The Earth's crust is the outermost solid layer of the planet, forming a protective shell that encompasses the continental and oceanic landmasses. Compositionally, it is primarily composed of solid rock materials, including silicate minerals such as quartz and feldspar. This layer is subdivided into two major types: continental crust, generally thicker and less dense, and oceanic crust, which is thinner and denser. The physical dynamics of the crust are governed by the movement of tectonic plates, large segments of the lithosphere that interact at boundaries. These interactions—including divergence, convergence, and transform movements—are responsible for major geological features such as ocean trenches, mountain ranges, and deep-sea rift valleys, and represent the fundamental driving force of plate tectonics.