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Earth’s Layers Review Which layer of the Earth is broken into sections that move? 1. 2. 3. 4. Core Lithosphere Asthenosphere Continental Crust 0% 1 0% 2 0% 3 0% 4 What do the lithospheric plates float on top of? 1. 2. 3. 4. Asthenosphere Oceanic Crust Outer Core Continents 0% 1 0% 2 0% 3 0% 4 What causes the lithospheric plates to move? 1. 2. 3. 4. Seismic Waves Continental Drift Sea-Floor Spreading Convection Currents 0% 1 0% 2 0% 3 0% 4 Plate Boundaries Plates The lithosphere (crust and upper mantle) is broken into separate sections called plates. Floating Plates The plates float on top of the asthenosphere because of convection currents. The Theory of Plate Tectonics Pieces of the Earth’s lithosphere are in constant, slow motion. This theory explains the movement of plates on Earth, called Plate Tectonics. The Movement of the Plates The lithospheric plates move because of convection currents and the plates meet at boundaries. Where The Plates Meet • There are 3 kinds of plate boundaries: –Transform Boundary –Divergent Boundary –Convergent Boundary Transform Boundary Sketch of Boundary Direction of Plate Movement • Plates slide past each other Description/Feature of TRANSFORM plate boundary • Earthquakes are very frequent • Causes faults (cracks) Example San Andreas Fault (California) Divergent Boundary Sketch of Boundary Direction of Plate Movement Two plates move away from each other. Description/Feature of DIVERGENT plate boundary Continental Plates form a RIFT VALLEY (deep valley) Oceanic Plates form MID-OCEAN RIDGE Divergent Boundaries Continental Plate Examples Oceanic Plate • Examples • Rio Grande Rift (US) • Great Rift Valley (Africa) Mid-Atlantic Ridge (Atlantic Ocean) Convergent Boundary • At a convergent boundary, two plates come together, or converge (“collide”) Sketch of Boundary • There are 3 types of Convergent Boundaries: Direction of Plate Movement – Oceanic crust collides with oceanic crust – Oceanic crust collides with continental crust – Continental crust collides with continental crust When two plates collide, the density of the plates determines which one comes out on top. Oceanic crust is more dense than continental crust. Oceanic vs. Oceanic When the crust comes together at a trench, the less dense crust on the plate is on top. The crust that is more dense dives (“sinks”) under the other one and returns to the mantle (this is called subduction). Oceanic vs. Continental The plates come together and the oceanic crust sinks because it is more dense. Continental Oceanic Continental vs. Continental Plates come together and neither sinks. Mountains are formed. Example: Himalaya Mountains Slow Motion… • The plates move from 1 to 10 centimeters per year. • North America and Eurasia move apart 2.5 centimeters per year this is how fast your fingernails grow- Plate Movement Review Which of the following is not a plate boundary? 1. 2. 3. 4. Convergent Divergent Persistent Transform 0% 1 0% 2 0% 3 0% 4 Which boundary occurs when two plates slide past each other? 1. 2. 3. 4. Convergent Transform Divergent Oceanic 0% 1 0% 2 0% 3 0% 4 Which type of plates collide to form mountains? 1. 2. 3. 4. Oppositional Continental Divergent Oceanic 0% 1 0% 2 0% 3 0% 4 Which plate boundary features the mid-ocean ridge for sea-floor spreading? 1. 2. 3. 4. Continental Transform Divergent Oceanic 0% 1 0% 2 0% 3 0% 4 What occurs when oceanic plates collide? 1. 2. 3. 4. Sea-Floor Spreading Mountain Building Earthquakes Subduction 0% 1 0% 2 0% 3 0% 4