Daniel and Kelly’s Extraordinary Universe - Origins of life (featuring Dr. Katrine Whiteson)

Episode Date: August 20, 2026

Daniel, Kelly, and Katrine take on the origins of life. They discuss competing definitions for "life", whether it's even helpful to have a definition, the oldest evidence we have for life, and how we think life got started.See omnystudio.com/listener for privacy information.

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You're hired to fill the space with you. Listen to Joy 101 with Hoda Kotby on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. How do you go from a barren planet being bombarded with asteroids to a planet that over four billion plus years has been home to what is probably billions of species? This is Daniel and Kelly's Extraordinary Universe, so you're not going to be surprised to learn that we're not 100% sure yet. But as this is one of the most profound questions humans can ask, scientists have certainly been working on it. So on today's show, we're going to talk about what we know so far about the origins of life. Welcome to Daniel and Kelly's extraordinary universe.

Hi, I'm Daniel. I'm a particle physicist who likes to think about aliens, and I consider the origin of life. to be sort of the big bang of biology. Oh, hello. I'm Kelly. I study parasites and space. And go ahead, elaborate. Why is Ool Origins of Life analogous to the Big Bang? Because it's so important. It's so mysterious.

It's not widely understood by scientists in the sense that it's still, you know, an open question. And how much we don't understand about it is deeply misunderstood by the public. Yeah. Yeah. I learned so much when I was researching this episode. So I would definitely agree with you. This was quite a journey to go on. And it's a journey that a bunch of our listeners have wanted us to go on for a while.

So we've gotten a lot of requests for early life episodes. When you study early life, that sounds like a biology question. But it's a chemistry question, guys. It's a chemistry question. So I've been trying to avoid this for a while. But I could put it off no longer because it is actually a fascinating topic. And it turns out chemistry is kind of unavoidable. Yeah, that's right. So hat tip to Jeff for asking us for episodes on early life and to Frank, who suggested that I check out Dr. Nick Lane's work. He wrote a great book called The Vital Question, for example, and I did read that. And because neither of us are chemists, but I'm married to somebody who has a PhD in biochemistry, we decided to bring on the podcast our favorite pinch hitter.

Yay. So let's waste no time because nobody really wants to hear you and I talk when they could hear Katrina talk. So let's bring Katrina on the show. Okay, then it's my pleasure again to welcome back to the podcast, our favorite guest or maybe co-host. Katrina Whiteson, director of the Whiteson Institute Center for Fermented Beverages of Dubious Safety. Katrina, welcome back to the podcast. Wow, these intros have taken a very interesting turn. But I just want to say I'm way more of a sidekick on this one. This is not something where, you know, I've spent a lifetime learning, but it's something I'm very interested in. So I'm glad we're going to get to talk about it.

are always very happy to have your microbial expertise on these questions. And a lot of this stuff is philosophical. And so just having another, you know, fun person to bounce philosophical ideas off of is good. And Daniel, are you ever going to move past this kombucha thing? Because it feels like it's living rent-free in your head. And we hear about it all the time. When she turns into a billion-dollar business, I'll accept it. All right.

That did happen here in SoCal, but I doubt that's going to be my life plan. There was a guy, the GT kombucha guy. Katrina's crunchy kombucha. Oh, wait, no, that's a terrible acronym. Nope, no, no, yep. So let's run away from this conversation and into another conversation that's a bit safer. So how about what is life? So, you know, when you're trying to figure out where life came from, what you need is a definition

so that when you see a thing, you can say, okay, that's life. And so that's what we're working towards. And it would be helpful if you had a definition for. life that worked here or anywhere else in the universe. But we're kind of constrained to what we know is happening here. And so what we've observed happening on Earth, here are some features of life on Earth that can sort of get the ball rolling. One of those features is that it's carbon-based.

And we did a whole listener question on why we think it's carbon as opposed to something like silicon. Silicon. Silicon is different. Silicon here in SoCal, yeah. That's right. That's right, silicate. It depends on water.

And information is carried in DNA or RNA. And so it's genetic. We used to think that you also had to get energy from the sun, either directly or indirectly by, like, eating plants that got energy from the sun. But in, like, the 70s, we discover that you can get energy from hydrothermal vents. So even in the last, you know, 50, 60 years, we've been, like, changing our definition of what we think life is. So is there anything you two would add? two features of life on Earth?

I think it's a pretty good list, but I want to highlight the difference between features of life on Earth and what we think life is. Because we're interested in this question, what is life? Because we're also curious about like, where is life and how common is life?

And so we're interested in like, is there life on Enceladus or, you know, on that other planet? And we don't necessarily expect it to have all these features. But it's really important to have a definition so that when we do see it, we're like, well, is it life? And also so we can like have a conversation because, you know, every good philosophy conversation starts with the definition. So you make sure you're at least

talking about the same thing and not discovering, you know, 50 pages later that you're having two different arguments. So do you really think that this is a situation where we need to have a definition? Because I was listening to an interview with Nick Lane, who's a guy who does a bunch of of work on this. And it was actually, he was on Brian Keating show. And Brian Keating asked, like, what is life. How would you define it? And he said, well, I can't tell you. It's one of those funny questions where if you get an answer from someone, it'll be a bad answer. And then later, he actually referred to coming up with the definition as, quote, actively unhelpful. And so, so what do you do, does a definition hamstring us? Because we, like, especially if you're searching for life out in the

universe, it might be totally outside of what we're familiar with. So how important do you think a definition is? I mean, I have to say, I find the definition thing a little boring, if not unhelpful. And I'm glad we're starting with it. Yeah. Because, because, because, so for, you know, I've studied viruses a lot. And viruses are always, there's this debate about whether they're alive or not, and it's something that you teach in every virology class. And I, honestly, I just, I can't get excited about that debate. I'm not exactly sure why. I guess I just feel like, we understand how the viruses work. We know in what ways they fail the definition that you just brought up, which is that they are not able to replicate by themselves. They have to go borrow a host cell. It's like, you know, if you rent an Airbnb, you're not going to bring a washing machine. You're just going to borrow the one that's there. And that's what viruses do. But they have a program. They know what they're doing. And they also are probably the most diverse entity on the planet when it comes to biology. They are like rocking it in terms of. of what information they create because they are so diverse.

And so to leave them out of the definition of life just never made any sense to me. I mean, if you landed on an alien planet and only found viruses, you wouldn't be like, yawn. I guess this place is boring, right? No, definitely not. But if I only saw viruses, I would think, oh, this is like a weird shadow of something that happened somewhere else. Or they killed all the cells, I guess, because that's not a stable system that is actually

able to sustain life. So, I mean, in that sense, the definition matters, of course, because, you know, viruses can't do that by themselves. Can I ask you a question that I absolutely should know the answer to, but I don't. So, okay, so people always say, you know, like life arose once. And so I don't usually think about where viruses are on the tree of life. Did viruses arise separate from bacteria, archaea, and eukaryotes? Or did they branch off at one point? Do we know?

I think they got their first. And I hear this whole only. evolved once thing, but I mean, I don't think we really know that. We know what we have now. Yeah. I think it's possible. I mean, whatever happened in the very, very beginning was probably, you know, this biochemical soup. And there were probably little self-replicating genetic entities going on there, which were not yet cells and were also not yet viruses. But I would say that as soon as we had any kind of successful entity going, there were quickly genetic parasites, which in a way are akin to viruses. I think that probably started very early, if not right

away. I mean, I think the second there was something good going on, there were like hitchhikers jumping in, you know? You're totally pandering to Kelly with genetic parasites. Nice. Yeah. I say the same thing to people. And I was like, now, I don't know this for sure, but I'm so glad that a very smart person thinks the same thing. Now I feel very confident. But I think it is important that we have a definition, even if there are fascinating things that fall outside of it, right? And I have nothing against Airbnb guests.

You know, it's wonderful. And I'm a guest myself. I hope the viruses clean up after themselves and don't, you know, bother the neighbors and all that good stuff. Unlikely. Unlikely. They're not very constrained. But I do think we want to sharpen the question.

We want to know what we're talking about. I don't care. People agree when we find aliens, whether it's life or not. But we're interested in this question, so we have to at least know what we're talking about. Why is this question interesting? And maybe, Kachina, you're saying, it's a spectrum. And there's a blend of stuff, and you can call it life or not. But there's an interesting into it and there's a non-interesting into it, like, you know, rocks, like basically everything we've only found so far.

But I think we at least need to identify the direction of that interestingness. so that even if we aren't sure where the threshold is, we can say like, oh, look, what we found here, this is fascinating and it's similar in some respects to what we're doing over here on Earth. Well, so then let's go through a couple definitions that I've identified. No, that Katrina has told us, this is not an interesting question. Let's dwell on it. Let's dig into the boring question of what is life. I'm just kidding. So I got to pick on you too sometimes, Katrina.

You can't just be Daniel. Yes. That's getting up on Katrina. Yes. No. Okay, so Irwin Trondinger in 1944 said that life is a thing that... Famous biologist. I thought he was a physicist.

Yes, exactly. That's the joke. Oh, all right. Well, I was starting with a not-so-good definition, so I wanted to... No, I'm just kidding. I'm just kidding. All right. I'm going after both of the whites in today. Nice.

All right, so life is a thing that avoids the decay into equilibrium. And so I feel like this focuses on metabolism, because you need metabolism to, like, like push against the decay into equilibrium. But what do you think of that definition? I think it works both in a metabolism way and in an information way, information being more about the genetic organization where we store our information. I mean, that is the opposite of just like a total neutral chaos where there's no organization. So I think that kind of works.

I don't know. Does that help us when we send a mass spec up to Mars and look for molecules and we're like, does this tell us that something was alive here? I'm not sure because those things could happen randomly here or there and you would need to see like interesting concentrations of things maybe. But even then, I don't know, that's where the definition gets helpful. I see what you're saying. No disrespect to Schrodinger, of course. But I think that's interesting.

But I'm not sure it captures everything. Like you could also, for example, build a robot. Like a Roomba is, you know, organizing and cleaning and fighting against entropy and stuff. But nobody would say a Roomba is alive. And so maybe, I don't know, the metabolic aspect of it there would disqualify a Roomba. I think it's getting at something. You know, it's capturing the sense that life is self-maintaining. It's fighting against, you know, the laws of thermodynamics.

Yeah, but the Roomba will eventually disintegrate. I mean, I don't know the details about the plastics in there, but you know what I'm saying? It's not going to be able to sustain that of regenerations. But so will we? We're going to disintegrate. Is it that the Roomba doesn't make babies? that's the yeah what did you

what were you thinking of in particular that like the plastic is going to fall apart because I'm falling apart pretty quickly it feels like well I guess I was saying there might be something that is still organized in a way that wasn't there before the Rumba was manufactured eons from now despite the fact that

they won't have progeny but I guess I was yeah I was saying it wasn't sustainable because they won't reproduce okay I feel like Katrina was mentioning that this is like not super helpful because how, what do you do with this? Like, if you go to Mars, what are you looking for in particular from this definition? It doesn't really tell you that.

It's kind of like too vague to be helpful, I guess, is my thought. But this was from, you know, like 80 years ago, right? And so we've got some other definitions to chat about. And that was before we knew DNA. I mean, that was a really early moment to be thinking about that. Yeah, that's a good point. That's a good way. We shouldn't be too harsh on Schroding.

Yeah. It was a pioneer. So in 1994, NASA had a working group, and they came up with a definition. And their definition is that life is a self-sustaining chemical system capable of Darwinian evolution. That's a little more specific. So self-sustaining, like, it's its own entity, it can acquire its own food and, like, keep itself going. It's a chemical system and undergoes Darwinian evolution.

So, like, DNA is sort of implied in there, or at least some information that can gets passed from generation to generation and, like, reflects changes that are happening over time. So this is, like, at least a little bit more specific. What do you all think of this one? I like that it's more specific. It also seems more descriptive, though, right? It doesn't feel like it's unearthing a core concept here. It's just, like, what is life have in common? And I think that's a step towards it, right? It's like you start out with a bunch of observations, and then later you understand the underlying concepts that are unifying at all. And we're not there yet. We're still just like understand the pieces. You know, it's like when we saw magnets and we saw

lightning, we did realize, oh, these are two sides of the same coin. And there's a reason why they both come from the same thing. So I feel like we're sort of at that stage here. We're like making lists without understanding where they come from. Well, I've got another list to throw at you. And then we can move on to something more interesting. So the last definition that I found was a definition that's sometimes called the Seven Pillars of Life. It came out of UC Berkeley in 2002. Daniel, when were you at Berkeley?

I was Berkeley 98 to 2000, and I was at Fermi Lab while still a Berkeley student until 2003. Okay, so you were there while Daniel Koshland was working on this. Oh, yeah. I studied biology at Berkeley, 96 to 2000, and one of our buildings was named Coshlin, so that's interesting.

Oh, fantastic. Okay. All right. Well, so here we go. Here are the seven pillars. One pillar is program. And for us, that's DNA. It's the thing that carries the instructions for life. And then you've got improvisation. And this, I think, is meant to cover, like, natural selection. Improvisation doesn't feel quite like the right word to use for that. Yeah, because that's just like mutants arise and then the best ones arrive. That's not like on the spot. They, like, invented a new thing. That's interesting. Right. Yeah, yeah. So I'm not loving the word, but I get that the point is they're like things that change through natural selection. Yeah, like a Roomba couldn't do that. Right. Yeah, yeah, yeah. Roomba's going to be our

go-to thing, I can see now. Compartmentalization. So like, it's not just like part of an ooze. It sort of separates itself from the rest of the environment in some way. Like, you know, often a lipid bilayer is how cells do that. They separate themselves from other cells. Energy. So they take in energy and use that energy to do things like replicate themselves. Regeneration. And this is things like growing the size of your population, having babies, healing, covers a lot of things. Adaptability. So this is adapting to, like, responding to your environment.

Adaptability felt like that's the word I associate with natural selection. It's kind of, I'm still stuck on improvisation, not feeling like a good word. Yeah, those are interesting sides of the same coin. I don't quite get the difference. I have to think about that. I bet this person was a physicist. And then seclusion, which is like having your own chemical processes that are going on inside of you. And so now I'm not sure what the difference between seclusion and compartmentalization are.

But anyway, so I feel like there's some redundancies in here, as I understood the definition, and a couple words that maybe I wouldn't have picked. But with these letters, you can have the acronym Pickerus or Pisceris. And I don't know, maybe they were going for that. But how do those feel as criteria for life? So, Daniel, this is getting a little more specific. But I really know if it's a theory as opposed to, like, a summary of observations. It's still a summary of observations.

And I feel like it's too biased towards the kind of things we see here on Earth. I'm especially not a fan of this compartmentalization and exclusion business. I feel like that's not even very well defined. Like, where exactly does my body end anyway? It's not very clear. I have a surface covered with microbes. Are they part of me? Are they not part of me?

I feel like that's just a cultural framework we're imposing on even Earth biology where it doesn't really work. And I can imagine situations where you have life that doesn't have clear boundaries, but you would still understand it to be life. And then they might think of themselves differently. And we've talked about this on the podcast before, or like plasma currents in the atmosphere of a star could be self-sustaining and interesting and even intelligent, but they might not have the concept of like counting numbers if they don't have

like boundaries between their bodies and other people's bodies. And so they might like just think in real numbers instead of integers. And so this feels like a little too earth-centric to me. But again, it's like a list. It's a description of what we see on Earth, which is mostly accurate. And I think the next big leap would be like, let's understand the core concepts, but it doesn't seem like we're there yet. Sounds like Coshlin needed to smoke some banana peals to have a broader, broader view of things. And while you were talking, I was, one, totally listening, but two, I also looked up seclusion

and compartmentalization again to see what I was getting wrong. And it looks like maybe seclusion is more about, like, stuff that's happening intracellularly. And anyway, but still the point is sort of like separation of stuff. so your point still stands. All right, well, I think we have had enough of a chat about this. The point is people are trying to identify things that are important for life here, are thinking about what might be important for life and other places in the universe. But at the end of the day, we've only seen what has succeeded here on Earth.

And as Katrina was alluding to earlier, life could have popped up multiple times, but there was like one instance that gave rise, there was one instance we think, that gave rise to everything that we see today. But maybe life popped up and then just kind of died. And so we don't really know what the other options could have been. And so anyway, we are going to plow forward in our conversation without a definition that everybody agrees on because this is biology. And that is what we do. If this was philosophy, we would just stay here for 400 years arguing about it.

That's right. That's right. The good news is that there have been a lot of experiments and that we are moving forward despite having a definition towards trying to get something life-like happening. happening in the lab. So let's take a break. And when we get back, we'll talk about when we think life arose and what Earth was kind of like at that time so that we can ground our experiments in something sort of reasonable. two nights in Nashville. To see Cameron Whitcomb at the legendary Ryman Auditorium.

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How about we flip this script? What is the surprise woman? But actually you think is the straight man is actually the one who's acting weird. Adam Scott, this entire time you've been expecting Adam Sandler to come to visit the show. I would never expect. I would never set expectations for something like that to happen. If the universe allows for something like that to happen, I'm open to it. I'm always going to accept.

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Will Ferrell told us personally he loves the show and he wants to be a guest on every episode, but he's just so busy. Listen to Hollywood Handbook on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. All right, we're back and we're talking about

what is life, the origins of life, and we're trying to keep Katrina from being too bored. Kelly, what are we talking about next? Oh, no. Well, the good news is we're talking about bacteria-related stuff. So I think that's going to, yeah, there we go. All right.

So I'm on track now. She's interested, folks. That's right. So if you're trying to figure out how life came to be, you want to sort of know what the environment was like when life started. And to do that, you need to know when life started. And so basically we have to go to the fossil record to try to figure out where is the first evidence that we see something that could be life showing up. Also, this is like amazing, fascinating history, right? like the deep history of life on earth, like how things began.

Wow, I would love to jump into time machine and see all this stuff happen. And it's our history, right? And it happened a certain way. And there might be clues they reveal it. So it's like some of the most fascinating science there is, in my opinion. Yeah. I agree with you, physicist, because it's biology that we're looking at. Okay.

So there's a bunch of fossils out there from varying time points. And some of them we agree are definitely. evidence of bacteria way more than we agree about some other stuff. So the most widely agreed upon fossil, as far as I could tell, was from Australia and it's stromatolites that are three and a half billion years old. Wow. About three and a half billion. Yeah. And so Katrina, at this point, I was hoping I could throw to you and be like, what are stromatolites? But I didn't prepare you for that at all. So stromatolites are amazing evidence we think of life. That's three point five billion years old, and it comes from microbial mats. We've talked about biofilms before,

and so the stromatolites are layered rock structures that built up over time by microbial mats. We think they were primarily cyanobacteria, and they changed the shape of the rocks. This is like a morphological piece of evidence. So they would trap sediment and calcify the rock, and they created this huge macroscopic evidence of life on Earth. And it is a little controversial because there's questions about whether that could have been created by something that's not alive. But we think that biofilms, essentially, microbial mats of these cyanobacteria that did an ancient form of photosynthesis. So they were getting energy from sunlight, we think, and maybe also from some of the sediments in the rocks. And they left behind massive changes

in the shapes of the rocks. And that's why we think there was life there. What is it about these things that makes it convincing that there's no abiotic way to reproduce them? Well, we know what those look like in modern times, and it really is the shape of the leftover calcified sediment that happened in a massive scale. And so, you know, it's a guess, you know, or that's maybe the wrong word, but it's... It's an inference, yeah.

It's just based on how they look. I don't think we have, like, great other kinds of chemical, physical evidence. There is some isotope ratio, carbon isotope ratio. carbon isotope ratio evidence, but, you know, that signal can be debated. Also, they look really weird. There are these funny blobs sitting in the ocean, right? It's cool. Got to be aliens.

Yeah. Got to be aliens. Don't go with the conspiracy theories. Come on. That's what I do. All right. So in Australia, there's this stromatolite that is pretty broadly agreed upon as, like, definitely being a stromatolite.

and that ages to about 3.5 billion years old. There's also some other things that we found in like Canada, Greenland, some other parts of the world that could age older, something like 3.7, maybe even up to 4.2 billion years old. And so definitely older than what we've seen in Australia. But all of these other instances are things where people debate, like, is that a stromatolite? We're not really sure.

So we feel pretty good about this 3.5 billion-year-old date. but it could be even older. It's just really hard to date stuff that's that old. And you're saying 3.7, and it might not sound like a big difference, like 3.5, 3.7, but that's 200 million years. Remember, it's been 66 million since the dinosaurs. So, like, 200 million years is a long time. It's a lot of podcasts. Yes.

That's the best way to measure things. When I was a kid, we used to measure things in Ghostbuster episodes, that cartoon that was... So I'd asked my dad how many more. more Ghostbuster episodes. Anyway, 0.2 billion years is a lot of Ghostbuster episodes. Yes, exactly. So we're not totally sure, but now, Daniel, I'm going to put you on the spot. Oh, boy. There's a limit for how much we know about what the early Earth was like, or even our ability to, like, age the early Earth. And we usually have to go outside of Earth to get these estimates for, like, how old Earth is, for example. Why is that, Daniel?

Well, the early solar system was hot and nasty, you know. That sounds like a judgment call. I mean that only in a positive way. This is getting too personal. Move on. Like, you know, somebody asks me, how's that pasta sauce? Ooh, hot and nasty. That sounds delicious.

Anyway, so the early solar system, you know, collapses from a big cloud of gas and you get the sun. And then you have a little other gravitational seeds that coalesce heavier stuff. to make like the earth in a rocky planets. And then the radiation from the sun blows off most of the gas. And so you expose the, you know, heavier stuff, silicon and carbon and all this kind of stuff and oxygen that makes up the earth. But it's hot. And so, you know, the rocks are constantly being reformed. And because of the pressure, the gravitational pressure.

So the early stuff is mostly destroyed. And so like if you want to find out the age of the earth, you have to find like the age of the oldest rock. but a lot of the rocks from the early days had been remelted, right? They're gone. So that's why the age of the solar system is easiest to discover away from the Earth and like asteroids, right?

Smaller chunks that were still molten early but cooled and have been frozen essentially ever since and have been like pushed down into the Earth magma and melted. Yeah. Awesome. Yeah. And so there's a limit on what we can even say about the early Earth because it doesn't really exist in the same form anymore.

It's been like melted and reorganized. And so we have found life that's 3.5 billion years old. Maybe there's life that's 4.6 billion years old. I doubt it. That's as old as the Earth and the solar system is. But if it had shown up right at the beginning, it would have been just like obliterated and we wouldn't have fossil evidence of it anymore. But it's really important to understand this gap between when the Earth formed and when

life formed because it's the only piece of data we have to speculate about how long it takes life to form, which is a big question, right? If life forms like almost as soon as possible after conditions are ready for it, that suggests with n equals 1 that it forms often when conditions are ready, right? Whereas if it took like billions of years, that suggests that it might take a long time on average. And we shouldn't expect to find it everywhere. So it's like super valuable piece of information. Yeah, absolutely. That's really interesting.

But I feel like it also depends on having gradients of temperature and water and those conditions. I mean, if you got those right, you know, maybe. Maybe it really just takes a much smaller amount of time with those conditions, which we obviously are not going to triangulate from evidence on Earth, but it's fun to think about. Yeah, totally. But another nice thing about knowing about when life popped up is that then you can try to figure out what Earth was like at that time so that then you can say, okay, what things were in the atmosphere, what are like the starting materials that we're likely to have, what's the temperature

like. And this isn't, I'll note, this isn't perfect because just because the earth was an average of, I'm making a number up, 100 degrees Fahrenheit or something everywhere, there's still a ton of variability, right, depending on if you're at the bottom of the ocean or something like that. And so it's helpful to know, but it doesn't necessarily tell us everything we need to know because there was a lot of variability depending on where you are on the earth. But now that I've gone ahead and been like, we're going to tell you what Earth is like, but it's not interesting because there was variability. Let's go ahead and talk about what Earth was like, about three and a half billion years old. And we call this time period the Hadean, which is like the hell like.

Hot and nasty. Hot and nasty, which Daniel's into. And so... We could also call it like an autoclave. Because, you know, these days, if we want to sterilize something, we put it in an autoclave, which is hot and high pressure. And I would call it extremely clean. So, you know. Oh, good. That's good. Maybe not great for life, but clean is good. Useful, yeah.

Useful. That's right. So another thing is that the sun back then was dimmer, but because we didn't have an ozone layer, space radiation, UV radiation, hit the surface a lot more often, which probably also contributed to some of this sterilizing of the surface like an autoclave. The temperature and the atmospheric pressure were probably different than what we experienced. today, and partly that's because the atmosphere, we think, was made of different stuff than we see now. So eventually when life came around, we started producing a bunch of oxygen that got into the

atmosphere, produced ozone, et cetera. But we think that some of the starting materials in Earth's atmosphere were things like carbon dioxide, methane, ammonia, and water vapor. But again, not a lot of oxygen. And this mostly came from volcanoes, right? We talked earlier about how Earth's first atmosphere, like most of the universe, and most of the solar system is hydrogen and helium, but that was blown away because of the sun's radiation. And then we had a second atmosphere, which came from volcanic outgassing. And also you get like a bombardment from asteroids, and so some of the stuff on those melt. And that's where the second atmosphere comes from.

Cool. Yeah. Thank you for that. And yeah, so the asteroids that you're talking about, a lot of those fell during the late heavy bombardment, which was 4.1 to like 3.8 billion years ago. where we were just getting absolutely hammered. Though it sounds like a battle in World War II, doesn't it? It does. It does. But yeah, we got totally hammered. And as I understand it, a lot of the craters on the moon are evidence of the late heavy bombardment because our craters got sort of like eroded away over time and you can't see them anymore. But there's evidence on the moon of them still.

Although I think that's suspect now because we only landed in a small region on the moon and that might have been unrepresented. So this controversy now about whether the late heavy bombardment was a real thing or not. Really? I thought we knew a lot about the geography of the moon. We only know about the areas where we landed. We know a lot from observations, but we don't have samples from a lot of the moon. Oh, I see. Anyway, that's a whole other topic we can dig into in another episode.

But yeah. Well, but that's actually totally related to my next point, because now that we've laid out, like, okay, this is what the early Earth was like, there are other people you can talk to, other experts who are like, yes, this story of what the early Earth was like, has become very, you know, popular, very well known. But actually, there's a lot of evidence that we don't, we can't be totally sure that the early atmosphere had exactly the, you know, compounds that we were talking about. We could be wrong about a lot of this stuff. And it could be that the early Earth wasn't super different than Earth today, except that it definitely wouldn't have had as much oxygen in the atmosphere. Because that's definitely a sign of life. But so we're doing our

best to guess what it was like, you know, billions and billions of years. And, you know, billions and billions of years ago. It's amazing that we have anything to work from for something that's that old. But yeah, so I'm waving my hands in the air a little bit. What I'm telling you about what Earth was like four billion years ago, because this is just the best evidence that we have right now. And it's amazing that we know anything about what happened billions of years ago, like what incredible detective work, right? And as Hazel likes to say, science is like, stuff happened, and we're trying to figure out what? Yes, that's totally, that's a good, that's a good explanation.

Okay, so now that we have talked about what early Earth was like, or now that we've admitted that we're not totally sure, let's talk about how life arose. And to figure out how life arose, we tend to want to think about how certain things that we usually see in life popped up. So, for example, lipids, these are things that are usually used to make the cell membranes. So to, like, give you a compartment that you can use to separate yourself from the rest of the world, for example. Carbohydrates, these are like sugars and cellulose, they are delicious.

Amino acids, these are used to make up proteins and nucleic acids, which are used to make up DNA and RNA. And so a lot of the folks who study origins of life are looking for conditions where you mix stuff together that were likely to be together about three and a half billion years ago or older. And then you wait to see, do any of these things pop up. And so like what do you need to do to start getting these? But this is actually a pretty hard problem to think about because like often to get one of these things that we're talking about, you need others. So for example, to get DNA or to copy DNA, that's done with proteins. So what came first? The protein or the DNA. And so trying to figure out how these things pop up and work together.

And in what order they show up is like a huge part of what this field is doing, as I understand it. Yeah, 100%. I mean, most things that happen in biology are possible without the help of all of our fancy proteins and cellular machinery. They're just very unlikely. They just take like a massive amount of time and energy. The biology is just easing the process and making it faster and more doable. So if you were to give things a lot of time and a couple of lightning strikes for some energy, then that's the theory is that a lot of these molecules may have started to just form. their own without any biology to guide them. And then maybe you're going to get into the RNA world hypothesis, Kelly. But, you know, we don't have to debate between DNA and protein because we have this intermediate molecule RNA, ribonucleic acids, that are able to do some of this chemistry that proteins are good at and also they can store information. So they're kind of a jack-of-all-trades of a molecule.

So we think that life probably started there. But RNA doesn't have the same PR that DNA has. Like fewer people know about it. It doesn't seem to get as much press. Like does Starbucks put it in their coffees with the big sign about protein shakes and stuff? So Katrina was talking about ribosimes, right? Yeah. We're going to jump into that a little bit more when we come back.

But I wanted to end this segment, if that's okay, with aliens again. And so. That woke Daniel right up. Yeah. What? Yeah. Before we go to the break, let's really. quick, jump into aliens again. And so there are some people who are, you know, talking about like,

well, how do you get these four things with the conditions that we had here on Earth four billion years ago or something? And there are others that say, well, what if life just came here from space? And this is the panspermia idea where, you know, maybe life arose on Mars, something smashed into Mars and that rock eventually lands on Earth. And now Earth is seeded with life that started somewhere else. What do you think, Daniel? I think that's a really cool story, and it's really important to understand whether life started on Earth or somewhere else because it changes how we feel about ourselves and who we are, and it's interesting. But I don't think it's really relevant to this scientific question of how life starts, because it just sort of says, well, maybe life started on Earth or maybe it started somewhere else. It doesn't answer the question of how did it start.

It doesn't really matter to me if it started on Mars and then landed here for the biological. question of how does life start? Of course, I'm curious about whether we're all secretly Martians, but it sort of seems to me like kicking the question down the road instead of answering it. Yeah. It also impacts how often these things happen, though, getting back to understanding the initial conditions. I mean, if the conditions are so rare that it really only happened once somewhere in the universe, not even on Earth, that makes it seem even harder. Yeah, and I think we have no evidence at all really for like pan-spermia, especially directed panspermia as some like professor from Harvard likes to talk about our interstellar visitors, maybe being like alien capsules

containing seeds of life. Like there's no evidence for that. And if anybody was going to be excited about that, it would be me. So the fact that I'm being skeptical about it should tell you something. Daniel's never an alien's wet blanket, but in this case he is. So that's all you need to know. Follow the data. All right, let's take a break, and when we get back, we'll talk about the Miller-Yuri experiment and whether metabolism or RNA came first. spending cast just listen to pure country for 10 minutes a day on the free iHeart radio app and you're in to win camera welcome stream the new single kingdom of fear available now if your bookshelf and your for you page are equally important to your personality welcome home this is prose society the weekly podcast that's

part book club part group chat for thought daughters pop culture obsessives and anyone who thinks pride and and Love Island deserve the same level of discourse. I'm Eli Rallo, and every week we're connecting the dots between books, the internet, and the conversations everyone can't stop having. I'm going to have to look up this story. I'm obsessed. I'm obsessed. From bestselling authors and your favorite book talk creators to the latest pop culture moments,

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We've had a lot of great guests like Sarah Sherman, not that great. Actually, can you help me shape this? How about we flip it on his head, right? How about we flip the script? What is the surprise woman? Actually, you think is the straight man is actually the one who's acting weird. Adam Scott This entire time

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Do you two remember learning about the Miller-Yury experiment when you were in school? Definitely. Yeah, they had like a flask of some stuff and they zapped it and it turned into more interesting life-like stuff. Is that right? Yeah, I don't need to explain it. I mean, that's almost exactly what my notes have. I mean, in particular, they had ammonia, methane, and hydrogen. So they had stuff that they thought was present on early Earth.

Actually, they were using Jupiter's atmosphere as sort of a proxy for what they thought early Earth was like, which we no longer necessarily think was the right thing to be working with. But anyway, then they zapped it with some electricity to simulate lightning strikes. And they ended up getting some amino acids. But one of the problems is that we no longer necessarily think that the war, they created in this flask is necessarily like what we thought early Earth was going to be like. But it did show that, like, you throw some stuff together that isn't life and you start getting the building blocks of life out of it, which is pretty darn exciting. And since we've done a bunch

of experiments where we've sort of updated the gases that are in there, the sources of energy that are being input into the system, and surprisingly pretty often you do still get, like, things that look like the building blocks of life popping up. And so, getting things like amino acids just sort of randomly in the environment doesn't actually seem like it's that hard. And so then the question is how do you go from there to something that, you know, responds to Darwinian evolution or something like that? And so the question there is, do you start with metabolism? So the ability to do like chemical reactions that give yourself energy so that then you can do other stuff. And I've probably done a really bad job of defining

metabolism because it still kind of blows my mind. So I'm going to throw to Katrina and second. And then the other hypothesis is the RNA world that maybe you started with RNA first, and then from RNA, you sort of structure things together and then start using metabolism to build things that are more complicated. So Katrina, go. I don't even really know. This is where I start to feel overwhelmed because this is where it becomes a lot of biochemistry. Yeah. Well, metabolism as a word, I find fascinating. And when I get asked that question when I'm over at the integrative health center in the teaching kitchen and people ask me about metabolism, they're asking, you know, how can I boost my metabolic rate so I can, you know, lose weight and eat lots of

delicious things. A good goal. Which is a good goal. But for, you know, what we're talking about for life is the chemistry of getting energy and using that energy. So, yeah, it's really interesting to think about that in the context of early life. I think it gets back to some of the seclusion and compartmentalization definitions that you were bringing up earlier because everything runs on gradients. And so building up differences in concentration of molecules against a membrane of some kind is a way to store energy and to use energy to propel your processes forward. So in my mind, metabolism comes down to being able to organize systems for obtaining energy and using chemicals to do that.

So let me see if I understand from a physics point of view. You're saying that we're looking for a process that we see a lot in life, which is use of energy to run yourself. Yeah. And that we do this chemically by storing stuff up gradients, which sounds complicated, but it's basically like if you carried a bunch of rocks up a hill and left them at the top of the hill, that would have stored energy in it, which you could release when you wanted to by rolling them down the hill. and then the rock gets all this speed, which you could then use to, like, you know, spin a wheel and grind your flour or something. Exactly. Yeah, that's a really good analogy. I like that a lot. But yeah, it's exactly. It's like pushing chemical molecules onto one side of a barrier, and then that stores energy. I'm going to do my best to summarize one hypothesis for how life could have started around hydrothermal vents. But I'm going to preface this by saying this is pretty chemistry.

heavy, which we all know how I feel about that. Okay, so here's one idea for how life could have started. So if you are at a hydrothermal vent, the stuff that's getting pushed out of the vent is at a very different pH than the water outside of the vent. And so this is a gradient that can be used to generate energy. And so at these hydrothermal vents, you've got this energy source. These hydrothermal vents also have rocks that tend to be sort of sponge shaped. And if you look at a sponge, there's like all of these little sort of like pores and holes in it. And each one of those pores or holes could have acted sort of like a cell membrane, sort of separating into compartments so that stuff could happen in each of those different compartments. And so now you

have like primitive compartments and you have a source of energy and some of the minerals in that area can be used to catalyze reactions. And when I say used to catalyze reactions, I'm not even totally sure I know what that means. But anyway, so hydrogen, hydrothermal vents are supposed to have all of these different features where you could imagine metabolism arising first, and then you're able to, through some other kind of chemistry magic, get RNA and the ball gets rolling. And for anyone who wants a really great book on it by a chemist who knows what he's talking about, check out Nick Lane's book, The Vital Question, which is all about the metabolism first hypothesis. What do you think? Did that make any sense, Katrina?

Yeah, very much so. I mean, I really like that. that idea of almost like a life rock hybrid scenario where the shapes of all those porous rocks around the hydrothermal vents are providing some of the structure that modern cells provide. And so they could just kind of borrow that. And, you know, I could imagine like little seals of lipids forming at the surface of a little pore. And then that's almost like a little prototype for a cell where you could get concentrated organic molecules on one side or the other.

And yeah, I really love thinking about that. There's so much room for heterogeneity and diversity in that environment. Yeah. And is it going to be ironic if, like, down the road, it turns out that this worked and, like, life depended on rocks. And all the time we're like, you go from a gradient of rocks to life. It's like the rocks would be like, you really didn't appreciate us. So you couldn't be here without us. Totally.

Yeah. They're not just this like impartial, inert bystander. They were, like, important. Yeah. So you're saying essentially that like you're building a little chemical engine here, something that's taking advantage of energy to do something. There's no like genome. There's no heredity. You just have like little bags of stuff that have an energy source and some kind of driving reaction and it's being contained by these little rocks.

And, you know, if we found just that on an alien planet, would you call that life? No. And I don't think that the people who study origins. of life would call that life either. But I think that they would argue that this is a first step. And I should say that there are like many, many, many different hypotheses for where this stuff started. Maybe it's not hydrothermal vents. Maybe it's hot spring somewhere. And maybe it's not the white smokers. It's the black smokers because there's different kinds of hydrothermal vents. I've been talking about a very early step for one hypothesis. But there's a ton of different other

ideas and I suspect the people who study the idea that I tried to summarize would say, yeah, and then we have like a whole different set of hypotheses for what happens next. But first, we're just trying to get this one step going. And what's kind of amazing is that by creating these very specific hypotheses, they've created scenarios that they can recreate in the lab. And they do a bunch of these experiments. They're actually trying to, you know, create the origin of life in the lab or, you know, simulate the conditions under which life. started in the lab. And then they go out in the field and they try to see, well, are we seeing similar things happening in the field? So this isn't just a philosophical debate, although the

philosophical debate part is amazing. This is actually like there's experiments going on where, you know, year after year we're sort of whittling away at which one of these options that we talk about are feasible and which ones aren't. So we're actually, you know, we're making progress. It's chemistry progress. So it's hard to share exactly what's happening. But people are working on it. And then there's the RNA world hypothesis. Katrina, could you go into a little bit more detail about ribozymes, which are amazing because they both store genetic information and replicate themselves, which we used to think you needed proteins for? Yeah, exactly. So, and, you know, in my mind, this hypothesis about the RNA world goes hand in hand with the metabolism first thinking,

because you're going to need energy and those building blocks of life to build up the kinds of polymers that have been so important for the basis of life. But RNA, ribonuclear, acids are very similar to DNA, just one of the important building blocks, the ribonucleic acid molecule itself, has an additional oxygen. And so RNA molecules are inherently both more unstable, but also more creative and capable of interesting kinds of catalysis. And so when you build a chain of RNA molecules, they have the capacity to fold over on themselves and build structures that you can use to do the same kind of projects that proteins do. So the chains of RNA that build themselves up into a little macromolecule called a ribozyme, they are capable of some

of the same chemistry that proteins can do. So what proteins do is they go grab a couple of substrates that they want to put together into a reaction and they hold them in a position that makes it favorable for that reaction to happen. And so ribosines can do that too. They can build a little structure, and then they can grab onto molecules in their environment and put the two substrates near each other and let the magic happen. So that's really all they're doing. They're not like forcing the reaction. They're just making it way more likely. And so ribozymes are chains of RNA. They're still a big part of the molecular central dogma of how molecular biology works in our current modern cells. But in those days, we probably didn't have DNA or

proteins yet. We only had RNA. So that's the RNA world hypothesis was that the first molecules to form were chains of RNA that can store energy, just like DNA. The molecules that comprise RNA are super similar to DNA. There's just one extra hydroxyl group. But then because of that extra hydroxyl group, they have more capacity for catalysis. They're not as good for storing genetic information because they break more easily. That oxygen makes them less stable. Huh. I didn't know. Most of that, which probably means I slept through a really important lecture. But that's amazing. It's such a good story. Yeah, I love getting to tell that one to students because it's like so apparent to just look at that hydroxyl hanging off the ribose and you're like, look at all the stuff that made happen, you know?

So you're clearly team RNA in the RNA versus DNA debate. I mean, I would not give up my DNA, man. DNA is like critical. Yeah. But I mean. But you did have a sparkle in your eye when you were talking. about the RNA. Yeah, I think it's fun to imagine that world before we had the DNA or the protein. And I think it's cool that we understand why. But when it comes down to it, you know, I trust my DNA. Okay.

So, you know, this is a Daniel and Kelly's Extraordinary Universe episode. So we talked a lot about what we don't know and sort of the limits of our knowledge. But I am still super excited about how far we've gotten, like how many different conditions we've considered in the lab and in the field and how we've seen the building blocks of life showing up in these different sorts of environments. I mean, there have been papers that I read where like something had to happen in the ocean and then it got thrown up on top of the land and then it dried and the drying was important for a step and then it gets washed back into the ocean and that's important for the next step and they've simulated all of this stuff in the lab.

Amazing. Totally amazing. But of course the more steps that are involved, the more complicated, it probably is for life to arise. And one of the questions that that really stuck with me while I was doing this reading was, you know, in situation after situation, it seems like we're figuring out how to come up with the building blocks of life, which makes it surprising to me that we don't see life popping up more often. And I guess the point is that, you know, if you're talking about it, you know, first it happens in the ocean, then it gets washed up on a volcano bank and then it has to, you know, fall back in. There's a lot of steps and it's super complicated.

But it's kind of amazing that this thing may have only happened and then really, taken off once, and now here we all are. And I don't really know where I'm going with this, but I had a lot of fun researching this, even though there's a lot of chemistry. And I'm really fascinated in this question of, like, how often did it happen? Like, it's true that there's a lot of evidence that all life on Earth has a single common ancestor. But I'm not sure that rules out an independent strain of life developing and then getting squashed by or outcompeted, right? Yeah. And that was a point that I saw made in these articles. over and over again is that what we see is the one instance where life sort of really got going

and then stuck around and diversified. But then to me, there's this other question of, are the conditions so different now that it just could never happen again? Like, why does life not start fresh now? And maybe it is something about the earth being so different, our conditions being so different now that you just couldn't get it happening again. But it makes me feel pretty lucky to be here. I think, yeah, I also thought about that a lot of I think that the oxygen and the atmosphere, I'm sure you read all about this, is a major reason that it's harder for these delicate initial life forms that were probably emerging three and a half billion years ago. You know, those guys could not stand the sight of a molecule of oxygen. They would immediately croak.

So I think our current conditions make that harder. But, you know, it could be that down in the deep sea thermal vents, those conditions are still ripe for new origins. And so it could be that some of those initial steps are happening. They might not make it that far these days because there's so much competition. But I would not be surprised if there are places where those conditions still exist on Earth. And check out our interview with Dr. Andrew David Thaler, where he's talking about what's happening at hydrothermal vents and why we might want to be careful about mining them,

because this could be, these vents could be a really great place for us to be studying the origins of life and trying to see if, you know, maybe it could ever happen again. But if we mine the heck out of them and destroy them, we'd lose the ability to study them. Well, we don't know, but I suspect the origins of life are hot and nasty and not very boring. Thanks everybody for listening. Please go and do us a favor and rate the show on whatever podcast app you're using. It really helps people find us. Daniel and Kelly's Extraordinary Universe is edited by the amazing Matt Kesselman.

He really is a wizard. You can also find us online on Blue Sky, Instagram, and, X, D&K Universe. Come engage with us. You can email us at Questions at Danielandkelly.org. We really do want to hear from you. And you can find our website, www.org, where you'll also find an invitation to join our Discord where everybody comes and talks about the amazing universe. And we also have the most amazing moderators. This is an I-Heart podcast. Thanks for joining us. If your bookshelf and your for-you page are equally important to your personality, welcome home.

Pro Society is a weekly podcast that's part book club, part group chat for anyone who thinks pride and prejudice and love island to serve the same level of discourse. Each week, we're connecting the dots between books, the internet, and pop culture, with your favorite writers, book talk creators, and plenty of overthought opinions. Yeah, I'm obsessed. I'm obsessed. Listen to Pro Society on the IHeart Radio app, Apple Podcasts, or wherever you get. your podcasts. On the new podcast, Solita, we share the messy reality of traveling alone as a woman. I can wait four hours for the next bus or this random dude is offering me a ride on his motorcycle.

I chose option B. I'm Julie Pinero and I travel by myself because it's a rare space where I can say yes without asking anyone else first. I'm on a mission to reclaim the word Solita, trading the pity for possibility. Listen to Solita on the I-Hurt. Radio app, Apple Podcasts, or wherever you got your podcasts. I'm Nick Tuturo. You probably know me from NYPD Blue, the longest yard, or Spike Lease Black Plansman.

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