UNDERSTANDING WHY EARTH IS A PLANET WITH PLATE-TECTONICS

Plate tectonics theory does not explain why Earth has plate tectonic movements, in the same way that the theory of seismology does not explain why Earth is seismically active. The occurrence of plate-tectonic movements on Earth but their absence on Venus should concentrate our attention on this theoretical inadequacy. As a way into this puzzle, some of the key concepts of plate tectonics are discussed and their limits emphasized. A direct link between the presence of water and the persistence of plate tectonic activity for billions of years is advocated as a basis for a solution to why Earth still has plate tectonic movements but Venus does not.