What's the chance of life didn't happen at all?

  1. all the information points to that life started on earth by pure chance

    what are the chance that life didn't happen at all on planet earth
  2. jcsd
  3. 68.993121 percent.
  4. Ryan_m_b

    Staff: Mentor

    What do mean life started by pure chance? There is no comprehensive theory of abiogenesis yet but we know enough to know that there was a probability of life forming eventually. Other than the we can't really say what the percentage chance was, there are too many variables (most of them unknown).
  5. epenguin

    epenguin 2,391
    Homework Helper
    Gold Member

    But there has been life on earth for most of its history, in fact last i heard you can't really identify a time when there wasn't, which suggests the chance is high.
    Last edited: Aug 20, 2013
  6. Sooner it later. Given enough time, the the random permutations of protein molecules will eventually form DNA. So there are going to be life forms on other planets too. It's inevitable.
  7. That's not bad I believe. Mostly so. Had to cool first but soon after, I believe a few tens of millions of years, early forms of life began to appear. And I also agree the relatively quick appearance of life on earth suggest the chance of life evolving on similar planets is high.
    Last edited: Aug 20, 2013
  8. Ryan_m_b

    Staff: Mentor

    What are you basing this on? Proteins and DNA are not made from the same components. Are you suggesting that proteins alongside nucleic acids will eventually build DNA because that isn't how it works. Indeed abiogenesis was likely to be dominated by RNA rather than proteins or DNA.
  9. "RNA world" makes sense to me:


    Here's an interesting quote:

    Keep in mind nucleic acids are made of rings of cyanide (carbon-nitrogen bonds) and I believe cyanide is a common compound found in meteoroids. You may want to investigate that.
    Last edited: Aug 20, 2013
  10. HallsofIvy

    HallsofIvy 41,063
    Staff Emeritus
    Science Advisor

    Surely that is not what you meant to ask? I am living proof that "the chance that life didn't happen at all on planet earth" is 0!
  11. Pythagorean

    Pythagorean 4,472
    Gold Member

    Scientists are philosophers: they can follow branches of philosophy like empiricism, scientific reailsm, platonism. Physicsforums tries to stick to empiricism for the most part. Currently, I don't think we have enough empirical evidence to posit the probability of life "in general". It would essentially be a long chain of Bayesian conditionals like the Drake equation.

    If we specify that we mean the probability of life given we already had an Earth (as the OP seems to suggest) then there's many aspects of basic chemistry and geology (both in terms of mechanisms and molecules) that provide many of the basic building blocks for life that it might have been hard to avoid.
  12. Has life originated on Earth more than once, and if it hasn't, would that suggests that life happened by chance?
  13. Pythagorean

    Pythagorean 4,472
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    You can design a deterministic system that has a single saturation event.

    "originated more than once" is kind of loaded. In the RNA world hypothesis it seems it would be a more 'global' event (not necessarily Earth-wide, but encompassing the whole system of emerging lifiness). So it was happening more than once both spatially and temporally. And it was (is still?) a process, not a singular event. If life is more of a spectrum thingy than an switch thingy, then maybe we want to look at the continuous lifiness value over time rather than a step function.

  14. epenguin

    epenguin 2,391
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    No, it is first-comer takes all. Newcomers don't stand chance against established life forms.
  15. Would separate forms of life occupying completely different niches still interfere? e.g. if creatures initially developed using a form of photosynthesis, would it be possible for a separate type of life utilizing chemosynthesis to flourish?
  16. Not necessarily. We don't know that we came from first-comers. We could have easily been the second-comers at the dawn of life, but outcompeted all the other comers.

    Also taking competition into account, you first have to become an organism at all, and that's a long way from a self-replicating molecule. There's a good chance both types of life in their separate areas would have the same kinds of habitat and adapt to those, so when a bridge between the areas appeared, there'd still be competition, with both kinds having their own chemosynthesizing life, as an example. The fact that one side didn't fit into the balance of the other, which was more fecund or more developed, could have easily driven one side into extinction, just like marsupials in South America.
  17. Pythagorean

    Pythagorean 4,472
    Gold Member

    Agreed that we might not have been the first. However, I think epenguin's statement still holds water, now that our lineage(s) (the only surviving lineage(s) on Earth) have saturated the environment. Macromolecules that would become new lifeforms (from scratch) don't stand a chance; they are food to already-established populations.
  18. Is it also possible that when life first originated on Earth, it changed the environment to where it wouldn't be possible for life to originate again?
  19. Pythagorean

    Pythagorean 4,472
    Gold Member

    I don't think origination is such a simple topic that you can talk about it as some instance that occurred. As iansmith's quote about RNA world implies, life "originated" 3 times independently depending on where you define something as living vs. not living.

    There's also this additional potential confusion:

    In it's most simplest form, endosymbiotic theory suggests one single celled bacteria ate other bacteria and instead of digesting them, entered into an advantageous relationship... many cells became part of one (a possible explanation of why mitochondria have their own DNA or why cynaobacteria look so much like chloroplasts).

    I don't know whether the precursor bacteria would be of the same lineage or not, or whether we should include that as an event of new life. It would be a new level of life, I think: emergent consequence of two organisms is they become one more complex organism.

    In the next step of life, instead of consumption, there was cooperation between cells, role assignment (differentiation) which lead to multicellular life which, as far as I know, is limited to eukaryotes (the cells that contain mitochondria).
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