Mantle convection Natural convection

convection within earth s mantle driving force plate tectonics. mantle convection result of thermal gradient: lower mantle hotter upper mantle, , therefore less dense. sets 2 primary types of instabilities. in first type, plumes rise lower mantle, , corresponding unstable regions of lithosphere drip mantle. in second type, subducting oceanic plates (which largely constitute upper thermal boundary layer of mantle) plunge mantle , move downwards towards core-mantle boundary. mantle convection occurs @ rates of centimeters per year, , takes on order of hundreds of millions of years complete cycle of convection.

neutrino flux measurements earth s core (see kamland) show source of two-thirds of heat in inner core radioactive decay of k, uranium , thorium. has allowed plate tectonics on earth continue far longer have if driven heat left on earth s formation; or heat produced gravitational potential energy, result of physical rearrangement of denser portions of earth s interior toward center of planet (i.e., type of prolonged falling , settling).