Which theory describes the gradual movement of continents on tectonic plates?

The correct answer is the theory that captures the gradual movement of continents on tectonic plates. This theory involves the concept that Earth's continents were once joined together in a single landmass called Pangaea and have since slowly drifted apart over geological time. This vast movement allows for the explanation of how continents shift their positions on the surface of the Earth through processes involving plate boundaries and interactions.

While the Continental Drift Theory focuses on the movement of the continents specifically, the Plate Tectonics Theory is broader as it encompasses the mechanisms and forces driving this movement, including interactions between different tectonic plates. Sea-floor Spreading Theory explains how new oceanic crust is formed and pushes continents apart, mainly at mid-ocean ridges. Conversely, Landform Development Theory addresses the development of landforms but does not specifically relate to the dynamics of continental movement. Each of these theories connects with geological processes, but the Continental Drift Theory distinctly emphasizes the movement of the continents themselves.