Chance of life on other planets

Discussion in 'Astronomy, Exobiology, & Cosmology' started by James R, Sep 4, 2010.

  1. keith1 Guest

    All of the above. Given the preconditions are exactly widespread. And that was the conclusion I stated.
     
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  3. keith1 Guest

    If the "stuff we were spawned from" was the "main widespread ingredients available", and the conditions prevalent, then yes.

    Duh Neverfly.
    It would be conjecture to reason something that is undetectable.
    As a dirigible (full of humans) can pass over a New Guinea tribal camp (full of humans) at night...undetected.

    Your banal response gives further credence that the "wool could be easily pulled" over ones eyes, in front of ones nose, and way over ones head.
     
    Last edited by a moderator: Sep 24, 2010
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  5. Neverfly Banned Banned

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    That is a Very Big "if."



    Detected. Easily.
    I've watched dirigibles fly by overnight. Also, irrelevant.
    You did not say anything about detecting (Which is a whole 'nother story)-- you said "Unrecognizable."

    Keep your story straight.
     
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  7. keith1 Guest

    Detect, recognize. Whatever.
    It surpasses your "if" in culpability.
    You keep my story straight.
     
  8. Neverfly Banned Banned

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    Yeah, whatever. Two very different things.

    Hardly.

    This doesn't even make sense. Who do you think you're kidding?
     
  9. keith1 Guest

    I can't help you. next.
     
  10. Dinosaur Rational Skeptic Valued Senior Member

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    Eburacum45: I would expect a lot of similarites.
    I would expect the following similarities.
    • Carbon based organic chemistry similar to ours. The chemistry might be incompatible with ours (EG: Not able to digest the same foods).

    • Bilateral symmetry. Binocular vision & direction-detecting hearing.

    • Evolved from Quadruped Vertebrates. Very unlikely to be as small as squirrels/rabbits nor larger than Kodiak bears/Gorillas. Possibly evolved from something other than primates. For example: A feline evolution seems possible. Not evolved from flying or aquatic creatures.

    • Hands capable of holding & manipulating tools. Very possibly a different number of fingers and/or two thumbs instead of one. I would expect a minimum of three fingers & an opposing thumb. One thumb & 4 fingers seems like an excellent compromise: Less fingers seem less useful. More fingers & a second thumb seem like extra complexity for little extra utility.
    A biologist/zoologist with a good knowledge of evolution might be able to provide a better list with good explanations.
     
  11. granpa Registered Senior Member

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    Arthropod bodies are naturally waterproof so
    they would tend to be the first to colonize land on any planet.
    I think social insects are more likely to develop intelligence first.
    The idea that their bodies would be too heavy is bunk.
    Look at your own ribcage and skull.
    If anything insect bodies would be lighter.

    I suspect that ecosystems derived from extremely high tech terraforming nanobots are not rare.
    They may even be the rule rather than the exception.
    Over time they would eventually evolve into some very impressive highly intelligent half-robot half-animal creatures.
     
    Last edited: Sep 24, 2010
  12. Neverfly Banned Banned

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    V'ger.

    Dinosaur:
    What you're doing is taking the only thing that you know and applying it to the unknown.
    You could be correct or you could be wildly missing the mark. I don't know.

    What I can say, though, is that the possibilities for diversity appear to be far, far greater than you are giving credit to.

    Hands with fingers and thumbs are our way, but most certainly not the ONLY way to hold and manipulate tools.
    For example, if you posted a thread asking for advice on writing a description of an alien form for a Science Fiction piece, I would likely suggest (For effect more than anything else) that you think as best you can of what is Outside of our familiarity.
    Imagine a creature that, rather than arms with fingers on hands, has a series of fluid-filled tubes and filaments that extend from the body that can grasp, manipulate and delicately apply instruments at many lengths and intervals.

    Check out how the Lyre bird vocalizes sometime. Granted, it is native to Earth, but it's still a unique look at diversity in how to make something work. Even in ways far superior to our own.
     
  13. eburacum45 Valued Senior Member

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    Here's a little sci-fi thing I did a few years ago about an ecosphere evolved from terraforming biomorphs
    http://www.orionsarm.com/eg-topic/48027affd38eb
     
  14. eburacum45 Valued Senior Member

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    • Not necessarily. Life may arise on planets quite unlike our own, and have very different biochemical basis. See this on-line book
      The Limits of Organic Life in Planetary Systems

      Even a biosphere which has a fairly similar chemistry to our own may have a different atmopheric density or different gravity, so humanoids would be unlikely to evolve there.


      Possibly a high fraction of intelligent lifeforms may have bilateral symmetry, but by no means all of them. Radial symmetry is good for many environments.
      A reasonably high fraction of intelligent lifeforms may have binocular vision, assuming they evolve eyes in the first place. Eyes appear to have evolved only once on this planet;
      http://www.sciencenews.org/sn_arc97/5_10_97/bob1.htm
      they may not evolve in the same way on other worlds (for instance they may emerge from heat-sensitive organs instead of light sensitive organs).


      There are no members of the phylum 'vertebrata on any other planets.
      http://en.wikipedia.org/wiki/Vertebrate
      There may be organisms which vaguely resemble the vertebrates of Earth but they will have evolved from completely different ancestors, and have many differences when examined in detail.

      Certainly manipulators of some sort are very likely to be part of an intelligent species toolkit; but they may not take the form of anything we call a hand.

      Any idea that the humanoid form is commonplace is based on post-hoc reasoning; when we finally get to examine alien species I expect we'll find a fantastically wide variety of bodyplans among intellegent creatures.

      Even if we are lucky enough to find a few vaguely humanoid types, they will look so different to humans in detail they will probably be even more disturbing than most non-humanoid forms.
      http://en.wikipedia.org/wiki/Uncanny_valley
     
  15. granpa Registered Senior Member

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    vertebrates, arthropods, & molluscs correspond to the 3 modes of moving used by worms:wriggling, walking, & sliding.
    This is suficiently basic that I would assume that it would evolve on any planet.
     
  16. eburacum45 Valued Senior Member

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    Wriggling forms are likely to be very common, leading to many mobile heterotrophs which vaguely resemble a worm, in the same way that a nematode resembles a snake. But there are many differences between a snake and a nematode.

    Walking forms are likely to be very common, but even on Earth the diversity of walking forms is very great. A millipede does not closely resemble a deer.

    Sliding forms are likely to be very common, but there is very little resemblance between a snail and a slime mold, when you examine them closely.

    Swimming forms are likely to occur on many worlds, but a bony fish only vaguely resembles a giant squid, which only vaguely resembles a box jellyfish.

    There may be superficial similarities between creatures occupying similar niches on different worlds, but when examined closely the differences will be very great in most cases.
     
  17. Dinosaur Rational Skeptic Valued Senior Member

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    Unlike Mathematics, physics, & chemistry evolution does not follow laws providing precise descriptions of its effects.

    However, there are some basic principles which are applicable. For example.
    • Radial symmetry is a reasonable design for an aquatic enviroment, but not very suitable for flying creatures or land lubbers. Bilateral symmetry is more suited to the latter two types of creatures.

    • For creatures larger than insects, more than 4 limbs does not improve running or jumping ability much (if at all), while requiring extra energy resources, more neural circuitry, & extra brain cells.

    • An appendage capable of holding a stick is a precursor to the evolution of intelligence.
    I think that many who are posting to this thread are too influenced by SciFi literature & have not spent much time applying some analysis to the issue.
     
  18. Neverfly Banned Banned

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    Dinosaur,
    This is a much better post than the one I had replied to earlier. Probably because you removed the detailed assumptions and focused more on the logical assumptions in this post.
    It almost made me feel a wee bit foolish for having jumped on your back earlier.

    Please Register or Log in to view the hidden image!


    Nonsense.
    Star Trek is an excellent resource for what to expect out there.
    Especially the Vulcans.
     
  19. eburacum45 Valued Senior Member

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    Nothing you have posted so far suggests that an alien biosphere will closely parallel that found on Earth.

    There are no mammals on any planet apart from Earth, and there won't be unless they are taken there by spacecraft. There may be organisms that resemble mammals, but they will have many differences, some of which will be easily noticable.

    There are no vertebrates on any planet apart from Earth, and there won't be unless they are taken there by spacecraft. There may be organisms that resemble vertebrates, but they will have many differences, some of which will be easily noticable.

    There are no insects on any planet apart from Earth, and there won't be unless they are taken there by spacecraft. There may be organisms that resemble insects, but they will have many differences, some of which will be easily noticable.

    Strictly speaking there are no members of the domain/kingdom 'Animalia' on any planet apart from Earth, and there won't be unless they are taken there by spacecraft. There may be organisms that resemble Animalia, but they will have many differences, some of which will be easily noticable.

    There are no humans on any planet apart from Earth, and there won't be unless they travel there by spacecraft. The chances of any intelligent alien species resembling humanity in more than a few repects are very remote indeed.
     
  20. eburacum45 Valued Senior Member

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    Bilateral symmetry may be a very widespread bodyform, I agree. But even on Earth bilateral symmetry produces a very wide range of creatures, such as the amphisbaena, the robber crab and the antelope. If alien creatures are as diverse as that, I would gladly accept that bilateral symmetry is advantageous.

    But a radially symmetrical organism could not only function on land, but could thrive, and even become intelligent, in some circumstances, especally if they are well provided with manipulatory appendages (see below). Note as well that many plants have neither bilateral or radial symmetry, but are instead branching organisms; even mobile branching organisms could thrive on land and become intelligent under certain circumstances.

    Why do so many arthropods have so many limbs, in that case? The reason tetrapods don't have more limbs is due to their evolutionary history. Large land animals with extra limbs would not only be viable, but may often have an advantage; so much so that some large animals (such as elephants) have evolved extra appendages from non-limb structures.


    Agreed. But that appendage need not resemble the modified tetrapod walking limbs that hominids use; it could evolve from a proboscis like an elephant's, or from modified mouthparts, or from muscular arms or tentacles as used by octopoids and squids.

    Don't be misled by science fiction like Star Trek and Star Wars; if we ever get to another planet with a complex biosphere, many or most of the organisms there will only bear a vague resemblance to anything on Earth.
     
  21. Fraggle Rocker Staff Member

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    And the primates. Interesting that the most advanced primates (the apes) lost their tails.
    And only if the atmosphere, temperature and other environmental conditions resemble Earth's. If life evolves in a non-planetary environment we might not even recognize it! Even the writers of Star Trek eventually got around to admitting that.
    The pinnipeds are among the most intelligent of animals and all their appendages are good for is swimming. The cetaceans are probably second only to primates in intelligence, and they've lost two of their appendages.

    The psittacines (and a few other avians) can hold a stick with their zygodactylic feet, but the other highly intelligent birds, such as the corvids, have to settle for doing it with their beaks.
     
  22. Neverfly Banned Banned

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    How about technology?
     
  23. Fraggle Rocker Staff Member

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    There's considerable speculation that at least several species of cetaceans have already invented language. Each individual has a unique name and each pod has a unique song that might be something like a war cry or a national anthem.

    Language is a key technology--unto itself--because it vastly increases the ability of individuals to plan, cooperate, report and pass down learned knowledge. Even without hands, a group of dolphins could manipulate materials by several of them grabbing it with their mouths.

    One of the candidate dates for the invention of human language is some time before 60,000BCE. That was when the first successful migration out of Africa finally occurred. Humans are adventurous and surely it had been tried before. Perhaps the quantum improvement in our ability to plan, organize and manage the trek is what made the difference.
     

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