1. Plate Tectonics
Plate movement is driven by convection currents.

2. Convection Currents Currents are caused by heat in Earth’s interior
Hotter material is less dense, rises toward the surface
Cooler material pushed out of the way, sinks back toward the core
Lithosphere is pushed up and melted above rising convection currents
Lithosphere is pulled downward above sinking currents

3. Convection connection
New crust is formed where magma is rising at Divergent boundaries
Old crust is destroyed where magma is sinking at Convergent boundaries

4. Sea floor Spreading Creates a mid-ocean ridge (MOR)
New crust is forming at the center of the ridge
Age of crust increases as distance from ridge increases

5. Sea floor age

6. Sea Floor Spreading
The sea floor in the center of the ridge is the youngest material.
As you move toward the coastlines, the sea floor is made of older material.

8. Magnetic Reversals
Lava forming on the seafloor contains iron oxide which points to magnetic north when it cools and hardens.
These rocks provide a record of where magnetic north was located when the lava was formed.

9. Magnetic Reversals
Scientists can match up the bands on either side of the mid-ocean ridge to prove that the seafloor is spreading.
Scientists have also found that the bands alternate between pointing north and pointing south. This indicates that the Earth’s magnetic poles have reversed many times.

10. Measuring magnetic field in ocean floor

11. The earth's magnetic field has reversed approximately 170 times over the last 100 million years.