Plate Tectonics (1) The earth gets rid of heat and keeps a nearly constant internal temperature through convection in the mesosphere and asthenosphere ■ Plate tectonics theory says that earth’s outermost100km“ eggshell”(the lithosphere) is cracked in about a dozen large pieces.Plate Tectonics (1) ◼ The Earth gets rid of heat and keeps a nearly constant internal temperature through convection in the mesosphere and asthenosphere. ◼ Plate tectonics theory says that Earth’s outermost 100 km “eggshell” (the lithosphere) is cracked in about a dozen large pieces