1. GrandJury
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    GrandJury Member

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    Evolution on alien worlds

    Discussion in 'Plot Development' started by GrandJury, Mar 28, 2016.

    Hello,
    I am wondering how life would evolve on a world that has 3x the gravity of Earth. Its covered with oceans and has large continents, varied climates, unique physical features, so aside from the gravity/size its in many ways very earthlike.

    Its likely they would be shorter, stockier and stronger yes?

    Thank you
     
  2. Robert Musil
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    Robert Musil Contributing Member

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    Yes. Though it's hard to get much more specific than that, if we don't know anything besides the gravity.
     
  3. tonguetied
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    tonguetied Contributing Member Contributor

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    Quite possibly life would evolve further in the ocean environment than ours has since this would compensate for the extra gravity. Land bound creatures would have to be smaller or made up of a much stronger skeleton form than mammals on Earth, exoskeleton creatures might be dominant; especially considering 3x gravity means higher density atmosphere, assuming similar to our own atmosphere composition. Another factor that might come into play is distance to the sun, I think larger planets usually are further from their orbiting sun due to mass creating orbiting issues closer in, but that is just conjecture on my part.
     
  4. Witchymama
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    Witchymama Active Member

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    I am thinking that if the gravity is 3x that of Earth that there are other things besides just the evolutionary things to consider, like weather. Something like rain, which on Earth can be strong enough to wash out river banks and the like, would on the world you describe have the potential to be an outright destructive force. In my mind this begs the question, how do the inhabitants deal with weather? What has evolution given them to compensate? I mean if the planet is Earth like, how do they deal with something like hail? Here in the south we sometimes have hail storms that damage buildings and vegetation. How would 3x gravity effect that?
     
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  5. HelloImRex
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    HelloImRex Contributing Member

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    Amount of oxygen in the atmosphere matters more than gravity with organism size on Earth. Sure, there's a limit, but something as large as a dinosaur can walk around on land without gravity troubling it. All the animals now are at least 3x smaller (okay, gravity would stress 3d stuff exponentially, i get that, i'm just ignoring it, i'm not sure 9x smaller is exactly right either) so there's nothing saying the animals on this planet couldn't be the same size as stuff on Earth. The constraining factor is more likely to be the amount of food something has to eat, the amount of air it has to breathe, and others things like that.
     
    Last edited: Mar 28, 2016
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  6. Wreybies
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    Wreybies The Ops Pops Operations Manager Staff Contest Administrator Supporter Contributor

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    The size of arthropods (external skeletons) is definitely tied to levels of free oxygen. At least on Earth they don't have a pulmonary system that allows them to grow to larger sizes unless there's much more oxygen present than today. We know they were much larger in the past and that oxygen levels were correspondingly higher. There's an upper limit to the structural strength of the material they use for their exoskeletons that doesn't allow for anything super-gigantic, but they can be a lot larger than what we have today with more O2.

    And the size of some of the larger dinosaurs is a good example that, yes, you can have a creature with a body plan not too different from what we know and still cary some serious tonnage.

    With that said, even on Earth, body plans on the land tend to be horizontally oriented, rather than vertical. That strange ape known as Humans is one of the exceptions, not the rule. Even if you can grow a body that's taller than it is long, it makes more sense for it to grow sideways rather that up. If the gravity is higher, I think this would be even more of a limiting/guiding factor. It wouldn't necessarily mean that everything has to be like a centipede, but I would think a horizontal body plan would be even more favored than it is on Earth, where such a body plan is already very favored compared to other layouts.
     
  7. Seraph751
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    Seraph751 If I fell down the rabbit hole...

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    Check out deep sea marine life as the pressure is much greater than the gravity we people deal with everyday.
     
  8. GingerCoffee
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    GingerCoffee Web Surfer Girl Contributor

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    Pressure and gravity are two different forces @Seraph751. A creature can compensate for pressure by having internal and external pressures equalized.

    Despite the fact a large animal can compensate for the increased weight it experiences, gravity still affects the way life evolves. But there are also means of neutralizing gravity such as the buoyancy that allows whales (and other water creatures) to overcome gravity. At some point gravity is going to limit the size birds might get the same way animals with exoskeletons are limited by the concentration of oxygen in the atmosphere.

    The point is not that life cannot evolve under these different conditions, but rather how would the conditions affect evolution. So for example, very large dinosaurs needed circulation boosters to overcome the effect of gravity on circulation.

    Of Barosaurus and Blood Pressure
     
  9. Miller0700
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    Miller0700 Contributing Member

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    Life there may be gelatinous to thrive in such strong gravity compared to Earth's gravity. Any lifeforms with a skeletal structure may have very thick and strong bones to makes sure they don't simply explode by walking under the sheer weight. Think elephants and their bones. Life there may be short in stature because it'll take a longer time for blood to reach important regions such as the brain under such intense gravity.

    I think the majority of life will be in the oceans.
     
  10. GingerCoffee
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    GingerCoffee Web Surfer Girl Contributor

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    From the single example we have (Earth), it appears more like life naturally evolves to fill any and every niche it can possibly exploit.
     
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  11. GingerCoffee
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    GingerCoffee Web Surfer Girl Contributor

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    One thing I've done on my ET planet is consider a couple basics: Life needs a means of sensing its environment and a means of locomotion. Life needs fuel, and a mechanism for releasing the energy from food and maintaining homeostasis (kidneys, liver, digestive organisms, breathing, blood stream, brain and nervous system). Think about the basics and then look at how life evolved on Earth from some of the first precursor lifeforms.

    So for some examples, vision and flight evolved twice, with some overlap. Dark skin in humans evolved twice, first in Africa. Then as people migrated north skin lightened and then it darkened as people migrated back toward the equator in the Americas.

    There are precursors to hands, feet and limbs in fish. So was there a single life form that we coincidentally evolved from or were fins and limbs inevitable?

    Insects all have the same model of six appendages, that in some insects grow antennae where others using the same precursor model develop legs and some developed wings all from the initial basic form.

    Prey develop wide vision, predators develop 3D vision and you can see this in the position of the eyes in many species. But every once in a while you get something completely different.

    How many eyes does a spider have?

    Marvelling at the Eyes of a Jumping Spider

    Mix and match, keep the basics in mind (locomotion, sensing, metabolism and circulation).

    And reproduction, forgot to add that one. Also consider how lifeforms might be synergistic like the birds that keep lice and ticks off large animals.

    One last thing to consider, how the flora evolve will affect how the fauna evolves as well.

    Create your own biospheres, consider latitude and the effect of mountain ranges and deserts on climate.

    Sorry, getting carried away. I'll stop here.
     
  12. Cave Troll
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    Cave Troll Bite the bullet, do your own thing. Contributor

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    I will admit cheating a tad (probably one of the few who will), when it comes down to evolution of my Aliens. :D

    With that out of the way, you have many possibilities to go on. The creatures would be low to the ground, or short and have possibly extra limbs to help them get around (think like insects but with bones instead of exoskeletons). Next what is the core (base) element that comprises the creatures? Are they carbon or silicon based? Each has its strengths/weaknesses. Elevation is also a factor as the higher you get the elements and pressure on them is different. You could even have floating jellyfish like creatures with gas filled bladders that allow them to float, instead of wings. Alternatively you can have slender creatures that have less mass to have the gravity affect them as much. Though a dense skeletal/muscle structure will make this a tad easier on their frame. Oddly enough you can have a highly advanced giant amoebas, or something that can travel without having a 'solid' body. Just a few ideas, but hey their are a lot more reasonable explanations from the other lovely people who have already commented. Good luck. :)
     
  13. tonguetied
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    tonguetied Contributing Member Contributor

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    A lot of unique thoughts about this and Cave Troll's amoeba concept made me think that what if the advanced life form was stationary, like a tree? Some trees simply stack on top of old growth that provides a supporting structure and I believe there is evidence that some trees can signal each other with the release of chemicals when attacked by some pests so communication is already possible on Earth. With your story the 'ground is the limit' (3x gravity makes the sky less likely :) ) so you can go in any direction you want. Having an intelligent life form that is not mobile may sound more fantasy than sci-fi but I see no reason for that to be the case. It would be hard to see how an immobile life form could make things so maybe they are just deep thinkers, the philosopher tree species. Of course pill bugs that could roll from place to place would interesting IMO.
     
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  14. Wreybies
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    Wreybies The Ops Pops Operations Manager Staff Contest Administrator Supporter Contributor

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    Another thing I was pondering yesterday as regards this thread...

    Right now, we have only one example of a planet with life: our Earth. At this point we have no idea what the range is for planets that have life as regards gravity. Wouldn't it be funny if, in the grand scheme of things, Earth were regarded as a "high gravity" planet compared to the rest?
     
  15. GingerCoffee
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    GingerCoffee Web Surfer Girl Contributor

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    The hometrees in Avatar had some form of spirituality.

    Life on Earth is plenty strange:
    Chytrid fungus '40,000 years old'
     
  16. GingerCoffee
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    GingerCoffee Web Surfer Girl Contributor

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    Swimming in the atmosphere also comes to mind, not flying but having some kind of buoyancy in the air. Such creatures might live in the atmosphere of gas giants.
     
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  17. Wreybies
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    Wreybies The Ops Pops Operations Manager Staff Contest Administrator Supporter Contributor

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    Exactly. We ponder this idea of 3x greater gravity and what it would mean for life, but what if we're the hulking, stocky, big boned, brutes of the universe? :ohno: :-D


    ETA: In David Brin's Uplift Universe, he uses the idea of sentient beings from gas giants as a kind dividing line. Beings evolved on terrestrial worlds don't mix with those evolved on gas giants. He makes them quite the mystery. :)
     
  18. ToeKneeBlack
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    ToeKneeBlack Contributing Member Contributor

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    The main effect is most life would be shorter. A tree can only grow as tall as it can push water up from the ground, so no giant redwoods. Additionally, a human heart (for example) has to create more pressure to push blood higher when compensating for gravity. Shorter animals can get by with lower blood pressure.

    Overall you would see shorter, wider and longer creatures than on earth. Rain and hail stones would be dangerous, so animals with tough skin or exoskeletons would do well, though these wouldn't be needed as much in the oceans where buoyancy counters gravity and the water protects from rain and hail. Water pressure would be higher in the depths of the oceans.

    Atmospheric pressure would also be higher, resulting in higher boiling points for liquids. It also increases the melting point of most solids, except for water, which has a lower melting point at higher pressures. Assuming similar temperatures to earth, there would be less ice on the planet. This would result in more oceans and smaller land masses.

    Flying animals would face huge challenges, and may not evolve at all.
     
  19. Robert Musil
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    Robert Musil Contributing Member

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    I'm not sure that the relationship between surface gravity and atmospheric pressure is that simple? Saturn's moon Titan has a surface gravity of only 0.14 g but its surface atmospheric pressure is 146.7 kPa, about 40% higher than Earth's. Likewise Venus has slightly less than 1 g on the surface but its atmosphere is much thicker than Earth's, and Mars has over 1/3 Earth's gravity but its atmosphere is less than 1% as thick.

    There's just other factors that come into play--for example, Mars' atmosphere has been stripped by solar winds due to its lack of a magnetic field.
     
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  20. Cave Troll
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    Cave Troll Bite the bullet, do your own thing. Contributor

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    Who are we kidding Tardigrades will inherit the universe and have trillions of miniature outposts all over the darn place. :p
     
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  21. GingerCoffee
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    GingerCoffee Web Surfer Girl Contributor

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    I thought this was useful:
    Writing Sci-Fi? First Understand How Elephants Aren't Dragonflies (Op-Ed)
     
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