The outer layer of the Earth is known as the crust. This rigid layer varies in thickness and composition, comprising landforms like mountains, valleys, and ocean floors. The crust is mainly composed of rock and is divided into continental crust, which forms landmasses, and oceanic crust, which underlies the ocean basins. It serves as the surface on which we live and is critical for various geological processes, including the movement of tectonic plates. The Earth's crust is relatively thin compared to the underlying mantle and core, making it a dynamic and constantly changing environment due to geological activity.