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.
Tectonic plates are segments of the Earth's lithosphere, the hard  rocky outer shell composed of the crust and the uppermost mantle.  This shell is divided by lines of faultâ¦s, ridges of plate creation,  and zones of plate destruction.