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November 14, 2018 37 mins

Humans have faced existential risks since our species was born. Because we are Earthbound, what happens to Earth happens to us. Josh points out that there’s a lot that can happen to Earth - like gamma ray bursts, supernovae, and runaway greenhouse effect. (Original score by Point Lobo.) 

Interviewees: Robin Hanson, George Mason University economist (creator of the Great Filter hypothesis); Ian O’Neill, astrophysicist and science writer; Toby Ord, Oxford University philosopher.

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Episode Transcript

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Speaker 1 (00:03):
Existential risks aren't new to us. Ever since our species
was born. There have always been lots of catastrophes ready
and waiting to wipe the human race off the face
of the earth. It's just that these risks are of
our own making. The history of humanity is relatively brief,
and we've been fortunate to have come along during a

(00:23):
period of relative calm in Earth's history. Maybe we couldn't
have come along had things been more tumultuous. Who knows,
but there's something to bear in mind that pops up
a lot when you look into existential threats. Whatever lessons
the past may offer, it doesn't teach us enough about
the future. Just because things have gone smoothly so far

(00:46):
doesn't mean they will always go that way. Every so often,
some massive catastrophe happens on Earth that brings life to
the brink of extinction. There are a lot of things
in space and on Earth that can devastate life. We
call these natural existential risks. It's worth noting that we

(01:07):
humans pose an existential threat to just about every other
species that we share the planet with, but there are
also natural catastrophes that pose a threat to all of us.
Creatures living on Earth, including us humans. In this episode,
we'll look at a few of them to get a
feel for just how badly things can go on Earth.

(01:30):
Let's travel back to one particular day during the most
strictan age of the Upper Cretaceous period, about sixty six
million years ago, give or take three hundred thousand years,
and on this day, a light streaks across the sky
above Earth. That light, it turns out, is an asteroid,
six miles across, about the size of downtown Los Angeles,

(01:54):
is traveling at about forty four thousand miles per hour,
times faster than a bullet when it passes through the
Earth's atmosphere as if it's not even there, and strikes
the planet. The impact creates a blast with one hundred
million megatons of energy. For comparison, the Czar BOMBA, the

(02:16):
largest nuclear bomb that humans have ever detonated, was fifty megatons.
One got past Jupiter, you could say. The asteroid strikes
the Earth along what is now called the Yucatan, the
spur like peninsula that juts out of southern Mexico into
the Gulf. It drives itself into the Earth, digging out

(02:39):
a crater a hundred and ten miles in diameter and
nine miles deep, so deep, in fact, it nearly punctures
a hole all the way through the crust. The impact
is felt all over the world as enormous shocks of
energy that travel along the borders between tectonic plates. This
sets off earthquakes and volcanoes across Earth unimaginably large tsunamis

(03:00):
from the Gulf of Mexico Wash as far north as St. Louis.
The impact kicks a tremendous amount of earth and sea
into the air. Boulders the size of cars are launched
hundreds of miles from the impact site, as far away
as Believes. The pressure and heat from the collision is
so great that it instantly melts the rocky earth below.

(03:21):
That melted rock sprays into the air, where it turns
to glass before it can reach the ground. Continents away.
Quartz is pressed into crazy angles, and minerals into tiny
spheres of metal, And when the heavier bits among all
that kicked up dirt and rock and metal come back down,
it heats up. It brings a tremendous amount of energy
with it, flash heating the Earth's surface, embroiling alive anything

(03:46):
that can't take cover underground or underwater. And as the
earthquakes and tsunamis raging across the Earth and the fire
raining from the sky begin to subside, things go from
bad to worse. The finer particles from all that pulverized
earth and liquefied rock launched into space stay aloft, forming

(04:07):
a vast globe spanning shroud that blocks out the Sun
for months. Photosynthesis grants to a halt back on Earth.
The world's plants can no longer make their food, and
since they, in one way or another, feed the rest
of life on Earth, everything is still alive begins to starve.
But as bad as the asteroid makes things for life

(04:27):
on Earth, it is made even worse by a fluke,
a stroke of sheer bad luck. The Yucatan, the area
where the asteroid strikes, is one of the most sulfur
rich areas on Earth, and when that asteroid hit, as
much as five hundred billion metric tons of sulfur instantly
rose from deep inside the Earth up into the atmosphere,

(04:48):
like dust rising from a table when a heavy book
is dropped on it. In the sky, that sulfur mixes
with water vapor and is bombarded by ultra violet radiation
from the sun, so it becomes sulfur aerosol, the type
of atmospheric pollution that just happens to be the most
efficient at absorbing sunlight and blocking it from reaching the Earth.

(05:08):
The sudden presence of aerosols in the sky makes the
darkness complete. Sulfur aerosols also form acid rain and freshwater
lakes and the surface of the oceans are poisoned by it.
Life on Earth comes disturbingly close to total extinction. Millions
of years later, humans will call this cataclysmic event the

(05:30):
Cretaceous Tertiary extinction. It had such a profoundly colossal effect
on the planet that it serves as the sudden and
abrupt dividing line between one geological age, the Cretaceous, and
the one that followed it, the Tertiary or Paleogene, as
it's called these days. Around of the species alive on

(05:50):
Earth at the time died during the event and the
hard times that followed the asteroid's arrival. Three out of
four species death swept across Earth and waves that lasted
for tens of thousands of years. Those species that did
manage to survive had an extremely hard time of it.
They hung on by a thread. In many cases, they

(06:12):
were whittled down to just a few individuals that were
somehow able to carry on their species. Animals that were
able to burrow to feed off the carcasses of the
unlucky ones, and whatever plants still reached upward towards a
sun that no longer shown. Those are the ancestors of
everything alive on Earth today. We are descended from the
toughest band of animals that ever lived. But for most

(06:36):
species of dinosaurs, the asteroid was the end of the line,
the Kuda grass. They succumbed to their existential threat. We
know all of this thanks to a father's son science
team known as Luis and Walter Alvarez. As a geologist

(06:56):
working in Italy in the seventies, Walter Alvarez found a
thin layer of clay dating back to around sixty five
million years before. It was peculiar because immediately below the
strip of clay there was a wide variety of fossils
of different types of forums, tiny single celled organisms that
have shells, but right above the clay there was only

(07:17):
one type. Forums are an excellent indicator species They eat
plants and animals that degrade on the seafloor, and they
are very sensitive to changes in the environment. If something
happens to forums, it means that something happened to everything else,
and something definitely did seem to have happened to the
forums around the time that clay strip was deposited that

(07:38):
drastically reduced their diversity. There was something similar among plants too.
Just below the clay strip were fossils of a wide
variety of plants, where just above there were only fern spores.
Walter would have been surprised to know that the strip
of clay he was scraping at with his trowel in
the center of Italy was actually from Mexico. Walter had

(08:01):
a very famous scientist, Dad Louise, a physicist who developed
the first atomic bombs for the US, among many other things.
By the late seventies. When Walter approached his father with
the curious find of the clay strip, Louise worked at
one of the national labs where he had some colleagues
who ran a mess spectrometer. He asked them to take
a look at the samples of the clay layer. What

(08:23):
they found was surprising the clay layer contained about six
hundred times more iridium than the layer above or below
the clay. This is very weird because i ridium, which
is a metal in the platinum family, isn't found much
in Earth's crust. It certainly isn't found at six hundred
times the background amount. It is, however, found in abundance

(08:44):
on things like asteroids. As Walter started looking around the world,
he found that same clay layer at other sites, and
it had all the same characteristics as the first site
in Italy. Iridium in aces in abrupt shift in diversity.
By that time, paleontologists had already established that the dinosaurs
had died out around sixty five or so million years earlier.

(09:07):
The clay layers geological age matched that extinction precisely, But
at the time, the prevailing theory was that it had
been a million year period of volcanic activity that had
been responsible for killing off the dinosaurs, all that gas
erupting and poisoning the air and rain. But what the
Alvarez Boys were seeing suggested an asteroid, a colossal one,

(09:29):
one so colossal it had brought the Earth to the
brink of near total extinction, and in their theory got
a shot in the arm with the discovery of the
chick s Aloub Crater on the Yukatamp Peninsula, the site
of the destruction sixty six million years before. Eventually, the
debate was laid to rest. In two thousand ten forty

(09:50):
one scientists and fields like paleontology, astronomy, geology, and others
released a review of the literature on the KT extinction
in the astro evidence and concluded that it was in
fact an asteroid that killed off the dinosaurs. It's as
close as science comes to being settled. There's something that

(10:12):
gets overshadowed by the story of the dinosaurs extinction. That
life on Earth rebounded. Those smaller animals that could burrow
and dive held fast and among all the darkness and death,
they continued on. They reproduced and raised their young, and
as the Earth slowly shook off that extraordinarily bad day,

(10:32):
it became again a fertile place, a place friendly to life,
and that bottle that created by the asteroid open wide,
and life spread again and grew diverse. And from that
calamity we humans arose amid the vacuum left by the
sudden loss of life. The dinosaurs existential catastrophe proved to
be our existential triumph, which is to say that life

(10:56):
is tough and it is very, very difficult to extinguish
it entirely in the coming centuries. That will be a
mark in its favor. M hm hm. We humans are

(11:21):
an earth bound species, and so whatever happens to Earth
happens to us. Like the dinosaurs, we live under the
threat of death from huge rocks traveling at unimaginable speeds
hurtling toward us. But unlike the dinosaurs, we are in
a position to do something about it. In the coming years.
Is our technology to travel through space develops and we

(11:42):
become capable of spreading out around our solar system and
eventually our galaxy, we will have made the biggest shift
in our species since at least when we settled down
and began raising crops. That see change in human ecology.
The advent of agriculture led to sweeping changes for humans.
It was, as Nick Bostrom would put it, a pan
generational change in how humans lived. By coaxing food from

(12:07):
the ground on a predictable schedule, and by taming animals
and creating a reliable supply of meat and milk. We
changed a lot about ourselves, our bones, the shapes of
our skulls, the workings of our guts, the color of
our skin. And it changed our culture too. As anthropologist
Jared Diamond points out in his nine seven essay The

(12:28):
Worst Mistake in the History of the Human Race, about
the advent of agriculture, we started to have a surplus
of food, something that our hunter gatherer ancestors never would
have experienced. This meant that some people had more than others,
which creates an imbalance and power, and hence agriculture also
led to things like kings and armies and social classes.

(12:51):
When we settled down our cities developed. Agriculture can support
more people than hunting and gathering, and the more people
there are, the more brilliant ideas there are too, so
our civilization began to advance by leaps and bounds in
the last nine or ten thousand years. Ideas spread more
quickly among those people who lived together in those new cities,
so innovations were able to develop over the span of

(13:13):
a handful of years rather than millennia. Almost everything we
have in the world today can be traced back to
our collective decision to settle down and raise crops. It was,
to say the least, a sweeping change for us humans.
With our next great leap spreading out into space, we
are effectively doing the opposite of when we settled down

(13:34):
into cities. Rather than contracting, we will be expanding from
that huge coming together, we will spread out. Over time,
humans will begin to colonize other planets, and generations of
little human babies will be borne on planets other than Earth.
They will be shaped by forces and experiences that no
earth bound human will have ever encountered, and they will

(13:56):
learn to adapt to their home planet just like we did.
We are quite capable of becoming all the things that
it's possible to become. Life that starts from us and
radiates out can not only spread to different places, it
can create different styles and techniques and cultures and approaches.
All of the life that you see on Earth started

(14:17):
out from a much smaller amount of variation, but with
time it could explore lots of different niches and ways
of living. And that's probably what would happen to us too.
If we're the only life around it, we can survive,
We will radiate, We will become diverse and different and
fill thousand million billion different niches of different ways of being.

(14:38):
Over time, perhaps their physical connection to humans on Earth
will become distant enough that new species of humans will form,
and the universe will be home to more than one
species of human again, just as it was fifty years ago.
We will become the aliens we seek, and later on
they might be surprised to learn that they came from
something that was simple and not as very It's odd

(15:02):
to think of, but humans are in an evolutionary bottleneck
of our own. Right now. There's only one species of us,
and with the exception of maybe half a dozen astronauts
on the International Space Station at any given time, we
are all stranded on this island Earth. Those astronauts aboard
the I s S showed just the faintest beginnings of

(15:23):
our future. If we become a space faring species, all
of humanities eggs will no longer be in just the
one basket of Earth. Should some catastrophe befall those of
us here on Earth, there will be other humans living
elsewhere to carry on. We will begin to trickle from
our bottle neck and spread throughout the universe, and when

(15:44):
we do, we will have made it through the Great Filter.
Colonizing beyond Earth is something we should begin working on
as soon as we can, because Earth is vulnerable to
a wide variety of catastrophes that are pretty hostile to life,
things like exploding stars, the death of our Sun, even
Earth's zone systems going haywire. Take our son for starters.

(16:09):
Remember that Goldilocks zone, that habitable area around a star
where a planet can sustain life. Earth is in the
Sun's Goldilocks zone, but it's not a permanent position as
a star. The Sun is currently in its main sequence.
It has plenty of hydrogen atoms in its core that
it fuses into helium, and these constant nuclear reactions release

(16:30):
tremendous amounts of energy, which we gratefully accept as light
and heat here on Earth. But the Sun is slowly
using up its available fuel, and as it does, its
core shrinks in size. That smaller core means that it's
closer to the center of the Sun, which means that
gravity exerts more force on it, making it denser. All

(16:51):
of this is what one would expect, but we're talking
about cosmic stuff here, and as with all cosmic stuff,
something weird always happens to because the core grows denser
as it grows smaller. That means more fuel is closer
at hand for the Sun to burn, so its main
sequence begins to speed up. It uses fuel more quickly,
actually shortening its own lifespan, at least compared to what

(17:14):
it would be if it managed to maintain a slow,
steady burn during its entire life. As the Sun burns
through its fuel supply more quickly, it's actually going to
grow larger, much much larger, and about one point one
billion years, the Earth will no longer be in the
Sun's goldilocks song. It will be a lot closer, and
it will keep getting closer from there. This is estrophysicist

(17:38):
Ian O'Neill. When it goes through this end stage, when
it starts to turn, is what's called a red giant,
and it's pretty much a red giant is pretty descriptive.
A boy, what's going to be. It will expand, possibly
out to the orbit of Earth. So this the Sun
will basically fill up our entire, our entire sky. You
look out the window, it will just be a big

(17:58):
seething mess of of star. So you can imagine that
with the Sun right on top of Earth, there won't
be much room for life, but billions of years before
that point, the biggest issue will have to deal with
is the increase in solar radiation. Sure, things will get
much much hotter on Earth than they are today, but
as with the fallout from the kt asteroid, there are

(18:20):
places that some life could go underground, deep underwater. Sorry cows,
sorry elephants, sorry feral pigs. Sure, but as we've seen,
life is persistent. If anything, it would almost certainly find
a way to adapt to the changes from the increased
heat on Earth, at least at first. But the radiation

(18:40):
from the growing Sun will be so intense that it
will tear apart the very molecules that make up Earth's atmosphere.
All aerobic life. Life that breathes oxygen would die, obviously,
but even anaerobic life would find it impossible to continue
on Earth without an atmosphere to regulate temperatures. The wild
swings between tense heat and cold on a daily basis

(19:02):
would evaporate the oceans, leaving Earth a dead, lifeless rock.
A planet without an atmosphere is a dead planet. So
we have a billion years to figure out either how
to slow the Sun's burn right and vastly extend its
main sequence, or how to live away from Earth, and
the odds aren't that bad actually that we may be
able to do both within that time. That same issue,

(19:28):
a star reaching the end of its productive life poses
another natural threat to Earth as well. Depending on the
size or the type of the star, could explode at
the end of its life. As a star nears the
end of its life and its fuel core becomes denser
and denser, the force of gravity acts ever more strongly
on it, and just the same way as the singularity

(19:50):
of a black hole. But a black hole singularity is
so massive and so dense that the force of gravity
acting on it actually presses it into the fabric of
space time, creating a bottomless depression. Not all stars are
as massive as this, though, so there are other outcomes
that it can have within a black hole. One of
those is a supernova. Over the star's lifespan, the nuclear

(20:13):
fusion reactions that carried out left behind his byproducts increasingly
heavier elements hydrogen fused into helium, helium fused into oxygen,
oxygen fused into neon, and so on, until the elements
the star burned towards the end of its life become
heavy metals like iron and nickel, so eventually it will
start to try and burn elements as big as a

(20:34):
iron and any star the stars to try to fuse
iron is basically on this deathbed. The force that holds
the nuclei of these types of atoms together is so
strong that they can't be fused together even by something
like a star. But the force that gravity exerts on
this extraordinarily dense core of iron and nickel is strong

(20:56):
enough that it actually compresses the individual atoms, pushing them
into tight, tiny balls. When the atoms that make up
the core shrink, the core itself does as well, becoming denser,
and so the force of gravity acts even more strongly
on it, creating a feedback loop. The star's core, in
other words, suddenly collapses. And all of this happens in

(21:17):
the fraction of a second. So is this weird point
where as soon as you hit iron, almost immediately within milliseconds,
the star just fulls apart. It just the whole system
in this core breaks down and it will undergo a
core collapse. But since the star isn't massive enough to
become a black hole, since one of the laws of

(21:38):
physics is that matter cannot occupy the same space at
the same time. There's a limit to how tightly packed
the iron atoms at the star's core can become. When
they reached that limit, the collapse suddenly stops, kind of
like hitting a brick wall. All that force of the
collapsing core has to go somewhere, though, and it reverberates
back outward. Exploding in a supernova one of the most

(22:00):
fantastic displays in the universe. All of the mass that
star sheds is shot outward as energy, so much in fact,
that planets that orbited the star just moments before may
be blown out of their solar system into space if
they're not outright destroyed. That is, tremendous amounts of light
and heat are released. For a few minutes, the dying

(22:21):
star can shine brighter than the combined luminosity of an
entire galaxy. The explosion since tremendous amounts of heat and
radiation spewing into space, bathing anything nearby with The only
explosion in our universe larger than a supernova was the
Big Bang. Sometimes, if the supernova is large enough, it

(22:44):
can emit a gamma ray burst. Gamma radiation is the
most energetic type of radiation on the electromagnetic spectrum. Gamma
rays are so energetic that they excite any atom they
come in contact with, causing the atom to move temporarily
to its higher energy state, causing its a release energy
itself as it moves back to its normal ground state.

(23:05):
It's like gamma rays get everybody else wound up, and
to calm down, everyone has to let out a little shout.
Just thinking about this happening to an individual atom sounds
like chaos. So you can imagine what a burst big
enough to flood an entire planet with gamma radiation might be. Like,
let's say, for argument's sake, that Earth just happens to

(23:27):
be in the path of that beam of energy. A
sudden flood of gamma radiation would burn those of us
walking around on Earth's surface to a crisp Sadly, we
would probably not all be transformed into incredible hulks. The
life that did manage to survive the initial burst would
have a rough time of it afterward. Gamma radiation is
particularly good at burning away the ozone layer, the protective

(23:49):
blanket of O three atoms that reflects most of the
Sun's radiation. When flooded with energetic gamma rays, those O
three molecules would destabilize and the ozone layer would deteriorate,
leaving Earth exposed to the full brunt of ultra violet
radiation from the Sun. UV from the Sun could be
bad enough with the folows on layer, without it, it

(24:11):
would be utterly catastrophic. The intensity of the UV would
prove too much for even photosynthesis and plants, so, following
the blueprints of the KT extinction, in a matter of
days or weeks, the bottom of the food chain would collapse,
and everything else above it would starve. As a result,
the oceans too would be crippled by the increase in UV.

(24:31):
It would destroy the plankton that makes up the basis
of the marine food webs. The effect would be pronounced
enough that a gamma ray burst is considered to be
able to sterilize a planet close enough in its path,
and it's possible that the Earth has experienced them before.
One theory for the Ordovician extinction four hundred and forty

(24:52):
million years ago is that Earth got in the way
of a gamma ray bursts. As majestically dangerous as they
are gamma ray burst upened in the universe once a
day at least, well that's how often we noticed them
since the nineteen sixties. I should say humans have been
aware of supernova for thousands of years, first noting the

(25:12):
appearance of bright new stars in China almost two thousand
years ago. But we spent the entire lifespan of our
species up until the nineteen sixties blissfully unaware that invisible
death rays went off in our universe at all. It
was all because of the Cold War that we ever
found them. In ninety three, the US the USS are

(25:33):
in Great Britain signed a treaty banning nuclear detonations in
the atmosphere, underwater or in outer space. But we didn't
precisely trust our comrades, and so the US launched the
satellite capable of detecting large sudden spikes and nuclear radiation,
and the satellite found it. But it wasn't from nuclear
tests that satellite provided the first evidence of gamma ray bursts,

(25:56):
and since then we found that they are extremely common.
Stars collapse all the time. It seems the universe is
full of rocks and collapsing stars and gamma ray bursts,
which by the way. It can also form from two
black holes merging, or from the hiccup of an exotic
and frightening type of star called magnet Or, which is

(26:19):
a type of dwarf star made of nickel. It's been
hundreds of times per second and produces the strongest magnetic
field in the universe. This is a dangerous place out there.
I mean that the universe is has got no care
for life on Earth, and and I think that it's
worth remembering that when you look up in the nice sky,
when it looks very you know, peaceful and static, and

(26:43):
and it's unlook particularly dangerous. Being alive in the twenty
one century. You're probably fairly well versed in the basics
of climate change. We all are, and whether you believe
humans contribute to it or not, it's plain to everyone
that has advanced as we've become, we are still very

(27:05):
much at the mercy of the Earth's climate. All of
the bad news about climate change, though it seems incremental,
a few degrees increase in temperature here, a couple of
feet of sea level rise there, it just seems so well,
I hate to say it, but distant, distant and sort
of non threatening. Now there's a whole series I could

(27:25):
do just on how those sentiments aren't correct at all.
But enough doubt has been sown that it feels like
we have the luxury of time to keep arguing about
something as silly as whether humans are contributing in a
climate change or not, but whether you believe we do
or not, and we definitely do, there's something you should
know about climate change. Earth has a point of no

(27:47):
return climate wise, and should we find that we've pushed
it past that point, we would also find, to our
great peril that the changing climate would be neither distant
nor non threatening. With an overabundance of carbon dioxide, the
atmosphere could become a blanket that traps heat from escaping
into space, heating Earth up to an unbearable degree. Literally,

(28:12):
it's called a runaway greenhouse effect. If you were alive
in the nineties, you were introduced to the greenhouse effected
byproduct of climate change that can lead to global warming.
The basics are that as we burn more fossil fuels,
we contribute new large amounts of carbon dioxide to the
atmosphere that wouldn't otherwise be there. They would still be
locked underground as deposits of oil and gas. When sunlight

(28:35):
shines on Earth, the planet absorbs some of it and
is warmed by it, but it also re emits some
of it back into space as infrared heat. The trouble
is CO two is an extremely efficient absorber of that
infrared heat. When there's a lot of CO two in
the atmosphere, the atmosphere is a whole warms, so we
end up with a warm planet and a warmer than

(28:57):
normal atmosphere. Things become warmer all around, but when temperatures
rise on Earth, the planet just releases more radiated heat,
and so eventually temperature is cool again. It's as if
Earth overwhelms the CEO two in the atmosphere with sheer
multitudes of infrared. There's just not enough CEO two to
trap it all, and the planet overcomes the greenhouse effect

(29:19):
easy peasy. But there's a limit to how much heat
Earth can release into space, and so once the planet
reaches the point where it can emit no more infrared.
As c O two levels continue to rise, the tables
can turn, and it can be the carbon dioxide that
overwhelms Earth. A runaway greenhouse effect is triggered when a

(29:40):
positive feedback loop arises. As the planet grows warmer, more
water evaporates from the surface of the oceans. Water vapor
is also particularly good at absorbing reflected heat and trapping
it in the atmosphere, So the atmosphere goes even warmer,
causing more of the oceans to evaporate, adding more water
vapor to the atmosphere, trapping more escaping heat, warming the

(30:02):
planet even more and evaporating more of the oceans. Eventually,
it reaches a point where the entire planet becomes so
hot that the oceans boil off. You will be relieved
to hear that there is a point where the feedback
loop is broken and the runaway greenhouse effect ends. But
I regret to say that that doesn't happen until the

(30:23):
atmospheric temperature reaches about three thousand degrees fahrenheit, when the
emitted heat moves to a wavelength that water vapor is
incapable of absorbing. Long before that we humans would have
ceased to exist, and eventually, with the oceans boiled off,
any life hanging on in the seas would meet the
same fate as us. This is what astronomers believe happened

(30:45):
to Venus Venus is about the same size as Earth,
but it's far closer to the Sun, and it's not
within the Goldilocks zone. It's not the closest planet to
the Sun. That distinction goes to Mercury, but it is
the hottest planet in the entire Solar System by far,
are despite being almost twenty eight million miles further away
from the Sun than Mercury is. Venus is average surface

(31:07):
temperature of eight hundred and sixty four degrees fahrenheit is
hundreds of degrees hotter than Mercuries, hot enough to melt
let that's because Venus has an atmosphere thick with CEO two.
On the surface of the planet. The atmospheric pressure is
almost a hundred times that of Earth's at sea level,
about what you would experienced three thousand feet underwater in

(31:27):
one of Earth's oceans. There's no surface water on Venus
that evaporated away eons ago, but at some point in
its distant past, Venus may have been habitable. It is
to our great fortune that natural existential risks seem to

(31:47):
be rare. This is philosopher Toby ord. Humanity has survived
about two thousand centuries so far, so that's two thousand
centuries worth of natural risk. Asteroid comments, supervolcanos, supernovas, everything
put together that could have killed humanity. We've survived two

(32:09):
thousand centuries of that risk. UH. And this, this fact
allows us to put a bound on how much risk
these natural things could be causing UH. And if you
do the mathematics on this, you can show that it
can't be much higher than about one in a thousand
chance of extinction per century from natural causes, which works

(32:29):
out to a point zero zero one percent chance of
humanity going extinct from natural risks during any given year,
a thousandth of a percent, not too menacing. Most atmospheric
models show that human contributed CEO two definitely exacerbates the
greenhouse effect, but that it would be extremely unlikely that

(32:50):
we humans could push it into a runaway greenhouse. In
the paper where they introduced the world to the concept
of a dinosaur killing asteroid, the alvarez Is and their
colleagues calculated how frequently such a catastrophic event might take place.
They concluded that an asteroid with that scope of devastation
might come along once every hundred million years, which would

(33:11):
leave us with around thirty four million years left on
the clock before we can expect a similarly destructive asteroid.
With something approaching certainty. A gamma ray burst close enough
to Earth to cause a mass extinction might happen once
every billion years, and Earth would have to be lined
up in the path of the relatively narrow beam of
gamma radiation to experience the full effect. There are stars

(33:35):
nearby that could collapse in supernova, but the closest I
k pegasy A isn't expected to for another five million years.
The next two closest and Terris and Beetlejuice, could explode
at any time in the next million years, but it
should be too far away to damage Earth. And again,
the Sun has more than a billion years before it
reaches the end of its main sequence and begins to

(33:58):
grow unbearably hot for us. But it pays to keep
an open mind. It is entirely possible that our current
understanding of these risks is flawed in some way or incomplete,
that there's some factor we're not aware of yet that
could make any one of these disasters much more likely.
In that slight, limital space of uncertainty is where existential

(34:20):
risks live. The chances of them happening are minuscule, but
the consequences they bring if they do, are so catastrophic
that they demand to be taken into account. Atmospheric scientists,
for example, don't understand the extraordinarily complex interactions that make
up Earth's atmosphere, and so maybe we could accidentally trigger

(34:42):
a runaway greenhouse effect by burning fossil fuels. It's unlikely,
but it's unlikely under our current understanding, and with the
addition of information that understanding can change. Human misunderstanding doesn't
prevent calamity. In fact, it makes it like clear. But
here's the thing about natural existential risks. Being earth bound,

(35:06):
we can't do much about them right now. In the future,
we will, our artificial intelligence will be able to predict
gamma ray bursts to give us plenty of warning. Our
spacecraft will be able to ferry us around a safer planets,
and maybe we'll build structures to capture the energy from
those bursts and store it for later. But so long
as we remain bound to Earth, we will be vulnerable

(35:28):
to the same threats that it is. More so, really,
Earth is likelier to bounce back from a cataclysmic asteroid
or a gamma ray burst than we are. But there's
an entirely different class of existential risks, ones that we
have a much greater chance of controlling because they are
of our own making, but also ones that pose significantly

(35:50):
greater danger. These are anthropogenic existential risks. Anthropogenic risks. However,
um we can't apply such an argument to bound the probabilities,
and to show that there must be quite small. I
would say that there's maybe something like if there was
something like a risk of extinction from anthropogenic causes in

(36:12):
the twentieth century, this century, I think it's it's growing.
My best guest would be something like one and six
Russian Roulette, and then next century, well, if we don't
get our act together even higher. Those technologies that pose
an anthropogenic risk to us, we're beginning to develop them
right now. Some are already here and almost know what

(36:35):
is paying attention to the danger they are bringing our way.
On the next episode of the End of the World
with Josh Clark, it was a cold, windy day in
January nine when the robots took their first human life.
As we create more intelligent algorithms that are capable of

(36:58):
improving themselves, we run the risk that they may take
over their own development and quickly evolved beyond our control.
There is no good outcome for us if that happens.

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