Abiogenesis , multiple times?

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Discussion by: degeus

Hi there,

Somebody asked me why Abiogenesis happened only once.

My response was that it may very well have happened multiple times but that the Earth's atmosphere transitioned from 'reduced' to 'non-reduced' when fotosynthesis evolved and that this resulted in the extinction of all the other strains of life (the Great Oxygenation Event).

However, this can not account for it wholy because what about life forms that do chemosynthesis?  How much have these life forms been examined? Are they known to be part of that same life strain (and simply well shielded from the non-reduced atmosphere and therefor unaffected? Or is the research pointing in another direction? A second abiogenssis? A remainder from the first? A return to the 'basics' comparable to the return of the whale to water?

Cheers,

Benny

24 COMMENTS

  1. Abiogenesis is a gradual complexity-increasing process beginning from simple organic chemicals – the very chemicals life eats in a hurry. Once life enters an area, abiogenesis becomes impossible there. It’s probable that the reason abiogenesis only happened once on Earth is that life spread from its starting point across the world before abiogenesis could occur a second time somewhere else.

  2. How do we know how many times it happened? It’s a bloody big universe and, for all we know, it happened multiple times throughout the universe. All we know about is our own planet and to extrapolate what we know about this little ball of rock onto the entire universe is a bit of a stretch.

    • In reply to #2 by jel:

      How do we know how many times it happened? It’s a bloody big universe and, for all we know, it happened multiple times throughout the universe. All we know about is our own planet and to extrapolate what we know about this little ball of rock onto the entire universe is a bit of a stretch.

      But the original post was about Earth. The poster even talks about Earth’s atmosphere. Besides, any discussion of life outside Earth would be wild speculation, even a bigger speculation than the proposed topic.

  3. There is, to the best of my (limited) knowledge, no evidence for a single or for multiple abiogenesis events.I would think that if there were multiple events one strain became dominant to the exclusion of all other strains.

    Until we gather more information on abiogenesis, as in producing it under lab conditions, I don’t think there can be a useful answer. Just many useful questions.

  4. As I remember there was a lot of excitement over a pool of microbes metabolizing arsenic. further investigations showed it was based on the same DNA as the rest of us so for now it looks like all other proto-life forms were lost to our type.

    as for of abiogenisis happened once or many times, to me that’s an unanswerable question at the moment since it’s a bit of a catch-all term so it begs the question exactly “what is it that happened once or many times?”

    onr thing that must be considered though is the available time-slot for it to occour within. we have a good idea of how old organic life is and how old the earth is but these aren’t much help either. the surfave of the earth was very hot for a very long time. proto-life could have started up on cooler islands any number of times before being subducted and destroyed. there’s also the question of the involvement of comets and asteroids as incubators for early replicators.

    all i can say is anything we call living right now uses DNA and/or RNA to replicate. molecular clocks may be able to pinpoint some sort of genesis but I suspect we’ll need to understand a lot more about the solar system first. I’m sure it’s not just an earth story

  5. First, I really dislike the term abiogenesis. Life never just suddenly started. Some people like to say that evolution starts after life appears, as a dodge to questions about the origin of life. The truth, however, is that evolution was part of the process the moment a single molecule formed that was capable of replicating itself. No one would classify such a simple molecule, if it appeared today, as alive, so to call such an event “life from non-life” seems inappropriate. There’s no hard line between the two.

    Second, I don’t think such an event was at all uncommon. It probably happened a great many times, giving rise to no small number of life lineages. But examination of DNA shows that only one of those lineages fostered all surviving lifeforms today. The others simply lost the race.

    Or, the path to DNA (which was certainly not the first replicator), with it’s particular base/amino acid mapping, is not so contingent as we tend to believe. It’s possible that several lineages of replicators were forced onto the same general path, whether before or after the development of DNA storage. There’s no way to distinguish that hypothesis from the standard single-surviving-origin one.

    Oh, and I also think the effect of atmospheric oxygenation is overstated. It took a very long time for levels to rise from trace to those we aerobic eukaryotes appreciate so much today. Any prokaryote that lived in an environment exposed to oxygen would have developed the molecular tools to either tolerate it or exploit it. And the fact that there are readily discoverable anaerobic prokaryotes alive today that cannot tolerate oxygen should show that there’s something wrong with the notion that there was any kind of mass microbial extinction.

    • In reply to #5 by Thanny:

      First, I really dislike the term abiogenesis. Life never just suddenly started. Some people like to say that evolution starts after life appears, as a dodge to questions about the origin of life. The truth, however, is that evolution was part of the process the moment a single molecule formed tha…

      Why dislike the word ‘abiogenesis’ and not e.g. the words ‘life’ or ‘non-life; or ‘replicator’ or ‘gene’ ?
      They’re all loose definitions. Something Richard Dawkins is well aware of as he often explains them at length in his books to avoid confusion. But in these posts we don’t have such luxury and yet everybody seems to understand very well what is ment, possibly thanks to the context.

    • In reply to #5 by Thanny:

      First, I really dislike the term abiogenesis. Life never just suddenly started.

      I don’t see a reason to dislike the term, but it does need to be emphasized that it is an extended process, not a single event!

      Some people like to say that evolution starts after life appears, as a dodge to questions about the origin of life.

      I think the confusion arises, because Darwin’s theory is about the on-going process of evolution, – nominally taken from LUCA onwards.
      There is also confusion among theists, because the pseudoscientific “Theistic Evolution”. lumps cosmic evolution together with biological evolution. (see below)

      RCC Theistic Evolution

      The Church has deferred to scientists on matters such as the age of the earth and the authenticity of the fossil record. Papal pronouncements, along with commentaries by cardinals, have accepted the findings of scientists on the gradual appearance of life. In fact, the International Theological Commission in a July 2004 statement endorsed by Cardinal Ratzinger, then president of the Commission and head of the Congregation for the Doctrine of the Faith, later Pope Benedict XVI, now Pope Emeritus Benedict XVI, includes this paragraph:

      According to the widely accepted scientific account, the universe erupted 15 billion years ago in an explosion called the ‘Big Bang’ and has been expanding and cooling ever since. Later there gradually emerged the conditions necessary for the formation of atoms, still later the condensation of galaxies and stars, and about 10 billion years later the formation of planets. In our own solar system and on earth (formed about 4.5 billion years ago), the conditions have been favorable to the emergence of life. While there is little consensus among scientists about how the origin of this first microscopic life is to be explained, there is general agreement among them that the first organism dwelt on this planet about 3.5–4 billion years ago. Since it has been demonstrated that all living organisms on earth are genetically related, it is virtually certain that all living organisms have descended from this first organism. Converging evidence from many studies in the physical and biological sciences furnishes mounting support for some theory of evolution to account for the development and diversification of life on earth, while controversy continues over the pace and mechanisms of evolution.[5]

      The Church’s stance is that any such gradual appearance must have been guided in some way by God, but the Church has thus far declined to define in what way that may be. Commentators tend to interpret the Church’s position in the way most favorable to their own arguments.

      Thanny:- The truth, however, is that evolution was part of the process the moment a single molecule formed that was capable of replicating itself.

      There would undoubtedly be selection processes in action from the earliest stages of replication.

      No one would classify such a simple molecule, if it appeared today, as alive, so to call such an event “life from non-life” seems inappropriate. There’s no hard line between the two.

      It would seem likely that chemical reactions would take similar courses under similar conditions, but the chemistry of Earth, and competition from existing life, have radically altered since those conditions initially existed.

      Second, I don’t think such an event was at all uncommon. It probably happened a great many times, giving rise to no small number of life lineages.

      There is still much to learn about RNA World and early stages.

      But examination of DNA shows that only one of those lineages fostered all surviving lifeforms today. The others simply lost the race.

      That seems the most credible explanation. The remnants of endosymbiosis in the form of chloroplasts and mitochondria indicate early evolution.

      • In reply to #20 by Alan4discussion:

        Just to pick out simple illustrations to my earlier comment and detailed link, on the evolution of mitochondria and chloroplasts in Eukaryotes: -

        Alt Text – - -
        Alt Text – (Right click and select “view image”)

  6. To go from inorganic soup to life requires some logical intermediate steps and each of these steps is/has been researched by groups of scientists and awesome experimentation. A short list of the steps would include: inorganic chemicals generating organic monomers….This would be followed by the organic monomers polymerizing….then the polymers would have to self assemble into protocells….. then the protocells would have to gain the replicator….

    If you’d like to look into research regarding each of these steps, I’d guide you to oparin/haldane and miller/urey for the “heterotroph hypothesis” and the famous miller urey experiment.

    If you’d like to read up on the polymerization step, look to A.G.Cairns-Smith and the hot clay hypothesis.

    If you want to spend 15 delightful minutes watching the TED video that I just shared with 75 honors Biology students, please reference
    http://www.ted.com/talks/martin_hanczyc_the_line_between_life_and_not_life.html

    Martin Hanczyc delivers a whopper of a talk and “matter of fact–ly” demonstrates why his lab will probably synthesize a living thing in the next few years!

    If you’d like to gain knowledge concerning replicators, a good “wet your appetite” piece, see Speigleman’s monster” and google the “RNA world”….

    These steps are a framework for how to go from inorganic soup to life. It is really evolution for chemists. If you go from the big bang to earth’s formation, you are really talking about evolution for physics. Then, when life is established, we can (finally) talk about Biological evolution.

    Creationists want this to occur in a moment; when in reality it would take time, perhaps even deep time. Also, as far as abiogenesis happening once, I think that it happened lots and lots of times over the course of lots and lots of years and the heterotrophic nature of the early cells led to dominance by one “type”. We’d have competition from the get go…..

    • In reply to #6 by crookedshoes:

      To go from inorganic soup to life requires some logical intermediate steps and each of these steps is/has been researched by groups of scientists and awesome experimentation. A short list of the steps would include: inorganic chemicals generating organic monomers….This would be followed by the or…

      Thanks for your lengthy response but I think you misinterpreted the question which was specifically asking about life forms that do chemosynthesis vs those that do photosyntesis. I’m curious how much we know about those that do chemo-synthesis : if we can safely assume that the they are in the same tree of life as those that do photosynthesis, or not (to rephrase the question).

      I would add the Craig Venter Institute to your list though, for completeness. :)

      • hey, I guess I am guilty of something strange here; I was not really trying to answer the question!!! I was more responding to one of the other answers and providing an off the top of my head list of cool stuff.

        My list was incomplete and, you are dead on correct to include Venter!

        As far as the actual question is concerned, i am of the opinion that before chemo or photo autotrophs evolved, the world was full of heterotrophs. So as far as asking about abiogenesis, there was probably a very long time between the life generating series of events and the appearance of the first photo or chemo synthetic organisms.

        Sorry for the initial confusion!

        In reply to #12 by degeus:

        In reply to #6 by crookedshoes:

        To go from inorganic soup to life requires some logical intermediate steps and each of these steps is/has been researched by groups of scientists and awesome experimentation. A short list of the steps would include: inorganic chemicals generating organic monomers……

        • In reply to #13 by crookedshoes:

          hey, I guess I am guilty of something strange here; I was not really trying to answer the question!!! I was more responding to one of the other answers and providing an off the top of my head list of cool stuff.

          My list was incomplete and, you are dead on correct to include Venter!

          As far as the…

          Hi, no problem for the misunderstanding :-) I noticed most people did not respond to the question either :-D
          Then again, I should have said “Why didn’t abiogensis happen twice on Earth” , which was really the question I got. Your email wasn’t a waste though : I’m keeping it for later reference as I compiled something similar (amongst other from Chapter 14 in the Ancestor’s Tale, probably my favourite of Dawkin’s books… ) but my notes are unstructured and your mail does a nice job of tidying it up.
          As we’re compiling a list : seems that TNA is on the way of becoming the new candidate for the first common replicator , there’s another topic here at the forum that points to some interesting stuff.

          • Cool! Do yourself a huge service and reference the TED talk. It is just awesome. There is a moment when the “lifeless sac of chemicals” replicates. It takes my breath away.
            crooked

            In reply to #14 by degeus:

            In reply to #13 by crookedshoes:

            hey, I guess I am guilty of something strange here; I was not really trying to answer the question!!! I was more responding to one of the other answers and providing an off the top of my head list of cool stuff.

            My list was incomplete and, you are dead on correct…

          • In reply to #15 by crookedshoes:

            Cool! Do yourself a huge service and reference the TED talk. It is just awesome. There is a moment when the “lifeless sac of chemicals” replicates. It takes my breath away.
            crooked

            In reply to #14 by degeus:

            In reply to #13 by crookedshoes:

            hey, I guess I am guilty of something strange here;…

            The link in your mail did not work (copy/pasting links from TED does not work, apparantly) but I found it with a search and watched it.
            I truly hope that the progress in this field continues at this pace.
            But on ted.com there’s a great search function :-)
            Craig Venter also has some great talks on creating Synthetic Life up on Ted.com.
            Hopefully they work better towards youtube :

            Life and Not life Ted talk :

            Creation of Synthetic cell :

  7. I think of it as a “most recent common ancestor” thing. This time the most recent common ancestor of all living things. Doesn’t mean the ancestor lived on its own, just that none of its peers had offspring that survive today.

  8. This could be a somewhat difficult matter to settle, as traces of steps towards the first organisms may not be preserved. Laboratory simulations might give pointers though. I think part of the interest in extreme or vary obscure habitats is to see if there is evidence for parallel life forms from a different route – but that could be very hard to establish apart from living organisms and so far all life has profoundly similar chemistry.

    Like others, I doubt oxygenation would be significant – that surely came well after life was established and yet there are ‘extremophile’ survivors to this day, not just in caves, ocean depths etc but, I think, in everyone’s bowels – if anaerobic bacteria are considered such.

  9. An interesting question I have often pondered, though I have no expertise with which to answer, but I might make a semantic contribution. I think there is some confusion over the word “once”. Since many people are primed with stories of Adam and Eve and live in an individualistic culture, they will tend to think in terms of individuals. They seek the “first” individual that crossed the line into life. Leaving aside that no such line has ever been clearly demarcated, early on we are talking about chemical reactions, not biological evolution. It makes very little sense to me to ask which molecule was the first to react in a particular chemical reaction. In chemical reactions you have an environment that facilitates the reaction and you have a population of molecules that participate in the reaction. You can’t meaningfully reduce the “once” here to a single individual.

    It is possible that there was a single local that was exceptional in some way where a new chemical pathway was facilitated that begins the long history of life. But if a relatively common environment gave rise to the same reaction in multiple locations, because it is the same reaction we would not, looking back, be able to identify the multiple sites of abiogenesis and the result would be a single new chemical form—it would appear to us as a single instance of abiogenesis, confounding a particular chemical pathway with an “instance” (a location in space and time of an event) of abiogenesis.

    I think people asking the question, “did life arise more than once” need to sharpen their question. They need to think a little more deeply about what it is they are asking and ask it in a less ambiguous manner.

  10. The truth, however, is that evolution was part of the process the moment a single molecule formed that was capable of replicating itself.

    For evolution to occur you need a means for making less than faithful copies. Simple replicating molecules most likely lack that.

    It is really evolution for chemists. If you go from the big bang to earth’s formation, you are really talking about evolution for physics.

    For the same reason above. Simple transformation of one thing into another (a prior stage into a more advanced stage) is not evolution. We speak loosely, but incorrectly, of the “evolution of the universe from the big bang”. Evolution depends on the possibility of bad copies. There is nothing in cosmology at all comparable.

    • In reply to #10 by baon:

      For evolution to occur you need a means for making less than faithful copies. Simple replicating molecules most likely lack that.

      That is a rather narrow view of evolution, perhaps based on the concept of evolution-natural selection couple. Thinking about the universe, for example, you can think of a selection process from the initial pool of possibilities. It doesn’t mean that universes have to replicate themselves, it only means that there must be enough variations to start with. The same can be applied to chemical reactions: you can have competing reactions happening at the same time. The one better suited to the environment will produce more product.

  11. Very cool. Venter seems to be going at the “basic life” question by paring down living things while Hanczyc is going at it by building up systems towards life. Although they are approaching the task from different angles, one, the other, or both are going to be successful in the near future!!! Stay tuned.

    • In reply to #23 by doriansecularworld:

      I’ve seen a documentary where a species NOT carbon based was found.

      Do a search for it.

      Do you have details?
      It sounds like the Felisa Wolfe-Simon flawed Mono Lake claims about arsenic!

      NASA Smackdown — 2011 Mono Lake Arsenic-Based Life Claims Refuted

      But then other scientists began their standard peer review process and dug into the details outlining NASA’s research and findings, and they’re now two years later, charging that the research behind it is seriously flawed.
      .
      “I was outraged at how bad the science was,” Redfield said in an interview with Slate’s Carl Zimmer back in 2011. Redfield also posted a scathing critique of the report on her blog.

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