can refer to the outer layer of a planet
, its lithosphere
. Planetary crusts are generally composed of a less dense
material than that of deeper layers. On partially-molten planets, such as Earth
, the crust is floating
interior layers. Such floating crusts are often broken into tectonic plates
that, because of fluidity underneath, can move (see continental drift
Crust can refer to the outer edge of baked bread or the shell of a pie.