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.
In geology, a theory that explains the distribution of continents, earthquakes, volcanoes,, mountains and other geologic phenomena in terms of the formation, movement, and destruction of tectonic plates. These plates move in response to forces deep within the Earth.