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Plate Tectonics Oceans 11 PANGEA • In 1912 Alfred Wegener thought that all of the continents were connected as one supercontinent called PANGEA. • This was about 300 million years ago and over time they drifted apart. Continental Drift Theory http://www.suu.edu/faculty/colberg/Hazards/PlateTectonics/18_Pangaea.htm The Structure of Earth • The Earth is made up different types of layers. • The Lithosphere is divided into large plates. • Convection currents in the asthenosphere move the plates. LAYERS OF THE EARTH I. Crust: • Rigid surface of the Earth. It can be between 0-100 km thick, depending on where it is. • 2 Types: – Continental Crust: Thicker parts of the crust; above the ocean – Oceanic Crust: Thinner parts of the crust; under the ocean LAYERS OF THE EARTH II. Mantle: • • • • • Between the crust and the core. Largest volume of the earth. Mg, Fe, O, Si Upper Mantle: Solid part of the mantle Lithosphere: Crust and upper mantle. Lower mantle: Loose moving due to heat from the core. LAYERS OF THE EARTH III. Core: • Outer part is liquid and about 2300km thick. • Inner is solid and mostly nickle and iron. **Believed to control the Earth’s magnetic field.** Tectonic Plates • The lithosphere is broken into 9 large, rigid pieces called plates. • The plates are all moving in different directions and at different speeds (from 2 cm to10 cm per year) Plates meet at Plate Boundaries • There are 3 main plate boundaries: • 1) Convergent Boundary • 2) Divergent Boundary • 3) Transform Boundary 1. Convergent Boundaries • Occurs when 2 plates collide. • Oceanic plate is more dense and is forced under the continental plate. • Some of the rock in the Oceanic plate melts as the plate sinks. The melted rock rises up causing earthquakes and volcanic eruptions. • Where they collide is called a SUBDUCTION ZONE. When a continental plate has crashed into a continental plate: • The 2 continental plates are the same density. • This causes folding and bending of the plates as well as earthquakes. • Continental plates are folded into mountains. Example of a Convergent Plate Boundary South America: • Oceanic Nazca Plate collides into the South America plate. • Formed the Andes Mountains (volcanoes along the mountain crest) • Formed a deep trench off the coast in the Pacific Ocean. Divergent Plate Boundaries • Plates are being pulled apart by convection currents in the mantle. • As the plates separate along the boundary, the block between the faults cracks . • Magma from the mantle rises through the cracks. • This cools and new crust is formed along the boundary. • Earthquakes occur along the faults, and volcanoes form where the magma reaches the surface. Mid Atlantic Ridge • Mid-Atlantic Ridge is a Divergent Plate Boundary. • Over 15000 km long. • Average height of 3km. • Mid Atlantic Ridge Video • http://www.youtube.co m/watch?feature=endscr een&v=GyMLlLxbfa4 &NR=1 Transform Boundary • Places where plates slide past each other. • Transform boundaries are not marked by spectacular surface features, their sliding motion causes lots of earthquakes. • Example: San Andreas Fault http://www.youtube.com/watc h?v=ZxPTLmg0ZCw • The slice of California to the west of the fault is slowly moving north relative to the rest of California. • http://www.youtube.com/watch? v=hReS4Fm94L4