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SETI: Let the Search Continue

Most people think that SETI is worth doing, whether or not they actually believe there are other technological civilizations in the galaxy. Ben Zuckerman, a professor of astronomy at UCLA, is certainly in the skeptics’ camp, thinking there are no technological ETs in the Milky Way, but he’s quoted in this story from QUEST (KQED San Francisco) as calling for more SETI. “Given that the costs are not very high,” says Zuckerman, “why not continue the search?” Zuckerman, who once worked with Carl Sagan in graduate school, no longer thinks we live in a crowded galaxy, but a potential discovery of this magnitude justifies the relatively modest expenditure.

It’s not surprising to find Jill Tarter echoing Zuckerman. The recent funding problems of the Allen Telescope Array have not daunted the woman who more than anyone else has come to represent the search for other intelligent life. And although she believes we may one day come to the ‘extraordinary conclusion’ that we really are alone, the time for drawing that conclusion is hardly near. We have hundreds of billions of stars to choose from in the Milky Way and hundreds of billions of galaxies beyond our own, and in those terms, we’ve barely begun to search.

Image: SETI searcher Jill Tarter. Credit: Sven Klinge.

The KQED story takes note of the new element in SETI research, which has to do with the Kepler mission. With the discovery of more than a thousand planets orbiting stars in its field of view, Kepler may well have found the first true Earth analogues — we’ll know as its data continue to be analyzed. The Kepler findings give us a targeted list of stars that should be high priority for the SETI hunt. “This,” says Kepler team member Dimitar Sasselov, “is where we should be looking for the signals coming from other civilizations.”

Just a month after the hibernation of the Allen Telescope Array due to money problems, the Green Bank radio telescope facility in West Virginia announced its own effort to study 86 of the stars chosen from the Kepler list, scanning an 800 mHz range of frequencies simultaneously (that’s 300 times the range available at Arecibo). Among the 86 stars Green Bank will be studying are 54 candidate systems identified by Kepler as potentially having a planet in the habitable zone. Thus the largest steerable radio telescope in the world picks up on the Kepler work, another case of SETI soldiering on when resources are scarce.

And fortunately, the Allen Telescope Array itself is back in business, thanks to more than $200,000 in donations from some 2400 donors and an infusion of money from the U.S. Air Force, which should keep the project running for the next several months. In the longer term, the ATA needs $2.5 million per year to keep operational, so fund-raising will doubtless become a permanent fixture of the facility’s operations. The SETI Institute’s page supporting a search of the Kepler candidates using the ATA continues to gather donations, a reminder that while SETI may be for now a relatively low-key project, it’s one that generates wide public interest.

Image: A single antenna of the Allen Telescope Array, night. Credit: Allen Telescope Array.

My own views on SETI parallel those of Ben Zuckerman. I doubt intelligent life is widespread in the galaxy, but the whole point of science is to extend our knowledge. By all means, let’s keep SETI in business, and maybe we skeptics will be proven wrong. And just letting the imagination run, it’s fascinating to ponder the world we might live in if one of the Kepler planets turns out to be leaking some kind of artificial radiation. Remember that Kepler is looking out along the Milky Way’s Orion arm, in an area where fewer than one percent of the stars the mission examines are closer than 600 light years. If we were to detect a transmission, it would take 1200 years to receive any return to our potential response. I suspect a detected signal, after revolutionizing our view of ourselves in the cosmos, would probably remain unrepeated and untranslatable, a mystery for our time, an enigma speaking of all we have yet to learn.

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Comments on this entry are closed.

  • Ronald September 6, 2011, 8:05

    Avatar2.0, in response to Gunnar:
    “Your maths example is fortunately not that relevant since not all configurations are equally likely. Configurations that can multiply themselves successfully are much more likely than configurations that can’t.”

    “Actually, it’s highly relevant.”

    Can you please elaborate on that? I do think Gunnar has a point in that your math is faulty. See my own comment above, mathematically: it is not a multiplication of many chance events, since *only independent chances may be multiplied!*.
    The outcome of the mentioned chain of events is, although admittedly of a (very) small likelihood, not a series of independent chances, but rather *interdependent* events, one making the next one more likely.

  • Ronald September 6, 2011, 8:15

    A comment on ‘experimental failure as a proof of concept’: how telling is this really? There are plenty of complex macromolecules which we humans still cannot synthesize in a lab, but do occur in (even abiotic) nature.

  • Chris T September 6, 2011, 12:39

    The question isn’t, ‘is radio SETI worth spending resources on?’, but ‘is radio SETI worth spending resources on compared to other projects we could spend those resources on?’. There are any number of low cost projects, but funding them all would quickly bankrupt us. For me, the likely return is far too low to justify it WRT other projects; particularly since more direct methods are only a decade or two away.

    The scientific utility of rSETI is questionable. In most of science, a null result narrows the range of potential solutions, but a continued null result for rSETI does nothing to narrow that range. The only thing it rules out is that an ETI is signalling at a particular time, place, and frequency. Beyond that, there are far too many possible reasons that we did not receive a message and cannot provide useful information about those reasons.

    My preference would be to concentrate on expanding our capabilities for directly detecting and studying other worlds. An endeavor that will provide considerable data on the ETI question regardless of the result.

    WRT Fermi Paradox – The paradox cannot rule out other ETIs, but it does put an upper constraint on the number. As N rises, the probability that at least one will attempt interstellar colonization increases as well. Either there is an unknown barrier to interstellar travel or N is in the lower range (possible equal to just 1 – us).

  • Bob Steinke September 6, 2011, 12:42

    The estimates that an intelligent species would colonize the galaxy in 5-10 million years are far too short. They are based on the colonization being some kind of goal directed program, colonizing as fast as possible. There is no way that such a program would be maintained for millions of years. Colonization of the galaxy is likely to be a slow diffusion process of people occasionally going a little ways to get some currently unused resources.

    Humans colonized the Americas from Alaska to Argentina in a few thousand years. I couldn’t find the reference, but I remember reading it was a net travel rate of something less than 100 feet per day. That’s a thousand times slower than if a person set out to walk straight there in the minimum time. Most likely galactic colonization will be similar and it could take 5-10 billion years for it to happen. That’s comparable to the current age of the galaxy. So there could be aliens currently colonizing the galaxy that just haven’t gotten here yet.

  • Interstellar Bill September 6, 2011, 16:23

    To Bob Steinke and others skeptical of rapid colonization of the Galaxy:
    Only a space-based civilization could undertake interstellar travel, and there could only be one motivation for something so expensive–demographic ambition. Once there are tens of thousands of solar-orbiting mega-habitats, with total population far greater than Earth’s, those cultures with expanding populations will eventually outnumber the rest, and cast their eye on other star systems, particularly those with a high asteroid load.

    First there will be small precursor expeditions to the target star, with the object of building a deceleration laser for the heavy traffic from Earth. A specialist caste of interstellar ship-builders and operators will not just disband when a target system has been reached. The ships and their sails will be refurbished and sent out to farther stars, once more lasers are built.

    With 10-15 light years between attractive asteroid-rich stars, only a few centuries would elapse between the successive colonization waves.

    Simple Darwinian logic guarantees that the most demographically ambitious space-based cultures will be the star-traveling ones. Slouches planning to take 5 billion years to colonize the Galaxy will lose to those planning to do it in 1 million.

  • Eniac September 6, 2011, 19:44

    @Ronald

    I disagree and am actually puzzled by such an unfounded assertion,…

    If you had read on from where you cite me, you would have seen me say “not much of a limit”. Anyway, if fl were close to 1, we would reasonably expect life on Mars, Venus, Europa, and probably a few other places were we would have had a good chance to detect it even this early in the search. The upper limit on fl has been (gently) coming down since before the time Percival Lowell’s Martian canal’s were discredited. Based on available data, it should be pegged well below 1 by now, although of course you are right that this is far from a firm conclusion.

    @coolstar: I think the situation with abiogenesis is not quite as dire as you paint it, there are very interesting and plausible theories that could help bridge the gap between random chemistry and life, such as Manfred Eigen’s hypercycles and quasispecies. Not likely enough to bring fl all the way up near 1, but perhaps just enough to bring it up to that reciprocal of the number of planets in the universe. Would be a funny coincidence, now. Or would it?

    Some commenters here still do not seem to understand that when or if a technological species reaches the point where it can and will colonize neighboring stars, there is no turning back and expansion throughout the galaxy is inevitable. Plus, there is no chance of the entire species dying out, ever. Therefore, even a single such case should be readily observable by us. One Single Case. Regardless of distance, in space or time. Moreover, had this process been completed in our past (which, if it was common, would be a sure thing), we should be descended from this species and know it. You can question the observability and displacement arguments in various contrived ways, but the notion that there could be multiple such species in the galaxy that are locally or temporally confined and have no chance to meet is clearly not tenable.

    I did not make this up myself. I believe it is exactly Fermi’s reasoning. Fermi was a clever guy, very much respected, and with a good eye for simple and powerful arguments. It is mysterious to me why so many seem to have difficulty following him on this.

    Now, it may not be fl (alone?) that is the culprit, but the alternatives are not pleasant. Especially the one that is about our future, the one that says technological species never reach the stage where they can and will colonize neighboring stars.

  • Rob Henry September 6, 2011, 20:42

    Ronald, I often disagree with you, but this is the first time that I find a substantial part of your argument based on a plain misperception.

    Quoting you:
    “People often tend to draw a fundamental line between life and lifeless, but let’s not forget that the fundamental laws and chemical principles are just the same, it is still biochemistry, not magic. It rather looks as if, beyond a certain threshold that we call ‘life’, biochemical complexity can really take off.”

    Answer:
    Such a scientific position could be maintained right up until the 1950’s when modern synthesis displaced Darwin’s theory (and all other then contemporary variants of evolutionary hypotheses). Now it is known that genes have an associated information content over which mutation works. This means that natural selection works to select against any improvement unless the fidelity of the reproduced information content is greater than the selective advantage over its nearest “molecular rival”. Once one trait in a non-living “species” is found to meet this criterion this DOES NOT provide a new base to work from. Unlike in biology a chemical species can’t outcompete its “rivals” to extinction (if for no other reason that they are continuously being generated de novo, or we would have no starting point) and if a second trait is also found to meet this criterion it, it would occur in another such species. If, per chance, this second trait did occurred in the same species, then this hybrid would carry such a burden of additional complexity as to be close to the barrier where selection for reduced complexity predominates no matter what the selective advantage. The only exceptions are if that selected for variation happens to also reduce the mutation rate – but here’s the catch. Higher reproductive fidelity means stronger bonding for the improved species during the replication of its genetic code, and thus a slower reproductive rate. Natural selection would normally select against these types of improvements.

    The whole situation is not quite a desperate as it might seem from the above. It is possible to create highly elaborate and unstable schemes under which it is conceivable that (if these knife-edge conditions persist long enough) the gap from life to non life can be bridged. The details of this were outlined by Manfred Eigen, and they pertain to more than just a RNA-world beginning as is commonly believed.

  • Eniac September 6, 2011, 20:43

    The estimates that an intelligent species would colonize the galaxy in 5-10 million years are far too short. They are based on the colonization being some kind of goal directed program, colonizing as fast as possible. There is no way that such a program would be maintained for millions of years. Colonization of the galaxy is likely to be a slow diffusion process of people occasionally going a little ways to get some currently unused resources.

    There is no way that single program would be maintained for millions of years, nor is it necessary. Instead, there will be many programs, whenever the people of one colony feel that it is possible and appropriate. The process is not a diffusion, because it is directed. You can only colonize outwards, with few exceptions. The boundary will expand with approximately constant speed. Bacterial growth in a petri dish is the closest analogy I can think of, or growth of a wildfire.

    Humans colonized the Americas from Alaska to Argentina in a few thousand years. I couldn’t find the reference, but I remember reading it was a net travel rate of something less than 100 feet per day. That’s a thousand times slower than if a person set out to walk straight there in the minimum time. Most likely galactic colonization will be similar and it could take 5-10 billion years for it to happen. That’s comparable to the current age of the galaxy. So there could be aliens currently colonizing the galaxy that just haven’t gotten here yet.

    A few thousand years is about right. Say colonization occurs only every 5000 years in a given frontier world, and that the average reach per colonization event is only the closest of stars, or 10 light years on average. The Milky Way is 100,000 ly in diameter. It would thus take less than 50 million years to complete the expansion. I fail to see where you get the other three orders of magnitude from.

    Bill is right, the rate of expansion will be determined by the fastest colonizers, so the 5,000 year estimate between efforts is probably a very conservative assumption.

  • Eniac September 6, 2011, 21:17

    @Ronald:

    People often tend to draw a fundamental line between life and lifeless, but let’s not forget that the fundamental laws and chemical principles are just the same, it is still biochemistry

    There is indeed a very fundamental line between life and lifeless: The ability of autonomous self-replication. There is no such thing as “simple” life, even the most humble of organisms is a very, very complex machine that could not possibly have been originated by random combination of molecules. That said, as others have ,emtioned, there must have been a process where one thing led to another, but it is a process that goes very much up-hill against entropy without the benefit of stable “genes” that enable evolution. Once self replication with a sufficiently stable genome was achieved, increasing complexity became a downhill process, driven by well known Darwinian principles. The crest of that hill is what separates life from non-life. We know the way down pretty well, but we know next to nothing about the uphill path, nor about the “height” of the hill. But we do know that it does not come easy, to say the very least.

    In other words, precursors to life (e.g. prions and the like) may be originating all the time, but not getting any foothold.

    Prions are not alive by any definition, they are but single proteins among many made and used by an organism that happen to have an autocatalytic reaction that is detrimental. The earliest precursors to life must be looked for among autocatalytic processes between inorganic nucleotides that may lead to the buildup of ever longer chains of RNA. The “miracle” occurs if one such chain can produce more than one copy of itself before it disintegrates. This is not easy or straightforward at all. Look up Manfred Eigen’s hypercycles and quasipecies, which to me are the best theories I have seen on this subject.

  • Rob Henry September 6, 2011, 21:40

    Several times it has been suggested here that the early appearance of life on Earth implies a high value for fl. This would provide a very strong argument, were it not that it is likely that life’s origin may have required a particular type of high energy conditions that might only exist in the early stages after a planets formation.

  • Anthony Mugan September 7, 2011, 4:24

    I am intrigued by the Darwinian selection concept that Interstellar Bill mentions. With at least a billion years of time since metallicity reached an appropriate level for life in the galaxy (ignoring for the moment anywhere else) and combining this with the conclusion that our existance establises that the probability of an advanced technological civilisation emerging in a suitable habitat is not zero, we can logically conclude that a number (inderterminate -possibly relatively small) such civilisations would have emerged during the past billion years, or perhaps slightly earlier for the first rapidly developing ‘outliers’.
    The incommesurability problem (to which the later article concerning Dolphins is interestingly relevant), makes it very difficult to draw any general conclusions around culture, values, aspirations and psychology. The Darwinian concept is valuable however, if we allow for a degree of variation in such characteristics. The most ambitious species (from amongst the earlier civilisations) with the strongest urge to expand and explore would win the race for resources. Those with a strong ‘push’ factor such as an ageing home star or a strong ‘pull’ factor such as an unusually close nearby star with some interesting planets might also recieve a pretty strong incentive to overcome the economic hurdles of the early stage of interstellar travel.
    By the way…just if anyone feels my earlier post indicated incipient mental derrangement – they might want to check out the recent views of Professor Michi Kaku, the work of Professor Peter Sturrock or the comments of former CIA director Admiral Roscoe Hillenkoetter on that particular strand of thought…and I shall leave it at that.

  • Ronald September 7, 2011, 5:15

    Eniac, thanks for clarifying, I agree on everything, but only diverge on one thing, the cause for lack of techno civs in our MW galaxy: I still maintain that it is not (primarily) fl, but rather fi and fc.
    Your ominous statement ‘but the alternatives (of fl) are not pleasant’ is not necessarily true, you obviously refer to extinction level events for a species that has already reached technological level.
    However, if by far most species never even come close to such a level, the answer to Fermi’s paradox is simpler and less dramatic at the same time. And an interesting fact is, that this is one on the very few factors that is indeed verifiable: of the millions upon millions of species in Earth’s history, only a few ever reached the level of intelligence of ‘self-awareness’, problem-solving and tool-use; and only one ever made it technological level, after hundreds of millennia of trial and error, sometimes a close call, a ‘dime on its edge’.
    High intelligence is no obvious and inevitable outcome of evolution.
    The MW may be crawling with life, but without any other technological level intelligence.
    Of course, this discussion remains purely academic, since the result, with regard to ETC, is the same.
    It would be very relevant and fascinating in this context if and when, for instance, we find bacterial life on Mars and/or spectroscopic biosignatures on terrestrial planets near sunlike stars. That would settle an important part of the Drake equation and also Fermi: in that case, indeed, I would be right and fl is not the problem, but rather fi and fc. If, after many decades of spectroscopic surveys with powerful space-based interferometers (or even Maccone’s FOCAL mission), etc., do not turn up any biosignatures, then apparently fl itself is the bottleneck.

  • Rob Henry September 7, 2011, 6:53

    Ronald, sorry about my needed heavy criticism of you earlier, but here is some more in a much lighter vein.

    I again quote you, this time in regard to Avatar2.0,s scheme of abiogenesis:
    “Your argumentation is about the same as stating that the beautiful and complex ‘flower’ shapes of some crystals cannot arise spontaneously, because the end result has a too small calculated chance of happening.”

    I can see that this is an interesting point, but it is not nearly as telling as you think. A small set of instructions really can describe something that appears to have great complexity, and some types of chemistry that are far from equilibrium, really can naturally complexity with time. These processes have absolutely nothing to do with natural selection (the real process, as demanded by modern synthesis, requires that there is an associated transfer of genetic information), and we have almost no reason to believe that any of these structures will be biologically useful.

    Above I wrote “almost no reason” since the fact that life has arisen in our universe at all would make it more likely that our universe was fine tuned to allow life, and that includes the possible existence of a simple process that can produce a high fidelity genetic apparatus that had properties that might allow it to naturally link to enzyme production.

  • kzb September 7, 2011, 7:16

    @Bob Steinke
    Models of galactic colonisation have been run with generation periods of as long as 100,000 years. The conclusion is still the same: the colonisation time is SHORT compared to the time available for civilisations to have arisen.

    I mean even if you allow 100 million years to colonise the galaxy, that is still only one-fortieth the time since the first civilisations arose in the MW (according to models). So it just is not a satisfactory solution to the FP.

  • kzb September 7, 2011, 7:48

    As a further illustration of my point, a short while back we were discussing the discovery of (potentially) terrestrial planets in three of our neighbouring systems:

    The HARPS search for Earth-like planets in the habitable zone: I — Very low-mass planets around HD20794, HD85512 and HD192310
    http://arxiv.org/abs/1108.3447

    Now the AGES of these three stars are given as 5.61, 5.76 and 7.81 billion years. If any of these systems had Earth-like planets (and it looks like they came very close to doing so), they would have had over a billion years head-start on us. That is, if you follow the train of thought that says development of life and intelligence on Earth is “typical”.

  • Bob Steinke September 7, 2011, 11:48

    @Interstellar Bill, @Eniac, @kzb – Re: speed of colonizing the galaxy

    The reason I mentioned the Amerind colonization of the Americas is because that’s an actual historical example where colonization velocity was three orders of magnitude slower than directed travel velocity. And that situation had multiple societies. Some would have been faster colonizers at various times, but there would also have been cultural change and the fast colonizers would not have always stayed fast colonizers. There would be wars and dark ages and times when society turns inward. There would be frontier colonies that fail and the frontier moves backwards. Yes, the trend would be a growing sphere, but it would still have some attributes of a random walk. And just because there’s a constant average outward velocity doesn’t mean that velocity has to be fast.

    Obviously, you can’t draw any firm conclusions with just one example, but it is possible that the general trend is that most societies spend the vast majority of their time not colonizing. The Fermi paradox does require some solution, and everything else we’ve thought of is just speculation too.

    @kzb

    If it takes 100,000 years for each 10 light year hop then that would be 1 billion years to go 100,000 light years.

    Even if the galaxy were colonized in 100 million years then the chance that we are less than 100 million years younger than the first civilizations is small, but not vanishingly small. The solution to the Fermi paradox could still be that something somewhat unlikely happened.

  • andy September 7, 2011, 17:57

    On a somewhat related subject, I have to say I do find this New Scientist article pretty amusing in terms of the breakdown of the scientists who have given responses to the “alien message encoded in DNA” idea… the physicists and astronomers seem to be enthusiastic, the biologists are highly sceptical.

    On the whole I’m more inclined to trust the biologists on biological matters. But I guess the SETI types don’t need to know about such soft sciences, after all they’ve got physics and astronomy, and everything else just derives from that, right?

  • Eniac September 7, 2011, 21:02

    @Bob:

    Obviously, you can’t draw any firm conclusions with just one example, but it is possible that the general trend is that most societies spend the vast majority of their time not colonizing.

    Of course, you are right, but I believe that this has been generously accounted for by postulating a 5000 year period of no colonization, longer than that among the American Indians you speak of, if I understand correctly. It think you are getting hung up on that “ratio to travel velocity”. Even if there were any relationship between colonization frequency and travel velocity, it surely would not be linear, so that ratio makes no sense.

  • Eniac September 7, 2011, 21:22

    I agree on everything, but only diverge on one thing, the cause for lack of techno civs in our MW galaxy: I still maintain that it is not (primarily) fl, but rather fi and fc.

    It appears we understand each other quite well, and I agree with you that small fi and fc are another possibility to explain the apparent absence of colonizers. To me, though, mostly due to the uphill/downhill image I presented earlier, it is much easier to see how fi and fc might be large than fl.

    To begin with, I disagree that there is much of a gulf between “complex” and “simple”. As I said, there is no such thing as simple life. The fact there were millions of species before us that were not complex or sentient just means that it takes a while for complexity and sentience to develop, not that it is unlikely. The fact that all the complex and “nearly” intelligent species are recent and the documented increase in complexity and brain size ratio during evolution both indicate that there was a progression towards complexity/intelligence, rather than a chance event. The fact that we are the only intelligent species means nothing, because it is very plausible that the first precludes all others. Then one is the maximum, and we would not expect to see more under any circumstances, even if fi and fc were equal to 1.

  • Rob Henry September 7, 2011, 23:28

    Bob Steinke, I think that your analogy with colonization of the America’s really would work to demonstrate how the process could be slowed, if only you could think of some reason that the entire process of galactic colonisation might be driven by accident and opportunity. For the moment, the rest of us are having great trouble envisioning how planning and design doesn’t occasionally intervene when small Neolithic tribes do not drive the process.

  • Avatar2.0 September 8, 2011, 3:26

    Ronald

    About bichemistry – previous posters already answered this point you made.
    Until one has a compund capable to reliably self-replicate (meaning this compund is highly complex) biochemistry is not driven by some mystical drive toward complexity.
    Only afterwards can one make the case that compunds that can better replicate (in most cases, more complex) have an advantage.

    “Avatar2.0, in response to Gunnar:
    “Your maths example is fortunately not that relevant since not all configurations are equally likely. Configurations that can multiply themselves successfully are much more likely than configurations that can’t.”

    “Actually, it’s highly relevant.”

    Can you please elaborate on that?”

    There’s a long road until one reaches configurations that can multiply themselves successfully, Ronald.
    Until then, there’s no mechanism towards increased complexity – meaning, the factorials apply more accurately.

    This is not to say that my mathematical example is not a huge oversimplification; it ignores a LOT of factors (for example, I assume there could only be 100 – or 1000, 10000 – environments on early earth, when, in fact, there were billions; etc).
    I only gave it in order to give a general ideea of the improbabilities we’re talking about – which are not even close to being as large as 0.2 or 1.

    “The outcome of the mentioned chain of events is, although admittedly of a (very) small likelihood, not a series of independent chances, but rather *interdependent* events, one making the next one more likely.””

    “Interdependent”?
    What are you takling about, Ronald?
    After self-replicating molecules have appeared, the ones that can replicate better make more copies of themselves. And much later, the fittest forms of live survive. That’s about it.
    As to biochemistry’s “interdependence”: a given substance undergoes different chemical/physical changes when subjected to different environments. There’s no drive towards a specific chain of chemical reactions, no “interdependence”.

    “Avatar2.0: the fact that life did not arise more than once, is most likely because of biochemical and ecological niches already been taken.”

    Firstly, why did life not appear more times on early earth? What are the chances of a single tree of life outcompeting the others so completely in ALL of the available ecological niches?

    Secondly, many theories about the appearance of life place this appearance in extreme environments – hot vents, ice, etc – places on earth where our life doesn’t have much of a presence (extremophiles are rather rare). Why did new trees of life not develop in such places for billions of years?
    The biosphere as known proves that primitive forms of life survive just fine along highly complex ones. Protocells belonging to such new trees of life have a very good chance of surviving alongside our tree of life – even more so, considering the fact that there would be few or no predators fine tunned to attack them.
    Where are these protocells – or, by now, fulld developed trees of life? They were all outcompeted by ours? Again, what are the chances of that?

    “A comment on ‘experimental failure as a proof of concept’: how telling is this really? There are plenty of complex macromolecules which we humans still cannot synthesize in a lab, but do occur in (even abiotic) nature.”

    There are plenty of substances which we cannot make – due to lack of the needed periods of time, of temperatres, pressures, etc – but we DO know how they were made, Ronald.

    But – molecules which are not a result of life bichemistry, about which we do not know how they were made?
    Tell me, do you think that any such substance can be made in less than a few hundred steps – especially a substance we’ve been trying – and failing – to make for decades?

  • Avatar2.0 September 8, 2011, 3:38

    Ronald

    “Your argumentation is about the same as stating that the beautiful and complex ‘flower’ shapes of some crystals cannot arise spontaneously, because the end result has a too small calculated chance of happening.”

    Not even close, Ronald.

    My argumentation goes as fowllows:
    You have found one such complex ‘flower’ shaped crystal and you calculate that the chance of it (or a similar ‘flower’ shaped crystal) coming into being is exceedingly small.
    Now you can tell, by using mathematical probability, that, almost certainly, another such ‘flower’ shaped crystal does not exist on earth. To put it simply, there are not enough dice being thrown on earth for one to win such a lottery. In our solar system, more dice are being thrown, so the chances for such a ‘flower’ crystal existing are greater; etc.

  • Ronald September 8, 2011, 5:07

    Rob Henry: “Ronald, sorry about my needed heavy criticism of you earlier”.

    Please, don’t apologize, I like this kind of discussion, it highly instructive and sharpens our thinking. I do not mind at all to be corrected and I love to learn more from the more knowledgable.

  • Ronald September 8, 2011, 7:31

    Eniac: “The fact there were millions of species before us that were not complex or sentient just means that it takes a while for complexity and sentience to develop, not that it is unlikely”.

    We were almost complete in our agreement, but still not quite :-)

    No, I disagree here: there is nothing to suggest that this means that ‘intelligence just takes a while’. In that case there should have been increasing brainsizes and intelligence visible in all sorts of lineages in life’s history. But, as you state yourself, large complex brains and increasing brain size and intelligence seem to be a recent phenomenon and mainly among some mammals and birds (crows, parrots). Life has been doing well without it for hundreds of millions or even billions of years.
    That does not point toward a required time period, but rather to a pure and very rare chance event.

  • kzb September 8, 2011, 7:34

    @Bob (and Eniac)

    Bob wrote:
    <>

    Well there you go, you’ve just answered your own question (so to speak). 1 billion years is FAR SHORTER that the time civilisations in the galaxy should have existed.

    There’s two other associated points:
    (1) 100,000 LY is the entire width of the stellar disk. That’s an improbable distance according to GHZ models. It’s much more likely early civs arose towards the inner galaxy, or if you take the original Lineweaver model, within 1 or 2 kpc of the sun’s galactic radius. So a more realistic distance would be perhaps 25,000 LY or even a lot shorter.

    (2) On the multi-million year timescales we are considering, differential galactic rotation and stellar diffusion mix things up a lot. A civ that arose 1 bn years ago on the other side of the MW won’t be in the same position now. In fact it has made several orbits of the MW and had lots of different stellar neighbours.

  • Bob Steinke September 8, 2011, 11:53

    @Bob

    “most societies may spend the vast majority of their time not colonizing.”

    @Eniac

    “I believe that this has been generously accounted for by postulating a 5000 year period of no colonization. It think you are getting hung up on that “ratio to travel velocity”. Even if there were any relationship between colonization frequency and travel velocity, it surely would not be linear, so that ratio makes no sense.”

    That’s a good point that wait time before deciding to make a hop may be a better model than a ratio between travel speed and colonization front speed.

    I think the wait time per hop model applies best when wait time is much longer than travel time. For example, if you colonize by slow world ship that goes 1/1000th the speed of light, and it takes you 10,000 years to go 10 light years are you really going to get antsy to go on another 10,000 year journey after only 5,000 years?

    @Rob Henry

    “Bob Steinke, I think that your analogy with colonization of the America’s really would work to demonstrate how the process could be slowed, if only you could think of some reason that the entire process of galactic colonisation might be driven by accident and opportunity. For the moment, the rest of us are having great trouble envisioning how planning and design doesn’t occasionally intervene when small Neolithic tribes do not drive the process.”

    Von Braun planned to go to the moon, and then on to Mars, then the asteroid belt, then the moons of Jupiter. But Apollo only went to the moon. It’s not that I think there won’t be any planning, but I think the accident and opportunity come in with how long a plan will be carried out before a society changes direction.

    You do make a good point that neolithic tribes didn’t have any concept of the Americas as a finite continent that they could fully explore so there wasn’t a motivation to go explore it all. Whereas any interstellar society is going to understand the galaxy as a finite thing and that might drive more directed colonization.

    @kzb

    “Well there you go, you’ve just answered your own question (so to speak). 1 billion years is FAR SHORTER that the time civilisations in the galaxy should have existed.”

    Ah, I had gotten a mistaken impression from your previous post:

    “the colonisation time is SHORT compared to the time available for civilisations to have arisen. I mean even if you allow 100 million years to colonise the galaxy…”

    From that I got the impression that when you said short you meant less than 100 million years.

    But I also want to address the main point that 1 billion years is shorter than the time civilizations should have existed in the galaxy. How do you know how long civilizations should have existed? You are using models that assume the Earth is typical.

    The oldest stars in the galactic disk are 8.8 billion years old and on Earth it took 4.5 billion years between the formation of the sun and our emergent spacefaring civilization, so you say there should have been spacefaring civilizatons on the oldest stars 4.3 billion years ago. But you are mis-using the word should in that sentence. What you can say is there COULD have been spacefaring civilizations 4.3 billion years ago, but with only one data point you can’t say anything about the expected value of when civilizations SHOULD have arisen.

    For three billion years on Earth the most complicated life form was blue-green algae before multi-celled organisms formed. Maybe the average time delay for that step is ten billion years, and we just got lucky to get it done in three.

    “100,000 LY is the entire width of the stellar disk. So a more realistic distance would be perhaps 25,000 LY or even a lot shorter.”

    Yes, it’s unlikely that a society will start up right at the edge of the disk and have to go all the way to the opposite side before they encounter us. But they also won’t be traveling in a straight line. Hopping from star to star will give a zig-zag path that will be longer than the straight line distance. And there may be things that you have to go around like nebula with too much dust that makes it dangerous to travel fast. And maybe you can’t cross the gaps between the spiral arms. You have to go down one arm to the galactic center, then back up another arm. For my rule of thumb calculations I assume those two effects cancel and the diameter of the galaxy is a good order of magnitude distance.

    “On the multi-million year timescales we are considering, differential galactic rotation and stellar diffusion mix things up a lot. A civ that arose 1 bn years ago on the other side of the MW won’t be in the same position now. In fact it has made several orbits of the MW and had lots of different stellar neighbours.”

    That’s a good point that I hadn’t thought of. On 100 million or billion year time scales proper stellar motion will speed up colonization by bringing you new neighbors.

  • Eniac September 8, 2011, 23:28

    Avatar 2:

    Firstly, why did life not appear more times on early earth? What are the chances of a single tree of life outcompeting the others so completely in ALL of the available ecological niches?

    Actually, the chances for that are very good. 100%, really.

    According to the principles of genetics, given enough time, only one of many original lineages will survive, always. This is why we all descend from a single male who lived not too long ago (about 200,000 years). Search for “Y-chromosomal Adam”. All the male lineages that existed contemporaneously with “Adam” have died out. This holds the same for female lineages and in general for haploid lineages, as in simple organisms. It holds even without selection, emerging as a property of random propagation. With natural selection, the process is accelerated.

    Having a lot of different niches makes things more complicated (slows things down), but there are a lot of adaptations that are universal across niches, such as the use of peptides and proteins for improved catalysis, or the use of DNA for improved genome storage. Any such innovation would quickly spread across all niches and eliminate all inferior competitors.

    In other words, just because we can trace the ancestry of all present life to a single organism (we can) does not mean there were not other organisms around at that time. All of whose lineages have died out. They may or may not have been independent trees of life. We will never know that for sure, but I think not.

    Besides just a small fl, there are also various reasons why life may preclude repeated abiogenesis. Oxygen, for example, is likely very detrimental to the process, and the prior presence of organisms the eat organics will not help, either.

  • Ronald September 9, 2011, 5:47

    With regard to the age of stars and chances for life, intelligence and civilization in the MW, I hate to be the party pooper but advanced age is not necessarily a good thing: as a (solar type) star ages it gets brighter and hotter, our own sun about 10% per gy.
    I don’t have the publications at hand (Lineweaver?), but the average solar type star in the Galactic disc seems te be about 1 gy older than the sun. That is no problem for longer-lived later G (from about G5 on) and early K stars, but for the early G and latest F stars it would imply that they have evolved so much in the main sequence, and have become soo bright, that it is likely that any inner terrestrial planets have already left the Habitable Zone on the inside, as we ourselves will do within the next gy orso.
    That is, in about 0.5 – 0.6 gy the earth will become too hot for most life except thermophile bacteria and the like, and in about 1 gy for any life.
    The bigger and brighter the star (i.e. ‘earlier’ spectral type), not only the shorter its total lifespan, but also: the faster its HZ moves outward and the shorter the temporal ‘window of opportunity’ for life. I guesstimate that (on the hot side) beyond about spectral type F7 – F9, a star simply has a too short ‘habitable lifespan’, or in other words, the continuously habitable zone (CHZ) becomes too narrow (or rather: the CHZ moving outward too fast) for for (higher) life to develop.

  • kzb September 9, 2011, 7:35

    @Ronald, yes I’m sure you’re absolutely right that some more massive stars will have too narrow an opportunity to evolve civilisation. HOWEVER, is it not a fair assumption that, once a space-capable civ HAS arisen, it will not be rendered extinct by the slow heat increase from its star? When this comes to US in 0.5bn years, are we just going to sit here and fry?

    Also of course, dimmer stars are more common than brighter ones, so the too-narrow timespan problem does not lose us too many systems.

    @Bob
    I think you’ve got the point that I was trying to get across, and that is, in the Gyr timescales we are talking about, some of the glib explanations of the FP are just not logical.
    EITHER the development of Earth and its life is very highly untypical OR there is something very wrong with models of the GHZ.

    Theories such as civs lasting only a very short time are not satisfactory explanations when the deep time aspect is taken on board. It means that EVERY SINGE ONE, out of thousands of civs, over billions of years, have basically destroyed themselves before establishing interstellar travel.

  • Avatar2.0 September 9, 2011, 9:20

    Eniac

    “”Firstly, why did life not appear more times on early earth? What are the chances of a single tree of life outcompeting the others so completely in ALL of the available ecological niches?”

    Actually, the chances for that are very good. 100%, really.”

    When we’re talking about a single ecological niche, indeed, the chances are close to 100%.

    When we’re talking about thousands (at least) of ecological niches – the situation is not so simple:

    “Having a lot of different niches makes things more complicated (slows things down), but there are a lot of adaptations that are universal across niches, such as the use of peptides and proteins for improved catalysis, or the use of DNA for improved genome storage. Any such innovation would quickly spread across all niches and eliminate all inferior competitors.”

    Will such basic adaptations spread quickly – as in, before other trees of life get them – across niches?
    There will be little or no transfer of genetic material between organisms belonging to the same tree of life, which diverged long ago, becoming quite different.
    For example, such a mutation gained by trees will not reach humans any time soon – there is no efficient mechanism for the transfer of genetic material between different forms of life.

    And, of course, different niches require different adaptations – specific to these niches. A characteristic that gives an advantage in a niche will be a disadvantage in another.
    A tree of life whose fundamental biochemistry enables it to quickly adapt to an environment will be ill-suited to adaptation in another environment, due to the same biochemistry.

    Our tree of life outcompeting all the others is like a competitor winning the Olympics at all the disciplines (more like thousands of different disciplines), when faced with many opponents with different/specific abilities.
    In other words, if this is the case, our tree of life should be called “super-life” – it gained first fundamental adaptations in all niches (in each niche, largely independently); it gained first the specific adaptations needed in different niches.

  • Avatar2.0 September 9, 2011, 10:09

    Eniac

    “Besides just a small fl, there are also various reasons why life may preclude repeated abiogenesis. Oxygen, for example, is likely very detrimental to the process, and the prior presence of organisms the eat organics will not help, either.”

    Both are valid points – however, like much related to abiogenesis, Alexander Oparin’s theories – including these ones – are lacking in details.

    An extremely small fl (which, in my opinion, is the case) is more than enough to explain why there are no other trees of life on earth.
    There’s no need for further ’causes’ – and here, occam’s razor applies.

  • Bob Steinke September 9, 2011, 11:49

    @kzb

    “I think you’ve got the point that I was trying to get across, and that is, in the Gyr timescales we are talking about, some of the glib explanations of the FP are just not logical. EITHER the development of Earth and its life is very highly untypical OR there is something very wrong with models of the GHZ.”

    Yes, that’s why it deserves the name paradox. Not just some of the explanations, EVERY explanation that we can think of has some problem with it. Even the theory that life is rare and we are alone is problematic because planets are ubiquitous, the chemical building blocks of life are ubiquitous, and life developed so quickly on Earth.

    But if it takes 1/8th the age of the galaxy for colonizers to find us then we only have to be mildly atypical, not highly atypical, to have not been found yet in a galaxy with active colonizers. Even if the time is 1/80th it’s still not a vanishingly small chance.

  • Rob Henry September 9, 2011, 18:50

    Wow Eniac, your reply to Avatars 2’s concerns over the single origin of life misleads with its confidence. You introduce the topic by first demonstrating the effect in the well understood case of intraspecies genetics. Beyond this case competition to extinction is made very different by the grossly unequal quality of the competitors. Competition is made far stronger by larger competitive advantages different species have over each other and far weaker by specialised adaptations to various niches.

    I well remember reading with fascination, a popular book by Gould that claimed modelling of extinction patterns best fitted the assumption that these two factors balanced at all taxonomic levels. Gould also extrapolated to the ultimate, as you had done, and claimed that life may have arisen up to ten different times on Earth and it still be possible that one branch remains.

    So far Eniac I seem to back you, so my complaint? Simply that you started off stating 100% confidence on a model extrapolated way beyond our data set.

  • Eniac September 9, 2011, 21:57

    There will be little or no transfer of genetic material between organisms belonging to the same tree of life, which diverged long ago, becoming quite different.

    Well, yes, and that is precisely the reason why the first to develop, say, proteins, will absolutely completely replace good old fragile RNA based lifeforms.

    And, of course, different niches require different adaptations – specific to these niches. A characteristic that gives an advantage in a niche will be a disadvantage in another.

    Not for all. That was the point of my argument about universal adaptations.

  • Eniac September 9, 2011, 22:06

    An extremely small fl (which, in my opinion, is the case) is more than enough to explain why there are no other trees of life on earth.
    There’s no need for further ’causes’ – and here, occam’s razor applies.

    I agree with the first part, but I do not like my opinions supported with arguments that are not convincing, and the absence of other trees of life really does not say much about fl, because there are so many other explanations for it.

  • Eniac September 9, 2011, 22:18

    So far Eniac I seem to back you, so my complaint? Simply that you started off stating 100% confidence on a model extrapolated way beyond our data set.

    The beauty of population genetics is that it is a highly mathematical discipline, which can be done with some accuracy even without data supporting it all the way. Kind of like theoretical physics, where accurate predictions have often been made before there was any data.

    That said, no, I wasn’t really sure, but I knew that there was a good chance that the answer would be 100%, so I simplified matters a little… My mistake. I am happy to hear that Gould came to similar conclusions with more complicated calculations.

  • Avatar2.0 September 10, 2011, 10:25

    Eniac

    “There will be little or no transfer of genetic material between organisms belonging to the same tree of life, which diverged long ago, becoming quite different.”

    Well, yes, and that is precisely the reason why the first to develop, say, proteins, will absolutely completely replace good old fragile RNA based lifeforms.”

    The first lifeform to develop proteins will absolutely replace RNA based lifeforms IN A SPECIFIC ECOLOGICAL NICHE – its NICHE.

    This lifeform will NOT be in competition with life (any kind of life) which occupies different ecological niches; thus, it won’t replace such life.
    Not for a VERY LONG TIME (until it evolves AGAIN forms which can use these niches – which gives a LOT of time to other trees of life to develop such adaptations).

    This lifeform won’t transfer the protein-making information to lifeforms which exist in other niches and belong to its tree of life – there’s no efficient/fast mechanism for this (if you know of one, point it out).
    Meaning, in the other ecological niches, life belonging to this tree of life will have to find such universal adaptations largely independently.

    As said, what are the chances of a tree of life being the first to develop these adaptations in each of thousands of niches?

    “And, of course, different niches require different adaptations – specific to these niches. A characteristic that gives an advantage in a niche will be a disadvantage in another.”

    Not for all. That was the point of my argument about universal adaptations.”

    As already said, the problem with these universal adaptations is that they don’t transfer efficiently/fast between ecological niches; life from a tree of life developing such adaptations in a niche gives no advantage to life belonging to the same tree of life from other niches.

    “An extremely small fl (which, in my opinion, is the case) is more than enough to explain why there are no other trees of life on earth.
    There’s no need for further ’causes’ – and here, Occam’s razor applies.”

    I agree with the first part, but I do not like my opinions supported with arguments that are not convincing, and the absence of other trees of life really does not say much about fl, because there are so many other explanations for it.”

    These other ‘explanations’ are little more than speculations – it’s easy to find counterarguments (equally speculative):
    Places where current theories place the apparition of life – hot vents, for example – are largely sterile (except from rare extremophiles); there are few microbes to eat organics. Many such places contain little or no oxygen. Etc.

    I find Occam’s razor more convincing than such arguments – and counterarguments. You don’t need such speculations to resolve the “why are there no other trees of life” issue if you can convincingly support a small probability of life appearing.

  • Avatar2.0 September 10, 2011, 11:37

    Related to one term of Drake’s equation (and, consequently, SETI), the newest from exoplanet hunt this monday:

    http://www.eso.org/public/announcements/ann11061/

  • Eniac September 10, 2011, 14:54

    Avatar, you seem to assume an improved organism in one niche can never leave this niche and colonize, adapt to, and compete in others. I believe this to be an unfounded assumption. There is always interchange between niches. Not of genetic material between organisms (although that can happen, too), but simply by organisms moving from niche to niche. After all, the niche somehow got populated in the first place. Or take the Cetaceans moving back in with the fish for an example where migration took the reverse path. Lastly, please name a plausible niche in which organisms with protein and DNA would not eventually outcompete those based on RNA alone.

    Even speculative “other explanations” can ruin the stringency of an argument. You say: “There is only one tree of life, therefore fl must be small”. I suggest that there could be just one tree of life even if fl is large, and I provide several plausible reasons. Speculative or not, the “must be” part of your assertion needs to be rejected even if those other reasons are merely plausible.

    Actually, forget about population genetics, there are other plausible arguments that are easier to understand: I think it is pretty clear that it took some sort of “primordial soup”, a pretty special environment with a large or continuously refreshed store of organic molecules to make the transition between chemistry and life happen. It is also pretty clear that any successful proto-organisms evolving in that soup would make it their first order of business to eat it up. Those that survived the ensuing very first extinction event would be adapted to more common and less hospitable environments and proceed to spread across the face of the Earth, in due time eliminating the possibility of ever again having a primordial soup of the right kind, anywhere.

  • Eniac September 10, 2011, 15:45

    Yes, that’s why it deserves the name paradox. Not just some of the explanations, EVERY explanation that we can think of has some problem with it. Even the theory that life is rare and we are alone is problematic because planets are ubiquitous, the chemical building blocks of life are ubiquitous, and life developed so quickly on Earth.

    Funny, I almost wrote earlier that it does NOT deserve the name paradox. It is simply evidence for one or more of the Drake factors to be very small, after adding an “interstellar colonization” factor. This is ‘problematic’ only if you WANT there to be aliens. To me, it is not problematic at all. We have a lot of options left. My bet would be on fl as the most plausible to be small.

    The nice thing about this is that we will find out when we send our probes to the stars. We may find them devoid of life, or full of “simple” life, or populated with complex life that is not intelligent, or with civilizations that never took to the stars. Either way, after examining a few dozens of systems at close range we will have the truth pretty well pinned down.

  • Avatar2.0 September 10, 2011, 17:22

    Eniac

    “Avatar, you seem to assume an improved organism in one niche can never leave this niche and colonize, adapt to, and compete in others. I believe this to be an unfounded assumption.”

    Actually, I assumed the contrary – I even took this evolution of the organism into account in my previous post – the improbabilities remained:
    The first lifeform to develop proteins will absolutely replace RNA based lifeforms IN A SPECIFIC ECOLOGICAL NICHE – its NICHE.

    This lifeform will NOT be in competition with life (any kind of life) which occupies different ecological niches; thus, it won’t replace such life.
    Not for a VERY LONG TIME (until it evolves AGAIN forms which can use these niches – which gives a LOT of time to other trees of life to develop such adaptations).

    This lifeform won’t transfer the protein-making information to lifeforms which exist in other niches and belong to its tree of life – there’s no efficient/fast mechanism for this (if you know of one, point it out).
    Meaning, in the other ecological niches, life belonging to this tree of life will have to find such universal adaptations largely independently.

    As said, what are the chances of a tree of life being the first to develop these adaptations in each of thousands of niches?

    “Those that survived the ensuing very first extinction event would be adapted to more common and less hospitable environments and proceed to spread across the face of the Earth, in due time eliminating the possibility of ever again having a primordial soup of the right kind, anywhere.”

    Yet another generic explanation – what king of organic soup; what composition?
    And, of course, it’s easy to come with equally generic counter-arguments: the current theories of where and how life developed would have similar-enough conditions (with regard to the primordial ‘organic soup’, anyway) exist even today.
    “Plausible reasons”? Anything so generic is ‘plausible’, simply because one can’t prove it wrong; the ususal term is ‘not even wrong’.

    “Even speculative “other explanations” can ruin the stringency of an argument. You say: “There is only one tree of life, therefore fl must be small”.”

    This is not what I’m saying, Eniac.
    I’m talking about Occam’s razor: ~If something can be explained in more than one way, the simplest explanation is usually the right one.

    Explanation 1 – life is improbable, so only one tree of life appeared.
    Explanation 2 – life is improbable, but more trees of life appeared anyway; and all but one lost thousands of largely indepedent evolutive ‘battles’ (in different ecological niches) to a single one. And the only ‘explanations’ for why new trees of life did not appear later are generic speculations.

    Of course, in this case, Occam’s razor might be overkill, considering the improbabilities implied in explanation nr 2, which don’t exist in explanation nr 1.

  • Rob Henry September 10, 2011, 17:49

    Another thing I feel that I should add to the “significance of the single tree of life” discussion is how very hard it is for a complex organism to out compete a simple one. By example, if we came back to Earth in 100 million years time and reported that somehow cyanobacteria and angiosperms had come into such close competition that only one group survived, everyone would realise that the bacteria must have “won”.

    While it is easy to imagine a rapid displacement of a organism based on RNA enzymes*, with equally complex organisms base on more substrate specific and faster protein enzymes, I find it hard to believe that this process was likely if the replacing type was much more complex than the replaced.

    That at least one such displacement seems likely to have happened, since our ancestors can be inferred to also be of this form. That is a little evidence that other similar beginnings were also replaced. But yet another factor disturbs me…

    If ever a ready answer is given to “where are these forms now?”, it is that they are viruses. With the work of Craig Venter showing that their aquatic genes seem so numerous that they are about a million times more common than some previous estimates, it makes me wonder it they really are all viruses, or could they be mostly due to related free-living forms?!

    A continuation on from that research, and a search for a “shadow biosphere” in general are germane to these question, yet our researches have only begun there.

    *the word “enzyme”, and the systematic cataloguing of several thousand of them predates the knowledge that contemporary forms are protein based, so I think it better to reserve “ribozyme” for a molecule that just acts on itself

  • Rob Henry September 10, 2011, 20:19

    Avatar, I hate to get into arguments that sound very touchy-feely, but our biosphere has some holistic type aspects that might help lessen your quandary.

    Few organisms are completely biochemically self-contained, such that they can survive off sunlight (or hydrothermal chemicals) and build all of their own biomolecules. Most live in tight interdependent association with others. If, say, a common set of amino acids was used by a significant subfraction of them, then all scavenging and predation would favor these forms as a class, since they would require less reprocessing.

    There are also much greater biogeochemical cycles that may help explain Gaia type effects. Only life-forms that successful establish such cycles for all their inorganic inputs can thrive, the rest would end up confined to cryptic environments. If, say, one form required sulphur to be more readily available than carbon, but its actions resulted in sulphur being sequestered, then its success would be capped.

    While it may be very difficult to find a conclusive answer to the question of how efficient nascent trees of life are at pushing each other to extinction, I think that there should be much less doubt that one such tree is likely to dominate all others so completely that the descendants of others are extremely hard to detect.

  • Eniac September 11, 2011, 2:13

    Avatar, you seem to assume an improved organism in one niche can never leave this niche and colonize, adapt to, and compete in others. I believe this to be an unfounded assumption.

    Actually, I assumed the contrary – I even took this evolution of the organism into account in my previous post – the improbabilities remained:
    The first lifeform to develop proteins will absolutely replace RNA based lifeforms IN A SPECIFIC ECOLOGICAL NICHE – its NICHE.

    This lifeform will NOT be in competition with life (any kind of life) which occupies different ecological niches; thus, it won’t replace such life.

    Let me try to paraphrase, to cut through the argumentative and capital-enriched fog:

    Avatar, you assume organisms cannot move into and compete in other niches.

    Actually, I assumed the contrary –
    The first protein lifeform will replace RNA based lifeforms ONLY in its niche, because it cannot move into and compete in other niches.

    If I paraphrased correctly, you have an unusual way of using the word “contrary”. Perhaps you could point out where I misunderstood.

  • Eniac September 11, 2011, 2:29

    Explanation 1 – life is improbable, so only one tree of life appeared.
    Explanation 2 – life is improbable, but more trees of life appeared anyway…

    You forgot the all-important third possibility:

    Explanation 3 – life is probable, but we observe only one tree of life because the others either became extinct or were preempted.

    Since we are interested in fl, we need to weigh 1+2 against 3. The observation that there is only one tree of life supports both 1 and 3, with, unfortunately, opposite conclusions for fl. Therefore, observing only one tree of life does not help answer the question at hand.

  • Ronald September 12, 2011, 4:51

    Eniac: “The nice thing about this is that we will find out when we send our probes to the stars. We may find them devoid of life, or full of “simple” life, or populated with complex life that is not intelligent, or with civilizations that never took to the stars. Either way, after examining a few dozens of systems at close range we will have the truth pretty well pinned down.”

    At least for detecting life we may not even need probes. Spectroanalysis can do this job in many if not most cases. That’s why I consider powerful space-based telescopic platforms, interferometers (such as TPF, Darwin) such a top priority: we may be able to establish fl, or at least a lower bound for it, on the basis of this relatively simple and low-cost approach.

  • Gunnar Larsson September 12, 2011, 5:17

    @Ronald: Thanks for you kind words and for clarifying the relevant chemistry well beyond my capabilities!

    @Avatar 2.0:
    Consider the case that your maths was correct. The number of atoms in the universe is likely somewhat less than 10^80, of which only a small fraction is available to form life. The universe has lasted for a bit over 10^20 seconds. Reaction rates obviously depend on the local circumstances, taking N2 and O2 in air as a rough guide gives a number of about 10^10 reaction/second & atom. In total therefore about 10^110 chemical reactions have taken place in the universe so far (very roughly!). If your maths was correct and relevant the number of times life would have formed would be:

    If 100 steps were needed: about 10^-47
    If 1000 steps were needed: about 10^-2457
    If 10000 steps were needed: about 10^-35549

    Now, we now that the actual number is at least 1. Give and take a few magnitudes to account for “freak accidents” and we end up with you numbers being wrong by an order of magnitude of more than 40 for the case of 100 steps and by a factor of more than 35,500 for the case of 10,000 steps. It would be more correct to say that life formed by every single reaction that has every happened than to say that your maths for the 1,000 and 10,000 steps scenarios would be right.

  • Gunnar Larsson September 12, 2011, 5:22

    With regards to the tree of life I think it is important to remember that the properties of the last universal ancestor (such as the citric acid cycle, ATP, DNA etc.) are not some kind of special adaptations; they are the engine, currency and blueprint of life. They are likely the most efficient way to do what they do, as they otherwise would have been outcompeted by faster chemical reactions (in the case of the citric acid cycle) or more resilient information storage systems (DNA etc.). Also, the citric acid cycle is likely to have been both the first manufacturer of advanced organic molecules and the fastest one as chemically speaking a reaction that is fast is also one where the probability of having the involved reactions is high. Being the first further have the advantage of producing many copies that can mutate to forms that might later on (but possibly before the appearance of competitors) be more optimised for any local environment. For example the reason that the vents might appear relatively less lively today than other places is that as life evolved it was able to develop more efficient ways to extract energy from the surroundings (i.e. photosynthesis) than the (easier) chemical ones used in the vents.

  • Ronald September 12, 2011, 8:07

    Gunnar Larsson: I like the way you use Avatar2.0’s argumentation in an opposite way, even amusing.
    Am I right if I summarize it by stating that, precisely because the chance of life originating by pure chance events, as step calculated by Avatar2.0, is so infinitesimally small, some completely different driving mechanism must have been at work?
    I am not endorsing creationism or ID here, but would rather call it ‘largely unknown, but highly effective biochemistry’.
    And is then also reasonable to state that, precisely because we are here against all odds, thanks to this creative biochemistry, chances of other life in the universe may actually be pretty good?

  • Ronald September 12, 2011, 8:17

    I realize now that Gunnar’s and my own previous posts are also fairly in line with the cosmological principle: the reasonable working assumption that the physical laws and matter are valid uniformly and universally.

    Unique life on earth and that even against all biochemical odds seems a strong violation of the cosmological principle.