Cratons are the oldest and most stable parts of the continental lithosphere and shields are the exposed area of a craton(s). Microplates are tiny tectonic plates, terranes are fragments of crustal material formed on one tectonic plate and accreted to crust lying on another plate, and zones are bands of similar rocks on a plate formed by terrane accretion or native rock formation. Terranes may or may not have originated as independent microplates: a terrane may not contain the full thickness of the lithosphere.