This document discusses the theory of plate tectonics and the movement of tectonic plates. It describes how early theories like catastrophism were replaced by uniformitarianism. It then explains how the theory of continental drift was proposed and how evidence from paleomagnetism supported it. It discusses how seafloor spreading was discovered through mapping of the seafloor and analysis of magnetic properties in the rocks. This led to the modern theory of plate tectonics, where lithospheric plates move through divergent, convergent, and transform boundaries. The movement of plates has shaped continents over geologic time.