The deepest borehole ever drilled is just over 12km, it's 6371km to the Earth's core. If the Earth was the size of a basketball that would get you around 1/8th

The deepest borehole ever drilled is just over 12km, it's 6371km to the Earth's core. If the Earth was the size of a basketball that would get you around 1/8th of a millimeter into the surface. The reason geothermal's easier in Iceland is that the heat's close to the surface, so you can get away with shallower boreholes. I'd think the overall effect would be trivial either way, but I don't see how the thickness of the crust would make a difference.