Complex life may be more rare in the universe than we thought

Quanta has a pretty interesting article up today: A Solution to the Faint-Sun Paradox Reveals a Narrow Window for Life. Our understanding of the physics of the sun indicate that it should have been only 70% as bright as it is today. But if so, early Earth should have been a snowball not really capable of sustaining life. Yet the earliest evidence for life goes back 4.1 billion years.

The article chronicles the investigation of this paradox over the decades. The current answers seem to indicate a combination of shifting factors, such as the level of carbon dioxide in the atmosphere, with variances from geological processes, and the initial close orbit of the moon and its gravitational tidal effects, both on Earth’s oceans and geology. Given those factors, if the early sun had been as bright as it is today, it would have resulted in a “steam Earth” too hot for life. Earth’s continuing habitability over the eons ends up hinging on a complex series of shifting coincidences.

The implications for extraterrestrial life aren’t promising.

For planets in other solar systems, the faint young sun problem complicates the question of extraterrestrial life. In December 2020, Tyrrell calculated that Earth’s continuing habitability is mostly due to chance. He created a computer model of 100,000 planets. Each started out as habitable. He then subjected each planet to 100 simulations of various climate feedback scenarios. For 91% of the planets, not a single simulation kept the planet habitable over geological timescales. “Earth’s success was not an inevitable outcome but rather was contingent,” he wrote. “It could have gone either way.” Thus, in order for exoplanets to have the potential to develop life, perhaps they need to have the right ingredients in just the right circumstances — like Earth.

It’s worth noting however the case of Mars, for which there’s good evidence that water existed on it in its early history.

Mars presents a trickier conundrum. According to new data from NASA’s Perseverance rover, Mars appears to have had rivers and lakes on its surface at least 3.7 billion years ago. It’s unclear how that would have been possible at its greater distance from the sun.

“On Mars the puzzle is enhanced,” said Kirsten Siebach, a planetary scientist at Rice University and a member of the science team for multiple robotic Mars missions, including Perseverance. “Ancient Mars would have required twice the greenhouse effect we have on Earth today.” Samples being collected by Perseverance, to be returned to Earth in the 2030s, could tell us if this was possible.

This, to me, indicates a couple of possibilities. One is that we don’t understand the sun’s processes and overall evolution as well as we think we do. Or two, that the conditions that made early life on Earth possible weren’t as freakish as they might seem.

Still, Mars’ biosphere, if it ever had one, is most likely long gone. That implies that while biospheres may be reasonably common in the universe, their window of existence may average a lot less than what we’ve had on Earth. It may be that the typical biosphere gets a few hundred millions years of life before the conditions that allow it dry up. Earth’s four billion year old biosphere may be a freakish event.

If so, given that it took complex life 3.5 billion years to really get going here, that type of life may be extremely rare.

The Fermi paradox is the observation that, if intelligent life is pervasive in the universe, we should have been colonized long ago, but there’s no evidence for it. The most straightforward solution to this paradox is that intelligent life is profoundly rare. Given that intelligence as we understand it depends on complex life, and complex life itself may be very rare, we might have to shift intelligent life from profoundly to sublimely rare.

Unless of course I’m missing something?

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62 thoughts on “Complex life may be more rare in the universe than we thought

  1. You know me. I think microbial life is probably common out there, multicellular life is rare, and intelligent life is extremely rare. The nearest alien civilization may be many galaxies away. The real question for me is always how common is common and how rare is rare.

    But I’m not inclined to take a study like this too seriously. It was once thought that life on Earth wouldn’t be possible without a giant planet like Jupiter shielding us from asteroids and comets. Then it was realized that Jupiter has been gravitationally nudging asteroids out of the asteroid belt and sending them hurtling our way. It’s very unclear now if life on Earth is better or worse off having Jupiter nearby.

    With something like the faint young sun paradox, I don’t think scientists understand enough yet to make reliable predictions about what it means for other planets. In general, I still think microbes are common, complex life is rare, and intelligent life is super rare. But I don’t think we can put numbers to how common is common or how rare is rare based on this.

    Liked by 3 people

    1. Yeah, the Jupiter thing never made a whole lot of sense to me. Honestly, speculation about the moon didn’t make much sense to me either until this article. I never considered that its tidal effects when it was much closer to the earth might have added heat to the geology. But I mentioned the Mars point because its further out and, in theory, should have been even more affected by the sun’s luminosity, yet it apparently had water in its early history, with no large moon to heat it up.

      I agree about microbes being fairly common, complex life being rare, and intelligent life extremely rare, and that we can’t put any precise numbers on it.

      But it does seem like the average lifespan of a biosphere could be a lot shorter than ours. Maybe. It’s worth noting that none of this seems like it would affect life in underground oceans far from the sun.

      Liked by 2 people

      1. That’s probably true. Mars might have had a biosphere before the planet dried up, and some people say Venus could have had a biosphere as well before the runaway greenhouse effect took over. If so, then only one out of three planets in this solar system was able to maintain a long term biosphere on its surface.

        Liked by 3 people

        1. I’m kind of sad we’ll never be able to meet aliens, at least not intelligent ones. Although there is some solace is knowing a superior intelligence can’t exterminate us. We just have to worry about exterminating ourselves.

          Liked by 1 person

      1. What’s nice about it is the validation of our thought processes about thing. It means one understands. My logic didn’t depend on the Sun, so even if we do learn more surprising things, it doesn’t change anything in my view (which, you’ll recall, was based solely on mere odds).

        Noticed you mentioned the Moon. The thought was that, in providing tides, it provided tidal pools that fomented an easier transition from sea life to land life.

        Liked by 1 person

        1. That’s what I’ve heard as well. It depends on just how crucial those tidal pools were.

          But the article also talks about how close the moon was to the early Earth, and that its effects on Earth’s geology might have included tidal heating similar to what happens to some of the gas giant moons. Seems plausible, except that Mars didn’t have a large moon to warm it, and it apparently also had water flowing early on, despite being further out.


          1. Yeah, who knows. It’s a reasonable story. I can certainly see how tidal pools might allow transition. They’re ever changing, those pools, even on a daily basis, so life would have been challenged and possibly encouraged.

            I understood that much of Earth’s heat was due to radioactives decaying, so maybe Mars didn’t get a fair share? (Or maybe the Martians screwed up with technology and ruined everything! 👽)


  2. The Quanta article is about origin of life, not “complex” life which are different matters.

    Isn’t the 4.1 billion time frame somewhat in dispute?

    “Life on Earth began at the end of this period called the late heavy bombardment, some 3.8 billion years ago. The earliest known fossils on Earth date from 3.5 billion years ago and there is evidence that biological activity took place even earlier – just at the end of the period of late heavy bombardment.”.,period%20of%20late%20heavy%20bombardment.

    Early life could have been powered by geological processes and not require solar energy to a great degree. The sun might not be the deciding factor in the origin if life originated deep in the earth or in geothermal vents in the oceans. Both Europa and Enceladus likely have liquid water and probably have geological activity.

    Liked by 3 people

  3. ““We inferred that these potentially were the remains of organisms that lived at or before 4.1 billion years ago when they got trapped in this crystal,” Bell said.

    Funny thing. Every time evidence of evidence of biology on Venus or Mars is found it’s written off to a geological process. Yet when it comes to life on earth, some form of carbon tapped in zirconium is presumed from a biological source.

    Liked by 3 people

    1. The complex life thing was my own inference based on what the article discussed. Admittedly, this assumes that it does in fact take billions of years for complex life to evolve, that the molecular toolkits worked out over those eons were necessary.

      But it’s worth noting that oxygen levels in the atmosphere rose dramatically just before animal life took off. It that had happened much earlier in Earth’s history, maybe some form of complex life could have developed earlier. Of course, all that oxygen came from billions of years of biological processes and how long it took before Earth’s geology was saturated enough for it to build up in the atmosphere. So getting off that timeframe seems difficult.

      To your point, the question might be, how dependent is complex life on the sun? Also, is there a path for it that doesn’t involve high levels of oxygen?

      I’ve wondered the same thing about early evidence for life. Are we holding it to the same standard we hold extraterrestrial sources to? Or are we letting our knowledge that life did eventually develop here influence our assessment of the early evidence. I’d like to think the evidence in Earth geology is more conclusive, but I don’t know the answer. And you’re right, before about 3.7 billion years (I think that’s that’s the current cutoff), the evidence is controversial.

      Liked by 2 people

      1. I’ve wondered if it were possible that life originated outside a planetary system but frankly have never seen a scenario that made it possible.

        A planetary system with a star would be likely be needed for life in my view; however, life in its more basic forms might be able in many different types of planetary systems with many different types of stars and on or in many different types of planets if it arose primarily from geothermal energy. Even planets distant from a sun could develop life if liquid water and sufficient energy existed somewhere either on the surface or at some depth in oceans or the crust. That could be still relatively rare or very common. There’s probably no way to know for sure until we have found a likely pathway for abiogenesis. My argument would be that earth is not likely extremely unusual so it isn’t likely the only place in the galaxy that has developed life.

        Great complexity in life is another matter and really has only arisen in the last 600-1,000 million years on earth. First animals were on land 420 million years ago. It probably would require relatively stable environment with some oxygen in the atmosphere, liquid water, so likely a habitable zone from the sun and probably a planetary system that has calmed from its initial creation and moved away from hazardous galactic areas like zones with frequent supernovas. Still things can happen pretty quickly and, even with some bad luck like a big asteroid strike 65 million years ago, earth still ended up with humans.

        To me this timeframe when complex life arises is going to be the gating factor for intelligent life and civilizations.

        Liked by 2 people

        1. It’s conceivable life could arise in an underground ocean inside a rogue planet with heat from a radioactive core, similar to Earth’s. Or from a moon in orbit around a rogue gas giant whose gravity is tidal warming it up enough for an underground ocean. But obviously we’re not going to get land animals in that scenario. Even complex water life seems unlikely. But who knows.

          I definitely don’t think Earth would be the only place that life developed. But it might be unusual in that long lasting stable habitable zone thing. Stories like Mars might be a lot more common.

          Liked by 1 person

          1. Long lasting, yes, but how long? Earth probably wasn’t all that habitable for complex life before a billion years ago. Humans came from other species in less than three million years even after some major extinction events in the last 100 million. A few million years seems long to us but a million years isn’t much in the life of the universe. A narrow window may be sufficient for intelligent life to evolve.

            Liked by 2 people

  4. 2^70 unique is looking better and better.

    I hold that we have one and only one example of technologically capable, electromagnetic energy wielding life. Determining how that life came to be, all the coin-flips that aligned to allow that life to exist, thrive and succeed is our only channel of analysis regarding the solution to the Paradox. How unique we are will determine our baseline for comparison.

    Narrow windows of opportunity will no doubt continue to be discovered. “The clock is ticking, life, better get your act together.” Other windows are just as, ahem, impactful. MTBF (I recall a post I wrote about this:

    The knowledge that biospheres are relatively short-lived? More fuel to the “we are unique” fire, as far as I’m concerned.
    Thanks for sharing this.

    Liked by 4 people

    1. Thanks.

      2^70 is pretty unique. I’m assuming that’s one in 2^70 stars having a civilization around it? If so, that comes out to 1 in 10^21 stars. Interestingly, there are an estimated 2 X 10^23 stars in the observable universe, so that would still leave around 200 civilizations in our observable universe. Of course, statistically that would put our nearest neighbor tens of billions of light years away, outside of our current Hubble volume, and so outside of any chance of us ever encountering each other, although we might eventually be able to detect each other.

      That said, it wouldn’t take too much of a variance in any of these estimates to push our nearest neighbor far outside of the observable universe, or somewhere much closer.

      But the overall message is we’re effectively alone. No one is going to ride in and save us if we mess up. Any conceivable encounter is hundreds of millions of years in the future, at best.

      Liked by 4 people

      1. Unique = Special? Maybe. Depends on your Nihilistic quotient. Maybe quantum research will give us a hint — someday.
        Perhaps proceeding with the assumptions that we’re special — until we’re not, is the wisest approach.

        Liked by 3 people

      2. Does 2^70 represent ever or any point in time in the past or future? That would be a difference between only 200 civilizations ever in the universe vs. thousands with old ones dying off and new ones coming into existence. I would think some, even if a small number, of the civilizations would have some longevity beyond a few million years.

        If we compare the human example, we would begin the evolution of civilization producing life 2-3 million years ago with the use of tools. It took about 2 million to evolve Homo sapiens, but only a few hundred thousand years after that to achieve agriculture, language, tools, architecture, and significant control over the environment, and only a few thousand years after that to achieve space flight.

        You’re right it also wouldn’t take much variance to push the numbers hugely in either direction.

        Liked by 3 people

        1. Not sure about points in time. This is Anonymole’s framework. I took it to be a civilization around a star that currently survives, but that may not be his view.

          Humans did evolve in a few million years, but that happened on the foundation of evolved great apes, which was on the foundation of primates, mammals, vertebrates, motility, multicellularity, sexual reproduction, eukaryotic cells, etc. So that few million years was only possible due to the foundations from orders of magnitude more time. Doesn’t mean intelligence might not be able to evolve faster than it did here. We just can’t justify it with our own case.

          It is noteworthy that our civilization lifespan so far (starting from the rise of agriculture) is about 0.00022% of the lifetime of the Earth. Anatomically modern humans have been around a more impressive 0.0066% of that lifetime. Our existence so far is a blink in cosmic time. If it’s in the nature of civilizations to destroy themselves, then our nearest alive neighbor may be far beyond our cosmological horizon.

          Liked by 1 person

          1. Sure, you can start the human timeline any time you want – 4 billion years ago if you want. The fact is that there wasn’t/isn’t a civilization capable genus before or since Homo and it arose on a foundation of complex life relatively quickly in geological and cosmic times. The foundation might be more like an octopus or something else on another planet but it still might not need a big window to become a civilization once the foundation is in place. With 40 billion possible systems (11 billion systems similar to earth/sun) in the Milky Way alone, unless earth is a miracle, complex life is probably somewhere else than here.

            Liked by 1 person

          2. I’d be surprised if none of those 40 billion had any form of complex life. (With the understanding that complex life is a pretty broad category including plants, sponges, and jellyfish.) But if most biospheres have brief lifespans, it doesn’t seem like we should expect high numbers. And complex life is not intelligent civilization producing life. Among the millions of different species in our biosphere, only one turned out to have the necessary combination of intelligence, dexterity, and ecological niche, and that combination seems to have been dependent on a lot of chance events.

            Octopuses are an interesting possibility since they do have intelligence and dexterity. The problem is they’re aquatic, short lived, and not social. It seems like they’re unlikely to ever master fire or form cooperative societies. There may be other paths for mastering energy other than fire, but some version of cooperative societies seem essential.


          3. What do you mean by biosphere? Earth’s biosphere has been here over 3 billion years. There are about 11 billion year-like systems in the Milky Way by that estimate. If you mean ecological niche, then life is still adaptable. It actually tends to develop greater diversity during ecological challenges. It might not be a complete coincidence that humans developed during the Quaternary glaciation. Ecological challenges are like getting extra rolls of the dice. You only have to hit once.

            I see you took my octopus example quite literally. Okay, imagine a longer lived and land living/ semi-aquatic octopus, then give it three million years on land.


          4. I mean biosphere in the normal sense, as the sum total of all biological and ecological systems in a particular environment, like a planet.

            The point of the article is that the billions of years of our particular biosphere may be extremely unusual. But water on early Mars may provide a counter to that argument.

            Your octopus example just hit on something I’ve thought about. Octopuses lose much of their physical capabilities on land. It’s hard to see them spending a lot of time there unless they evolve something functionally equivalent to skeletons, which seems likely to require a lot more evolutionary time than three million years. And I have no idea how long it would take for them to become a social species. It’s an easier thing for mammals and birds to develop, since it’s just an extension of the care they provide for their young, and so hardwired into their reproduction. But there are a lot of social insects, so who knows.


          5. What if it were a planet with weaker gravity?

            A lot of their survival is built on camouflage. To me a critical precursor would be a mechanism for manipulating the environment (hands and fingers) finely or at least some precursor to that. Technology began when we started to extend our abilities to manipulate the environment.


          6. A weaker gravity implies a lower mass planet, which might also imply a shorter lived magnetic field and quicker loss of atmosphere due to solar wind, and so a shorter lived biosphere. Another possibility is a higher pressure atmosphere which, if high enough. might be conducive to the octopus form. Although there it seems like the exact chemical makeup is crucial to avoid the fate of Venus.

            It’s worth noting that technology, in the sense of tool use, isn’t solely a human phenomenon. Apes and crows use sticks and other objects as primitive tools. But totally agreed that when thinking about human level technology, the hand is as important as the brain.

            Liked by 1 person

    2. I thought it was pretty cool how, when we compared our two ideas, they came within an order of magnitude of each other. log10(2^70)=21.07 versus log10(10^4^5)=20.0 Big honkin’ numbers either way.

      Interesting correspondence for two different rough estimate approaches, I thought.

      Liked by 3 people

      1. That is pretty neat.
        I like thinking in powers of two (as I’ve prolly mentioned) as to me, they’re just a set of coin flips — all landing heads. Find a new link in our chain of uniqueness? One (or more) coin-flips. Heads, heads, heads… One out of a million? 2^20: twenty coins — all heads (approx.). Easy to imagine throwing 20 pennies in the air. Dazzling to imagine all of them landing heads!

        Liked by 2 people

        1. The problem with the coin flip analogy is that you may not be quite thinking of it correctly.

          For example, the specific human species may come from a long line of coin flips with low odds for occurring. However, what if evolution is more like a thousand chances to hit one, then a thousand chances to hit the next, to end with a civilization capable species of some sort but not necessarily human-like.

          Liked by 2 people

          1. I hear you and have gone down that wide and branching road of exobiology speculation. That journey is an entertaining one — SciFi has done wonders for presenting the possibilities.
            Rather than going out, this theory goes in. We have only one example of a tech-advanced species in the Universe. Let’s examine the factors that allowed humanity to ascend to this level. That is, what did it take for us to get here. Maybe other species would take a shorter path. Maybe not. But that’s pure speculation. I propose to examine what we know (or mostly know) rather than what we can only dream.
            Humanity’s present situation is the result of: A whole list of lucky breaks. Just how many? I propose that that number can be modeled as a series of coin flips. Any “tails” would have negated our existence. Is is simplistic and silly? Of course. But all of this exo-spec is nothing but pontificating the “what ifs”.

            Liked by 1 person

          2. In my example, if tails had negated sapiens, then neanderthalensis might have created a civilization. If not apes, then some other primate. If not primates, birds. If not mammals, then some evolution from an octopus-like creature. There are a lot of potential evolutionary pathways to a civilization producing genius and species.

            Liked by 1 person

          3. *maybe*
            We don’t know, do we? Your proposals are all pure speculation. My theory is to not speculate about fantastic beasts and where to find them, but to analyze the one example we do have.


          4. I agree.
            It’s just another stack of what-ifs.
            We “know” we exist. How hard was it for us to get here? What lucky breaks do we enjoy? I figure it’s about 70. But that number is all speculation.
            To me it does give some idea as to how hard it is to get where we are, that’s all.

            Liked by 1 person

          5. I thought it was very interesting how two relatively low-theory approaches — a theory based only on the notion of unspecified chances — turned out results within a magnitude of each other and that both posit our existence as rare. I took an approach with a handful of low-odds (1/10000) events; Anonymole’s approach has many more high-odds (1/2) events.

            And yet, only an order of magnitude between them. Yeah, it’s just speculation (which, James, is certainly an area not foreign to you), but I thought it was interesting that such low-theory back-of-the-envelope thinking comes up with nearly identical results. 🤔

            Liked by 1 person

    1. That’s a good point. I read a while back that the gas giants might have started out closer and migrated out (although I don’t remember the exact time frames). It seems like that could have perturbed the orbits of the inner planets.


  5. BTW, have you read A New History of Life?

    I got interested because one of the authors did some of magnetite research I posted about. The other one is tied to the Rare Earth hypothesis.

    A couple of tidbits.

    Earth had about ten mass extinctions. Complexity finds a way!

    Until oxygenation there wasn’t much in the way of complex life. So complex life could be dependent upon plant life/photosynthesis.

    Liked by 1 person

    1. I haven’t read it. The first time I saw the description of this book, I was a bit put off by the hype of radical new theories. I know marketing people love to put that kind of stuff in the description, but most of the time I find it a red flag, something to avoid in a popular science book. If you’re having to sell your radical new theories to the public, it means you’ve failed to sell it to your colleagues, who are in the best position to judge it.

      But the paperback description seems much more grounded. Together with your tidbits (which are compatible with what I’ve read elsewhere), it’s making me reconsider. Thanks!

      The history of oxygen levels on Earth is interesting, particularly if you know when the Ediacaran and Cambrian happened (635-485 million years ago).

      Liked by 1 person

      1. I don’t see anything super radical in the book.

        They do speculate that life could have originated on Mars because the conditions for formation of ribose were not favorable on Earth. We may need to look at the capabilities of planetary systems to produce life rather than single planets.

        What’s interesting is some of the future projections. We lose our CO2 eventually as it becomes stored in carbon sinks. That triggers huge reduction in plantlife which mostly requires certain minimum levels . That leads to little oxygen in the atmosphere. On geological timescales, it isn’t that far off.

        Liked by 1 person

        1. Thanks James. I’m grateful to you for calling my attention back to this book. On your initial description, I bought it last night and have it queued up.

          That is the sobering thing. The window for our own biosphere is finite and will close. I usually see 500-1000 million years as the likely timeline, although that could shift on new information.

          Liked by 1 person

          1. That is more of the less the number from the book. If it holds up, then the period of peak complex life would be slightly more than a billion years with humans appearing about in the middle. Still a lot of time.

            Liked by 1 person

          2. The question, I think, is how dependent is that billion year window on all the developments of the previous 3 billion years? From what I’ve read, oxygen had to be generated by the biosphere until the geology was saturated enough for it to build up in the atmosphere. And complex life as we understand it seems dependent on the molecular toolkit hammered out over those 3 billion years. If a planet’s biosphere is cut short after a billion or so years, it seems hard for it to develop complex life.

            Liked by 1 person

    1. It’s true that the origins of life aren’t well understood. However, the fossil record shows increasingly simpler unicellular life forms as we go back to progressively older rock strata. Amoebas, as eukaryotes, are relatively recent and sophisticated on this scale. Earlier prokaryotic life would have been much simpler. But the ingredients of life are abundant, and evolution only needs some kind of self reproducing molecule to get started.


        1. I haven’t studied the various hypotheses enough to have informed opinions. I do understand the reasons why RNA is a good candidate (in that sense viroids are pretty interesting), but it wouldn’t shock me if the beginnings are somewhere else, or even if there were actually multiple beginnings prior to LUCA: the last universal common ancestor.

          Liked by 1 person

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