Plate tectonics is the scientific theory that explains the structure and motion of the Earth's outer shell, known as the lithosphere. This theory posits that the lithosphere is divided into several large and small plates that float on the semi-fluid asthenosphere beneath them, leading to various geological phenomena. The movement of these tectonic plates is responsible for many natural events, such as earthquakes, volcanic eruptions, and the formation of mountain ranges. Understanding plate tectonics helps scientists predict geological activity and comprehend the Earth's history, including the formation of continents and ocean basins.