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 faults, ridges of plate creation, and zones of plate destruction. The plates are composed of crustal rock and solid upper mantle which is called the lithosphere. * 2  Plates are composed of continental and oceanic crust. 3  The oceanic crusts are continually moving, spreading from the center, sinking at the edges, in a process of recycling.