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.
Definition: What is plate tectonics. The concept that describes and explains how the major features of the Earth form and/or deform. The essential processes of plate tectonics are 1)seafloor spreading and 2) subduction.These two processes operate on basic units called plates. Key surface features such as mountain ranges form in particular tectonic settings when these processes act on plates directly or indirectly.he concept that describes and explains how the major features of the Earth form and/or deform. The essential processes of plate tectonics are 1)seafloor spreading and 2) subduction. These two processes operate on basic units called plates.