Brings it "home" doesn't it? Spaceship earth and how limited its life support supplies are.

I suspect equally instructive would be if someone was to make a calculation of the useable TOPSOIL available - I'm not sure if one would want to try and split this into two piles, one for arable use, and total topsoil still "wild", or perhaps further subdivide topsoil used for arable, and that which could be used for arable, and then areas that support lots of life but don't have much in the way of "useable" (by humans) topsoil (I gather a lot of rainforests are of this nature, an intricate house of vegetative cards erected upon some pretty leached out and thin material, all recycling nutrients like mad to keep going).

And then there would be the ball that makes up the topsoil being destroyed by inappropriate human activity - run off, windblown, soil structure destruction through overexploitation and chemical fertilisation that doesn't contribute humous, and so forth.

Then we'd get an idea of what little of the thin skim of skin is left...

If anyone can dig out a link or work on visualising this as well as the air and water it would make a very impactive graphic indeed! I wouldn't know where to start.