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 margin. A Dictionary of Earth Sciences. Â© A Dictionary of Earth Sciences 1999, originally published by Oxford University Press 1999. plate margin (plate boundary) The boundary of one of the plates that form the upper layer (the lithosphere) and together cover the surface of the Earth. Plate margins are characterized by a combination of tectonic and topographic features: oceanic ridges, Benioff zones, young fold mountains, and transform faults.