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Transcript
The Structure of the Earth and Plate Tectonics Structure of the Earth Mantle • The Earth is made up of 3 main layers: Outer core Inner core – Core – Mantle – Crust Crust The Crust • This is where we live! • The Earth’s crust is made of: Continental Crust Oceanic Crust - thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old - thin (~7 km) - dense (sinks under continental crust) - young How do we know what the Earth is made of? • Geophysical surveys: gravity, magnetics, electrical etc • Acquisition: land, air, sea and satellite – Geological surveys: fieldwork, boreholes, mines What is Plate Tectonics? • If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle. Pangaea Continental Drift Theory • Continental drift is the movement of the Earth's continents relative to each other by appearing to drift across the ocean • Developed by Alfred Wegener in 1912, developed concept of Pangaea “oneearth” Plate Tectonics • The Earth’s crust is divided into 12 major plates which are moved in various directions. • This plate motion causes them to collide, pull apart, or scrape against each other. • Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. • The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction. World Plates What are tectonic plates made of? • Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle. What lies beneath the tectonic plates? • Below the lithosphere (which makes up the tectonic plates) is the asthenosphere. Convection Currents – The mantle is made of much denser, thicker material, because of this the plates "float" on it like oil floats on water. – Caused by very hot material at the deepest part of the mantle rising, then cooling, sinking again and then heating, rising and repeating the cycle over and over Example • The next time you heat anything like soup or pudding in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the mantle they also move the crust. The crust gets a free ride with these currents. A conveyor belt in a factory moves boxes like the convection currents in the mantle moves the plates of the Earth. Plate Movement • “Plates” of lithosphere are moved around by the underlying hot mantle convection cells Sea Floor Spreading • Magma comes up from the mantle in the ocean • Pushes previous crust that creates Mid Ocean Ridges (mountain chains) on the sea bed • Magma creates new crust that spreads out in its place Sea Floor Spreading Subduction of Crust • Opposite of mid ocean ridges • Earth’s crust is going into the mantle and melts into the magma • Continental crust and Oceanic Crust collide creates subduction zone • Ex. worlds oceanic trenches (deepest part of earth’s surface) Subduction of Crust