What is the origin of life on Earth?

Discussion in 'Biology & Genetics' started by valich, Oct 10, 2005.

  1. valich Registered Senior Member

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    Please don't reply with any extraterrestrial explanation. I am looking for the form of life that the scientific community would consider as the first form of life to appear on Earth, approximately 3.8 billion years ago - or before. And then evolved into the animal diversity that we have today.
     
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  3. It probably wouldn't have been Life, not in the accepted sense of the term. Something akin to Viral RNA and precious little else, except a self contained environment it could exist in. It would have been its "container" which would have distinguished it as being living, not so much the actual thing itself.
     
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  5. valich Registered Senior Member

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    It's that crossover from non-life to life that I'm looking for. Some bacteria (Gram-negative Firmicutes) have no self containg cell wall. The origin of life would have had to have been a precursor to an anaerobic thermophile bateria capable of being created in the harsh, extreme, anaerobic environments that existed before 3.8 bya. What elements necessary for life were there then: water, nitrogen, hydrogen, light, lightning. We've experimentally created 11 amino acids under these types of environments.
     
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  7. CharonZ Registered Senior Member

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    I suppose you are refering to Mycoplasmas. They don't have a cell wall but of course a cell membrane. They are not old in that sense because it is likely that they lost their cell wall due to adaptation to a parasitic life style.
    Regarding first life form, the question is far more complex. In fact, there are a myriad of assumptions and theories, some of which are summarized in this intersting Review:

    Unfortunately I only got it as pdf, and it seems that I can't easily extract the figures and text passages out of it. If I got time I might try it again.
     
  8. valich Registered Senior Member

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    Firmicutes are Gram-positive bacteria, and only some have no cell wall, but you're right, they still have a single membrane.

    Thanks a lot for posting that summary and giving the citation too. That's sounds like a very interesting article and I'm going to find it and read the whole thing - it's just what I'm after! Especially the assumption that it may have been one gene: "a self-replicative model...a primitive self-catalytic matabolic network..." That a sounds very plausible. Do bad there's probably no scientific evidence of such, like a fossil record.

    Thanks a lot!
     
  9. Hipparchia Registered Senior Member

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    Wow, a great question valich. I guess the problem is that all the life still around is really advanced compared with the first life. [I don't even want to get into definitions of what is life!] The first life all got eaten up by the latecomers.
    I like the idea that the first forms were some kind of rock based thermophile. If they arose and were living deep underground then they would have been protected during the heavy bombardment phase.
    If not that, have you seen the stuff about clay minerals forming the templates for the first life? Google Cairns-Smith.

    Can I ask why you don't want an extraterrestrial explanation? I mean I don't really buy into pan spermia, but why would you reject it outright?
     
  10. spidergoat Valued Senior Member

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    What you are looking for is the holy grail of evolutionary biologists, it hasn't been discovered yet. One good reason is that it probably evolved in conditions very different from when the vast majority of life forms evolved.
     
  11. Hipparchia Registered Senior Member

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    Not if its one of my subterranean thermophiles?

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  12. valich Registered Senior Member

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    I don't reject panspermia at all, I'm just trying to limit the scope of this thread to a scholarly level. If we start adding the extraterrestrial hypothesis then I'm sure you can imagine where this thread might start heading to: UFOs, aliens...

    Yes, I am somewhat familiar with the life originating from clay theory, but I don't find the reasonings as convincing as other theories. Don't know?

    CharonZ: Thanks again for the excellent paper that you quoted from "Controversies on the origin of life." I printed it out but will have to study it to understand it better throughout the week. More importantly, though is that it was just written this year and contains an excellent source of 42 reference articles at the end. Geez, that'll keep me occcupied for weeks. I'm ordering some of those references right now.
     
  13. I wouldn't presume here to reply for Valich, but the pan spermia idea, though ostensibly offering a possible answer towards the origins of life on this world doesn't in anyway adequately address the question of the origin of life - if we leave the answer to extraterrestrial sources we just shift the problem elsewhere.

    If life processes began else where in the Universe and got seeded about the place all willy-nilly, then by what process, exactly, did it begin elsewhere?

    The Pan Spermia conjecture tells only that it did, not how....

    No answer there really, just what sounds like answers.
     
  14. Ophiolite Valued Senior Member

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    Unlike Hipparchia I do buy into pan spermia as plausible theory. The objection you have raised is the one that always comes up when pan spermia is mentioned. In my view this is a seriously flawed objection. If the problem i.e. the origin of life, actually lies elsewhere, then it is wholly proper to shift it there.
    Saying life on Earth originated from out there is not a cop-out. It is not the end of the discussion and investigation, it is merely the beginning. The questions remain the same, it is just the geography that has changed.
    Pan spermia provides two immediate benefits:
    It addressess the problem of the very rapid appearance of life on Earth.
    It provides a far larger theatre in which chance can play its role in developing replicating molecules and metabolisms.
     
  15. spuriousmonkey Banned Banned

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    24,066
    Someone else would call that two immediate disadvantages.

    However, rapid on a geological scale is nothing to worry about on the life scale of time. Especially if we talk about very simple organisms or semi organisms with rapid reproductive cycles. Then a million years is almost an umlimited amount of tme. Imagine 100 millions of years through the eyes of a bacterium.

    A greater theatre doesn't help us with anything because we have hardly a clue what the conditions were on earth exactly, let alone all over the universe.
     
  16. Ophiolite Valued Senior Member

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    Until we have established a plausible, detailed, quantitative pathway from non-life to life this is everything to worry about. The glib 'geological time is so long' excuse has offended me for decades. I am not attacking you here spuriousmonkey, but the excuse. That is all it is. Moving the problem off planet yields the benefit of giving us astronomical as opposed to geologic time. That merely opens up the range of options open to us. The question how still remains.
    I am not saying, well out there we have so much time (and so much more space) so something was bound to happen. I am saying by providing the increased time and volume we open up the possibility of other pathways. Those still have to be defined - plausibly, in detail, with quantitative definition.
    The problem isn't solved by bacterial generations: bacteria are hugely complex, highly advanced life forms, that would eat for breakfast (and almost certainly did) the earliest life forms. It's how we got to the bacteria that remains the problem. And did it in a couple of hundred million years at most - and yet took more than two billion years to develop signigicant multi-cellular beasts from an already advanced bacterium using evolution.
    We also have a pretty good idea of conditions on early Earth and at least as good an idea of conditions in comets and gas clouds.
     
  17. spuriousmonkey Banned Banned

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    I don't see why we would need more time.
     
  18. invert_nexus Ze do caixao Valued Senior Member

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    Ah-ha!!
    Someone said it finally. This has been on my mind since reading through the pdf quoted by Charonz a while back (I searched the web and found the entire document. Interesting read.)

    My mind has been circling around the implications of Godel's Incompleteness Theorem in conjunction with the various therems of Turing, Church, and Tarksi. This idea you have of 'establishing a plausible, detailed, quantitative pathway from non-life to life" is, I think, proved unlikely by these concepts.

    The problem is that evolutionary processes are not a simple enough system to escape the implications of incompleteness. We can look at your search for this plausible evolutionary path as the search for justification of a theorem in a formal system. We have the theorem (life as we know it) and we want to trace the path of evolution to lead back to some axiom (reverse derivation back to the origins of life.)

    Now. There's nothing that says that we won't get lucky and come across a derivation that works (although the lack of axioms does make this incredibly unlikely) but we can say that there is no surety that such a derivation will ever be found.

    The problem is that determining the derivation of a theorem is not primitive recursive (guaranteed to end) it's general recursive and this means that the recursion can go infinitely deep and we stumble onto Turing's Halting Problem.

    The derivation of life, the determination of the axioms of life, is an undecidable proposition in any sufficiently quantitative system.

    The only hope, of course, centers on the word 'plausible'. However, plausibility is just that and any derivation that might be achieved would be highly tentative at best.

    There can be no surety in this matter.

    We might as well have spontaneously generated like the proverbial fly from feces...

    However, I have little doubt that even though this derivation can never truly answer the question as to the origins of life, it could help us in problems of the now and the future. It can help us to understand the mechanisms of life and evolution and it could shape our future in quite significant ways. Even if a plausible derivation is never achieved, the search might be just as fruitful as a discovery in this regard.


    Now. As to that pdf. I was pleasantly surprised to see my own private thoughts echoed within. I've been pondering this very issue on the beginnings of life for quite some time and a distinction I keep coming up against in my own thoughts is the question on which came first? Metabolism or evolution? Did the first life-forms replicate themselves? Or did the first life-forms metabolise simpler molecules to power further cycles of metabolisation?

    A huge problem in this discussion of the 'origins of life' is the problem of definitions. "Life" is poorly defined. It's derived from layman's language and has never been adequately defined to a scientific level. What is life? Is it replication? Is it metabolic activity? Is it both? The cell was once the definition of life. But, much as the atom, the cell is no longer the indivisible unit that it once was. How far down do you go before you stop calling it life and start calling it chemical?

    Tricky.

    And, what of the question of cells? Were there life-forms prior to the formation (or acquisition) of the cell membrane?

    So many questions to answer. So many definitions that need to be elucidated.


    And. As to pan spermia. I have no problem with the theory. It's true that it pushes the problem into space without solving it, but the problem will never be 'solved'. Pushing it into space is merely one of the optional twists and turns that might have taken place in the derivation. It's a legal move and has a good deal of evidence backing up the possibility. The truth will never be known for sure though. This must be accepted (but shouldn't deter the search...)


    One last thing:
    I disagree. I say the early conditions of both the Earth and the Solar System are debatable. I suspect that, while this question falls prey to Godel's theorem as do so many others, it does not do so quite as severely as the question of the origin of Life. But, there's still no guarantee of working out the derivation....

    Anyway. I recently referenced an article in another thread which pushed back the formation of Earth's oceans by half a billion years. From 3.8 to 4.3 billion years ago. The point being that we don't know the conditions of the early Earth. These conditions are debated strongly and as such the question on the materials which the original life forms had to work with are unknown.

    Axioms. In search of axioms.
    It's funny how mathematics proceeds from axioms to theorems, but life must follow the opposite path.

    We're like crabs.
    Scuttling around in search of beginnings.
    Unfortunately time is unidirectional unlike musical notes.


    Spurious,

    Do you not see why we do not need no more time?
    Muaha!!

    The question isn't one of need.
     
  19. spuriousmonkey Banned Banned

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    What then? You want more time?
     
  20. invert_nexus Ze do caixao Valued Senior Member

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    It doesn't have anything to do with want either....

    It comes down to this.
    Does pushing the origins of life (or organic material) to space harm anything?
    Or does it benefit anything?
    What is there to harm or benefit? The idea that a solution will ever be found? Pshaw. No such thing as solutions. Plausible scenarios, yes. But not solutions.
    There are practically an infinite number of scenarios of the derivation of life.
    Some of these plot through space.
    Some of them are purely terrestrial.

    What's the harm of thinking of the possibility of either/or?

    I can think of a benefit. By contemplating pan spermia, we are able to contemplate vastly more systems (environments) which might have churned out organic molecules.

    Remember. This isn't about solutions. This is about problem solving. What problem are we seeking to solve? The origins of life? Unsolveable. But, there are other problems which might be addressed by the contemplations of this issue and the contemplation of an extraterrestrial origin of organic molecules surely has applications of its own.
    (Also. Organic molecules have been shown to exist in comet ice and such, yes? It got there somehow.)

    So. What's the harm in thinking of solutions to these problems using all possible avenues of derivation?
     
  21. spuriousmonkey Banned Banned

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    24,066
    What is the harm in asking the following question:

    why is scientology just as shit as Tom cruise's acting?

    No harm...
     
  22. invert_nexus Ze do caixao Valued Senior Member

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    I suspect that this theorem is not deriveable from the axioms under question (general and vague as they may be.) However, it is impossible to say for sure as there are too many possible paths of derivation to rule them all out. This is an interesting aspect of human cognition. We break the rules with intuition. Just like your intuition tells you that the course of derivation of life would fall only on the terrestrial path rather than the extraterrestrial.

    Anyway.
    I'm not saying that anything is as good as another. Far from it. Merely that I see no harm in positing an extraterrestrial orgin for some organic molecules (especially seeing as how the extraterrestrial organic molecules (precursors at least) have been found to exist already...)
    If you do see harm in it, then why don't you make your reasoning plain? The only harm that I can think of would be that it would be a waste of time if it were an unfruitful avenue of exploration. But, how can you know? You can't. You're guessing.

    I'm also not saying that only the pan spermia idea should be examined. Merely that it shouldn't be excluded out of hand.

    You obviously deny the possiblity that the derivation can take an extraterrestrial route, so you'd limit your searches along the purely terrestrial route. That's your choice. But, do you accept that your path of inquiry is no more nor no less likely to come up with a solution than any other plausible path? Would you deny a plausible derivation out of hand simply because it a portion of it took an extraterrestrial route?
     
  23. Ophiolite Valued Senior Member

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    9,232
    Invert: pessimist
    Ophiolite: optimist.

    We shall solve the origin of life as a consequence of three factors:
    1) We shall figure out how to create life, or more precisely engineer the conditions in which it can arise. Your refutation of figuring out by backward analysis may or may not be valid, but it is certainly irrelevant.
    2) We shall find other life 'forms out there'. By 'comparing and contrasting' the different life types we encounter, a clearer picture of my 'plausible pathway' will emerge.
    3) We shall witness life originating in situ, 'out there'.

    By the way the extraterrestrial origin for organic molecules is arguably now the leading notion as to how the building blocks at least reached the Earth. [Interesting side note. If you hammer an ice bullet loaded with amino acids with the sort of energy you'd expect from a cometary impact they link up nicely to form polypeptides.]
     

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