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 science and study of the causes of, and  relative motions of, Earth's lithospheric plates.    The lithospheric plates are composed of the rocky â¦crust and  outermost rocky layer of the mantle which are fused together.