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Sea Floor Spreading
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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.

Published in: Technology, Automotive

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  • 1. Sea-Floor Spreading
  • 2. Standard
    • Explain how constructive and destructive forces (e.g. continental drift, earthquakes, volcanoes, weathering, erosion) change the Earth’s surface.
  • 3. Essential Question
    • Is the Earth getting bigger or smaller?
  • 4. 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
  • 5. 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.
  • 6. The Earth’s longest mountain range is underwater
    • Mid-Ocean Ridge
  • 7.
    • The mid-ocean ridge (shown in red) winds its way between the continents much like the seam on a baseball.
  • 8. 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.
  • 9.  
  • 10. Example of sea floor spreading
  • 11. Evidence of sea-floor spreading
    • New Molten Material
  • 12. Evidence of sea-floor spreading
    • Magnetic stripes
  • 13.  
  • 14.
    • 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.
  • 15. 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.
  • 16. Why doesn’t the Earth get bigger?
    • Subduction
  • 17.  
  • 18.
  • 19.
    • 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.
  • 20.
    • Subduction is causing the Pacific ocean to get smaller.
    • The Atlantic ocean has few subduction zones and is therefore getting larger.
  • 21. 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.
  • 22. Major Tectonic Plates
  • 23.
    • 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.
  • 24. 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.
  • 25.  
  • 26. 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.
  • 27.  
  • 28. 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.
  • 29.