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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
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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