UNDERSTANDING WHY EARTH IS A PLANET WITH PLATE-TECTONICS

Plate tectonics theory does not explain why Earth has plate tectonic m ovements, in the same way that the theory of seismology does not expla in why Earth is seismically active. The occurrence of plate-tectonic m ovements on Earth but their absence on Venus should concentrate our at tention on this theoretical inadequacy. As a way into this puzzle, som e of the key concepts of plate tectonics are discussed and their limit s emphasized. A direct link between the presence of water and the pers istence of plate tectonic activity for billions of years is advocated as a basis for a solution to why Earth still has plate tectonic moveme nts but Venus does not.