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Transcript
The Earth’s Interior Interior is characterized by gradually increasing temps, pressure, and density at increasing depths. There are 3 main layers in Earth’s interior: The top layer is called the CRUST – Oceanic: thin but dense (heavy, “sinks”); composed of basalt rock – Continental: thick but less dense; large variety of rock, mainly granite. Earth’s 2 main layer is called the Mantle: 85% of the Earth’s volume. • The Mantle has a thin, solid part below the crust. • Next is a viscous layer similar to pudding or silly putty (convection currents in this viscous layer causes tectonic plates to slide) • The bottom layer of the mantle is very thick. It is solid. Earth’s 3rd main layer is called the Core – Outer core: liquid iron that generates Earth’s magnetic field – Inner core: solid iron Continental Drift: Alfred Wegener’s theory • Continents moved horizontally to their current location. • Believed that all continents were once one large landmass called: PANGEA Evidence of Continental Drift • Fossils of mesosaurus and glossopteris – Found widely in rocks on separate landmasses • Rock types: – Mountain ranges in South America and Africa are the same. • Climate evidence: – Fossils of tropical plants found near Arctic Ocean – Scratches in rocks made by glaciers found in South Africa Scientists did not support Wegener’s theory because… • He could not prove how, when, or why the continental plates moved. Sea Floor Spreading • Harry Hess found evidence which helped support the theory of continental drift. • His theory was sea floor spreading. http://highered.mcgrawhill.com/sites/0072402466/studen t_view0/chapter19/animations_a nd_movies.html Evidence to support Sea Floor Spreading • Reverse Magnetic Polarity: – The rocks were deposited with different magnetic polarity based on the spin of the earth • Age of rocks: – The farther you are away from the spreading center the older the age of the rock Important things to remember from the Theory of Plate tectonics: • The lithosphere (crust & upper mantle) is broken into puzzle pieces called tectonic plates. • Oceanic plates are more dense than continental. • Therefore, oceanic plates will be subducted (pushed underneath) continental. There are three types of possibilities for plate collisions When 2 plates collide… • Oceanic to continental: subduction When 2 plates collide… • Oceanic to oceanic: volcanic ring or islands When 2 plates collide… • Continent to continent: mountain building When plates move away from each other under water… • A mid-ocean ridge is formed. • Magma rises from within the mantle at the midocean ridge. Magma is called lava once it hits Earth’s surface and flows out to create new ocean floor. This is a constructive process since there is a buildup of new ocean floor. When 2 plates slide past each other… • Two plates grind together and slip past each other horizontally No material made or destroyed • Slipping causes…EARTHQUAKES! • http://www.classzone.com/books/ earth_science/terc/content/ So how do the plates move? • Remember the asthenosphere layer in the mantle? It is the heated, soft-plastic-like layer similar to silly-putty. • The outward flow of heat from Earth’s interior creates convection currents in this soft layer, allowing it to flow slowly. The motion is called convection cells Global Positioning Systems (GPS) • Scientists have been using GPS to verify where plates used to be. They measure the current speed of plate movements (in cm/yr) with GPS, then backtrack. They also observe offset geologic features such as mountains, mid-ocean ridges, and subduction zones.