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 Tectonic Theory. 1  Plate tectonics is the theory that explains the global distribution of geological phenomena. Principally it refers to the movement and interaction of the earth's lithosphere. 2  The mantle below the crust makes up over 80% of the earth's volume.