Speaker 1: Existential risks aren't new to us. Ever since our species
Speaker 1: was born. There have always been lots of catastrophes ready
Speaker 1: and waiting to wipe the human race off the face
Speaker 1: of the earth. It's just that these risks are of
Speaker 1: our own making. The history of humanity is relatively brief,
Speaker 1: and we've been fortunate to have come along during a
Speaker 1: period of relative calm in Earth's history. Maybe we couldn't
Speaker 1: have come along had things been more tumultuous. Who knows,
Speaker 1: but there's something to bear in mind that pops up
Speaker 1: a lot when you look into existential threats. Whatever lessons
Speaker 1: the past may offer, it doesn't teach us enough about
Speaker 1: the future. Just because things have gone smoothly so far
Speaker 1: doesn't mean they will always go that way. Every so often,
Speaker 1: some massive catastrophe happens on Earth that brings life to
Speaker 1: the brink of extinction. There are a lot of things
Speaker 1: in space and on Earth that can devastate life. We
Speaker 1: call these natural existential risks. It's worth noting that we
Speaker 1: humans pose an existential threat to just about every other
Speaker 1: species that we share the planet with, but there are
Speaker 1: also natural catastrophes that pose a threat to all of us.
Speaker 1: Creatures living on Earth, including us humans. In this episode,
Speaker 1: we'll look at a few of them to get a
Speaker 1: feel for just how badly things can go on Earth.
Speaker 1: Let's travel back to one particular day during the most
Speaker 1: strictan age of the Upper Cretaceous period, about sixty six
Speaker 1: million years ago, give or take three hundred thousand years,
Speaker 1: and on this day, a light streaks across the sky
Speaker 1: above Earth. That light, it turns out, is an asteroid,
Speaker 1: six miles across, about the size of downtown Los Angeles,
Speaker 1: is traveling at about forty four thousand miles per hour,
Speaker 1: times faster than a bullet when it passes through the
Speaker 1: Earth's atmosphere as if it's not even there, and strikes
Speaker 1: the planet. The impact creates a blast with one hundred
Speaker 1: million megatons of energy. For comparison, the Czar BOMBA, the
Speaker 1: largest nuclear bomb that humans have ever detonated, was fifty megatons.
Speaker 1: One got past Jupiter, you could say. The asteroid strikes
Speaker 1: the Earth along what is now called the Yucatan, the
Speaker 1: spur like peninsula that juts out of southern Mexico into
Speaker 1: the Gulf. It drives itself into the Earth, digging out
Speaker 1: a crater a hundred and ten miles in diameter and
Speaker 1: nine miles deep, so deep, in fact, it nearly punctures
Speaker 1: a hole all the way through the crust. The impact
Speaker 1: is felt all over the world as enormous shocks of
Speaker 1: energy that travel along the borders between tectonic plates. This
Speaker 1: sets off earthquakes and volcanoes across Earth unimaginably large tsunamis
Speaker 1: from the Gulf of Mexico Wash as far north as St. Louis.
Speaker 1: The impact kicks a tremendous amount of earth and sea
Speaker 1: into the air. Boulders the size of cars are launched
Speaker 1: hundreds of miles from the impact site, as far away
Speaker 1: as Believes. The pressure and heat from the collision is
Speaker 1: so great that it instantly melts the rocky earth below.
Speaker 1: That melted rock sprays into the air, where it turns
Speaker 1: to glass before it can reach the ground. Continents away.
Speaker 1: Quartz is pressed into crazy angles, and minerals into tiny
Speaker 1: spheres of metal, And when the heavier bits among all
Speaker 1: that kicked up dirt and rock and metal come back down,
Speaker 1: it heats up. It brings a tremendous amount of energy
Speaker 1: with it, flash heating the Earth's surface, embroiling alive anything
Speaker 1: that can't take cover underground or underwater. And as the
Speaker 1: earthquakes and tsunamis raging across the Earth and the fire
Speaker 1: raining from the sky begin to subside, things go from
Speaker 1: bad to worse. The finer particles from all that pulverized
Speaker 1: earth and liquefied rock launched into space stay aloft, forming
Speaker 1: a vast globe spanning shroud that blocks out the Sun
Speaker 1: for months. Photosynthesis grants to a halt back on Earth.
Speaker 1: The world's plants can no longer make their food, and
Speaker 1: since they, in one way or another, feed the rest
Speaker 1: of life on Earth, everything is still alive begins to starve.
Speaker 1: But as bad as the asteroid makes things for life
Speaker 1: on Earth, it is made even worse by a fluke,
Speaker 1: a stroke of sheer bad luck. The Yucatan, the area
Speaker 1: where the asteroid strikes, is one of the most sulfur
Speaker 1: rich areas on Earth, and when that asteroid hit, as
Speaker 1: much as five hundred billion metric tons of sulfur instantly
Speaker 1: rose from deep inside the Earth up into the atmosphere,
Speaker 1: like dust rising from a table when a heavy book
Speaker 1: is dropped on it. In the sky, that sulfur mixes
Speaker 1: with water vapor and is bombarded by ultra violet radiation
Speaker 1: from the sun, so it becomes sulfur aerosol, the type
Speaker 1: of atmospheric pollution that just happens to be the most
Speaker 1: efficient at absorbing sunlight and blocking it from reaching the Earth.
Speaker 1: The sudden presence of aerosols in the sky makes the
Speaker 1: darkness complete. Sulfur aerosols also form acid rain and freshwater
Speaker 1: lakes and the surface of the oceans are poisoned by it.
Speaker 1: Life on Earth comes disturbingly close to total extinction. Millions
Speaker 1: of years later, humans will call this cataclysmic event the
Speaker 1: Cretaceous Tertiary extinction. It had such a profoundly colossal effect
Speaker 1: on the planet that it serves as the sudden and
Speaker 1: abrupt dividing line between one geological age, the Cretaceous, and
Speaker 1: the one that followed it, the Tertiary or Paleogene, as
Speaker 1: it's called these days. Around of the species alive on
Speaker 1: Earth at the time died during the event and the
Speaker 1: hard times that followed the asteroid's arrival. Three out of
Speaker 1: four species death swept across Earth and waves that lasted
Speaker 1: for tens of thousands of years. Those species that did
Speaker 1: manage to survive had an extremely hard time of it.
Speaker 1: They hung on by a thread. In many cases, they
Speaker 1: were whittled down to just a few individuals that were
Speaker 1: somehow able to carry on their species. Animals that were
Speaker 1: able to burrow to feed off the carcasses of the
Speaker 1: unlucky ones, and whatever plants still reached upward towards a
Speaker 1: sun that no longer shown. Those are the ancestors of
Speaker 1: everything alive on Earth today. We are descended from the
Speaker 1: toughest band of animals that ever lived. But for most
Speaker 1: species of dinosaurs, the asteroid was the end of the line,
Speaker 1: the Kuda grass. They succumbed to their existential threat. We
Speaker 1: know all of this thanks to a father's son science
Speaker 1: team known as Luis and Walter Alvarez. As a geologist
Speaker 1: working in Italy in the seventies, Walter Alvarez found a
Speaker 1: thin layer of clay dating back to around sixty five
Speaker 1: million years before. It was peculiar because immediately below the
Speaker 1: strip of clay there was a wide variety of fossils
Speaker 1: of different types of forums, tiny single celled organisms that
Speaker 1: have shells, but right above the clay there was only
Speaker 1: one type. Forums are an excellent indicator species They eat
Speaker 1: plants and animals that degrade on the seafloor, and they
Speaker 1: are very sensitive to changes in the environment. If something
Speaker 1: happens to forums, it means that something happened to everything else,
Speaker 1: and something definitely did seem to have happened to the
Speaker 1: forums around the time that clay strip was deposited that
Speaker 1: drastically reduced their diversity. There was something similar among plants too.
Speaker 1: Just below the clay strip were fossils of a wide
Speaker 1: variety of plants, where just above there were only fern spores.
Speaker 1: Walter would have been surprised to know that the strip
Speaker 1: of clay he was scraping at with his trowel in
Speaker 1: the center of Italy was actually from Mexico. Walter had
Speaker 1: a very famous scientist, Dad Louise, a physicist who developed
Speaker 1: the first atomic bombs for the US, among many other things.
Speaker 1: By the late seventies. When Walter approached his father with
Speaker 1: the curious find of the clay strip, Louise worked at
Speaker 1: one of the national labs where he had some colleagues
Speaker 1: who ran a mess spectrometer. He asked them to take
Speaker 1: a look at the samples of the clay layer. What
Speaker 1: they found was surprising the clay layer contained about six
Speaker 1: hundred times more iridium than the layer above or below
Speaker 1: the clay. This is very weird because i ridium, which
Speaker 1: is a metal in the platinum family, isn't found much
Speaker 1: in Earth's crust. It certainly isn't found at six hundred
Speaker 1: times the background amount. It is, however, found in abundance
Speaker 1: on things like asteroids. As Walter started looking around the world,
Speaker 1: he found that same clay layer at other sites, and
Speaker 1: it had all the same characteristics as the first site
Speaker 1: in Italy. Iridium in aces in abrupt shift in diversity.
Speaker 1: By that time, paleontologists had already established that the dinosaurs
Speaker 1: had died out around sixty five or so million years earlier.
Speaker 1: The clay layers geological age matched that extinction precisely, But
Speaker 1: at the time, the prevailing theory was that it had
Speaker 1: been a million year period of volcanic activity that had
Speaker 1: been responsible for killing off the dinosaurs, all that gas
Speaker 1: erupting and poisoning the air and rain. But what the
Speaker 1: Alvarez Boys were seeing suggested an asteroid, a colossal one,
Speaker 1: one so colossal it had brought the Earth to the
Speaker 1: brink of near total extinction, and in their theory got
Speaker 1: a shot in the arm with the discovery of the
Speaker 1: chick s Aloub Crater on the Yukatamp Peninsula, the site
Speaker 1: of the destruction sixty six million years before. Eventually, the
Speaker 1: debate was laid to rest. In two thousand ten forty
Speaker 1: one scientists and fields like paleontology, astronomy, geology, and others
Speaker 1: released a review of the literature on the KT extinction
Speaker 1: in the astro evidence and concluded that it was in
Speaker 1: fact an asteroid that killed off the dinosaurs. It's as
Speaker 1: close as science comes to being settled. There's something that
Speaker 1: gets overshadowed by the story of the dinosaurs extinction. That
Speaker 1: life on Earth rebounded. Those smaller animals that could burrow
Speaker 1: and dive held fast and among all the darkness and death,
Speaker 1: they continued on. They reproduced and raised their young, and
Speaker 1: as the Earth slowly shook off that extraordinarily bad day,
Speaker 1: it became again a fertile place, a place friendly to life,
Speaker 1: and that bottle that created by the asteroid open wide,
Speaker 1: and life spread again and grew diverse. And from that
Speaker 1: calamity we humans arose amid the vacuum left by the
Speaker 1: sudden loss of life. The dinosaurs existential catastrophe proved to
Speaker 1: be our existential triumph, which is to say that life
Speaker 1: is tough and it is very, very difficult to extinguish
Speaker 1: it entirely in the coming centuries. That will be a
Speaker 1: mark in its favor. M hm hm. We humans are
Speaker 1: an earth bound species, and so whatever happens to Earth
Speaker 1: happens to us. Like the dinosaurs, we live under the
Speaker 1: threat of death from huge rocks traveling at unimaginable speeds
Speaker 1: hurtling toward us. But unlike the dinosaurs, we are in
Speaker 1: a position to do something about it. In the coming years.
Speaker 1: Is our technology to travel through space develops and we
Speaker 1: become capable of spreading out around our solar system and
Speaker 1: eventually our galaxy, we will have made the biggest shift
Speaker 1: in our species since at least when we settled down
Speaker 1: and began raising crops. That see change in human ecology.
Speaker 1: The advent of agriculture led to sweeping changes for humans.
Speaker 1: It was, as Nick Bostrom would put it, a pan
Speaker 1: generational change in how humans lived. By coaxing food from
Speaker 1: the ground on a predictable schedule, and by taming animals
Speaker 1: and creating a reliable supply of meat and milk. We
Speaker 1: changed a lot about ourselves, our bones, the shapes of
Speaker 1: our skulls, the workings of our guts, the color of
Speaker 1: our skin. And it changed our culture too. As anthropologist
Speaker 1: Jared Diamond points out in his nine seven essay The
Speaker 1: Worst Mistake in the History of the Human Race, about
Speaker 1: the advent of agriculture, we started to have a surplus
Speaker 1: of food, something that our hunter gatherer ancestors never would
Speaker 1: have experienced. This meant that some people had more than others,
Speaker 1: which creates an imbalance and power, and hence agriculture also
Speaker 1: led to things like kings and armies and social classes.
Speaker 1: When we settled down our cities developed. Agriculture can support
Speaker 1: more people than hunting and gathering, and the more people
Speaker 1: there are, the more brilliant ideas there are too, so
Speaker 1: our civilization began to advance by leaps and bounds in
Speaker 1: the last nine or ten thousand years. Ideas spread more
Speaker 1: quickly among those people who lived together in those new cities,
Speaker 1: so innovations were able to develop over the span of
Speaker 1: a handful of years rather than millennia. Almost everything we
Speaker 1: have in the world today can be traced back to
Speaker 1: our collective decision to settle down and raise crops. It was,
Speaker 1: to say the least, a sweeping change for us humans.
Speaker 1: With our next great leap spreading out into space, we
Speaker 1: are effectively doing the opposite of when we settled down
Speaker 1: into cities. Rather than contracting, we will be expanding from
Speaker 1: that huge coming together, we will spread out. Over time,
Speaker 1: humans will begin to colonize other planets, and generations of
Speaker 1: little human babies will be borne on planets other than Earth.
Speaker 1: They will be shaped by forces and experiences that no
Speaker 1: earth bound human will have ever encountered, and they will
Speaker 1: learn to adapt to their home planet just like we did.
Speaker 1: We are quite capable of becoming all the things that
Speaker 1: it's possible to become. Life that starts from us and
Speaker 1: radiates out can not only spread to different places, it
Speaker 1: can create different styles and techniques and cultures and approaches.
Speaker 1: All of the life that you see on Earth started
Speaker 1: out from a much smaller amount of variation, but with
Speaker 1: time it could explore lots of different niches and ways
Speaker 1: of living. And that's probably what would happen to us too.
Speaker 1: If we're the only life around it, we can survive,
Speaker 1: We will radiate, We will become diverse and different and
Speaker 1: fill thousand million billion different niches of different ways of being.
Speaker 1: Over time, perhaps their physical connection to humans on Earth
Speaker 1: will become distant enough that new species of humans will form,
Speaker 1: and the universe will be home to more than one
Speaker 1: species of human again, just as it was fifty years ago.
Speaker 1: We will become the aliens we seek, and later on
Speaker 1: they might be surprised to learn that they came from
Speaker 1: something that was simple and not as very It's odd
Speaker 1: to think of, but humans are in an evolutionary bottleneck
Speaker 1: of our own. Right now. There's only one species of us,
Speaker 1: and with the exception of maybe half a dozen astronauts
Speaker 1: on the International Space Station at any given time, we
Speaker 1: are all stranded on this island Earth. Those astronauts aboard
Speaker 1: the I s S showed just the faintest beginnings of
Speaker 1: our future. If we become a space faring species, all
Speaker 1: of humanities eggs will no longer be in just the
Speaker 1: one basket of Earth. Should some catastrophe befall those of
Speaker 1: us here on Earth, there will be other humans living
Speaker 1: elsewhere to carry on. We will begin to trickle from
Speaker 1: our bottle neck and spread throughout the universe, and when
Speaker 1: we do, we will have made it through the Great Filter.
Speaker 1: Colonizing beyond Earth is something we should begin working on
Speaker 1: as soon as we can, because Earth is vulnerable to
Speaker 1: a wide variety of catastrophes that are pretty hostile to life,
Speaker 1: things like exploding stars, the death of our Sun, even
Speaker 1: Earth's zone systems going haywire. Take our son for starters.
Speaker 1: Remember that Goldilocks zone, that habitable area around a star
Speaker 1: where a planet can sustain life. Earth is in the
Speaker 1: Sun's Goldilocks zone, but it's not a permanent position as
Speaker 1: a star. The Sun is currently in its main sequence.
Speaker 1: It has plenty of hydrogen atoms in its core that
Speaker 1: it fuses into helium, and these constant nuclear reactions release
Speaker 1: tremendous amounts of energy, which we gratefully accept as light
Speaker 1: and heat here on Earth. But the Sun is slowly
Speaker 1: using up its available fuel, and as it does, its
Speaker 1: core shrinks in size. That smaller core means that it's
Speaker 1: closer to the center of the Sun, which means that
Speaker 1: gravity exerts more force on it, making it denser. All
Speaker 1: of this is what one would expect, but we're talking
Speaker 1: about cosmic stuff here, and as with all cosmic stuff,
Speaker 1: something weird always happens to because the core grows denser
Speaker 1: as it grows smaller. That means more fuel is closer
Speaker 1: at hand for the Sun to burn, so its main
Speaker 1: sequence begins to speed up. It uses fuel more quickly,
Speaker 1: actually shortening its own lifespan, at least compared to what
Speaker 1: it would be if it managed to maintain a slow,
Speaker 1: steady burn during its entire life. As the Sun burns
Speaker 1: through its fuel supply more quickly, it's actually going to
Speaker 1: grow larger, much much larger, and about one point one
Speaker 1: billion years, the Earth will no longer be in the
Speaker 1: Sun's goldilocks song. It will be a lot closer, and
Speaker 1: it will keep getting closer from there. This is estrophysicist
Speaker 1: Ian O'Neill. When it goes through this end stage, when
Speaker 1: it starts to turn, is what's called a red giant,
Speaker 1: and it's pretty much a red giant is pretty descriptive.
Speaker 1: A boy, what's going to be. It will expand, possibly
Speaker 1: out to the orbit of Earth. So this the Sun
Speaker 1: will basically fill up our entire, our entire sky. You
Speaker 1: look out the window, it will just be a big
Speaker 1: seething mess of of star. So you can imagine that
Speaker 1: with the Sun right on top of Earth, there won't
Speaker 1: be much room for life, but billions of years before
Speaker 1: that point, the biggest issue will have to deal with
Speaker 1: is the increase in solar radiation. Sure, things will get
Speaker 1: much much hotter on Earth than they are today, but
Speaker 1: as with the fallout from the kt asteroid, there are
Speaker 1: places that some life could go underground, deep underwater. Sorry cows,
Speaker 1: sorry elephants, sorry feral pigs. Sure, but as we've seen,
Speaker 1: life is persistent. If anything, it would almost certainly find
Speaker 1: a way to adapt to the changes from the increased
Speaker 1: heat on Earth, at least at first. But the radiation
Speaker 1: from the growing Sun will be so intense that it
Speaker 1: will tear apart the very molecules that make up Earth's atmosphere.
Speaker 1: All aerobic life. Life that breathes oxygen would die, obviously,
Speaker 1: but even anaerobic life would find it impossible to continue
Speaker 1: on Earth without an atmosphere to regulate temperatures. The wild
Speaker 1: swings between tense heat and cold on a daily basis
Speaker 1: would evaporate the oceans, leaving Earth a dead, lifeless rock.
Speaker 1: A planet without an atmosphere is a dead planet. So
Speaker 1: we have a billion years to figure out either how
Speaker 1: to slow the Sun's burn right and vastly extend its
Speaker 1: main sequence, or how to live away from Earth, and
Speaker 1: the odds aren't that bad actually that we may be
Speaker 1: able to do both within that time. That same issue,
Speaker 1: a star reaching the end of its productive life poses
Speaker 1: another natural threat to Earth as well. Depending on the
Speaker 1: size or the type of the star, could explode at
Speaker 1: the end of its life. As a star nears the
Speaker 1: end of its life and its fuel core becomes denser
Speaker 1: and denser, the force of gravity acts ever more strongly
Speaker 1: on it, and just the same way as the singularity
Speaker 1: of a black hole. But a black hole singularity is
Speaker 1: so massive and so dense that the force of gravity
Speaker 1: acting on it actually presses it into the fabric of
Speaker 1: space time, creating a bottomless depression. Not all stars are
Speaker 1: as massive as this, though, so there are other outcomes
Speaker 1: that it can have within a black hole. One of
Speaker 1: those is a supernova. Over the star's lifespan, the nuclear
Speaker 1: fusion reactions that carried out left behind his byproducts increasingly
Speaker 1: heavier elements hydrogen fused into helium, helium fused into oxygen,
Speaker 1: oxygen fused into neon, and so on, until the elements
Speaker 1: the star burned towards the end of its life become
Speaker 1: heavy metals like iron and nickel, so eventually it will
Speaker 1: start to try and burn elements as big as a
Speaker 1: iron and any star the stars to try to fuse
Speaker 1: iron is basically on this deathbed. The force that holds
Speaker 1: the nuclei of these types of atoms together is so
Speaker 1: strong that they can't be fused together even by something
Speaker 1: like a star. But the force that gravity exerts on
Speaker 1: this extraordinarily dense core of iron and nickel is strong
Speaker 1: enough that it actually compresses the individual atoms, pushing them
Speaker 1: into tight, tiny balls. When the atoms that make up
Speaker 1: the core shrink, the core itself does as well, becoming denser,
Speaker 1: and so the force of gravity acts even more strongly
Speaker 1: on it, creating a feedback loop. The star's core, in
Speaker 1: other words, suddenly collapses. And all of this happens in
Speaker 1: the fraction of a second. So is this weird point
Speaker 1: where as soon as you hit iron, almost immediately within milliseconds,
Speaker 1: the star just fulls apart. It just the whole system
Speaker 1: in this core breaks down and it will undergo a
Speaker 1: core collapse. But since the star isn't massive enough to
Speaker 1: become a black hole, since one of the laws of
Speaker 1: physics is that matter cannot occupy the same space at
Speaker 1: the same time. There's a limit to how tightly packed
Speaker 1: the iron atoms at the star's core can become. When
Speaker 1: they reached that limit, the collapse suddenly stops, kind of
Speaker 1: like hitting a brick wall. All that force of the
Speaker 1: collapsing core has to go somewhere, though, and it reverberates
Speaker 1: back outward. Exploding in a supernova one of the most
Speaker 1: fantastic displays in the universe. All of the mass that
Speaker 1: star sheds is shot outward as energy, so much in fact,
Speaker 1: that planets that orbited the star just moments before may
Speaker 1: be blown out of their solar system into space if
Speaker 1: they're not outright destroyed. That is, tremendous amounts of light
Speaker 1: and heat are released. For a few minutes, the dying
Speaker 1: star can shine brighter than the combined luminosity of an
Speaker 1: entire galaxy. The explosion since tremendous amounts of heat and
Speaker 1: radiation spewing into space, bathing anything nearby with The only
Speaker 1: explosion in our universe larger than a supernova was the
Speaker 1: Big Bang. Sometimes, if the supernova is large enough, it
Speaker 1: can emit a gamma ray burst. Gamma radiation is the
Speaker 1: most energetic type of radiation on the electromagnetic spectrum. Gamma
Speaker 1: rays are so energetic that they excite any atom they
Speaker 1: come in contact with, causing the atom to move temporarily
Speaker 1: to its higher energy state, causing its a release energy
Speaker 1: itself as it moves back to its normal ground state.
Speaker 1: It's like gamma rays get everybody else wound up, and
Speaker 1: to calm down, everyone has to let out a little shout.
Speaker 1: Just thinking about this happening to an individual atom sounds
Speaker 1: like chaos. So you can imagine what a burst big
Speaker 1: enough to flood an entire planet with gamma radiation might be. Like,
Speaker 1: let's say, for argument's sake, that Earth just happens to
Speaker 1: be in the path of that beam of energy. A
Speaker 1: sudden flood of gamma radiation would burn those of us
Speaker 1: walking around on Earth's surface to a crisp Sadly, we
Speaker 1: would probably not all be transformed into incredible hulks. The
Speaker 1: life that did manage to survive the initial burst would
Speaker 1: have a rough time of it afterward. Gamma radiation is
Speaker 1: particularly good at burning away the ozone layer, the protective
Speaker 1: blanket of O three atoms that reflects most of the
Speaker 1: Sun's radiation. When flooded with energetic gamma rays, those O
Speaker 1: three molecules would destabilize and the ozone layer would deteriorate,
Speaker 1: leaving Earth exposed to the full brunt of ultra violet
Speaker 1: radiation from the Sun. UV from the Sun could be
Speaker 1: bad enough with the folows on layer, without it, it
Speaker 1: would be utterly catastrophic. The intensity of the UV would
Speaker 1: prove too much for even photosynthesis and plants, so, following
Speaker 1: the blueprints of the KT extinction, in a matter of
Speaker 1: days or weeks, the bottom of the food chain would collapse,
Speaker 1: and everything else above it would starve. As a result,
Speaker 1: the oceans too would be crippled by the increase in UV.
Speaker 1: It would destroy the plankton that makes up the basis
Speaker 1: of the marine food webs. The effect would be pronounced
Speaker 1: enough that a gamma ray burst is considered to be
Speaker 1: able to sterilize a planet close enough in its path,
Speaker 1: and it's possible that the Earth has experienced them before.
Speaker 1: One theory for the Ordovician extinction four hundred and forty
Speaker 1: million years ago is that Earth got in the way
Speaker 1: of a gamma ray bursts. As majestically dangerous as they
Speaker 1: are gamma ray burst upened in the universe once a
Speaker 1: day at least, well that's how often we noticed them
Speaker 1: since the nineteen sixties. I should say humans have been
Speaker 1: aware of supernova for thousands of years, first noting the
Speaker 1: appearance of bright new stars in China almost two thousand
Speaker 1: years ago. But we spent the entire lifespan of our
Speaker 1: species up until the nineteen sixties blissfully unaware that invisible
Speaker 1: death rays went off in our universe at all. It
Speaker 1: was all because of the Cold War that we ever
Speaker 1: found them. In ninety three, the US the USS are
Speaker 1: in Great Britain signed a treaty banning nuclear detonations in
Speaker 1: the atmosphere, underwater or in outer space. But we didn't
Speaker 1: precisely trust our comrades, and so the US launched the
Speaker 1: satellite capable of detecting large sudden spikes and nuclear radiation,
Speaker 1: and the satellite found it. But it wasn't from nuclear
Speaker 1: tests that satellite provided the first evidence of gamma ray bursts,
Speaker 1: and since then we found that they are extremely common.
Speaker 1: Stars collapse all the time. It seems the universe is
Speaker 1: full of rocks and collapsing stars and gamma ray bursts,
Speaker 1: which by the way. It can also form from two
Speaker 1: black holes merging, or from the hiccup of an exotic
Speaker 1: and frightening type of star called magnet Or, which is
Speaker 1: a type of dwarf star made of nickel. It's been
Speaker 1: hundreds of times per second and produces the strongest magnetic
Speaker 1: field in the universe. This is a dangerous place out there.
Speaker 1: I mean that the universe is has got no care
Speaker 1: for life on Earth, and and I think that it's
Speaker 1: worth remembering that when you look up in the nice sky,
Speaker 1: when it looks very you know, peaceful and static, and
Speaker 1: and it's unlook particularly dangerous. Being alive in the twenty
Speaker 1: one century. You're probably fairly well versed in the basics
Speaker 1: of climate change. We all are, and whether you believe
Speaker 1: humans contribute to it or not, it's plain to everyone
Speaker 1: that has advanced as we've become, we are still very
Speaker 1: much at the mercy of the Earth's climate. All of
Speaker 1: the bad news about climate change, though it seems incremental,
Speaker 1: a few degrees increase in temperature here, a couple of
Speaker 1: feet of sea level rise there, it just seems so well,
Speaker 1: I hate to say it, but distant, distant and sort
Speaker 1: of non threatening. Now there's a whole series I could
Speaker 1: do just on how those sentiments aren't correct at all.
Speaker 1: But enough doubt has been sown that it feels like
Speaker 1: we have the luxury of time to keep arguing about
Speaker 1: something as silly as whether humans are contributing in a
Speaker 1: climate change or not, but whether you believe we do
Speaker 1: or not, and we definitely do, there's something you should
Speaker 1: know about climate change. Earth has a point of no
Speaker 1: return climate wise, and should we find that we've pushed
Speaker 1: it past that point, we would also find, to our
Speaker 1: great peril that the changing climate would be neither distant
Speaker 1: nor non threatening. With an overabundance of carbon dioxide, the
Speaker 1: atmosphere could become a blanket that traps heat from escaping
Speaker 1: into space, heating Earth up to an unbearable degree. Literally,
Speaker 1: it's called a runaway greenhouse effect. If you were alive
Speaker 1: in the nineties, you were introduced to the greenhouse effected
Speaker 1: byproduct of climate change that can lead to global warming.
Speaker 1: The basics are that as we burn more fossil fuels,
Speaker 1: we contribute new large amounts of carbon dioxide to the
Speaker 1: atmosphere that wouldn't otherwise be there. They would still be
Speaker 1: locked underground as deposits of oil and gas. When sunlight
Speaker 1: shines on Earth, the planet absorbs some of it and
Speaker 1: is warmed by it, but it also re emits some
Speaker 1: of it back into space as infrared heat. The trouble
Speaker 1: is CO two is an extremely efficient absorber of that
Speaker 1: infrared heat. When there's a lot of CO two in
Speaker 1: the atmosphere, the atmosphere is a whole warms, so we
Speaker 1: end up with a warm planet and a warmer than
Speaker 1: normal atmosphere. Things become warmer all around, but when temperatures
Speaker 1: rise on Earth, the planet just releases more radiated heat,
Speaker 1: and so eventually temperature is cool again. It's as if
Speaker 1: Earth overwhelms the CEO two in the atmosphere with sheer
Speaker 1: multitudes of infrared. There's just not enough CEO two to
Speaker 1: trap it all, and the planet overcomes the greenhouse effect
Speaker 1: easy peasy. But there's a limit to how much heat
Speaker 1: Earth can release into space, and so once the planet
Speaker 1: reaches the point where it can emit no more infrared.
Speaker 1: As c O two levels continue to rise, the tables
Speaker 1: can turn, and it can be the carbon dioxide that
Speaker 1: overwhelms Earth. A runaway greenhouse effect is triggered when a
Speaker 1: positive feedback loop arises. As the planet grows warmer, more
Speaker 1: water evaporates from the surface of the oceans. Water vapor
Speaker 1: is also particularly good at absorbing reflected heat and trapping
Speaker 1: it in the atmosphere, So the atmosphere goes even warmer,
Speaker 1: causing more of the oceans to evaporate, adding more water
Speaker 1: vapor to the atmosphere, trapping more escaping heat, warming the
Speaker 1: planet even more and evaporating more of the oceans. Eventually,
Speaker 1: it reaches a point where the entire planet becomes so
Speaker 1: hot that the oceans boil off. You will be relieved
Speaker 1: to hear that there is a point where the feedback
Speaker 1: loop is broken and the runaway greenhouse effect ends. But
Speaker 1: I regret to say that that doesn't happen until the
Speaker 1: atmospheric temperature reaches about three thousand degrees fahrenheit, when the
Speaker 1: emitted heat moves to a wavelength that water vapor is
Speaker 1: incapable of absorbing. Long before that we humans would have
Speaker 1: ceased to exist, and eventually, with the oceans boiled off,
Speaker 1: any life hanging on in the seas would meet the
Speaker 1: same fate as us. This is what astronomers believe happened
Speaker 1: to Venus Venus is about the same size as Earth,
Speaker 1: but it's far closer to the Sun, and it's not
Speaker 1: within the Goldilocks zone. It's not the closest planet to
Speaker 1: the Sun. That distinction goes to Mercury, but it is
Speaker 1: the hottest planet in the entire Solar System by far,
Speaker 1: are despite being almost twenty eight million miles further away
Speaker 1: from the Sun than Mercury is. Venus is average surface
Speaker 1: temperature of eight hundred and sixty four degrees fahrenheit is
Speaker 1: hundreds of degrees hotter than Mercuries, hot enough to melt
Speaker 1: let that's because Venus has an atmosphere thick with CEO two.
Speaker 1: On the surface of the planet. The atmospheric pressure is
Speaker 1: almost a hundred times that of Earth's at sea level,
Speaker 1: about what you would experienced three thousand feet underwater in
Speaker 1: one of Earth's oceans. There's no surface water on Venus
Speaker 1: that evaporated away eons ago, but at some point in
Speaker 1: its distant past, Venus may have been habitable. It is
Speaker 1: to our great fortune that natural existential risks seem to
Speaker 1: be rare. This is philosopher Toby ord. Humanity has survived
Speaker 1: about two thousand centuries so far, so that's two thousand
Speaker 1: centuries worth of natural risk. Asteroid comments, supervolcanos, supernovas, everything
Speaker 1: put together that could have killed humanity. We've survived two
Speaker 1: thousand centuries of that risk. UH. And this, this fact
Speaker 1: allows us to put a bound on how much risk
Speaker 1: these natural things could be causing UH. And if you
Speaker 1: do the mathematics on this, you can show that it
Speaker 1: can't be much higher than about one in a thousand
Speaker 1: chance of extinction per century from natural causes, which works
Speaker 1: out to a point zero zero one percent chance of
Speaker 1: humanity going extinct from natural risks during any given year,
Speaker 1: a thousandth of a percent, not too menacing. Most atmospheric
Speaker 1: models show that human contributed CEO two definitely exacerbates the
Speaker 1: greenhouse effect, but that it would be extremely unlikely that
Speaker 1: we humans could push it into a runaway greenhouse. In
Speaker 1: the paper where they introduced the world to the concept
Speaker 1: of a dinosaur killing asteroid, the alvarez Is and their
Speaker 1: colleagues calculated how frequently such a catastrophic event might take place.
Speaker 1: They concluded that an asteroid with that scope of devastation
Speaker 1: might come along once every hundred million years, which would
Speaker 1: leave us with around thirty four million years left on
Speaker 1: the clock before we can expect a similarly destructive asteroid.
Speaker 1: With something approaching certainty. A gamma ray burst close enough
Speaker 1: to Earth to cause a mass extinction might happen once
Speaker 1: every billion years, and Earth would have to be lined
Speaker 1: up in the path of the relatively narrow beam of
Speaker 1: gamma radiation to experience the full effect. There are stars
Speaker 1: nearby that could collapse in supernova, but the closest I
Speaker 1: k pegasy A isn't expected to for another five million years.
Speaker 1: The next two closest and Terris and Beetlejuice, could explode
Speaker 1: at any time in the next million years, but it
Speaker 1: should be too far away to damage Earth. And again,
Speaker 1: the Sun has more than a billion years before it
Speaker 1: reaches the end of its main sequence and begins to
Speaker 1: grow unbearably hot for us. But it pays to keep
Speaker 1: an open mind. It is entirely possible that our current
Speaker 1: understanding of these risks is flawed in some way or incomplete,
Speaker 1: that there's some factor we're not aware of yet that
Speaker 1: could make any one of these disasters much more likely.
Speaker 1: In that slight, limital space of uncertainty is where existential
Speaker 1: risks live. The chances of them happening are minuscule, but
Speaker 1: the consequences they bring if they do, are so catastrophic
Speaker 1: that they demand to be taken into account. Atmospheric scientists,
Speaker 1: for example, don't understand the extraordinarily complex interactions that make
Speaker 1: up Earth's atmosphere, and so maybe we could accidentally trigger
Speaker 1: a runaway greenhouse effect by burning fossil fuels. It's unlikely,
Speaker 1: but it's unlikely under our current understanding, and with the
Speaker 1: addition of information that understanding can change. Human misunderstanding doesn't
Speaker 1: prevent calamity. In fact, it makes it like clear. But
Speaker 1: here's the thing about natural existential risks. Being earth bound,
Speaker 1: we can't do much about them right now. In the future,
Speaker 1: we will, our artificial intelligence will be able to predict
Speaker 1: gamma ray bursts to give us plenty of warning. Our
Speaker 1: spacecraft will be able to ferry us around a safer planets,
Speaker 1: and maybe we'll build structures to capture the energy from
Speaker 1: those bursts and store it for later. But so long
Speaker 1: as we remain bound to Earth, we will be vulnerable
Speaker 1: to the same threats that it is. More so, really,
Speaker 1: Earth is likelier to bounce back from a cataclysmic asteroid
Speaker 1: or a gamma ray burst than we are. But there's
Speaker 1: an entirely different class of existential risks, ones that we
Speaker 1: have a much greater chance of controlling because they are
Speaker 1: of our own making, but also ones that pose significantly
Speaker 1: greater danger. These are anthropogenic existential risks. Anthropogenic risks. However,
Speaker 1: um we can't apply such an argument to bound the probabilities,
Speaker 1: and to show that there must be quite small. I
Speaker 1: would say that there's maybe something like if there was
Speaker 1: something like a risk of extinction from anthropogenic causes in
Speaker 1: the twentieth century, this century, I think it's it's growing.
Speaker 1: My best guest would be something like one and six
Speaker 1: Russian Roulette, and then next century, well, if we don't
Speaker 1: get our act together even higher. Those technologies that pose
Speaker 1: an anthropogenic risk to us, we're beginning to develop them
Speaker 1: right now. Some are already here and almost know what
Speaker 1: is paying attention to the danger they are bringing our way.
Speaker 1: On the next episode of the End of the World
Speaker 1: with Josh Clark, it was a cold, windy day in
Speaker 1: January nine when the robots took their first human life.
Speaker 1: As we create more intelligent algorithms that are capable of
Speaker 1: improving themselves, we run the risk that they may take
Speaker 1: over their own development and quickly evolved beyond our control.
Speaker 1: There is no good outcome for us if that happens.