PLATE TECTONICS SLIP SLIDIN AWAY Plate Tectonic Theory

PLATE TECTONICS: “SLIP SLIDIN’ AWAY”

• Plate Tectonic Theory states the outermost layer of Earth is composed of 9 to 15 large plates and numerous small ones • Most plates are located on the ocean floor

• Cracked egg used as a Model for Earth’s tectonic plates

• Lithosphere composed of the crust and upper mantle forms the Earth’s tectonic plates • Asthenosphere composed of very hot, melted plastic-like material lies below the lithosphere • Giant plates drift around on the asthenosphere at a rate of 1 to 2 centimeters per year

• Area of interaction between adjacent plates referred to as the plate boundary • Three types of plate boundaries as determined by the type of interaction occurring are: divergent, convergent and transform

DIVERGENT BOUNDARY • Formed when two adjacent plates move apart • Causes molten rock to erupt to the surface and create new crust; seafloor spreading is a result of this process • Creates mid-ocean ridges such as the mid-Atlantic ridge (bottom of Atlantic Ocean) • Continues to form new rocks that move away from ridges, explaining how crust can move and supporting theory of Continental Drift • Causes underwater volcanos, earthquakes and forms rifts such as the Great Rift Valley in Eastern Africa

CONVERGENT BOUNDARY CONTINENTAL-CONTINENTAL • Formed when two plates move together • Plates’ crust type determines geologic activity at interaction point • Equally dense continental crust plates buckle and are pushed upward, forming mountain ranges • Examples: Himalayas (still forming), Alps and Appalachians

CONVERGENT BOUNDARY CONTINENTAL - OCEANIC SUBDUCTION • Oceanic crust is denser but less thick than continental crust • Oceanic crust collides with continental crust • Oceanic crust bends, slides under the continental crust, goes down into the mantle: this interaction is called subduction • Results in earthquakes, volcanos and rock deformation • Examples: Cascade Range in the Pacific Northwest and the Andes in South America

TRANSFORM BOUNDARY OR TRANSFORM FAULT MARGIN • Formed when two plates slide past each other • Usually move in opposite directions but may move in the same direction at different speeds • Fault: a deep crack in the Earth’s surface • Transform boundary : where plates catch and grind but crust is not produced or destroyed San Andreas Fault • Plates build tension along boundary and release it with a burst of energy and motion, resulting in earthquakes • Most transform boundaries located on the ocean floor • Notable exception is San Andreas Fault Zone in California which passes through two thirds of the state: it has produced many earthquakes, including those in San Francisco and Los Angeles

REVIEW OF THE THREE TYPES OF PLATE BOUNDARIES

WHAT’S ON YOUR PLATE? ? ?

COMPARE THREE LAYERS OF AN EGG TO THE THREE MAIN LAYERS OF THE EARTH A B EARTH C A B C

STRUCTURE OF THE EARTH • Three main layers of the Earth: Core (inner and outer), mantle (upper and lower) and crust • Inner core under extremely high pressure, solid state, very dense, composed mostly of iron • Outer core liquid state, composed mostly of iron • Mantle largest layer, composed of silicon, oxygen, magnesium and iron, divided into upper and lower divisions as determined by different seismic wave speeds • Crust outermost layer, varies in thickness from more than 60 km to less than 5 km • Contains higher percentage of silicon and aluminum and lower percentage of magnesium and iron than the mantle • Generally less dense than the mantle