Refer to the descriptions of the lithosphere and asthenosphere that follow the section on Earth's crust. The depth of oceanic crust increases with increasing distance from the mid-ocean ridge. Heat flow through the oceanic crust is almost 3 times as great as heat loss through continental crust. Most of Earth's internal heat energy flows outward toward space through the oceanic crust. The oceanic lithosphere thickens through the addition of cooled upper-mantle material from the asthenosphere.
Age increases with increasing distance away from the mid-ocean ridge.
The crust above active crustal asthenosphere is called a flake or an allochthon, because it is detached from the lower crust or upper-mantle lithosphere on which it formed.