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.
The plates are part of the crust, the upper layer of the Earth. The plates are moved by currents in the upper mantle. The plates and flexible upper mantle are referred to coll â¦ ectively as the lithosphere and sit atop the mantle layer called the aesthenosphere.