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?"