What theory explains the movement of the Earth's outer shell and its effects like earthquakes and volcanoes?

Plate tectonics is the theory that explains the movement of the Earth's outer shell, known as the lithosphere, which is segmented into several large and rigid plates. These tectonic plates float on the semi-fluid asthenosphere beneath them. The interactions and movements of these plates are responsible for various geological phenomena, including earthquakes, volcanic activity, mountain building, and oceanic trench formation.

The theory of plate tectonics synthesizes earlier ideas such as continental drift and seafloor spreading, providing a comprehensive framework for understanding how the continents and ocean floors have changed over geological time. This movement occurs due to a combination of forces including mantle convection, slab pull, and ridge push. As plates interact—either colliding, separating, or sliding past one another—they can cause significant geophysical events like earthquakes, which result from the sudden release of energy along fault lines, and volcanoes, which can form at divergent boundaries or at convergent boundaries where one plate subducts beneath another.

In contrast, continental drift primarily focused on the idea that continents move independently and was an early precursor to plate tectonics. Seafloor spreading pertains specifically to the formation and movement of the ocean floors, whereas geosynclinal theory was an earlier concept that attempted to explain