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.
conÂ·verÂ·gent plate boundary. A tectonic boundary where two plates are moving toward each other. If the two plates are of equal density, they usually push up against each other to form a mountain chain.If they are of unequal density, one plate usually sinks (subducts) beneath the other. Also called collision zone.onÂ·verÂ·gent plate boundary. A tectonic boundary where two plates are moving toward each other. If the two plates are of equal density, they usually push up against each other to form a mountain chain.