PLATE TECTONICS: “SLIP SLIDIN’ AWAY”

Most plates are located on the ocean floor 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 the 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 THE 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