Speaker 1: What exactly does figuring out if aliens exist have to
Speaker 1: do with the end of the world. Well, it turns
Speaker 1: out that the odd emptiness that we find in the
Speaker 1: universe can give us clues about what may have gone
Speaker 1: on or didn't go on before we humans came along.
Speaker 1: Did something bad happen? And if so, might it happen
Speaker 1: to us two? Looking around for signs of whether we're
Speaker 1: the only intelligent life to have ever evolved can help
Speaker 1: answer those questions. And when you look at it, the
Speaker 1: universe does seem amazingly large for Earth to be the
Speaker 1: only planet with life on it. Consider it like this.
Speaker 1: Let's say that you're a photon, a tiny packet of light,
Speaker 1: and one day you had the wherewithal this set out
Speaker 1: to travel across the universe. You would find that, perhaps
Speaker 1: to your great surprise, such a trip would take you
Speaker 1: around fifty billion years. Yes, you, light, which can travel
Speaker 1: at the speed of light, would take fifty billion years
Speaker 1: to cross from one side of the universe to the other.
Speaker 1: At least that's how long it would appear to take
Speaker 1: you to as humans. And this is just the observable universe.
Speaker 1: The amount of the universe that light like you has
Speaker 1: had time to travel across since the Big Bang. Within
Speaker 1: that vast space, there are anywhere from one billion to
Speaker 1: two trillion galaxies by our current causes, at least of
Speaker 1: which our own Milky Way is on the larger side
Speaker 1: of the spectrum. There are larger but there are also
Speaker 1: a lot of smaller ones too. Within these billions or
Speaker 1: trillions of galaxies are billions and billions and billions of stars,
Speaker 1: and probably exponentially more planets. The total number of planets
Speaker 1: and stars in our universe, the total number of places
Speaker 1: for life to exist, is mind bogglingly large. And so
Speaker 1: you packet of light or wavelength, depending on your mood,
Speaker 1: might think to yourself, as you traveled across the verse
Speaker 1: and saw that the Earth is the only planet that
Speaker 1: is home to intelligent life. Out of the attend to
Speaker 1: the who knows what power planets that could host life,
Speaker 1: You might think to yourself, in your little photon voice,
Speaker 1: what waste are we alone in the universe? And if
Speaker 1: we are alone, why? These are the questions at the
Speaker 1: heart of the Fermi paradox, and they continue to nag
Speaker 1: at us. The answer is plainly obvious if you look
Speaker 1: at it, but it depends on how you look at it.
Speaker 1: With the Fermi paradox, the same thing can look very
Speaker 1: different to any two people. And it's not just the
Speaker 1: paradox itself. Even the evidence is equally ambiguous. It's all
Speaker 1: like one big contradem words that have two meanings that
Speaker 1: are the opposite of one another, like how weather can
Speaker 1: mean both to wear away and to withstand something. The
Speaker 1: size of our empty universe can mean that we are
Speaker 1: both alone or one of many. Another example of this
Speaker 1: ambiguity is the very presence of life on Earth, something
Speaker 1: that people who believe that we're not alone in the
Speaker 1: universe point to. His evidence is that life here on
Speaker 1: Earth seems to have emerged the first chance that it had.
Speaker 1: The famous astronomer and science writer Carl Sagan was one
Speaker 1: of those people. He was an optimist when it came
Speaker 1: to the family paradox. He believed that life was out there,
Speaker 1: we just hadn't found it yet. Sagan pointed to evidence
Speaker 1: from the fossil record that here on Earth life began
Speaker 1: as early as five hundred million years after the Earth form.
Speaker 1: It was almost like it was waiting to emerge, and
Speaker 1: since it emerged quickly here on Earth, it stands to
Speaker 1: reason that life should emerge wherever it gets the chance,
Speaker 1: anywhere in our universe. When you take into account the
Speaker 1: idea that there are perhaps three hundred billion stars in
Speaker 1: the Milky Way alone, even if some small fraction of
Speaker 1: those have habitable planets that could host life, then we
Speaker 1: should expect to encounter it sometime soon as we spread
Speaker 1: out to explore the country side around planet Earth. But
Speaker 1: there's a problem with basing our view of the rest
Speaker 1: of the universe on our own existence. The idea that
Speaker 1: we can gain insight into our universe from our existence
Speaker 1: is called the anthropic principle, and it's vulnerable to a
Speaker 1: logical fallacy called selection bias. Being the only intelligent life
Speaker 1: in the universe, we're the only data point in our
Speaker 1: data set, and so we tend to skew the results
Speaker 1: a little bit. It's hard to resist the temptation of
Speaker 1: cherry picking the data when there's only one cherry. Yes,
Speaker 1: of course, life can arise. Our very existence proves that fact.
Speaker 1: But what it does not prove is that the emergence
Speaker 1: of intelligent life or any life, really is easy or inevitable.
Speaker 1: What if, instead, life emerging in our universe is really,
Speaker 1: really really hard. Perhaps the existence of living, breathing, intelligent
Speaker 1: things here on Earth doesn't show the emergence of life
Speaker 1: is inevitable. Perhaps as shows that it was the singularly
Speaker 1: most unlikely event in the history of our entire universe.
Speaker 1: If you could crack open a strand of your DNA
Speaker 1: and read the pairs of adenine, guanine, cite of scene
Speaker 1: and dimin the ones and zeros of your genetic code,
Speaker 1: you would find a history of life on Earth written
Speaker 1: into it. Not only does your DNA contain the blueprints
Speaker 1: for making a full version of you, but if you
Speaker 1: look at it correctly, it also bears the marks of
Speaker 1: those who have come before you. You'll find your parents genes,
Speaker 1: of course, and their parents. But as you go further
Speaker 1: back in time, you'll also find the contributions of all
Speaker 1: of the animals in bacteria that ever reproduced along the
Speaker 1: last several billion years to form a connected chain of
Speaker 1: life that eventually led to you. But you'll find that
Speaker 1: you run into a wall the further you go back.
Speaker 1: There's a point beyond which we can no longer read
Speaker 1: the taves of our DNA. It ends right before we
Speaker 1: get to the emergence of life here on Earth the
Speaker 1: very beginning. That is to say, no one is sure
Speaker 1: how life began as it stands now, the general consensus
Speaker 1: among sciences the concept of a biogenesis, that life emerged
Speaker 1: from nothing nothing living anyway, let's go back to the
Speaker 1: early Earth. About five million years after it formed, the
Speaker 1: surfaces just begun to cool enough that solid clay ground
Speaker 1: has begun to form, and with the cooling off, the
Speaker 1: muggy atmosphere cooled as well, condensing in the rain that
Speaker 1: began to collect in pools which would become the peatree
Speaker 1: dishes where life took its first steps. But to get
Speaker 1: from here to life, something extremely unlikely had to happen.
Speaker 1: Plain old, lifeless molecules had to spontaneously arrange themselves into
Speaker 1: new forms that became the building blocks of life. At
Speaker 1: this point, there was nothing but raw materials on Earth,
Speaker 1: and we have to get from here to living organisms.
Speaker 1: That means that not only do you have a functioning organism,
Speaker 1: it has to carry with it the encoded instructions to
Speaker 1: make a copy of itself, and some way to read
Speaker 1: those instructions and actually make that copy. It's like the
Speaker 1: idea of putting some plastic pellets and metal shavings into
Speaker 1: a bucket and expecting an autonomous three D printer to
Speaker 1: form from it, or more to the point, it would
Speaker 1: be like the idea of rotting meat growing maggots. For
Speaker 1: a long time, humans thought that this kind of thing
Speaker 1: spontaneous generation, was how some life arose. Prior to when
Speaker 1: science took up the mantle of explaining our universe, people
Speaker 1: relied on their everyday observations to explain occurrence is like
Speaker 1: maggots growing on rotting meat, seeming to appear out of nowhere.
Speaker 1: It seemed just as likely as anything that maggots could
Speaker 1: spontaneously generate, or baby mice from grain, which was another
Speaker 1: common folk belief. But eventually scientists figured out a way
Speaker 1: to disprove this idea, which really gained support when we
Speaker 1: realized that tiny, unseen life lived around us everywhere and
Speaker 1: that it had a hand in a lot of the
Speaker 1: things that we saw. Germ theory was developed and the
Speaker 1: concept of spontaneous generation was abandoned. That is until the
Speaker 1: nineteen fifties, when researchers started working hard on figuring out
Speaker 1: how life on Earth might have come about. Spontaneous generation
Speaker 1: made an unexpected comeback. A biogenesis holds that quadrillions upon
Speaker 1: quintillions of simple molecules present in Earth's early atmosphere and
Speaker 1: oceans randomly configured themselves into a mind bending number of
Speaker 1: different combinations. Some of these abominably large number of combinations
Speaker 1: happen to create useful complex molecules like amino acids, which
Speaker 1: are the precursors for proteins. Now, it's one thing to
Speaker 1: form simple molecules to randomly combined to form more complex molecules,
Speaker 1: but there is still the issue of replication. Ship If
Speaker 1: those molecules don't make a younger copy of themselves, that
Speaker 1: innovative chemical chain is broken and the new molecule loses
Speaker 1: the chance to continue to evolve in a new and
Speaker 1: even more complex things. And this is the point where
Speaker 1: science is currently stuck. Somehow, they say, some of those
Speaker 1: molecules managed to form a stable string of nuclear times,
Speaker 1: probably r N, a ribonucleic acid which is capable of
Speaker 1: doing two very important things. It can encode information in
Speaker 1: its nuclear tide chain, and it can also transcribe those
Speaker 1: nuclear tides to produce proteins. And once you have proteins,
Speaker 1: you can do all sorts of things that supports life.
Speaker 1: Back in two organic chemists Stanley Miller and Herald Urray
Speaker 1: saw it to show that this was possible by recreating
Speaker 1: the conditions of earlier Earth. In a flask. They simulated
Speaker 1: a primitive ocean and built an atmosphere out of the
Speaker 1: gases thought back in the fifties to have been present
Speaker 1: on Earth soon after it formed. They mimicked why in
Speaker 1: storms with the flickering electrical current, and when Miller inspected
Speaker 1: the broth that resulted, he found that nineteen amino acids
Speaker 1: and amans, the precursors to proteins, had assembled spontaneously. It
Speaker 1: seems that Miller had shown that when the conditions were right,
Speaker 1: the foundations for life would arise. But lately the idea
Speaker 1: that a biogenesis just happened randomly is falling out of favor. Instead,
Speaker 1: some scientists have begun to suspect that there is some
Speaker 1: set of organizing principles that serves as a driving force
Speaker 1: for life to emerge. Just like how gravity will draw
Speaker 1: a ball downhill, or how magnets will always repel or
Speaker 1: attract one another when they're close together, there is some
Speaker 1: fundamental governing force of nature that causes life to assemble
Speaker 1: along predictable lines. We just haven't figured out what that
Speaker 1: force or those lines are yet. This is a pretty
Speaker 1: surprising idea if you think of it. One of the
Speaker 1: laws of the universe, the second law of therm mom dynamics,
Speaker 1: is that things tend towards disorder, not order. The idea that,
Speaker 1: when presented with the right conditions, dead molecules in the
Speaker 1: universe will organize themselves into something living and breathing runs
Speaker 1: totally counter to that, and this new view also includes
Speaker 1: evolutionary biology as one stretch of these organizing principles of life.
Speaker 1: So the idea is that molecules arrange themselves into self replicating,
Speaker 1: metabolizing parts that form increasingly complex beings that eventually include
Speaker 1: you and me, which makes you wonder what the end
Speaker 1: point is. To some people, the idea that life arose
Speaker 1: from simple dead molecules that just happened to randomly assemble
Speaker 1: themselves in the living things is just too unlikely to accept,
Speaker 1: And even if we do accept that this is precisely
Speaker 1: how life arose on Earth, the idea that it could
Speaker 1: ever happen again anywhere else is too improbable. That virtually
Speaker 1: proves that we humans are alone in the universe. One
Speaker 1: issue people raise is time. They say that Earth just
Speaker 1: simply hasn't been around long enough for all of that
Speaker 1: random chemical trial and error to have taken place. The
Speaker 1: idea that life organizes along some unknown universal principles definitely
Speaker 1: addresses that idea of time, and so does pant spermia.
Speaker 1: Pant Spermia is a concept from astrobiology, and it says
Speaker 1: that the seeds of life are all over the universe
Speaker 1: in abundance everywhere. They can be found on board asteroids
Speaker 1: and other celestial objects, and that these seeds of life
Speaker 1: are constantly bombarding planets all over the universe. If the
Speaker 1: conditions on the planet happen to be right, well, then
Speaker 1: those sea needs of life will germinate and grow into
Speaker 1: something new and living. This certainly addresses the issue of time.
Speaker 1: Life could have evolved elsewhere in the universe, which is
Speaker 1: billions of years older than Earth, and then spread to
Speaker 1: our planet aboard an asteroid. We've recently found that some
Speaker 1: chemical precursors to life can be found on celestial objects
Speaker 1: like asteroids, and that they're able to survive re entry
Speaker 1: into an atmosphere, which can get pretty hot. This is
Speaker 1: important because it's widely accepted that an atmosphere is a
Speaker 1: precondition for life to emerge. If you take pants bermia,
Speaker 1: and you take the recent view that life follows some
Speaker 1: organizing principles as immutable as the laws of physics, then
Speaker 1: you arrive at a conclusion that Earth is just another
Speaker 1: place that happened to have the right conditions when a
Speaker 1: rock bearing the precursors to life landed around four billion
Speaker 1: years ago. In this view, then of course life is
Speaker 1: abundant in the universe. But then we find ourselves right
Speaker 1: back to where we started. Where is everybody? Perhaps the
Speaker 1: best answer to that comes not from an astrobiologist or
Speaker 1: an astronomer, but from an economist named Robin Hansen, who
Speaker 1: proposed that there must be something, some incredibly difficult step
Speaker 1: between the point where dead matter forms life and the
Speaker 1: point where intelligent life becomes a galactically colonizing civilization that
Speaker 1: no species has ever been able to overcome. He calls
Speaker 1: it the great filter. Every piece of matter in the
Speaker 1: universe is the sort of thing that could have started
Speaker 1: that process, started life, and then advanced life, etcetera. But
Speaker 1: so far nothing out there has done that. So the
Speaker 1: great filter is whatever is in the way, whatever makes
Speaker 1: it hard for any one piece of ordinary dead matter
Speaker 1: to produce expanding, lasting life. There's surely a countless number
Speaker 1: of steps along the path from dead matter to the
Speaker 1: emergence of a galactically visible civilization. But the Great Filter
Speaker 1: high Path says, supposes that a handful of them are really,
Speaker 1: really hard, and that one of them in particular must
Speaker 1: be so hard that is thus far prevented any life
Speaker 1: from reaching galactic proportions. This is Oxford University philosopher Toby
Speaker 1: ord if there were a hundred pieces you needed to
Speaker 1: get into the right order in order to create something
Speaker 1: that obeyed natural selection and and was it the basic
Speaker 1: level needed to actually bootstrap up towards complex life, then
Speaker 1: there are a hundred factorial ways you could arrange those pieces.
Speaker 1: That's that's more than uh tends to the power of
Speaker 1: a hundred different possibilities. And then it just turns out
Speaker 1: you need an incredibly rare event to get there. The
Speaker 1: Great Filter offers two possible solutions to the question posed
Speaker 1: by the Fermi paradox. Whereas everybody everybody never existed, or
Speaker 1: everybody is dead, if the Great Filter is in our past,
Speaker 1: it says pretty strongly that we are the first and
Speaker 1: only intelligent life that exists in the universe. If that's true,
Speaker 1: then by the Great Filter, there is something, some step,
Speaker 1: some right of passage you could call it, that has
Speaker 1: prevented every other life from reaching the point that we're at.
Speaker 1: And if that's the case, then we are the only
Speaker 1: life to have made it through the Great Filter. That
Speaker 1: means that we can be optimistic about our future. We
Speaker 1: made it through that right of passage that has kept
Speaker 1: every other attempt at life from evolving. It means our big,
Speaker 1: vast universe isn't wasted on us. It's just waiting there
Speaker 1: for us to use it, and guilt free too. Since
Speaker 1: no one else is around to use it, we have
Speaker 1: a responsibility to put it to use. You could even say.
Speaker 1: But there's another possibility to the Great Filter too. It
Speaker 1: may also lie just ahead in our future. Maybe intelligent
Speaker 1: life is a dime a dozen in the universe. But
Speaker 1: the reason we don't see other civilizations is because they've
Speaker 1: all died off. And if all of those intelligent civilizations
Speaker 1: all died before any any of them could make it
Speaker 1: off of their home planet and spread throughout the universe,
Speaker 1: the Great Filter is a big red flag for us.
Speaker 1: It tells us that we should expect to meet the
Speaker 1: same fate that every other intelligent life has. The Great
Speaker 1: Filter will spell the end of the world for us too.
Speaker 1: To answer the question of whether we face imminent doom
Speaker 1: or not, we have to look at the evolution of life,
Speaker 1: and to do that we have no choice but to
Speaker 1: turn to the one place where we know life evolved.
Speaker 1: At the risk of falling victim to the selection bias,
Speaker 1: we have to look to Earth for clues. We've already
Speaker 1: talked about how utterly improbable the origin of life appears
Speaker 1: to have been, but it's probably best to start looking
Speaker 1: even further back than that. If life emerged on Earth,
Speaker 1: that means that the conditions were right for life on Earth.
Speaker 1: That's the one day to point we have ipso fact, though,
Speaker 1: so the best way to find out what conditions life
Speaker 1: requires is to look at the conditions of our planet.
Speaker 1: And it turns out that Earth has some spectacularly peculiar
Speaker 1: characteristics that make it ripe for life. So peculiar, in fact,
Speaker 1: that a pair of researchers named Peter Ward and Donald
Speaker 1: Brownlee rolled all of them up into what they call
Speaker 1: the rare Earth hypothesis. It's just what it sounds like
Speaker 1: when you add up all of its peculiarities. Earth is
Speaker 1: not like other planets. First, Earth happened to form around
Speaker 1: the right kind of star. Our son is a main
Speaker 1: sequence star, which means it produces light and heat by
Speaker 1: fusing hydrogen into helium. Main Sequence stars aren't rare. They
Speaker 1: make up about nine of stars. But our Son also
Speaker 1: happened to be of the right size too. It's not
Speaker 1: so large that it will use up its fuel in
Speaker 1: just a few billion years. That means that the Sun's slow,
Speaker 1: steady burn would go on long enough to give life
Speaker 1: time to develop. The Sun also isn't too small to
Speaker 1: support life either. It is you could say, just right
Speaker 1: for life. Our Sun has also placed in a really
Speaker 1: great spot in our galaxy. We happen to be located
Speaker 1: out in the country, in a bit of a backwater
Speaker 1: when it comes to the Milky Way, about twenty eight
Speaker 1: thousand light years from the galactic center, in a galaxy
Speaker 1: that's one thousand light years across. For decades, study presumed
Speaker 1: that the center of the galaxy would be the most
Speaker 1: happening spot. That's where the most stars tend to be,
Speaker 1: and more stars would be more potentially habitable planets. Civilizations
Speaker 1: that arose in the center might even be in contact
Speaker 1: with one another, forming something of a galactic urban area.
Speaker 1: But recently it's become clear that the galactic center might
Speaker 1: not be so flourishing. After all. There are more stars, sure,
Speaker 1: but more stars also means that there are more collapsing stars,
Speaker 1: which release bursts of energy that can burn away the
Speaker 1: atmosphere of any planets in the vicinity, So the galactic
Speaker 1: center might actually be less of a bustling urban area
Speaker 1: and more like sterile and dead. Our Sun is pretty
Speaker 1: far away from the galactic center, way out past the
Speaker 1: suburbs where nothing much happens. In other words, that's good
Speaker 1: for life on Earth because it means that it cuts
Speaker 1: down on the number of sterilization events as life developed
Speaker 1: over Earth's history, giving it a good chance of succeeding.
Speaker 1: And Earth just so happens to be located within the
Speaker 1: Sun's goldilocks zone that I mentioned in the last episode.
Speaker 1: If it was a little nearer the Sun and about
Speaker 1: one and a half million kilometers closer, it would be
Speaker 1: too hot to support life, and much further away Earth
Speaker 1: would be too cold for it. It also turns out
Speaker 1: that where Earth is positioned in the Solar System is
Speaker 1: hugely important to giving life a fighting chance. Earth is
Speaker 1: the third rock from the Sun, with five others between
Speaker 1: us and the rest of the galaxy. Six if the
Speaker 1: math that suggests there's a planet nine out there turns
Speaker 1: out to be correct, or if you continue to count
Speaker 1: hapless Pluto, the Sun and the planets in our Solar
Speaker 1: System formed from a massive cloud of cosmic dust, that
Speaker 1: same stuff that might have blown up so many alien
Speaker 1: pilots traveling between the stars. We still aren't quite sure
Speaker 1: exactly how the planets formed. One model astoundingly suggested that
Speaker 1: they could have formed in as little as a thousand years,
Speaker 1: but the birth of the Solar System was likely a
Speaker 1: free for all grab of the elements that make up
Speaker 1: the planets today. Initially, astronomers presumed that the planets formed
Speaker 1: in their current arrangement, but lately it's become clear that
Speaker 1: that probably wasn't the case. The planets may have actually
Speaker 1: moved around and migrated from one spot to another in
Speaker 1: the early life of the Solar System before settling into
Speaker 1: the arrangement that we see them in today. If that's correct,
Speaker 1: then we were astoundingly lucky that Jupiter ended up where
Speaker 1: it didn't. Jupiter is a gas giant made up largely
Speaker 1: of hydrogen and helium with a metal and ice core.
Speaker 1: It's like a Sun that never started burning because it
Speaker 1: lacked the mass needed for gravity to kick start fusion.
Speaker 1: But Jupiter is massive, truly, you could fit around within it.
Speaker 1: It's the most massive planet in our Solar System, and
Speaker 1: because of its mass and its position between Earth and
Speaker 1: the chaos of the interstellar space outside of our Solar System,
Speaker 1: Jupiter acts as a huge defensive guard for our planet.
Speaker 1: When asteroids or comets or other flotsam and jetsam bent
Speaker 1: on destruction in oer our Solar System, Jupiter's extraordinary gravitational
Speaker 1: pull draws them into its orbit and slingshots them out
Speaker 1: back into space. Without Jupiter to run interference for Earth,
Speaker 1: it would have a steady diet of life ending bombardments
Speaker 1: from space. So thanks Jupiter. This is astronomer Donald brown Lee.
Speaker 1: He's one of the guys who came up with the
Speaker 1: rare Earth hypothesis. Jupers are actually pretty rare uh planets
Speaker 1: and um uh so uh in terms of rare Earth.
Speaker 1: You know whether it was juper is good or bad.
Speaker 1: Typical planet as systems probably don't have jupers. Our moon, too,
Speaker 1: seems to have played a number of factors and fostering
Speaker 1: life on Earth. Our moon's pretty unusual itself as far
Speaker 1: as moons go. It's enormous. It's about one point to
Speaker 1: percent the mass of the Earth and doesn't sound like much.
Speaker 1: But other planets moons like Phobos and Demos, which or
Speaker 1: a bit Mars, are closer to asteroids in size. Our
Speaker 1: moon more resembles a small planet, and because it's so big,
Speaker 1: it has some very peculiar effects on Earth. For one,
Speaker 1: it stabilizes our planet. The Earth doesn't sit upright as
Speaker 1: it spins around on its axis. It's tilted actually at
Speaker 1: about a twenty three degree angle. Because of this tilt,
Speaker 1: we have seas which create predictable variations in the temperature
Speaker 1: of regions on Earth over the course of the year.
Speaker 1: So when you think about the difference between winter and summer,
Speaker 1: you get a good idea how much variation a tilt
Speaker 1: can create. And add more of an angle to the
Speaker 1: tilt and the Earth and the temperature variations would become
Speaker 1: more severe. Since during winter or hemisphere would be further
Speaker 1: away than it is now from the Sun and much
Speaker 1: closer in the summer. And if you added in some wobble,
Speaker 1: like if the tilt of the Earth wasn't stable and fluctuated,
Speaker 1: all of these wild swings and temperature could make it
Speaker 1: very difficult for life to take hold. The Moon's mass
Speaker 1: actually exerts gravity over Earth and keeps it stable, not
Speaker 1: wobbling or tilting more than it does, and allowing for
Speaker 1: a nice, gradual, predictable and not two varying seasonal temperature
Speaker 1: shifts that we even have a moon appears to be
Speaker 1: a fluke itself. The current view is that the Moon
Speaker 1: was calved off from Earth following a head on collision
Speaker 1: in the Earth's early history with a planetoid about the
Speaker 1: size of Mars called Thea, which the Earth likely absorbed.
Speaker 1: This giant impact hypothesis explains a lot. The Moon is
Speaker 1: unusually large and unusually close to us because it was
Speaker 1: created of a mixture of Earth and that fateful planetoid.
Speaker 1: Because the Moon is so close to Earth, it's tidally
Speaker 1: locked and orbit around us. It doesn't spin on its axis,
Speaker 1: which is why we always see the same side of
Speaker 1: the Moon as it orbits us. This is an important
Speaker 1: feature because it also creates the tide you're on Earth.
Speaker 1: As the Moon orbits Earth, it pulls the oceans toward it,
Speaker 1: stretching them out on the ends and narrowing them in
Speaker 1: the middle. We hear on our planet experience this as
Speaker 1: low tide or high tide, depending on where you are.
Speaker 1: And it was in these tidal pools of young Earth's
Speaker 1: oceans where some people think life began. When those ancient
Speaker 1: tides came in, they deposited a flood of molecules into
Speaker 1: the tidle pools, and as they withdrew and the water
Speaker 1: evaporated in the sun, the increasing concentration of salt could
Speaker 1: have provided just the right laboratory conditions where those earliest
Speaker 1: chemicals could combine. Without a moon as large and as
Speaker 1: close as ours is, these tides could not have existed
Speaker 1: on Earth, and those early proteins would have lacked that
Speaker 1: kind of natural peatrie dish. So the moon itself is
Speaker 1: a collection of exquisite coincidences that supported life on Earth.
Speaker 1: But perhaps the most peculiar aspect of Earth is that
Speaker 1: it has massive plates that make up the crust, which
Speaker 1: slide along a molten bed underneath that. It, in other words,
Speaker 1: features plate tectonics. It thought that this is a major
Speaker 1: reason why the Earth has actually had an amazingly stable
Speaker 1: climate for most of you know, temperatures for for most
Speaker 1: of its uh age. So it's drastically different than Venus
Speaker 1: or or Mars, which are famously unstable over tri lage
Speaker 1: uh time scope. So so we really owe a lot
Speaker 1: uh to this. We don't really know why I played
Speaker 1: tectonics works on our on Earth. It doesn't work on Mars,
Speaker 1: it doesn't work on vines, it doesn't work on mercury,
Speaker 1: doesn't work on any Yeah, I mean they're there, are
Speaker 1: you know, movements of rocks rolled to each other, but
Speaker 1: not I played tectonics of the type that we that
Speaker 1: we have here, So so we think it's really important.
Speaker 1: As far as we know, Earth is the only planet
Speaker 1: to feature plate tectonics, which actually is a massive thermostat
Speaker 1: for the planet. When oceanic plates slide underneath the lighter
Speaker 1: continental plates, massive amounts of the oceanic crusts is crushed
Speaker 1: and absorbed into magma. The rock in those oceanic plates
Speaker 1: contains huge stores of carbon dioxide, so when volcanoes release
Speaker 1: magma from beneath the crust, it also contains some of
Speaker 1: that CEO two, which travels as a gas up into
Speaker 1: the atmosphere and there it hangs around and it absorbs sunlight,
Speaker 1: which in term warms the atmosphere and eventually the planet below.
Speaker 1: And when the planet warms, more of the oceans evaporate,
Speaker 1: warming the atmosphere even more. When you have a warm,
Speaker 1: wet atmosphere, you have lots of rain that rain brings
Speaker 1: dissolves c O two back down to Earth. Rocks on
Speaker 1: Earth are an excellent store of carbon, and when CO
Speaker 1: two rich, rain falls on them as the knock on
Speaker 1: effect of weathering them, meaning the wearing down definition, not
Speaker 1: the opposite one. All of that carbon in the rocks
Speaker 1: and rain makes its way to the sea, where it
Speaker 1: dissolves and eventually sinks to the ocean's bottom. As more
Speaker 1: carbon is removed from the atmosphere and stored, the planet
Speaker 1: begins to cool again. Over time, the carbon at the
Speaker 1: bottom of the ocean forms new oceanic plate crusts, and
Speaker 1: eventually it will find itself along an ocean ridge where
Speaker 1: it collides with the continental plate and the whole process
Speaker 1: begins again, and the Earth starts to warm once more.
Speaker 1: This unique property of Earth has kept the planet's climate
Speaker 1: stable more or less constantly for more than four billion years,
Speaker 1: which has allowed life on Earth to grow and flourish.
Speaker 1: When you take all of these details together, a weird
Speaker 1: picture of Earth emerges. It's almost freakishly perfect for life.
Speaker 1: That's so many different variables, each at just the right temperature,
Speaker 1: just the right location, heat time, whatever would come together
Speaker 1: to form a stable whole seems to make Earth a
Speaker 1: staggeringly improbable place. You couldn't ask for a better place
Speaker 1: for life to emerge. And maybe that's the point. Maybe
Speaker 1: the seeds of life are commonplace in the universe, but
Speaker 1: Earth is unique. We simply don't know. We still know
Speaker 1: so little about space, our galaxy, and the universe that
Speaker 1: we can't say if Earth is freakishly unique or one
Speaker 1: of many. And as we get better at deducing the
Speaker 1: existence of habit of planets with our space telescopes, they
Speaker 1: seem to pop out of the cosmos like a magic
Speaker 1: eye poster does when you lose focus in just the
Speaker 1: right way. Maybe planets that can sustain life are more
Speaker 1: abundantly the universe than we realize perhaps assembling those seeds
Speaker 1: into life is where the filter lies. The farther back
Speaker 1: we look in time, the less we understand. So if
Speaker 1: you're going to look for something that might be really hard,
Speaker 1: harder than it seems, farther back in time is the
Speaker 1: plausible place to look, because that's where we don't understand things. Uh,
Speaker 1: And the very first step from completely dead matter to
Speaker 1: some proto life that has to be the earliest step
Speaker 1: on the one we have the least knowledge of, and
Speaker 1: more plausibly it's the hardest step. Or perhaps not. Perhaps
Speaker 1: right now the universe is teeming with primitive life. Perhaps
Speaker 1: the great filter lies somewhere after that. There were, after all,
Speaker 1: some enormous steps to get from the emergence of life
Speaker 1: here on Earth in the moment we're sharing between us
Speaker 1: right now, m back on the early Earth, tucked away
Speaker 1: just so, in a solar system, tucked away just so,
Speaker 1: in the galaxy with its volcanoes chugging away at producing
Speaker 1: a warm atmosphere and its oceans producing a warm liquid
Speaker 1: medium for molecules to organize into life. At some point,
Speaker 1: one particular moment in Earth's history, all of those separate
Speaker 1: components came together to form a full fledged living cell.
Speaker 1: As far as we can tell, this moment happened around
Speaker 1: three point eight billion years ago. At first, these simple,
Speaker 1: single celled organisms were nothing more than gooey bags, with
Speaker 1: the parts for replicating themselves and the parts for converting
Speaker 1: food into energy all slashing together inside of the cell.
Speaker 1: They spread by dividing into exact replicas of themselves. But
Speaker 1: over time, over a very very long time, some new
Speaker 1: versions of these simple cells began to appear, and they
Speaker 1: had new specializations. Their interiors became compartmentalized, no longer slashing together,
Speaker 1: which meant that the processes they carried out, like converting
Speaker 1: that food to energy, became vastly more efficient. So processes
Speaker 1: like photosynthesis were able to develop. And after they did,
Speaker 1: the oxygen that this early cellular life excreted as waste
Speaker 1: started to settle into the atmosphere, creating an entirely new
Speaker 1: one that would eventually support the rise of new types
Speaker 1: of life. Then comes the invention of sex, a new
Speaker 1: type of reproduction where two entirely distinct individuals combined to
Speaker 1: form a new third version of themselves. And it's about
Speaker 1: here that natural selection cracks its knuckles and comes aboard
Speaker 1: as the driving force of evolution here on Earth. When
Speaker 1: natural selection is presented with new options rather than rough
Speaker 1: copies of the same thing, new adaptations emerge much more quickly,
Speaker 1: which kicks evolution into hyper drive. The simple celled organisms
Speaker 1: that made up life on Earth got better at being
Speaker 1: living things, and then for a long time nothing much changed.
Speaker 1: It seems as if life had reached the stasis, maxed out,
Speaker 1: come upon some invisible wall, and take into coasting. Rather
Speaker 1: than progressing toward ever more complexity, Earth seemed content with
Speaker 1: its fast seas teeming with specialized, extremely well adapted, single
Speaker 1: celled organisms. After that first three hundred million years of
Speaker 1: ceaseless innovation, life on earths stayed the same for the
Speaker 1: next three billion years. But around five hundred million years
Speaker 1: ago something huge happened. Life suddenly developed new ambitions, and
Speaker 1: it exploded into new, extremely complicated and sophisticated forms. And
Speaker 1: in geological terms, it happened overnight. Basically go from nothing
Speaker 1: to everything. This is Dr Phoebe Cohen. She's a paleontologist
Speaker 1: at Williams College in Massachusetts. So the vast majority of
Speaker 1: the history of life on Earth is that of microscopic organisms.
Speaker 1: Before the Cambrian almost all life was microscopic or at
Speaker 1: least very very small, and ecosystems were dominated by things
Speaker 1: like amiba and bacteria. And after the Cambrian ecosystems are
Speaker 1: dominated by animals, um and so it's a really, really
Speaker 1: huge shift in the biological evolution of our planet. This
Speaker 1: sudden surge in complexity is called the Cambrian Explosion. We
Speaker 1: aren't quite sure why it happened. It's possible it was
Speaker 1: triggered when the widespread glaciation that covered Earth just before
Speaker 1: it began to melt. Or perhaps it was the oxygen
Speaker 1: and levels in the atmosphere released by photosynthesis slowly displacing
Speaker 1: the Earth's atmosphere of carbon dioxide, ammonia, and methane. We
Speaker 1: need lots of oxygen to power the conversion of food
Speaker 1: to energy, and perhaps the Cambrian explosion was triggered when
Speaker 1: atmospheric oxygen reached a critical threshold that could support more
Speaker 1: complex life. So if you go into low oxygen areas
Speaker 1: of the ocean today, there's plenty of animals living with
Speaker 1: almost no oxygen, but they're not doing anything. They're very boring.
Speaker 1: They kind of just lay there because they don't have
Speaker 1: enough oxygen to do anything exciting. So one idea is
Speaker 1: that oxygen did reach some sort of threshold around the
Speaker 1: Cambrian that enabled organisms to start doing fun things like
Speaker 1: chasing after each other and ripping each other apart, and
Speaker 1: that that played a big role in changing sort of
Speaker 1: the structure of ecosystems that lead to a huge diversification
Speaker 1: um within the animal claid. Whatever the reason, half a
Speaker 1: billion years ago, most of the complex body plans that
Speaker 1: are still around on Earth to day suddenly arrived. It's
Speaker 1: as if those organizing principles of life entered a new phase.
Speaker 1: Within just thirty million years, plants made their debut on land,
Speaker 1: and just forty million years after that, animals followed them
Speaker 1: out of the water. It's astounding to think of, but
Speaker 1: within a span of just seventy million years, life on
Speaker 1: Earth went from nothing but single celled aquatic organisms to
Speaker 1: animals that lived and moved and walked around on land.
Speaker 1: Because life had remained so simple for so long before it,
Speaker 1: the Cambrian explosion makes an excellent candidate for the Great Filter.
Speaker 1: It could be so unlikely that it universally denies intelligent
Speaker 1: life from forming evolutionarily speaking, there's never been a more
Speaker 1: important event in the history of Earth. Following the emergence
Speaker 1: of life, twenty of the thirty six body plans that
Speaker 1: exist on Earth today, the plans that give shape to
Speaker 1: squid and the ish, and humans and worms, all suddenly
Speaker 1: appeared on Earth, and those new body plans led to
Speaker 1: a riot of evolution. The dinosaurs rose and fell, and
Speaker 1: small mammals emerged from their burrows and climbed the trees.
Speaker 1: Tree dwelling apes found their way out of the savannah
Speaker 1: and started walking upright, becoming the first contours of humans.
Speaker 1: And it's about here that we arrive at another step
Speaker 1: in the long span between the emergence of life on
Speaker 1: Earth and us, the evolution of intelligent life. Humans tend
Speaker 1: to think of intelligence is what differentiates us from other
Speaker 1: life on Earth, but instead we seem more like the
Speaker 1: current endpoint in an evolution of intelligence. Signs of intelligence,
Speaker 1: in some form or fashion are all around us. In
Speaker 1: two thousand eight, Japanese researchers showed that slime mold, a
Speaker 1: unicellular organism, can learn a schedule of electric shocks when
Speaker 1: they shocked the mold at regular intervals, and yes, they
Speaker 1: shocked mold. The mold learned to anticipate the next shock
Speaker 1: and recoil from it before it was delivered. The Moosta
Speaker 1: plants have shown that they can learn to differentiate between
Speaker 1: being dropped and being touched. Where initially the plants responded
Speaker 1: to both experiences in the same way by curling their leaves,
Speaker 1: after being dropped several times, they learned to keep their
Speaker 1: leaves unfurled, and they retain this learned behavior even after
Speaker 1: they haven't been dropped or touched for months. The use
Speaker 1: of tools, which we imagine is quintessentially human, isn't unique
Speaker 1: to us either. Chimpanzees use tools to make gathering food easier,
Speaker 1: like sticks to draw termites from their mountains by the fistful,
Speaker 1: and rocks to bash open hard shelled nuts to get
Speaker 1: to the meat inside. But at some point we drew
Speaker 1: away from the rest of life. In the development of
Speaker 1: our intelligence, we became the first animals to use tools
Speaker 1: to make other tools. This is the birth of technology.
Speaker 1: No longer were we relegated to using only what was
Speaker 1: found in nature. We learned to use nature to fashion
Speaker 1: new tools to better suit our needs. We made spearheads
Speaker 1: and axes, out of stone and learned to hunt large animals.
Speaker 1: Meat is more energy dense than plants, and we learned
Speaker 1: to cook food about eight hundred thousand years ago. When
Speaker 1: we did, we unlocked a tremendous amount of nutrients and
Speaker 1: energy that hadn't been available to us before. We developed language,
Speaker 1: which allowed us to better coordinate ourselves and hunt together
Speaker 1: and interact with one another more effectively. We learned to
Speaker 1: make clothes to keep us warm as we spread out
Speaker 1: beyond the subtropical climate we evolved in. We learned to
Speaker 1: make boats to carry us to new places. We learned
Speaker 1: to make ceramics to store our food. We learned to
Speaker 1: grow crops, which led to cities in the foundation of
Speaker 1: the modern era. And there was another quirk of that
Speaker 1: chance collision between the planetoid THEA, and Earth, which produced
Speaker 1: the Moon. It also produced massive deposits of minerals and
Speaker 1: metals near the surface that humans could easily get to.
Speaker 1: Over time, we abandon those stone tools in favor of
Speaker 1: more reliable metal ones, and eventually we put all of
Speaker 1: those millions of years of accumulated intelligence and technology into
Speaker 1: ships that broke the bonds of Earth and launched the
Speaker 1: first of our species into space. Within the astronomically short
Speaker 1: period of about a hundred thousand years, humans left the
Speaker 1: wild and went to space. But perhaps as unlikely as
Speaker 1: the emergence of human intelligence may seem, it may simply
Speaker 1: be the expected outcome of those organizing principles of life.
Speaker 1: There are two options before us. Then, either we humans
Speaker 1: are unique in our universe and utterly alone, or we
Speaker 1: are not. And if there is other life elsewhere, then
Speaker 1: that means that the great filter, the hardest step, lies
Speaker 1: not in our past, but in our future. It means
Speaker 1: that the challenge that lies ahead of us is more difficult,
Speaker 1: more improbable to overcome than dead molecules organizing themselves into
Speaker 1: living cells or apes learning to build ships to the moon,
Speaker 1: And rather than having millions of years to try and
Speaker 1: fail before succeeding, we will have one shot to get
Speaker 1: it right. If the great filter lies in our future,
Speaker 1: then it appears that we are entering it right now,
Speaker 1: now here in the twenty one century, four point three
Speaker 1: billion years after life emerged on Earth. We are entering
Speaker 1: the evolutionary step that no life in the universe has
Speaker 1: ever managed to survive. Carl Sagan had this this great
Speaker 1: phrase about humanity has grown powerful before it's grown wise
Speaker 1: um and our power through technology has been increasing exponentially,
Speaker 1: but our wisdom has been maybe it's been increasing a
Speaker 1: little bit, but suddenly not exponentially, and it's it's getting
Speaker 1: these two things have got out of check with each other.
Speaker 1: We've got an unsustainable level of risk. The technology that
Speaker 1: got us to this point is taking a new shape,
Speaker 1: one that we haven't encountered before, and it is presenting
Speaker 1: new risks to the survival of our species and indeed
Speaker 1: life on Earth. You right now are living in what
Speaker 1: maybe the beginning of the most dangerous period in the
Speaker 1: history of the human race. On the next episode of
Speaker 1: The End of the World with Josh Clark, if we
Speaker 1: are the only intelligent life, humans could have a bright,
Speaker 1: long future ahead of us, a triple less civilization based
Speaker 1: on super intelligence, super happiness, and super longevity. But between
Speaker 1: us and that bright future lay existential risks, and they're
Speaker 1: like nothing we've ever encountered before.