Convection Currents and Sea-Floor Spreading

Convection Currents• Occur in the asthenosphere• Heat from the core (both inner and

outer) drives the convection currents• Hotter material rises to be just below

the lithosphere because it is less dense

• Then it moves across, moving the lithospheric (tectonic) plate with it

• When it cools it sinks (because it is more dense) and draws the lithosphere down with it

Sea-Floor Spreading• Occurs at a mid-ocean ridge• Magma rises to the surface

becoming lava• Lava spreads the plates apart and

creates new crust• So, younger rock is found at mid-

ocean ridge & older rock is found at farthest point away from ridge