Extremes of Size in Living Things

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Bart Stewart
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Extremes of Size in Living Things

Postby Bart Stewart » Tue Jan 19, 2010 1:26 am

I was just pondering whether or not there is a maximum size that a living creature can attain. Let's say extraterrestrial life forms, with a planetary environment suitable for great size. Theoretically, how large could a life form become? Is there a limit?

I've heard that the giant insects in 1950s sci fi movies could never exist, because their exo-skeletons would break up under the weight. The dragonflies of the Cambrian era represent the top end for insect size. Anything bigger needs an interior skeleton. The Blue Whale is apparently the biggest animal that our earthly environment can produce. Or is it possible that bigger things existed at one time, and we just don't have the fossils for them? Actually there is an immense underground fungus that some consider to be the world's biggest living thing, and then there are the living coral reefs.

For maximum giganticism I would assume there is a balance that must be struck between the area of a planet and its gravity. For creatures of maximum size, you would need a planet big enough to allow space for them to attain great size, and yet not be so big that the gravity is too great to allow life to evolve. Of course this takes us into the controversy of "Life as we know it," meaning extraterrestrial life might be more alien than we can imagine, and might not be constrained by what we consider impossibilities.

Here we get into more subjective areas. The Gaia hypothesis you recall held that the Earth itself should be thought of as a living system, at least at its surface. It is all made up of interlocking eco-systems, like living parts of an organism, so the Earth should be thought of as an organism. (Not saying I agree, just floating their idea.) If there is any validity to that notion then the question arises, "Would we recognize a creature of sufficient size as being alive?"

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Re: Extremes of Size in Living Things

Postby vanderpoel » Tue Jan 19, 2010 2:24 am

Not sure, but I think guys like Gawd and BigTim might have heard this too:
"You're just too big".

Oh and let's not forget Ruben. They don't call him the King for nothing!
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Re: Extremes of Size in Living Things

Postby Aztexan » Tue Jan 19, 2010 3:04 am

awww shucks you :oops: me
This is a sentence. tHi5 iz a seN+3nce oN drUgs!!!

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vanderpoel
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Re: Extremes of Size in Living Things

Postby vanderpoel » Tue Jan 19, 2010 3:14 am

ruben lopez wrote:awww shucks you :oops: me

te nada
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Matthew Ellard
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Re: Extremes of Size in Living Things

Postby Matthew Ellard » Tue Jan 19, 2010 3:57 am

Bart Stewart wrote:I was just pondering whether or not there is a maximum size that a living creature can attain. Let's say extraterrestrial life forms, with a planetary environment suitable for great size. Theoretically, how large could a life form become? Is there a limit?


I don't think there is anyway of knowing. My only guess is that whales have neutral weight in water and this may hint that extra terrestrial life forms may use a similar trick if very large.
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Re: Extremes of Size in Living Things

Postby bigtim » Tue Jan 19, 2010 5:18 am

I suppose if the creature were anaerobic and could survive the hard vacuum of space then there is no limit...

The math for giant insects is true, it's due to the square/cube ratio. As the size of the animal increases by the square the volume increases by the cube and thus it's inteneral weight to the point of cracking the exoskeleton.
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Re: Extremes of Size in Living Things

Postby Matthew Ellard » Tue Jan 19, 2010 6:27 am

bigtim wrote:I suppose if the creature were anaerobic and could survive the hard vacuum of space then there is no limit....


Well done. I didn't even think of that.
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Re: Extremes of Size in Living Things

Postby Harry_rr » Sun Jul 18, 2010 10:35 pm

Depends on atmospheric pressures, gravity, structure of the life forms, and many other things. Animal life as we know it may have limitations. But, is that the only possibility? There is nothing that keeps life forms from being made up of structures as strong as tree trunks. It all depends on the structure of the cells that makeup the life forms. In another world, with much greater gravitational forces, we can still expect life forms to evolve to survive there. It all comes down to whether something like a single cell organism can evolve to survive in different environments.

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Re: Extremes of Size in Living Things

Postby Gord » Mon Jul 19, 2010 2:00 am

Size limits are interesting. They'll depend on physics. There will be a minimum size; anything smaller than that would be incapable of displaying enough characteristics to match a definition of "life." (We'd have to reach an agreement on that definition at some point, too.)

Likewise, anything that gets too big risks the danger of collapsing in on itself. Can a star be alive? What about a black hole? One could imagine something galaxy-sized, spinning around its centre, not collapsing -- but to maintain this spin, the parts would probably need to maintain independence (no physical ties), and can life operate over such distances, or individuality be defined in that way?

I can imagine a planet where the entire crust might be one individual life form, with other life forms living on its surface. But then we could ask how deep that massive life form could survive beneath the surface. Surely the mantle would not be able to sustain the same life form that lives at the surface, could it?
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Re: Extremes of Size in Living Things

Postby Bart Stewart » Tue Jul 20, 2010 2:32 am

Gord wrote:Size limits are interesting. They'll depend on physics ...
I can imagine a planet where the entire crust might be one individual life form, with other life forms living on its surface. But then we could ask how deep that massive life form could survive beneath the surface. Surely the mantle would not be able to sustain the same life form that lives at the surface, could it?


I'm thinking you're right that the environmental differences in the crust and mantle would be too much for one life form to comprise both. Deep sea life cannot exist at the surface, and vice versa.

Thinking about size limits raises the Gaia notion, where the surface of the Earth is considered one big interacting life form. It's a different perspective, that's all. I heard a scientist on the radio once who said we should consider social insect colonies to be single organisms made up of individual insects. I don't feel compelled to agree, but I'm not violently opposed to the idea, or that of Gaia.


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