Chapter 1-5

 Canadian scientist J. Tuzo Wilson observed that lithosphere is separated into different sections or plates  Plates carry continents, parts of ocean floor, or both  Combined this idea with sea floor spreading and continental drift to develop the theory of plate tectonics

 States that pieces of Earth’s lithosphere are in slow constant motion driven by convection currents in the mantle  Explains the formation, movement, and subduction of Earth’s plates.

 Geologist believe convection currents in mantle cause plates to move  When gravity pulls one edge of a plate down by subduction, the rest of the plate also moves  As plates move, they collide, pull apart, and grind forming volcanoes, mountains, and trenches

 Edges of Earth’s plates meet at plate boundaries  Faults form at plate boundaries  Plates move at these boundaries at rates from 1-24 cm per year  Ex: North American and Eurasian plates moving apart at 2.5 cm per year

 Where two plates move apart from each other  Occur at mid ocean ridge  Form rift valleys on land ◦ Great Rift Valley, E. Africa

 Where two plates come together  Cause collision  Denser plate sinks under less dense plate  Oceanic crust sinks under continental because it is more dense  When two continental plates converge, mountains form

 Plates slip past each other  Earthquakes form  Crust is neither created nor destroyed

 Scientists believe Pangaea formed about 260 million years ago when continents came together; broke apart about 225 million years ago  Plates still moving