Hi, Guest from Sanity. I enjoyed your quips.

Re: How much deeper would the ocean be without sponges?

I think this one has it backwards. If you took all the sponges out of the ocean, they wouldn't be taking up space any more, so the water level would drop and the ocean would be shallower, not deeper. (Notice that the question doesn't ask about removing sponges plus the water they contain.)

As for gravity, for me physics becomes less and less real all the time. Space-time, for example. I accept that it's true, but it's not real to me. I guess I'm Newtonian at heart. Goes with liking I,IV and V chords.