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DYNAMIC PLANET INVESTIGATION 3 NOTES CONVECTION CELLS • Definition – a motion in a fluid that is caused by heating from below and cooling from above Examples • • • • Heating of the corn syrup demonstration Oatmeal demonstration Home heating systems Convection oven Convection Cells • When a fluid is heated, it expands and lowers its density slightly • The expanded fluid (less dense) rises reaches cooler surroundings shrinks, becoming more dense sinks heated again… Forms CONVECTION CELLS Convection of the Earth’s Mantle • The mantle convects in the form of gigantic convection cells Material movement • Many materials act like solids on short time scales but like liquids on much longer time scales – Examples include: • Silly Putty • Glass • Wax • These materials flow and take on a new shape, even though it seems like a solid • The Earth’s mantle behaves in the same way • The speeds of flow in the mantle are only a few centimeters per year OR as fast as your fingernail grows The Lithosphere and Asthenosphere The Lithosphere • • • • • Outermost part of the Earth Cooler temperature Remains rigid Does not convect Made up of the crust & uppermost part of the mantle • Consists of several pieces called lithospheric plates The Asthenosphere • Below the lithosphere • Zone where mantle rocks are just hot enough & under enough pressure to deform & change shape • Able to convect moving the lithosphere Mid-Ocean Ridges • All the Earth’s oceans have a continuous mountain range, called a mid-ocean ridge • Located above rising currents in the mantle convection cells • Stand high because they are heated by hot rising material which expands the rocks • As hot mantle rock rises, some melts forming magma • Magma is less dense than surrounding rock, rises to form volcanoes along the ridge • As rock rises, temperature stays the same but pressure decreases (less weight of rock above) • Melting temperature decreases as pressure decreases, why some rising rock forms magma • Magma reaches surface, solidifies to form basalt New crust is formed, moves away from the crest of the ridge • Due to movement of the mantle • Due to downhill slope of the ridge away from the crest • Movement of new oceanic crust in both directions sea floor spreading