What Counts as Life? Astrobiology Series: Part 1

This is the first installment in the astrobiology series, adapted from the astrobiology course Dr. Dakotah Tyler taught at university. Expect to learn what astrobiology actually means, why sci-fi aliens are usually too human, why UFO claims require careful assumptions, and why defining life is harder than it sounds. We cover viruses, dormant microbes, ideas as information systems, chemical possibility, life as a physical process, habitability, synthetic life and biosignatures. As always, lead with curiosity.

Transcript

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Welcome, welcome, Dr. Star Kid Podcast. I am your host, Dr. Dakota Tyler, astrophysicist and professor of astrobiology. Today we are starting my astrobiology series. It is an adaptation of this course, this astrobiology course that I taught. A little bit of background. I did my PhD in astrophysics at UCLA. And for the last three years there, I actually taught my own astrobiology seminar to freshmen at UCLA during the spring quarter. And last year, I adapted that course and taught it at Pomona College. This series is going to be another adaptation of that astrobiology course that I taught. And it should have somewhere between 10 to 15 installments. This is the first installment in that series. So hopefully you enjoy this. I think it's a very interesting topic. So the first thing, and I have uh I have some of my notes from the course off to the side. So if you see me looking over there, that's why. So the the first thing is to address this what what what you image when you hear the word astrobiology. For me, as a sci-fi nerd, when I think of life out in the universe, something that is immediately triggered is like Avatar, the blue ones, the blue people, not the bald one, not the bald kid. And speaking of being a bald kid, how crazy is that? A bit of a side note. Uh, something uh uh a note on resilience if you follow me on my platforms, you know that I talk a lot about resilience, and there's nothing that can make a young man more resilient than being bald at a young age. Listen, I my hairline started receding when I was like 13 or 14. Can you imagine? Uh, do you know how badly you get bullied? I'm in eighth grade, ninth grade, hairline receding. It's insanity. It's insanity. But you know, they say the universe reserves its toughest challenges for its toughest soldiers. And I mean, I feel like I'm battle tested, you know. Matter of fact, I I feel like people are lucky I'm not a super villain. That's how you make a supervillain. Make a little boy, a young boy, a young man. Because y'all see how men be acting when they go bald at old age. It's like they can't, there's so much insecurity around hair. And it's like I dealt with that when I was like 14. You know what I'm saying? I wasn't even a grown man yet. I was still, I was still like growing larger, I was still developing as a man, anyways. So I'm thinking blue avatar folks. Okay, okay. I think that that's an interesting example, but when you think of James Cam, James Cameron's blue avatar, the Navi, you realize that they're actually quite human. I mean, a lot of them are hot. Why are they hot? Why would the, and hopefully y'all don't take that the wrong way, but why would why would they be hot? Why would they be attractive to us? You see uh the the the latest one, fire and ash. Why are they hot? Why are all the female characters hot? Why are all the male characters built like you know, Greek god swimmers? Why is everybody hot in that entire thing? And obviously, it's because they want us to connect with the characters, but they look very human-like. I mean, they look very human-like, two eyes, two ears, they have hair, they do have the weird hair, tentacle, uh hookup thing. Okay, that's a bit different, but it's like two legs, two arms. They're larger because they're on a moon, they're on a world that is less massive, so there's less gravity, so they can get larger. I mean, that's a creative scientific application, but they're they're they're just very human-like, right? They have like a uh one less finger, I think. And if you look at a lot of the animals on um Pandora, which is what the world's called, which is a moon that orbits uh Polythemus, which is a gas giant, sort of like Jupiter. So, I mean, it's a cool idea, it's a cool concept. Sci-fi is a great narrative for um exploring these scientific ideas like astrobiology. But one thing that I've noticed about almost all of the animals on that, on that world, they just have six legs, right? And so it's like the the creativity there was oh, this is a planet where instead of the uh animals that crawled out of the ocean having four legs, they had six. So, like they had the in the first one, you remember they had that black jaguar looking thing that had six legs, and the horses have six legs, and it's like I mean, they you know, this is it's a it's a surface level modification, in my opinion, and it's not really an exploration of what scientists mean when we talk about astrobiology and the different potential routes that life could take out in the universe. Um, another very common depiction is the alien monster. You think about a series like Alien, which I love the uh alien um franchise. I've really one of my favorite movies in the whole thing that I think is underrated is Prometheus. And this isn't a movie review, so I'm not gonna dig into that. I I can do, I think it's I think it's cool enough to talk about. I'll do that in a in a different video or episode. But I think an interesting thing to highlight there is that in the alien franchise, it's about projecting our fears onto the thing, right? It's it's it's got you know titanium teeth and a tail that you know could just could it's almost a machine that has been designed to terrify humans as opposed to a living organism that has been designed and uh evolved for a specific environment. And there's a lot of lore in that and reason for that. So, you know, I'm not dissecting that movie per se. I'm just I'm just poking at how insufficient, I think, most cinema um franchises are in exploring astrobiology in a way that is probably more closely tied to um possibilities or reasonable outcomes that we may expect based on what we know, which is what we have to go off of. Uh, Star Trek. You know, Star Trek, there's like all these different species of quote people. And essentially, what are they? They're people that have, and some of the people have pointy ears, and some of the people uh, you know, have masks and you know, just different features, but it's very obviously people in costumes, which you know, again, it's it's it's it's a scaled-down version of the avatar franchise, the the Navi. It's it's very it's very people-based, right? The advanced intelligence is very people-based. Um, in the way of water and fire and ash, even the super intelligent whale creatures in um the avatar movie are based on whales on earth, right? So it's like it's very hard to pry ourselves and our imaginations away from earth biology, uh, human-centric, you know, anthropomorphic, anthropocentric thinking. And that's something that we have to be able to do if we want to honestly and thoroughly explore the field of astrobiology. Something that this series is not going to be about. UAPs, uh, UFOs, whatever you want to call them. Not really what people are thinking about when they're thinking about um astrobiology. It doesn't really have anything to do with this. You know, it's a phenomenon. There are things that are flying around, don't know what they are. You can't identify them. But it's very important to be aware of the distinction between I can't identify this and I have identified this as an alien that traversed hundreds or thousands or millions or billions of light years across the universe to zoom around in the atmosphere on Earth for some unknown reason. And one of the things that is very important uh in general, I think, as a citizen of this modern age, but also in science and also in this series that we're going to explore is critical thinking, examining our assumptions. What assumptions have you made when you decide that you think that an unidentified craft should be instead of unidentified, positively identified as an alien species from somewhere else? There's so many assumptions that you have made there that are unnecessary. And it's okay to make assumptions. We have to, in fact, make assumptions, right? When you walk out of your house every day, you there are a number of assumptions that you're making. When you get in your car, there's a lot of assumptions you're making. You're you're you're assuming that the people on the road are gonna drive according to the rules. You're assuming that the laws of physics haven't changed overnight, and that when you start your engine and turn on the car, that some weird change in the laws of physics is gonna lead to your car exploding. You're assuming that. Now that's a safe assumption to make. That's not necessarily one that you have to examine, but when we get into the hypothetical space, like we have to do inherently in something like astrobiology, something like thinking about life in other places, you have to be aware of your assumptions. It's okay to make them, but you have to be aware of them. And I don't, I'm not sure that people are aware of the insane number of assumptions that are being made when they are assuming that there are aliens flying around our atmosphere. You're assuming that there's advanced life that's close enough that could find us, that they somehow found us. Mind you, Earth is one of eight planets orbiting the sun, which is one of several hundred billion stars in the Milky Way galaxy. There are, on average, four to five light years in between each star. You know, you're assuming that they scanned the entire universe and accurately found a planet that had sufficient life. I mean, this is su that this alone is an assumption that I I you can't possibly justify. You're assuming that they have crossed these immense distances in a relatively short amount of time. This is also a huge assumption. You cannot travel faster than the speed of light. This has been demonstrated that nothing can move faster than the speed of light. Nothing can travel at the speed of light, nothing with mass can travel at the speed of light. So, and again, this is something that's been demonstrated through experiment, through observation countless times. It's never once been violated. You're assuming that they can also violate that. You're assuming that essentially magic, you're assuming that the that they're so advanced that their technology vi violates physics. And you know, it's true that we don't know what we don't know. Always true. And I'm always open to new evidence, always 100%. And if I ever see evidence of anything that turns on its head something that I have believed in the past, it's time to update our beliefs, right? That that is that's what an intelligent person does. If you ask me, one of the highest signs of intelligence is what is your response when presented with new information, new evidence? What is your response? And I'll change my mind the moment that I see evidence to the contrary, but saying that they not only knew about us, mind you, light from Earth travels at the speed of light. And we've only been emitting things into space that are techno signatures, like the fact that we use radio communications and that sort of thing for uh a century, which means only places with a hundred within a hundred light years would even potentially know about us. But if you can't go anywhere near the speed of light, you know the the these are journeys that would take hundreds of thousands or millions of years. Anyways, let me get off that soapbox. One more interesting thing is that, and I'll throw this up, if you look at the map of UAP sightings, reported UFO sightings going back over a hundred years, you will notice that they are almost exclusively, almost, in the United States and Europe. All the places where there is this big UFO culture, big UAP culture, something interesting to think about. Now, what assumptions are baked in there? Well, somebody may say that there aren't necessarily uh mediums or avenues for reporting those UFO sightings in other places, and I think that that's you know, that's I think that that's a fair point to bring up. Another point to bring up is that UFOs are seen in the places where there is an intense UFO culture, you know. I I think that easily you can describe this map by people in the United States and Europe being obsessed with this idea of aliens. I think it has a lot more to do with the imagination. Again, when I see convincing evidence, that's all it takes. If you show me convincing evidence, I will believe anything. I'll believe anything that you say. If you show me evidence that life started on Earth three and a half billion years ago, it's very simple single-celled organisms, and slowly over time evolved into things like animals and plants and fungi, and that eventually it gets complex and things get big, and there's a whole bunch of different mass extinctions. And every time there's a mass extinction and all these things die off, a small number of things end up surviving, and then they grow on to dominate, and then there's a huge mass extinction, and then most of those things die. If you show me evidence for this, for that process happening and leading to two-legged, two-armed, two-eyed, bald Homo sapiens, I will believe it. If I see the evidence, I will believe anything. Moving on, the search for life outside of Earth goes back a long time. Back in the late 1800s, there was this Italian astronomer named Giovanni Schiaparelli. And he would observe, this is when telescopes were still in their early days, pretty primitive, they weren't super advanced yet. And he would look at Mars, and through his telescope, he saw these like lines, this what appeared to be a grid. Um, he called them canali, uh, channels on Mars. And he imagined that these channels on Mars, they were part of an interplanetary transport system. That there must be this advanced civilization on Mars that was using these channels to go from place to place, perhaps to bring water from the poles where you could see that there was frozen ice. Now, they didn't know that a lot of that was frozen CO2 instead of frozen H2O, and we do know that now, but they imagine that you know Mars was this, it was this dried out shell of a planet, and the Martians were doing everything, they were on their last leg, and they had this these systems of bringing that ice and bringing it to where it needed to be. Very imaginative, very much delusion, by the way. There are no such things on Mars, there are no channels on Mars, not in the way that that he saw it. We'll get to this in a later episode, but there actually are channels and tributaries that are dried from liquid water that Mars apparently used to have. Again, that's for a later episode. The point that I'm bringing out is that this idea of life on Earth, this idea of life outside of Earth, and us projecting from what we experience of being human elsewhere, it goes back as far as the field itself goes back. What are we really looking for? When we say astrobiology, what do we mean? Astro, of course, meaning star. Uh essentially at this point, anytime you hear the word astro, we're just talking about outside of Earth, right? Talking about out in space, astronomy, you know, the study of the motion of the stars, astrophysics, the study of physics at a cosmic scale for things that are happening outside of the earth, astrobiology, the study of life outside of the earth, in other star systems, in other galaxies. So the astro is easy to define. Let's just call that outside of the earth, the kind outside of the confines of the earth. But what about biology? Okay, biology, the study of life. But what is life? How do you define life? And it it's one of those questions that feels obvious, but when you start writing things down, when you start to get granular, I think it's actually much more difficult than it seems. So what is life? Is it something that can move? Is it something that grows? Is it something that can reproduce? Is it something that has to be able to do all of those things? Well, what if it can't do some of them? Does that mean that it's not living? What if it's what if it can do some of those things sometimes, but not all the time? Does that mean it's not living? What if it can't do any of those things, but you and I would still agree that it that it was life? It gets very murky, it's very difficult to define life, but we can go on a standard biological definition. Um, I'm gonna read the one that I favor myself. And I I will point out that if you look up, you just Google life, you'll get a definition. If you look in different um biology textbooks over time, you'll get different definitions. Like it, whatever you Google, the AI overview, what it tells you about life, what um uh Webster's dictionary tells you about life, what Wikipedia tells you about life, like none of these things are set in stone and none of these things are in strict agreement. And if you ask the leading 100 biologists on earth to define life in a way that will be strictly applicable elsewhere in the universe, I guarantee you're going to get many different answers because it's not so easy to define. Here is a typical standard biological definition. Life is a self-organizing system that maintains itself using energy and can reproduce with heritable information that allows evolution over time. Put in a slightly different way, life is a self-sustaining system that uses energy, right? So it's as a system that can sustain itself, it can go about what it needs on its own, that uses energy to maintain order. For us, that's like eating food. We get energy from the food we eat. Our body breaks it down, facilitates all of the processes that we need. We draw energy from the food, breaks down, we get rid of cells that die and rebuild new cells, right? So uses energy to maintain order and can pass information so populations can evolve. Talking about reproduction. When a mommy and a daddy love each other very much, they come together. You get 50% of the DNA from the dad, you get 50% of the DNA from the mom. That goes through. There's some errors in reproducing either of those genomes as they connect. And ultimately, you're gonna get some mutations, and you're gonna get some traits from the mom, you're gonna get some traits from the dad. And if this happens for an entire generation, it's just going to turn out that some of those members of the population are going to have an easier time surviving and reproducing, and some will not. So you end up with this selection process, and that selection process will be influenced by countless external variables from sexual selection to the you know, changes in the climate, to what other types of predators are hunting you, to what types Of energy sources are available to you, what type of food items are near you, and that leads to evolution over long time scales. Okay, so I'll just say that again. Life is a self-sustaining system that uses energy to maintain order and can pass on information so populations can evolve. Just a standard, standard biological definition. With what I just said, we can quickly highlight examples of things that kind of seem like they're living, depending on who you ask, but are yet excluded. Think of something like a virus, notoriously on the cusp, and I know biologists that will say that viruses are very clearly just machines that you could like replicate in a lab and are definitely not living. However, I know people who who are biologists who also disagree with that and do think that they should be included in the umbrella of life. They replicate, of course. I mean, in some sense, that's all a virus wants to do is replicate. They evolve, viruses evolve over time, uh, but they are not self-sustaining. They absolutely require a host. They cannot do anything without a host. They need a host, they need to hijack the machinery of a living cell to reproduce. They they deconstruct everything and then reconstruct just a bunch of versions of themselves. So they outsource metabolism, they they don't have that ability, they're not self-sustaining, and they can't reproduce without without a host either. And so, for a lot of people, that's just like not living. But you know, you you can't look at one under a microscope because they're smaller than visible wavelengths of light. So you you can't see one, but they move around and do stuff. You've ever seen one of those bacteriophagias, it's like it has like the little legs, it's kind of like a spider, and then has like a little column on top, and then um has like this genetic material sitting on top, and it's like it's moving around, it's doing things, it clearly has motivations and goals. It's you know what I mean? It's a it's trying to replicate itself. It seems like a living thing, you know. If if if I showed you a video of a uh bacteriophage, which again, you know, it would be a um a rendition of what it looks like as opposed to a real-time video, I and you said, hey, is this thing living? I I mean, it passes the eye test, right? Which it, you know, is not really a scientific argument, but you know, viruses to me they do pass the eye test. And then, of course, there are sterile organisms that we would absolutely agree are living that can't reproduce, like a mule. This is the offspring of a horse and a donkey. Is a mule not living because it can't reproduce? I don't know anybody that would say that. Okay, so we make an exception there. What about ants? Are ants living? The vast majority of ants that are alive now and ever have lived will not reproduce. In fact, they are incapable, they are not capable of reproducing. The queen in the colony, this is true for a lot of hive insects, it's the it's the queen that does all the reproducing. So are ants not alive because they can't they can't reproduce? I don't know anybody that would say that. Same same sort of thing is true for bees, same thing is true for sufficiently young or old humans. I mean, what about a human who's who can't reproduce? What about an astronaut that could potentially reproduce, but is in space by themselves on the ISS, and so there's nobody there to reproduce with. I think it's also illegal to have sex in space, which is kind of interesting. Nobody would say that an astronaut in space that can't reproduce isn't living. But if we're gonna get strict about that definition, the ability to reproduce, right? And so obviously there are workarounds, and you you could easily just probe the semantics a little bit and be like, uh, on a system level, the species needs to be able to reproduce, and it kind of will um you know marginalize out these instances of like older people or younger people or somebody who's stranded on an island by themselves. And so my point here is to point out that it's not so easy to define. And one thing that we are sure to do in our definition is put ourselves at the dead center. So no matter how we define it, we're sure that it includes us. And animals who are on the phrase, it's like, ah, well, you know, it doesn't include them as well. And then organisms that are on the phrase, like something that doesn't share our lineage back to the first life forms, like a virus. It's like, uh, well, you know, they don't really fit into that definition. This is something that's really interesting, is that viruses do evolve, and in fact, the human genome, in fact, the genome of all animals, has and plants and viruses or uh plants and fungi has viral DNA. It has become a piece of us, it has become a piece of what we are. Very interesting. Okay, now what about dormant like uh seeds, spores, uh microorganisms, little things like tardigrades that can kind of like go into these dormant phases for a long time. Is that is you know, is that a living thing? Is it alive? Is it dead? Something that is very, very interesting. Cryptobiosis, where living things can kind of like pause their lives and pick it up at a later time if conditions are satisfied. There was a discovery a few years ago, back in 2020. They found in marine sediment that there was microbial life that was as old as 100 million years. It was a hundred million years old. Dormant, it had been dormant for 100 million years, and they uh added some nutrients, whatever these microbes ate, and a lot of the microbes came back to life, they started activity, they started reproducing. That's insane that uh that life could go dormant for a hundred million years, and something that's very interesting that you will get this theme throughout the course of the series is that what we call intelligence and what we call thriving is very relative, right? It's very, it's very it's very subjective. We see ourselves as kings and queens of planet Earth, but microbes have been here for much longer. They dominate. I mean, your body, on average, a human body is made up of 30 or 40 trillion cells. Obviously, you know, this is gonna vary uh based on your size and uh you know your age and your your gender, your weight, whatever. Like maybe there's a whole bunch of different things. There's 30 or 40 trillion human cells. Individually, you got kidney cells, your muscle cells, your skeletal cells, your neurons, and the in the average human body, there's like 40 to 50 trillion bacterial cells. There is more microbes in your body right now, individual, independent microbes, than there have ever been humans that have ever lived in the history of earth in your gut right now. That I mean, this is this is crazy. Who is the dominant life on earth? I mean, how are we defining dominance? If something happened to the earth and it became uninhabitable for a hundred million years, you and I would be screwed by the end of the week or something, right? Maybe by the end of the day. But apparently, there are bacteria that just go into stasis for a while. 100 million years here, 100 million years there. Realize that this is what we found. For all we know, there may be bacterial life that has been dormant for a billion years, right? It's like we we don't know. Like this is the edge of discovery. This is, I mean, this is crazy. And I think it's important to realize what with what we with just what we know about life, it can thrive under pretty much any scenario, any circumstances. And and this is an important thing to keep in mind is that when life gets started, it it's so it's so mendable, it's so adaptable that it's almost always gonna find a way to survive. And this is a great example of that. If you thought you were gonna trap this micro this bacteria in a rock for 100 million years and for sure it was gonna be dead, you'd be wrong because it came back to life. There are some more really interesting edge cases, ideologies, cultures, trends, fads, ideas. Hmm. They spread, they can spread from person to person, they can shape entire cultures, they influence our behavior. The ideas that you have came from somewhere else, they grow in your mind, they reproduce, they evolve. You you take the pieces that you want, you get rid of the stuff that you don't want, you tell other people, you come together with them and you you produce a new idea. It's like all the things are there: reproduction, there's energy, right? Um, perhaps it's a little bit closer to a virus, and people have oftentimes spoke about ideas and memes as going viral. I think this is interesting. If the if the hosts all die, if people all die, then like you know, ideas die as well. Capitalism and communism can't exist without human minds to be propagated through. But I think that that's a very interesting perspective. And so, you know, I would ask, is an idea more or less alive than a virus? What do you think? I don't know. I think that's a I think that that's a very interesting conversation to have. Is it more or less alive than a coronavirus or a bacteriophage or you know, pick your favorite virus? They both have inheritance, they both have reproduction, they both have selection criteria, they both have evolution. Yet they are not autonomous physical systems. They don't metabolize, they don't maintain some homeostasis. Very just like a very interesting idea. But they are information patterns, both that replicate via living animals, plants, fungi, via brains, institutions, media, organizations, cultures. And so to wrap up this little segment, I think it's possible and important to consider that our definitions of life are insufficient for the possible forms that it could take. It's very important to point that out because we're talking about astrobiology. If we can't wrap boundaries around the biology part, that's important. That's important to understand. Think about this. There are roughly, this is an estimate, 10 to the 80 atoms in the entire universe. 10 to the 80 meaning a number, imagine a one with 80 zeros, whatever that number is, that's how many estimated atoms there are in the entire observable universe. Okay. Now, a molecule is just a string of atoms, and they can be configured in any number of ways. A molecule, let's take H2O. What does H2O have? It has an oxygen atom and it has two hydrogen atoms, and the electrons and the hydrogens hang out with are shared with the oxygen. So this is a molecule, it has bonded. These two hydrogen atoms, this one oxygen atom have bonded together. One of the most abundant molecules in the entire universe, by the way. If you take a bunch of oxygen and you take a bunch of hydrogen and you let them mingle, you can't stop them from pairing up. This is why it's so common. Oxygen is very common. It's like top five most common elements in the universe. Hydrogen, by far, number one most common element in the universe. When these two things meet, which they often do, you can't stop them from making water. So water is not, it's not rare. Now, it may be rare to find a place where you can have liquid water, but that's different. That's different. And it's important, this is important. We'll talk about this as well. Uh, the point is that you imagine very simple molecules um that just you know have bonds between, you know, the the dozen most common um elements in the universe, and there are actually more potential chemical configurations than there are atoms in the universe. So let me put this another way. If I gave you the complete list of all the different chemical configurations, all of the different potential molecules that could form, and I tasked you with the job of going through and making each one of them with the atoms that exist in the universe, you would run out of atoms, 10 to the 80. You would run out of atoms before you found out every molecule, every configuration that could potentially exist. This is what chemists are talking about when they say that there's this immense chemical space. There is this vast chemical parameter space of chemicals that could happen. Now, the reason that this is important, it's not like all of those things are going to exist. Some will be unstable, most will be completely useless and inert and you know, um, not helpful for life or have anything to do with life. But it's important to point out that all the chemistry that we know about is limited to the chemistry that we know about, and there could be much other chemistry that we don't know about. Now, that's different from saying that we don't understand physics. The physics is the same everywhere. This is an observable fact. You can take a telescope and we can look at a galaxy on the other side of the universe, and we can see that that galaxy is obeying the laws of physics as we know them. It's not gravity is not different over there. There's not different stuff. The same molecules are present, the same atoms are present in that galaxy. We can this is something that we can detect. You can do the you can get the spectrum and you can tell what this stuff is made of. So the physics is the same everywhere. If you're thinking in your head, well, how do we know the physics could be different on a different planet? No, it can't. Nope. The physics is the same everywhere. Chemistry, that can be different in different places. We only know the chemistry that we know. So the chemistry could be different, but the physics is the same. The atoms, the how atoms behave are the same. The laws of physics are the same. And so it's important to tie any sort of astrobiology discussion at the very least to ground level physics. That we know that the physics won't be different somewhere else. And this is one of the foundational concepts in all of physics. One of the first things that you learn is that the physics is the same everywhere. And again, countless observations that cannot falsify that. You cannot come up with a single example of the laws of physics being violated. There isn't one. There isn't one. There, there just isn't. So we can accept through evidence the laws of physics are the same everywhere and have been throughout time. You know, this is a very, very foundational, um, very evidence-based. But the chemistry, that's the that's the big question. You start working with some chemicals in uh, you know, phase states that we're not familiar with, and just in different conditions that we are not familiar with. And, you know, what can life, what can life do with that? You know, these are interesting questions. But it's very important, right, that we understand that at the base level, the physics is the same. The chemistry has a lot of space that we have that we have no idea about. And again, that doesn't mean that we know everything about physics. I'm not saying that. I'm just saying that the physics is the same. An interesting thing, keeping that in mind, this vast chemical parameter space, what we we we focus on talking about life as like a kind of stuff. It's like us it's stuff that does things, but instead of focusing on the stuff, maybe perhaps it's better to focus on it as a process. Thinking about instead of thinking about life as like, oh, these things are living and these things aren't, you think about life as a physical process. It's a bit of a shift in thinking of it. There's a uh a course, for example, called fluid dynamics. There's actually so many things in the universe that behave as a fluid, and you can use these fundamental um differential equations to describe how fluids interact. You look at an image or a video of Jupiter, it's spinning around, it's got all these gas and it's like swirling in the atmosphere. And you look at a cup of coffee, a hot cup of coffee with some cold milk poured in, and you see as that as that milk swirls around, it like it falls because it's cold and dense, then it heats up and it like bubbles up. And as it bubbles up, it spreads out and like falls again and it starts to swirl around. And you realize that wait a second, this this cup of coffee sitting on my desk on Earth and the planet Jupiter, which is so big that you can feel like a thousand earths inside of it. Uh, basically, all of the mass in our solar system that is not the sun is essentially in Jupiter. The the mass of the earth, Mercury, and Mars and Neptune, these are actually pretty much just like a rounding error. As big as those planets are, it's like a rounding error. Mostly it's Jupiter. And the same fluid dynamics, that process of substances that have many particles that have different densities and viscosities and temperatures, when you mix them together, the output that you see can be described by the equations of fluid dynamics. So this is very interesting. Two things that are seemingly unrelated both obey the process that we know about in fluid dynamics. And thinking about life in that way as a process, as opposed to, oh yeah, like here's a clearly living thing. But you think about things that if they obey those processes, then they fall under the umbrella of life. It's a bit of an abstract idea, but I think I like it a little bit more because then we don't have to sit back and do this thing where we say, well, nah, virus isn't really life. Uh uh prions aren't really life. There's these things called prions. I don't know if you know what prions are. Prions, they have no cell walls, they have no walls at all. They're less living than viruses. But prions are these little things, these little molecules, and they get folded in a strange way. Protein folding is an integral part of life. We'll get into that later. And they get folded in this in this weird way. And when they come into contact with something else, they force that thing to fold in the same way. And so in that way, it spreads like a virus. If this happens, like in a brain, you have a prion that folds in a certain way and then makes the next thing fold in that way, you'll wreck the brain. In fact, this is mad cow disease. Y'all remember mad cow disease? It's caused by prions in the brains of cows. This thing, it's not living, it's not a virus, it's a prion. It touches something else in the cow's brain, it folds in the exact same way. Touches something else, it folds in the exact same way. And you have like this way, this wave infestation of prions, are prions life? I don't know a single person, I know people who will argue that viruses are life. I don't know anybody who will argue that a prion is life. That is like on the edge of this process. And you just, if we consider some key features in this idea of life as a physical process, and hopefully you're I know you're you're sticking with me here. But life is a physical process. You know, some of the key features are going to be around how it organizes into systems that have the ability to store information, that have the ability to access and use that information that they've stored both to maintain themselves and to act in the world in goal-oriented ways. And if you adopt this sort of more open approach to defining something like life, I think it gives us, it gives us a little bit more breathing room to go out there and have an open mind about the types of things that we'll find, the types of things that um that are potentially existing out on other worlds. At any rate, for now, we have one data point. That's all we have. We only have one data point, and that's life on Earth. So that's where we start from. And a common thing that people will say, perhaps something you're thinking, is well, why would you start from life on earth when we're talking about life somewhere else? Well, it's like that's what we know. To have a grounded conversation in reality, you have to start with what you know. You'd be awake, you're always open to the unknown, but it doesn't make any sense to start thinking and searching for something you have no idea what you're talking about. You start from what you know, right? It's a good place to start. You know, if we wanted to, if we wanted to think about ourselves as average life, we I don't know if that's true. Um, but I think it's safe in astronomy to assume that what you have going on is pretty average. If there's 500 billion stars, most of the stars are going to be average. If you find yourself orbiting one, probably think that you're kind of an average planet, you're around an average star. It's not necessarily the case. We could be one in a trillion or one in a hundred trillion or one in a septillion. We could be the only life in the universe. People and people gloss over that. Oftentimes you'll hear people say, Well, it's it's it's impossible that we're the only life, or we're the only advanced life. It's not impossible. That is a physically allowed possibility. Now, I'm not saying that's what I think, I'm not saying that's probable or likely, but that is possible, right? Without further evidence, that is one of the possibilities. The possibilities are such that it's just it's just us. Like maybe we're the only ones who can build telescopes. I don't know. Like, we don't know. We don't have any evidence of other uh of other life forms building. Think about the earth. Think about on the earth who built telescopes. There's been countless billions, countless billions of living species, not organisms, species. There's been countless billions of species existing over billions of years, and it emerged once. You know, those aren't those aren't statistics that scream out to me, hey, this is happening. Now, if we went into the to the fossil record and we saw that Velociraptor, you know, had little Velociraptor Galileo had his little thing, and he was like, he was like drawing in the dirt the Jupiter and Jupiter's little moons. Okay, like, but I don't haven't seen anything like that. I have no reason to su to the I have nothing, I have no evidence to suggest that that's that that's reality. Again, if I see it, I'm gonna I'll be the first one to be like, nah, like we're just doing what the dinosaurs already did, but that's the thing. We don't have any evidence for that. Think about that. Billions of species on earth. Telescopes show up once, tick tock shows up once, computers show up once. We do have to start with what we know, and it turns out, although we're always learning something new, there is a lot that we know, there's a lot that we can start from. There's a lot we have a good base to go off of, so it's a good place to start. And the only reason I just did that, that little, you know, um thought train is because it's a great question. Why are we focusing on earth life? Why are we focusing on earth chemistry? It's a great question, but it's like that's what we know so far. And so you're gonna, you know, you're gonna start from somewhere, and at the very least, we know that this stuff is possible. So at the very least, we know that this is something that it makes sense to look for, and it's a great place, it's a great place to start. But I'm actually with you there. I I really lean towards if life is really dependent on the previous step, and you know, Earth is a planet that's gone through its own stuff, and our solar system is unique in a sense, and animals influence animals, and plants influence plants, and plants and animals influence each other, then the trajectory of life on Earth, it's gotta be unique, right? Like, not that you know, chemistry works in a different way somewhere else, not that there wouldn't also be plant life that does photosynthesis, not that there wouldn't be animals that walk around and some of them eat each other, and some of them eat things that are like plants, you know. I think probably uh big macroscopically, these things play out in other places, I'm sure, but the specifics are most likely unique, anyways. Very much interesting to explore there. So, another thing to keep in mind is planetary science. This is very important. Just hopping into the biology of it all is meaningless if you don't understand the planet. You know, we have eight planets in our solar system, we have many dwarf planets, shout out Pluto, shout out to the other uh dwarf planets, and we don't we don't know a ton about many of them. We know a ton about Earth, we know a good amount about Mars, not as much as we know about Earth, obviously. We know a good amount about Venus, but not as much as we know about Mars. And then from there, it's like a cascade. We, you know, we understand these things, we've sent instruments out to study them. We don't know about them as well as we as we know about Earth. And because Earth is the place that we find life in our solar system, it seems like at least Earth-based life cannot be maintained on many of these other places. However, there's a lot to learn about these other places, that'll be a part of this series. Another interesting thing is that in our solar system, there is diversity among those eight planets, which is really interesting because you're not seeing copies of things. Earth and and Venus are roughly the same size, and there's some evidence that they were roughly similar to each other at some point, both different than they are now, but similar to each other in the past, and uh and they both evolved down very different paths. In fact, all of the planets are different from one another. Uranus and Neptune are fairly similar to each other, but still different. Jupiter and Saturn are fairly similar to each other, but still a little different. And then Mercury, Venus, Earth, and Mars, similar to each other, but still quite different. I that is enticing to me because the sheer diversity in our own solar system, if it suggests anything, it suggests that the diversity of planets out in the universe is great and far greater than we can imagine. And from an astrobiology perspective, we you know we're I already talked about how there's this vast chemical parameter space. So if there's all of these potential chemicals that are a bit unknown to us, and there's this expansive diversity of planets that we can't fully imagine yet, that is enticing for different types, not just Earth types of life that we may recognize fairly easily, but other types of life. And it's hard for me to say what that means, which is why I think it's important that we think about life as a physical process as opposed to this thing that we've drawn boundaries around with us at the center. Hopefully, this is all making sense. So we kind of know how planets form. Um, you watch the first uh episode on this podcast, it's not in the series of astrobiology, but it's called Five Trillion Planet, Five Planets to Five Trillion, or something like that. And I talk a little bit about how planets form, so you go back and watch that for um reference. But ultimately, this process of forming planets, we know congregates things that are what we call the building blocks of life. Uh, we know that asteroids and comets have things like water and other frozen ices, CO2, methane. We know that they have nucleobases. DNA is, and we'll cover this in more depth later, is made up of four nucleobases, A, G, C, and T, right? Your entire genetic code is those four things, A, G, C, and T, just paired in different ways for countless, countless, countless, countless chains. We find those independent of DNA on asteroids and comets. You go out to a comet or an asteroid, take a scoop of it, come back, test it in the lab. Oh, you have all the stuff that you need to make DNA. You have all the stuff that you need to make RNA. And you have other nucleobases as well. There's many nucleobas, there are other nucleobases that we don't use in DNA and RNA. Now, could those be used in the like genetic store of information for alien life forms? I don't know. I have no idea. I think that's a very interesting question. If you go to uh you know, if you start life with different nucleobases than the ones that we've used, does it really matter? Can you do you ultimately end up making similar the same things? Or does that does that create like different constraints where life is fundamentally going to be different in in some way? I like I don't know. That's a really good question. I think that that's this is a question that's beyond our current knowledge boundary. That is very interesting to think about, but it's important to realize that comets, that the stuff that we need for life, water, all these nucleobases, they're all over the place. Something else interesting. When an asteroid or comet slams into a planet, very common. This is a part of the planet building process. Again, go watch five how we went from five planets to five trillion. And that process, there is something called shock synthesis, where if the comet has the right stuff, which, like I just said, the comets and asteroids do, and they slam into a planet with enough energy, it will that itself, it's called shock synthesis, will produce amino acids. The building blocks. So you have the building blocks that you need on the asteroid, you slam it into a planet and you produce more building blocks, you produce amino acids. So you like the stuff that has gone into our to Earth life to us, it's all over the place, it's everywhere. So another thing that we'll talk about is habitability. What does it mean for a planet to be habitable? Every headline that you ever see that talks about habitability is referring to a planet that when we put, when we use this simple theoretical equation that is trying to define something called the equilibrium temperature, basically the temperature on the surface of a planet based on how far it is from its star. Is that range of temperatures based on how close or far it is right for liquid water on the surface? It ignores the atmosphere, which we rarely know anything about, certainly don't know much about, especially for small rocky planets like the Earth or a Mars or Venus or Mercury. And it so it ignores the atmosphere, it ignores some other important stuff, but it gives you a rough idea of like if this planet what did happen to be very similar to Earth, could there be water on the surface? And you can trust the habitability estimate if you go into it with the assumption that the planet you're looking at is similar to Earth. But if it's different than Earth, then that habitability starts to lose its meaning. That's why it always says potentially habitable. So when you see in the headlines, astronomers found potentially habitable planet, da-da-da-da-da. You gotta take that with a grain of salt, a little baby grain of salt. Just a little small grain of salt, because we have no idea if that planet's earth-like or not. If it's not, then it may be it may be way too close to its ar or it may be way too far away, or it may not matter. So we'll cover habitability and something else that's um relatively new development is synthetic life. So we know that Earth formed life somehow. Abiogenesis is what it's called. The process of forming life from non-life. We've not really created life from scratch in like a science fiction way. But we have, I say we, I mean scientists on earth, um, crossed some major thresholds. We can chemically synthesize DNA. So this is like something, DNA, we can do it. You can do it in a lab. You can make your own. You make your own DNA. Very cool. Um, and we've put synthetic genomes into cells and have those cells reproduce. So you can create the genetic material and put it in something and have that thing reproduce. That's a big step in life. That's one of the key things that we say that life does, right? In 2016, they built a minimal synthetic bacterial cell that had only 473 genes, so relatively small number of genes. And in fact, this is like one of the smallest known genomes capable of self-replication. In the top-down sense, that basically is synthetic life. That's recreate, that's us creating synthetic life. You know, we're taking existing cellular machinery, you can rewrite the genome and see what the minimum recipe looks like for life. It's cool that we can do that. We're beginning to understand the process of life. We've also been able to expand the genetic alphabet. As I was saying, natural DNA uses A, T, G, and C. But researchers at scripts have been able to make semi-synthetic E. coli with two unnatural bases, X and Y, and showed that those bases could be transcribed into RNA and used to make proteins with unnatural amino acids. Here, it's not just that we have edited life, but we've started expanding the chemistry that life can use. Again, the reason that this is important, I mean, that may terrify you that they're creating other life forms in labs, but the reason that this is important is because one of the things I'm saying is that there are all these other nucleobases. There are all these other potential chemicals, potential chemical configurations, and they could be bases for life that is non-Earth biochemistry. This is like very interesting. We and we're demonstrating that these things are possible. I mean, this in terms of hard experiments is like at the forefront of astrobiology that these types of chemicals, that these other nucleobases, that these other genetic vehicles could produce life out there elsewhere. Like it's possible. We're showing that it's possible. This is so cool. And then a very recent one, 2026 Spud Cell pushes this further. So this is a synthetic cell-like system built from non-living components. It has a lipid membrane, DNA, and purified molecular machinery. So it can feed, it can grow, it can copy its genome, it can divide, it shows selection over generations, also known as evolution, adaptation. Now, that doesn't mean that that we fully solve the origin of life, but it's a huge step because it does mean that we can now assemble several of the core behaviors of life from known chemistry. So I mean, this is huge. Being able to, we're inching closer to replicating the things that naturally happened on Earth. We're inching closer to mimicking that with other things, using other nucleobases. I mean, this is all this is all fascinating. This is all fascinating stuff. So we think about life out there, we can dig into the nitty-gritty over the course of the series, we will, but there's a few statistical arguments that we can make to convince ourselves that there probably is quite a bit of life out there. We can make a statistical argument based just on the planetary science, right? Think about this. We have this modern understanding of how planets form, we have evidence that most stars have planets, and we understand at least to some capacity, conditions that make a planet habitable. Keeping in mind, you know, an asterisk here, that there can be additional conditions that may extend to habitability for different chemical setups, different chemical life. So this is a this is a strong statistical argument from the planetary science side. Vast number of stars should have habitable planets. 100 or 200 billion stars in the Milky Way, one or two trillion galaxies in the observable universe. This is ignoring the part that's too far for us to see. You can also make a strong statistical argument from the biological side of things. So we have evidence that life has appeared in the history of Earth. We know that life appeared on Earth. That's that's one of the things that we're most sure of. Okay. We have evidence that organic molecules form easily and naturally. You go take a scoop of a comet, take a scoop of an asteroid, there's your stuff. Slam it into the earth, you have more stuff. So we have evidence that the stuff required for life shows up in droves easily. We found organisms that can survive the radiation and vacuum of space. We found life that can survive at the bottom of the ocean. We found life that can survive underground. We know of life that can survive in all these different crazy, insane, harsh, extreme conditions. We'll get into extremophiles in this series as well. So from the biological and the planetary side, sort of combine this knowledge and convince ourselves with the statistical argument that life is probably common. Biology is probably common if this is what it takes, right? If if we can manipulate these things, and it's an intention for us, but you know, a big enough planet, enough planets, mixing enough of this stuff around, you know, you don't you don't need a uh a scientist and a lab co. The universe does that for you. It's a very cool thing. The universe is running these experiments on its own. So a big part of astrobiology is going to be examining these things, it's gonna be studying conditions conducive to the origin and evolution and maintenance and stability of life. It's going to be looking for conditions on other planets, on other worlds, in our solar system. I mean, if we can confirm life elsewhere in the solar system, then I think it's it's all but confirmed that life has to be everywhere. Then I think we can make that, then I think we can go a step further and be like, okay, it's not that there's only two places with life in the universe and they're both in the same solar system. It's that this stuff is it's just that common. It's probably gonna be everywhere. And another part of what we're gonna be doing is looking for those signs of life. That is really gonna be constrained to the signs of life that we're familiar with earth life, because you don't know, right? You may you may you may ask, well, why you know we're having all these conversations about all this potential extra chemistry? Why are we looking for earth signatures? And it's like, well, we don't know what those signatures of the other life would be. So we wouldn't even necessarily know if we found it, right? It's like, how do you how do we know that life forms on another planet are producing this other chemical? Like, we don't know that. We don't know that. We only know what we know. So a lot of the search, you know, the the the astronomical search, the observations with telescopes, is going to involve us thinking about biosignatures that we're aware of, or even techno signatures that we're aware of. This episode's getting pretty long, so I think this is a good place to cut off. Appreciate y'all. We'll drop these every Friday until we complete the series. It'll be a solo drop. And then if you check back on Tuesdays, I think on Tuesdays, I'll drop guest episodes that I have with experts. I'll try to get some good astrobiology and astrophysics guests on during the course of this series, but we also may expand um into other regions. You know, I've most recently had a bioengineer, Dr. S from the last episode. And it's again, it's very important to understand what we can understand about the biology here, right? The the the life forms here. My next guest episode is going to be with uh June Sass. She has a master's in biology and is an expert in mycology, fungi. And so we have some very interesting conversations on that. Again, that'll drop on Tuesday. But this astrobiology series is going to be every Friday. So I appreciate y'all tapping in as always and forever until the end of time. Lead with curiosity.