I’ve been watching Lex Fridman’s podcasts in 2023; they are a good source of learning. Lex interviewed Nathalie Cabrol [1] on 19 December 2022; these are my lessons learned.

What is Life? Where did Life come from?

Nathalie works in astrobiology, her life has been studying life on Earth and developing methods to look for signatures of life in our solar system. She noted there are something like 123 definitions of life. Here are snippets of Nathalie’s answer to the Schrodinger question of What is Life?:

• “Preserving information is what life does … 
• “… .the nature of life is really what is going to give you some universal signature to look for it all over the place ….”
• “…. the nature of life is telling you that life wants to get the most information possible around its surroundings and complexities, in fact the ability to gather and exchange and preserve the most information possible.” 
•  …. the nature of life is different, If really life is the best way the universe has to fight entropy there’s no bias there because physics is the same all across the universe at least the universe we know they might be other universes but the one we know works with the same physics. {This snippet came ten minutes after the others}

My own view of what is Life, derived from Nathalie’s answer is: life is the ability to gather, exchange, and preserve maximum information.  Very interesting, this answer is not dependent on a CHONPS [2] form of carbon-based life. She also mentioned  life as best way to fight entropy and cited the work of Jeremy England.[3]

A bit later in the interview, Nathalie used a beautiful language analogy to describe life:

[20:52] … languages and they can be very different languages but they all have the same purpose: exchange information, understand, 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 get together to create inorganic molecules then you have complex inorganic molecules. Then you get to organic molecules, complex organic molecules and then you have RNA, DNA etc.  Look at the structure of the language. We created alphabets,  letters, that’s your atom.  Then we put them together to create syllables. The syllables get together to create the words. Words tell you something but they are nothing without the verb that gives the direction that’s RNA and DNA and then you can put all the compliments 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 in sending probes to explore the universe I say we should also look inward to find the answers to some of the profound questions of who we are, what’s life, what’s the nature of life because we are expressing life …..

I am more interested in that because the day we understand the nature of life then we have a universal biosignature. It doesn’t matter whether this life responds 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 generational stars didn’t produce the kind of elements we are made. [4][5]

The idea that we are repeating patterns built up at multiple levels, like a human language,  really grabbed my attention.  “Our languages are built exactly as life is built. We are repeating patterns.  I call this the Mandelbrot universe and the fractal universe…”  I think we are truly living in something like a fractal universe. I hadn’t heard such an analogy before. [6] 

In a similar vein, it makes sense to me that “the day we understand the nature of life then we have a universal biosignature” because then we have a signal to search for.  But if life is information based, then the signatures may not be biosignatures alone. There could be other technical signatures based on physics rather than biology .[7]

Complexity

LF – Do we know what complexity is?

NP – 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 

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,  the 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 saying: we are the universe trying to understand itself. [8] And  the more we go, the more the universe becomes alive, maybe intelligent, and maybe also conscious.

Nathalie’s answer made me think of panpsychism [9] – the idea that mind is pervasive in the universe. Another way I think of this is that information processing (a definition of life) is ubiquitous.  When she says: “…. universe that becomes more and more complex with time, more and more able to gather information and interestingly enough why: to understand itself.”; that’s the universe being alive. A bit later she says: “… the more the universe becomes alive, maybe intelligent, and maybe also conscious.” I think this description maps to panpsychism, at least from my shallow knowledge of philosophy. 

 Fermi Paradox

The physicist Enrico Fermi asked: “But where is everybody?” What he was asking was why don’t we see sins of intelligent extraterrestrial life in the Universe. The discussion between Lex (LF) and Nathalie (NC) is illuminating. I have wondered about the same question often, especially when sitting out on a star-filled night. 

[51:26] LF – Everything I’ve seen from life it seems obvious that there’s life everywhere out there in fact maybe I don’t understand the jump from bacteria enough but it seems obvious that there are intelligent civilizations out there now I don’t know how to define intelligence but there’s beautiful complexity. I’ve looked at enough cellular automata which is a very primitive mathematical construction that when you run complexity emerges. I’ve looked at that enough to know that just seems like there’s complexity everywhere out there 

So, I think that’s why I’m deeply puzzled by  the Fermi paradox. It makes no sense to me. I mean I have trivial answers to it: why haven’t aliens at scale not shown up.  I think of  two possible options for me. Either we’re too dumb to see it, they’re already here; they have been talking to us through processes we just don’t understand. what we experience as life here on earth is actually they are everywhere.  Aliens could be consciousness; that when we feel love for one another that could be aliens. When we feel fear or whatever, that could be aliens.

NC – I have to agree with you none of this is scientifically provable right now. We talk a little bit  already about that but I would say that I do not adhere to the Fermi paradox because it’s very anthropomorphic.  It’s an interesting exercise, let’s put it that way but it’s a typical example of seeing the universe through our own eyes. And this is what the limitation is: understanding what’s going on with complexity as you said and looking at the biophysical model and theories for the nature of life. I would agree that probably this extraterrestrial message is all around us. We’re not yet capable of picking it up.

[54:10] Look at the shadow biosphere [11],  the idea that life didn’t appear only once on Earth but there were many different pathways of it. And, today we know when we study the tree of life that led us from LUCA [10]  to us and the shadow biosphere is telling us that there is or there are other pathways that came up at the time where life originated but they are so different that we can not recognize them as being the living.  And we cannot pick them up in our tests because our tests are being built to recognize life as we know it And for me again I don’t know if this theory we’ll be verify or it would be discredited but what I like about it is that it forces me to think on how do I look for life, I don’t know. So that starts here on our planet,  not even with the little green men, it starts with very simple life that can be so different that it might be just right in front of our nose and we don’t see it.

I hadn’t known anything about the shadow biosphere. Are there other forms of life on Earth we haven’t detected? What a good question. If I use the definition that life is the ability to gather, exchange, and preserve maximum information; then the laptop I’m typing on is a form of life. In some sense, I think machines are a form of life – they are obligate parasites of humanity. In other words, machines are organisms that cannot complete their life-cycle without exploiting a suitable host, humans. [13]

Life below the surface of Mars –  Be one with the microbe.  

The section about life below the surface of Mars was educational. Nathalie’s perspective makes sense: “to understand where microbes are located on Mars I have to become the microbe.”

LF – you’ve written about the history of life on Mars. You said you have kind of explored that by looking at the lakes here. Do you think there’s been life on Mars? Do you think there is life on Mars?

NP – … unambiguous evidence of life is going to be something interesting to prove because we don’t know what life is….

Ladder of life detection [14], which is that you have a series of rungs that you know you need to go through that actually are not proving you that you discover life but are making the possibility that what you discovered was made only by the environment more and more improbable. So we are trying to prove the contrary.

… if life appeared I would say it’s still there and probably underground where it can be you know in an environment that’s more stable 

 [1:51] You have to sit and look and listen, basically the story of my life: if I want to understand where microbes are located on Mars I have to become the microbe, this is a thought experiment. And if I want to understand where ET is, then I have to become ET. So,  it’s a big stretch but in an extreme environment you sit in the desert for a while and you just you know try to understand where the winds are coming from, where the humidity is, when it’s showing up and then you start to understand the patterns of those things.

LF – what are the useful signals the need for survival?

NC – You need to know where water is,  what the source of energy is going to be drawn from,  you need to find shelters and shelters don’t mean that…  For instance,  you can have a water column of a lake or a river or whatnot or the ocean. It can be also a very thin layer of dust or it can be a translucent rock. And you see what we call endolith, these are the same cyanobacteria but the different versions of them live inside those rocks, inside those crystals because they have the best of life. They are into translucent crystals so that they receive the light from the sun,  they can do the photosynthesis but there is enough of that crystals so that the nasty UV is being stopped. And they are in their little house. When you are looking at temperature within those rocks they tend to make it toastier [warmer] than the outside temperature.

The endolithic lichen [15] is a hardy  version of biological life on Earth. Life needs water, energy, and shelter. It makes sense that some biological life like  endolithic lichen might exist elsewhere in the solar system.  

Life, Love and the Future

The love for each other and for life was very apparent in the interview.  I highlighted a couple of key points. 

NC – my husband {Edmond Grin} and I were forty four years apart in age and it was just a pure love story. And he never looked at his age, never felt about himself or defined himself by his age. In fact, he reinvented life for himself at an age where everybody retires. We met when he was sixty six and that was a blessing and a curse but a blessing most of it because we took every single day as if it was the last. So we enjoyed life. 

… You know I have to really think of him, he just passed away last August. And for me it’s more like I have to draw from his example on[ of him always telling me: look forward. Trust life. Be happy. Live. You know today, every single day, I have to remind several times a day of this , it’s not easy but he had the recipe. He never thought about death because when you start thinking too much about death that prevents you from living.

LF – what’s the role of love in the human condition?

NC – I think I hope that this is the force that drives the universe though you know we might be experiencing the other side of it maybe just to learn how important love is. 

….

I would hope for humanity to reach that point where you can feel the same love for the person that is unknown in the street that you feel for the people you love. I think that at that point we are going to be reaching the maturity of that civilization we’re hoping for and seeing the universe through love. That doesn’t run spacecrafts of course but putting love into our intent of going into and settling into another planet instead of “Oh my god, we need to escape because we are freeing, messing up with our own planet.” I think that this is the answer to so many things

NC – …. as the dominant species at least you know technologically etcetera, maybe not the wisest one, but the dominant species. We have a responsibility to watch the entire biosphere because the decisions we’re making now not only affect us; they’re affecting the entire biosphere. And right now the choices we are making are leading to the disappearance of a hundred and fifty species every single day. All the big mammals on this earth today are on the brink of extinction. We are within the sixth greatest mass extinction; it’s unfolding before our eyes. And, I would strongly suggest that we use our smart to help a little bit this situation and we can do this. I think we can do this, we just need to redirect our energy.

Closing Quote

LF –  let me leave you some words from Stanislaw Lem in Solaris: how do you expect to communicate with the ocean when we can’t even understand one another?

Summary

I’ve rambled on quite a bit. I haven’t touched on the remarkable research and adventure of Nathalie and her team exploring life in high volcanic lakes [17]. It’s worth listening to this in the interview. Overall, Nathale and Lex covered a lot of ground on just what life might be. 

The most important lessons I learned from Nathalie and Lex in this interview:

• life wants to get the most information possible around its surroundings and complexities, in fact the ability to gather and exchange and preserve the most information possible.”
  • My own view of what is Life, derived from Nathalie’s answer is: life is the ability to gather, exchange, and preserve maximum information.
• Our languages are built exactly as life is built. We are repeating patterns.  I call this the Mandelbrot universe and the fractal universe…” 
• …. the universe that becomes more and more complex with time, more and more able to gather information and interestingly enough why: to understand itself. …. .. the more the universe becomes alive, maybe intelligent, and maybe also conscious.” 
• …. shadow biosphere is telling us that there is or there are other pathways that came up at the time where life originated but they are so different that we can not recognize them as being the living.
  • Made me think perhaps machines are a form of life – they are obligate parasites of humanity
•  “… when you start thinking too much about death that prevents you from living.”

I had a quick look at Nathalie’s papers in Google Scholar. I read a bit of the 1999 paper that she wrote with her husband: Distribution, classification, and ages of Martian impact crater lakes. She talked about this, it helped drive the landing site for the Spirit Martian Rover.  Here’s the conclusion:

“These results also confirm that ancient lakes in impact craters are important sites to study on Mars. They collected the record of the climatic and hydrogeologic changes on Mars. They were the receptacle of sedimentary rocks from which critical information about weathering, chemical, and physical processes on Mars could be learned. They might as well be among the most promising sites for the search for life and/or precursors of life on Mars. Lacustrine deposits are well known to be favorable environments for the preservation of life (extant and/or extinct). Lakes provide the best conditions for fossilization processes. The absence of crustal recycling on Mars opens up the possibility that fossilized life forms could be exposed right at the surface of the crater floors. The dataset resulting from this study is aimed at providing information to help identify the potential best candidates.”

I also saw a current research project that Nathalie is associated with, summarized in the paper:

“Orbit-to-ground framework to decode and predict biosignature patterns in terrestrial analogues”  I should give this paper a read and see what I can decipher – and learn. It’s interesting to glean that the team used artificial intelligence methods to look for biosignatures in Chile as a surrogate for Mars. [17] 

Notes

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

https://www.youtube.com/watch?v=yyBosLx7bbM Watched in January 2023

[2] CHONPS carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur: the main elements that occur naturally in carbon-based living systems on Earth. https://en.wiktionary.org/wiki/CHONPS 

Accessed 9 April 2023

[3] Jeremy England has a YouTube video explaining his work 

How Thermodynamics Explains the Origins of Living Things and is the author of a 2020 book: Every Life Is on Fire: How Thermodynamics Explains the Origins of Living Things

[4] I did some editing of this section, I hope I did not alter the intent of what Nathalie said. 

[5] One example is the iron atoms in our hemoglobin, I remember thinking about this in biochemistry class. The origin of iron:

“Stars fuse light elements to heavier ones in their cores, giving off energy in the process known as stellar nucleosynthesis. Nuclear fusion reactions create many of the lighter elements, up to and including iron and nickel in the most massive stars. Products of stellar nucleosynthesis remain trapped in stellar cores and remnants except if ejected through stellar winds and explosions. ” https://en.wikipedia.org/wiki/Nucleosynthesis Accessed 9 April 2023

 Or as I remember Carl Sagan explaining in Cosmos:  “we are star stuff.”

[6] John 1:1 KJV: In the beginning was the Word, and the Word was with God, and the Word was God. https://www.kingjamesbibleonline.org/John-1-1/  Accessed 9 April 2023

[7] Technical signatures are discussed in David Kipping: Alien Civilizations and Habitable Worlds | Lex Fridman Podcast #355 https://www.youtube.com/watch?v=uZN5xjoS6TU 

[8] “The cosmos is within us. We are made of star-stuff. We are a way for the universe to know itself.” as stated by Carl Sagan in Cosmos: A Personal Voyage, Ep. 1

[9] “In the philosophy of mind, panpsychism  is the view that the mind or a mindlike aspect is a fundamental and ubiquitous feature of reality. https://en.wikipedia.org/wiki/Panpsychism Accessed 9 April 2023Accessed 9 April 2023

[10] Fermi paradox https://en.wikipedia.org/wiki/Fermi_paradox 

[11] What is  last universal common ancestor (LUCA)?

“The last universal common ancestor (LUCA) is an inferred evolutionary intermediate that links the abiotic phase of Earth’s history with the first traces of microbial life in rocks that are 3.8–3.5 billion years of age. Although LUCA was long considered the common ancestor of bacteria, archaea [a] and eukaryotes newer two-domain trees of life have eukaryotes arising from prokaryotes,making LUCA the common ancestor of bacteria and archaea. Previous genomic investigations of LUCA’s gene content have focused on genes that are universally present across genomes, revealing that LUCA had 30–100 proteins for ribosomes and translation. In principle, genes present in one archaeon and one bacterium might trace to LUCA, although their phylogenetic distribution could also be the result of post-LUCA gene origin and interdomain lateral gene transfer (LGT), given that thousands of such gene transfers between prokaryotic domains have been detected.”

Weiss MC, Sousa FL, Mrnjavac N, Neukirchen S, Roettger M, Nelson-Sathi S, Martin WF. The physiology and habitat of the last universal common ancestor. Nat Microbiol. 2016 Jul 25;1(9):16116. doi: 10.1038/nmicrobiol.2016.116. PMID: 27562259  . PAYWALL 

“All known life forms trace back to a last universal common ancestor (LUCA) that witnessed the onset of Darwinian evolution. One can ask questions about LUCA in various ways, the most common way being to look for traits that are common to all cells, like ribosomes or the genetic code. With the availability of genomes, we can, however, also ask what genes are ancient by virtue of their phylogeny rather than by virtue of being universal. That approach, undertaken recently, leads to a different view of LUCA than we have had in the past, one that fits well with the harsh geochemical setting of early Earth and resembles the biology of prokaryotes that today inhabit the Earth’s crust.”

Weiss MC, Preiner M, Xavier JC, Zimorski V, Martin WF (2018) The last universal common ancestor between ancient Earth chemistry and the onset of genetics. PLoS Genet 14(8): e1007518. https://doi.org/10.1371/journal.pgen.1007518

https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007518

[a]  Carl Woese is famous for defining the Archaea (a new domain of life) in 1977 through a pioneering phylogenetic taxonomy of 16S ribosomal RNA, a technique that has revolutionized microbiology. https://en.wikipedia.org/wiki/Carl_Woese  Accessed 9 April 2023

[12] A shadow biosphere is a hypothetical microbial biosphere of Earth that would use radically different biochemical and molecular processes from that of currently known life. Although life on Earth is relatively well studied, if a shadow biosphere exists it may still remain unnoticed, because the exploration of the microbial world targets primarily the biochemistry of the macro-organisms. https://en.wikipedia.org/wiki/Shadow_biosphere Accessed 9 April 2023

[13] I modified a sentence from the Wikipedia article on Obligate parasites: “An obligate parasite or holoparasite is a parasitic organism that cannot complete its life-cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce.”
https://en.wikipedia.org/wiki/Obligate_parasite Accessed 9 April 2023

[14] …. Ladder of Life Detection, a tool intended to guide the design of investigations to detect microbial life within the practical constraints of robotic space missions. To build the Ladder, we have drawn from lessons learned from previous attempts at detecting life and derived criteria for a measurement (or suite of measurements) to constitute convincing evidence for indigenous life. We summarize features of life as we know it, how specific they are to life, and how they can be measured, and sort these features in a general sense based on their likelihood of indicating life.

Neveu M, Hays LE, Voytek MA, New MH, Schulte MD. The Ladder of Life Detection. Astrobiology. 2018 Nov;18(11):1375-1402. doi: 10.1089/ast.2017.1773. Epub 2018 Jun 4. PMID: 29862836; PMCID: PMC6211372. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6211372/ 

[15] Here’s a good reference: Alteration of rocks by endolithic organisms is one of the pathways for the beginning of soils on Earth https://www.nature.com/articles/s41598-018-21682-6 

[16] Here’s a link to some info https://highlakes.seti.org/science.html  Accessed 9 April 2023

[17] Warren-Rhodes, K., Cabrol, N.A., Phillips, M. et al. Orbit-to-ground framework to decode and predict biosignature patterns in terrestrial analogues. Nat Astron (2023). https://doi.org/10.1038/s41550-022-01882-x PAYWALL

 I got the reference from a press release https://www.seti.org/press-release/can-artificial-intelligence-help-find-life-mars-or-icy-worlds