 In the meantime, I have the privilege, the honor of welcoming my friend and colleague, soon-to-be-doctor and peer graduate student at the University of Washington in the Earth and Space Sciences program, Joshua Christensen, to be joining me and welcoming Josh. So maybe you saw the title of my talk tonight, something about all rocks and looking for alien life. And maybe you came here expecting to see this guy. So I'm very sorry you disappointed me here, it's not that spectacular. I'm really talking science tonight. Also, as much as I think the title of the going song is asking a really interesting question, whether there's life on Mars or elsewhere in the solar system, for the purposes of tonight's talk, I'm going to be focused on looking for life on planets around other stars on exoplanets. So as I'm sure you're all well aware, there are literally thousands of exoplanets that have been discovered in recent years. And so we basically know that every every star has a planet, statistically speaking. And so here are some lovely exoplanets. Of course, these aren't real. These are artificial editions. You don't get pictures like that because they're far away. And because the techniques we use to detect these planets for indirect methods, right, you don't see the planet directly, you see the effect that hasn't stopped the transit. So because the techniques are indirect, we don't, for any given exoplanet, we don't actually get a lot of information, right. And so for many of these, these planets, you can basically write everything we know about them in the back of a postcard. So I've done that for a particular exoplanet, right. This is everything we know about Trappist 1e, more or less. I chose Trappist 1e because it is literally named after Peter. And so that seemed appropriate. But this is what we know, right? We know it's mass roughly. We know some things about its orbit, how much light it receives from its host star. We know it's radius. So you can combine the mass and radius to get some proved estimates of its density, right. It's overall composition, whether it's rocky, icy, or gas. But that's about it. We know its atmosphere is probably not high due, but that's all. And so it's, with these indirect techniques, it's difficult to say much. If you want to memorize everything on this postcard, you know as much as anyone knows about this pipe. But this will change soon, right. So, you know, despite the frustrating delays, the James Webb Space Telescope is going to launch sometime in the next few years. And you can see it, right. It's basically a complete constraint. They got to fix some things up, then it will go. And then a little further in the future, there are three very large ground-based telescopes that will begin observations in the 2020s. They're all under construction. And then looking a little further ahead, the selection process for NASA's next flagship mission has just begun. And three of the four possible designs for that mission with all the capable of doing a lot of detailed exoplanet observations. And so we can expect, I should say that since of all the telescopes I just mentioned, they will all be capable of looking at rocky exoplanets in more detail. So how do you do that? Basically, you take the light from the planet and with a bit of help from McFly, you split it into its exoplanet wavelengths, right. And so if you look at the amount of light, you get a different wavelength. You can look for the diagnostic absorption features of particular gases in that planet's atmosphere, right. You get the atmospheric composition. And so you can look for the gases that might be produced by life. So what we can expect in the not too distant future is a slightly more detailed postcard, right. This is what we might expect from Travis Clonnie with some James Webb observations. In addition to the mass, the radius, the orbital stuff we already know, we will start to get information about atmospheric composition, right. What are the gases in this finance atmosphere? Are there gases produced by life? And so when we get to this point, so let's just assume for a minute that all that goes to fine, right. The telescopes work as advertised, you get this information back. You're then left with a very difficult question of interpretation, right. Does this planet have life or not based just on the atmospheric composition? And so this is no longer just a question of astronomy, right. This is a question that is relevant to geology, atmospheric chemistry, geochemistry, and indeed biology. And by the way, that's sort of what astrobiology is, right. It's an attempt to bring together these people from different areas, different talking to try and answer these difficult, interdisciplinary questions. So we can expect information like this and expect to have to answer this difficult interpretive question. And we want to get it right, right. We don't want to make these observations and then say, now it's to the world, we've found life. Why do they take so far? I mean, to realize a couple years later, oh, actually, it was just a weird volcano. But we also want to avoid the opposite. We overlook something that looks not like the life we're expecting and miss that really profound discovery. So my next slide kind of tries to capture the complexity of this question of interpretation, right. So so we get a limited information on a planet. And how do we decide if it's a living world, right, something that requires life to explain what you see in the atmosphere or something dead, something that can be explained by purely geological chemical processes is basically a lifeless and boring place. Moving on. Anyway, so so with all of that, with all of that is introduction, the knowledge that we assume going to face difficult questions. What I'd really like to convince you of today is that by learning about the early earth, learning about the early earth can help answer, help us answer that question, help us interpret those observations, right. Now, just to be clear, what I mean, when I say the early earth, that probably conjures up images, you know, mine, something like this, right, like dinosaurs wandering around a tropical forest, you meet each other having a good time. But this, for all intents and purposes, is the modern earth, right. So you look at the timeline of Earth history, the Earth formation four and a half billion years ago to the present. Every plant or animal you've ever heard of has only existed for this time yet, right. And so you have the rest of the very vast history, which is more typical of Earth's state, right. And by learning about that very alien place, I think this can help guide our search for life elsewhere. Right, so geologists, paleobiologists have worked very hard to kind of reconstruct the history of Earth as best as possible from the rock record. And so both myself and Mike, you've sort of conveyed to me, I'm going to just give you a few examples of things on this figure and why they might be important. To motivate that more specifically, though, okay, so how do you detect life on an exit point, right. You look for the gases that are produced by life. And the most obvious candidate for that, as I'm sure you probably guess, is oxygen, right. Oxygen is a pretty good biosignature gas. It's produced by photosynthesis, either plants or cyanomacteria. And it's virtually all the oxygen in the air we breathe is produced by life. And if life would disappear from the surface of the Earth, the oxygen wouldn't hang around, right, would very quickly react with surface rocks, react with things coming out of volcanoes and be gone. And so the persistence of oxygen in a rocky planet's atmosphere is a pretty good biosignature. Now, we have been able to reconstruct the history of atmospheric oxygen, right. And I think this gives us some reason to be cautious about, you know, going out there and expecting to easily find oxygen as a sign of life in other planets. So this is the story of oxygen on Earth, right. We're just plotting the amount of oxygen in the air from four billion years ago to the present. And you can see that oxygen levels have only really been high at sort of modern, in modern levels to the last half a billion years, right. And so how we know this is kind of a complicated story and Mike's going to talk a bit more about that. But there are some, basically it's from the rock record, right. So if you look at more modern rocks, you see fossilized evidence of wildfires, right. And so you can't combust things that are organic matter with oxygen if there isn't a decent amount of oxygen. So that kind of gives you a floor oxygen here. Other than in earlier times, it's very good evidence that oxygen was significantly lower or virtually absent from Earth's atmosphere, right. This is a large scale over here. And I don't really have time to dive into how we know that. It's a really fascinating story. Rocks, these really old rocks, you can look at the sulfur in them and how that sulfur is being modified by atmospheric reactions. It's a very clear signature of an oxygen free and safe. Anyway, this is the picture of Earth's oxygen through time. And this is potentially a problem, right. Because if you're looking for oxygen elsewhere as a sign of life, for starters, there's no guarantees that oxygen making photosynthesis is a common thing. Even if life is common, right, there's no guarantee that that particular metabolism is common. It seems to have only evolved once here on Earth. It's a very complicated metabolism. But even if it is common, that's still no guarantee that oxygen biosignatures are common, right. We know that life on Earth is being around pretty much this whole time. Oxygen making photosynthesis has been around most of this time. It just took a long time for oxygen to accumulate to a modern level. So there's no guarantee that modern Earth-like levels of oxygen are going to be easy to find out there. So what we'd really like to be able to do is to take life on these sorts of planets, right. These early Earth kind of planets that are more typical of Earth's history. So how might we do that? Well as a starting point, we want to reconstruct what the early Earth was like, as best you can create a picture of that. And at least as far as the atmosphere goes, you have a reasonable idea. You think that at those very early times when the atmosphere was oxygen-free, this is kind of what was going on in Earth's atmosphere. Still a lot of nitrogen around. A lot of CO2, a lot more than there is now. A lot of methane. How do we know that? Again, that's from the right book, right. So you can do neat things when you look at the size distribution of fossilized rain drops. And you can do the physics and back out something about atmospheric pressure. This tells you how to be some nitrogen around. I already mentioned, there's evidence of very low oxygen. How do we know CO2 is really high back then? There are multiple lines of evidence. Perhaps the most intuitive one is just the fact that the Sun was a lot dimmer back then, but the Earth wasn't totally frozen over. You know that from the rock rate. So there had to have been a much stronger greenhouse effect that had to have been much higher CO2. And there's also interesting recent evidence from the rock record that methane levels were quite high. So this is the picture we have of Earth's early atmosphere. And we know something else about this. If you put this combination of gases together, the methane doesn't hang around. You wait a few tens of thousands of years, a blink of an eye really, geologically speaking, then the methane gets broken up by UV radiation, the hydrogen is lost, and the methane is gone. So to sustain such an atmosphere on the Earth, there really needed to be a very large flux of methane into the atmosphere from the surface replenishing the methane continuously. And we're pretty sure that this flux was provided by life, by biology. This kind of life, right? No oxygen around. But microbes, microbes, microbial production in their veins are very common, common metabolism. So what this shows is that the atmosphere of the early Earth was this, it was very clearly biological, right? There was bright neon signs, life is here, life has been obvious on Earth, to any external observer for billions of years. And this raises the, I guess, the next question. Is it okay? This is what was happening on the early Earth, right? Suppose you see this on an exoplanet, right? Now you've just got the postcard, remember, no one's thinking about the surface anymore, you just get the atmospheric composition. But just from the atmospheric composition, and the knowledge that there must be methane replenishment, can you then infer that this planet has life? And so this has kind of been a subject of some of my research and thinking about, well, okay, see, we see this on an exoplanet. Can you explain it by some other process? So you can kind of work through what is geochemically plausible and think about these different scenarios of methane coming out of volcanoes or from reactions with rock and think about, not only are they likely, but if they did happen, what other clues would they leave? What are the other observations you can make that would distinguish these things? And without diving into the details, the tentative conclusion is, yeah, you can probably rule these things out. And so if you could see such an atmosphere and make these observations, you could make a reasonable inference to life. This is just a fun little aside. So when we published this paper, various news organizations deemed it sufficiently worthy to do a little thing on it, and it was kind of fun to see it filter through. So you know, have like reputable organizations like Scientific American, like Times, Facebook, got it right, and they said, yeah, here's some new ideas about how you might look for life on a planet without oxygen in the atmosphere. But you know, it filtered down, and some of the headlines were quite amusing, this is my favorite, revealed the huge scientific breakthrough that proves alien life on other planets. So that was interesting for me just to see how science gets manipulated. I also liked that Fox News categorized it under UFOs. Just briefly to link things back to how I started and saying this is something that's detectable soon. This is some other work I've done, which is kind of more standard astronomy. This is just saying, remember our postcard planet, Trappos-1e? And this paper, we said, let's pretend that Trappos-1e is likely earlier, right, with this methane and CO2 in its atmosphere. Who should detect that? Was James Webb? And the answer seems to be yes, right? This is just the amount of light, different wavelength. This is the big flow thing again. And yeah, with table bits, you can potentially see it. And detecting this early Earth by signature might actually be easier than detecting an oxygen by signature, at least James Webb. So that's kind of what I had. I guess to summarize that, then looking for the modern Earth as an exoplanet, this is sort of the obvious thing to do, right? Of course, we should go out there and look for oxygen-rich atmosphere as a by signature. But by thinking about the early Earth and thinking about how the biosphere changed the atmosphere in this oxygen-free world, it presents another possibility, another way of looking for life. And I haven't really dived into this, but one could make the argument that these sorts of biospheres are maybe more common than these sorts, right? Not only from the story of Earth history, but also just from the fact that oxygen productions, a very complicated metabolism, methane production, relatively simple, seems to have emerged almost immediately after the origin of life and has emerged multiple times independently. So potentially this is more ubiquitous. And in general, this is just one example of how learning about the early Earth can reform the search for life elsewhere. So yeah, telescopes come with swimming, but again, look at the atmospheric composition of rocky planets. That's pretty exciting. But how are we going to know if we've found life or not? So I'm trying to convince you that the Earth's history in deep time can help us with that question. But provide examples of alternative life solutions. So that's all I'll have. I'll be very happy to answer questions and do stick around for Mike's talk. He's going to talk more about the story of oxygen, how it relates to the life and really care about complex life. Thank you, Mike. So yeah, with that, thank you very much. So the question was, what is the victimization? It's something that I flashed off on an earlier slide. So this is a process that might produce methane without life, right? So whatever reacts with rock in the sea, all of this releases hydrogen gas. And that hydrogen gas can then react with CO2, which is hanging around to produce methane. So potentially you can make a lot of methane this way. But we've done some calculations to show it's still considerably less than what we've made off in life. So the question was whether these exoplanets are certainly going to have some kind of atmosphere or not. We really don't know at this point. It could be the case that some of these planets get lasted by such intense radiation that they start to make these life-less rocks like move. Even for the relatively easy ones to observe like a trapezoid, it's still not going to have an atmosphere like that. So the question was asked about the hydrogen hydrogen gas with the large methane leaks. And this kind of gets into a solve that we talk about. But it's really the methane and CO2 together which has a slight life rather than methane alone. The reason for that is that methane is CO2. It's covered in opposite ends of the redox spectrum like it's most oxidized form that's disoxidized form. You can produce either end with non-biological processes. Produce those two extremes without life. That's really hard to do. So the question was asked how on it can you get learning about the atmosphere from the shape of rain drops? So it's the size distribution. I forget the details of the physics, but basically the size of the rain drop difference. I'm telling you something about the maximum velocity of the rain drop supply. It's that velocity in the way of the density of the atmosphere. The question was asked how does looking for the life of the candidates? So that's how the earlier step went. We wanted to verify that there's a planet keeping it out of the way to begin before you start looking for possible signs of it. So whether it's possible for a look at what might have said this. So that's something that we wanted to verify. Actually, in the sense that the planet's not sure of it as a fact, how do you might do that? Okay, one more question. The question was asked why the sun is dimming. That just comes from the physics and the region of the core that you've been trying to figure out how to do some of the benefits and problems that you've seen. So I'll be around if you want to come and chat. Thanks for the question. All right, who's ready for some trivia answers? Moons are hard, but you guys are awesome. Okay, it's not the second known convertible object of the moon. There's Eris, there's Pluto, there's seven...