Unit 3:  Plate Tectonics

Once the Earth formed it began to cool.  Differentiated layers formed due to different densities of Earth’s materials.  Dense metals of Iron and Nickel formed the Earth’s core while less dense silicates formed the mantle and outer crust.  Evidence for the Earth’s layers come from seismograph recordings of P and S-waves that travel through the Earth after an earthquake.   Once the Earth cooled and the layers formed Plate Tectonics started forming the land and ocean features such as mountain ranges, ocean trenches, mid-oceanic ridges, trenches, and islands.  Evidence of plate tectonics can be found on the ocean floor by evaluating the age of the ocean floor and magnetic field reversal patterns as well as earthquakes patterns at oceanic trenches.  Plate tectonics is caused by the convection of the mantle driven by Earth’s internal heat.