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Sea floor spreading
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  • 1. http://www.youtube.com/watch?v=GyMLlLx bfa4&feature=related While you watch….look for  Harry Hess  How did they find the mountain ranges?
  • 2. A. The Mid-Ocean Ridge is the longest chain of mountains in the world and are located on the ocean floor.
  • 3. : www.ocean.udel.edu The Mid-Ocean Ridge system, shown above snaking its way between the continents, is more than 56,000 kilometers (35,000 mi) long. It circles the earth like the stitching on a baseball!
  • 4. This is a model of sea floor spreading at a divergent boundary called a mid ocean ridge.
  • 5. B. Sonar is a device that bounces sound waves off underwater objects and then records the echoes of these sound waves. Scientists use sonar to study the ocean floor.
  • 6. C. Evidence for Sea-Floor Spreading The mid-ocean ridge forms along cracks in the oceanic crust 2. At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge 3. Sea floor spreading is the process by which new material is continually added to the ocean floor. 4. Several types of evidence is used to support seafloor spreading – magnetic stripes, molten material, and drilling samples 1.
  • 7. m.y. means million years ago Notice this compass.
  • 8. Can you explain this diagram!?
  • 9. http://platetectonics.pwnet.org/img/blocks.gif As the sea floor spreads, the lava cools according to the magnetic poles at the time. The rocks on the ocean floor have proved that the earth’s magnetic field sometimes reverses. The inner core flips and so the north pole moves to the southern hemisphere! The earth itself does not flip.
  • 10. D. Subduction at Deep-Ocean Trenches 1. Deep ocean trenches are where the ocean floor plunges into deep underwater canyons. They are formed where the oceanic crust bends toward the mantle. 2. Subduction – process by which the ocean floor sinks beneath a deep ocean trench and back into the mantle 3. At deep ocean trenches, subduction allows part of the ocean floor to sink back into the mantle, over tens of millions of years.
  • 11. The PACIFIC ocean is where most of the crust is getting subducted back into the Earth. Here, there are lot of volcanoes and earthquakes. It’s known as the Ring of Fire!