3The Theory of Plate Tectonics Earth’s crust and part of the upper mantle are broken up into plates that move on a plastic-like layer of the mantleEarth’s surface is made up of rigid plates known as the Lithosphere.80 km thick (up to 200 km thick beneath continents), very brittle, easily fractures at low temperature.These plates “float” over the upper mantle called the Asthenosphere.250 km thick - solid rock, but it is soft and flows easily (ductile).There are 7 major plates and about 18 minor plates.Most of the major plates are located under the continents
5What moves the plates?Mantle ConvectionRidge PushSlab Pull
6What causes these Plates to move? Mantle ConvectionWhat causes these Plates to move?Convection Currents Demonstration
7Mantle Convection Mantle Convection Convection Current Examples Any movement of matter that results from differences in densityDifferences of density within the earth are caused by differences in temperatureExamples“Lava” in a lava lampBoiling WaterMaking popcorn in an air popper“Hot air rises!”
9RADIOACTIVE DECAY OF ELEMENTS REVIEW: Earth is HOTEARTH’S FORMATIONRADIOACTIVE DECAY OF ELEMENTSMoving objects have kinetic energy. When objects collide, kinetic energy is converted into thermal energy.When Earth formed, objects in the solar system collided, generating thermal energy.When the earth was molten, it began to separate into layers based on density. Particles of matter had gravitational potential energy, so as gravitational force acted to separate these particles according to density, the particles experienced friction (because they were moving past one another). A byproduct of friction is thermal energy.What is radioactive decay?Some elements have an unstable nucleusTo become more stable, the nucleus of the radioactive element breaks apartWhen a nucleus breaks apart, heat is released.The decay of radioactive elements into more stable elements releases heat inside the Earth, making the interior of the Earth hotRadioactive elements have been present within Earth since the Earth was formed and still exist within Earth today, therefore, heat continues to be generated in Earth’s interior.
10Convection CurrentsConvection currents transfer heat through the movement of heated fluid material (i.e. molten rock)The asthenosphere is heated by the inner and outer core of the Earth. This heat is transferred through the mantle.
11When materials like solid rock are heated, they expand and become less dense Hot, less dense plastic-like material rises, coming in contact with the lithosphere (crust and uppermost mantle)It cools at the lithosphere (or Earth’s outermost layer) and becomes more dense causing the material to sinkThe constant rotation of the material creates a current that is able to pull the plates
12How Plates MoveCONVECTION CURRENTS IN ASTHENOSPHERE
13Forces Causing Plate Motion Rising mantle material at mid-ocean ridges creates the potential for plates to move away from the ridgeMoves lithosphere in opposite directions away from a mid-ocean ridgeRidge PushWhen tectonic plates collide, the denser plate (slab) will sink in to the mantleAs a slab sinks, it pulls on the rest of the plate with a force called slab pullSlab Pull
18Why does the Oceanic Crust go under the Continental Crust? Density!!!
19Oceanic Crust Continental Crust Mostly Basalt Young (0-200 myo) High in Iron (5-10%)Low in Silica (45-60%)Young (0-200 myo)New rock formed at MORThin (8-10 km thick)Dense (3.0 g/cm3)Mostly GraniteLow in Iron (2-5%)High in Silica (65-75%)Sits on top of OceanicOld (up to 4 byo)Thick ( km thick)Low Density (2.7 g/cm3)