Plate Tectonics Plate movement is driven by convection currents.

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

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

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

Sea floor age

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.

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.

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.

Measuring magnetic field in ocean floor

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