The theory of plate tectonics explains the dynamics of the Earth's lithosphere, which is divided into several large and small tectonic plates. These plates float on the semi-fluid asthenosphere beneath them and constantly move, resulting in various geological phenomena, including earthquakes, volcanoes, and the formation of mountain ranges. The interactions between plates can be divergent, convergent, or transform, defining how landforms evolve over geological timescales. This theory is fundamental in understanding Earth's structural changes.