 226 00:12:27,500 --> 00:12:32,633 (rumbling) 227 00:12:32,633 --> 00:12:35,100 (steam hissing) 228 00:12:37,700 --> 00:12:41,533 NARRATOR: While the scorching Earth slowly cools, 229 00:12:41,533 --> 00:12:46,200 the sky is undergoing a dramatic transformation. 230 00:12:51,767 --> 00:12:55,567 The vast sea of stars becomes obscured. 231 00:12:55,567 --> 00:12:58,600 ♪ 232 00:12:58,600 --> 00:13:03,500 And as the young sun rises, 233 00:13:03,500 --> 00:13:07,233 color bursts across Earth's sky. 234 00:13:10,700 --> 00:13:13,433 These dense gases are the beginnings 235 00:13:13,433 --> 00:13:16,800 of the atmosphere as we know it. 236 00:13:19,233 --> 00:13:24,967 What this fledgling atmosphere looked like is debated. 237 00:13:24,967 --> 00:13:27,933 Because it's hard to know the precise amounts 238 00:13:27,933 --> 00:13:30,967 of the various gases it contained. 239 00:13:32,067 --> 00:13:34,833 Gases like methane. 240 00:13:34,833 --> 00:13:37,033 PIERREHUMBERT: If there's enough methane, 241 00:13:37,033 --> 00:13:40,000 it can reach a concentration where it starts breaking up 242 00:13:40,000 --> 00:13:42,400 under the action of ultraviolet light 243 00:13:42,400 --> 00:13:44,700 and then recombining into longer molecules, 244 00:13:44,700 --> 00:13:47,433 making these smoggy substances. 245 00:13:47,433 --> 00:13:49,167 That can actually make these hazes 246 00:13:49,167 --> 00:13:50,900 which cause an orangey glow. 247 00:13:50,900 --> 00:13:53,933 ♪ 248 00:13:53,933 --> 00:13:56,167 NARRATOR: With enough methane, 249 00:13:56,167 --> 00:14:01,833 thick, intermittent orange hazes would have covered the planet. 250 00:14:01,833 --> 00:14:05,233 TIKOO: There was probably carbon dioxide. 251 00:14:05,233 --> 00:14:08,967 There might have been carbon monoxide, water vapor. 252 00:14:08,967 --> 00:14:10,400 There might have been 253 00:14:10,400 --> 00:14:12,100 some nitrogen or cyanide. 254 00:14:12,100 --> 00:14:13,767 All in all, it was a pretty 255 00:14:13,767 --> 00:14:15,867 noxious combination of stuff. 256 00:14:16,933 --> 00:14:19,133 HAZEN: If you were dropped onto early Earth 257 00:14:19,133 --> 00:14:20,900 and experienced that early atmosphere, 258 00:14:20,900 --> 00:14:23,067 you'd die very quickly because there was no oxygen. 259 00:14:24,100 --> 00:14:26,367 Carbon dioxide, some of the other molecules 260 00:14:26,367 --> 00:14:28,200 that might have been present in the atmosphere, 261 00:14:28,200 --> 00:14:30,300 you just simply couldn't live on those. 262 00:14:34,233 --> 00:14:37,300 ♪ 263 00:14:37,300 --> 00:14:42,700 NARRATOR: And the planet is inhospitable for another reason-- 264 00:14:42,700 --> 00:14:47,533 the landscape has never seen a drop of liquid water. 265 00:14:52,533 --> 00:14:55,233 But Earth does have water. 266 00:14:55,233 --> 00:14:56,767 (thunder crackling) 267 00:14:56,767 --> 00:15:01,533 It is suspended high above the searing surface, 268 00:15:01,533 --> 00:15:04,267 pumped into the atmosphere by volcanoes 269 00:15:04,267 --> 00:15:08,033 as water vapor with the other early gases. 270 00:15:08,033 --> 00:15:11,700 ♪ 271 00:15:11,700 --> 00:15:13,533 (woman vocalizing, thunder crackling) 272 00:15:13,533 --> 00:15:17,567 If this ocean in the sky could reach the ground, 273 00:15:17,567 --> 00:15:22,000 it would have the power to utterly transform the planet. 274 00:15:22,967 --> 00:15:25,800 (water rushing) 275 00:15:25,800 --> 00:15:28,600 (roaring) 276 00:15:32,300 --> 00:15:37,100 ♪ 277 00:15:37,100 --> 00:15:39,633 Today, over 70% of our world 278 00:15:39,633 --> 00:15:41,767 is covered in water. 279 00:15:44,833 --> 00:15:46,900 A planet of abundant blue 280 00:15:46,900 --> 00:15:49,933 with endless rivers, 281 00:15:49,933 --> 00:15:53,400 freezing icebergs, 282 00:15:53,400 --> 00:15:58,333 and vast oceans. 283 00:15:58,333 --> 00:16:00,567 ♪ 284 00:16:00,567 --> 00:16:03,867 GIRGUIS: Water that we get out of our tap 285 00:16:03,867 --> 00:16:06,300 has been through a long journey. 286 00:16:06,300 --> 00:16:08,967 ♪ 287 00:16:08,967 --> 00:16:10,500 DOTTIN: And the water on our planet 288 00:16:10,500 --> 00:16:15,400 gets incorporated into various aspects of our life, 289 00:16:15,400 --> 00:16:17,500 including weather, into the food that we eat. 290 00:16:17,500 --> 00:16:19,133 And because of this, the water is recycled 291 00:16:19,133 --> 00:16:25,033 over and over and over again throughout Earth's history. 292 00:16:25,033 --> 00:16:27,133 WONG: So the water that we drink 293 00:16:27,133 --> 00:16:29,167 was consumed by dinosaurs 294 00:16:29,167 --> 00:16:30,533 and had the first microbes 295 00:16:30,533 --> 00:16:32,133 swimming around in it. (laughs) 296 00:16:32,133 --> 00:16:34,967 (distant rumbling) 297 00:16:34,967 --> 00:16:36,733 NARRATOR: On the early Earth, 298 00:16:36,733 --> 00:16:39,500 water is stuck in the atmosphere. 299 00:16:39,500 --> 00:16:41,367 (wind howling, thunder crackling) 300 00:16:41,367 --> 00:16:45,500 But that is about to change. 301 00:16:45,500 --> 00:16:50,900 ♪ 302 00:16:50,900 --> 00:16:52,467 High up in the sky, 303 00:16:52,467 --> 00:16:55,200 droplets of water, 304 00:16:55,200 --> 00:17:00,467 just a fraction of a millimeter across, are condensing. 305 00:17:00,467 --> 00:17:05,800 So light and small, they just float, 306 00:17:05,800 --> 00:17:07,700 drifting in the air. 307 00:17:10,567 --> 00:17:13,733 Colliding and merging with others... 308 00:17:13,733 --> 00:17:15,500 (squishing) 309 00:17:15,500 --> 00:17:19,433 ...they slowly grow until a tipping point is reached. 310 00:17:19,433 --> 00:17:24,500 ♪ 311 00:17:32,067 --> 00:17:35,200 Earth's gravity draws them downwards... 312 00:17:37,467 --> 00:17:40,233 but the journey is short-lived. 313 00:17:43,167 --> 00:17:45,900 The planet is still hot. 314 00:17:45,900 --> 00:17:47,967 (sizzling) 315 00:17:47,967 --> 00:17:52,367 So any drops nearing the ground... 316 00:17:52,367 --> 00:17:56,233 (hissing) 317 00:17:56,233 --> 00:17:58,433 ...simply evaporate. 318 00:18:00,033 --> 00:18:05,067 ♪ (wind whipping) 319 00:18:07,000 --> 00:18:08,833 But over time, 320 00:18:08,833 --> 00:18:11,933 that heat is radiating out into space. 321 00:18:15,367 --> 00:18:18,600 Earth is cooling down. 322 00:18:18,600 --> 00:18:22,167 (wind whistling) 323 00:18:22,167 --> 00:18:23,967 (fizzing) 324 00:18:32,567 --> 00:18:38,433 ♪ 325 00:18:40,567 --> 00:18:42,767 (thunder booming) 326 00:18:42,767 --> 00:18:48,033 (rain falling) 327 00:18:48,033 --> 00:18:49,100 (lightning crackling) 328 00:18:49,100 --> 00:18:50,267 A deluge of rain 329 00:18:50,267 --> 00:18:52,767 begins to pour down on the surface. 330 00:18:52,767 --> 00:18:54,667 (booming) 331 00:18:54,667 --> 00:18:58,867 (rain pelting down) 332 00:19:02,200 --> 00:19:05,700 Huge storms sweep through the atmosphere. 333 00:19:05,700 --> 00:19:10,200 (thunder rumbling) 334 00:19:10,200 --> 00:19:13,200 Oceans of water are dumped onto the land. 335 00:19:14,867 --> 00:19:20,100 (rain pouring) 336 00:19:20,100 --> 00:19:23,333 (thunder rumbling) 337 00:19:23,333 --> 00:19:27,033 ♪ 338 00:19:27,033 --> 00:19:28,700 (lightning striking) 339 00:19:30,167 --> 00:19:35,467 The atmosphere has unleashed a key molecule for life. 340 00:19:39,467 --> 00:19:40,600 Water changes the surface 341 00:19:40,600 --> 00:19:41,833 of a planet. 342 00:19:41,833 --> 00:19:43,067 It evaporates, 343 00:19:43,067 --> 00:19:44,067 it allows clouds to form 344 00:19:44,067 --> 00:19:45,433 and rain to fall, 345 00:19:45,433 --> 00:19:47,267 it erodes things, 346 00:19:47,267 --> 00:19:49,467 and it also became a medium 347 00:19:49,467 --> 00:19:52,200 that would eventually harbor life. 348 00:19:52,200 --> 00:19:56,867 (wildlife chittering) 349 00:19:56,867 --> 00:19:57,933 Without liquid water, 350 00:19:57,933 --> 00:19:58,967 we certainly would not 351 00:19:58,967 --> 00:20:00,533 get life as we know it. 352 00:20:00,533 --> 00:20:02,967 ♪ 353 00:20:02,967 --> 00:20:04,633 LANE: Things that life needs it to do 354 00:20:04,633 --> 00:20:05,767 here on Earth, 355 00:20:05,767 --> 00:20:06,933 to have structures like cells, 356 00:20:06,933 --> 00:20:08,000 for example, 357 00:20:08,000 --> 00:20:09,167 and all kinds of machinery 358 00:20:09,167 --> 00:20:10,400 that operate in water, 359 00:20:10,400 --> 00:20:11,567 that works really well. 360 00:20:11,567 --> 00:20:15,367 ♪ 361 00:20:15,367 --> 00:20:18,600 NARRATOR: The early atmosphere had started a transformation 362 00:20:18,600 --> 00:20:21,800 that would set our planet apart 363 00:20:21,800 --> 00:20:25,600 from every other in the solar system. 364 00:20:34,200 --> 00:20:39,933 ♪ 365 00:20:42,067 --> 00:20:47,033 The young planet is only a few hundred million years old. 366 00:20:47,033 --> 00:20:50,967 The atmosphere has made Earth a water world. 367 00:20:50,967 --> 00:20:53,633 (waves crashing) 368 00:20:53,633 --> 00:20:56,800 ♪ 369 00:20:56,800 --> 00:21:01,467 And in that water, something remarkable is happening... 370 00:21:01,467 --> 00:21:04,967 ♪ 371 00:21:04,967 --> 00:21:10,067 Arguably, the most pivotal moment in Earth's history. 372 00:21:11,433 --> 00:21:17,133 It would lead to the reshaping of the entire atmosphere. 373 00:21:17,133 --> 00:21:19,900 ♪ 374 00:21:19,900 --> 00:21:23,433 So much of this moment is still a mystery. 375 00:21:25,467 --> 00:21:30,067 But we do know that one day on Earth, 376 00:21:30,067 --> 00:21:33,833 complex molecules come together 377 00:21:33,833 --> 00:21:38,367 to form something never seen on the planet before... 378 00:21:40,100 --> 00:21:42,467 Life. 379 00:21:44,333 --> 00:21:46,033 WONG: The origin of life 380 00:21:46,033 --> 00:21:48,200 is one of the greatest questions in science, 381 00:21:48,200 --> 00:21:50,633 and it's fair to say that we don't know when, 382 00:21:50,633 --> 00:21:52,933 where, or how life started. 383 00:21:52,933 --> 00:21:55,867 ♪ 384 00:21:55,867 --> 00:21:59,133 (waves crashing) 385 00:21:59,133 --> 00:22:03,967 NARRATOR: A shallow rock pool is one of the leading theories. 386 00:22:03,967 --> 00:22:05,500 ANDERSON: People think that shallow pools 387 00:22:05,500 --> 00:22:06,800 would have been 388 00:22:06,800 --> 00:22:07,967 a potentially important site 389 00:22:07,967 --> 00:22:09,267 for the origin of life, 390 00:22:09,267 --> 00:22:10,400 because they can get wet and dry 391 00:22:10,400 --> 00:22:11,533 over and over again. 392 00:22:11,533 --> 00:22:14,400 (waves lapping) 393 00:22:14,400 --> 00:22:17,800 LYONS: Through this repeated cycling of wetting and drying, 394 00:22:17,800 --> 00:22:19,333 reflooding and evaporating, 395 00:22:19,333 --> 00:22:20,900 maybe through a tide, 396 00:22:20,900 --> 00:22:22,467 maybe through seasonal variation, 397 00:22:22,467 --> 00:22:25,267 more and more complex molecules can form. 398 00:22:27,333 --> 00:22:29,533 ANDERSON: And that process could've been the precursors 399 00:22:29,533 --> 00:22:32,000 for things like DNA, which is what makes up 400 00:22:32,000 --> 00:22:33,733 the information in our cells today. 401 00:22:35,667 --> 00:22:37,867 NARRATOR: But there are many other theories 402 00:22:37,867 --> 00:22:41,200 about how life could have started. 403 00:22:41,200 --> 00:22:45,200 ♪ 404 00:22:45,200 --> 00:22:46,867 LINGAPPA: Some scientists think 405 00:22:46,867 --> 00:22:50,333 life began in a deep sea hydrothermal vent. 406 00:22:52,367 --> 00:22:55,333 LANE: Hydrothermal vents are sources of gases-- 407 00:22:55,333 --> 00:22:57,533 like hydrogen sulfide, for example-- 408 00:22:57,533 --> 00:22:59,867 and provide the kind of reactive conditions 409 00:22:59,867 --> 00:23:02,667 between hydrogen and CO2 to make the building blocks of life. 410 00:23:02,667 --> 00:23:06,933 ♪ 411 00:23:06,933 --> 00:23:09,600 LINGAPPA: Others think that 412 00:23:09,600 --> 00:23:10,700 life originated somewhere 413 00:23:10,700 --> 00:23:11,700 completely else, 414 00:23:11,700 --> 00:23:13,333 not on the Earth at all, 415 00:23:13,333 --> 00:23:17,333 and landed here on a meteorite. 416 00:23:17,333 --> 00:23:21,600 (crashing, booming) 417 00:23:21,600 --> 00:23:23,100 All of these different theories 418 00:23:23,100 --> 00:23:24,433 have sort of different details, 419 00:23:24,433 --> 00:23:26,033 but the punchline is 420 00:23:26,033 --> 00:23:27,933 that life needed water, 421 00:23:27,933 --> 00:23:31,267 and it needed a way to harness energy. 422 00:23:31,267 --> 00:23:33,667 ♪ 423 00:23:33,667 --> 00:23:35,900 NARRATOR: Scientists have some idea 424 00:23:35,900 --> 00:23:38,100 what early life might have looked like. 425 00:23:41,100 --> 00:23:42,700 The very first lifeform 426 00:23:42,700 --> 00:23:43,967 that existed was probably 427 00:23:43,967 --> 00:23:45,767 a little bit of genetic material 428 00:23:45,767 --> 00:23:48,033 enclosed in a bubble 429 00:23:48,033 --> 00:23:50,033 of fatty material. 430 00:23:50,033 --> 00:23:52,467 ♪ 431 00:23:52,467 --> 00:23:54,300 NARRATOR: And while simple, 432 00:23:54,300 --> 00:23:56,367 some of these early organisms 433 00:23:56,367 --> 00:24:00,167 would have a powerful effect on the atmosphere. 434 00:24:02,100 --> 00:24:04,867 We think that one of the earliest organisms 435 00:24:04,867 --> 00:24:07,267 were organisms that produce methane 436 00:24:07,267 --> 00:24:09,700 as part of the way they eat, and breathe, and live. 437 00:24:09,700 --> 00:24:12,667 ♪ 438 00:24:12,667 --> 00:24:16,200 NARRATOR: They take in carbon dioxide and hydrogen, 439 00:24:16,200 --> 00:24:19,467 producing water and methane as waste products. 440 00:24:19,467 --> 00:24:22,300 LYONS: So it is reasonable to estimate 441 00:24:22,300 --> 00:24:24,233 that a vast portion of the early atmosphere 442 00:24:24,233 --> 00:24:26,000 contains large amounts of methane. 443 00:24:26,000 --> 00:24:28,833 ♪ 444 00:24:28,833 --> 00:24:30,467 NARRATOR: This increased methane 445 00:24:30,467 --> 00:24:33,433 could have made the orange hazes thicker. 446 00:24:36,567 --> 00:24:38,267 The evolution of our atmosphere is, in many respects, 447 00:24:38,267 --> 00:24:40,533 the story of the evolution of life on our planet. 448 00:24:40,533 --> 00:24:42,800 (wind howling) 449 00:24:42,800 --> 00:24:45,767 Life can change a planet fundamentally. 450 00:24:47,633 --> 00:24:51,267 But it's always this cause and effect kind of dance 451 00:24:51,267 --> 00:24:53,433 between the environment changing life 452 00:24:53,433 --> 00:24:55,233 and life changing the environment. 453 00:24:55,233 --> 00:24:59,100 ♪ 454 00:24:59,100 --> 00:25:02,533 NARRATOR: And it's the story of life that reveals how we got from 455 00:25:02,533 --> 00:25:06,033 this orange hazy atmosphere 456 00:25:06,033 --> 00:25:09,933 to the blue, oxygen-rich one we know today. 457 00:25:12,567 --> 00:25:18,600 ♪ 458 00:25:20,100 --> 00:25:23,633 This young world is not one we could survive in. 459 00:25:25,800 --> 00:25:28,833 Earth's early oceans are blue-green, 460 00:25:28,833 --> 00:25:32,733 full of dissolved iron, 461 00:25:32,733 --> 00:25:36,067 and they've absorbed large amounts of carbon dioxide, 462 00:25:36,067 --> 00:25:39,367 making them acidic. 463 00:25:39,367 --> 00:25:42,900 (waves crashing) 464 00:25:42,900 --> 00:25:44,700 ANDERSON: Early life would have been 465 00:25:44,700 --> 00:25:46,633 adapted specifically to living in high temperatures 466 00:25:46,633 --> 00:25:49,167 or fairly acidic conditions. 467 00:25:51,467 --> 00:25:53,767 ROTHSCHILD: The ultraviolet radiation was incredibly harsh 468 00:25:53,767 --> 00:25:56,133 because there was no ozone layer. 469 00:25:57,900 --> 00:25:59,800 Furthermore, there was no oxygen in the atmosphere; 470 00:25:59,800 --> 00:26:01,367 it was a very different composition. 471 00:26:03,500 --> 00:26:06,700 NARRATOR: And some organisms today offer clues 472 00:26:06,700 --> 00:26:09,233 to how life survived in this early environment. 473 00:26:09,233 --> 00:26:13,233 ♪ 474 00:26:13,233 --> 00:26:15,800 High in the Andes is one of 475 00:26:15,800 --> 00:26:18,067 the largest geyser fields in the world. 476 00:26:18,067 --> 00:26:23,133 ♪ 477 00:26:26,167 --> 00:26:29,000 LINGAPPA: This environment is extreme for a lot of reasons. 478 00:26:29,000 --> 00:26:31,467 First of all, the water that's coming 479 00:26:31,467 --> 00:26:33,633 out of this pool is boilingly hot. 480 00:26:33,633 --> 00:26:35,467 And the altitude means 481 00:26:35,467 --> 00:26:37,633 that this environment is subject 482 00:26:37,633 --> 00:26:38,833 to a lot of ultraviolet 483 00:26:38,833 --> 00:26:40,233 radiation from the sun. 484 00:26:42,367 --> 00:26:47,033 NARRATOR: These are conditions most animals would find toxic. 485 00:26:48,867 --> 00:26:52,633 But amongst the boiling water and steam, 486 00:26:52,633 --> 00:26:56,300 life is flourishing. 487 00:26:56,300 --> 00:26:58,000 LINGAPPA: So the colors that we see 488 00:26:58,000 --> 00:26:59,800 in these mats around this pool 489 00:26:59,800 --> 00:27:02,033 are billions of thriving bacteria 490 00:27:02,033 --> 00:27:04,567 that have sort of carved out a niche 491 00:27:04,567 --> 00:27:06,500 in this extreme environment. 492 00:27:07,667 --> 00:27:11,500 It's incredible to find so much life, 493 00:27:11,500 --> 00:27:16,633 not just surviving, but thriving in these conditions. 494 00:27:16,633 --> 00:27:20,500 NARRATOR: Organisms like these are called extremophiles. 495 00:27:22,267 --> 00:27:25,000 They can survive in environments most complex life 496 00:27:25,000 --> 00:27:29,033 would struggle to live in. 497 00:27:29,033 --> 00:27:30,467 LANE: We call them extremophiles 498 00:27:30,467 --> 00:27:33,867 because we didn't really think that life could exist 499 00:27:33,867 --> 00:27:35,267 in such extreme conditions. 500 00:27:37,933 --> 00:27:40,900 ROTHSCHILD: In fact, we know of organisms 501 00:27:40,900 --> 00:27:45,167 that can live up to 122 centigrade. 502 00:27:45,167 --> 00:27:48,200 So this is well over the boiling temperature of water, 503 00:27:48,200 --> 00:27:50,233 and, conversely, we know of ones 504 00:27:50,233 --> 00:27:52,600 that can live well below freezing. 505 00:27:52,600 --> 00:27:54,500 Bacteria could survive in outer space 506 00:27:54,500 --> 00:27:55,900 quite comfortably as well. 507 00:27:55,900 --> 00:27:58,867 These are behaviors that we consider to be extreme 508 00:27:58,867 --> 00:28:00,400 because we would die in them. 509 00:28:03,100 --> 00:28:06,900 NARRATOR: Today, life on Earth is prolific, 510 00:28:06,900 --> 00:28:10,267 thriving in the most unlikely of places. 511 00:28:11,500 --> 00:28:14,067 From under ice sheets, 512 00:28:14,067 --> 00:28:17,933 to acid-filled pools, 513 00:28:17,933 --> 00:28:23,100 and the dark, high-pressure depths of the oceans. 514 00:28:23,100 --> 00:28:26,967 And researching these modern extremophiles 515 00:28:26,967 --> 00:28:30,300 can hint at what was happening 516 00:28:30,300 --> 00:28:33,600 in the early atmosphere. 517 00:28:33,600 --> 00:28:36,067 LINGAPPA: There's been extremophiles 518 00:28:36,067 --> 00:28:37,933 as long as there's been life on Earth. 519 00:28:38,967 --> 00:28:41,867 Studying today's extremophiles 520 00:28:41,867 --> 00:28:44,433 expands our understanding of what life can do 521 00:28:44,433 --> 00:28:45,600 and what life can look like, 522 00:28:45,600 --> 00:28:47,533 including trying to understand 523 00:28:47,533 --> 00:28:52,000 the earliest life and our most ancient ancestors. 524 00:28:52,000 --> 00:28:56,033 GIRGUIS: Life originated on an earth without oxygen. 525 00:28:56,033 --> 00:28:58,500 So looking at the microbes that live 526 00:28:58,500 --> 00:29:00,767 in areas without oxygen 527 00:29:00,767 --> 00:29:03,367 helps us understand how they evolved 528 00:29:03,367 --> 00:29:06,067 to do well in those environments. 529 00:29:06,067 --> 00:29:08,033 (water fizzing) 530 00:29:08,033 --> 00:29:12,633 NARRATOR: But evolving to live in one very specialized habitat 531 00:29:12,633 --> 00:29:15,633 can have its drawbacks. 532 00:29:15,633 --> 00:29:17,833 At this period of time in Earth's history, 533 00:29:17,833 --> 00:29:22,100 life would have been limited in its energy sources. 534 00:29:23,400 --> 00:29:24,867 LINGAPPA: If you're dependent 535 00:29:24,867 --> 00:29:28,067 on something that's being released from a vent in order 536 00:29:28,067 --> 00:29:32,000 to generate energy to be alive, you're going to be 537 00:29:32,000 --> 00:29:36,733 extremely limited in how fast you can grow. 538 00:29:36,733 --> 00:29:40,367 NARRATOR: Because the energy sources early life used 539 00:29:40,367 --> 00:29:44,000 to survive in the oceans were comparatively rare, 540 00:29:44,000 --> 00:29:48,100 organisms struggled to proliferate. 541 00:29:48,100 --> 00:29:50,333 PIERREHUMBERT: They had to take various chemicals 542 00:29:50,333 --> 00:29:52,167 that were produced by geology 543 00:29:52,167 --> 00:29:54,533 and then combine them to release energy. 544 00:29:57,400 --> 00:29:59,633 WONG: But there's about to be 545 00:29:59,633 --> 00:30:04,367 a grand innovation by life that will open up 546 00:30:04,367 --> 00:30:07,100 a nearly limitless source of energy. 547 00:30:09,233 --> 00:30:11,533 NARRATOR: An innovation that would also change 548 00:30:11,533 --> 00:30:16,267 the course of the evolution of the atmosphere. 549 00:30:16,267 --> 00:30:20,300 ♪ 550 00:30:23,833 --> 00:30:25,500 Today, life can be found 551 00:30:25,500 --> 00:30:28,700 in puddles, lakes, and oceans across the planet. 552 00:30:31,700 --> 00:30:33,400 (waves crashing) 553 00:30:33,400 --> 00:30:34,533 LINGAPPA: Our world today 554 00:30:34,533 --> 00:30:36,867 is absolutely teeming with life. 555 00:30:36,867 --> 00:30:40,933 Just a single drop of water from the ocean 556 00:30:40,933 --> 00:30:44,933 would contain tens of thousands of cells, 557 00:30:44,933 --> 00:30:48,667 and among them, you would find organisms called cyanobacteria. 558 00:30:50,600 --> 00:30:54,300 NARRATOR: There are over 2,000 known types of cyanobacteria, 559 00:30:54,300 --> 00:30:57,000 and they come in all shapes and sizes. 560 00:30:59,867 --> 00:31:01,000 From long filaments 561 00:31:01,000 --> 00:31:05,233 to geometric shapes. 562 00:31:06,233 --> 00:31:07,767 LYONS: Cyanobacteria evolved, 563 00:31:07,767 --> 00:31:09,400 as best as we understand, 564 00:31:09,400 --> 00:31:11,567 around three billion years ago. 565 00:31:11,567 --> 00:31:13,600 They are astounding, in that 566 00:31:13,600 --> 00:31:16,167 they have the ability to adapt to environmental change, 567 00:31:16,167 --> 00:31:18,400 and to change the environment 568 00:31:18,400 --> 00:31:21,467 because they can be so abundant. 569 00:31:21,467 --> 00:31:24,333 NARRATOR: Cyanobacteria sometimes changed 570 00:31:24,333 --> 00:31:26,867 their local environments by creating structures, 571 00:31:26,867 --> 00:31:31,800 which they used as habitats to live in. 572 00:31:31,800 --> 00:31:36,667 This is one of the clear-cut examples that life was living 573 00:31:36,667 --> 00:31:37,933 even three billion years ago. 574 00:31:37,933 --> 00:31:40,033 This is a formation called a stromatolite. 575 00:31:40,033 --> 00:31:44,900 It's really inspiring that you can pick up a rock like this 576 00:31:44,900 --> 00:31:47,067 and read the history of what was happening 577 00:31:47,067 --> 00:31:48,300 billions of years ago. 578 00:31:48,300 --> 00:31:50,567 That's an amazing book to read. 579 00:31:50,567 --> 00:31:53,967 ♪ 580 00:31:53,967 --> 00:31:56,100 LINGAPPA: Cyanobacteria are some of the most 581 00:31:56,100 --> 00:32:00,100 successful organisms ever to live on our planet. 582 00:32:00,100 --> 00:32:04,167 They completely transformed the world. 583 00:32:06,867 --> 00:32:09,033 NARRATOR: This transformation was due 584 00:32:09,033 --> 00:32:10,933 to a revolutionary process 585 00:32:10,933 --> 00:32:16,567 that changed the fundamental composition of the atmosphere. 586 00:32:19,367 --> 00:32:21,867 Around three billion years ago, 587 00:32:21,867 --> 00:32:25,367 Cyanobacteria are developing a unique way 588 00:32:25,367 --> 00:32:28,600 to produce energy. 589 00:32:28,600 --> 00:32:31,833 They capture sunlight 590 00:32:31,833 --> 00:32:36,867 and use it to combine hydrogen from nearby water molecules... 591 00:32:38,533 --> 00:32:43,300 with the carbon dioxide dissolved in the oceans. 592 00:32:43,300 --> 00:32:46,267 With this, they make carbohydrates... 593 00:32:50,333 --> 00:32:55,900 And a very reactive waste product-- 594 00:32:55,900 --> 00:32:59,533 oxygen. 595 00:32:59,533 --> 00:33:02,267 LINGAPPA: So this vial contains a culture 596 00:33:02,267 --> 00:33:04,967 of cyanobacteria that I grew. 597 00:33:04,967 --> 00:33:06,700 And these are cyanobacteria of today, 598 00:33:06,700 --> 00:33:10,933 but they are descended from the organisms 599 00:33:10,933 --> 00:33:13,633 that first evolved the ability 600 00:33:13,633 --> 00:33:16,867 to do oxygen-producing photosynthesis. 601 00:33:19,567 --> 00:33:20,600 LANE: There are these 602 00:33:20,600 --> 00:33:22,433 moments in the history of life 603 00:33:22,433 --> 00:33:23,600 that seem to have 604 00:33:23,600 --> 00:33:24,900 only happened once. 605 00:33:24,900 --> 00:33:28,800 Oxygen-producing photosynthesis is one of them. 606 00:33:28,800 --> 00:33:30,267 Was it a freak accident? 607 00:33:30,267 --> 00:33:32,800 We just don't know. 608 00:33:32,800 --> 00:33:36,300 Suddenly, the oceans became the fuel. 609 00:33:36,300 --> 00:33:38,500 It allowed life to scale up at least tenfold. 610 00:33:40,500 --> 00:33:42,967 NARRATOR: Lifeforms can now make energy 611 00:33:42,967 --> 00:33:46,167 using one of the most abundant raw materials 612 00:33:46,167 --> 00:33:51,400 on the planet's surface: water. 613 00:33:51,400 --> 00:33:54,900 This kind of photosynthesis now enables organisms 614 00:33:54,900 --> 00:33:58,567 to get energy from virtually anywhere, 615 00:33:58,567 --> 00:34:03,000 allowing them to spread throughout the oceans. 616 00:34:05,800 --> 00:34:09,600 One cyanobacteria cell becomes two; 617 00:34:09,600 --> 00:34:11,700 two become four. 618 00:34:13,533 --> 00:34:18,600 Multiplying again and again... 619 00:34:20,133 --> 00:34:25,233 until there are trillions. 620 00:34:32,100 --> 00:34:36,067 And we can still find evidence of them everywhere we look, 621 00:34:36,067 --> 00:34:40,667 including in the harshest environments. 622 00:34:44,167 --> 00:34:45,300 LINGAPPA: If you look really closely 623 00:34:45,300 --> 00:34:48,000 in the mats in this pool, 624 00:34:48,000 --> 00:34:50,033 you can see in some of these greener areas 625 00:34:50,033 --> 00:34:54,333 little bubbles that are literally the oxygen 626 00:34:54,333 --> 00:34:56,067 being produced by them 627 00:34:56,067 --> 00:34:58,667 doing photosynthesis right now. 628 00:35:01,333 --> 00:35:04,200 Cyanobacteria demonstrate the power of life on Earth 629 00:35:04,200 --> 00:35:06,800 like nothing else does. 630 00:35:06,800 --> 00:35:08,233 Over two billion years ago, 631 00:35:08,233 --> 00:35:11,267 the ancestors of these extraordinary microbes 632 00:35:11,267 --> 00:35:13,733 unlocked this spectacular ability. 633 00:35:15,833 --> 00:35:18,200 LANE: Cyanobacteria were the first, 634 00:35:18,200 --> 00:35:19,733 and the only, organisms 635 00:35:19,733 --> 00:35:25,433 that ever evolved oxygen-producing photosynthesis. 636 00:35:25,433 --> 00:35:27,067 As soon as they cracked the problem 637 00:35:27,067 --> 00:35:28,800 of how to use water as a fuel, 638 00:35:28,800 --> 00:35:30,900 the oceans became the fuel, and they could 639 00:35:30,900 --> 00:35:34,833 live almost anywhere. 640 00:35:37,100 --> 00:35:40,400 These are seaweeds from the ocean-- 641 00:35:40,400 --> 00:35:43,333 ooh, right off the West Coast of Scotland-- 642 00:35:43,333 --> 00:35:46,667 and oxygen-producing photosynthesis 643 00:35:46,667 --> 00:35:49,500 was such a brilliant innovation, 644 00:35:49,500 --> 00:35:52,067 that some organisms at that time 645 00:35:52,067 --> 00:35:54,967 actually swallowed the cyanobacteria, 646 00:35:54,967 --> 00:35:59,233 and that's how we got algae like this. 647 00:35:59,233 --> 00:36:01,467 And then the algae ultimately gave rise 648 00:36:01,467 --> 00:36:03,067 to the plants, as well. 649 00:36:03,067 --> 00:36:05,900 (thunder rumbling) 650 00:36:05,900 --> 00:36:09,200 NARRATOR: While life was spreading through the oceans, 651 00:36:09,200 --> 00:36:12,033 above the waves, 652 00:36:12,033 --> 00:36:14,267 the atmosphere was also undergoing 653 00:36:14,267 --> 00:36:16,000 a dramatic transformation. 654 00:36:26,067 --> 00:36:29,633 ♪ 655 00:36:31,433 --> 00:36:34,100 Over millions of years, 656 00:36:34,100 --> 00:36:36,033 tectonic movements in the earth 657 00:36:36,033 --> 00:36:40,033 are forging the first large-scale landmass. 658 00:36:45,567 --> 00:36:47,900 And this directly affects 659 00:36:47,900 --> 00:36:50,567 the dynamics of the atmosphere. 660 00:36:50,567 --> 00:36:55,633 ♪ 661 00:36:55,633 --> 00:36:57,733 (wind howling) 662 00:36:57,733 --> 00:37:00,100 Air warmed by the new land 663 00:37:00,100 --> 00:37:03,667 drives novel weather patterns across the globe. 664 00:37:03,667 --> 00:37:05,433 (wind blowing) 665 00:37:05,433 --> 00:37:07,967 (thunder rumbling) 666 00:37:07,967 --> 00:37:13,867 Winds sweep dust high up into the air, 667 00:37:13,867 --> 00:37:17,833 where tiny particles seed vast pillars of clouds. 668 00:37:17,833 --> 00:37:20,667 ♪ 669 00:37:20,667 --> 00:37:24,033 Something resembling our modern-day weather system 670 00:37:24,033 --> 00:37:28,567 is, at last, taking shape. 671 00:37:28,567 --> 00:37:30,933 HAZEN: The appearance of large continental masses 672 00:37:30,933 --> 00:37:33,333 had a huge impact on the atmosphere. 673 00:37:33,333 --> 00:37:34,633 We would have seen 674 00:37:34,633 --> 00:37:35,633 high-pressure systems, 675 00:37:35,633 --> 00:37:36,733 low-pressure systems, 676 00:37:36,733 --> 00:37:38,467 prevailing winds, rains, 677 00:37:38,467 --> 00:37:41,200 very much like the modern world. 678 00:37:41,200 --> 00:37:45,267 ♪ 679 00:37:48,300 --> 00:37:50,167 NARRATOR: Meanwhile, in the oceans, 680 00:37:50,167 --> 00:37:52,233 trillions of cyanobacteria 681 00:37:52,233 --> 00:37:56,600 are photosynthesizing and producing oxygen. 682 00:37:56,600 --> 00:37:59,967 The first time it has ever been made 683 00:37:59,967 --> 00:38:03,367 in significant amounts on Earth. 684 00:38:05,533 --> 00:38:08,933 Oxygen bubbles race upwards. 685 00:38:08,933 --> 00:38:12,567 ♪ 686 00:38:15,667 --> 00:38:21,533 But most vanish before they can reach the surface. 687 00:38:21,533 --> 00:38:23,767 (waves crashing) 688 00:38:23,767 --> 00:38:26,667 Earth's early atmosphere seems destined 689 00:38:26,667 --> 00:38:31,000 to stay as thick orange hazes. 690 00:38:33,567 --> 00:38:39,133 So what is making the oxygen disappear? 691 00:38:39,133 --> 00:38:44,200 The answer lies in a unique property oxygen has. 692 00:38:44,200 --> 00:38:46,567 Oxygen is an extremely reactive element. 693 00:38:48,633 --> 00:38:51,000 DOTTIN: What's unique about oxygen 694 00:38:51,000 --> 00:38:53,267 is that it has a chemical makeup 695 00:38:53,267 --> 00:38:55,433 that allows it to bond with 696 00:38:55,433 --> 00:38:57,600 so many different elements; 697 00:38:57,600 --> 00:39:01,033 almost all of the elements that exist. 698 00:39:01,033 --> 00:39:03,767 NARRATOR: And this incredible reactive power 699 00:39:03,767 --> 00:39:06,067 is the reason many scientists think 700 00:39:06,067 --> 00:39:10,333 oxygen struggled to escape the water. 701 00:39:14,000 --> 00:39:21,300 ♪ 702 00:39:21,300 --> 00:39:24,367 Around three billion years ago, 703 00:39:24,367 --> 00:39:26,933 Earth's oceans were packed 704 00:39:26,933 --> 00:39:30,467 full of dissolved metals. 705 00:39:30,467 --> 00:39:33,467 Metals like iron. 706 00:39:34,500 --> 00:39:36,267 This key that we see here 707 00:39:36,267 --> 00:39:37,300 is rusty, 708 00:39:37,300 --> 00:39:39,067 and in order to form rust 709 00:39:39,067 --> 00:39:40,400 we need three ingredients. 710 00:39:40,400 --> 00:39:42,100 The first is iron, which is 711 00:39:42,100 --> 00:39:43,867 what this key is made of, 712 00:39:43,867 --> 00:39:45,067 the second is water, 713 00:39:45,067 --> 00:39:46,633 or water vapor in the air, 714 00:39:46,633 --> 00:39:48,900 and the third crucial ingredient 715 00:39:48,900 --> 00:39:51,300 is oxygen. 716 00:39:51,300 --> 00:39:53,100 NARRATOR: And in Earth's early oceans, 717 00:39:53,100 --> 00:39:58,667 oxygen began to react more and more with iron and other metals, 718 00:39:58,667 --> 00:40:02,767 as cyanobacteria spread across the oceans. 719 00:40:02,767 --> 00:40:06,633 ♪ 720 00:40:10,300 --> 00:40:12,867 Below the surface... 721 00:40:14,667 --> 00:40:17,600 it's raining. 722 00:40:17,600 --> 00:40:21,867 As oxygen and iron interact, 723 00:40:21,867 --> 00:40:25,133 rust particles form in the water, 724 00:40:25,133 --> 00:40:27,000 and sink down to the seabed... 725 00:40:29,433 --> 00:40:32,000 trapping the oxygen and iron 726 00:40:32,000 --> 00:40:36,433 to form solid rock at the bottom of the ocean. 727 00:40:37,567 --> 00:40:42,400 Vast swaths of the water turn red. 728 00:40:42,400 --> 00:40:43,700 LYONS: There were many, 729 00:40:43,700 --> 00:40:45,200 many ingredients in the ocean 730 00:40:45,200 --> 00:40:46,767 at that time that would 731 00:40:46,767 --> 00:40:48,400 readily react with oxygen. 732 00:40:50,033 --> 00:40:52,533 HAZEN: So there was no way for atmospheric oxygen 733 00:40:52,533 --> 00:40:54,667 to build up to any significant level. 734 00:40:57,133 --> 00:40:59,533 (seagulls calling) 735 00:40:59,533 --> 00:41:01,300 NARRATOR: A record of the reactions 736 00:41:01,300 --> 00:41:04,200 that happened long ago can be seen 737 00:41:04,200 --> 00:41:08,400 in formations today. 738 00:41:08,400 --> 00:41:09,933 This is a sedimentary rock, 739 00:41:09,933 --> 00:41:12,100 meaning it's made up of many different layers 740 00:41:12,100 --> 00:41:13,367 that were all deposited 741 00:41:13,367 --> 00:41:14,467 on the sea floor 742 00:41:14,467 --> 00:41:15,800 over millions of years. 743 00:41:18,733 --> 00:41:20,600 NARRATOR: And this sample is evidence 744 00:41:20,600 --> 00:41:25,433 of how iron can react to form solid rock. 745 00:41:25,433 --> 00:41:27,433 This particular sedimentary rock 746 00:41:27,433 --> 00:41:29,167 is a banded iron formation, 747 00:41:29,167 --> 00:41:30,900 and we can see red color 748 00:41:30,900 --> 00:41:32,067 in the rock here, 749 00:41:32,067 --> 00:41:33,800 and that red is evidence 750 00:41:33,800 --> 00:41:36,033 of iron oxidation or rust. 751 00:41:37,367 --> 00:41:39,533 NARRATOR: As these reactions continued, 752 00:41:39,533 --> 00:41:41,667 the metals in the ocean water 753 00:41:41,667 --> 00:41:46,400 started to diminish, locked away in the seafloor. 754 00:41:46,400 --> 00:41:47,867 LINGAPPA: Eventually, 755 00:41:47,867 --> 00:41:49,700 the oceans would have 756 00:41:49,700 --> 00:41:51,300 been depleted of the things 757 00:41:51,300 --> 00:41:52,467 that would readily react 758 00:41:52,467 --> 00:41:56,967 with the oxygen that was being released. 759 00:41:56,967 --> 00:42:01,033 NARRATOR: But cyanobacteria continued to produce oxygen. 760 00:42:02,333 --> 00:42:07,433 ♪ 761 00:42:11,867 --> 00:42:14,300 For up to half a billion years, 762 00:42:14,300 --> 00:42:16,000 this oxygen has been trapped 763 00:42:16,000 --> 00:42:18,967 in the oceans. 764 00:42:26,267 --> 00:42:29,233 But now, increasing amounts are free to escape. 765 00:42:29,233 --> 00:42:34,233 (water bubbling) 766 00:42:34,233 --> 00:42:38,667 ♪ 767 00:42:38,667 --> 00:42:41,833 Over just a few million years, 768 00:42:41,833 --> 00:42:45,633 oxygen floods into the atmosphere. 769 00:42:45,633 --> 00:42:47,833 (bubbling intensifies) 770 00:42:47,833 --> 00:42:51,900 ♪ 771 00:43:00,867 --> 00:43:06,133 The very composition of the atmosphere itself is changing. 772 00:43:09,433 --> 00:43:16,200 ♪ 773 00:43:21,500 --> 00:43:26,733 This is known as the Great Oxidation Event. 774 00:43:27,933 --> 00:43:29,900 DOTTIN: The Great Oxidation Event 775 00:43:29,900 --> 00:43:33,067 was one of the most significant periods in Earth's history. 776 00:43:33,067 --> 00:43:37,333 ♪ 777 00:43:37,333 --> 00:43:39,000 It was a period of time 778 00:43:39,000 --> 00:43:40,567 over which oxygen built up 779 00:43:40,567 --> 00:43:43,367 in the atmosphere. 780 00:43:43,367 --> 00:43:44,867 LINGAPPA: Not only did it 781 00:43:44,867 --> 00:43:46,867 completely change the environment, 782 00:43:46,867 --> 00:43:50,433 it also completely changed the possibilities 783 00:43:50,433 --> 00:43:52,467 available for life. 784 00:43:52,467 --> 00:43:53,733 ROTHSCHILD: It is almost 785 00:43:53,733 --> 00:43:57,233 impossible to overstate how important 786 00:43:57,233 --> 00:44:00,567 the production of oxygen on the Earth was 787 00:44:00,567 --> 00:44:04,200 to the history of planet Earth. 788 00:44:04,200 --> 00:44:07,833 All of a sudden, new chemical possibilities arose 789 00:44:07,833 --> 00:44:09,600 all over the surface of Earth, 790 00:44:09,600 --> 00:44:11,933 and amazing changes were to follow. 791 00:44:13,067 --> 00:44:15,933 NARRATOR: Oxygen is used by organisms today 792 00:44:15,933 --> 00:44:17,533 to release energy 793 00:44:17,533 --> 00:44:20,300 from the food they eat, so their bodies can use it. 794 00:44:20,300 --> 00:44:22,900 And since oxygen is so reactive, 795 00:44:22,900 --> 00:44:27,000 this energy release is immense. 796 00:44:27,000 --> 00:44:30,533 ROTHSCHILD: If you use oxygen, 797 00:44:30,533 --> 00:44:33,400 you are 19 times more efficient 798 00:44:33,400 --> 00:44:37,700 than an organism that doesn't use oxygen. 799 00:44:40,767 --> 00:44:45,967 ♪ 800 00:44:45,967 --> 00:44:48,300 NARRATOR: Because of its reactive power, 801 00:44:48,300 --> 00:44:52,700 one of the first consequences of oxygen in the atmosphere 802 00:44:52,700 --> 00:44:57,000 is on the rocks themselves. 803 00:44:57,000 --> 00:44:58,633 Now, depending on your perspective, 804 00:44:58,633 --> 00:45:02,167 oxygen can be a creative or a destructive force. 805 00:45:02,167 --> 00:45:08,400 ♪ 806 00:45:08,400 --> 00:45:10,533 NARRATOR: As it spreads through the atmosphere, 807 00:45:10,533 --> 00:45:13,167 oxygen begins to react vigorously 808 00:45:13,167 --> 00:45:17,100 with the surface of the Earth. 809 00:45:17,100 --> 00:45:20,433 Rocks with metals like iron react 810 00:45:20,433 --> 00:45:24,400 with the oxygen and crumble. 811 00:45:24,400 --> 00:45:29,833 All the elements are in place for vast dust storms to form. 812 00:45:32,167 --> 00:45:37,333 The young world is being ripped up by its own atmosphere. 813 00:45:39,067 --> 00:45:43,533 Earth's surface is changing color 814 00:45:43,533 --> 00:45:47,067 as new minerals are created. 815 00:45:50,600 --> 00:45:52,767 TIKOO: We had the formation of all these minerals 816 00:45:52,767 --> 00:45:54,467 that did not exist prior 817 00:45:54,467 --> 00:45:56,100 to the Great Oxidation Event. 818 00:45:56,100 --> 00:45:57,233 Copper minerals like these, 819 00:45:57,233 --> 00:45:58,933 blue and green minerals, 820 00:45:58,933 --> 00:46:01,733 yellow and orange, uranium minerals, 821 00:46:01,733 --> 00:46:03,833 minerals of molybdenum, minerals of nickel, 822 00:46:03,833 --> 00:46:07,000 minerals of cobalt, color of the rainbow, 823 00:46:07,000 --> 00:46:08,900 all in new minerals 824 00:46:08,900 --> 00:46:12,200 form because of the Great Oxidation Event. 825 00:46:14,067 --> 00:46:18,000 NARRATOR: It isn't just minerals. 826 00:46:18,000 --> 00:46:21,533 Oxygen also makes key nutrients vital for life 827 00:46:21,533 --> 00:46:23,833 far more available 828 00:46:23,833 --> 00:46:29,500 by reacting with a number of elements to form acids. 829 00:46:29,500 --> 00:46:31,167 Things like sulfuric acid 830 00:46:31,167 --> 00:46:32,500 and nitric acid, 831 00:46:32,500 --> 00:46:35,033 and acid has this property 832 00:46:35,033 --> 00:46:37,067 that when it rains out onto the surface of the earth, 833 00:46:37,067 --> 00:46:39,600 it can dissolve rocks, cause weathering 834 00:46:39,600 --> 00:46:42,467 and runoff of nutrients and minerals 835 00:46:42,467 --> 00:46:44,467 into lakes and oceans. 836 00:46:46,567 --> 00:46:48,200 HAZEN: Those nutrients flowed 837 00:46:48,200 --> 00:46:50,600 into the ocean, there were new opportunities for life. 838 00:46:50,600 --> 00:46:52,267 It really was a game changer. 839 00:46:57,533 --> 00:47:00,633 LYONS: And as oxygen began to increase in the atmosphere, 840 00:47:00,633 --> 00:47:03,033 the relatively minor elements 841 00:47:03,033 --> 00:47:06,067 that are essential for all the processes of life 842 00:47:06,067 --> 00:47:07,833 became more abundant. 843 00:47:07,833 --> 00:47:10,267 In many cases, those are metals. 844 00:47:12,433 --> 00:47:15,800 ♪ 845 00:47:19,100 --> 00:47:22,133 LINGAPPA: Life on Earth evolved 846 00:47:22,133 --> 00:47:25,267 because of the conditions that the Earth provided. 847 00:47:25,267 --> 00:47:29,033 But, in turn, life has completely remodeled 848 00:47:29,033 --> 00:47:31,633 the planet, and the world that we know today 849 00:47:31,633 --> 00:47:36,800 is, in so many ways, been created by life. 850 00:47:36,800 --> 00:47:40,167 (flamingos squawking) 851 00:47:43,233 --> 00:47:47,100 ♪ 852 00:47:47,100 --> 00:47:49,000 NARRATOR: This co-evolution 853 00:47:49,000 --> 00:47:54,233 of earth and the atmosphere is apparent everywhere we look. 854 00:47:54,233 --> 00:47:55,767 (waves crashing) 855 00:47:55,767 --> 00:47:57,733 ANDERSON: These particular cliffs were formed 856 00:47:57,733 --> 00:47:59,733 when dinosaurs walked the earth. 857 00:47:59,733 --> 00:48:01,367 But the beautiful red that you can see 858 00:48:01,367 --> 00:48:03,000 in these bands here is formed 859 00:48:03,000 --> 00:48:04,833 from the iron in these cliffs 860 00:48:04,833 --> 00:48:08,500 combined with water and oxygen to create iron oxides. 861 00:48:08,500 --> 00:48:12,300 So we see an example of oxygen changing the very landscape. 862 00:48:14,233 --> 00:48:19,733 NARRATOR: Oxygen transformed our oceans, reshaped our land, 863 00:48:19,733 --> 00:48:22,633 and became a vital ingredient for life today. 864 00:48:24,533 --> 00:48:26,233 But this volatile gas 865 00:48:26,233 --> 00:48:31,033 was to have one more dramatic impact on the world. 866 00:48:31,033 --> 00:48:38,667 ♪ 867 00:48:38,667 --> 00:48:44,133 Across the globe, oxygen levels are rising, 868 00:48:44,133 --> 00:48:47,533 slowly enriching the air, reacting with the methane 869 00:48:47,533 --> 00:48:49,867 to form carbon dioxide and water. 870 00:48:49,867 --> 00:48:54,133 (waves crashing) 871 00:48:54,133 --> 00:48:55,800 Over millions of years, 872 00:48:55,800 --> 00:48:59,100 the orange hazes are fading away. 873 00:49:03,467 --> 00:49:08,667 Sunlight is scattered by the nitrogen and oxygen, 874 00:49:08,667 --> 00:49:11,633 producing Earth's first oxygen-rich 875 00:49:11,633 --> 00:49:14,733 blue skies. 876 00:49:14,733 --> 00:49:21,900 ♪ 877 00:49:21,900 --> 00:49:24,267 In the upper atmosphere, 878 00:49:24,267 --> 00:49:26,500 ultraviolet light from the sun 879 00:49:26,500 --> 00:49:30,167 causes the oxygen to form a new protective molecule... 880 00:49:31,800 --> 00:49:33,800 ozone. 881 00:49:33,800 --> 00:49:34,933 HAZEN: Ozone is made 882 00:49:34,933 --> 00:49:38,033 of three oxygen atoms bonded together, 883 00:49:38,033 --> 00:49:40,767 and they absorb ultraviolet radiation really well. 884 00:49:40,767 --> 00:49:42,400 So, if you put a little bit of ozone 885 00:49:42,400 --> 00:49:44,633 in the atmosphere, it's like sunblock. 886 00:49:48,200 --> 00:49:50,467 NARRATOR: The level of oxygen in the atmosphere 887 00:49:50,467 --> 00:49:55,400 will fluctuate over the next two billion years, 888 00:49:55,400 --> 00:49:59,433 but eventually, reach the 21% we have today. 889 00:50:04,300 --> 00:50:07,533 ♪ 890 00:50:07,533 --> 00:50:11,133 But the story of our atmosphere is not over. 891 00:50:11,133 --> 00:50:13,067 It will continue to evolve, 892 00:50:13,067 --> 00:50:17,267 both naturally, and under the influence of human activity. 893 00:50:19,133 --> 00:50:20,300 ROTHSCHILD: If we don't understand 894 00:50:20,300 --> 00:50:21,867 the history of the atmosphere, 895 00:50:21,867 --> 00:50:24,633 how can we possibly be the stewards 896 00:50:24,633 --> 00:50:26,433 of the atmosphere moving forward? 897 00:50:29,533 --> 00:50:31,533 PARAI: Because our atmosphere is totally unique, 898 00:50:31,533 --> 00:50:33,167 there's nothing like it that we found 899 00:50:33,167 --> 00:50:36,600 on any other planetary body. 900 00:50:36,600 --> 00:50:40,233 WONG: Our atmospheric composition may actually be 901 00:50:40,233 --> 00:50:43,033 the thing that is screaming out to the cosmos, 902 00:50:43,033 --> 00:50:46,100 a signal to the universe that we're here, 903 00:50:46,100 --> 00:50:48,533 that life exists on our world. 904 00:50:48,533 --> 00:50:49,700 DOTTIN: But then, 905 00:50:49,700 --> 00:50:51,267 in many ways, we're going back in time, 906 00:50:51,267 --> 00:50:53,067 where we're putting all of 907 00:50:53,067 --> 00:50:57,433 the chemicals that are toxic to life into the atmosphere. 908 00:50:59,667 --> 00:51:02,167 WONG: Over the past couple hundreds of years, 909 00:51:02,167 --> 00:51:03,900 humanity has made a difference 910 00:51:03,900 --> 00:51:05,933 in the chemical composition of our atmosphere, 911 00:51:05,933 --> 00:51:09,033 most predominantly through the release of 912 00:51:09,033 --> 00:51:13,633 carbon dioxide, and this causes myriad effects on our world. 913 00:51:15,267 --> 00:51:17,833 HAZEN: The atmosphere isn't fragile. 914 00:51:17,833 --> 00:51:19,167 But we are. 915 00:51:19,167 --> 00:51:20,400 We can make changes 916 00:51:20,400 --> 00:51:22,767 to the atmosphere that will make Earth 917 00:51:22,767 --> 00:51:25,333 a very unpleasant place to live. 918 00:51:25,333 --> 00:51:27,433 And so we need to look to ourselves 919 00:51:27,433 --> 00:51:30,933 when we think about changes to the atmosphere. 920 00:51:32,900 --> 00:51:35,033 LINGAPPA: We have immense power 921 00:51:35,033 --> 00:51:36,267 over our planet. 922 00:51:36,267 --> 00:51:40,067 Our atmosphere is precious. 923 00:51:40,067 --> 00:51:43,633 And, if we change it too much, 924 00:51:43,633 --> 00:51:45,767 the whole world will pay the price. 925 00:51:45,767 --> 00:51:47,633 (magma rushing) 926 00:51:47,633 --> 00:51:50,667 GIRGUIS: But by understanding the huge and complex steps 927 00:51:50,667 --> 00:51:54,200 it took to develop our atmosphere, hopefully, 928 00:51:54,200 --> 00:51:55,400 we can develop approaches 929 00:51:55,400 --> 00:51:57,400 to take care of it for generations to come. 930 00:51:57,400 --> 00:51:57,500 ♪