Nathalie Cabrol: Search for Alien Life | Lex Fridman Podcast #348

My friend is telling me that the volcano seems to be starting to erupt. If that volcano goes off, we have nowhere to go. That got my attention. So if you say scared, I would say that I got the realization that what that meant I went cold for like a fraction of a second. But that meant that just my adrenaline started to kick in. And it was a very, very strange experience because now you have tunnel vision. It's about survival.

The following is a conversation with Natalie Cabral, an astrobiologist and scientist at the SETI Institute directing the Carl Sagan center for the Study of Life in the Universe. She explores some of the harshest places on Earth, including free diving and volcanic lakes, all in the pursuit of understanding living organisms beyond Earth. For this, she holds the woman's world record for diving at altitude, both scuba and free diving. She's amazing. This is the Lex Friedman podcast to support it. Please check out our sponsors in the description. And now, dear friends, here's Natalie Cabral. You are the director of the Carl Sagan center for Research at the SETI Institute. SETI, of course, stands for Search for Extraterrestrial Intelligence. One of the things you do as part of that is travel to some of Earth's most extreme and dangerous environments in search of organisms that live in conditions analogous to those on Mars. First, let me ask what the job posting for the work you do looks like. Is it like Shackleton's ad in 1900 that said people wanted for hazardous journey to the South Pole? Small wages, bitter cold, long months of complete darkness, constant danger. And also, where do I apply?

That's funny, because there was not really a job application. In fact, when you're a scientist, you have questions in your mind and you have hypothesis and you start to list the kind of thing you need to answer. And then when you see the kind of thing you have to answer, then you kind of know the places where you need to go to do that. As far as science is concerned. Started with analyzing data from Mars missions and I had written a PhD about water on Mars, first looking at channels and the history evolution of water. But then during my postdoc I started to look where that water was ponding. Interestingly enough, everybody was about channels and water and whether catastrophic or whatnot or seepage. But when you are talking about pounding water like lakes or ocean, people were started waving their arms a little bit. So it was a little bit of a battle. Interestingly enough, you. Yeah, but that got us on track with my husband. We were working together and we started developing the idea the Concept of lakes in impact craters. So why in impact craters? Just because the Viking mission at the time, which is what we were working with, the resolution and the topography were so poor that there was really no way of telling where you had a real low in the topography. The only thing thing you knew was a hole in the ground was an impact crater.

So when you saw valleys, what was the Viking mission?

The Viking mission landed on Mars in 1976, and there were two landers and two orbiters. So they were really our first feet on the ground on Mars. But they were lander, they were not moving, they were not going up.

And that was the data you were looking at.

It was already in the 90s, but we didn't have yet the, the Mars Global Surveyor and whatnot. We still work. For 20 years, we worked on that. I did my master and my PhD thesis on Viking missions.

You mentioned that the places you go to are defined by the questions you want to ask. Let's just step back. What questions have always tugged at your heart?

Well, that's the thing. That's why I was looking at those images and saw some lakes. And then came time to where we started talking about sending landers and rovers on Mars and looking maybe at the possibility that Mars was habitable. And lakes are particularly good places to look for those questions. So this is how it all ties up.

So you were always curious about life out there?

I have been always curious about life in the universe and about questions on how we got to be here. And the bigger question now, with 25 years more in that business, it's more about understanding the origin and nature of life rather than whether there is life or not on Mars. This was really, for me, a stepping stone to bigger questions. But they were definitely important because they helped me frame my way of thinking about those questions. And so looking at Mars, at lakes, understanding what the conditions were 3.5 billion years ago or close to 4 billion years ago, then I knew the type of environment I needed to explore here on Earth as analogous to be able to understand what type of life still survives in those environment and what kind of instrument and what kind of resolution do I need to actually detect it. So this is how the whole thing started. And it started with a small grant, literally 40K. It was, it was a discretionary fund. And this is how I got started in my, in my career.

And so many of these questions you can answer by looking at life and extreme conditions here on Earth. But let's, let's step back a little bit and look at Mars. And lakes on Mars. Just going back to your PhD and before and maybe today. What do we understand about life on Mars? What do we understand about lakes on Mars? Is there water on Mars? What do we understand about the conditions from 4 billion years ago on Mars?

Well, we've gone a long way. Remember from, from the Viking, where we had no resolution. Well, we had a little bit more resolution with, than with mariners.

What did you think at that time? Sorry to interrupt. It was just take us back to that mindset.

It was really the exploration, like your first look at a planet. You have to remember that the first mission that successfully snapped some pictures of Mars was Mariner 4. And then everybody at that time was still under the spell of, you know, H. Wells. And the idea that Mars looked with telescope so similar to the Earth polar caps, we could see them with a telescope and we knew it had season. The actual tilt is pretty much the same as the one for Earth. So when Mariner 4 left, everybody pretty, not everybody, but a lot of people thought that we were silly crystal cities and domes and stuff, that another civilization might have evolved in parallel to us in the solar system. And of course, when the first images came back and Mars looked with that kind of resolution it had, like the Moon, it was a huge disappointment. Then Mariner 9 came and that changed everything. There was a little bit of drama because Mars started one of the biggest dust storm it ever experienced. And so for three months we had an orbiter circling around Mars and not seeing anything. But then when the dust cleared, all of a sudden we started discovering volcanoes, valleys, ancient channels, dune fields, polar caps. And see, when I'm talking to you, I don't need to invent any words to describe Mars. And although the myth of extraterrestrial civilization on Mars was gone, all of a sudden, the imagination of the scientists started to pick up because right away we were seeing something that was familiar that we could describe. So right away, Viking was put on the fast track. And the idea was, so Mars looks so much like Earth could have been, although it's arid and there is little atmosphere, et cetera. Could there be life? And of course, behind this, at the time there were people like Klein and Sagan, Carl Sagan, just, you know, thinking about how can we test the idea of biology of life on Mars. So this is what Viking did. But of course, at the time when the two landers arrived on Mars, we didn't have the context of the geology of the environment. We didn't have much data at all. So the data that Viking sent back Was very confusing. Some people still think today that we discovered life on Mars at the time because some of the experiment turned out to show a strange signal. But most of the community think that it can be explained by chemical reaction that we see today. So it was so confusing that NASA decided say, okay, if we want to be serious about looking for life on Mars, we have to understand the environment. Because life and environment co evolve. So as cause or effect, a planet is going to give you the physicochemical environment for life to happen. These are the boundaries. But once life is here, it's going to change everything. One of the biggest impact of life was to inject oxygen into the atmosphere of the Earth three, two billion years ago. And that changed everything, including our signature in space. So there is this co evolution. So if you want to understand one, you have to remove the other from the equation. It's kind of a two unknown equation.

So even though oxygen changes our signature today, what if all life on Earth died? And now we fast forward a billion years, what would be the traces left? So the question I'm trying to ask is if life had existed on Mars, what would be the signs we would look for?

That's a very good question. The thing is that if you draw the parallel with Earth, it took 82% of Earth history, geological history, to go from very simple life, microbial life, to complexity. And when I'm saying complexity, I'm not even talking about us, I'm talking about animals. So Mars is smaller, lost its magnetic field very fast and lost its atmosphere very fast. Life also appeared on Earth very fast. So the condition being quite similar at that time between the Earth and Mars. Let's assume for a moment that life appeared on Mars. It would have been simple life when conditions started to degrade, which was less than a billion years after the planet had formed. So everything at the surface would have disappeared, except maybe for morphological traces of the interaction between life and its environment. So on Earth the best example are what we call stromatolites. These are rock formation that are built by microbes. So we know that, we know how to recognize them. You could have chemical traces as well. There is some interesting question marks right now, but carbon isotopes at Gale Crater, because we found an abundance of C12, which normally is used by life on Earth, but it can be produced by other things. So it's not that it's a real biosignature in itself, but it's intriguing. We have now the C12 and we have methane. But going back, it's a time on Mars, 3.5 billion years ago, where you have lots of destructions, where you have lots of impact cratering, et cetera. But we still have very old rocks that are, that survive from that time. So these are good, good places. That's why we're sending the rovers in those places. Ancient lakes and impact craters and places where you have very old rocks.

So when you say ancient lakes and impact craters, the simple question. So impact crater is a crater created by a giant rock hitting the planet.

And yes, a big rock that can be metal or rock, or it can be a comet as well, mostly ice.

So is that good for life or bad for life? For creating life and destro.

Both. It's actually both, interestingly enough. The building blocks of life, the bricks, the stuff we are made of, carbon, hydrogen, oxygen, nitrogen and phosphorus, they were included on our planet. They were built in just because our planet is made of this kind of rocks. Asteroids and comets coming together by what we call accretion. So they were built in. When an asteroid comes, there is a lot of destruction going on, but at the same time, those rocks, they bring with them those bricks of life and they create lots of energy. And if the environment around is favorable, you might possibly have some seeding going on. That's one of the aspect of what we call panspermia, which is the fact that comets and asteroids have the building blocks of life embedded in them and that given favorable condition, they might be able to see planets. This is a theory.

What percent of you, when you're looking up at the stars and wondering about this stuff, thinks that panspermia is what happened on Mars or on Earth, which is the building blocks of life came from elsewhere?

Well, but, you know, that's the thing. Panspermia is a vector, potential vector, which means that he actually distributes the stuff of life left and right, but it doesn't explain the origin of life. It's not the environment itself. It just promotes. Maybe, and we still have to prove this, but what we know is that the stuff we are made of is very abundant all over the place, including in interstellar medium. So it's all over. It's all over. The idea is that maybe it just waits to have the proper environment. And we know what it needs here on Earth. It needs water. It needs energy, shelter and nutrients.

So you're fundamentally interested in the origin of life and the big leaps in evolutionary history that could be like an origin of something. Origin of eukaryotes, origin of photosynthesis, origin of whatever. I just think if we're a civilization here on Earth and we survive another few hundred years, I think it would be a good idea to take a big gun and just shoot life out there, like a life gun. Basically try to create panspermia. That's a good backup solution. So one way is to actually copy our brains and actual humans some complex information and send it out there. Another way to preserve life is just to like send the basic building blocks. Send a bunch of bacteria, a bunch of whatever the rugged organisms are on Earth, just send a bunch of those.

These are not the building blocks. They are actual organism.

Isn't that a nice shortcut or do we want to? Because you said building blocks are everywhere.

Yeah. The bricks of life, the carbon, hydrogen, et cetera, they were produced by the death of previous stars. So this is how they were produced. And stars like our sun started to form 10 billion years ago. That doesn't mean that the sun is the only kind of star that produce life or enables life, but actually was produced 10 billion years ago. Now what you're talking about is a little different. Right now. There are many efforts to do the type of thing you are talking about, which is to put our DNA on whatever kind of substrate and preserve it in vaults either in different place on Earth or on the moon. Some people are already thinking about putting DNA on the moon as far as brain's concerned. And it's drawing towards transhumanism, which is the enhancement of who we are through AI and machine learning. Of course, having backups is a good thing. For me, I would say that taking care of our planets and going back to a place where we are in equilibrium with our environment would be also maybe the best backup possible and let evolution do its things. Right now we are like teenagers with enough brain to create cool tools, but we don't have enough brain to understand yet the consequences of what we are doing. And right now we are paying for this. So the question is whether we are going to be able to move forward and learn from the mistakes we are making to become a mature civilization. You probably heard of the Drake equation. That would be the L at the very end. The duration.

Duration of intelligent civilization.

Exactly. And or at least the length of time a civilization remains detectable. It can disappear from the radar screen literally for a number of reasons. The first one is destroy itself or being destroyed by external events. Or it can become so in tune with the universe and so advanced that it disappears because it melts really in the background and it's not visible anymore. There are some wild theories out there saying that civilization might be so advanced that you cannot distinguish them from physical processes. And that was an example, doesn't say that this is the case. But some people say, imagine that in fact all the dark matter that we see or we theorized about is in fact some sort of a biological process. So you can think about a number of things. Personally, I believe that what you talk about, about preserving our information is kind of what life does. We need to look at ourselves as not different of what the little cell that started off was. And this is what tells you not about the origin of life, but in fact the nature of life, which is a lot more interesting to me because it is the nature of life is really what is going to give you some universal signature to look for it all over the place. And not only around ponds of water for life as we know it. But the nature of life is telling you that life wants to get the most information possible around its surroundings. And complexity is in fact the ability to gather and exchange and preserve the most information possible. And so what you're saying is kind of preserving the kind of information we have. So in the things that we are doing, as life happened, and I say happened because we don't know what life is, we have 123 definitions of life. And some people are saying we don't have any definition, we only have descriptions of life. And that's true. And that's true. So think about it for two minutes. We are looking for something we don't know it is. But we have a few clues about the nature of life. There are some really good theories. The first one was Schrodinger, right in the 40s, right now there is a guy named Jeremy England. It's another biophysical theory of life. It says life is the inevitable result of thermophysics. This is the best way to beat entropy, to fight entropy. But when you look at what we are doing, if you want to know what, what the nature of life is, look at our languages. And they can be very different languages, but they all have the same purpose, right? Exchange information, understand, you know, store information. And also, whether it is with somebody at the outside or thought in yourself, that's the same thing the cell was doing. But now when you're looking at life and at the structure of our languages, life started with an atom. So it's an atom. They got together to create inorganic molecules. Then you have complex inorganic molecules. Then you get to organic molecules, complex in organic molecules. And then you have RNA, DNA, etc. Look at the structure of Our language, we created alphabets, letters, that's your atom. Then we put them together to create syllables, right? Those syllables get together to create words. Words tell you something, but they are nothing without a verb that gives the direction. That's RNA and DNA. And then you can put all the complements you want. Our languages are built exactly as life is built. We are repeating patterns. I call this the Mandelbrot universe and the fractal universe, because this is exactly what it is. I would say that as much as I do believe to sending probes to explore the universe, I say we should also look inward to find the answer to some of the profound question of who we are. What's life? What's the nature of life? Because we are expressing life so searching.

Not for life, but for the nature of life.

The nature of life, absolutely. I am more interested in that because the day we understand the nature of life, then we have a universal biosignature. And it doesn't matter whether this life respond to the same kind of biochemical processes as we do. Although it makes sense. I told you about the generational aspect of the bricks of life, the stuff we are made of. The sun is part of the youngest generation of stars. And the first two generations of stars didn't produce the kind of elements we are made of. They were stars that were either without metal, just made of helium and hydrogen, or poor in metals. So the stars died off and stars like the sun were born from those. And this is why we have elements like carbon, hydrogen, oxygen, et cetera now. And that's the life we are built on. So I think it's not stupid to be looking for something that looks like us, because right now in the universe, this is the stuff that's the most abundant. And we see with the exoplanet, with Kepler, with Tess and now with Jamsweb, we see that there are many, many different type of planets that may be habitable. In the habitable zone of their stars. There are countless stars like the sun. But more interestingly enough, there are other type of stars where you do have habitable zone as well, and where the duration of the stars are sometimes a thousand times more than our sun. So you can imagine all sorts of things and you can imagine what type of life would be around those stars. The biochemistry might be quite similar, in fact, and especially for the simple life, because simple life starts really quickly on Earth. So my take on this is that the universe is full of cyanobacteria, but as far as intelligent life, it takes more time. So that can take different aspects.

Do you think it's possible that the universe is full of bacteria? And even those stars that last a thousand times longer than the sun, Even on the planets that orbit those stars, maybe bacteria for billions and billions and billions of years.

We actually don't know what triggered the evolution to complexity on Earth. That's still a big question mark.

Is that the most impressive invention on Earth to you?

That Cambrian revolution is really what took us towards what we are. And in the meantime there were the dinosaurs, et cetera. The dinosaurs were wiped out. So the evolution could have taken a completely different turn. It's always, I would say mass extinction that are going to drive what's the end game. But yeah, you take two planets and you change those asteroid impacts, all those big geological events that wipe out like 90% of life at any time. The thing that seemed to be interesting, there are two things. The first one is where you are located on our galaxy matters a lot. We actually are in the habitable zone of our galaxy. And if you are too close to the center, then it's a lot denser. And remember, we have the Oort cloud around our solar system. And if you are in the region of the galaxy that's too populated, then you are going to run interaction, gravitational interaction with all these stars. And since it's more dense, you will have more of the comets that are living in the Oort cloud being ejected from the Oort cloud and coming towards the inner solar system and collide with with planets. So you will have more of these impacts if you are too close to the center of the galaxy. Not to mention the radiation. There is a place in our galaxy where it's a really bad neighborhood. You don't want to be there. You wouldn't be able to have life. But what really matters is extinctions. But also the climate history of a planet has a role to play. And it seems that it's a theory. It still has to be backed up by more observation. But there is a good correlation between not only the passage of the solar system towards the center of the galaxy. There is one place where we get hit by asteroid because of the interaction I was telling you about. But the other one is the climate. With the Milankovitch cycles. Big jumps in life's evolution seem to be associated with snowball Earth episodes. We don't know why yet. Snowball episode. Intuitively you would think that they are connected to a decrease in life because the whole Earth is covered in ice. But for some reason there were big jumps in evolution right after each of those episodes and today, there are other things, like why all of a sudden you have mutation that seems to be responsible for a big jump in evolution. We are not clear yet. So all of those things when you're thinking about life elsewhere are going to come into play. And I cannot tell you that a planet that remains habitable for much longer than the Earth will have an evolutionary path that's the same or different. Depends on extinction, depends on climate, depends on whatnot.

It's a little bit surreal that we're two descendants of apes.

Well, I think that some, some people.

Trying to figure out what the heck is going on. And I mean, we're very biased even as. So you. We're biased as humans, you're less biased as a scientist. But we still love Earth. We still don't know anything but this Earth. And so even though you try to get escape from thinking of what life is, in the search for the nature of life, we still kind of connected to the way we understand the nature of life here on Earth.

So I think that it's a little different than that we are biased when it comes to the origin of life. Yes. Because, well, we are the only model we know. And as I said, it makes sense because it seems that a lot of stars like the sun appear 10 billion years ago and there are lots of world that really resemble the Earth, and lots of water out there and lots of conditions that could be a repeat of what we know. And we know that this biochemistry works. So again, as I mentioned, what is going to change is really the evolution of a planet extinction, geology, et cetera. But our model is probably very abundant. I'm not saying that the end game is going to resemble us because of all these extinctions, et cetera. But this is a good bias. It's one that has the number for it. You know, the principle of mediocrity. I think that in that case it really applies where the earth is representative of an abundance of other words. Now of course there can be other biochemistry. We have some examples in our own solar system. Titan might be a representative of that. We are not very clear the kind of biochemistry that can come out of a world where you have hydrocarbon lakes and rains and things like that. But we are going there, so we will learn something about this. So the bias is right there. The nature of life is different. If really life is the best way the universe has to fight entropy. There is no bias there because physics is the same all across the universe. At least the universe we know there might be Other universes, but. But the one we know works with the same physics.

So if life is the. The best way to fight entropy, you can imagine that life permeates the entire universe. And then the question might change to, like, flavors of ice cream. What are the flavors of complexity that this process, this nature of life leads to? And there we might have bias about what complexity looks like, what beautiful complexity looks like. We look at humans that operate a certain physical scale and timescale, and we think this is intelligence.

We have another problem. We don't know what life is, we don't know what intelligence is, and we don't know what consciousness is. But we are trying to tackle the.

Big question, do we know what complexity is Also, you know, no.

I think that we have to be honest. And as a scientist, and I'm going to step back and talk about intelligence, for me, a bacteria that has survived, like cyanoid bacteria that has survived just like us, 4 billion years in one incarnation or another, and actually they are very similar to the one that they were 3.5 billion years ago. It has some intelligence about its environment. So for complexity, it might be that we need to take the world literally, which is an assemblage or additional capacity to gather, collect, store information. Maybe this is something like that, or actually use that information to do something with it. But I do completely agree with you when you talk about flavor of ice cream. I think this is exactly it. And I have a basic education about what physics is doing right now. And I look at quantum physics and what it says about the universe and about the connection, about an atom here and an atom here, a photon here and a photon there. And I am starting to put, maybe wrongfully, two and two together. But in my mind, and of course, it's nothing until I can prove it. But in my mind, the universe is connected everywhere in all different places. So this life connection is something that, as you said, permeates the universe. And the way to find life might be very different than to look for the origins of life. I think it's a good thing to go out there and look for the origin of life somewhere else, because it's the manifestation of the nature of life that all of a sudden becomes apparent, evident to our eye. But what I think would be our greatest achievement is that if we can find that process of life, because at that point, in my mind, the universe all of a sudden is going to illuminate itself with actually its living force, what I can only call a living force. To me, this is what we are looking at a universe that becomes more and more complex with time, more and more able to gather information and interestingly enough, why? To understand itself. So Sagan was right when he was telling we are the universe trying to understand itself. And the more we go, the more the universe become alive. Maybe intelligent and maybe also conscious.

Conscious, self aware.

Exactly.

Through us. It does make me a little bit sad as a human just watching all the breakthroughs on artificial intelligence side when applied to natural sciences. Now more and more to physics, that the creatures that will solve the question of the origin of the nature of life or just the process, the nature of life.