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. The concept that describes and explains how the most significant features on the Earth's surface are produced by processes within the Earth when it acts units at the Earth's surface called plates. As a result, the plates to move around, and change in size and number over time.