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Extraterrestrial Species

  1. Apr 27, 2010 #1


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    Every time I'm out in nature looking at the birds, snails, frogs, fish, plants and other wildlife I get this 2 part question going on in my mind.

    1. On a planet like our own in orbit around a sun not unlike our own.. would the wildlife have similar features? Would there be "robins" and "thrushes" and eagles... carnivores, and herbivores and would the squirrels have the same tail or would there be squirrels at all?

    2. If an extraterrestrial person came to our planet, would all of our wildlife and natural environment seem familiar to them? Or would they not recognize most of what we call the "great outdoors"?

    If there are some answers among you, as speculative as you like... but based on scientific observations and calculations... please enter them here! Thank you.
  2. jcsd
  3. Apr 28, 2010 #2
    I think a better question is whether life on that planet would bear any resemblance whatever to anything that has ever existed on earth. Our fossil record shows that the forms of animal life don't stand still, they're in constant flux. There are animals that existed at various times that you don't even know about because those periods haven't been popularized. No telling what microscopic animals have existed that we'll never know about. The early simple life forms on that other planet might end up evolving along completely different lines such that the dominant kind of life for millions of years would be huge, mobile, blobby plant things that "eat" everything in their path; all the immobile, rooted plants, such that anything vaguely reptilian, birdlike, or mammalian never gets a chance to flourish and evolve larger in size, there being very little to eat in the wake of the giant cannibal plants.
  4. Apr 28, 2010 #3
    I assume you mean in the entire evolutionary history of two appropriate planets, were there ever similarities between the life forms.

    Life is massively contingent and as such it's evolution is greatly affected by it's history. Our world is also massively non-linear and sensitive to initial conditions. Finally, evolution is constrained by chemical and physical laws: you can only be so heavy and be successful with wings. I believe the first two factors would cause great variation between planets and the thirid, significant chemical similarity. Personally, I do not believe non-carbon-based complex life forms is possible. Once that is assumed and starting with sufficient chemical complexity, luck, and an energy source, proteins and nucleic acids follow and ultimately the process of Natural Selection leading to life forms on other habitable planets, chemically similar to earth life, but quite different in phenotypes because of non-linear effects.
  5. Apr 28, 2010 #4
    I would place bets that at a certain point in development for all intelligent species there comes at least one fork in the road where they decide whether or not to rebuild themselves. Once that happens their original biological form is moot and not worth talking about since they could adapt to any environment their technology allowed and lose their original form altogether.
  6. Apr 28, 2010 #5


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    Jackmell has done an excellent job of pointing out some of the parameters involved in the development and evolution of extraterrestrial species.

    I know my second question involves seeing our planet's species through extraterrestrial eyes but I'm trying to stay away from the "intelligent species" idea and to focus on the differences and similarities between terrestrial and extraterrestrial flora and fauna.

    Jackmell points out that a planet with a slightly different g force may either give rise to or prohibit species that can fly. Of course, as adaptable as biological life is, a flying species would either evolve a lighter body or bigger wings in some cases. These sorts of conditions and adaptations are exactly what I'd like to see discussed. Colouration and how it can define species and sub-species is another.
  7. Apr 28, 2010 #6
    I don't know about gross anatomy here, but I think we can expect some similar features IF a particular trait arose. What I mean, is this: No one can really say whether flying or burrowing species will evolve, but IF they did, we can then make some predictions I think:

    1: Scales, Feathers, Carapace, Skin: If life as we understand it exists and it can fly, we can reasonably expect structures similar to flaps of skin, feathers, scales, or insectoid features. Even if we're talking about radically different biology, the physics of flight remain unchanged (on a similar world).

    The need for defense against the elements might or might not be significant, but any complex organism is going to have a partition between itself and its environment. That might be a jellyfish's bell, or armadillo armor, or even silica plates! It doesn't matter.

    If there is a contrast in light vs. darkness, it would seem impossible for it NOT to be advantageous to have means to sense that. How that's accomplished could be myriad, from something like sight, to an EM sense, or temperature senses.

    Scent is up for grabs, but anything that eats needs a way to determine what is food, and what is not. Smell, taste, sight, touch, sonar, radar, and other options still represent another sense needed to navigate the world of what is or is not food.

    So, I don't know if you can say with current knowledge that a given form of life will evolve, but if it does (and we're not talking about something swimming in Jupiter's atmosphere or something equally exotic) we can probably expect basic functions to be filled.

    That said, I think Zoobyshoe has the right of this, and it's more likely we wouldn't recognize alien life at all. If it followed thermodynamic processes familiar to all life on earth (eat, excrete [heat or other]) we'd have a chance. Then again, maybe we'd conclude that the silicate equivalent of a plant was a crystalline formation?
  8. Apr 28, 2010 #7


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    From the examples of convergent evolution it seems safe to say that an earth-like planet would produce a reasonably familiar story no matter how many times evolution was re-run.


    This is a standard example of the power of downward-acting global constraints in systems thinking of course.

    If the global constraints are the same, local evolutionary accidents can only wander about so far in what is invisibly perhaps a constricted phase space of possible outcomes.
  9. Apr 28, 2010 #8
    I think it would have to be Earth, not just Earth-Like. Once you change major issue such as long-term climate patterns, and change the history of its impacts, I don't believe that convergent evolution other than (maybe) enzymatic and metabolic pathways would necessarily be similar. It isn't hard to imagine a hotter, oxygen rich "Earth" in which insects and plants dominated all other species before reptiles or mammals could evolve.
  10. Apr 29, 2010 #9


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    But exoskeletons are such a constraint on size that endoskeletons would surely arise at some point. Then away we go.
  11. Apr 29, 2010 #10
    They are a constraint on size, based on the availability of (in the case of Earth) Oxygen. Besides, add a few more G's, and maybe being BIG isn't all it's cracked up to be. Remember, a big creature needs a big biosphere to feed on, but that might not be possible. A highly coordinated group of smaller organisms, such as ants, seems to be effective. I can see how endoskeletons would be advantageous in some forms, so I'm not saying the idea is outrageous or anything like that. I don't think it's a forgone conclusion however. If this other Earth is subject to frequent bombardment beyond what our planet is, then larger life might not be advantageous at all. If life in that planet is subject to more extreme changes in temperature, or the need to be in oceans or underground for much of the time, then endoskeletons start to look a bit unhelpful.
  12. Apr 29, 2010 #11
    Yup, so maybe organisms on other planets the size of elephants on Earth can 'fly' or maybe they can just float.
    Sure, no doubts here.
    Why do you make this assumption? I do not believe this is a correct or valid assumption to make from a scientific point of view. Can you back it up with sources??? What about life in an NO2 atmosphere... or NH3 atmosphere. It's been shown that P-N organisms could possibly develop in these situations. So why then should we dismiss the possibility and assume that carbon based life that we know and love here on Earth is the only possible way for life to rise?

    I'm not sure what you mean by 'habitable planets' I sure hope it's not another assumption about life in the universe necessarily requiring Earth-like conditions. I also don't agree that we should assume life on other planets should be chemically similar to what we have on Earth. Even assuming life elsewhere in the universe is carbon based why can't they use different amino-acids? I'm pretty sure we've even found amino-acids on meteorites... which are not (or haven't been) found on Earth...
    Last edited: Apr 29, 2010
  13. Apr 29, 2010 #12
    Other non-carbon aggregates may be possible but I do not believe they can attain any level of living complexity: containment, metabolize, reproduce, and evolve. I say that because of the chemistry of carbon:


    "There are two elements noted for their ability to form long strings of atoms and seemingly endless varieties of molecules: one is carbon, and the other is silicon, directly below it on the periodic table."

    http://astrobiology.nasa.gov/ask-an-astrobiologist/question/?id=144: [Broken]

    "Carbon is an ideal element for complicated living systems because it has four unpaired electrons enabling it to have four stable covalent bonds with other elements. With such bonding versatility, (not to mention the given abundance of carbon in the universe), carbon is able to form long chains, rings, and other complex molecules. Cabon-based molecules can take on many different forms from DNA and neurotransmitters to human hair and squid ink! No other element has yet shown the bonding versatility and stability of carbon, not to mention the property of self-replication unique to some carbon-based molecules. "

    Then that means to me we have only two choices for complex life forms: carbon or silicon. But silicon-based complex life forms are unlikely:

    Quote: http://www.daviddarling.info/encyclopedia/S/siliconlife.html

    "Conceivably, some strange life-forms might be built from silicone-like substances were it not for an apparently fatal flaw in silicon's biological credentials. This is its powerful affinity for oxygen. When carbon is oxidized during the respiratory process of a terrestrial organism (see respiration), it becomes the gas carbon dioxide – a waste material that is easy for a creature to remove from its body. The oxidation of silicon, however, yields a solid because, immediately upon formation, silicon dioxide organizes itself into a lattice in which each silicon atom is surrounded by four oxygens. Disposing of such a substance would pose a major respiratory challenge.

    Life-forms must also be able to collect, store, and utilize energy from their environment. In carbon-based biota, the basic energy storage compounds are carbohydrates in which the carbon atoms are linked by single bonds into a chain. A carbohydrate is oxidized to release energy (and the waste products water and carbon dioxide) in a series of controlled steps using enzymes. These enzymes are large, complex molecules (see proteins) which catalyze specific reactions because of their shape and "handedness." A feature of carbon chemistry is that many of its compounds can take right and left forms, and it is this handedness, or chirality, that gives enzymes their ability to recognize and regulate a huge variety of processes in the body. Silicon's failure to give rise to many compounds that display handedness makes it hard to see how it could serve as the basis for the many interconnected chains of reactions needed to support life."

    Also, "different amino acids" in my opinion is similar chemistry because of the amide bonds between them.
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  14. Apr 29, 2010 #13


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    This sort of reasoning also applies to many areas with reference to the conditions created by the type of sun and resultant light.. the abundance of minerals is also a factor and how its distributed. The atmosphere, as has been pointed out, could be any of the large number of variations possible with atmospheric gases. All these factors weigh, heavily, on the form and function of the evolutionary outcome, the species. About non-carbon based life forms. I've never met one, or if I have they didn't introduce themselves as such.
  15. Apr 29, 2010 #14
    You've been to other planets :/???
  16. Apr 30, 2010 #15


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    Not that I know of. I'm just saying that if a pool of methane is supporting life, I haven't recognized what its supporting as life.

    There are a series of questions we could work with to help understand what environmental constraints would produce what features of adaptation in extraterrestrial species. We already started this with the idea the gravity produced by each different planet will determine the sizes of the species and the form and function of any flying creatures.

    What if the planet were ultra rich in iron?

    What if the bedrock was pure quartz or another mineral rather than granite?

    There are so many variables. Would the stages of evolution be similar? Would there be a distinct division between plant and animal life?... etc...
  17. Apr 30, 2010 #16
    The biggest difference would be an element other than Nitrogen dominating our atmosphere. As it happens, undersea vents have shown bacteria which utilize methane. That said, all of this is constrained by the initial conditions of life on this planet, and the fact that methane isn't the dominant element here. A planet which was never hospitable to life based on a scaffold of carbon, filled with water, and breathing nitrogen (inert for us or not) would provide a place for those organisms to develop in more than a niche.
  18. Apr 30, 2010 #17
    Is is narrow-minded to think just carbon and similar biochemistry throughout the Universe? I'm tempted to think so just because it's so big and we're so small. But we're working with the same elements on the other side of the galaxy and other galaxies and those elements are still constrained by the same quantum mechanical properties we observe on earth.

    We're familiar with Punctuated Equilibrium but what does it really mean? In our Universe change is not smooth and continuous but rather "punctuated" by events which if reached, cause abrupt and dramatic change often resulting in qualitatively different behavior. It is the existence of these "critical points" which I believe is a major driving force in evolution.

    But since the universe is so non-linear, we can't expect the same sequence of event to happen in the same order anywhere in the Universe: on another planet just like ours, even after 4 billion years of evolution, there may still only be invertebrate-like creatures because events did not conspire to reach the critical points necessary for further evolution. Likewise, on still other planets, evolution may have gone further then on our planet.

    Still though I believe the limiting factors of chemistry will constrain the evolution of life on other planets to follow some similar patterns found on earth and so have some similar morphologies in their evolutionary history and quite similar biochemistry.
  19. Apr 30, 2010 #18
    I don't think it's narrow-minded at all, even if I don't agree. It's hard to imagine some of the forms of life that exist HERE on Earth, never mind novel chemistries or a Carbon Earth. I think it's fair to say that life based on the same compounds we find on earth would at least use similar metabolic pathways. I don't believe that holds at all for forms of life that might exist in extremes of temperatures and in elements we're simply not able to study here. I'd say this is a fine argument for more research in the lab of our solar system.
  20. Apr 30, 2010 #19


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    All in all I think your first statements are correct in comparison to later in your post... since the universe is non-linear there is nothing that says evolution would unfold in the same manner it has on earth. However, the only evidence of extraterrestrial species we have to date suggests that the beginning stages resemble what has occurred here on earth... when we look at the (proposed) fossil record of the planet mars.

    [PLAIN]http://blog.everythingdinosaur.co.uk/meteorite_mars_life.jpg [Broken]

    Again, however, mars is subject to the same radiation as earth from the same sun, and is probably composed of similar minerals, being from the same solar system.
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  21. Apr 30, 2010 #20
    That's a fair statement, which is yet another good reason to start firing probes to return samples sooner rather than later.
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  22. May 1, 2010 #21
    Agreed. Although, I stand by my original statement that it is far too early in the bioastronomy game to definitively say organisms can only be carbon based.
  23. May 1, 2010 #22
    I agree with that as well, and in fact I'm in you camp when it comes to belief that while carbon based life is possible, so is life based on other chemistry. The nature of their primary, their orbit, and initial conditions for life would be VERY critical. If life based on our scaffolding can't exist on a given planet, but another chemistry COULD dominate, not having to compete with ours changes matters.

    From the standpoint of evidence however, baywax has it.
  24. May 1, 2010 #23


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    Here's an answer from NASA to a grade 10 student who asked if life could exist on Europa (where the rain on the plain is methane).


    The basics for forming life as we know it seem too fundamental to try and compromise or switch and bait with. That's why I'm really more interested in the variety of life we'd see else where. The varieties and the determining factors that bring about that variety are a huge chunk to bite off... as it is
  25. May 1, 2010 #24
    Given carbon as the sine qua non of life, the next step would be to determine how many possible initial leaps there are from that which is just chemical to that which is life. It could be there's only one possible way, which means we could go to the next step and ask to what extent variations are possible from the first thing which is life to the next step. And so on. As more branches become possible you could start eliminating the ones that were taken on earth in order to arrive eventually at the most "alien" possible variations. In this way you could get a sketch of how very different life could be.
  26. May 1, 2010 #25


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    Good point Zooby... sorry I missed your first post on this thread.

    With regard to the two starting points of life on a planet... abiogenisis and panspermia... I like to try and calculate the percentage of probability for each beginning of life on a planet. What are the odds for "habitable planets" to be seeded with interstellar or inter planetary viruses or megabacteria and what are the odds for the same to support the actual formation of life... from scratch?

    For instance, earth may well have been an incubator for life that simply drifted here from mars... with mars being the site of abiogenisis... (as an hypothetical example).
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