I am creating a fantasy world where a given race is mystically tied to the planet. Predominately this race will be earth-dwellers, quite happy and content to burrow underground, but I'd like some of the race to be happier in the sea. The world is very Earth-like, so it works as a good model.
I know that the Earth's surface is covered by 71% water and roughly 10% by ice. And I know the Earth is about 0.023% water by mass, but that's a comparison against the total mass of the Earth. Neither of those figures however are what I'm after; surface area gives too large a percentage and the total percent by mass is probably too low.
So, the question is how much of the Earth's crust water by mass? As in what is the mass of the oceans, seas, rivers, and so on, compared just to the stones and rocks that make up the surface of the planet: the continents, sea-floors, and everything down to the mantle? I'm not even sure I'd know where to begin on that calculation, so even a rough ballpark would be helpful.