1. Plate Motion

2. Remember that the planet is divided into four sections… Remember that the planet is divided into four sections… The Inner Core The Inner Core The Outer Core The Outer Core The Mantle The Mantle The Crust The Crust

3. Convection Currents Circular patterns of motion created in the mantle when material heats, expands, becomes less dense and rises >>> followed by the cooling, contraction, and sinking of denser material. Circular patterns of motion created in the mantle when material heats, expands, becomes less dense and rises >>> followed by the cooling, contraction, and sinking of denser material.

4. As the moving magma circulates, it runs along the underside of the crust, pushing it along (ever so slowly).

5. Ridge Push The movement of tectonic plates away from a mid-ocean ridge >>> toward an area of subduction, such as a trench (occurring at position “B”). Gravity is believed to be playing a role. The movement of tectonic plates away from a mid-ocean ridge >>> toward an area of subduction, such as a trench (occurring at position “B”). Gravity is believed to be playing a role.

6. Slab Pull The movement of tectonic plates into an area of subduction (a trench). As the leading edge is pulled into the mantle and recycled (melted), the trailing edge is pulled into the trench (occurring at position “C”). Gravity is believed be playing a role here as well. The movement of tectonic plates into an area of subduction (a trench). As the leading edge is pulled into the mantle and recycled (melted), the trailing edge is pulled into the trench (occurring at position “C”). Gravity is believed be playing a role here as well.

7. So which is which? There is some debate as to whether ridge push is “pushing” the plates away from the ridges, or if slab pull is “pulling” the plate into the trenches. There is some debate as to whether ridge push is “pushing” the plates away from the ridges, or if slab pull is “pulling” the plate into the trenches. There is also debate as to whether ridge push and slab pull are playing a bigger/smaller role than convection currents. There is also debate as to whether ridge push and slab pull are playing a bigger/smaller role than convection currents. It is most likely a combination of the three. It is most likely a combination of the three.

8. Some unanswered questions How did these currents originate? How did these currents originate? Are convection currents permanent features? Are convection currents permanent features? Do they shift positions over time? Do they shift positions over time? What causes them to stop? What causes them to stop? How big are these currents? How big are these currents? Is convection only taking place in the upper mantle? Is convection only taking place in the upper mantle? Does subduction cause convection currents? Does subduction cause convection currents?