The hydrosphere is a theoretical water barrier which filters out deep space radiation. You see when the core remade the earth it was smart enough to install a "water barrier" around the entire planet, this barrier consists of a vast amount of pure water which surrounds the entire planet much like the ozone layer only without holes or weak spots. It is in just the right spot outside our atmosphere (the sweet spot) where it is held in tension between its mass expansion attribute and the attraction of earth's gravity. So there it holds position neither drifting into space nor being pulled down into the atmosphere.
Is it spinning? I have no idea, maybe, I don't think that's important. In the space shuttle when they are up in space and an astronaut spills some water it forms into a glob, and if left undisturbed it forms into a sphere. similarly so in space the water barrier forms into a bubble of an exact consistent width all the way around. The effect of the water barrier is manifold. First off it protects the earth and its inhabitants from harmful ambient cosmic radiations. Second it acts as a kind of lens that warps light from the outside, both reflecting off of the inner surface and extending the range of illumination so that more of the planet is exposed to light at once. I cannot describe the overall effect, but it's a good thing, the space where there is darkness is very small in comparison to what we are accustomed to, this causes the total environment of all earth to be different, meteorological conditions are more stable, temperature variations are very slight.