1 00:00:03,080 --> 00:00:07,080 Speaker 1: Existential risks aren't new to us. Ever since our species 2 00:00:07,200 --> 00:00:10,840 Speaker 1: was born. There have always been lots of catastrophes ready 3 00:00:10,840 --> 00:00:13,280 Speaker 1: and waiting to wipe the human race off the face 4 00:00:13,280 --> 00:00:16,360 Speaker 1: of the earth. It's just that these risks are of 5 00:00:16,400 --> 00:00:20,520 Speaker 1: our own making. The history of humanity is relatively brief, 6 00:00:21,120 --> 00:00:23,639 Speaker 1: and we've been fortunate to have come along during a 7 00:00:23,720 --> 00:00:28,360 Speaker 1: period of relative calm in Earth's history. Maybe we couldn't 8 00:00:28,360 --> 00:00:31,760 Speaker 1: have come along had things been more tumultuous. Who knows, 9 00:00:32,479 --> 00:00:34,720 Speaker 1: but there's something to bear in mind that pops up 10 00:00:34,760 --> 00:00:38,760 Speaker 1: a lot when you look into existential threats. Whatever lessons 11 00:00:38,840 --> 00:00:42,320 Speaker 1: the past may offer, it doesn't teach us enough about 12 00:00:42,360 --> 00:00:46,080 Speaker 1: the future. Just because things have gone smoothly so far 13 00:00:46,600 --> 00:00:50,680 Speaker 1: doesn't mean they will always go that way. Every so often, 14 00:00:51,120 --> 00:00:55,320 Speaker 1: some massive catastrophe happens on Earth that brings life to 15 00:00:55,360 --> 00:00:59,080 Speaker 1: the brink of extinction. There are a lot of things 16 00:00:59,080 --> 00:01:02,840 Speaker 1: in space and on Earth that can devastate life. We 17 00:01:02,960 --> 00:01:07,679 Speaker 1: call these natural existential risks. It's worth noting that we 18 00:01:07,920 --> 00:01:11,720 Speaker 1: humans pose an existential threat to just about every other 19 00:01:11,760 --> 00:01:15,080 Speaker 1: species that we share the planet with, but there are 20 00:01:15,120 --> 00:01:18,920 Speaker 1: also natural catastrophes that pose a threat to all of us. 21 00:01:18,959 --> 00:01:23,759 Speaker 1: Creatures living on Earth, including us humans. In this episode, 22 00:01:23,880 --> 00:01:26,679 Speaker 1: we'll look at a few of them to get a 23 00:01:26,720 --> 00:01:29,600 Speaker 1: feel for just how badly things can go on Earth. 24 00:01:30,280 --> 00:01:33,760 Speaker 1: Let's travel back to one particular day during the most 25 00:01:33,760 --> 00:01:37,959 Speaker 1: strictan age of the Upper Cretaceous period, about sixty six 26 00:01:37,959 --> 00:01:41,240 Speaker 1: million years ago, give or take three hundred thousand years, 27 00:01:41,520 --> 00:01:44,560 Speaker 1: and on this day, a light streaks across the sky 28 00:01:44,640 --> 00:01:48,920 Speaker 1: above Earth. That light, it turns out, is an asteroid, 29 00:01:49,440 --> 00:01:53,160 Speaker 1: six miles across, about the size of downtown Los Angeles, 30 00:01:54,400 --> 00:01:57,520 Speaker 1: is traveling at about forty four thousand miles per hour, 31 00:01:58,600 --> 00:02:01,480 Speaker 1: times faster than a bullet when it passes through the 32 00:02:01,480 --> 00:02:05,280 Speaker 1: Earth's atmosphere as if it's not even there, and strikes 33 00:02:05,360 --> 00:02:10,160 Speaker 1: the planet. The impact creates a blast with one hundred 34 00:02:10,440 --> 00:02:16,160 Speaker 1: million megatons of energy. For comparison, the Czar BOMBA, the 35 00:02:16,280 --> 00:02:21,520 Speaker 1: largest nuclear bomb that humans have ever detonated, was fifty megatons. 36 00:02:22,639 --> 00:02:30,040 Speaker 1: One got past Jupiter, you could say. The asteroid strikes 37 00:02:30,080 --> 00:02:32,440 Speaker 1: the Earth along what is now called the Yucatan, the 38 00:02:32,480 --> 00:02:35,640 Speaker 1: spur like peninsula that juts out of southern Mexico into 39 00:02:35,639 --> 00:02:39,400 Speaker 1: the Gulf. It drives itself into the Earth, digging out 40 00:02:39,440 --> 00:02:41,920 Speaker 1: a crater a hundred and ten miles in diameter and 41 00:02:42,040 --> 00:02:45,560 Speaker 1: nine miles deep, so deep, in fact, it nearly punctures 42 00:02:45,560 --> 00:02:48,480 Speaker 1: a hole all the way through the crust. The impact 43 00:02:48,560 --> 00:02:51,560 Speaker 1: is felt all over the world as enormous shocks of 44 00:02:51,639 --> 00:02:55,560 Speaker 1: energy that travel along the borders between tectonic plates. This 45 00:02:55,680 --> 00:03:00,919 Speaker 1: sets off earthquakes and volcanoes across Earth unimaginably large tsunamis 46 00:03:00,919 --> 00:03:04,680 Speaker 1: from the Gulf of Mexico Wash as far north as St. Louis. 47 00:03:05,880 --> 00:03:08,600 Speaker 1: The impact kicks a tremendous amount of earth and sea 48 00:03:08,680 --> 00:03:11,880 Speaker 1: into the air. Boulders the size of cars are launched 49 00:03:11,960 --> 00:03:14,720 Speaker 1: hundreds of miles from the impact site, as far away 50 00:03:14,760 --> 00:03:17,920 Speaker 1: as Believes. The pressure and heat from the collision is 51 00:03:17,960 --> 00:03:21,200 Speaker 1: so great that it instantly melts the rocky earth below. 52 00:03:21,800 --> 00:03:24,639 Speaker 1: That melted rock sprays into the air, where it turns 53 00:03:24,680 --> 00:03:27,959 Speaker 1: to glass before it can reach the ground. Continents away. 54 00:03:28,840 --> 00:03:32,400 Speaker 1: Quartz is pressed into crazy angles, and minerals into tiny 55 00:03:32,440 --> 00:03:35,520 Speaker 1: spheres of metal, And when the heavier bits among all 56 00:03:35,560 --> 00:03:38,200 Speaker 1: that kicked up dirt and rock and metal come back down, 57 00:03:38,560 --> 00:03:41,760 Speaker 1: it heats up. It brings a tremendous amount of energy 58 00:03:41,800 --> 00:03:46,000 Speaker 1: with it, flash heating the Earth's surface, embroiling alive anything 59 00:03:46,040 --> 00:03:50,920 Speaker 1: that can't take cover underground or underwater. And as the 60 00:03:50,920 --> 00:03:54,280 Speaker 1: earthquakes and tsunamis raging across the Earth and the fire 61 00:03:54,400 --> 00:03:57,839 Speaker 1: raining from the sky begin to subside, things go from 62 00:03:57,840 --> 00:04:02,960 Speaker 1: bad to worse. The finer particles from all that pulverized 63 00:04:03,000 --> 00:04:07,400 Speaker 1: earth and liquefied rock launched into space stay aloft, forming 64 00:04:07,440 --> 00:04:10,640 Speaker 1: a vast globe spanning shroud that blocks out the Sun 65 00:04:10,720 --> 00:04:14,680 Speaker 1: for months. Photosynthesis grants to a halt back on Earth. 66 00:04:15,200 --> 00:04:18,040 Speaker 1: The world's plants can no longer make their food, and 67 00:04:18,120 --> 00:04:20,440 Speaker 1: since they, in one way or another, feed the rest 68 00:04:20,480 --> 00:04:24,120 Speaker 1: of life on Earth, everything is still alive begins to starve. 69 00:04:25,360 --> 00:04:27,799 Speaker 1: But as bad as the asteroid makes things for life 70 00:04:27,800 --> 00:04:30,320 Speaker 1: on Earth, it is made even worse by a fluke, 71 00:04:30,680 --> 00:04:34,400 Speaker 1: a stroke of sheer bad luck. The Yucatan, the area 72 00:04:34,440 --> 00:04:37,279 Speaker 1: where the asteroid strikes, is one of the most sulfur 73 00:04:37,400 --> 00:04:40,720 Speaker 1: rich areas on Earth, and when that asteroid hit, as 74 00:04:40,800 --> 00:04:44,560 Speaker 1: much as five hundred billion metric tons of sulfur instantly 75 00:04:44,680 --> 00:04:47,720 Speaker 1: rose from deep inside the Earth up into the atmosphere, 76 00:04:48,080 --> 00:04:50,479 Speaker 1: like dust rising from a table when a heavy book 77 00:04:50,600 --> 00:04:54,200 Speaker 1: is dropped on it. In the sky, that sulfur mixes 78 00:04:54,240 --> 00:04:57,600 Speaker 1: with water vapor and is bombarded by ultra violet radiation 79 00:04:57,640 --> 00:05:01,360 Speaker 1: from the sun, so it becomes sulfur aerosol, the type 80 00:05:01,400 --> 00:05:04,160 Speaker 1: of atmospheric pollution that just happens to be the most 81 00:05:04,160 --> 00:05:07,799 Speaker 1: efficient at absorbing sunlight and blocking it from reaching the Earth. 82 00:05:08,600 --> 00:05:11,200 Speaker 1: The sudden presence of aerosols in the sky makes the 83 00:05:11,279 --> 00:05:16,560 Speaker 1: darkness complete. Sulfur aerosols also form acid rain and freshwater 84 00:05:16,680 --> 00:05:19,120 Speaker 1: lakes and the surface of the oceans are poisoned by it. 85 00:05:19,880 --> 00:05:27,400 Speaker 1: Life on Earth comes disturbingly close to total extinction. Millions 86 00:05:27,400 --> 00:05:30,599 Speaker 1: of years later, humans will call this cataclysmic event the 87 00:05:30,600 --> 00:05:35,719 Speaker 1: Cretaceous Tertiary extinction. It had such a profoundly colossal effect 88 00:05:35,720 --> 00:05:38,240 Speaker 1: on the planet that it serves as the sudden and 89 00:05:38,320 --> 00:05:42,919 Speaker 1: abrupt dividing line between one geological age, the Cretaceous, and 90 00:05:42,960 --> 00:05:46,359 Speaker 1: the one that followed it, the Tertiary or Paleogene, as 91 00:05:46,400 --> 00:05:50,760 Speaker 1: it's called these days. Around of the species alive on 92 00:05:50,800 --> 00:05:53,800 Speaker 1: Earth at the time died during the event and the 93 00:05:53,839 --> 00:05:57,719 Speaker 1: hard times that followed the asteroid's arrival. Three out of 94 00:05:57,760 --> 00:06:02,480 Speaker 1: four species death swept across Earth and waves that lasted 95 00:06:02,520 --> 00:06:06,479 Speaker 1: for tens of thousands of years. Those species that did 96 00:06:06,520 --> 00:06:09,240 Speaker 1: manage to survive had an extremely hard time of it. 97 00:06:09,600 --> 00:06:12,360 Speaker 1: They hung on by a thread. In many cases, they 98 00:06:12,360 --> 00:06:15,120 Speaker 1: were whittled down to just a few individuals that were 99 00:06:15,160 --> 00:06:18,720 Speaker 1: somehow able to carry on their species. Animals that were 100 00:06:18,760 --> 00:06:21,479 Speaker 1: able to burrow to feed off the carcasses of the 101 00:06:21,600 --> 00:06:24,800 Speaker 1: unlucky ones, and whatever plants still reached upward towards a 102 00:06:24,839 --> 00:06:27,919 Speaker 1: sun that no longer shown. Those are the ancestors of 103 00:06:28,000 --> 00:06:31,440 Speaker 1: everything alive on Earth today. We are descended from the 104 00:06:31,520 --> 00:06:36,000 Speaker 1: toughest band of animals that ever lived. But for most 105 00:06:36,040 --> 00:06:39,279 Speaker 1: species of dinosaurs, the asteroid was the end of the line, 106 00:06:39,720 --> 00:06:48,960 Speaker 1: the Kuda grass. They succumbed to their existential threat. We 107 00:06:49,000 --> 00:06:51,839 Speaker 1: know all of this thanks to a father's son science 108 00:06:51,880 --> 00:06:56,200 Speaker 1: team known as Luis and Walter Alvarez. As a geologist 109 00:06:56,240 --> 00:06:59,599 Speaker 1: working in Italy in the seventies, Walter Alvarez found a 110 00:06:59,680 --> 00:07:02,800 Speaker 1: thin layer of clay dating back to around sixty five 111 00:07:02,839 --> 00:07:07,240 Speaker 1: million years before. It was peculiar because immediately below the 112 00:07:07,279 --> 00:07:10,040 Speaker 1: strip of clay there was a wide variety of fossils 113 00:07:10,080 --> 00:07:13,880 Speaker 1: of different types of forums, tiny single celled organisms that 114 00:07:13,920 --> 00:07:17,320 Speaker 1: have shells, but right above the clay there was only 115 00:07:17,320 --> 00:07:21,800 Speaker 1: one type. Forums are an excellent indicator species They eat 116 00:07:21,840 --> 00:07:24,640 Speaker 1: plants and animals that degrade on the seafloor, and they 117 00:07:24,680 --> 00:07:28,080 Speaker 1: are very sensitive to changes in the environment. If something 118 00:07:28,120 --> 00:07:31,679 Speaker 1: happens to forums, it means that something happened to everything else, 119 00:07:32,800 --> 00:07:35,320 Speaker 1: and something definitely did seem to have happened to the 120 00:07:35,320 --> 00:07:38,280 Speaker 1: forums around the time that clay strip was deposited that 121 00:07:38,480 --> 00:07:43,600 Speaker 1: drastically reduced their diversity. There was something similar among plants too. 122 00:07:44,160 --> 00:07:46,560 Speaker 1: Just below the clay strip were fossils of a wide 123 00:07:46,600 --> 00:07:50,280 Speaker 1: variety of plants, where just above there were only fern spores. 124 00:07:51,600 --> 00:07:53,840 Speaker 1: Walter would have been surprised to know that the strip 125 00:07:53,880 --> 00:07:55,880 Speaker 1: of clay he was scraping at with his trowel in 126 00:07:55,920 --> 00:08:01,640 Speaker 1: the center of Italy was actually from Mexico. Walter had 127 00:08:01,640 --> 00:08:05,280 Speaker 1: a very famous scientist, Dad Louise, a physicist who developed 128 00:08:05,280 --> 00:08:08,600 Speaker 1: the first atomic bombs for the US, among many other things. 129 00:08:09,400 --> 00:08:12,280 Speaker 1: By the late seventies. When Walter approached his father with 130 00:08:12,360 --> 00:08:15,520 Speaker 1: the curious find of the clay strip, Louise worked at 131 00:08:15,520 --> 00:08:18,040 Speaker 1: one of the national labs where he had some colleagues 132 00:08:18,040 --> 00:08:21,000 Speaker 1: who ran a mess spectrometer. He asked them to take 133 00:08:21,040 --> 00:08:23,800 Speaker 1: a look at the samples of the clay layer. What 134 00:08:23,880 --> 00:08:27,400 Speaker 1: they found was surprising the clay layer contained about six 135 00:08:27,480 --> 00:08:30,400 Speaker 1: hundred times more iridium than the layer above or below 136 00:08:30,440 --> 00:08:33,920 Speaker 1: the clay. This is very weird because i ridium, which 137 00:08:33,960 --> 00:08:36,600 Speaker 1: is a metal in the platinum family, isn't found much 138 00:08:36,600 --> 00:08:39,800 Speaker 1: in Earth's crust. It certainly isn't found at six hundred 139 00:08:39,840 --> 00:08:44,040 Speaker 1: times the background amount. It is, however, found in abundance 140 00:08:44,040 --> 00:08:48,920 Speaker 1: on things like asteroids. As Walter started looking around the world, 141 00:08:49,000 --> 00:08:52,440 Speaker 1: he found that same clay layer at other sites, and 142 00:08:52,480 --> 00:08:55,000 Speaker 1: it had all the same characteristics as the first site 143 00:08:55,040 --> 00:08:59,240 Speaker 1: in Italy. Iridium in aces in abrupt shift in diversity. 144 00:09:00,160 --> 00:09:03,720 Speaker 1: By that time, paleontologists had already established that the dinosaurs 145 00:09:03,720 --> 00:09:06,840 Speaker 1: had died out around sixty five or so million years earlier. 146 00:09:07,360 --> 00:09:12,280 Speaker 1: The clay layers geological age matched that extinction precisely, But 147 00:09:12,360 --> 00:09:14,960 Speaker 1: at the time, the prevailing theory was that it had 148 00:09:15,000 --> 00:09:18,320 Speaker 1: been a million year period of volcanic activity that had 149 00:09:18,360 --> 00:09:21,760 Speaker 1: been responsible for killing off the dinosaurs, all that gas 150 00:09:21,880 --> 00:09:25,200 Speaker 1: erupting and poisoning the air and rain. But what the 151 00:09:25,200 --> 00:09:29,560 Speaker 1: Alvarez Boys were seeing suggested an asteroid, a colossal one, 152 00:09:29,920 --> 00:09:32,440 Speaker 1: one so colossal it had brought the Earth to the 153 00:09:32,480 --> 00:09:37,680 Speaker 1: brink of near total extinction, and in their theory got 154 00:09:37,679 --> 00:09:39,800 Speaker 1: a shot in the arm with the discovery of the 155 00:09:39,880 --> 00:09:42,960 Speaker 1: chick s Aloub Crater on the Yukatamp Peninsula, the site 156 00:09:43,000 --> 00:09:47,480 Speaker 1: of the destruction sixty six million years before. Eventually, the 157 00:09:47,559 --> 00:09:50,920 Speaker 1: debate was laid to rest. In two thousand ten forty 158 00:09:50,920 --> 00:09:55,720 Speaker 1: one scientists and fields like paleontology, astronomy, geology, and others 159 00:09:56,080 --> 00:09:59,280 Speaker 1: released a review of the literature on the KT extinction 160 00:09:59,400 --> 00:10:02,559 Speaker 1: in the astro evidence and concluded that it was in 161 00:10:02,600 --> 00:10:06,200 Speaker 1: fact an asteroid that killed off the dinosaurs. It's as 162 00:10:06,240 --> 00:10:12,160 Speaker 1: close as science comes to being settled. There's something that 163 00:10:12,240 --> 00:10:16,080 Speaker 1: gets overshadowed by the story of the dinosaurs extinction. That 164 00:10:16,240 --> 00:10:20,560 Speaker 1: life on Earth rebounded. Those smaller animals that could burrow 165 00:10:20,600 --> 00:10:24,120 Speaker 1: and dive held fast and among all the darkness and death, 166 00:10:24,160 --> 00:10:28,480 Speaker 1: they continued on. They reproduced and raised their young, and 167 00:10:28,559 --> 00:10:31,880 Speaker 1: as the Earth slowly shook off that extraordinarily bad day, 168 00:10:32,280 --> 00:10:35,800 Speaker 1: it became again a fertile place, a place friendly to life, 169 00:10:36,679 --> 00:10:39,680 Speaker 1: and that bottle that created by the asteroid open wide, 170 00:10:39,800 --> 00:10:42,840 Speaker 1: and life spread again and grew diverse. And from that 171 00:10:42,920 --> 00:10:46,520 Speaker 1: calamity we humans arose amid the vacuum left by the 172 00:10:46,559 --> 00:10:51,720 Speaker 1: sudden loss of life. The dinosaurs existential catastrophe proved to 173 00:10:51,760 --> 00:10:55,960 Speaker 1: be our existential triumph, which is to say that life 174 00:10:56,000 --> 00:10:59,400 Speaker 1: is tough and it is very, very difficult to extinguish 175 00:10:59,400 --> 00:11:03,040 Speaker 1: it entirely in the coming centuries. That will be a 176 00:11:03,120 --> 00:11:21,559 Speaker 1: mark in its favor. M hm hm. We humans are 177 00:11:21,559 --> 00:11:24,360 Speaker 1: an earth bound species, and so whatever happens to Earth 178 00:11:24,440 --> 00:11:28,280 Speaker 1: happens to us. Like the dinosaurs, we live under the 179 00:11:28,360 --> 00:11:32,000 Speaker 1: threat of death from huge rocks traveling at unimaginable speeds 180 00:11:32,080 --> 00:11:36,080 Speaker 1: hurtling toward us. But unlike the dinosaurs, we are in 181 00:11:36,080 --> 00:11:39,760 Speaker 1: a position to do something about it. In the coming years. 182 00:11:39,840 --> 00:11:42,760 Speaker 1: Is our technology to travel through space develops and we 183 00:11:42,880 --> 00:11:45,720 Speaker 1: become capable of spreading out around our solar system and 184 00:11:45,720 --> 00:11:48,800 Speaker 1: eventually our galaxy, we will have made the biggest shift 185 00:11:48,840 --> 00:11:51,480 Speaker 1: in our species since at least when we settled down 186 00:11:51,480 --> 00:11:55,520 Speaker 1: and began raising crops. That see change in human ecology. 187 00:11:55,880 --> 00:11:59,559 Speaker 1: The advent of agriculture led to sweeping changes for humans. 188 00:12:00,160 --> 00:12:02,680 Speaker 1: It was, as Nick Bostrom would put it, a pan 189 00:12:02,760 --> 00:12:07,439 Speaker 1: generational change in how humans lived. By coaxing food from 190 00:12:07,440 --> 00:12:10,480 Speaker 1: the ground on a predictable schedule, and by taming animals 191 00:12:10,480 --> 00:12:13,400 Speaker 1: and creating a reliable supply of meat and milk. We 192 00:12:13,600 --> 00:12:17,560 Speaker 1: changed a lot about ourselves, our bones, the shapes of 193 00:12:17,600 --> 00:12:20,440 Speaker 1: our skulls, the workings of our guts, the color of 194 00:12:20,440 --> 00:12:24,920 Speaker 1: our skin. And it changed our culture too. As anthropologist 195 00:12:25,000 --> 00:12:28,000 Speaker 1: Jared Diamond points out in his nine seven essay The 196 00:12:28,040 --> 00:12:30,720 Speaker 1: Worst Mistake in the History of the Human Race, about 197 00:12:30,760 --> 00:12:34,040 Speaker 1: the advent of agriculture, we started to have a surplus 198 00:12:34,040 --> 00:12:37,680 Speaker 1: of food, something that our hunter gatherer ancestors never would 199 00:12:37,679 --> 00:12:42,040 Speaker 1: have experienced. This meant that some people had more than others, 200 00:12:42,080 --> 00:12:45,800 Speaker 1: which creates an imbalance and power, and hence agriculture also 201 00:12:45,880 --> 00:12:49,040 Speaker 1: led to things like kings and armies and social classes. 202 00:12:51,200 --> 00:12:54,960 Speaker 1: When we settled down our cities developed. Agriculture can support 203 00:12:55,000 --> 00:12:57,760 Speaker 1: more people than hunting and gathering, and the more people 204 00:12:57,800 --> 00:13:01,160 Speaker 1: there are, the more brilliant ideas there are too, so 205 00:13:01,200 --> 00:13:04,160 Speaker 1: our civilization began to advance by leaps and bounds in 206 00:13:04,160 --> 00:13:07,679 Speaker 1: the last nine or ten thousand years. Ideas spread more 207 00:13:07,760 --> 00:13:10,600 Speaker 1: quickly among those people who lived together in those new cities, 208 00:13:11,000 --> 00:13:13,560 Speaker 1: so innovations were able to develop over the span of 209 00:13:13,600 --> 00:13:17,680 Speaker 1: a handful of years rather than millennia. Almost everything we 210 00:13:17,760 --> 00:13:19,840 Speaker 1: have in the world today can be traced back to 211 00:13:19,840 --> 00:13:24,080 Speaker 1: our collective decision to settle down and raise crops. It was, 212 00:13:24,240 --> 00:13:27,080 Speaker 1: to say the least, a sweeping change for us humans. 213 00:13:28,400 --> 00:13:31,440 Speaker 1: With our next great leap spreading out into space, we 214 00:13:31,480 --> 00:13:34,240 Speaker 1: are effectively doing the opposite of when we settled down 215 00:13:34,240 --> 00:13:39,240 Speaker 1: into cities. Rather than contracting, we will be expanding from 216 00:13:39,280 --> 00:13:43,640 Speaker 1: that huge coming together, we will spread out. Over time, 217 00:13:43,720 --> 00:13:47,160 Speaker 1: humans will begin to colonize other planets, and generations of 218 00:13:47,200 --> 00:13:50,199 Speaker 1: little human babies will be borne on planets other than Earth. 219 00:13:50,840 --> 00:13:53,720 Speaker 1: They will be shaped by forces and experiences that no 220 00:13:53,880 --> 00:13:56,760 Speaker 1: earth bound human will have ever encountered, and they will 221 00:13:56,800 --> 00:13:59,439 Speaker 1: learn to adapt to their home planet just like we did. 222 00:14:00,280 --> 00:14:03,880 Speaker 1: We are quite capable of becoming all the things that 223 00:14:03,920 --> 00:14:07,440 Speaker 1: it's possible to become. Life that starts from us and 224 00:14:07,520 --> 00:14:10,079 Speaker 1: radiates out can not only spread to different places, it 225 00:14:10,160 --> 00:14:14,199 Speaker 1: can create different styles and techniques and cultures and approaches. 226 00:14:15,080 --> 00:14:17,240 Speaker 1: All of the life that you see on Earth started 227 00:14:17,240 --> 00:14:19,800 Speaker 1: out from a much smaller amount of variation, but with 228 00:14:19,880 --> 00:14:23,120 Speaker 1: time it could explore lots of different niches and ways 229 00:14:23,120 --> 00:14:26,760 Speaker 1: of living. And that's probably what would happen to us too. 230 00:14:26,800 --> 00:14:29,400 Speaker 1: If we're the only life around it, we can survive, 231 00:14:30,040 --> 00:14:33,880 Speaker 1: We will radiate, We will become diverse and different and 232 00:14:33,960 --> 00:14:38,320 Speaker 1: fill thousand million billion different niches of different ways of being. 233 00:14:38,920 --> 00:14:41,760 Speaker 1: Over time, perhaps their physical connection to humans on Earth 234 00:14:41,800 --> 00:14:45,520 Speaker 1: will become distant enough that new species of humans will form, 235 00:14:45,560 --> 00:14:47,360 Speaker 1: and the universe will be home to more than one 236 00:14:47,400 --> 00:14:51,160 Speaker 1: species of human again, just as it was fifty years ago. 237 00:14:52,080 --> 00:14:55,680 Speaker 1: We will become the aliens we seek, and later on 238 00:14:56,480 --> 00:14:58,600 Speaker 1: they might be surprised to learn that they came from 239 00:14:58,640 --> 00:15:02,240 Speaker 1: something that was simple and not as very It's odd 240 00:15:02,240 --> 00:15:05,680 Speaker 1: to think of, but humans are in an evolutionary bottleneck 241 00:15:05,760 --> 00:15:09,360 Speaker 1: of our own. Right now. There's only one species of us, 242 00:15:09,840 --> 00:15:12,480 Speaker 1: and with the exception of maybe half a dozen astronauts 243 00:15:12,520 --> 00:15:15,760 Speaker 1: on the International Space Station at any given time, we 244 00:15:15,840 --> 00:15:20,600 Speaker 1: are all stranded on this island Earth. Those astronauts aboard 245 00:15:20,600 --> 00:15:23,400 Speaker 1: the I s S showed just the faintest beginnings of 246 00:15:23,440 --> 00:15:27,440 Speaker 1: our future. If we become a space faring species, all 247 00:15:27,480 --> 00:15:30,400 Speaker 1: of humanities eggs will no longer be in just the 248 00:15:30,480 --> 00:15:34,360 Speaker 1: one basket of Earth. Should some catastrophe befall those of 249 00:15:34,440 --> 00:15:37,360 Speaker 1: us here on Earth, there will be other humans living 250 00:15:37,400 --> 00:15:40,920 Speaker 1: elsewhere to carry on. We will begin to trickle from 251 00:15:40,920 --> 00:15:44,400 Speaker 1: our bottle neck and spread throughout the universe, and when 252 00:15:44,400 --> 00:15:47,480 Speaker 1: we do, we will have made it through the Great Filter. 253 00:15:48,840 --> 00:15:51,680 Speaker 1: Colonizing beyond Earth is something we should begin working on 254 00:15:51,960 --> 00:15:55,160 Speaker 1: as soon as we can, because Earth is vulnerable to 255 00:15:55,280 --> 00:15:59,280 Speaker 1: a wide variety of catastrophes that are pretty hostile to life, 256 00:16:00,080 --> 00:16:04,000 Speaker 1: things like exploding stars, the death of our Sun, even 257 00:16:04,080 --> 00:16:08,400 Speaker 1: Earth's zone systems going haywire. Take our son for starters. 258 00:16:09,080 --> 00:16:12,800 Speaker 1: Remember that Goldilocks zone, that habitable area around a star 259 00:16:12,880 --> 00:16:15,840 Speaker 1: where a planet can sustain life. Earth is in the 260 00:16:15,880 --> 00:16:20,320 Speaker 1: Sun's Goldilocks zone, but it's not a permanent position as 261 00:16:20,320 --> 00:16:23,120 Speaker 1: a star. The Sun is currently in its main sequence. 262 00:16:23,760 --> 00:16:26,120 Speaker 1: It has plenty of hydrogen atoms in its core that 263 00:16:26,160 --> 00:16:29,960 Speaker 1: it fuses into helium, and these constant nuclear reactions release 264 00:16:30,040 --> 00:16:33,560 Speaker 1: tremendous amounts of energy, which we gratefully accept as light 265 00:16:33,640 --> 00:16:37,120 Speaker 1: and heat here on Earth. But the Sun is slowly 266 00:16:37,200 --> 00:16:40,640 Speaker 1: using up its available fuel, and as it does, its 267 00:16:40,720 --> 00:16:44,920 Speaker 1: core shrinks in size. That smaller core means that it's 268 00:16:44,960 --> 00:16:47,680 Speaker 1: closer to the center of the Sun, which means that 269 00:16:47,720 --> 00:16:51,640 Speaker 1: gravity exerts more force on it, making it denser. All 270 00:16:51,680 --> 00:16:54,480 Speaker 1: of this is what one would expect, but we're talking 271 00:16:54,480 --> 00:16:57,680 Speaker 1: about cosmic stuff here, and as with all cosmic stuff, 272 00:16:57,960 --> 00:17:02,360 Speaker 1: something weird always happens to because the core grows denser 273 00:17:02,400 --> 00:17:05,199 Speaker 1: as it grows smaller. That means more fuel is closer 274 00:17:05,240 --> 00:17:07,640 Speaker 1: at hand for the Sun to burn, so its main 275 00:17:07,680 --> 00:17:11,280 Speaker 1: sequence begins to speed up. It uses fuel more quickly, 276 00:17:11,640 --> 00:17:14,879 Speaker 1: actually shortening its own lifespan, at least compared to what 277 00:17:14,920 --> 00:17:17,040 Speaker 1: it would be if it managed to maintain a slow, 278 00:17:17,080 --> 00:17:20,879 Speaker 1: steady burn during its entire life. As the Sun burns 279 00:17:20,920 --> 00:17:23,840 Speaker 1: through its fuel supply more quickly, it's actually going to 280 00:17:23,880 --> 00:17:28,240 Speaker 1: grow larger, much much larger, and about one point one 281 00:17:28,280 --> 00:17:30,399 Speaker 1: billion years, the Earth will no longer be in the 282 00:17:30,400 --> 00:17:34,240 Speaker 1: Sun's goldilocks song. It will be a lot closer, and 283 00:17:34,320 --> 00:17:38,240 Speaker 1: it will keep getting closer from there. This is estrophysicist 284 00:17:38,280 --> 00:17:41,600 Speaker 1: Ian O'Neill. When it goes through this end stage, when 285 00:17:41,640 --> 00:17:43,639 Speaker 1: it starts to turn, is what's called a red giant, 286 00:17:43,840 --> 00:17:46,280 Speaker 1: and it's pretty much a red giant is pretty descriptive. 287 00:17:46,280 --> 00:17:49,200 Speaker 1: A boy, what's going to be. It will expand, possibly 288 00:17:49,280 --> 00:17:52,080 Speaker 1: out to the orbit of Earth. So this the Sun 289 00:17:52,119 --> 00:17:55,879 Speaker 1: will basically fill up our entire, our entire sky. You 290 00:17:55,880 --> 00:17:57,639 Speaker 1: look out the window, it will just be a big 291 00:17:58,720 --> 00:18:02,439 Speaker 1: seething mess of of star. So you can imagine that 292 00:18:02,480 --> 00:18:04,520 Speaker 1: with the Sun right on top of Earth, there won't 293 00:18:04,520 --> 00:18:07,879 Speaker 1: be much room for life, but billions of years before 294 00:18:07,920 --> 00:18:10,280 Speaker 1: that point, the biggest issue will have to deal with 295 00:18:10,440 --> 00:18:14,040 Speaker 1: is the increase in solar radiation. Sure, things will get 296 00:18:14,119 --> 00:18:17,080 Speaker 1: much much hotter on Earth than they are today, but 297 00:18:17,160 --> 00:18:20,040 Speaker 1: as with the fallout from the kt asteroid, there are 298 00:18:20,040 --> 00:18:25,440 Speaker 1: places that some life could go underground, deep underwater. Sorry cows, 299 00:18:25,720 --> 00:18:29,920 Speaker 1: sorry elephants, sorry feral pigs. Sure, but as we've seen, 300 00:18:30,000 --> 00:18:33,120 Speaker 1: life is persistent. If anything, it would almost certainly find 301 00:18:33,119 --> 00:18:35,440 Speaker 1: a way to adapt to the changes from the increased 302 00:18:35,480 --> 00:18:40,200 Speaker 1: heat on Earth, at least at first. But the radiation 303 00:18:40,320 --> 00:18:42,960 Speaker 1: from the growing Sun will be so intense that it 304 00:18:42,960 --> 00:18:46,320 Speaker 1: will tear apart the very molecules that make up Earth's atmosphere. 305 00:18:47,000 --> 00:18:51,480 Speaker 1: All aerobic life. Life that breathes oxygen would die, obviously, 306 00:18:52,000 --> 00:18:55,200 Speaker 1: but even anaerobic life would find it impossible to continue 307 00:18:55,200 --> 00:18:59,119 Speaker 1: on Earth without an atmosphere to regulate temperatures. The wild 308 00:18:59,160 --> 00:19:02,320 Speaker 1: swings between tense heat and cold on a daily basis 309 00:19:02,480 --> 00:19:06,080 Speaker 1: would evaporate the oceans, leaving Earth a dead, lifeless rock. 310 00:19:06,840 --> 00:19:11,280 Speaker 1: A planet without an atmosphere is a dead planet. So 311 00:19:11,320 --> 00:19:13,640 Speaker 1: we have a billion years to figure out either how 312 00:19:13,680 --> 00:19:16,480 Speaker 1: to slow the Sun's burn right and vastly extend its 313 00:19:16,480 --> 00:19:19,919 Speaker 1: main sequence, or how to live away from Earth, and 314 00:19:20,000 --> 00:19:22,399 Speaker 1: the odds aren't that bad actually that we may be 315 00:19:22,480 --> 00:19:28,040 Speaker 1: able to do both within that time. That same issue, 316 00:19:28,240 --> 00:19:31,080 Speaker 1: a star reaching the end of its productive life poses 317 00:19:31,119 --> 00:19:34,439 Speaker 1: another natural threat to Earth as well. Depending on the 318 00:19:34,600 --> 00:19:38,159 Speaker 1: size or the type of the star, could explode at 319 00:19:38,200 --> 00:19:42,320 Speaker 1: the end of its life. As a star nears the 320 00:19:42,440 --> 00:19:44,880 Speaker 1: end of its life and its fuel core becomes denser 321 00:19:44,880 --> 00:19:47,880 Speaker 1: and denser, the force of gravity acts ever more strongly 322 00:19:47,960 --> 00:19:50,280 Speaker 1: on it, and just the same way as the singularity 323 00:19:50,280 --> 00:19:53,280 Speaker 1: of a black hole. But a black hole singularity is 324 00:19:53,320 --> 00:19:56,240 Speaker 1: so massive and so dense that the force of gravity 325 00:19:56,280 --> 00:19:59,159 Speaker 1: acting on it actually presses it into the fabric of 326 00:19:59,160 --> 00:20:03,400 Speaker 1: space time, creating a bottomless depression. Not all stars are 327 00:20:03,440 --> 00:20:06,560 Speaker 1: as massive as this, though, so there are other outcomes 328 00:20:06,560 --> 00:20:08,919 Speaker 1: that it can have within a black hole. One of 329 00:20:08,920 --> 00:20:13,680 Speaker 1: those is a supernova. Over the star's lifespan, the nuclear 330 00:20:13,720 --> 00:20:17,520 Speaker 1: fusion reactions that carried out left behind his byproducts increasingly 331 00:20:17,600 --> 00:20:22,560 Speaker 1: heavier elements hydrogen fused into helium, helium fused into oxygen, 332 00:20:22,760 --> 00:20:26,360 Speaker 1: oxygen fused into neon, and so on, until the elements 333 00:20:26,400 --> 00:20:28,399 Speaker 1: the star burned towards the end of its life become 334 00:20:28,480 --> 00:20:32,359 Speaker 1: heavy metals like iron and nickel, so eventually it will 335 00:20:32,400 --> 00:20:34,480 Speaker 1: start to try and burn elements as big as a 336 00:20:34,720 --> 00:20:39,359 Speaker 1: iron and any star the stars to try to fuse 337 00:20:39,520 --> 00:20:43,240 Speaker 1: iron is basically on this deathbed. The force that holds 338 00:20:43,280 --> 00:20:45,800 Speaker 1: the nuclei of these types of atoms together is so 339 00:20:45,840 --> 00:20:49,399 Speaker 1: strong that they can't be fused together even by something 340 00:20:49,440 --> 00:20:52,800 Speaker 1: like a star. But the force that gravity exerts on 341 00:20:52,840 --> 00:20:56,240 Speaker 1: this extraordinarily dense core of iron and nickel is strong 342 00:20:56,400 --> 00:21:00,760 Speaker 1: enough that it actually compresses the individual atoms, pushing them 343 00:21:00,760 --> 00:21:04,159 Speaker 1: into tight, tiny balls. When the atoms that make up 344 00:21:04,200 --> 00:21:07,960 Speaker 1: the core shrink, the core itself does as well, becoming denser, 345 00:21:08,359 --> 00:21:10,800 Speaker 1: and so the force of gravity acts even more strongly 346 00:21:10,840 --> 00:21:14,119 Speaker 1: on it, creating a feedback loop. The star's core, in 347 00:21:14,119 --> 00:21:17,679 Speaker 1: other words, suddenly collapses. And all of this happens in 348 00:21:17,720 --> 00:21:20,879 Speaker 1: the fraction of a second. So is this weird point 349 00:21:20,920 --> 00:21:25,960 Speaker 1: where as soon as you hit iron, almost immediately within milliseconds, 350 00:21:26,000 --> 00:21:29,760 Speaker 1: the star just fulls apart. It just the whole system 351 00:21:29,760 --> 00:21:32,919 Speaker 1: in this core breaks down and it will undergo a 352 00:21:32,960 --> 00:21:36,119 Speaker 1: core collapse. But since the star isn't massive enough to 353 00:21:36,160 --> 00:21:38,480 Speaker 1: become a black hole, since one of the laws of 354 00:21:38,480 --> 00:21:41,199 Speaker 1: physics is that matter cannot occupy the same space at 355 00:21:41,200 --> 00:21:44,040 Speaker 1: the same time. There's a limit to how tightly packed 356 00:21:44,040 --> 00:21:47,080 Speaker 1: the iron atoms at the star's core can become. When 357 00:21:47,160 --> 00:21:50,480 Speaker 1: they reached that limit, the collapse suddenly stops, kind of 358 00:21:50,520 --> 00:21:53,359 Speaker 1: like hitting a brick wall. All that force of the 359 00:21:53,400 --> 00:21:56,800 Speaker 1: collapsing core has to go somewhere, though, and it reverberates 360 00:21:56,840 --> 00:22:00,520 Speaker 1: back outward. Exploding in a supernova one of the most 361 00:22:00,560 --> 00:22:04,560 Speaker 1: fantastic displays in the universe. All of the mass that 362 00:22:04,720 --> 00:22:08,000 Speaker 1: star sheds is shot outward as energy, so much in fact, 363 00:22:08,240 --> 00:22:11,400 Speaker 1: that planets that orbited the star just moments before may 364 00:22:11,400 --> 00:22:14,479 Speaker 1: be blown out of their solar system into space if 365 00:22:14,480 --> 00:22:18,920 Speaker 1: they're not outright destroyed. That is, tremendous amounts of light 366 00:22:18,960 --> 00:22:21,879 Speaker 1: and heat are released. For a few minutes, the dying 367 00:22:21,920 --> 00:22:25,360 Speaker 1: star can shine brighter than the combined luminosity of an 368 00:22:25,520 --> 00:22:29,879 Speaker 1: entire galaxy. The explosion since tremendous amounts of heat and 369 00:22:30,000 --> 00:22:34,960 Speaker 1: radiation spewing into space, bathing anything nearby with The only 370 00:22:35,000 --> 00:22:38,840 Speaker 1: explosion in our universe larger than a supernova was the 371 00:22:38,880 --> 00:22:44,560 Speaker 1: Big Bang. Sometimes, if the supernova is large enough, it 372 00:22:44,600 --> 00:22:48,119 Speaker 1: can emit a gamma ray burst. Gamma radiation is the 373 00:22:48,160 --> 00:22:52,480 Speaker 1: most energetic type of radiation on the electromagnetic spectrum. Gamma 374 00:22:52,560 --> 00:22:55,359 Speaker 1: rays are so energetic that they excite any atom they 375 00:22:55,400 --> 00:22:58,520 Speaker 1: come in contact with, causing the atom to move temporarily 376 00:22:58,560 --> 00:23:01,680 Speaker 1: to its higher energy state, causing its a release energy 377 00:23:01,720 --> 00:23:04,520 Speaker 1: itself as it moves back to its normal ground state. 378 00:23:05,440 --> 00:23:08,199 Speaker 1: It's like gamma rays get everybody else wound up, and 379 00:23:08,240 --> 00:23:11,080 Speaker 1: to calm down, everyone has to let out a little shout. 380 00:23:12,840 --> 00:23:16,080 Speaker 1: Just thinking about this happening to an individual atom sounds 381 00:23:16,119 --> 00:23:19,080 Speaker 1: like chaos. So you can imagine what a burst big 382 00:23:19,200 --> 00:23:22,520 Speaker 1: enough to flood an entire planet with gamma radiation might be. Like, 383 00:23:24,200 --> 00:23:27,000 Speaker 1: let's say, for argument's sake, that Earth just happens to 384 00:23:27,000 --> 00:23:29,480 Speaker 1: be in the path of that beam of energy. A 385 00:23:29,560 --> 00:23:32,480 Speaker 1: sudden flood of gamma radiation would burn those of us 386 00:23:32,480 --> 00:23:35,639 Speaker 1: walking around on Earth's surface to a crisp Sadly, we 387 00:23:35,640 --> 00:23:40,280 Speaker 1: would probably not all be transformed into incredible hulks. The 388 00:23:40,359 --> 00:23:42,840 Speaker 1: life that did manage to survive the initial burst would 389 00:23:42,840 --> 00:23:46,000 Speaker 1: have a rough time of it afterward. Gamma radiation is 390 00:23:46,040 --> 00:23:49,800 Speaker 1: particularly good at burning away the ozone layer, the protective 391 00:23:49,800 --> 00:23:52,560 Speaker 1: blanket of O three atoms that reflects most of the 392 00:23:52,560 --> 00:23:56,680 Speaker 1: Sun's radiation. When flooded with energetic gamma rays, those O 393 00:23:56,880 --> 00:24:00,920 Speaker 1: three molecules would destabilize and the ozone layer would deteriorate, 394 00:24:01,320 --> 00:24:04,240 Speaker 1: leaving Earth exposed to the full brunt of ultra violet 395 00:24:04,359 --> 00:24:07,760 Speaker 1: radiation from the Sun. UV from the Sun could be 396 00:24:07,760 --> 00:24:11,040 Speaker 1: bad enough with the folows on layer, without it, it 397 00:24:11,040 --> 00:24:15,000 Speaker 1: would be utterly catastrophic. The intensity of the UV would 398 00:24:15,040 --> 00:24:19,240 Speaker 1: prove too much for even photosynthesis and plants, so, following 399 00:24:19,240 --> 00:24:22,040 Speaker 1: the blueprints of the KT extinction, in a matter of 400 00:24:22,119 --> 00:24:25,000 Speaker 1: days or weeks, the bottom of the food chain would collapse, 401 00:24:25,359 --> 00:24:27,800 Speaker 1: and everything else above it would starve. As a result, 402 00:24:28,560 --> 00:24:31,080 Speaker 1: the oceans too would be crippled by the increase in UV. 403 00:24:31,600 --> 00:24:33,960 Speaker 1: It would destroy the plankton that makes up the basis 404 00:24:34,000 --> 00:24:37,720 Speaker 1: of the marine food webs. The effect would be pronounced 405 00:24:37,800 --> 00:24:40,280 Speaker 1: enough that a gamma ray burst is considered to be 406 00:24:40,320 --> 00:24:43,119 Speaker 1: able to sterilize a planet close enough in its path, 407 00:24:44,880 --> 00:24:47,840 Speaker 1: and it's possible that the Earth has experienced them before. 408 00:24:48,720 --> 00:24:52,080 Speaker 1: One theory for the Ordovician extinction four hundred and forty 409 00:24:52,119 --> 00:24:54,400 Speaker 1: million years ago is that Earth got in the way 410 00:24:54,440 --> 00:24:58,560 Speaker 1: of a gamma ray bursts. As majestically dangerous as they 411 00:24:58,600 --> 00:25:01,440 Speaker 1: are gamma ray burst upened in the universe once a 412 00:25:01,520 --> 00:25:05,520 Speaker 1: day at least, well that's how often we noticed them 413 00:25:05,560 --> 00:25:08,760 Speaker 1: since the nineteen sixties. I should say humans have been 414 00:25:08,800 --> 00:25:12,399 Speaker 1: aware of supernova for thousands of years, first noting the 415 00:25:12,440 --> 00:25:15,440 Speaker 1: appearance of bright new stars in China almost two thousand 416 00:25:15,520 --> 00:25:18,679 Speaker 1: years ago. But we spent the entire lifespan of our 417 00:25:18,720 --> 00:25:23,200 Speaker 1: species up until the nineteen sixties blissfully unaware that invisible 418 00:25:23,240 --> 00:25:26,040 Speaker 1: death rays went off in our universe at all. It 419 00:25:26,080 --> 00:25:28,080 Speaker 1: was all because of the Cold War that we ever 420 00:25:28,119 --> 00:25:32,800 Speaker 1: found them. In ninety three, the US the USS are 421 00:25:33,200 --> 00:25:36,439 Speaker 1: in Great Britain signed a treaty banning nuclear detonations in 422 00:25:36,480 --> 00:25:40,960 Speaker 1: the atmosphere, underwater or in outer space. But we didn't 423 00:25:41,000 --> 00:25:44,159 Speaker 1: precisely trust our comrades, and so the US launched the 424 00:25:44,200 --> 00:25:48,200 Speaker 1: satellite capable of detecting large sudden spikes and nuclear radiation, 425 00:25:48,920 --> 00:25:51,800 Speaker 1: and the satellite found it. But it wasn't from nuclear 426 00:25:51,840 --> 00:25:55,840 Speaker 1: tests that satellite provided the first evidence of gamma ray bursts, 427 00:25:56,480 --> 00:25:58,960 Speaker 1: and since then we found that they are extremely common. 428 00:25:59,520 --> 00:26:06,520 Speaker 1: Stars collapse all the time. It seems the universe is 429 00:26:06,560 --> 00:26:10,159 Speaker 1: full of rocks and collapsing stars and gamma ray bursts, 430 00:26:10,680 --> 00:26:12,760 Speaker 1: which by the way. It can also form from two 431 00:26:12,760 --> 00:26:15,960 Speaker 1: black holes merging, or from the hiccup of an exotic 432 00:26:16,000 --> 00:26:19,280 Speaker 1: and frightening type of star called magnet Or, which is 433 00:26:19,320 --> 00:26:22,199 Speaker 1: a type of dwarf star made of nickel. It's been 434 00:26:22,359 --> 00:26:26,000 Speaker 1: hundreds of times per second and produces the strongest magnetic 435 00:26:26,040 --> 00:26:28,760 Speaker 1: field in the universe. This is a dangerous place out there. 436 00:26:28,760 --> 00:26:32,200 Speaker 1: I mean that the universe is has got no care 437 00:26:32,320 --> 00:26:36,920 Speaker 1: for life on Earth, and and I think that it's 438 00:26:36,960 --> 00:26:39,160 Speaker 1: worth remembering that when you look up in the nice sky, 439 00:26:39,320 --> 00:26:43,080 Speaker 1: when it looks very you know, peaceful and static, and 440 00:26:43,080 --> 00:26:52,479 Speaker 1: and it's unlook particularly dangerous. Being alive in the twenty 441 00:26:52,480 --> 00:26:55,640 Speaker 1: one century. You're probably fairly well versed in the basics 442 00:26:55,680 --> 00:26:59,080 Speaker 1: of climate change. We all are, and whether you believe 443 00:26:59,160 --> 00:27:01,919 Speaker 1: humans contribute to it or not, it's plain to everyone 444 00:27:02,000 --> 00:27:04,960 Speaker 1: that has advanced as we've become, we are still very 445 00:27:05,040 --> 00:27:08,439 Speaker 1: much at the mercy of the Earth's climate. All of 446 00:27:08,480 --> 00:27:12,240 Speaker 1: the bad news about climate change, though it seems incremental, 447 00:27:12,840 --> 00:27:15,639 Speaker 1: a few degrees increase in temperature here, a couple of 448 00:27:15,640 --> 00:27:19,080 Speaker 1: feet of sea level rise there, it just seems so well, 449 00:27:19,119 --> 00:27:22,400 Speaker 1: I hate to say it, but distant, distant and sort 450 00:27:22,440 --> 00:27:25,960 Speaker 1: of non threatening. Now there's a whole series I could 451 00:27:25,960 --> 00:27:28,160 Speaker 1: do just on how those sentiments aren't correct at all. 452 00:27:28,640 --> 00:27:31,240 Speaker 1: But enough doubt has been sown that it feels like 453 00:27:31,320 --> 00:27:34,240 Speaker 1: we have the luxury of time to keep arguing about 454 00:27:34,280 --> 00:27:36,840 Speaker 1: something as silly as whether humans are contributing in a 455 00:27:36,920 --> 00:27:39,959 Speaker 1: climate change or not, but whether you believe we do 456 00:27:40,280 --> 00:27:43,800 Speaker 1: or not, and we definitely do, there's something you should 457 00:27:43,800 --> 00:27:47,320 Speaker 1: know about climate change. Earth has a point of no 458 00:27:47,480 --> 00:27:50,960 Speaker 1: return climate wise, and should we find that we've pushed 459 00:27:51,000 --> 00:27:53,639 Speaker 1: it past that point, we would also find, to our 460 00:27:53,720 --> 00:27:56,920 Speaker 1: great peril that the changing climate would be neither distant 461 00:27:57,280 --> 00:28:03,000 Speaker 1: nor non threatening. With an overabundance of carbon dioxide, the 462 00:28:03,080 --> 00:28:06,160 Speaker 1: atmosphere could become a blanket that traps heat from escaping 463 00:28:06,200 --> 00:28:11,160 Speaker 1: into space, heating Earth up to an unbearable degree. Literally, 464 00:28:12,040 --> 00:28:15,879 Speaker 1: it's called a runaway greenhouse effect. If you were alive 465 00:28:15,920 --> 00:28:18,680 Speaker 1: in the nineties, you were introduced to the greenhouse effected 466 00:28:18,800 --> 00:28:21,720 Speaker 1: byproduct of climate change that can lead to global warming. 467 00:28:22,440 --> 00:28:25,480 Speaker 1: The basics are that as we burn more fossil fuels, 468 00:28:25,480 --> 00:28:28,439 Speaker 1: we contribute new large amounts of carbon dioxide to the 469 00:28:28,480 --> 00:28:31,280 Speaker 1: atmosphere that wouldn't otherwise be there. They would still be 470 00:28:31,320 --> 00:28:35,440 Speaker 1: locked underground as deposits of oil and gas. When sunlight 471 00:28:35,480 --> 00:28:38,200 Speaker 1: shines on Earth, the planet absorbs some of it and 472 00:28:38,320 --> 00:28:41,040 Speaker 1: is warmed by it, but it also re emits some 473 00:28:41,080 --> 00:28:44,760 Speaker 1: of it back into space as infrared heat. The trouble 474 00:28:44,880 --> 00:28:48,120 Speaker 1: is CO two is an extremely efficient absorber of that 475 00:28:48,200 --> 00:28:50,880 Speaker 1: infrared heat. When there's a lot of CO two in 476 00:28:50,920 --> 00:28:54,720 Speaker 1: the atmosphere, the atmosphere is a whole warms, so we 477 00:28:54,840 --> 00:28:57,440 Speaker 1: end up with a warm planet and a warmer than 478 00:28:57,480 --> 00:29:02,720 Speaker 1: normal atmosphere. Things become warmer all around, but when temperatures 479 00:29:02,800 --> 00:29:06,240 Speaker 1: rise on Earth, the planet just releases more radiated heat, 480 00:29:06,720 --> 00:29:09,880 Speaker 1: and so eventually temperature is cool again. It's as if 481 00:29:09,920 --> 00:29:12,800 Speaker 1: Earth overwhelms the CEO two in the atmosphere with sheer 482 00:29:12,880 --> 00:29:16,080 Speaker 1: multitudes of infrared. There's just not enough CEO two to 483 00:29:16,160 --> 00:29:19,440 Speaker 1: trap it all, and the planet overcomes the greenhouse effect 484 00:29:19,680 --> 00:29:23,040 Speaker 1: easy peasy. But there's a limit to how much heat 485 00:29:23,120 --> 00:29:26,280 Speaker 1: Earth can release into space, and so once the planet 486 00:29:26,280 --> 00:29:28,760 Speaker 1: reaches the point where it can emit no more infrared. 487 00:29:29,160 --> 00:29:32,080 Speaker 1: As c O two levels continue to rise, the tables 488 00:29:32,120 --> 00:29:34,880 Speaker 1: can turn, and it can be the carbon dioxide that 489 00:29:34,920 --> 00:29:40,080 Speaker 1: overwhelms Earth. A runaway greenhouse effect is triggered when a 490 00:29:40,120 --> 00:29:44,320 Speaker 1: positive feedback loop arises. As the planet grows warmer, more 491 00:29:44,360 --> 00:29:47,920 Speaker 1: water evaporates from the surface of the oceans. Water vapor 492 00:29:48,040 --> 00:29:51,840 Speaker 1: is also particularly good at absorbing reflected heat and trapping 493 00:29:51,840 --> 00:29:55,360 Speaker 1: it in the atmosphere, So the atmosphere goes even warmer, 494 00:29:55,800 --> 00:29:58,960 Speaker 1: causing more of the oceans to evaporate, adding more water 495 00:29:59,040 --> 00:30:02,800 Speaker 1: vapor to the atmosphere, trapping more escaping heat, warming the 496 00:30:02,800 --> 00:30:07,280 Speaker 1: planet even more and evaporating more of the oceans. Eventually, 497 00:30:07,480 --> 00:30:10,080 Speaker 1: it reaches a point where the entire planet becomes so 498 00:30:10,160 --> 00:30:15,360 Speaker 1: hot that the oceans boil off. You will be relieved 499 00:30:15,360 --> 00:30:17,600 Speaker 1: to hear that there is a point where the feedback 500 00:30:17,640 --> 00:30:21,120 Speaker 1: loop is broken and the runaway greenhouse effect ends. But 501 00:30:21,360 --> 00:30:23,640 Speaker 1: I regret to say that that doesn't happen until the 502 00:30:23,720 --> 00:30:27,880 Speaker 1: atmospheric temperature reaches about three thousand degrees fahrenheit, when the 503 00:30:27,920 --> 00:30:30,680 Speaker 1: emitted heat moves to a wavelength that water vapor is 504 00:30:30,680 --> 00:30:35,080 Speaker 1: incapable of absorbing. Long before that we humans would have 505 00:30:35,120 --> 00:30:39,280 Speaker 1: ceased to exist, and eventually, with the oceans boiled off, 506 00:30:39,320 --> 00:30:41,280 Speaker 1: any life hanging on in the seas would meet the 507 00:30:41,320 --> 00:30:45,520 Speaker 1: same fate as us. This is what astronomers believe happened 508 00:30:45,520 --> 00:30:48,680 Speaker 1: to Venus Venus is about the same size as Earth, 509 00:30:48,760 --> 00:30:50,880 Speaker 1: but it's far closer to the Sun, and it's not 510 00:30:50,960 --> 00:30:54,320 Speaker 1: within the Goldilocks zone. It's not the closest planet to 511 00:30:54,360 --> 00:30:57,240 Speaker 1: the Sun. That distinction goes to Mercury, but it is 512 00:30:57,280 --> 00:30:59,880 Speaker 1: the hottest planet in the entire Solar System by far, 513 00:31:00,000 --> 00:31:03,960 Speaker 1: are despite being almost twenty eight million miles further away 514 00:31:03,960 --> 00:31:07,040 Speaker 1: from the Sun than Mercury is. Venus is average surface 515 00:31:07,040 --> 00:31:10,480 Speaker 1: temperature of eight hundred and sixty four degrees fahrenheit is 516 00:31:10,560 --> 00:31:13,640 Speaker 1: hundreds of degrees hotter than Mercuries, hot enough to melt 517 00:31:13,720 --> 00:31:18,320 Speaker 1: let that's because Venus has an atmosphere thick with CEO two. 518 00:31:18,880 --> 00:31:21,560 Speaker 1: On the surface of the planet. The atmospheric pressure is 519 00:31:21,600 --> 00:31:24,280 Speaker 1: almost a hundred times that of Earth's at sea level, 520 00:31:24,640 --> 00:31:27,680 Speaker 1: about what you would experienced three thousand feet underwater in 521 00:31:27,720 --> 00:31:31,560 Speaker 1: one of Earth's oceans. There's no surface water on Venus 522 00:31:31,600 --> 00:31:35,080 Speaker 1: that evaporated away eons ago, but at some point in 523 00:31:35,120 --> 00:31:44,200 Speaker 1: its distant past, Venus may have been habitable. It is 524 00:31:44,240 --> 00:31:47,840 Speaker 1: to our great fortune that natural existential risks seem to 525 00:31:47,880 --> 00:31:53,160 Speaker 1: be rare. This is philosopher Toby ord. Humanity has survived 526 00:31:53,280 --> 00:31:57,040 Speaker 1: about two thousand centuries so far, so that's two thousand 527 00:31:57,120 --> 00:32:04,160 Speaker 1: centuries worth of natural risk. Asteroid comments, supervolcanos, supernovas, everything 528 00:32:04,320 --> 00:32:08,960 Speaker 1: put together that could have killed humanity. We've survived two 529 00:32:09,000 --> 00:32:12,840 Speaker 1: thousand centuries of that risk. UH. And this, this fact 530 00:32:13,040 --> 00:32:15,600 Speaker 1: allows us to put a bound on how much risk 531 00:32:15,720 --> 00:32:18,520 Speaker 1: these natural things could be causing UH. And if you 532 00:32:18,560 --> 00:32:21,520 Speaker 1: do the mathematics on this, you can show that it 533 00:32:21,600 --> 00:32:24,600 Speaker 1: can't be much higher than about one in a thousand 534 00:32:25,200 --> 00:32:29,760 Speaker 1: chance of extinction per century from natural causes, which works 535 00:32:29,760 --> 00:32:33,080 Speaker 1: out to a point zero zero one percent chance of 536 00:32:33,160 --> 00:32:36,960 Speaker 1: humanity going extinct from natural risks during any given year, 537 00:32:37,600 --> 00:32:42,600 Speaker 1: a thousandth of a percent, not too menacing. Most atmospheric 538 00:32:42,640 --> 00:32:46,520 Speaker 1: models show that human contributed CEO two definitely exacerbates the 539 00:32:46,520 --> 00:32:50,000 Speaker 1: greenhouse effect, but that it would be extremely unlikely that 540 00:32:50,040 --> 00:32:53,760 Speaker 1: we humans could push it into a runaway greenhouse. In 541 00:32:53,800 --> 00:32:57,080 Speaker 1: the paper where they introduced the world to the concept 542 00:32:57,080 --> 00:33:00,120 Speaker 1: of a dinosaur killing asteroid, the alvarez Is and their 543 00:33:00,160 --> 00:33:04,320 Speaker 1: colleagues calculated how frequently such a catastrophic event might take place. 544 00:33:05,080 --> 00:33:08,160 Speaker 1: They concluded that an asteroid with that scope of devastation 545 00:33:08,240 --> 00:33:11,840 Speaker 1: might come along once every hundred million years, which would 546 00:33:11,880 --> 00:33:14,400 Speaker 1: leave us with around thirty four million years left on 547 00:33:14,440 --> 00:33:18,120 Speaker 1: the clock before we can expect a similarly destructive asteroid. 548 00:33:18,440 --> 00:33:23,320 Speaker 1: With something approaching certainty. A gamma ray burst close enough 549 00:33:23,360 --> 00:33:26,120 Speaker 1: to Earth to cause a mass extinction might happen once 550 00:33:26,160 --> 00:33:29,280 Speaker 1: every billion years, and Earth would have to be lined 551 00:33:29,360 --> 00:33:31,600 Speaker 1: up in the path of the relatively narrow beam of 552 00:33:31,640 --> 00:33:35,840 Speaker 1: gamma radiation to experience the full effect. There are stars 553 00:33:35,880 --> 00:33:39,000 Speaker 1: nearby that could collapse in supernova, but the closest I 554 00:33:39,160 --> 00:33:43,160 Speaker 1: k pegasy A isn't expected to for another five million years. 555 00:33:44,000 --> 00:33:47,680 Speaker 1: The next two closest and Terris and Beetlejuice, could explode 556 00:33:47,680 --> 00:33:50,160 Speaker 1: at any time in the next million years, but it 557 00:33:50,200 --> 00:33:53,320 Speaker 1: should be too far away to damage Earth. And again, 558 00:33:53,480 --> 00:33:55,720 Speaker 1: the Sun has more than a billion years before it 559 00:33:55,760 --> 00:33:58,360 Speaker 1: reaches the end of its main sequence and begins to 560 00:33:58,400 --> 00:34:02,440 Speaker 1: grow unbearably hot for us. But it pays to keep 561 00:34:02,440 --> 00:34:06,280 Speaker 1: an open mind. It is entirely possible that our current 562 00:34:06,320 --> 00:34:10,319 Speaker 1: understanding of these risks is flawed in some way or incomplete, 563 00:34:10,880 --> 00:34:13,120 Speaker 1: that there's some factor we're not aware of yet that 564 00:34:13,160 --> 00:34:16,040 Speaker 1: could make any one of these disasters much more likely. 565 00:34:16,960 --> 00:34:20,799 Speaker 1: In that slight, limital space of uncertainty is where existential 566 00:34:20,920 --> 00:34:25,400 Speaker 1: risks live. The chances of them happening are minuscule, but 567 00:34:25,480 --> 00:34:29,080 Speaker 1: the consequences they bring if they do, are so catastrophic 568 00:34:29,480 --> 00:34:34,040 Speaker 1: that they demand to be taken into account. Atmospheric scientists, 569 00:34:34,080 --> 00:34:38,040 Speaker 1: for example, don't understand the extraordinarily complex interactions that make 570 00:34:38,120 --> 00:34:42,320 Speaker 1: up Earth's atmosphere, and so maybe we could accidentally trigger 571 00:34:42,400 --> 00:34:46,799 Speaker 1: a runaway greenhouse effect by burning fossil fuels. It's unlikely, 572 00:34:47,320 --> 00:34:51,400 Speaker 1: but it's unlikely under our current understanding, and with the 573 00:34:51,440 --> 00:34:57,360 Speaker 1: addition of information that understanding can change. Human misunderstanding doesn't 574 00:34:57,360 --> 00:35:01,799 Speaker 1: prevent calamity. In fact, it makes it like clear. But 575 00:35:01,880 --> 00:35:06,000 Speaker 1: here's the thing about natural existential risks. Being earth bound, 576 00:35:06,080 --> 00:35:09,200 Speaker 1: we can't do much about them right now. In the future, 577 00:35:09,239 --> 00:35:12,600 Speaker 1: we will, our artificial intelligence will be able to predict 578 00:35:12,640 --> 00:35:15,719 Speaker 1: gamma ray bursts to give us plenty of warning. Our 579 00:35:15,760 --> 00:35:18,800 Speaker 1: spacecraft will be able to ferry us around a safer planets, 580 00:35:19,440 --> 00:35:22,319 Speaker 1: and maybe we'll build structures to capture the energy from 581 00:35:22,320 --> 00:35:25,719 Speaker 1: those bursts and store it for later. But so long 582 00:35:25,760 --> 00:35:28,880 Speaker 1: as we remain bound to Earth, we will be vulnerable 583 00:35:28,960 --> 00:35:32,200 Speaker 1: to the same threats that it is. More so, really, 584 00:35:32,680 --> 00:35:35,920 Speaker 1: Earth is likelier to bounce back from a cataclysmic asteroid 585 00:35:36,000 --> 00:35:39,480 Speaker 1: or a gamma ray burst than we are. But there's 586 00:35:39,520 --> 00:35:43,319 Speaker 1: an entirely different class of existential risks, ones that we 587 00:35:43,400 --> 00:35:46,279 Speaker 1: have a much greater chance of controlling because they are 588 00:35:46,320 --> 00:35:50,600 Speaker 1: of our own making, but also ones that pose significantly 589 00:35:50,640 --> 00:35:57,680 Speaker 1: greater danger. These are anthropogenic existential risks. Anthropogenic risks. However, 590 00:35:58,320 --> 00:36:01,879 Speaker 1: um we can't apply such an argument to bound the probabilities, 591 00:36:01,920 --> 00:36:04,200 Speaker 1: and to show that there must be quite small. I 592 00:36:04,239 --> 00:36:07,000 Speaker 1: would say that there's maybe something like if there was 593 00:36:07,200 --> 00:36:12,319 Speaker 1: something like a risk of extinction from anthropogenic causes in 594 00:36:12,360 --> 00:36:15,800 Speaker 1: the twentieth century, this century, I think it's it's growing. 595 00:36:16,360 --> 00:36:18,720 Speaker 1: My best guest would be something like one and six 596 00:36:18,960 --> 00:36:23,120 Speaker 1: Russian Roulette, and then next century, well, if we don't 597 00:36:23,120 --> 00:36:27,120 Speaker 1: get our act together even higher. Those technologies that pose 598 00:36:27,160 --> 00:36:30,920 Speaker 1: an anthropogenic risk to us, we're beginning to develop them 599 00:36:31,000 --> 00:36:35,120 Speaker 1: right now. Some are already here and almost know what 600 00:36:35,840 --> 00:36:39,759 Speaker 1: is paying attention to the danger they are bringing our way. 601 00:36:44,960 --> 00:36:47,040 Speaker 1: On the next episode of the End of the World 602 00:36:47,040 --> 00:36:50,360 Speaker 1: with Josh Clark, it was a cold, windy day in 603 00:36:50,440 --> 00:36:54,440 Speaker 1: January nine when the robots took their first human life. 604 00:36:55,480 --> 00:36:58,560 Speaker 1: As we create more intelligent algorithms that are capable of 605 00:36:58,600 --> 00:37:01,919 Speaker 1: improving themselves, we run the risk that they may take 606 00:37:01,960 --> 00:37:05,760 Speaker 1: over their own development and quickly evolved beyond our control. 607 00:37:06,800 --> 00:37:09,240 Speaker 1: There is no good outcome for us if that happens.