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Theory of Plate Tectonics Oceans 11 But first…a little about the internal structure of the Earth A Brief look Earth’s 2 major layers Earth’s Internal Structure • • • • Earth can be divided into 3 main layers: Crust (outside of Earth) Mantle Core (very inside) Earth’s Crust • Crust is the outermost layer. • Two Parts of Crust: – Continental crust • Mainly granite • Up to 75km thick • Density 2.6g/cm3 – Oceanic crust • Made up of basalt rock (type of volcanic rock) • Up to 8 km thick • Density 3.0g/cm3 The Mantle • The mantle is the next layer. • This zone is about 2900km thick and makes up great 82% of Earth’s volume. • Fragments of the mantle have been brought to the surface by volcanic eruptions. Earth’s Core • Earth’s core is extremely hot – hot as the sun! • Divided into two parts. – Outer Core • Liquid iron and nickel – Inner Core • Solid iron Now let’s look at the Theory of Plate Tectonics… Plate Tectonics – brief history • 1912 – Alfred Wegener, German geophysicist and meteorologist – Wegener thought that all landmasses formed one supercontinent approximately 225 mya “Pangaea” meaning all earth. Wegener’s research: • • • • Geologic record (rock strata) Fossil record Climatic record of continents A KEY FINDINGS: – Southern America & Africa have many similarities • Large coal deposits Resistance… • Wegener was met with a lot of skepticism from other scientists and the church. • 1950 to 1960’s – Geologic Discoveries: • Similar fossils on each continent • Same age rock on coast lines • It wasn’t until the 1960’s that Wegener’s theory was accepted and coined Theory Plate Tectonics Animation of Continental Drift • http://education.sdsc.edu/optiputer/flash/p angea_4.htm PANGEA Definition of Plate Tectonics • Tectonic – Greek meaning “building” or “construction” • Refers to the configuration of Earth’s crust as a result of internal forces. Plate Tectonic Processes • Include: – Upwelling of magma – Crustal plate movements – Sea-floor spreading – Subduction of crust – Earthquakes – Volcanic activity – Warping, folding and faulting of crust. Earth’s Plates • Plates are made up of: – Continental crust – Oceanic crust • These plates float upon the moving asthenosphere. • Plates move 1 to 19 cm per year – Movement of plates are a result of convection currents in the asthenosphere – http://education.sdsc.edu/optiputer/flash/convection.htm Earth’s Plates • What do you notice about the relationship between volcanoes(red), earthquakes (yellow) and location of plate boundaries? 3 Main types of Plate Boundaries 1. Divergent plate boundary 2. Convergent plate boundary 3. Transform plate boundary Divergent Plate Boundaries • Plates separate (move away from each other) • Almost always occurs between two ocean plates. • When ocean plates separate, new crust is formed through the upwelling of magma. This is called sea-floor spreading. – http://education.sdsc.edu/optiputer/flash/seafloorspread.htm – Mid-oceanic ridges – http://www.planetseed.com/files/flash/science/features/earth/livingplanet /plate_boundaries/en/index2.html?width=570&height=475&popup=true • Iceland, "the land of fire and ice", is being split by an oceanic ridge that surfaces to create an oceanic island (left and below) in the North Atlantic Ocean. • Red triangles show Iceland's active volcanoes, including Krafla. Reykjavik is Iceland's capital. Divergent Plate Boundaries • Something interesting!!! • Great Rift Valley in Africa • A continental plate is breaking up! • Convection currents under the crust are pulling this area apart! • http://www.youtube.com/watch?v= w7Y2R4KBwvo Convergent Plate Boundaries • These plate boundaries can occur between: – Oceanic and Continental plates • “Subduction Zones” • http://www.planetseed.com/files/flash/science/features/earth/livingplanet/plate_boundaries/en/index2.html?wi dth=570&height=475&popup=true – Continental and Continental plates • Mountain building • http://www.planetseed.com/files/flash/science/features/earth/livingplanet/plate_boundaries/en/index2.html?wi dth=570&height=475&popup=true Transform Plate Boundaries • These are where plates move side-to-side. • Trigger earthquakes • http://www.planetseed.com/files/flash/science/features/earth/livingplanet/plate_bound aries/en/index2.html?width=570&height=475&popup=true Your Task • Complete the “checking your understanding” questions and hand in. • Complete the Plate Tectonic Map Activity