WEBVTT - Natural Risks 0:00:03.080 --> 0:00:07.080 Existential risks aren't new to us. Ever since our species 0:00:07.200 --> 0:00:10.840 was born. There have always been lots of catastrophes ready 0:00:10.840 --> 0:00:13.280 and waiting to wipe the human race off the face 0:00:13.280 --> 0:00:16.360 of the earth. It's just that these risks are of 0:00:16.400 --> 0:00:20.520 our own making. The history of humanity is relatively brief, 0:00:21.120 --> 0:00:23.639 and we've been fortunate to have come along during a 0:00:23.720 --> 0:00:28.360 period of relative calm in Earth's history. Maybe we couldn't 0:00:28.360 --> 0:00:31.760 have come along had things been more tumultuous. Who knows, 0:00:32.479 --> 0:00:34.720 but there's something to bear in mind that pops up 0:00:34.760 --> 0:00:38.760 a lot when you look into existential threats. Whatever lessons 0:00:38.840 --> 0:00:42.320 the past may offer, it doesn't teach us enough about 0:00:42.360 --> 0:00:46.080 the future. Just because things have gone smoothly so far 0:00:46.600 --> 0:00:50.680 doesn't mean they will always go that way. Every so often, 0:00:51.120 --> 0:00:55.320 some massive catastrophe happens on Earth that brings life to 0:00:55.360 --> 0:00:59.080 the brink of extinction. There are a lot of things 0:00:59.080 --> 0:01:02.840 in space and on Earth that can devastate life. We 0:01:02.960 --> 0:01:07.679 call these natural existential risks. It's worth noting that we 0:01:07.920 --> 0:01:11.720 humans pose an existential threat to just about every other 0:01:11.760 --> 0:01:15.080 species that we share the planet with, but there are 0:01:15.120 --> 0:01:18.920 also natural catastrophes that pose a threat to all of us. 0:01:18.959 --> 0:01:23.759 Creatures living on Earth, including us humans. In this episode, 0:01:23.880 --> 0:01:26.679 we'll look at a few of them to get a 0:01:26.720 --> 0:01:29.600 feel for just how badly things can go on Earth. 0:01:30.280 --> 0:01:33.760 Let's travel back to one particular day during the most 0:01:33.760 --> 0:01:37.959 strictan age of the Upper Cretaceous period, about sixty six 0:01:37.959 --> 0:01:41.240 million years ago, give or take three hundred thousand years, 0:01:41.520 --> 0:01:44.560 and on this day, a light streaks across the sky 0:01:44.640 --> 0:01:48.920 above Earth. That light, it turns out, is an asteroid, 0:01:49.440 --> 0:01:53.160 six miles across, about the size of downtown Los Angeles, 0:01:54.400 --> 0:01:57.520 is traveling at about forty four thousand miles per hour, 0:01:58.600 --> 0:02:01.480 times faster than a bullet when it passes through the 0:02:01.480 --> 0:02:05.280 Earth's atmosphere as if it's not even there, and strikes 0:02:05.360 --> 0:02:10.160 the planet. The impact creates a blast with one hundred 0:02:10.440 --> 0:02:16.160 million megatons of energy. For comparison, the Czar BOMBA, the 0:02:16.280 --> 0:02:21.520 largest nuclear bomb that humans have ever detonated, was fifty megatons. 0:02:22.639 --> 0:02:30.040 One got past Jupiter, you could say. The asteroid strikes 0:02:30.080 --> 0:02:32.440 the Earth along what is now called the Yucatan, the 0:02:32.480 --> 0:02:35.640 spur like peninsula that juts out of southern Mexico into 0:02:35.639 --> 0:02:39.400 the Gulf. It drives itself into the Earth, digging out 0:02:39.440 --> 0:02:41.920 a crater a hundred and ten miles in diameter and 0:02:42.040 --> 0:02:45.560 nine miles deep, so deep, in fact, it nearly punctures 0:02:45.560 --> 0:02:48.480 a hole all the way through the crust. The impact 0:02:48.560 --> 0:02:51.560 is felt all over the world as enormous shocks of 0:02:51.639 --> 0:02:55.560 energy that travel along the borders between tectonic plates. This 0:02:55.680 --> 0:03:00.919 sets off earthquakes and volcanoes across Earth unimaginably large tsunamis 0:03:00.919 --> 0:03:04.680 from the Gulf of Mexico Wash as far north as St. Louis. 0:03:05.880 --> 0:03:08.600 The impact kicks a tremendous amount of earth and sea 0:03:08.680 --> 0:03:11.880 into the air. Boulders the size of cars are launched 0:03:11.960 --> 0:03:14.720 hundreds of miles from the impact site, as far away 0:03:14.760 --> 0:03:17.920 as Believes. The pressure and heat from the collision is 0:03:17.960 --> 0:03:21.200 so great that it instantly melts the rocky earth below. 0:03:21.800 --> 0:03:24.639 That melted rock sprays into the air, where it turns 0:03:24.680 --> 0:03:27.959 to glass before it can reach the ground. Continents away. 0:03:28.840 --> 0:03:32.400 Quartz is pressed into crazy angles, and minerals into tiny 0:03:32.440 --> 0:03:35.520 spheres of metal, And when the heavier bits among all 0:03:35.560 --> 0:03:38.200 that kicked up dirt and rock and metal come back down, 0:03:38.560 --> 0:03:41.760 it heats up. It brings a tremendous amount of energy 0:03:41.800 --> 0:03:46.000 with it, flash heating the Earth's surface, embroiling alive anything 0:03:46.040 --> 0:03:50.920 that can't take cover underground or underwater. And as the 0:03:50.920 --> 0:03:54.280 earthquakes and tsunamis raging across the Earth and the fire 0:03:54.400 --> 0:03:57.839 raining from the sky begin to subside, things go from 0:03:57.840 --> 0:04:02.960 bad to worse. The finer particles from all that pulverized 0:04:03.000 --> 0:04:07.400 earth and liquefied rock launched into space stay aloft, forming 0:04:07.440 --> 0:04:10.640 a vast globe spanning shroud that blocks out the Sun 0:04:10.720 --> 0:04:14.680 for months. Photosynthesis grants to a halt back on Earth. 0:04:15.200 --> 0:04:18.040 The world's plants can no longer make their food, and 0:04:18.120 --> 0:04:20.440 since they, in one way or another, feed the rest 0:04:20.480 --> 0:04:24.120 of life on Earth, everything is still alive begins to starve. 0:04:25.360 --> 0:04:27.799 But as bad as the asteroid makes things for life 0:04:27.800 --> 0:04:30.320 on Earth, it is made even worse by a fluke, 0:04:30.680 --> 0:04:34.400 a stroke of sheer bad luck. The Yucatan, the area 0:04:34.440 --> 0:04:37.279 where the asteroid strikes, is one of the most sulfur 0:04:37.400 --> 0:04:40.720 rich areas on Earth, and when that asteroid hit, as 0:04:40.800 --> 0:04:44.560 much as five hundred billion metric tons of sulfur instantly 0:04:44.680 --> 0:04:47.720 rose from deep inside the Earth up into the atmosphere, 0:04:48.080 --> 0:04:50.479 like dust rising from a table when a heavy book 0:04:50.600 --> 0:04:54.200 is dropped on it. In the sky, that sulfur mixes 0:04:54.240 --> 0:04:57.600 with water vapor and is bombarded by ultra violet radiation 0:04:57.640 --> 0:05:01.360 from the sun, so it becomes sulfur aerosol, the type 0:05:01.400 --> 0:05:04.160 of atmospheric pollution that just happens to be the most 0:05:04.160 --> 0:05:07.799 efficient at absorbing sunlight and blocking it from reaching the Earth. 0:05:08.600 --> 0:05:11.200 The sudden presence of aerosols in the sky makes the 0:05:11.279 --> 0:05:16.560 darkness complete. Sulfur aerosols also form acid rain and freshwater 0:05:16.680 --> 0:05:19.120 lakes and the surface of the oceans are poisoned by it. 0:05:19.880 --> 0:05:27.400 Life on Earth comes disturbingly close to total extinction. Millions 0:05:27.400 --> 0:05:30.599 of years later, humans will call this cataclysmic event the 0:05:30.600 --> 0:05:35.719 Cretaceous Tertiary extinction. It had such a profoundly colossal effect 0:05:35.720 --> 0:05:38.240 on the planet that it serves as the sudden and 0:05:38.320 --> 0:05:42.919 abrupt dividing line between one geological age, the Cretaceous, and 0:05:42.960 --> 0:05:46.359 the one that followed it, the Tertiary or Paleogene, as 0:05:46.400 --> 0:05:50.760 it's called these days. Around of the species alive on 0:05:50.800 --> 0:05:53.800 Earth at the time died during the event and the 0:05:53.839 --> 0:05:57.719 hard times that followed the asteroid's arrival. Three out of 0:05:57.760 --> 0:06:02.480 four species death swept across Earth and waves that lasted 0:06:02.520 --> 0:06:06.479 for tens of thousands of years. Those species that did 0:06:06.520 --> 0:06:09.240 manage to survive had an extremely hard time of it. 0:06:09.600 --> 0:06:12.360 They hung on by a thread. In many cases, they 0:06:12.360 --> 0:06:15.120 were whittled down to just a few individuals that were 0:06:15.160 --> 0:06:18.720 somehow able to carry on their species. Animals that were 0:06:18.760 --> 0:06:21.479 able to burrow to feed off the carcasses of the 0:06:21.600 --> 0:06:24.800 unlucky ones, and whatever plants still reached upward towards a 0:06:24.839 --> 0:06:27.919 sun that no longer shown. Those are the ancestors of 0:06:28.000 --> 0:06:31.440 everything alive on Earth today. We are descended from the 0:06:31.520 --> 0:06:36.000 toughest band of animals that ever lived. But for most 0:06:36.040 --> 0:06:39.279 species of dinosaurs, the asteroid was the end of the line, 0:06:39.720 --> 0:06:48.960 the Kuda grass. They succumbed to their existential threat. We 0:06:49.000 --> 0:06:51.839 know all of this thanks to a father's son science 0:06:51.880 --> 0:06:56.200 team known as Luis and Walter Alvarez. As a geologist 0:06:56.240 --> 0:06:59.599 working in Italy in the seventies, Walter Alvarez found a 0:06:59.680 --> 0:07:02.800 thin layer of clay dating back to around sixty five 0:07:02.839 --> 0:07:07.240 million years before. It was peculiar because immediately below the 0:07:07.279 --> 0:07:10.040 strip of clay there was a wide variety of fossils 0:07:10.080 --> 0:07:13.880 of different types of forums, tiny single celled organisms that 0:07:13.920 --> 0:07:17.320 have shells, but right above the clay there was only 0:07:17.320 --> 0:07:21.800 one type. Forums are an excellent indicator species They eat 0:07:21.840 --> 0:07:24.640 plants and animals that degrade on the seafloor, and they 0:07:24.680 --> 0:07:28.080 are very sensitive to changes in the environment. If something 0:07:28.120 --> 0:07:31.679 happens to forums, it means that something happened to everything else, 0:07:32.800 --> 0:07:35.320 and something definitely did seem to have happened to the 0:07:35.320 --> 0:07:38.280 forums around the time that clay strip was deposited that 0:07:38.480 --> 0:07:43.600 drastically reduced their diversity. There was something similar among plants too. 0:07:44.160 --> 0:07:46.560 Just below the clay strip were fossils of a wide 0:07:46.600 --> 0:07:50.280 variety of plants, where just above there were only fern spores. 0:07:51.600 --> 0:07:53.840 Walter would have been surprised to know that the strip 0:07:53.880 --> 0:07:55.880 of clay he was scraping at with his trowel in 0:07:55.920 --> 0:08:01.640 the center of Italy was actually from Mexico. Walter had 0:08:01.640 --> 0:08:05.280 a very famous scientist, Dad Louise, a physicist who developed 0:08:05.280 --> 0:08:08.600 the first atomic bombs for the US, among many other things. 0:08:09.400 --> 0:08:12.280 By the late seventies. When Walter approached his father with 0:08:12.360 --> 0:08:15.520 the curious find of the clay strip, Louise worked at 0:08:15.520 --> 0:08:18.040 one of the national labs where he had some colleagues 0:08:18.040 --> 0:08:21.000 who ran a mess spectrometer. He asked them to take 0:08:21.040 --> 0:08:23.800 a look at the samples of the clay layer. What 0:08:23.880 --> 0:08:27.400 they found was surprising the clay layer contained about six 0:08:27.480 --> 0:08:30.400 hundred times more iridium than the layer above or below 0:08:30.440 --> 0:08:33.920 the clay. This is very weird because i ridium, which 0:08:33.960 --> 0:08:36.600 is a metal in the platinum family, isn't found much 0:08:36.600 --> 0:08:39.800 in Earth's crust. It certainly isn't found at six hundred 0:08:39.840 --> 0:08:44.040 times the background amount. It is, however, found in abundance 0:08:44.040 --> 0:08:48.920 on things like asteroids. As Walter started looking around the world, 0:08:49.000 --> 0:08:52.440 he found that same clay layer at other sites, and 0:08:52.480 --> 0:08:55.000 it had all the same characteristics as the first site 0:08:55.040 --> 0:08:59.240 in Italy. Iridium in aces in abrupt shift in diversity. 0:09:00.160 --> 0:09:03.720 By that time, paleontologists had already established that the dinosaurs 0:09:03.720 --> 0:09:06.840 had died out around sixty five or so million years earlier. 0:09:07.360 --> 0:09:12.280 The clay layers geological age matched that extinction precisely, But 0:09:12.360 --> 0:09:14.960 at the time, the prevailing theory was that it had 0:09:15.000 --> 0:09:18.320 been a million year period of volcanic activity that had 0:09:18.360 --> 0:09:21.760 been responsible for killing off the dinosaurs, all that gas 0:09:21.880 --> 0:09:25.200 erupting and poisoning the air and rain. But what the 0:09:25.200 --> 0:09:29.560 Alvarez Boys were seeing suggested an asteroid, a colossal one, 0:09:29.920 --> 0:09:32.440 one so colossal it had brought the Earth to the 0:09:32.480 --> 0:09:37.680 brink of near total extinction, and in their theory got 0:09:37.679 --> 0:09:39.800 a shot in the arm with the discovery of the 0:09:39.880 --> 0:09:42.960 chick s Aloub Crater on the Yukatamp Peninsula, the site 0:09:43.000 --> 0:09:47.480 of the destruction sixty six million years before. Eventually, the 0:09:47.559 --> 0:09:50.920 debate was laid to rest. In two thousand ten forty 0:09:50.920 --> 0:09:55.720 one scientists and fields like paleontology, astronomy, geology, and others 0:09:56.080 --> 0:09:59.280 released a review of the literature on the KT extinction 0:09:59.400 --> 0:10:02.559 in the astro evidence and concluded that it was in 0:10:02.600 --> 0:10:06.200 fact an asteroid that killed off the dinosaurs. It's as 0:10:06.240 --> 0:10:12.160 close as science comes to being settled. There's something that 0:10:12.240 --> 0:10:16.080 gets overshadowed by the story of the dinosaurs extinction. That 0:10:16.240 --> 0:10:20.560 life on Earth rebounded. Those smaller animals that could burrow 0:10:20.600 --> 0:10:24.120 and dive held fast and among all the darkness and death, 0:10:24.160 --> 0:10:28.480 they continued on. They reproduced and raised their young, and 0:10:28.559 --> 0:10:31.880 as the Earth slowly shook off that extraordinarily bad day, 0:10:32.280 --> 0:10:35.800 it became again a fertile place, a place friendly to life, 0:10:36.679 --> 0:10:39.680 and that bottle that created by the asteroid open wide, 0:10:39.800 --> 0:10:42.840 and life spread again and grew diverse. And from that 0:10:42.920 --> 0:10:46.520 calamity we humans arose amid the vacuum left by the 0:10:46.559 --> 0:10:51.720 sudden loss of life. The dinosaurs existential catastrophe proved to 0:10:51.760 --> 0:10:55.960 be our existential triumph, which is to say that life 0:10:56.000 --> 0:10:59.400 is tough and it is very, very difficult to extinguish 0:10:59.400 --> 0:11:03.040 it entirely in the coming centuries. That will be a 0:11:03.120 --> 0:11:21.559 mark in its favor. M hm hm. We humans are 0:11:21.559 --> 0:11:24.360 an earth bound species, and so whatever happens to Earth 0:11:24.440 --> 0:11:28.280 happens to us. Like the dinosaurs, we live under the 0:11:28.360 --> 0:11:32.000 threat of death from huge rocks traveling at unimaginable speeds 0:11:32.080 --> 0:11:36.080 hurtling toward us. But unlike the dinosaurs, we are in 0:11:36.080 --> 0:11:39.760 a position to do something about it. In the coming years. 0:11:39.840 --> 0:11:42.760 Is our technology to travel through space develops and we 0:11:42.880 --> 0:11:45.720 become capable of spreading out around our solar system and 0:11:45.720 --> 0:11:48.800 eventually our galaxy, we will have made the biggest shift 0:11:48.840 --> 0:11:51.480 in our species since at least when we settled down 0:11:51.480 --> 0:11:55.520 and began raising crops. That see change in human ecology. 0:11:55.880 --> 0:11:59.559 The advent of agriculture led to sweeping changes for humans. 0:12:00.160 --> 0:12:02.680 It was, as Nick Bostrom would put it, a pan 0:12:02.760 --> 0:12:07.439 generational change in how humans lived. By coaxing food from 0:12:07.440 --> 0:12:10.480 the ground on a predictable schedule, and by taming animals 0:12:10.480 --> 0:12:13.400 and creating a reliable supply of meat and milk. We 0:12:13.600 --> 0:12:17.560 changed a lot about ourselves, our bones, the shapes of 0:12:17.600 --> 0:12:20.440 our skulls, the workings of our guts, the color of 0:12:20.440 --> 0:12:24.920 our skin. And it changed our culture too. As anthropologist 0:12:25.000 --> 0:12:28.000 Jared Diamond points out in his nine seven essay The 0:12:28.040 --> 0:12:30.720 Worst Mistake in the History of the Human Race, about 0:12:30.760 --> 0:12:34.040 the advent of agriculture, we started to have a surplus 0:12:34.040 --> 0:12:37.680 of food, something that our hunter gatherer ancestors never would 0:12:37.679 --> 0:12:42.040 have experienced. This meant that some people had more than others, 0:12:42.080 --> 0:12:45.800 which creates an imbalance and power, and hence agriculture also 0:12:45.880 --> 0:12:49.040 led to things like kings and armies and social classes. 0:12:51.200 --> 0:12:54.960 When we settled down our cities developed. Agriculture can support 0:12:55.000 --> 0:12:57.760 more people than hunting and gathering, and the more people 0:12:57.800 --> 0:13:01.160 there are, the more brilliant ideas there are too, so 0:13:01.200 --> 0:13:04.160 our civilization began to advance by leaps and bounds in 0:13:04.160 --> 0:13:07.679 the last nine or ten thousand years. Ideas spread more 0:13:07.760 --> 0:13:10.600 quickly among those people who lived together in those new cities, 0:13:11.000 --> 0:13:13.560 so innovations were able to develop over the span of 0:13:13.600 --> 0:13:17.680 a handful of years rather than millennia. Almost everything we 0:13:17.760 --> 0:13:19.840 have in the world today can be traced back to 0:13:19.840 --> 0:13:24.080 our collective decision to settle down and raise crops. It was, 0:13:24.240 --> 0:13:27.080 to say the least, a sweeping change for us humans. 0:13:28.400 --> 0:13:31.440 With our next great leap spreading out into space, we 0:13:31.480 --> 0:13:34.240 are effectively doing the opposite of when we settled down 0:13:34.240 --> 0:13:39.240 into cities. Rather than contracting, we will be expanding from 0:13:39.280 --> 0:13:43.640 that huge coming together, we will spread out. Over time, 0:13:43.720 --> 0:13:47.160 humans will begin to colonize other planets, and generations of 0:13:47.200 --> 0:13:50.199 little human babies will be borne on planets other than Earth. 0:13:50.840 --> 0:13:53.720 They will be shaped by forces and experiences that no 0:13:53.880 --> 0:13:56.760 earth bound human will have ever encountered, and they will 0:13:56.800 --> 0:13:59.439 learn to adapt to their home planet just like we did. 0:14:00.280 --> 0:14:03.880 We are quite capable of becoming all the things that 0:14:03.920 --> 0:14:07.440 it's possible to become. Life that starts from us and 0:14:07.520 --> 0:14:10.079 radiates out can not only spread to different places, it 0:14:10.160 --> 0:14:14.199 can create different styles and techniques and cultures and approaches. 0:14:15.080 --> 0:14:17.240 All of the life that you see on Earth started 0:14:17.240 --> 0:14:19.800 out from a much smaller amount of variation, but with 0:14:19.880 --> 0:14:23.120 time it could explore lots of different niches and ways 0:14:23.120 --> 0:14:26.760 of living. And that's probably what would happen to us too. 0:14:26.800 --> 0:14:29.400 If we're the only life around it, we can survive, 0:14:30.040 --> 0:14:33.880 We will radiate, We will become diverse and different and 0:14:33.960 --> 0:14:38.320 fill thousand million billion different niches of different ways of being. 0:14:38.920 --> 0:14:41.760 Over time, perhaps their physical connection to humans on Earth 0:14:41.800 --> 0:14:45.520 will become distant enough that new species of humans will form, 0:14:45.560 --> 0:14:47.360 and the universe will be home to more than one 0:14:47.400 --> 0:14:51.160 species of human again, just as it was fifty years ago. 0:14:52.080 --> 0:14:55.680 We will become the aliens we seek, and later on 0:14:56.480 --> 0:14:58.600 they might be surprised to learn that they came from 0:14:58.640 --> 0:15:02.240 something that was simple and not as very It's odd 0:15:02.240 --> 0:15:05.680 to think of, but humans are in an evolutionary bottleneck 0:15:05.760 --> 0:15:09.360 of our own. Right now. There's only one species of us, 0:15:09.840 --> 0:15:12.480 and with the exception of maybe half a dozen astronauts 0:15:12.520 --> 0:15:15.760 on the International Space Station at any given time, we 0:15:15.840 --> 0:15:20.600 are all stranded on this island Earth. Those astronauts aboard 0:15:20.600 --> 0:15:23.400 the I s S showed just the faintest beginnings of 0:15:23.440 --> 0:15:27.440 our future. If we become a space faring species, all 0:15:27.480 --> 0:15:30.400 of humanities eggs will no longer be in just the 0:15:30.480 --> 0:15:34.360 one basket of Earth. Should some catastrophe befall those of 0:15:34.440 --> 0:15:37.360 us here on Earth, there will be other humans living 0:15:37.400 --> 0:15:40.920 elsewhere to carry on. We will begin to trickle from 0:15:40.920 --> 0:15:44.400 our bottle neck and spread throughout the universe, and when 0:15:44.400 --> 0:15:47.480 we do, we will have made it through the Great Filter. 0:15:48.840 --> 0:15:51.680 Colonizing beyond Earth is something we should begin working on 0:15:51.960 --> 0:15:55.160 as soon as we can, because Earth is vulnerable to 0:15:55.280 --> 0:15:59.280 a wide variety of catastrophes that are pretty hostile to life, 0:16:00.080 --> 0:16:04.000 things like exploding stars, the death of our Sun, even 0:16:04.080 --> 0:16:08.400 Earth's zone systems going haywire. Take our son for starters. 0:16:09.080 --> 0:16:12.800 Remember that Goldilocks zone, that habitable area around a star 0:16:12.880 --> 0:16:15.840 where a planet can sustain life. Earth is in the 0:16:15.880 --> 0:16:20.320 Sun's Goldilocks zone, but it's not a permanent position as 0:16:20.320 --> 0:16:23.120 a star. The Sun is currently in its main sequence. 0:16:23.760 --> 0:16:26.120 It has plenty of hydrogen atoms in its core that 0:16:26.160 --> 0:16:29.960 it fuses into helium, and these constant nuclear reactions release 0:16:30.040 --> 0:16:33.560 tremendous amounts of energy, which we gratefully accept as light 0:16:33.640 --> 0:16:37.120 and heat here on Earth. But the Sun is slowly 0:16:37.200 --> 0:16:40.640 using up its available fuel, and as it does, its 0:16:40.720 --> 0:16:44.920 core shrinks in size. That smaller core means that it's 0:16:44.960 --> 0:16:47.680 closer to the center of the Sun, which means that 0:16:47.720 --> 0:16:51.640 gravity exerts more force on it, making it denser. All 0:16:51.680 --> 0:16:54.480 of this is what one would expect, but we're talking 0:16:54.480 --> 0:16:57.680 about cosmic stuff here, and as with all cosmic stuff, 0:16:57.960 --> 0:17:02.360 something weird always happens to because the core grows denser 0:17:02.400 --> 0:17:05.199 as it grows smaller. That means more fuel is closer 0:17:05.240 --> 0:17:07.640 at hand for the Sun to burn, so its main 0:17:07.680 --> 0:17:11.280 sequence begins to speed up. It uses fuel more quickly, 0:17:11.640 --> 0:17:14.879 actually shortening its own lifespan, at least compared to what 0:17:14.920 --> 0:17:17.040 it would be if it managed to maintain a slow, 0:17:17.080 --> 0:17:20.879 steady burn during its entire life. As the Sun burns 0:17:20.920 --> 0:17:23.840 through its fuel supply more quickly, it's actually going to 0:17:23.880 --> 0:17:28.240 grow larger, much much larger, and about one point one 0:17:28.280 --> 0:17:30.399 billion years, the Earth will no longer be in the 0:17:30.400 --> 0:17:34.240 Sun's goldilocks song. It will be a lot closer, and 0:17:34.320 --> 0:17:38.240 it will keep getting closer from there. This is estrophysicist 0:17:38.280 --> 0:17:41.600 Ian O'Neill. When it goes through this end stage, when 0:17:41.640 --> 0:17:43.639 it starts to turn, is what's called a red giant, 0:17:43.840 --> 0:17:46.280 and it's pretty much a red giant is pretty descriptive. 0:17:46.280 --> 0:17:49.200 A boy, what's going to be. It will expand, possibly 0:17:49.280 --> 0:17:52.080 out to the orbit of Earth. So this the Sun 0:17:52.119 --> 0:17:55.879 will basically fill up our entire, our entire sky. You 0:17:55.880 --> 0:17:57.639 look out the window, it will just be a big 0:17:58.720 --> 0:18:02.439 seething mess of of star. So you can imagine that 0:18:02.480 --> 0:18:04.520 with the Sun right on top of Earth, there won't 0:18:04.520 --> 0:18:07.879 be much room for life, but billions of years before 0:18:07.920 --> 0:18:10.280 that point, the biggest issue will have to deal with 0:18:10.440 --> 0:18:14.040 is the increase in solar radiation. Sure, things will get 0:18:14.119 --> 0:18:17.080 much much hotter on Earth than they are today, but 0:18:17.160 --> 0:18:20.040 as with the fallout from the kt asteroid, there are 0:18:20.040 --> 0:18:25.440 places that some life could go underground, deep underwater. Sorry cows, 0:18:25.720 --> 0:18:29.920 sorry elephants, sorry feral pigs. Sure, but as we've seen, 0:18:30.000 --> 0:18:33.120 life is persistent. If anything, it would almost certainly find 0:18:33.119 --> 0:18:35.440 a way to adapt to the changes from the increased 0:18:35.480 --> 0:18:40.200 heat on Earth, at least at first. But the radiation 0:18:40.320 --> 0:18:42.960 from the growing Sun will be so intense that it 0:18:42.960 --> 0:18:46.320 will tear apart the very molecules that make up Earth's atmosphere. 0:18:47.000 --> 0:18:51.480 All aerobic life. Life that breathes oxygen would die, obviously, 0:18:52.000 --> 0:18:55.200 but even anaerobic life would find it impossible to continue 0:18:55.200 --> 0:18:59.119 on Earth without an atmosphere to regulate temperatures. The wild 0:18:59.160 --> 0:19:02.320 swings between tense heat and cold on a daily basis 0:19:02.480 --> 0:19:06.080 would evaporate the oceans, leaving Earth a dead, lifeless rock. 0:19:06.840 --> 0:19:11.280 A planet without an atmosphere is a dead planet. So 0:19:11.320 --> 0:19:13.640 we have a billion years to figure out either how 0:19:13.680 --> 0:19:16.480 to slow the Sun's burn right and vastly extend its 0:19:16.480 --> 0:19:19.919 main sequence, or how to live away from Earth, and 0:19:20.000 --> 0:19:22.399 the odds aren't that bad actually that we may be 0:19:22.480 --> 0:19:28.040 able to do both within that time. That same issue, 0:19:28.240 --> 0:19:31.080 a star reaching the end of its productive life poses 0:19:31.119 --> 0:19:34.439 another natural threat to Earth as well. Depending on the 0:19:34.600 --> 0:19:38.159 size or the type of the star, could explode at 0:19:38.200 --> 0:19:42.320 the end of its life. As a star nears the 0:19:42.440 --> 0:19:44.880 end of its life and its fuel core becomes denser 0:19:44.880 --> 0:19:47.880 and denser, the force of gravity acts ever more strongly 0:19:47.960 --> 0:19:50.280 on it, and just the same way as the singularity 0:19:50.280 --> 0:19:53.280 of a black hole. But a black hole singularity is 0:19:53.320 --> 0:19:56.240 so massive and so dense that the force of gravity 0:19:56.280 --> 0:19:59.159 acting on it actually presses it into the fabric of 0:19:59.160 --> 0:20:03.400 space time, creating a bottomless depression. Not all stars are 0:20:03.440 --> 0:20:06.560 as massive as this, though, so there are other outcomes 0:20:06.560 --> 0:20:08.919 that it can have within a black hole. One of 0:20:08.920 --> 0:20:13.680 those is a supernova. Over the star's lifespan, the nuclear 0:20:13.720 --> 0:20:17.520 fusion reactions that carried out left behind his byproducts increasingly 0:20:17.600 --> 0:20:22.560 heavier elements hydrogen fused into helium, helium fused into oxygen, 0:20:22.760 --> 0:20:26.360 oxygen fused into neon, and so on, until the elements 0:20:26.400 --> 0:20:28.399 the star burned towards the end of its life become 0:20:28.480 --> 0:20:32.359 heavy metals like iron and nickel, so eventually it will 0:20:32.400 --> 0:20:34.480 start to try and burn elements as big as a 0:20:34.720 --> 0:20:39.359 iron and any star the stars to try to fuse 0:20:39.520 --> 0:20:43.240 iron is basically on this deathbed. The force that holds 0:20:43.280 --> 0:20:45.800 the nuclei of these types of atoms together is so 0:20:45.840 --> 0:20:49.399 strong that they can't be fused together even by something 0:20:49.440 --> 0:20:52.800 like a star. But the force that gravity exerts on 0:20:52.840 --> 0:20:56.240 this extraordinarily dense core of iron and nickel is strong 0:20:56.400 --> 0:21:00.760 enough that it actually compresses the individual atoms, pushing them 0:21:00.760 --> 0:21:04.159 into tight, tiny balls. When the atoms that make up 0:21:04.200 --> 0:21:07.960 the core shrink, the core itself does as well, becoming denser, 0:21:08.359 --> 0:21:10.800 and so the force of gravity acts even more strongly 0:21:10.840 --> 0:21:14.119 on it, creating a feedback loop. The star's core, in 0:21:14.119 --> 0:21:17.679 other words, suddenly collapses. And all of this happens in 0:21:17.720 --> 0:21:20.879 the fraction of a second. So is this weird point 0:21:20.920 --> 0:21:25.960 where as soon as you hit iron, almost immediately within milliseconds, 0:21:26.000 --> 0:21:29.760 the star just fulls apart. It just the whole system 0:21:29.760 --> 0:21:32.919 in this core breaks down and it will undergo a 0:21:32.960 --> 0:21:36.119 core collapse. But since the star isn't massive enough to 0:21:36.160 --> 0:21:38.480 become a black hole, since one of the laws of 0:21:38.480 --> 0:21:41.199 physics is that matter cannot occupy the same space at 0:21:41.200 --> 0:21:44.040 the same time. There's a limit to how tightly packed 0:21:44.040 --> 0:21:47.080 the iron atoms at the star's core can become. When 0:21:47.160 --> 0:21:50.480 they reached that limit, the collapse suddenly stops, kind of 0:21:50.520 --> 0:21:53.359 like hitting a brick wall. All that force of the 0:21:53.400 --> 0:21:56.800 collapsing core has to go somewhere, though, and it reverberates 0:21:56.840 --> 0:22:00.520 back outward. Exploding in a supernova one of the most 0:22:00.560 --> 0:22:04.560 fantastic displays in the universe. All of the mass that 0:22:04.720 --> 0:22:08.000 star sheds is shot outward as energy, so much in fact, 0:22:08.240 --> 0:22:11.400 that planets that orbited the star just moments before may 0:22:11.400 --> 0:22:14.479 be blown out of their solar system into space if 0:22:14.480 --> 0:22:18.920 they're not outright destroyed. That is, tremendous amounts of light 0:22:18.960 --> 0:22:21.879 and heat are released. For a few minutes, the dying 0:22:21.920 --> 0:22:25.360 star can shine brighter than the combined luminosity of an 0:22:25.520 --> 0:22:29.879 entire galaxy. The explosion since tremendous amounts of heat and 0:22:30.000 --> 0:22:34.960 radiation spewing into space, bathing anything nearby with The only 0:22:35.000 --> 0:22:38.840 explosion in our universe larger than a supernova was the 0:22:38.880 --> 0:22:44.560 Big Bang. Sometimes, if the supernova is large enough, it 0:22:44.600 --> 0:22:48.119 can emit a gamma ray burst. Gamma radiation is the 0:22:48.160 --> 0:22:52.480 most energetic type of radiation on the electromagnetic spectrum. Gamma 0:22:52.560 --> 0:22:55.359 rays are so energetic that they excite any atom they 0:22:55.400 --> 0:22:58.520 come in contact with, causing the atom to move temporarily 0:22:58.560 --> 0:23:01.680 to its higher energy state, causing its a release energy 0:23:01.720 --> 0:23:04.520 itself as it moves back to its normal ground state. 0:23:05.440 --> 0:23:08.199 It's like gamma rays get everybody else wound up, and 0:23:08.240 --> 0:23:11.080 to calm down, everyone has to let out a little shout. 0:23:12.840 --> 0:23:16.080 Just thinking about this happening to an individual atom sounds 0:23:16.119 --> 0:23:19.080 like chaos. So you can imagine what a burst big 0:23:19.200 --> 0:23:22.520 enough to flood an entire planet with gamma radiation might be. Like, 0:23:24.200 --> 0:23:27.000 let's say, for argument's sake, that Earth just happens to 0:23:27.000 --> 0:23:29.480 be in the path of that beam of energy. A 0:23:29.560 --> 0:23:32.480 sudden flood of gamma radiation would burn those of us 0:23:32.480 --> 0:23:35.639 walking around on Earth's surface to a crisp Sadly, we 0:23:35.640 --> 0:23:40.280 would probably not all be transformed into incredible hulks. The 0:23:40.359 --> 0:23:42.840 life that did manage to survive the initial burst would 0:23:42.840 --> 0:23:46.000 have a rough time of it afterward. Gamma radiation is 0:23:46.040 --> 0:23:49.800 particularly good at burning away the ozone layer, the protective 0:23:49.800 --> 0:23:52.560 blanket of O three atoms that reflects most of the 0:23:52.560 --> 0:23:56.680 Sun's radiation. When flooded with energetic gamma rays, those O 0:23:56.880 --> 0:24:00.920 three molecules would destabilize and the ozone layer would deteriorate, 0:24:01.320 --> 0:24:04.240 leaving Earth exposed to the full brunt of ultra violet 0:24:04.359 --> 0:24:07.760 radiation from the Sun. UV from the Sun could be 0:24:07.760 --> 0:24:11.040 bad enough with the folows on layer, without it, it 0:24:11.040 --> 0:24:15.000 would be utterly catastrophic. The intensity of the UV would 0:24:15.040 --> 0:24:19.240 prove too much for even photosynthesis and plants, so, following 0:24:19.240 --> 0:24:22.040 the blueprints of the KT extinction, in a matter of 0:24:22.119 --> 0:24:25.000 days or weeks, the bottom of the food chain would collapse, 0:24:25.359 --> 0:24:27.800