Which theory explains the movement of the Earth's outer shell and its effects?

Plate tectonics is the theory that explains the movement of the Earth's outer shell, known as the lithosphere, which is broken into several large and small tectonic plates. These plates are constantly moving, albeit very slowly, due to the convective currents in the underlying semi-fluid asthenosphere. The interactions of these plates at their boundaries can lead to various geological phenomena, including earthquakes, volcanic activity, and mountain-building.

This theory encompasses various aspects of Earth's geology, including the creation of ocean basins, the formation of mountain ranges, and the occurrence of seismic events. It is a unifying concept that integrates previous theories, such as continental drift and seafloor spreading, by providing a comprehensive framework to understand the dynamic nature of the Earth's surface.

In contrast, while continental drift focuses specifically on the historical movement of continents away from each other, plate tectonics includes both continental and oceanic movements and their interactions. Core theory pertains more to the structure and behavior of the Earth’s inner core and outer core rather than surface movements. Seafloor spreading describes a specific process related to plate tectonics where new oceanic crust is created at mid-ocean ridges, but it does not encompass the entire scope of tectonic activity and plate interactions.