1 00:00:01,201 --> 00:00:04,937 [narrator] The earth is over 4.5 billion years old. 2 00:00:05,873 --> 00:00:09,241 Its history is shaped by disaster... 3 00:00:11,679 --> 00:00:13,045 ...after disaster. 4 00:00:14,081 --> 00:00:16,248 [Paul M. Sutter] Asteroid and comet collisions, 5 00:00:16,283 --> 00:00:18,017 flares from the Sun. 6 00:00:18,019 --> 00:00:19,685 [Jani Radebaugh] Mass extinctions, 7 00:00:19,753 --> 00:00:21,587 supernova explosions, 8 00:00:21,589 --> 00:00:23,589 cosmic ray bombardment. 9 00:00:23,591 --> 00:00:25,424 You name it, we've experienced it. 10 00:00:25,426 --> 00:00:27,459 It's kind of a miracle we're here at all. 11 00:00:29,530 --> 00:00:34,566 [narrator] These violent events could be why Earth has life 12 00:00:34,568 --> 00:00:37,836 [Nina Lanza] We tend to thin of disaster as a bad thing, 13 00:00:37,838 --> 00:00:40,939 but out of chaos can come possibility. 14 00:00:40,941 --> 00:00:41,807 When we destroy something, 15 00:00:41,809 --> 00:00:44,943 we can also create something new. 16 00:00:46,747 --> 00:00:49,314 [narrator] Earth has walked the line between survival.. 17 00:00:49,917 --> 00:00:51,417 ...and destruction. 18 00:00:51,919 --> 00:00:54,386 It's tipping that fine balance of luck 19 00:00:54,388 --> 00:00:57,256 between a good disaster and a bad disaster. 20 00:00:57,357 --> 00:01:02,094 [narrator] Could catastrophe and chaos be the essential ingredient 21 00:01:02,229 --> 00:01:03,362 for life? 22 00:01:20,581 --> 00:01:22,047 2021. 23 00:01:22,083 --> 00:01:25,451 Scientists investigate something mysterious 24 00:01:25,453 --> 00:01:28,420 buried deep inside the earth 25 00:01:28,489 --> 00:01:32,157 It's a long hidden clue to our violent past. 26 00:01:34,061 --> 00:01:35,360 [Michelle Thaller] Deep down 27 00:01:35,362 --> 00:01:37,463 1,800 miles below the surface of the earth, 28 00:01:37,465 --> 00:01:39,998 our core is surrounded by fluid rock, 29 00:01:40,201 --> 00:01:41,366 but inside that, 30 00:01:41,735 --> 00:01:43,402 600 miles high 31 00:01:43,437 --> 00:01:44,503 and thousands of miles across 32 00:01:44,571 --> 00:01:46,472 are two denser regions, 33 00:01:46,474 --> 00:01:50,075 and they kind of cup the core of our planet like two hands. 34 00:01:51,679 --> 00:01:54,680 One of them is, you know, half the size of Australia, for crying out loud. 35 00:01:54,715 --> 00:01:56,815 So, I mean, they're big lumps down there. 36 00:01:56,884 --> 00:01:58,750 There's no reason they should be there. 37 00:01:58,752 --> 00:02:00,119 It's a mystery to us. 38 00:02:02,857 --> 00:02:03,922 [narrator] To solve this mystery, 39 00:02:03,924 --> 00:02:06,458 scientists need to examine the rocks 40 00:02:06,460 --> 00:02:10,028 buried over 1,000 miles beneath the surface. 41 00:02:11,699 --> 00:02:14,800 We don't really know what these two big rocks are made of, 42 00:02:14,868 --> 00:02:15,867 sitting there on the core. 43 00:02:15,869 --> 00:02:17,669 However, we've been able to sample them. 44 00:02:17,671 --> 00:02:18,937 How in the world is that possible? 45 00:02:20,641 --> 00:02:23,342 Well, these blobs are actual feeding mantle plumes 46 00:02:23,377 --> 00:02:25,277 that are rising up through the mantle. 47 00:02:26,814 --> 00:02:29,314 [Dan Durda] So, volcanoes in Iceland and Samoa, for instance, 48 00:02:29,316 --> 00:02:32,718 will dredge up some of these lumps of rock from the mantle. 49 00:02:32,786 --> 00:02:35,921 It's a precious chance for us to sample some of that deep rock 50 00:02:35,989 --> 00:02:38,323 that we'd normally not get a chance to see. 51 00:02:41,262 --> 00:02:42,661 [narrator] These rocks are old. 52 00:02:42,696 --> 00:02:44,229 Very old. 53 00:02:44,632 --> 00:02:47,032 [Radebaugh] It turns out that the samples in the lav 54 00:02:47,100 --> 00:02:49,635 that we think came from these blobs of rock in the mantle 55 00:02:49,637 --> 00:02:52,671 are 4.5 billion years old. 56 00:02:52,706 --> 00:02:55,374 That is as old as the age of the earth. 57 00:02:56,410 --> 00:02:58,443 [Durda] So, they tell us something about, you know, 58 00:02:58,445 --> 00:03:02,381 how the internal structure of our planet was, uh, arranged 59 00:03:02,383 --> 00:03:04,416 in the earliest days of the formation of our planet, 60 00:03:04,418 --> 00:03:08,220 so getting samples from that time is very, very important. 61 00:03:08,222 --> 00:03:12,357 [narrator] The age of the rocks may be a clue to their origin. 62 00:03:12,359 --> 00:03:16,995 They date back to a time of monstrous cosmic mayhem. 63 00:03:21,569 --> 00:03:22,801 [Kevin Walsh] 4.5 billion years ago, 64 00:03:22,803 --> 00:03:25,237 the solar system was still a pretty wild place. 65 00:03:26,807 --> 00:03:29,374 We're approaching the end of the formation of planets. 66 00:03:29,376 --> 00:03:32,177 Earth would still be growing. 67 00:03:33,881 --> 00:03:37,249 [James Bullock] Back then, you wouldn't necessarily recognize the earth. 68 00:03:38,719 --> 00:03:40,919 In fact, you wouldn't recognize the earth at all. 69 00:03:40,921 --> 00:03:42,154 For example, no moon. 70 00:03:42,156 --> 00:03:44,289 The earth did not have a moon when it first formed. 71 00:03:45,726 --> 00:03:50,095 [narrator] The young earth orbits the S with other infant planets. 72 00:03:51,565 --> 00:03:55,367 One of them is an object scientists call Theia... 73 00:03:57,238 --> 00:04:00,939 ...and it's on a collision course with our home. 74 00:04:06,880 --> 00:04:09,848 [Bullock] The Theia collision would ha been a spectacular event. 75 00:04:09,850 --> 00:04:10,949 It would've been one of the coolest things 76 00:04:11,018 --> 00:04:12,384 you could possibly witness 77 00:04:12,386 --> 00:04:13,919 in the origin of the solar system, 78 00:04:13,954 --> 00:04:16,355 certainly the biggest event in the history of the earth. 79 00:04:20,628 --> 00:04:22,861 [Konstantin Batygin] The Theia event is 80 00:04:22,863 --> 00:04:26,098 something that completely reshaped the earth. 81 00:04:26,100 --> 00:04:29,668 The planet that the earth was before the Theia event 82 00:04:29,736 --> 00:04:31,203 is gone forever. 83 00:04:31,672 --> 00:04:34,006 [narrator] The impact melts rock 84 00:04:34,008 --> 00:04:38,277 and throws out over a billio billion tons of debris. 85 00:04:39,546 --> 00:04:41,880 [Thaller] During this incredible collision, 86 00:04:41,882 --> 00:04:43,915 these two planets were literally broken apart 87 00:04:43,917 --> 00:04:46,718 and combined into one big planet. 88 00:04:46,720 --> 00:04:49,388 Huge chunks of Theia stayed together 89 00:04:49,390 --> 00:04:52,391 as the now molten earth began to form anew. 90 00:04:52,893 --> 00:04:55,027 [Radebaugh] Now, we can kind of paint a picture 91 00:04:55,029 --> 00:04:56,728 of where these big lumps of rock might have come from. 92 00:04:56,797 --> 00:04:58,997 They're very old. 93 00:04:58,999 --> 00:05:02,034 They're, in fact, the same age as that large impact event. 94 00:05:03,237 --> 00:05:04,869 They could be pieces of Thei 95 00:05:07,174 --> 00:05:11,310 [narrator] The giant slabs of Theia sink down into our planet... 96 00:05:12,646 --> 00:05:16,381 ...and lie undiscovered for billions of years. 97 00:05:21,355 --> 00:05:26,958 Earth reforms from the ruin of both planets. 98 00:05:26,960 --> 00:05:30,529 Now, you might think that a collision like this is just devastating, 99 00:05:30,531 --> 00:05:31,830 there's no upside at all, 100 00:05:31,898 --> 00:05:33,832 but there's some things that came out of this collision 101 00:05:33,834 --> 00:05:37,235 that may have led to the possibility of life. 102 00:05:38,639 --> 00:05:40,672 [narrator] When these two planets combined, 103 00:05:40,674 --> 00:05:45,143 parts of Theia's iron core merged with Earth's. 104 00:05:46,613 --> 00:05:48,880 So, that means that Earth collected a much bigger core 105 00:05:48,882 --> 00:05:50,615 than it might have possessed on its own. 106 00:05:50,684 --> 00:05:51,883 This is good news for us 107 00:05:51,885 --> 00:05:54,219 because the core is the source of the magnetic field 108 00:05:54,287 --> 00:05:56,321 that protects us. 109 00:05:56,323 --> 00:05:59,424 [narrator] Liquid metal flowing around in the outer core 110 00:05:59,493 --> 00:06:02,027 generates Earth's magnetic field... 111 00:06:02,763 --> 00:06:05,263 ...a protective shield from the Sun. 112 00:06:08,302 --> 00:06:10,669 [Thaller] The Sun can actual output billions of tons 113 00:06:10,671 --> 00:06:14,139 of high-energy protons and electrons in a single burp. 114 00:06:15,642 --> 00:06:18,143 That, eventually, would hav stripped away our atmosphere 115 00:06:18,145 --> 00:06:19,911 If it weren't for that active core 116 00:06:19,913 --> 00:06:20,912 and that magnetic field, 117 00:06:20,947 --> 00:06:22,514 we would look like Mars, 118 00:06:22,516 --> 00:06:25,584 just sort of a bare and barren desert. 119 00:06:25,586 --> 00:06:27,786 [narrator] Thanks to Theia's extra iron, 120 00:06:27,854 --> 00:06:31,123 Earth's molten outer core is large... 121 00:06:31,959 --> 00:06:33,759 ...so it cools slowly, 122 00:06:33,761 --> 00:06:35,694 staying molten, 123 00:06:35,696 --> 00:06:39,965 and keeps on generating a strong magnetic shield. 124 00:06:41,668 --> 00:06:43,034 [Thaller] Because of that collision, 125 00:06:43,036 --> 00:06:45,203 the extra iron, the extra heat, 126 00:06:45,272 --> 00:06:46,872 we've stayed active. 127 00:06:46,940 --> 00:06:47,839 We have a magnetic field. 128 00:06:47,841 --> 00:06:49,574 We are protected, 129 00:06:49,609 --> 00:06:52,277 and, in fact, that's why we're here talking about it. 130 00:06:53,680 --> 00:06:57,783 [narrator] The catastrophic impact helped life in other ways. 131 00:06:57,785 --> 00:07:00,118 [Walsh] The Theia event was absolutely huge, 132 00:07:00,120 --> 00:07:04,623 and not an impact like a 100-mile asteroid making a big crater in the desert, 133 00:07:04,625 --> 00:07:07,859 but a planet hitting a planet, 134 00:07:07,861 --> 00:07:11,830 causing a huge disk of debris spread out from the earth, 135 00:07:11,832 --> 00:07:13,999 out of which formed the Moon 136 00:07:18,772 --> 00:07:19,938 [narrator] After the collision, 137 00:07:20,006 --> 00:07:22,407 the earth tilts on its side 138 00:07:22,443 --> 00:07:24,476 and spins incredibly fast. 139 00:07:26,580 --> 00:07:29,247 A day only lasts a few hours 140 00:07:31,885 --> 00:07:35,320 The earth itself rotates slightly on its side, 141 00:07:35,322 --> 00:07:38,723 and, if left to its own devices, 142 00:07:38,725 --> 00:07:43,962 would, in fact, experience unpredictable, chaotic wobbling. 143 00:07:43,964 --> 00:07:45,897 The fact that the Moon is there 144 00:07:45,933 --> 00:07:47,432 stabilizes the earth, 145 00:07:47,434 --> 00:07:49,935 stabilizes our climate. 146 00:07:51,605 --> 00:07:55,106 [narrator] The Moon's gravitational pull on our oceans 147 00:07:55,108 --> 00:07:59,010 creates tides and slows down the earth's spin... 148 00:07:59,746 --> 00:08:03,815 ...creating a world primed for life. 149 00:08:03,817 --> 00:08:07,486 We actually owe quite a bit to the Moon and Theia, 150 00:08:07,488 --> 00:08:08,720 its progenitor, 151 00:08:08,722 --> 00:08:12,991 for making Earth a hospitable planet for life. 152 00:08:13,861 --> 00:08:15,827 [Sutter] A giant collision 4.5 billion years ago 153 00:08:15,896 --> 00:08:18,663 sounds like a catastrophe, 154 00:08:18,732 --> 00:08:21,099 but it was probably the best thing to happen to the earth. 155 00:08:22,769 --> 00:08:24,569 Theia, I would shake your ha 156 00:08:24,571 --> 00:08:27,038 because we have a lot to owe you. 157 00:08:28,442 --> 00:08:31,443 [narrator] We also owe the science of chance 158 00:08:31,979 --> 00:08:33,512 because we lucked out 159 00:08:33,514 --> 00:08:36,515 with a one in a million impact. 160 00:08:36,517 --> 00:08:38,817 If the impact from Theia had been a little bit harder, 161 00:08:38,819 --> 00:08:41,653 the earth may not have recovered as well as it did, 162 00:08:41,655 --> 00:08:44,523 and we may not be here to talk about it right now. 163 00:08:44,525 --> 00:08:46,758 If it had been a little bit less forceful, 164 00:08:46,760 --> 00:08:50,061 then the impact of it may no have made the changes 165 00:08:50,063 --> 00:08:52,664 that we think were needed for us to be here now. 166 00:08:52,666 --> 00:08:54,666 We got lucky. 167 00:08:54,668 --> 00:08:57,669 Most planets don't get to survive a collision like that 168 00:08:57,737 --> 00:09:00,205 and get a bonus moon out of the deal. 169 00:09:03,544 --> 00:09:06,077 [narrator] Earth's huge collision with Theia 170 00:09:06,079 --> 00:09:09,080 was not our planet's first brush with danger. 171 00:09:10,784 --> 00:09:12,984 An earlier explosive event 172 00:09:13,053 --> 00:09:14,886 could have stopped the solar system 173 00:09:14,888 --> 00:09:17,122 from sparking into life... 174 00:09:17,424 --> 00:09:20,458 ...and the earth from formin 175 00:09:31,838 --> 00:09:36,374 [narrator] Supernovas are one of the universe's most destructive events... 176 00:09:37,844 --> 00:09:40,211 ...releasing, in one second. 177 00:09:41,114 --> 00:09:43,882 ...as much energy as our sun will 178 00:09:43,884 --> 00:09:46,051 in its entire lifetime. 179 00:09:47,387 --> 00:09:49,955 But rather than wipe us out 180 00:09:49,957 --> 00:09:53,458 supernovas may have kick-started the solar syste 181 00:09:53,794 --> 00:09:54,992 4.6 billion years ago, 182 00:09:54,994 --> 00:09:57,362 the solar system's not even really the solar system. 183 00:09:57,364 --> 00:09:59,397 It's the precursor of the solar system. 184 00:10:01,935 --> 00:10:06,404 [Phil Plait] So, what we ha was a cloud of gas and dust collapsing in on itself, 185 00:10:06,473 --> 00:10:08,206 forming the Sun in the cente 186 00:10:08,575 --> 00:10:09,774 a big, flat disk around it 187 00:10:09,776 --> 00:10:13,878 out of which all the planets were forming. 188 00:10:13,880 --> 00:10:18,116 [Thaller] There are all kind of vast clouds of dust and g floating around the Galaxy. 189 00:10:18,118 --> 00:10:20,619 What actually causes them to start collapsing 190 00:10:20,621 --> 00:10:22,053 and forming new stars? 191 00:10:22,055 --> 00:10:25,156 Well, you have to give that cloud a push. 192 00:10:25,158 --> 00:10:29,961 [narrator] Scientists think this push could be a stellar blast... 193 00:10:31,531 --> 00:10:33,465 ...a supernova. 194 00:10:34,935 --> 00:10:39,371 [Sarafina Nance] Supernova are some of the most powerfu events in the universe. 195 00:10:41,608 --> 00:10:46,311 One explosion can light up brighter than a galaxy. 196 00:10:46,880 --> 00:10:50,749 So, not only do they eject elements and material, 197 00:10:50,784 --> 00:10:53,485 they also eject a lot of light and energy. 198 00:10:53,553 --> 00:10:56,888 [narrator] A supernova explosion sends a shock wave 199 00:10:56,890 --> 00:11:01,426 racing out into space at 18,000 miles per second. 200 00:11:04,898 --> 00:11:07,132 The shock wave from a nearby supernova 201 00:11:07,134 --> 00:11:08,633 compresses material together 202 00:11:08,669 --> 00:11:11,102 until it begins to collapse under its own gravity. 203 00:11:14,808 --> 00:11:17,442 [narrator] Was this how our solar system started? 204 00:11:19,246 --> 00:11:21,846 [Bullock] So far, it's been really difficult to find, uh, evidence 205 00:11:21,882 --> 00:11:23,415 that there was some supernova, 206 00:11:23,483 --> 00:11:24,482 or point to something that happened 207 00:11:24,484 --> 00:11:27,719 that really kick-started the solar system. 208 00:11:27,754 --> 00:11:32,257 [narrator] The ancient supernova blast faded away a long time ago. 209 00:11:35,796 --> 00:11:37,696 [Plait] Imagine a crime scen 210 00:11:37,698 --> 00:11:40,932 Now, imagine waiting 4.6 billion years 211 00:11:40,934 --> 00:11:42,400 after the crime is committed, 212 00:11:42,436 --> 00:11:43,968 and looking at it and going, 213 00:11:43,970 --> 00:11:44,569 "There's... There's nothing here. 214 00:11:44,571 --> 00:11:45,703 What are we doing?" 215 00:11:45,705 --> 00:11:48,273 Uh, that's kinda what we're trying to do here. 216 00:11:49,576 --> 00:11:52,277 [narrator] Researchers from the University of Minnesota 217 00:11:52,312 --> 00:11:55,914 tried to solve this ancient crime... 218 00:11:55,982 --> 00:12:00,351 ...by studying asteroids that fell to Earth as meteorites. 219 00:12:00,386 --> 00:12:04,189 Asteroids are critical for understanding the early solar system, 220 00:12:04,191 --> 00:12:07,792 and this is because they have frozen in place all the conditions 221 00:12:07,794 --> 00:12:10,628 that existed in that very early solar nebula, 222 00:12:10,630 --> 00:12:12,997 right at 4.5 billion years ago. 223 00:12:14,167 --> 00:12:16,735 [narrator] The asteroids contain information 224 00:12:16,737 --> 00:12:21,339 about the time leading up to the birth of the Sun and the solar system. 225 00:12:23,610 --> 00:12:25,510 When a massive star ends its life as a supernova, 226 00:12:25,545 --> 00:12:27,679 it undergoes what we call nucleogenesis. 227 00:12:27,681 --> 00:12:30,849 In fact, we call it explosive nucleogenesis. 228 00:12:30,851 --> 00:12:34,786 Literally, the explosion is generating new types of nuclei, 229 00:12:34,788 --> 00:12:37,088 new elements, heavier elements. 230 00:12:38,625 --> 00:12:41,192 Well, it turns out the types of elements it makes 231 00:12:41,194 --> 00:12:43,161 depends on the star that blew up. 232 00:12:46,767 --> 00:12:49,667 [narrator] The Minnesota tea ran computer simulations 233 00:12:49,669 --> 00:12:53,037 to investigate which elements form 234 00:12:53,039 --> 00:12:58,009 when a star up to 12 times the mass of the Sun explodes 235 00:12:59,780 --> 00:13:02,514 Then, they compared the results 236 00:13:02,516 --> 00:13:06,117 with analysis of elements found in asteroids 237 00:13:06,119 --> 00:13:09,154 dating back to the birth of the solar system. 238 00:13:09,990 --> 00:13:11,923 They match. 239 00:13:13,994 --> 00:13:18,530 [Nance] So, the remains of this supernova was actual under our noses all along 240 00:13:18,598 --> 00:13:22,467 in the elements that have been in our solar system for ages. 241 00:13:23,236 --> 00:13:26,004 [narrator] And perhaps in the earth as well. 242 00:13:27,707 --> 00:13:30,608 [Thaller] The earth has lots of rocks that's made of, uh, silicon. 243 00:13:30,677 --> 00:13:33,812 That's only produced in supernova explosions, 244 00:13:33,814 --> 00:13:35,146 and the very core of our earth, 245 00:13:35,148 --> 00:13:36,548 the thing that keeps us alive, 246 00:13:36,550 --> 00:13:38,016 that's iron, nickel. 247 00:13:38,018 --> 00:13:41,319 Again, you only get that in supernova explosions. 248 00:13:42,756 --> 00:13:44,722 [narrator] In February 2021 249 00:13:44,724 --> 00:13:47,725 scientists shed light on the supernova explosions 250 00:13:47,727 --> 00:13:49,961 that helped seed our solar system 251 00:13:49,963 --> 00:13:53,198 and provided the materials to build our planet. 252 00:13:55,769 --> 00:13:58,036 The research examined fragments 253 00:13:58,038 --> 00:14:01,239 blasted off the giant space rock, Vesta... 254 00:14:02,776 --> 00:14:04,776 ...4.5 billion years ago, 255 00:14:04,778 --> 00:14:07,045 and later landed on Earth. 256 00:14:11,117 --> 00:14:13,585 These asteroid fragments contain the fingerprints 257 00:14:13,587 --> 00:14:14,886 of not one, 258 00:14:14,954 --> 00:14:19,691 but at least two supernova explosions. 259 00:14:19,759 --> 00:14:26,097 Our solar system was seeded, was enriched, by at least two separate supernova explosions. 260 00:14:26,366 --> 00:14:27,832 That's incredibly lucky 261 00:14:27,867 --> 00:14:32,136 because that is what delivers the ingredients necessary for life. 262 00:14:33,974 --> 00:14:37,642 [narrator] Scientists believ that these two supernovas 263 00:14:37,644 --> 00:14:40,111 may have enriched different parts 264 00:14:40,113 --> 00:14:41,679 of the infant solar system. 265 00:14:41,681 --> 00:14:43,915 One provided the materials 266 00:14:43,917 --> 00:14:46,317 that helped form the outer gas planets. 267 00:14:48,788 --> 00:14:52,790 The other supernova seeded the inner solar system 268 00:14:52,792 --> 00:14:56,027 with elements that built the rocky planets, 269 00:14:56,363 --> 00:14:57,996 including the earth. 270 00:15:00,600 --> 00:15:03,935 Once again, our fate came down to pure chance. 271 00:15:04,771 --> 00:15:08,840 A series of extraordinarily violent supernova blasts 272 00:15:08,842 --> 00:15:11,709 gave the solar system the kick-start it needed 273 00:15:11,711 --> 00:15:14,412 and the elements to build the planets 274 00:15:14,480 --> 00:15:17,749 without destroying our future home. 275 00:15:17,817 --> 00:15:21,085 It's a fine line between being too close to a supernova, 276 00:15:21,087 --> 00:15:23,888 which will just shred your pre-stellar cloud... 277 00:15:23,957 --> 00:15:27,158 ...and not too far away that you don't get any of the good stuff. 278 00:15:29,262 --> 00:15:33,064 Supernova play both creation stories 279 00:15:33,066 --> 00:15:34,032 and destruction stories. 280 00:15:34,034 --> 00:15:35,400 They play both roles. 281 00:15:37,337 --> 00:15:38,536 [narrator] We lucked out. 282 00:15:38,538 --> 00:15:41,940 This chapter of the story ends well. 283 00:15:41,942 --> 00:15:46,311 The solar system gets the ingredients it needs to build planets. 284 00:15:47,147 --> 00:15:49,747 Earth forms in a good location, 285 00:15:49,782 --> 00:15:51,082 close to its star. 286 00:15:52,852 --> 00:15:54,352 The future looks bright, 287 00:15:54,788 --> 00:15:55,954 but then, 288 00:15:56,022 --> 00:15:58,323 the biggest bombardment in history 289 00:15:58,625 --> 00:16:01,092 smashes into the earth. 290 00:16:12,772 --> 00:16:15,106 [narrator] From the moment our planet formed... 291 00:16:16,810 --> 00:16:18,142 ...we've been under fire. 292 00:16:22,449 --> 00:16:23,814 2021. 293 00:16:23,816 --> 00:16:27,051 A fireball streaks across the night sky in Europe. 294 00:16:28,855 --> 00:16:30,154 2018. 295 00:16:30,156 --> 00:16:35,126 A 1,500-ton meteor explodes over the Bering Sea 296 00:16:35,128 --> 00:16:38,463 with 10 times the energy of an atomic bomb. 297 00:16:41,835 --> 00:16:43,067 2013. 298 00:16:43,136 --> 00:16:45,503 An asteroid explodes over Russia, 299 00:16:45,505 --> 00:16:48,039 injuring over 1,000 people. 300 00:16:50,610 --> 00:16:53,144 The earth is hit by quite a few asteroids every day. 301 00:16:53,146 --> 00:16:53,845 You see them as shooting stars, 302 00:16:53,847 --> 00:16:55,413 meteors in the sky. 303 00:16:56,316 --> 00:17:00,118 [narrator] These events are violent and destructive 304 00:17:00,120 --> 00:17:05,957 but these space invaders also brought something every living planet needs: 305 00:17:05,992 --> 00:17:07,759 volatiles. 306 00:17:07,761 --> 00:17:08,993 [Radebaugh] When we say volatiles, 307 00:17:08,995 --> 00:17:11,195 what we mean are elements that are really light 308 00:17:11,197 --> 00:17:12,697 and easily moved around. 309 00:17:12,699 --> 00:17:13,731 Often, they're gases, 310 00:17:13,800 --> 00:17:16,868 so that's oxygen, and water, and carbon dioxide, 311 00:17:16,870 --> 00:17:18,603 and just all those light elements 312 00:17:18,605 --> 00:17:21,539 that are really important building blocks for life. 313 00:17:21,541 --> 00:17:24,976 [narrator] These elements ar abundant on our planet today 314 00:17:24,978 --> 00:17:28,913 but were not when it first formed. 315 00:17:28,948 --> 00:17:31,849 [Thaller] From observing other solar systems forming all around us in space, 316 00:17:31,885 --> 00:17:35,386 we know that planets as close to their stars as we are to the Sun, 317 00:17:35,455 --> 00:17:37,655 when they form, they're very hot and dry. 318 00:17:37,723 --> 00:17:39,690 There's probably some littl bit of water around there, 319 00:17:39,759 --> 00:17:41,259 but really not very much. 320 00:17:42,662 --> 00:17:43,995 [Hakeem Oluseyi] So, what this means 321 00:17:43,997 --> 00:17:47,498 is any volatiles will basically be boiled away. 322 00:17:47,567 --> 00:17:49,700 If you have a molten surface, 323 00:17:49,702 --> 00:17:53,004 anything like water is gonna get boiled away. 324 00:17:54,774 --> 00:17:57,742 [narrator] Young Earth was a dry planet, 325 00:17:57,777 --> 00:18:01,145 devoid of all the precious volatiles needed for life. 326 00:18:02,315 --> 00:18:07,351 These materials must have been delivered to Earth after its formation. 327 00:18:11,491 --> 00:18:15,960 We think volatiles arrived in the early days of the solar system... 328 00:18:16,830 --> 00:18:19,430 ...when the giant planets, including Jupiter, 329 00:18:19,432 --> 00:18:20,998 moved around... 330 00:18:21,835 --> 00:18:24,368 ...and stirred up the conten of the solar system. 331 00:18:26,406 --> 00:18:27,671 [Plait] As Jupiter moves, 332 00:18:27,673 --> 00:18:29,941 its gravity is pulling on all the objects in there 333 00:18:29,943 --> 00:18:31,609 basically speeding them up, 334 00:18:31,611 --> 00:18:33,678 and there's a little bit of chaos there in the first place, 335 00:18:33,680 --> 00:18:36,080 but now, Jupiter is basically supercharging it. 336 00:18:36,916 --> 00:18:40,818 [narrator] Jupiter's path sends countless asteroids and comets 337 00:18:40,820 --> 00:18:43,321 on a collision course with the earth. 338 00:18:44,891 --> 00:18:47,024 [Radebaugh] It would have been utterly chaotic. 339 00:18:47,093 --> 00:18:49,293 This is a rain of large objects 340 00:18:49,295 --> 00:18:50,895 onto all of the inner planets, 341 00:18:51,030 --> 00:18:56,000 but these objects that came screaming into Earth were gigantic. 342 00:18:57,704 --> 00:18:59,871 [narrator] Four billion years ago, 343 00:18:59,873 --> 00:19:03,007 a storm of giant asteroids and comets 344 00:19:03,042 --> 00:19:04,142 hits the earth. 345 00:19:05,011 --> 00:19:08,045 Some are tens of miles wide 346 00:19:08,448 --> 00:19:09,914 They bring the volatiles 347 00:19:09,982 --> 00:19:11,682 that help fill the earth's oceans 348 00:19:11,684 --> 00:19:13,951 and build its atmosphere... 349 00:19:15,155 --> 00:19:17,922 ...but cosmic deliveries can both give 350 00:19:17,990 --> 00:19:19,357 and take. 351 00:19:20,827 --> 00:19:22,860 The importance of impacts for atmosphere 352 00:19:22,929 --> 00:19:23,961 could go either way. 353 00:19:23,963 --> 00:19:25,830 You could have a... A really big, 354 00:19:25,865 --> 00:19:27,298 really powerful impact... 355 00:19:28,101 --> 00:19:29,433 ...that blows away the atmosphere 356 00:19:29,469 --> 00:19:31,936 of a small, fledgling planet 357 00:19:31,938 --> 00:19:36,040 or you could have a bunch of small impacts of water-rich asteroids 358 00:19:36,042 --> 00:19:38,843 that are simply contributing water, and volatiles, 359 00:19:38,845 --> 00:19:40,545 and new chemicals to the surface 360 00:19:40,547 --> 00:19:43,981 that might help the atmosphe that's already there. 361 00:19:43,983 --> 00:19:45,917 [Oluseyi] When you think about an object coming to Earth, 362 00:19:45,919 --> 00:19:47,985 is it gonna land on Earth, 363 00:19:47,987 --> 00:19:49,754 and if it does land, 364 00:19:49,756 --> 00:19:53,457 is it gonna be a... An erosive event, 365 00:19:53,459 --> 00:19:55,693 where material is lost from the earth, 366 00:19:55,761 --> 00:19:57,695 or is it gonna be an accretion event, 367 00:19:57,763 --> 00:20:00,631 where the earth gains material? 368 00:20:00,633 --> 00:20:02,300 Well, the devil's in the details. 369 00:20:03,836 --> 00:20:06,804 [narrator] Details like the size of the impactor. 370 00:20:06,839 --> 00:20:08,806 One study suggests 371 00:20:08,808 --> 00:20:13,678 that asteroids between 60 fe and 3,300 feet wide 372 00:20:13,680 --> 00:20:17,348 add more to the atmosphere than they take away. 373 00:20:24,891 --> 00:20:28,292 And speed at the point of impact also matters. 374 00:20:29,362 --> 00:20:31,662 Asteroids are orbiting the sun. 375 00:20:31,664 --> 00:20:34,532 And when they fall towards the sun, they are gaining speed, 376 00:20:34,600 --> 00:20:36,567 they're gaining velocity. 377 00:20:36,569 --> 00:20:40,037 Imagine dropping a coin into one of those spiral wells. 378 00:20:40,974 --> 00:20:42,573 As the coin gets closer and closer to the middle, 379 00:20:42,575 --> 00:20:45,042 it spins up faster and faste 380 00:20:47,747 --> 00:20:50,615 [narrator] The closer an asteroid gets to the sun 381 00:20:50,617 --> 00:20:53,451 the stronger the sun's gravitational pull... 382 00:20:54,520 --> 00:20:57,121 ...and the faster the asteroid travels. 383 00:20:59,726 --> 00:21:01,959 [Jessie Christiansen] So proximity to your star 384 00:21:01,961 --> 00:21:04,428 is a vital factor in how intense any impacts will be. 385 00:21:14,173 --> 00:21:15,673 [James Bullock] It's possibl that the Earth 386 00:21:15,708 --> 00:21:18,109 is the right distance from its host star 387 00:21:18,111 --> 00:21:19,277 so that when an impact happens, 388 00:21:19,312 --> 00:21:22,213 the energy isn't insanely high. 389 00:21:22,215 --> 00:21:26,050 It's just the right amount that it's the right speed to make everything work. 390 00:21:27,720 --> 00:21:30,721 [narrator] Supernovas seed the solar system 391 00:21:30,723 --> 00:21:33,824 with the elements to build the planets. 392 00:21:33,860 --> 00:21:39,664 Asteroids and comets delive volatile chemicals to the surface of the Earth 393 00:21:39,666 --> 00:21:44,502 Together they create a habitable environment. 394 00:21:44,504 --> 00:21:49,473 So we need those impacts to happen to have life on Earth. 395 00:21:49,475 --> 00:21:54,745 [narrator] Disasters create a planet primed for life. 396 00:21:54,747 --> 00:21:57,615 But it appears that even mor mayhem and chaos 397 00:21:57,683 --> 00:22:01,952 are needed to trigger life itself. 398 00:22:10,863 --> 00:22:14,065 [narrator] An asteroid tear through the solar system, 399 00:22:14,133 --> 00:22:18,169 hurdling through space at 40,000 miles an hour. 400 00:22:19,906 --> 00:22:21,038 It's destination, 401 00:22:21,040 --> 00:22:22,339 Earth. 402 00:22:23,743 --> 00:22:27,211 Will this space rock inflic unimaginable damage... 403 00:22:27,947 --> 00:22:31,015 ...or will it bring the spark of life? 404 00:22:34,787 --> 00:22:36,554 This idea of a spark of life, 405 00:22:36,556 --> 00:22:37,621 we've all kinda seen it 406 00:22:37,690 --> 00:22:39,990 in the Frankenstein movies, right? "It's alive!" 407 00:22:40,560 --> 00:22:43,594 This comes from legend, from myth, from history 408 00:22:43,629 --> 00:22:46,597 that there's some sort of a spark that differentiates 409 00:22:46,599 --> 00:22:49,700 cold inanimate matter from living stuff. 410 00:22:49,702 --> 00:22:52,370 And in some sense it's kind of true. 411 00:22:56,109 --> 00:22:59,510 [narrator] On Earth, we thin this spark may have arrived 412 00:22:59,512 --> 00:23:01,946 over 4 billion years ago. 413 00:23:04,684 --> 00:23:07,818 The Hadean Eon was the time from the Earth's formation 414 00:23:07,887 --> 00:23:10,187 about 4.6 billion years ago 415 00:23:10,222 --> 00:23:11,756 to about 4 billion years ago. 416 00:23:11,758 --> 00:23:14,425 It's named after literally Hades. 417 00:23:14,460 --> 00:23:18,229 So the conditions on Earth were literally hellish. 418 00:23:20,566 --> 00:23:23,701 [Dan Durda] It was hot and soupy, a lot of water vapor around 419 00:23:23,769 --> 00:23:26,370 high pressure atmosphere, very intense heat. 420 00:23:26,806 --> 00:23:28,506 You wouldn't survive. 421 00:23:28,574 --> 00:23:30,374 The planet would literally kill you back then. 422 00:23:34,447 --> 00:23:37,882 It's shocking. And I mean, really shocking 423 00:23:37,884 --> 00:23:40,885 that the evidence of first life that we have on Earth 424 00:23:40,953 --> 00:23:42,953 dates to the Hadean Eon. 425 00:23:42,988 --> 00:23:45,623 This was a terrible place, 426 00:23:45,625 --> 00:23:48,893 molten and poisonous and awful. 427 00:23:48,895 --> 00:23:52,196 And yet life somehow arose in all of that mess. 428 00:23:54,967 --> 00:23:56,934 [narrator] June 2020, 429 00:23:57,002 --> 00:23:59,770 Japanese scientists simulat the conditions 430 00:23:59,839 --> 00:24:02,039 of this hellish planet... 431 00:24:02,842 --> 00:24:06,944 ...and then try to recreate the spark of life. 432 00:24:06,946 --> 00:24:09,713 So what the scientists were trying to do was mimic those conditions 433 00:24:09,715 --> 00:24:11,081 and see what would happen. 434 00:24:11,150 --> 00:24:13,951 If you smash a meteorite into the ocean back then, 435 00:24:13,953 --> 00:24:15,719 could it produce sort of the same chemicals 436 00:24:15,754 --> 00:24:18,956 that we see life using today? 437 00:24:18,958 --> 00:24:23,928 [narrator] They use a mix of carbon dioxide, nitrogen water, and iron 438 00:24:23,930 --> 00:24:27,031 to replicate the Hadean environment. 439 00:24:29,569 --> 00:24:35,039 Firing a mini meteor at 2,000 miles an hour into this chemical soup 440 00:24:35,041 --> 00:24:39,210 triggers a reaction between the basic organic elements.. 441 00:24:40,480 --> 00:24:43,047 ...creating amino acids. 442 00:24:44,517 --> 00:24:47,952 We call amino acids the building blocks of life. 443 00:24:47,954 --> 00:24:49,920 Really they're the building blocks of proteins. 444 00:24:49,922 --> 00:24:52,423 And life needs proteins to exist. 445 00:24:52,491 --> 00:24:53,891 But that's why they're so important. 446 00:24:53,893 --> 00:24:56,060 Without amino acids, there's no proteins, 447 00:24:56,128 --> 00:24:58,462 without proteins, no life as we know it. 448 00:25:00,800 --> 00:25:02,366 [narrator] The experiment proves 449 00:25:02,368 --> 00:25:06,303 that meteorite impacts can help build the components for life. 450 00:25:09,775 --> 00:25:12,109 But for these building block to come together 451 00:25:12,177 --> 00:25:14,044 and create life, 452 00:25:14,046 --> 00:25:15,412 we need more. 453 00:25:17,183 --> 00:25:18,782 It's like making a cake. 454 00:25:18,784 --> 00:25:21,919 You can put together the oil, and the flour, and the butter, and the sugar, 455 00:25:21,921 --> 00:25:22,953 but if you don't put it in an oven, 456 00:25:22,955 --> 00:25:24,655 you're not gonna end up with a cake. 457 00:25:24,657 --> 00:25:26,190 You're gonna end up with something else. 458 00:25:26,993 --> 00:25:29,827 [narrator] We thought that the violence of asteroid impacts 459 00:25:29,829 --> 00:25:32,363 prevented life from forming 460 00:25:35,268 --> 00:25:40,004 Now, we think they could be an essential ingredient. 461 00:25:40,973 --> 00:25:43,741 [Phil Plait] If the asteroid impact is big enough and fast enoug 462 00:25:43,743 --> 00:25:46,076 it can punch right through the crust. 463 00:25:47,980 --> 00:25:49,947 Then you're getting geothermal heat, 464 00:25:49,982 --> 00:25:52,349 heat the bubbles up from the mantle. 465 00:25:52,418 --> 00:25:56,754 And it is certainly possibl to get an asteroid impact that big. 466 00:25:56,756 --> 00:26:01,892 [narrator] Large meteorite impacts can create hydrothermal vent 467 00:26:01,894 --> 00:26:05,329 which some scientists believ were the cradles of life. 468 00:26:06,365 --> 00:26:09,633 They provide warm, wet environments 469 00:26:09,635 --> 00:26:13,237 and bring up chemicals from deep inside the Earth's crust... 470 00:26:14,974 --> 00:26:18,275 ...the perfect place for life to begin. 471 00:26:20,179 --> 00:26:22,713 As bad as those conditions seem to us, 472 00:26:22,715 --> 00:26:27,918 to the molecules that are beginning to combin and do their thing, 473 00:26:27,920 --> 00:26:30,054 that was a wonderful place to be. 474 00:26:30,122 --> 00:26:31,789 That could actually be that the conditions 475 00:26:31,791 --> 00:26:33,724 that are best for early life 476 00:26:33,726 --> 00:26:36,427 might actually be those just after an impact. 477 00:26:37,563 --> 00:26:40,764 So you have sort of this petri dish environment 478 00:26:40,766 --> 00:26:43,267 in which life could really thrive. 479 00:26:47,273 --> 00:26:48,405 [narrator] These vents might be similar 480 00:26:48,474 --> 00:26:52,042 to those we see in the oceans today. 481 00:26:53,212 --> 00:26:57,047 [Lewis Dartnell] These hydrothermal vents provide little window 482 00:26:57,049 --> 00:27:00,517 into what the conditions on the primordial Earth would've been like. 483 00:27:00,553 --> 00:27:02,586 And the sort of chemistry 484 00:27:02,588 --> 00:27:05,589 that goes on in those hydrothermal fluids 485 00:27:05,625 --> 00:27:10,160 seems to be the right kind of chemistry for creating life. 486 00:27:12,798 --> 00:27:16,000 [narrator] Once again, Earth got lucky. 487 00:27:17,937 --> 00:27:22,006 Impacts that could've destroyed everything... 488 00:27:22,642 --> 00:27:26,944 ...may have helped spark life into existence. 489 00:27:28,381 --> 00:27:31,148 [Hakeem Oluseyi] I once hear this quote from Confucious.. 490 00:27:31,150 --> 00:27:35,319 ...that creation is quiet but destruction is loud. 491 00:27:36,689 --> 00:27:38,722 Well, these impacts 492 00:27:38,724 --> 00:27:43,093 were both destructive, but they also may have been creators. 493 00:27:43,763 --> 00:27:47,064 [narrator] Earth leaves behi the Hadean age. 494 00:27:47,767 --> 00:27:51,335 The planet calms, and life takes hold. 495 00:27:51,337 --> 00:27:55,506 But disaster is our constant companion 496 00:27:55,541 --> 00:28:00,444 as we prepare to face a stor of deadly cosmic bullets. 497 00:28:12,758 --> 00:28:16,093 [narrator] The universe is a dangerous place for lif 498 00:28:16,095 --> 00:28:18,429 There are asteroid impacts.. 499 00:28:22,068 --> 00:28:24,001 ...black holes... 500 00:28:25,738 --> 00:28:27,204 ...and exploding stars. 501 00:28:29,175 --> 00:28:31,508 But public enemy No. 1 502 00:28:31,510 --> 00:28:32,842 cosmic rays... 503 00:28:35,047 --> 00:28:39,650 ...lethal energic particles born in violent events. 504 00:28:39,652 --> 00:28:42,886 Cosmic rays are incredibly small 505 00:28:42,888 --> 00:28:46,056 but travel so fast, near the speed of light, 506 00:28:46,058 --> 00:28:49,293 but they can tear through our DNA and damage i 507 00:28:49,895 --> 00:28:51,595 Your full of DNA. 508 00:28:51,597 --> 00:28:53,764 If that DNA gets broken apart, guess what happens? 509 00:28:53,766 --> 00:28:57,067 That could lead to cancer and death. 510 00:28:57,069 --> 00:29:01,605 At first glance, these cosmic rays are the worst things for life. 511 00:29:01,607 --> 00:29:03,107 They're terrible. 512 00:29:03,743 --> 00:29:05,976 [narrator] Despite their frighting rap sheet, 513 00:29:06,044 --> 00:29:10,214 cosmic rays may have played a crucial roll in the evolution of life. 514 00:29:14,453 --> 00:29:16,019 2020, 515 00:29:16,054 --> 00:29:18,589 scientists at New York and Stanford universities 516 00:29:18,591 --> 00:29:23,093 investigate biological molecules that have a twin... 517 00:29:24,196 --> 00:29:28,365 ...mirror image versions called chiral molecules. 518 00:29:29,468 --> 00:29:31,635 The concept of chirality in chemistry 519 00:29:31,637 --> 00:29:33,570 is when you have two molecules, two chemicals, 520 00:29:33,572 --> 00:29:34,938 that are physically the same 521 00:29:34,940 --> 00:29:37,541 They're made of exactly the same things, 522 00:29:37,576 --> 00:29:38,876 but their structure is different. 523 00:29:38,911 --> 00:29:40,744 And they're not just different, 524 00:29:40,746 --> 00:29:42,613 they're reflections of each other. 525 00:29:42,615 --> 00:29:44,148 It's literally called handedness 526 00:29:44,216 --> 00:29:45,582 because look here's my right hand 527 00:29:45,584 --> 00:29:47,785 with my thumb over here and my fingers over here, 528 00:29:47,787 --> 00:29:50,721 here's my left hand with my thumb over here and my fingers over here. 529 00:29:50,789 --> 00:29:53,490 I can't wear a left glove on my right hand. 530 00:29:53,492 --> 00:29:56,960 There's nothing I can do to make these guys the same. 531 00:29:56,962 --> 00:29:59,830 And it turns out this is true not just for hands, 532 00:29:59,832 --> 00:30:05,169 but also for large number of simple organic compounds, 533 00:30:05,204 --> 00:30:08,438 things like amino acids or sugars, 534 00:30:08,440 --> 00:30:12,342 which are the building blocks of all life on Earth. 535 00:30:13,846 --> 00:30:16,980 [narrator] Billions of years ago, early life may have had 536 00:30:16,982 --> 00:30:21,318 both left- and right-handed DNA and RNA. 537 00:30:22,555 --> 00:30:26,557 But life chose to use mostly right-handed molecule 538 00:30:26,559 --> 00:30:29,359 The reason may have been cosmic rays. 539 00:30:33,833 --> 00:30:37,267 When cosmic rays hit Earth's atmosphere... 540 00:30:38,437 --> 00:30:42,606 ...they degrade into even smaller subatomic particles 541 00:30:42,608 --> 00:30:44,041 called muons. 542 00:30:44,577 --> 00:30:48,779 Most muons spin in one direction. 543 00:30:48,781 --> 00:30:51,515 So we have these little muons, which are very energetic, 544 00:30:51,517 --> 00:30:53,450 and they're spinning a certain way. 545 00:30:53,452 --> 00:30:56,386 And when they hit a molecule they interact with it. 546 00:30:56,455 --> 00:30:59,489 They can disrupt it. They can change it. 547 00:30:59,491 --> 00:31:02,893 [narrator] Some scientists believe these spinning muons 548 00:31:02,961 --> 00:31:07,264 interact more readily with right-handed DNA and RNA... 549 00:31:09,602 --> 00:31:12,536 ...triggering mutations. 550 00:31:12,604 --> 00:31:15,906 [Plait] Some mutations are beneficia but they have to get a chanc 551 00:31:15,908 --> 00:31:19,343 So if you have right-handed molecules and left-handed molecules, 552 00:31:19,345 --> 00:31:21,311 and they're both being hit by muons, 553 00:31:21,313 --> 00:31:26,149 the one that's hit more gets more chances to have a beneficial mutation. 554 00:31:27,086 --> 00:31:30,854 [narrator] Cosmic rays may have given right-handed life 555 00:31:30,856 --> 00:31:32,990 an evolutionary advantage. 556 00:31:34,059 --> 00:31:37,261 Left-handed life could not compete. 557 00:31:38,864 --> 00:31:39,796 It's like throwing dice. 558 00:31:39,798 --> 00:31:41,598 If you're trying to get double sixes, 559 00:31:41,667 --> 00:31:43,867 and the left hand only gets to throw ten times, 560 00:31:43,936 --> 00:31:46,603 and the right hand gets to throw 100 times, 561 00:31:46,605 --> 00:31:47,738 more likely to get double sixes 562 00:31:47,740 --> 00:31:50,307 with the right hand than the left hand. 563 00:31:51,877 --> 00:31:55,746 [narrator] But the dice don't always land in our favor. 564 00:31:55,781 --> 00:32:00,183 359 million years ago, Earth's luck ran out. 565 00:32:00,953 --> 00:32:04,688 And cosmic rays may have lived up to their reputation 566 00:32:04,756 --> 00:32:07,257 as the baddest particle on the block. 567 00:32:09,862 --> 00:32:13,263 [Dartnell] Earth's oceans were teeming with marine lif 568 00:32:15,868 --> 00:32:17,567 And by this period as well, 569 00:32:17,569 --> 00:32:22,639 plants had started to colonize onto the contents and landmasses, 570 00:32:22,641 --> 00:32:26,143 attracting animal life, insects, millipedes. 571 00:32:26,645 --> 00:32:29,446 And it's in this environmen 572 00:32:29,448 --> 00:32:33,417 the Earth experienced one of the greatest mass extensions 573 00:32:33,419 --> 00:32:35,152 in the history of life. 574 00:32:38,757 --> 00:32:44,895 [narrator] Something killed off 97% of all vertebrae species. 575 00:32:44,930 --> 00:32:49,199 We call this wipeout the end Devonian extinction 576 00:32:53,505 --> 00:32:57,240 One possible explanation, a supernova. 577 00:32:58,243 --> 00:33:03,313 When some dying stars explod they fire out cosmic rays. 578 00:33:04,750 --> 00:33:09,486 [Dartnell] This radiation bombards the upper atmospher of the Earth 579 00:33:09,521 --> 00:33:14,992 and drives the chemistry of nitrogen, turning into nitrogen dioxide, 580 00:33:14,994 --> 00:33:17,828 a gas which itself then reacts with the ozone layer 581 00:33:17,896 --> 00:33:20,097 and destroys it. 582 00:33:20,799 --> 00:33:22,833 [narrator] Without the protective ozone layer, 583 00:33:22,835 --> 00:33:27,471 ultra violet radiation from the sun bombards Earth 584 00:33:28,574 --> 00:33:32,409 Radiation rains down for thousands of years... 585 00:33:33,946 --> 00:33:37,080 ...damaging the DNA of plants and animals. 586 00:33:40,319 --> 00:33:42,085 Many species die out. 587 00:33:45,691 --> 00:33:50,460 [Dartnell] The end Devonian mass extinction mostly effected marine life 588 00:33:50,462 --> 00:33:55,565 This is where we see the greatest percentage of deaths. 589 00:33:55,634 --> 00:34:00,303 [narrator] The oceans once populated by fish the size of school buses... 590 00:34:01,573 --> 00:34:05,042 ...now host fish no bigger than a sardine. 591 00:34:06,845 --> 00:34:10,914 These smaller fish reproduce quickly. 592 00:34:10,916 --> 00:34:12,182 In the challenging environment, 593 00:34:12,184 --> 00:34:17,287 they adapt and diversify faster than larger species. 594 00:34:17,322 --> 00:34:20,357 Mass extinction is not only wipe the slate clean 595 00:34:20,359 --> 00:34:24,694 and provide other animals and other life forms an opportunity, 596 00:34:24,763 --> 00:34:28,365 it creates a sort of chaoti and complex environment 597 00:34:28,367 --> 00:34:32,369 that drives natural selectio and evolution. 598 00:34:35,074 --> 00:34:38,575 [narrator] If a supernova was to blame for this extinction event, 599 00:34:38,577 --> 00:34:44,081 scientists believe that the culprit was 65 light years away. 600 00:34:45,751 --> 00:34:50,253 Any closer and Earth's luck would've run out completely 601 00:34:50,989 --> 00:34:52,422 It seems the existence of life 602 00:34:52,424 --> 00:34:54,090 is always balanced on a knife edge. 603 00:34:55,994 --> 00:34:59,196 When an exploding star goes off a little bit too close to us... 604 00:35:01,033 --> 00:35:03,166 ...and we are all destroyed 605 00:35:05,804 --> 00:35:08,271 So there's this wonderful balance 606 00:35:08,306 --> 00:35:10,640 between just violent enough and too violent. 607 00:35:10,709 --> 00:35:15,345 And we have been lucky enough to dance on that edge for 4.5 billion years. 608 00:35:16,615 --> 00:35:20,417 [narrator] This mass extinction reset life on Earth 609 00:35:20,452 --> 00:35:22,853 and paved the way for four-legged creatures, 610 00:35:22,921 --> 00:35:25,255 our distant ancestors. 611 00:35:28,827 --> 00:35:31,728 Cataclysmic events go hand in hand 612 00:35:31,730 --> 00:35:33,363 with human evolution. 613 00:35:33,799 --> 00:35:36,133 Some knocked us back 614 00:35:36,135 --> 00:35:40,971 and others like the event 66 million years ago 615 00:35:40,973 --> 00:35:42,372 gave us a push forward. 616 00:35:49,515 --> 00:35:50,914 [narrator] 66 million years ago 617 00:35:50,916 --> 00:35:54,451 a massive asteroid crashes into the Earth. 618 00:35:57,756 --> 00:36:01,424 It triggers a huge extinction event. 619 00:36:01,426 --> 00:36:05,095 Without it humans may have never evolved. 620 00:36:05,631 --> 00:36:07,297 [Nina Lanza] At this time in Earth's history, 621 00:36:07,365 --> 00:36:10,867 we had these enormous plants and gigantic insects 622 00:36:10,869 --> 00:36:14,404 that actually would be incredibly terrifying if we saw them today. 623 00:36:17,142 --> 00:36:19,609 [Christiansen] Pterosaurs sa through the air. 624 00:36:19,611 --> 00:36:22,145 Huge marine reptiles dominat the oceans. 625 00:36:22,648 --> 00:36:25,048 And the T. rex is the king of the world. 626 00:36:29,688 --> 00:36:33,423 [narrator] Then a glowing object appear in the sky. 627 00:36:38,597 --> 00:36:39,829 [Durda] I'm sitting on the beach 628 00:36:39,831 --> 00:36:43,800 what was then gonna be the Yucatan of Mexico 629 00:36:43,802 --> 00:36:46,436 enjoying a drink with a, you know, a little umbrella, 630 00:36:46,438 --> 00:36:49,906 but up there in the sky all of sudden 631 00:36:49,941 --> 00:36:52,909 approaching me at 40,000 miles an hour 632 00:36:52,945 --> 00:36:59,616 is Mount Everest glowing thousands of times more intensity than the sun... 633 00:36:59,618 --> 00:37:02,986 ...and it's just seconds away from dropping on my head. 634 00:37:03,789 --> 00:37:06,356 [narrator] A 6 mile wide asteroid... 635 00:37:07,459 --> 00:37:10,026 ...slams into the Earth. 636 00:37:15,534 --> 00:37:21,171 The impact throws trillions of tons of rock and dust into the ai 637 00:37:23,075 --> 00:37:26,209 The rocks heat up as they fall back to Earth.. 638 00:37:27,346 --> 00:37:29,412 ...setting the planet on fir 639 00:37:33,485 --> 00:37:37,387 That beach holiday suddenly turns into absolute nightmare. 640 00:37:39,057 --> 00:37:41,625 [narrator] The impact also throws up soot, 641 00:37:41,627 --> 00:37:43,460 chocking the atmosphere. 642 00:37:44,630 --> 00:37:47,797 Now, the skies are blotted out by all these materials, 643 00:37:47,799 --> 00:37:52,068 so the sun is no longer shining brightly on the surface. 644 00:37:52,971 --> 00:37:56,306 [narrator] Plants need sunlight to photosynthesize 645 00:37:57,776 --> 00:37:59,943 Without this vital energy source, 646 00:37:59,945 --> 00:38:02,112 many species die out. 647 00:38:04,783 --> 00:38:06,750 With their food source gone 648 00:38:06,818 --> 00:38:09,819 plant eating dinosaurs starv to death, 649 00:38:09,821 --> 00:38:12,389 followed by their predators 650 00:38:13,325 --> 00:38:16,626 It was a huge disruption to all of life on Earth. 651 00:38:16,628 --> 00:38:20,530 The dinosaurs have been around for 160 million years at this point. 652 00:38:20,532 --> 00:38:21,698 That's astronomical amount of time. 653 00:38:21,700 --> 00:38:24,034 And in one event, [snaps fingers] they're gone. 654 00:38:24,836 --> 00:38:28,772 [narrator] Again the dice ro is in our favor. 655 00:38:28,774 --> 00:38:31,007 Most dinosaurs become extinc 656 00:38:31,009 --> 00:38:34,477 paving the way for the evolution of mammals... 657 00:38:35,747 --> 00:38:39,082 ...leading eventually to humans. 658 00:38:40,085 --> 00:38:44,888 Without the asteroid impact we wouldn't be here. 659 00:38:44,890 --> 00:38:47,991 As a furry primate on this planet, I kinda like the K-Pg impact, right? 660 00:38:48,059 --> 00:38:48,692 I'm here because of it. 661 00:38:48,694 --> 00:38:50,360 We all are. 662 00:38:52,798 --> 00:38:55,198 [narrator] Some plants benefited from the asteroid strike. 663 00:38:56,868 --> 00:38:59,703 To learn out plants changed after the impact, 664 00:38:59,705 --> 00:39:05,075 Smithsonian scientist examined thousands of tropical plant fossils 665 00:39:05,077 --> 00:39:06,542 from the time of the die off 666 00:39:09,581 --> 00:39:13,116 This disaster opened the way for new types of plants to develop. 667 00:39:14,619 --> 00:39:17,887 [Christiansen] It transforme the plant kingdom... 668 00:39:17,889 --> 00:39:21,257 ...producing a richer and more diverse global ecosystem. 669 00:39:21,626 --> 00:39:23,727 [narrator] Before the asteroid strike, 670 00:39:23,729 --> 00:39:29,132 conifers and ferns dominate the tropical forests of South America. 671 00:39:29,968 --> 00:39:33,036 But afterwards, falling ash from the impact 672 00:39:33,038 --> 00:39:34,604 enriched the soil. 673 00:39:34,606 --> 00:39:39,042 And fast growing flowering plants took over. 674 00:39:40,579 --> 00:39:42,979 [Lanza] The impact was very hard to recover fro 675 00:39:43,047 --> 00:39:46,015 but it actually opened the opportunity 676 00:39:46,050 --> 00:39:47,517 for a greater diversity of plant life, 677 00:39:47,519 --> 00:39:50,120 which ultimately has benefited us as humans 678 00:39:50,155 --> 00:39:52,322 because it has allowed us to have more food sources. 679 00:39:54,559 --> 00:39:57,827 [narrator] This new world order eventually gave rise 680 00:39:57,829 --> 00:39:59,629 to the modern Amazon Rainforest, 681 00:39:59,631 --> 00:40:05,001 home to 10% of all species on Earth. 682 00:40:06,772 --> 00:40:10,440 [Christiansen] It really destroyed and rema our entire environment. 683 00:40:11,710 --> 00:40:13,877 The world grew back, of course it did, here we are, 684 00:40:13,879 --> 00:40:15,311 but it changed everything. 685 00:40:16,815 --> 00:40:21,651 [narrator] And another age may be just around the corne 686 00:40:21,653 --> 00:40:23,586 [Dartnell] We should absolutely expect 687 00:40:23,588 --> 00:40:25,922 that at some point in the future, 688 00:40:25,924 --> 00:40:28,591 and I'm not saying you should lose sleep over it, 689 00:40:28,593 --> 00:40:33,997 but at some point there will be another mass extinction. 690 00:40:36,935 --> 00:40:39,302 Maybe that will be the end our days. 691 00:40:40,505 --> 00:40:41,704 It's intriguing question is 692 00:40:41,773 --> 00:40:46,176 what might come after humans on planet Earth? 693 00:40:47,779 --> 00:40:51,581 [narrator] Catastrophe may b the universe's recipe for li 694 00:40:51,616 --> 00:40:53,349 throughout the cosmos... 695 00:40:54,553 --> 00:40:57,887 ...one that every planet must follow. 696 00:40:57,956 --> 00:40:59,756 [Plait] Looking at our own history, 697 00:40:59,758 --> 00:41:01,791 life thrives on catastrophes 698 00:41:01,793 --> 00:41:05,428 We need these disasters for evolution to work. 699 00:41:05,430 --> 00:41:09,532 So, hopefully, and I hate saying this, I know how it sounds, 700 00:41:09,534 --> 00:41:13,203 hopefully, these other plane have had terrible disasters as well. 701 00:41:14,806 --> 00:41:16,139 [Michelle Thaller] Think abo the word disaster. 702 00:41:16,141 --> 00:41:17,841 It means bad star. 703 00:41:17,843 --> 00:41:19,409 It means that something has gone wrong, 704 00:41:19,477 --> 00:41:20,777 something that's dangerous. 705 00:41:20,779 --> 00:41:24,147 We are children of disasters 706 00:41:25,484 --> 00:41:28,985 There's no way you get us without planets colliding... 707 00:41:30,388 --> 00:41:33,990 ...without asteroids and comets streaming through the atmosphere... 708 00:41:37,696 --> 00:41:40,296 ...without even stars exploding and supernovas. 709 00:41:44,803 --> 00:41:46,169 You are a child of that violence. 710 00:41:46,237 --> 00:41:49,973 That's part of the environment that we grew up in in a cosmic way. 711 00:41:49,975 --> 00:41:52,141 And I think that is tremendously beautiful.