Sea Floor Spreading


Published on

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

Published in: Technology, Automotive
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Sea Floor Spreading

  1. 1. Sea-Floor Spreading
  2. 2. Standard <ul><li>Explain how constructive and destructive forces (e.g. continental drift, earthquakes, volcanoes, weathering, erosion) change the Earth’s surface. </li></ul>
  3. 3. Essential Question <ul><li>Is the Earth getting bigger or smaller? </li></ul>
  4. 4. What caused Wegener’s theory to be accepted? <ul><li>Evidence of sea-floor spreading </li></ul><ul><li>New technology called sonar </li></ul><ul><li>Sonar allowed sea floor mapping </li></ul><ul><li>Huge crack discovered in the middle of the Atlantic Ocean </li></ul>
  5. 5. There is a chain of submerged mountains running through the center of the Atlantic Ocean. <ul><li>This chain is called the Mid-Atlantic Ridge. </li></ul><ul><li>This ridge is part of a system of ocean ridges. </li></ul><ul><li>Mid-ocean ridges are underwater mountain chains that run through Earth’s ocean basins. </li></ul>
  6. 6. The Earth’s longest mountain range is underwater <ul><li>Mid-Ocean Ridge </li></ul><ul><li> </li></ul>
  7. 7. <ul><li>The mid-ocean ridge (shown in red) winds its way between the continents much like the seam on a baseball. </li></ul>
  8. 8. Mid Ocean Ridges are where sea floor spreading occurs. <ul><li>Sea floor spreading is the process by which new oceanic lithosphere is created as older materials are pushed away. </li></ul><ul><li>As tectonic plates move away from each other, the sea floor spreads apart and magma rises to fill the gap. </li></ul>
  9. 10. Example of sea floor spreading <ul><li> </li></ul>
  10. 11. Evidence of sea-floor spreading <ul><li>New Molten Material </li></ul>
  11. 12. Evidence of sea-floor spreading <ul><li>Magnetic stripes </li></ul>
  12. 14. <ul><li>Drilling Samples </li></ul><ul><ul><li>The Glomar Challenger drilled for core samples. </li></ul></ul><ul><ul><li>Samples revealed that the rocks get older the further away from the ridge the samples are taken. </li></ul></ul>
  13. 15. The crust increases in age the farther it moves away from the mid-ocean ridge. <ul><li>What does this mean exactly? </li></ul><ul><li>It means that newer rock is closest to the ridge and older rock is farther away. </li></ul><ul><li>The oldest crust in the Atlantic Ocean is found near the edges of the continents. </li></ul>
  14. 16. Why doesn’t the Earth get bigger? <ul><li>Subduction </li></ul>
  15. 18. <ul><li> </li></ul>
  16. 19. <ul><li>Oceanic crust is denser than continental crust causing it to subduct under the continental crust when plates converge. </li></ul><ul><li>When oceanic plates converge, the older and denser plate subducts under the younger and less dense plate. </li></ul><ul><li>Continental plates converging create mountains. </li></ul>
  17. 20. <ul><li>Subduction is causing the Pacific ocean to get smaller. </li></ul><ul><li>The Atlantic ocean has few subduction zones and is therefore getting larger. </li></ul>
  18. 21. The theory of Plate Tectonics <ul><li>The proof of sea-floor spreading supported Wegener’s idea that continents move. </li></ul><ul><li>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. </li></ul>
  19. 22. Major Tectonic Plates
  20. 23. <ul><li>Plate tectonics is the theory that Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere. </li></ul><ul><li>Scientists have theorized that there are three different ways plates are able to move: convection, slab pull, and ridge push. </li></ul>
  21. 24. Convection <ul><li>In the process of convection, hot material from deep within the Earth rises while cooler material near the surface sinks. </li></ul><ul><li>When the warmer material cools, it becomes denser and begins to sink back down. </li></ul><ul><li>The motion of convecting mantle material drags tectonic plates sideways. </li></ul>
  22. 26. Ridge Push <ul><li>At mid-ocean ridges, the oceanic lithosphere is higher than it is where it sinks beneath continental lithosphere. </li></ul><ul><li>Ridge push is the process by which an oceanic plate slides down the lithosphere-asthenosphere boundary. </li></ul>
  23. 28. Slab Pull <ul><li>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. </li></ul>