Plate tectonics is the scientific theory that explains how the Earth's outer shell, or lithosphere, is divided into large, moving pieces called tectonic plates. These plates float on the semi-fluid layer beneath them, known as the asthenosphere. The movement of these plates is driven by forces such as mantle convection, gravity, and the Earth's rotation. The interactions between tectonic plates can lead to various geological events. For example, when plates collide, they can create mountains or cause earthquakes. When they pull apart, they can form new oceanic crust. Understanding plate tectonics helps scientists explain the formation of many features on Earth’s surface.