The Theory of Plate Tectonics Science 10

Evidence for Plate Tectonic Theory Volcano & Earthquake Locations Sea Floor Spreading & Rocks on the Ocean floor 3. Paleomagnetism 4. Direct Measurement

1. Volcano and Earthquake Locations: Do you notice anything about the location of earthquakes and volcanoes? They occur at plate boundaries!

2. Sea Floor Spreading Convection causes the hot magma to rise and it forces its way through the crust at mid-ocean ridges. As the magma pushes through the crust it forms new sea floor and pushes the older rock aside in both directions.

Younger rocks are found close to the Mid-Atlantic Ridge.

4. Paleomagnetism Earth is like a giant magnet with its own magnetic field. This magnetic field has not always been the same. Over thousands of years, it can actually switch—the north magnetic pole becomes a south pole and vice versa. This is called Magnetic Reversal.

4. Paleomagnetism continued… When rocks form in the presence of this magnetic field the iron and other metals in the rocks actually align with this field! This is Magnetite, a mineral that contains iron.

4. Paleomagnetism continued… When oceanographers used a magnetometer to measure magnetism on the sea floor, they noticed “stripes” of rock with the same magnetic polarity on both sides of the mid-Atlantic Ridge.. What do you think this means?

5. Direct Measurement We can actually measure the rate of sea floor movement! You can go see for yourself in Iceland where the Mid-Atlantic Ridge comes onto the land.

Iceland Rift