The theory of plate tectonics explains that Earth's outer shell, the lithosphere, is divided into several large and small rigid plates that float and move on the underlying, weaker, plastic-like asthenosphere. These plates move slowly, driven primarily by mantle convection and the sinking of denser oceanic lithosphere at subduction zones, causing them to diverge, converge, or slide past each other along their boundaries

. This movement of plates explains many geological phenomena:

• The formation, movement, and breakup of continents (continental drift) as continents are embedded in these plates and drift with them over millions of years

• The creation of new oceanic crust at mid-ocean ridges where plates diverge (seafloor spreading) and the destruction of old oceanic crust at subduction zones where plates converge

• The occurrence of earthquakes, volcanic activity, and mountain building primarily at plate boundaries where plates interact by colliding, pulling apart, or sliding past each other

• The recycling of Earth's crust, maintaining a roughly constant surface area despite seafloor spreading and subduction

• The shaping of Earth's surface features, including ocean basins, mountain ranges, and trenches, as well as influencing Earth's atmosphere, oceans, climate, and the environment for life evolution over geological time

In essence, plate tectonics provides a unifying framework to understand the structure and dynamic processes of Earth's crust and major surface changes throughout its history