Plate Tectonics

Plate movement is driven by 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 Currents

New crust is formed where magma is rising at Divergent boundaries

Old crust is destroyed where magma is sinking at Convergent boundaries

Convection connection

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

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.

Sea Floor Spreading

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.

Magnetic Reversals

Measuring magnetic field in ocean floor

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