I think it's more compelling, however, to just think about how much bigger the interior of the planet is than our existence at the surface.

We live on maybe ±1km of the surface or so; we don't dig much deeper than that except perhaps when exploring very deep caves or so. The radius of the Earth is approximately 6300 km. One volume is (4 pi/3) R^3 and the other is 4 pi R^2 dR, so the one volume is larger by a factor of 6300/3; we can only hope to visit one two-thousandth of the Earth's total volume with holes 1km deep. Up that to 10km deep and you'll still only get one two-hundredth of the Earth. Oh, and we've only got about a third of that because oceans.