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 scientific theory explaining the movement of the earthâs crust. It is widely accepted by scientists today. Recall that both continental landmasses and the ocean floor are part of the earthâs crust, and that the crust is broken into individual pieces called tectonic plates (Fig. 7.14).