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The Moving Plates Boundary Interactions and the Origin of Earth Features Unit Five: Natural Disasters Part C Layers of the Earth: Inner Core Outer Core Mantle Asthenosphere Lithosphere The lithosphere is made of the crust and rigid upper mantle. It is broken into about 14 large plates. Mass: Percentages From Inside to Outside: Core 32% Mantle 66% Crust 2% The Core Composed of Iron and Nickel Inner Core – solid Outer Core – liquid High heat originates from gravitational pressure and radioactivity of heavy, unstable atoms. Heat source for convection in the mantle. Radioactive Decay Some atoms are unstable and decay or breakdown on their own. They release small particles. Certain heavy elements in the core, like Uranium, decay in such a way that they actually give off radiation. Gamma rays given off by decaying heavy elements in the core heat it up, like a flame heats a pot of soup. Magnetosphere (or E-M Field) The iron in the Earth’s core creates a magnetic blanket around our planet. It protects us from deadly radiation from the sun, deflecting it like a shield. Heat Transfer Heat moves through different materials in different ways. Conduction = moves through solids by contact. An example of conduction is burning your forehead with a curling iron. Convection = moves through fluids as density changes hotter = less dense, rises cooler = more dense, sinks Radiation = Decay of radioactive materials Gamma rays, alpha particles, etc. Heat Transfer cont. Heat is generated in the core via radiation. The heat in the core moves up through the lower solid mantle through conduction (or direct contact.) The upper mantle is partially molten and plastic, meaning it is able to flow. Heat moves through it by convection. It is made of fluid rock, known as magma. Heat Transfer cont. The heat from the lower mantle moves into the upper mantle through convection. Magma is heated and becomes less dense so it rises. When it nears the crust, it cools, becomes more dense, and begins to sink. The rising and falling current is like a conveyor belt, moving in a circular pattern forever. This current moves the plates. Convection in the Upper Mantle (Asthenosphere): The Asthenosphere The mantle is the thickest layer of the Earth. It is mostly solid and very dense. The mid to upper layer -the asthenosphere -- is fluid and supports the rigid, solid layer above it. The Lithosphere The “lithosphere” contains continental crust & oceanic crust & the rigid portion of the upper mantle The lithosphere is the “plate” in plate tectonics The Major Plates Location of Earthquakes and Volcanoes Plate Interactions: Types of Plate Boundaries: Divergent (tensional force = ) Transform (shearing force = ) Convergent (compressional force = ) Continental to continental collision Continental to oceanic collision Oceanic to oceanic collision Subduction (compressional force = ) Continental to oceanic collision Hot Spots Divergent Plate Boundary: Plates move away from each other. New crust is formed at the boundary between the plates in a central rift valley --> Lava flows out and is added to both plates. Features: mid-ocean ridge, rift, fissure, rift valley, lava flows, shallow earthquakes Ocean Ridges & Rises: Ridges are the longest chains of mountains found on Earth, looking like the seams on a baseball. A rift valley runs down the center and the ridge is offset along its length. Lava flows out from the central fissure, adding new sea floor to the edges of the plates. Small earthquakes are frequent along the ridge’s transform faults. Ex. = Mid-Atlantic Ridge, East Pacific Rise, Antarctic Ridge, Mid-Indian Ridge. Magnetic Polarity: Magnetic Polarity: The rocks forming along the edges of the mid-ocean ridge show a banded pattern of polarity reversals in the Earth’s magnetic field. The rocks closets to the ridge are the youngest and the rocks farthest away are the oldest. The age of the rocks near the coasts of N. America and Europe show that they formed 200 million years ago-just like Wegener speculated! Divergent Boundary (cont): Divergent boundaries form over time: Step 1. Continental Bulge -- magma pushes up. Step 2. Rift Valley -- land rifts apart and new crust is created. Ex. = East African Rift Valley. Step 3. Linear Sea -- rift valley floods with ocean water and becomes a long, thin sea. Ex. = Red Sea. Step 4. Ocean -- millions of years later, the sea widens to oceanic proportions. A mid-ocean ridge with a rift valley is found in the middle. Ex. = Atlantic Ocean.* *When one ocean opens, another has to close! Transform Boundary: At a transform boundary, plates slide past each other The San Andreas Fault is an example of a transform boundary The North American Plate is sliding past the Pacific Plate. Transform Boundary: 2 or more plates slide past each other slowly at a fault. Stress builds up in the rocks over time and slippage occurs abruptly. The energy released causes an earthquake. Features: fault, shallow hypocenter earthquakes Ex. = San Andreas Fault, California (N. Am plate + Pacific plate) C-C Convergent Boundary: Continental to continental convergence creates folded, non-volcanic mountains. A period of mountain building is called an orogeny. The densities of the two continental plates are equal, so they bend upwards. The heat and pressure created by the slow, unstoppable plate motion folds the rock layers. Syncline Anticline Non-Volcanic Mountain Ranges Mountains form when the two plates collide and get shorter and thicker. The tops are eroded by wind, water, and ice. Ex. = Appalachians, Atlas, Alps, Caucusus, Himalayas, & Urals C-O Convergent Boundary: Continental to oceanic convergence exhibits the collision of different types of crust. Ocean crust is most dense & sinks beneath the continental crust into the asthenosphere and melts. Features: subduction zone, oceanic trench (deepest parts of the Earth’s surface), deep hypocenter earthquakes, volcanic coastal mountains, and volcanic island arcs. Ex. = Andes (S. America), Cascades (N. America), Japanese Is., Philippine Is., Java & Sumatra, Caribbean Is. C-O Convergent Boundary: Most trenches are named for the country or islands they parallel; i.e. Peru-Chile, Japan, Filipino, Java, Aleutian, Caribbean, etc. Deep Earthquakes! O-O Convergent Boundary Older plate subducts beneath younger plate Very deep trench Part of subducted plate melts and forms volcanoes on ocean floor “Island Arcs” if volcanoes rise above ocean Aleutian Islands, Alaska The Rocky Mtns Are Weird: The Rockies formed when the N. American plate overran the Pacific Plate and the East Pacific Rise (the Kula & Farallon Plates). The heat from the mid-ocean rift valley created a range of mountains. Plutons (bubbles of magma) pushed up the land, then were eroded by moving ice into the jagged peaks visible today. Hot Spots: Hot Spots are volcanic regions in the middle of plates, away from edges. They feature single shield volcanoes (continental or island), hot springs and geysers. They form as a column of magma punches through a plate as it passes over. Ex. = Hawaii, Bermuda, & Yellowstone Natl. Park. Hot Spots of the World: Earth Features: Plate Tectonics Cannot Yet Explain: -Tectonics of Earliest Earth -Location of Many Small Plate Fragments -Future Plate Motions -Global Pattern of Plates (Is there a geometrical pattern?) -How and Where Plates Will Fragment -Details of Driving Mechanism