Transcription
[Music] [Music] And now I'm happy to announce the next talk. It's Anuka. She is a PhD student in the University of Hong Kong, and she also describes herself as a lifelong Star Trek fan. Uh, she's hopeful that we will find alien life within the century and is working hard to make it happen. So please, the next talk is called "Microbes versus Mars: A Hacker's Guide to Finding Alien Life." And she promised that we are going to take a journey and look behind the scenes of the search for life on Mars, but also a new appreciation for the strange and wonderful life on Earth.
[Applause] Applause. You all have energy after four days of congress with very little sleep and a lot of people, a lot of information. But I'm very happy that you're here today and that you're happy to learn about some aliens. Um, so as you already heard, um, I'm a PhD student at the University of Hong Kong, and I'm an astrobiologist. So basically, astrobiology is the search for life in the universe, and um, I basically have like the typical, like very interdisciplinary, like work life that is typical for astrologists. So I go, for example, like on faraway places, on extreme environments to deserts and high mountains. I also get to work with robots. I was part of a very cool project, um, project at the DLR where we had five robots for one month, um, on the volcano Etna in Sicily, and we basically like played around with a planetary mission there and tested the capabilities of these rovers and how they work in teams. And I also do some lab work. So basically, in a typical day, I use knowledge from geochemistry, planetary science, microbiology, physics, and chemistry. And this is actually like quite normal for astrologists because we are very interdisciplinary.
And so the way that I came into this discipline, I want to talk, talk also a little bit about this. So this is me when I was like, I was 6 years old in the first picture and 9 years old in the second one. And already as a little kid, I really liked science, and I really liked biology and physics. And this was the big problem for me because like I really love life, and I really love the history of life. I love dinosaurs, and I also liked like insects and weird little squishy things. I went to go to the pond every day. Then you can see it there, like I had like a little kind of like, you know, like a little net with which I would like catch things out, and I just really loved all the diversity and all the strange stuff of life, especially the things that people usually overlook and not appreciate enough because things are a little like, you know, a little like little ugly or a little like scary or just like too tiny to notice.
And then I went, become like, when I became older, as a teenager, I was really fascinated by physics too and by the like the large expanse of the cosmos, of planets, of other universes possibly, maybe of other galaxies. And so when came time for me to decide if I'm going to go into biology or physics, I chose physics because like I want to know about space and all the cool stuff. So, um, I did my master's in physics at the University of Heidelberg. I specialized in astrophysics, but already doing my bachelor's, I got part, I noticed a very nice lecture series that we had there about astrobiology, and that actually set me on the course for the course of research that I am in now, which is, as you guess, astrobiology. So, um, for my master's research, um, in physics still, I went to the Atacama Desert in Chile, where I used physical methods like Raman spectroscopy to look at microbes. And now I am doing my PhD officially in the department of geosciences—again, very typical. I'm working on microbes, but I'm in the department of geosciences. My like professional background is in physics—very normal for astrologists. We are very interdisciplinary people, and at conferences, we have people from all kinds of different fields because it takes a lot of knowledge to really kind of like to grapple such a complicated problem like the search for alien life.
So I talked a lot about what is astrobiology. The general definition that we usually agree on is it is the study of the past, present, and future of life in the universe. And usually where we start, of course, is life on Earth because, well, that is like the only life that we currently know of, but it is already something quite interesting and something that we don't really understand. So if we understand life on Earth better, where it came from, what is about the whole diversity of it, we, we hope that we get like a better understanding of where to look for life in the universe and what to look for.
So if we try to break this further down, what kind of different areas we might have in astrobiology, like this is quite a good overview. This is from the European roadmap in astrobiology, so like a bunch of European astrologists got together and said, "Okay, people, let's talk. Um, what do we all do research in? How can we better organize ourselves?" And so these are like the big topics that we came about. So we want to understand, um, the origin of planetary systems, how they form, maybe like also how often habitable planets form. Then we want to understand organic components like in space. For example, we know that meteoroids contain amino acids, and they rain down in early planets and bring the first organic compounds, maybe starting the primordial soup. Then we come to the next step. We want to understand how life starts—right, very complicated question. People are working very hard on it, but we don't really know it at the moment. And then the next two topics are closely related to the research that I do. It's life and habitability because very recently we found out that life is actually much more hardy and much tougher than we originally thought it is because we keep finding life in all kinds of extreme and unsuspected environments. And then the next one that is also related to research I do is biosignatures. So with biosignatures, we usually mean fingerprints of life. Imagine you're a detective, you're at a crime scene, and you want to prove that that crime has taken place. You look for evidence, right? And the best evidence is, of course, evidence that you can be very certain of, that is like of very high quality, that you can also convince other people of. And these kinds of things are biosignatures—certain things that are very indicative of life.
So, um, having understood all of this, we have talked a lot about life, but we have not really come up with a really clear understanding or the definition, what exactly is life? Because if you close your eyes for a moment and think, okay, life on Earth, you might think of, I don't know, your cat, your house plant, maybe yourself, you know, like maybe like a rainforest or coral reef. You might come up with something like this, right? This is like usually what we picture of when we think biodiversity, ecosystems, you know, life. But if you are a little bit of a biology nerd, you will notice that this is actually only like a very, very small subsection of the actual diversity of life because this is all the life that we usually see with our own eyes and that we interact with. Maybe you don't interact with a coral reef on your, you know, like daily life, but I don't know, I don't know your life, maybe you do, but usually this is like what we think of—life, macroscopic stuff that usually is animals, plants, and fungi. However, if you were had a microscope, you would realize there's much more around than that, right? Maybe you have tardigrades, slime molds, you have archaea—also very weird, like they are symbionts—and you have stuff also like bacteria, right? And then you say like, okay, but we also have stuff like viruses, and we also have stuff like crystals, but these ones we usually don't really consider life, right? We would like say, "No, that is not life." So although we have like kind of like, we know that life can look very different, it can be like very big and very small, we sort of have an intuitive understanding of what we mean when we say life. We know crystals are not life. We know like viruses are a complicated case you can discuss about, but for example, a tardigrade is undeniably life, right? Even when it goes into its like dormant state and you can like freeze it and send into space, and when it comes back up, it's definitely life. So the question is like, what can we come up with, like some kind of definition or some kind of understanding that we can really say, "Okay, this is life, and when we see it, we know it." So it is a very complicated question. It's like maybe also a little bit of a philosophical question, and many people have argued about this. Usually, maybe what you think of when you think, "What is life?" You have encountered definitions like this, maybe in high school or maybe in biology classes, but it's not really a definition, right? Just like a shopping list of ingredients, and it also feels like very Earth-centered because like if you look at this, you can probably think of a science fiction novel where someone came up with something else, like organization and cells, you can probably think of or imagine some kind of alien life form that doesn't have that, right? Or like growth, maybe there's something that just like exists forever in like the same size and doesn't grow, right? So it's all very dependent on Earth.
So if you want to come up with something that maybe a little bit more expansive, there's my personal, um, like favorite definition of life because like I'm a physicist, and um, so like Erwin Schrödinger, you know, famous for quantum mechanics and cats, you know, cool dude, and he came up with an idea, of course, like from a very physical mindset, is that basically life is something really weird because in physics we know that like usually systems tend to increase their entropy over time. This is like, you know, what will eventually lead to the heat death of the universe—like generally things go to chaos. You know, like entropy is not chaos, I know, but like just like as a general understanding of it. However, what life does is it can repair itself. So if you drop a coffee cup, it will just like, be there in charts, but if you cut yourself on something, your body will repair itself over time. So basically, it can like re-establish order that has been broken up, and re-establish order is something that goes against entropy. So if you want to have like a very kind of like, you know, like bird's-eye perspective view of life, maybe we can think about, okay, life is something that can somehow like kind of like go to negative, negative entropy. It can reduce the entropy within itself. Of course, entropy overall is still maintained because it usually has to do some kind of energy system and like energy exchange. It warms up the environment; it kind of like, um, like eats something, excretes something. So if you put it in a closed container, the entropy within that container will still increase over time, but the entropy within the system will be reduced. That's like a pretty cool like feature. And um, so both of these are not really usable if you're an astrologist because for biologists, as if you're a biologist, this might be an interesting philosophical exercise, but you don't really care, right? Because you look at life, and you know it's life. You're not really interested in determining if something is alive or not. That's not part of your business. You're just there to study the life, but if you're an astrobiologist, it's a really important, crucial question for you because at some point you might encounter something, and you have to tell people if that is an alien or not, right? That's like a really kind of like big responsibility you have, so you better come up with some sort of workable definition where you can like work around how you're going to deal with that. So and NASA is in that business, so they come up with this kind of definition that also like colloquially used also among other astrologists, even if you're not associated with NASA, it's a good working definition. So you come up, life is a self-sustaining chemical system. Self-sustaining, we have like the Schrödinger idea of basically negative entropy, right? It can like repair itself or sustain itself over time. Chemical system, we little bit have like this stuff that we observe on Earth, biochemistry and these kinds of stuff, metabolism, energy changes going on, and we have Darwinian evolution, right? So that's like also a very important thing that we see—adaptation to stuff over time and changes. This is like kind of like our working definition. This is not the, you know, like not the last kind of like decision on this; it's just something that we work with right now because it serves us really well.
All right, so we have sort of an understanding of like what life is or how we can at least sort of define it, but the question is, where does all this life on Earth really come from, right? Like what, why is there so much different stuff, and how could we somehow categorize this in a neat little way, right? How can we say, "Okay, some things are similar to each other, some things are a little bit more like, like different from each other"? And so we come up with something like this. Maybe you've seen something like this before. So this is basically like, um, a large map of the life we have on Earth. It is like not the current view anymore, but right now it is still like very useful to look at it as a simple idea. So you see three big names, um, one of those you might be familiar with—bacteria. The second one you might not have heard unless you're a biology nerd—archaea. And the third one is eukarya. So I have good news for you: We are all eukarya, all in this room. We are all eukarya, and so is your cat, so is your plant, you know, like so the like the mushrooms. So it's actually basically any life that you can see with your naked eye. So basically, eukarya is like the large part of life that consists of all the multicellular organisms. There are also some single-celled, but I can, you don't see them usually. And then we have the other stuff—bacteria and archaea. They're usually what we think of as microbes, but some eukaryotes are also microbial. And the interesting thing is bacteria; we've known about them for a very long time, but archaea we actually only found out in the last century, at the end of the last century, because we started being able to sequence genomes. And the reason for this is that bacteria can make ill—some of bacteria, very few of them are pathogens. So we had a vested interest in understanding and studying them, growing them on Petri dishes, you know, like trying to understand like how to combat them when we get sick. But archaea are very innocent. Archaea just lived their lives. Many of them are extremophiles; they just like, you know, live their life in like in hot springs and like deep-sea vents and like salt lakes, and they don't disturb anyone at all. So we never knew about them. The other problem is we cannot really grow archaea in labs. There are some people who are able to do this, but it's really difficult. So basically, usually we cannot culture them, and the stuff we cannot culture, we cannot grow in a lab, we don't really understand that well. So we only found archaea once we were able to start sequencing genomes, and then we found stuff that doesn't actually fit in with the other stuff. And if you compare genomes, we can maybe sort of like build a family tree, and then we found, "Wait, these archaea, they are like, they look under the microscope sort of like bacteria, but they are very different from bacteria in many, many, many ways, and actually are more similar with us, with the eukarya." And this is like why you actually see that archaea as like this little branching out of eukarya and of eukarya and archaea. Um, so the general understanding at the moment, by the way, is that we were originally like descendants of archaea and that archaea might be actually one of the like most ancient forms of life. What you also see, what's also interesting about this is, so by the way, yes, for your orientation, you're here. If you didn't see it, Animalia—you're all animals. You know, this is like how you find, find out we're all animals. And down here, the branching of where we all come together, um, we also call this LUCA—the last universal common ancestor. So because of evolution, we understand and we know that all life on Earth is basically one very, very large extended family, right? So you're basically cousins with every single life we will ever encounter. If you have a bacterial infection, it's sort of a family conflict, right? Because it's like, so basically like whenever you encounter life in some way, it's sort of like it stays within the family because we're all related. It goes like our connections go back a little further, like you're very closely related to your cat, also quite closely related to your plant, you know, house plants, bacteria—a little bit further relations, but still same family. So you can also trace us back like a family tree and think, okay, like if we're all related, what is our like great, great, great, great, great, great grandparent, right? So when was this like grandparent alive? You also know this, this now; it was like very long, like several billion years ago. And um, we can also sort of like backtrack what this like last universal common ancestor, like we call it LUCA, that's like a cute nickname, so what it might have looked like because if you compare all the genomic sequences of every life on Earth, you can sort of see, okay, this one is shared, and this one is shared, and, "Oh, they all share this one." So we can sort of a little bit backtrack what it looked like. We now have, have a certain, some people believe it maybe lived in a like in a, um, in a hydrothermal vent in the deep ocean. Other people disagree with this, but we kind of like understand it was like an extremophile of some sort, was like quite simple, but was the one basically like, like the one organism from which all other life on Earth evolved. It doesn't mean it was the only one around at this time, but everyone else, like everyone else's like descendants went extinct at some time. So this is like the one where all the descendants, like not all the descendants, but where the descendants are still alive nowadays. LUCA was also not the first life on Earth. That's why the tree like has like this little like, you know, like the stem that goes down. There was life before that; that was just the one before it branched out to everyone else who is still alive today. Okay, all right. But I already told you, um, this one is slightly outdated nowadays because we have gone much better with genomic sequencing, and now the most—this is like what it looks like now. I know it's a lot; that's why I showed you the first one. You know, this one was a little bit easier to understand. I also know the names are all really tiny and small. Um, for a little bit of orientation, so this one was published in 2016 with new genomic sequencing methods, and as an orientation, you are down here. Um, it didn't even make it to Animalia, you know, so it's just like a fiston if you can read it, and the fisticons is like fungi and animals, 'cause like we're sort of like more closely related to them than the plants. So it's like we are not even that important that we made it to like an extra branch with animals because what this actually is is a map of genomic diversity, and what you can see is we are at this sort of like little like trail end branch next to the archaea, by the way. So like the other kind of branches next to us, the pink ones are the eukaryotes, and the other ones that are like next to it are all the archaea, and this big kind of like all the big, big branches at the top are all the bacteria. What we also found with this one is, if you see this like weird green-yellow thing that goes to the to the right part of it, this is like an archaeal film, so like a very big part of an evolutionary order that we didn't even know about. And so it was, it just showed up in the genomic sequencing data because this is all stuff that cannot be cultured. So this kind of like led to a little bit of a revolution in understanding because it was like, "There are all these organisms and all this incredible diversity, and we didn't even know about it. Like, how can we miss this? Like, we live on the same planet, right?" And they also live like in soil and kind of like environments that we see every day, but because our microbiological methods were so much focused on like culturing stuff that grows on Petri dishes, we actually overlooked most of the diversity of life on Earth. So actually, if you want to have like a mental picture of the diversity of life on Earth, this is what it should look like because like if you think of polar bears and like butterflies and stuff, they are all in the same tiny branch as yourself. So the actual diversity is actually like out there among bacteria, and there's like crazy diversity.
So if I say diversity, you might also wonder what exactly does this mean because they're all tiny, right? So the diversity cannot really be in size, and it's not. So what I usually mean with that is metabolisms—how do you gain your energy? So we are all aware we need food, and we breathe oxygen, and then we make like CO2, you know, and the plants kind of like, they need CO2, and they make oxygen, you know, like all nice, but there are a lot of other ways that you can get like your energy. So basically, we are a very complicated biochemical system; we get our nutrients, like we metabolize them, and we get energy from that, and you can basically do this with any other kind of like chemical reaction. You can get out energy in the end, and life has done this for a very long time. So if you like, I don't know, like who's are biologists, if you don't, if you're not a biologist, you can also see something like there is anaerobic and aerobic, and the heterotrophs—I'm sorry, they are all complicated terms, but don't be scared by them, okay? So basically, chemoliths is stuff that uses stuff that we don't consider usually nutrients, so it's not organic stuff; it's stuff like iron oxides, you know, or sulfur oxides, you know, like weird stuff like rust that you would not usually consider something as edible, but there are a lot of organisms that think it's very yummy, and they just live their entire lives on that and like live happily and can make energy from it. And um, so basically, anaerobic and aerobic is if you can survive under oxygen. Now, as you might be aware, we have a lot of oxygen on this planet, right? So you might also wonder how as an organism do you survive if you cannot tolerate oxygen, and the answer to this is actually very interesting because it goes very back into the past of our planet, and I want to take you on a little journey to explain like why microbes have this crazy diversity, why they have all these different ways of making energy, and to answer this, we have to like time travel a little bit, and um, yes, of course, like this is like also what you have in your head now—mostly the diversity of life on Earth's microbial if you don't take anything away with you from this talk, please remember that. Okay, so let's go on a little like travel through time. If you think of the natural history of Earth, um, I understand that most of us will be thinking of dinosaurs. I also think of dinosaurs, um, and so that's usually how we illustrate like our natural history textbooks, right? We have like dinosaurs, and then somewhere between dinosaurs they were like weird amphibians, and before the amphibians were fish, and before the fish were trilobites, and then there was nothing. So basically, this is like how you, how people illustrated it, right? So like interesting stuff happens, and then 500 million years ago we had like the first trilobite, but before that, no, there wasn't really anything. And of course, it's not the truth. So like, um, Earth is already 4.5 billion years old, and multicellular life, as we are and as trilobites are, has only been around 500 million years. So this gives you four billion years of life on Earth where life was there, but people don't usually pay a lot of attention to it because, you know, like we as multicellular life are a little bit biased towards other multicellular life, so we usually only want to think about that, um, but I little bit want to, you know, like rectify this picture. So, um, this is like usually how we do this. So maybe you, you might be aware of it; we have like the Mesozoic—Mesozoic is dinosaur stuff. Paleozoic is stuff before the dinosaurs, but this is all still part of like something, an like an age of time that we call the Phanerozoic, and before the Phanerozoic there was the Precambrian because the Cambrian was the Cambrian explosion, that was when suddenly many, many, many fossils of multicellular life appears, but there's also a very interesting time before that. So let's talk about this time before that, the Precambrian. So this is like, as you can see, this is like to scale, and so you can also see that actually like this time of that is like was shown in this nib of spiral is really just like a really, really, really tiny part of like the actual like long, long, long, long history of life on Earth. And so before this, the long, long, long blue row that you see, that's the Precambrian, and in the Precambrian we mostly have single-celled life, and for most of that life or like for a long, long time there wasn't even like eukarya around, like our ancestors. We all come from single-celled organisms that were eukaryotes, but before the eukaryotes we already had bacteria and archaea. And if you were to time travel, if you were to step in a time machine, you know, like and go like three billion years in the past, please bring your oxygen mask because like three billion years ago there was no oxygen in the atmosphere to a large degree. So bring that, but if you were to step out of your time machine, what would you see? You would very likely see, um, a world that is mostly covered by water. You would see some volcanic islands, and you might spot something slightly weird in the water, like these little like pillow stones. These are stromatolites. They are very, very big macrocolonies of cyanobacteria, and they grow in colonies; that's why you can see them. They're like, like little microbial cities, and you know, they just exist, and they like enjoy the sunshine, like do photosynthesis long before plants, I say they were originally inventors, and they just live their happy life. You might also find a hot spring with some other microbial life happily living there. So this is kind of like the life that you see; it is already like quite abundant in like many, many different environments. It has already done different adaptations to different kinds of like environments—hot springs, maybe you also find something in like in cold glaciers somewhere, maybe you also find something in like the deep ocean. So you already have a lot of variety going on because it already had a long time to evolve before multicellular life appeared. You can even go a little bit further back. This is like the picture below that looks slightly brutal because it's like the Hadean, and I think the name always says like tells you it wasn't the most comfortable time to be around. You see this like the big yellow thing is not the sun; that's the Moon. It just formed; it's also super, super close because like the moon like formed quite close to the Earth, and then over time like went away and went away. So it would be like pretty impressive to see in the sky. It's also still molten 'cause you know, just formed. Earth is also still pretty hot; it is still also like regularly hit by meteoroids and stuff like this. But despite it being so uncomfortable and also despite the crust just recently being, you know, like kind of like cooled down from all the magma, it...
Formed out of once, and we still assume that life might have been around almost the moment conditions became sort of habitable. So it didn't take like 1 billion years for life to form; it looks like life was pretty quickly already there. And we know this because, like, for example, we find fossils of it—like these are fossil stromatolites. This also, like, what, like the lower picture tells you what they look like in our fossils. So it looks very cute, like a sort of layer cake. And lower ones—these are living stromatolites; they're in, like, the Hamelin Pool in Australia—very pretty. And um, so this is like how we understand what they look like; we we can still find living examples of those, and then we can compare them to fossils. And this is also a little bit the similar approach—keep this approach in mind—that we have like in mind when we want to approach Mars.
So the question is, this is like all the thing that was going on on Earth, right? But what was going on in Mars at the time? Because Mars was also around. This is like a size comparison of Mars and Earth, I want to show you, because like sometimes, like people very often don't show this, so that you understand, okay, Mars is much smaller than Earth. And this kind of like thing has been a big factor in the evolution for like, for Mars, for a very long time. Because one nice thing about this is, if you are a smaller planet and you just formed, your crust cools down faster, so you actually become habitable a little bit earlier than your bigger, like, Earth neighbor. However, the problem is, if you're smaller, like, likelihood is that your gravity is also less, so if you have an atmosphere, it becomes much more difficult to hold on to that. And also, if you have some kind of like, um, like tectonics going on and stuff like this, if you maybe have like, like a liquid core like we have, there's also a certain likelihood that you might kind of like cool down faster geologically—that you become like less geologically active much earlier. And this is sort of what we assume is the exact fate that happened to Mars.
So Mars started out as a very nice planet. You know, we know from many, many, like, rover observations that we have—this is like a map of every current rover that's still on Mars today; not all of them active anymore, but they are still on Mars. So like, it's getting a little crowded—you know, like, planet of robots—it's very nice. Um, but from these, these many observations, we now know, quite have a good picture of the history of Mars. We know, for example, there were lakes on Mars; we know, for example, that there were rivers on Mars; we know also that there are many, many, like, minerals that can only form in bodies of standing water. So we know deep in the history of Mars there was water abundantly around. The question is, what happened to it? And of that we also have a pretty good picture, because we think what happened to Mars was that it sort of like slowly, slowly died.
Um, so this is like a comparison, a little bit of, um, Earth and Mars below. For Earth, you see like Hadean and Archean—you already learned what what these what these names mean—so you have a little bit of a mental picture what looked like on Earth during the time. And for Mars, you see Pre-Noachian and Noachian—Noachian, by the way, because of Noah and the flood, you know, lots of water—that's the idea. And, uh, but it, and you also see a little bit of an artist's idea what Mars might have looked like over this time. Um, but the strategy of Mars is that these very nice conditions for life didn't last for a very long time, and Mars slowly died. The reason is, it lost its atmosphere; it got much colder; it lost its atmosphere, we believe, because it couldn't hold on to a magnetosphere. Magnetosphere is what protects planets from the solar wind. So basically, because like Mars became less active geologically, it like lost its magnetosphere; the solar wind carried away the atmosphere, and things became like much, much, much more harder on Mars. So very likely, um, like it soon became difficult for water to stay liquid on the surface. So if you were alive, you better migrate inwards, you know, because like on the surface is difficult—radiation and no water—so you go like underground. And it also became much colder. We don't really know right now what the conditions, the climate conditions were in early Mars; like, more scientists disagree—some say it was like nice and warm, other people say like, ah, it was mostly cold and we had intermittently warming events. So we don't know that yet for sure, but we know that sometimes we had liquid water.
Basically, Mars you can imagine is a sort of tragedy in a way, right? You had a like once nice planet that slowly, slowly, slowly became less habitable, while we, of course, like, still live on a very nicely habitable planet. So if you want to like picture that, this is like, of course, Earth and M, you know, today. So if you want to like travel back in the past, this is a little bit what you should imagine. Those two planets, by the way, they did not look like this at the exact same time—Earth is a little bit like more 3 billion years ago, and Mars is a little bit more like 4 billion years ago—but this is like what you could like have in mind if you think back of like an early Earth—mostly water, like, like in the Archean—and Mars, you like see some spots of, um, of water, you see some volcanic activity, you see maybe some glaciers. This is like what you can have in mind. Like, the thing with Mars is we don't really know how much water we ever had at the surface, so people will also disagree, but if you want a little bit of a mental picture, this is what it could look like.
All right, so we end up with all that we have learned about Mars with three possible histories, right? We could have like the occasion that maybe, yeah, there was water, but it doesn't mean that just because we had water and we had in generally like nice conditions for life that there really was life, right? We have one planet where that was the case, but because it was the case on this planet doesn't mean that whenever we have like water and sort of nice conditions that's suddenly magically life will appear, right? So maybe Mars is dead and has always been dead. Second possibility: Mars once had life, but it all died—I know, like, quite sad, but possible. If a if a planet becomes like less and less habitable over time, this is what might happen. Or maybe the life did survive; it adapted, and Mars is still alive, and that life is still around somewhere today. So let's go hunting for Martians, right? So if there are still like some aliens around, or maybe fossils of, of aliens, let's go and find them.
How could we do this? So we need three things for our hand: we have to know the right place to look, right? So we should like kind of like narrow down which are the best place to look for; then we should think about what are reliable tracks—what are like the biosignatures I talked about—and then also, because we're scientists, just having these two things is not enough; we also want sort of like understand how certain we can be about this, because we're still talking about aliens, right? There's like a big claim about life, so we have to be like even more sure and even more stringent than if we would look for these kind of things on Earth. So we have to find a way to evaluate our evidence and come to like an kind of like a way to look at it that we can sort of all agree on on whether this is like indicative of alien life or not. All right.
Um, the problem, a little bit, is like to study Mars we sort of also need Mars, right? Because like we want to have like a look what Mars might have looked like in the past, but we don't really have a time machine. So the best thing that we can do is to just find a Mars-like place, and this is exactly the research that I do. So basically, instead of, let's go hunting for Martians, we go for hunt to hunt for Martians on Earth, right? So we look for microbes that are similar to what we might expect Martian life to look like, and we just go look for it on Earth. So this is like what this looks like, for example. This is like—I know I really like this picture—because if you crop me out and like change the sky, it could actually also just be a picture of Curiosity or Perseverance, you know, if you like a little bit like, like put like filters on it and stuff. And but this is actually the Atacama Desert in Chile—maybe you heard of it—it's like one of the driest places on Earth. This is like a very special area; it's close, close to the Ojos del Salar—it's like the highest volcano on Earth—um, it's, um, almost 7,000 meters high. And, um, in this area, it's like, as you can see, very, very dry; it's also really high altitudes—it's like from 4,000 m up to well, all the 7,000, like all the 7,000 m of the volcano—so very high, extremely dry, and you find, um, maybe like lots of salt lakes, for example. There, this is like what this looks like, for example. This like was our lab truck; we had—we were very lucky to have a mobile lab with us that we could like take samples and prepare them in like sort of several conditions in the lab. And in the background you see one of those salt lakes where we looked for microbes. This is also like—life there is not only hard for microbes, it's also hard for a scientist to study them, you know. So we camped there; like, we went there for two weeks; it got very cold at night, very windy; you don't really have like good toilets around, you know; it's like, it's all really like, you just like survive and just do you do your science and you feel a lot of, you know, sympathy for the microbes who live there all year round. And, um, yeah, like this is like some things were also like quite nice, you know; you have a little barbecue in the evening after you do sciencing all day. And, um, yeah, life is pretty hard there. You find—this is like the skull of vicuña—they are the wild, um, relatives of the alpacas—very cute and cuddly. Vicuñas are not quite as cuddly; they are the only ones who sometimes visit this area, but even for them it's really difficult because there's basically no vegetation. And but yeah, this is like the kind of stuff that you find there if you look for life.
So this made me very happy; it was one of the first discoveries we had. These are so-called endoliths; so endolith means within, within rocks. This is like, like a gypsum salt crust on the Salt Lake, and you see is a little bit green, and green always makes us very happy because green usually means photosynthesis. And these are cyanobacteria; so cyanobacteria, they live inside this little greenhouse where they are shielded from the desert conditions; it's also a little bit more like wet there because, you know, salt pulls water. And so they live their happiest cyanobacteria life there just within the middle of the desert where basically nothing else survives. This is another good location to go hunting for life; this is a Salt Lake and close to the Salar. In the foreground is a hot spring. This is like also a nice environment; you have a lot of gradients—life loves gradients—because usually then you also have different chemical stuff going on. And this was very, very rich; it was like super abundant with all kinds of different life. This was some of the life that we found. The lower left picture are stromatolites—if you paid attention you remember—there's also stuff that we find like of very, very ancient life. This also made me very happy. The other thing that's like a layer microbial mat; it works a little bit like in a rainforest—you basically have different microbial communities, and everyone in like a different layer does different stuff—usually the one at the top they shelter everyone from everything else, and the one at the bottom sort of like cycle nutrients. These ones were very cool because like the bottom layer was actually anaerobic photosynthesizers, so um, they don't like oxygen; it's toxic for them because they evolved back on Archean Earth where there was no oxygen in the atmosphere, but they still survived by sheltering under other stuff where there is no oxygen.
All right, and this is like what you do—this like the biosignatures that you hunt for. This is like, for example, you, you are a scientist, so of course if you find cool microbes you shoot them with a laser, right? That's what you do. So like, I had my little laser with me and like I measured a Raman signal. This is like also the same instrument that we use on, um, on rovers on Mars, for example. And so this is like a very—this like, by the way, typical—don't worry about like all the different like names of it—but basically this is like a very complex spectra. So this is like, if you find life, life is made of very many different kinds of very complex organic molecules. So if you have like, um, like this kind of signal, it tells you, okay, there's like very complicated chemistry going on, and then you already know, aha, this must be life, and then you can start trying to find which like, which of these lines is which kind of molecule. All right.
Um, this is another location; this is like the location where I work right now for most of the time—this is in Western China. This has some also a lot of similarities; it is also very high, very dry, um, has very little water but a lot of salt, which is also like very what we would expect from Mars conditions, especially early Mars conditions, because we also find like things like salt; we also know it's very dry. This is like quite a good like environment to imagine if you want like a mental image also what like maybe early Mars might have looked like. So, um, you have these salt lakes—very highly concentrated brine—but of course you still find life. And here, this like the red things is actually interesting iron chemistry going on, and there are some bacteria who happily munch iron oxides. And these were the ones that—looking for—interestingly many of them actually live underground. So this was like a seep where water from underground was seeping up—this like a perfect location to look at this because we also expect that if life survived on Mars it might have also gone underground. So but like usually it's a little bit more difficult for us to go underground, so it's nice if like the life comes up and then we can study it. So this like also beautiful—you can see like the colors very red—as an astrobiologist, this always makes you very excited because this like red color usually means some interesting iron, uh, like iron bacteria going on there. And this is also what we found there. So yeah, this like a very exciting location. All right. And these like, these ones also are like relatives of the stromatolites that I showed you before; they have like a little bit—they look like a little bit like corals—but they also grow in a similar pattern. So these are just like different kind of, like, different morphologies that you can find, but the nice thing is, of course, you can see this with your naked eye, but you still know this is like made of microbes.
All right, so let's say, um, what we have like, like so far gathered on a hunt: we have—we found the right place, and we also have like found biosignatures. But the last point, of course, that we wanted to do is we want to be certain, right? We need a way to evaluate our evidence, and we recall our sort of like definitions, and the definition of NASA—and NASA came up with a sort of like, um, how to say, like, um, system to evaluate the quality of our evidence. I'm going to scare you like one moment now because this is what it looks like—so it's like a lot—I know it's like too small, you can't read it—but this is like a complicated system. But basically what you learned about like—keep it in mind—what we learned about for our definition of life. So basically, um, on the left side we have like different qualities of criteria; these are different things that we know about life, and they basically go in like, um, increasing, um, like quality of like what life is. At the top is the evolution; if you find something and you see it undergo Darwinian evolution, like it's life, you know, there's no question about it. But at the very low bottom is biofabric—so basically remember what the stromatolites look like, with the wavy pattern of the fossil—if you find something like this on Mars and nothing else, it's not really like a good thing to say like, yep, we found the aliens, because it could just have formed maybe with other things—like Mars is a different planet, maybe different stuff happens there and forms these rocks, and you don't need life to do it, right? So basically this is like kind of like an increasing like ladder of quality, and you can also see things like, for example, like what are the criteria, what are other criteria that you can use. So basically that you have like a guiding system—here's it's a little bit higher up—you can see like Darwinian evolution at the top, and then other kind of like things that also are like quite good indicators but are still not like a perfect proof. So what you usually do is you take a combination of these ones, and then then you kind of like decide on the quality of your data. So this is—I know that you might be like computer nerds and stuff—so like this is basically sort of like, um, a logical criterion for it. So, um, basically a rule trumps all other rules, all right? If you have—if you find Darwinian evolution, great, you know, you can basically declare and make a press release and say like, yeah, we found life; you don't need other stuff for it. However, if you find other stuff, you still have to be a little bit more careful. So what, what you basically want to end up with is you want to have like several of these things, and then you can sort of like evaluate your quality on the basis of this. It might look like something like this: okay, you have like the one and the zero things like for what your quality of evidence is, and in the very bottom of it you see like life detection results, you know, and then you can use this to, for example, like talk about like what the quality is if you find microfossils like this or this Master Meteorite that you might have heard about. This is all right.
And I'm pretty much at the end of my talk. Um, I just wanted to say that in the future we hope very much to like get even better, um, understanding of the life on Mars, because like NASA and also the Chinese Space Agency they are planning on sample return missions. So in the future we will not just have like rovers on Mars; we might even actually bring back samples and might observe some of these things like for real in our labs on Earth. Okay, all right. And this was my talk. Thank you so much. If you have [Applause] questions, um, I'm very sorry we did not have time for questions, but if you have questions, uh, find me outside where the planets are—you know, like the beautiful light installation with the planets—meet me there if you have questions; I'm happy for, like, looking forward to your questions. Thank you so much. Thank you very much. Thank you. [Music]