planet

Continental crust

The light, silica-rich crust — andesitic to granitic — that makes up continents and floats high above the denser ocean floor. The interesting part is where it comes from: you cannot make granite in any volume by melting dry mantle rock. You have to remelt basalt with water involved, and the setting that does that at planetary scale is a volcanic arc above a subducting plate. Which means a continent is not merely a kind of terrain. It is a statement that the planet has water, and a crust that moves.