Explore the fascinating realm of planetary geology in this 42-minute lecture from Spahn's Science Lectures. Delve into the structure and composition of terrestrial worlds, understanding how planets are layered by density and rock strength. Examine the factors influencing spherical worlds, internal heating and cooling processes, and the relationship between size and geological activity. Investigate the formation of magnetic fields and the various forces shaping planetary surfaces, including impact cratering, magma rise, and different types of volcanoes. Learn about volcanism, plate tectonics, and erosion processes. Conclude by discovering how craters can be used to determine the age of planetary surfaces.