Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Causes of Plate Movement After completing this section, the student will relate convection currents in the asthenosphere to plate movement (Standard PI – 042) and use evidence to support the Theory of Continental Drift (Standard PI-040) We know that the Earth’s surface is made up of moving plates. Most earthquakes and volcanoes occur at plate boundaries We don’t know what causes the plates to move. Scientists have proposed 3 theories to explain how the plates move • Mantle Convection • Ridge Push • Slab Pull Mantle Convection Heat from the Earth’s inner and outer cores is transferred by a process called mantle convection Magma that is hotter is less dense and rises. As it moves, it pulls a lithospheric plate with it As the magma cools, it becomes more dense and sinks, forming a convection current Many scientists think that mantle convection does not completely explain how plates move It doesn’t account for the force needed to move the plates Ridge Push The molten magma that rises at a mid-ocean ridge is very hot and heats the rocks around it As the lithosphere is heated, it expands and becomes elevated above the surrounding area Gravity causes the older, denser rock to slide away from the ridge Slab Pull At a subduction boundary, one plate is more dense and heavier than another The heavier plate begins to slide under the other As the dense plate slides down into the mantle, it pulls the rest of the plate with it The force that the sinking edge of the plate exerts on the rest of the plate is called slab pull Many scientists consider this to be a better theory than mantle convection or ridge push