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.
Geology's Unifying Theory. Plate tectonics is the framework in which geologists study and understand the inner workings of the earth. It provides us with a way to tie together what once was considered unrelated geologic processes and events.