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Sea Floor Spreading
 

Sea Floor Spreading

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Developed for 8th grade students. Describes the evidence Alfred Wegener used in his theory.

Developed for 8th grade students. Describes the evidence Alfred Wegener used in his theory.

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    Sea Floor Spreading Sea Floor Spreading Presentation Transcript

    • Sea-Floor Spreading
    • Standard
      • Explain how constructive and destructive forces (e.g. continental drift, earthquakes, volcanoes, weathering, erosion) change the Earth’s surface.
    • Essential Question
      • Is the Earth getting bigger or smaller?
    • What caused Wegener’s theory to be accepted?
      • Evidence of sea-floor spreading
      • New technology called sonar
      • Sonar allowed sea floor mapping
      • Huge crack discovered in the middle of the Atlantic Ocean
    • There is a chain of submerged mountains running through the center of the Atlantic Ocean.
      • This chain is called the Mid-Atlantic Ridge.
      • This ridge is part of a system of ocean ridges.
      • Mid-ocean ridges are underwater mountain chains that run through Earth’s ocean basins.
    • The Earth’s longest mountain range is underwater
      • Mid-Ocean Ridge
      • https://www.ocean.udel.edu/extreme2004/geology/mission/divelocation/ridge.html
      • The mid-ocean ridge (shown in red) winds its way between the continents much like the seam on a baseball.
    • Mid Ocean Ridges are where sea floor spreading occurs.
      • Sea floor spreading is the process by which new oceanic lithosphere is created as older materials are pushed away.
      • As tectonic plates move away from each other, the sea floor spreads apart and magma rises to fill the gap.
    •  
    • Example of sea floor spreading
      • http://www.uwsp.edu/geo/faculty/ritter/glossary/s_u/sea_flr_spread.html
    • Evidence of sea-floor spreading
      • New Molten Material
    • Evidence of sea-floor spreading
      • Magnetic stripes
    •  
      • Drilling Samples
        • The Glomar Challenger drilled for core samples.
        • Samples revealed that the rocks get older the further away from the ridge the samples are taken.
    • The crust increases in age the farther it moves away from the mid-ocean ridge.
      • What does this mean exactly?
      • It means that newer rock is closest to the ridge and older rock is farther away.
      • The oldest crust in the Atlantic Ocean is found near the edges of the continents.
    • Why doesn’t the Earth get bigger?
      • Subduction
    •  
      • http://ve.ou.edu/weaver/plates/subduct.htm
      • Oceanic crust is denser than continental crust causing it to subduct under the continental crust when plates converge.
      • When oceanic plates converge, the older and denser plate subducts under the younger and less dense plate.
      • Continental plates converging create mountains.
      • Subduction is causing the Pacific ocean to get smaller.
      • The Atlantic ocean has few subduction zones and is therefore getting larger.
    • The theory of Plate Tectonics
      • The proof of sea-floor spreading supported Wegener’s idea that continents move.
      • Both oceanic and continental crust appear to move, so a new theory was devised to explain both continental drift and sea-floor spreading: The Theory of Plate Tectonics.
    • Major Tectonic Plates
      • Plate tectonics is the theory that Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere.
      • Scientists have theorized that there are three different ways plates are able to move: convection, slab pull, and ridge push.
    • Convection
      • In the process of convection, hot material from deep within the Earth rises while cooler material near the surface sinks.
      • When the warmer material cools, it becomes denser and begins to sink back down.
      • The motion of convecting mantle material drags tectonic plates sideways.
    •  
    • Ridge Push
      • At mid-ocean ridges, the oceanic lithosphere is higher than it is where it sinks beneath continental lithosphere.
      • Ridge push is the process by which an oceanic plate slides down the lithosphere-asthenosphere boundary.
    •  
    • Slab Pull
      • Because oceanic lithosphere is denser than the asthenosphere, the edge of the oceanic plate sinks and pulls the rest of the tectonic plate with it in a process called slab pull.
    •