By Mayo Clinic Staff. Erectile dysfunction â the inability to get and keep an erection firm enough for sex â is a common problem. You've likely seen advertisements for erectile dysfunction herbs or supplements to increase your sexual performance..
plate tectonics. In geology, a theory that the Earth's lithosphere (crust and upper mantle) is divided into a number of large, plate-like sections that move as distinct masses. See Notes at fault, Gondwanaland, See more at tectonic boundary.
Plate tectonics is the geologic theory that Earth's crust is made up of rigid plates that float on the surface of the planet. Tectonics comes from the Greek word meaning builder. The movement of the plates toward or away from each other either directly or indirectly creates the major geologic features at Earth's surface. Plate tectonics revolutionized the way geologists view Earth. Like the theory of evolution in biology, plate tectonics is the unifying concept of geology.