a rigid layer of the Earth's crust that is believed to drift slowly
双语例句
The theory of plate tectonics holds that the surface of Earth is composed of a dozen or so huge crustal slabs that float on a sea of partially molten rock. 板块构造论认为，地球表面由十来个巨大的地壳板块构成，漂浮在浩瀚如海的部分熔岩上。
