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Chapter One: Plate Tectonics

Chapter One: Plate Tectonics. Section 4: Sea-Floor Spreading Pages 33-39. Do mountains exist under water?. Mid-Ocean Ridge. Longest chain of mountains in the world It extends into all of Earth’s oceans Most of the mountains are hidden under water

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Chapter One: Plate Tectonics

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  1. Chapter One: Plate Tectonics Section 4: Sea-Floor Spreading Pages 33-39

  2. Do mountains exist under water?

  3. Mid-Ocean Ridge • Longest chain of mountains in the world • It extends into all of Earth’s oceans • Most of the mountains are hidden under water • A steep-sided valley splits the top for most of its length • Mid Atlantic Ridge https://www.youtube.com/watch?v=bGye6vlOpbY • https://www.youtube.com/watch?v=sgDM6m0lUGY

  4. Sonar • Scientists use sonar to map the ocean floor. • Sonar = a device that bounces sound waves off underwater objects and then records theechoes of these sound waves. • The time it takes for the echo to arrive indicates the distance to the object.

  5. Scientists wondered… • What is this ridge? • How did it get here?

  6. Harry Hess • Harry Hess, an American geologist, was one of the scientists who studied the mid-ocean ridge. • In 1960, he suggested that the ocean floors move like conveyor belts, carrying the continents along with them. • Maybe Wegener was right!!!

  7. Sea-Floor Spreading • 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. • Hess called this process that continually adds new material to the ocean floor sea-floor spreading. • Bill Nye www.youtube.com/watch?v=GyMLlLxbfa4

  8. Evidence from Molten Material • Scientists traveled to the ocean floor in Alvin, a submersible built to handle the crushing pressure. • They discovered strange rocks shaped like pillows. • These rocks can only form when molten material hardens quickly after erupting under water.

  9. Evidence from Magnetic Stripes • Earth’s magnetic poles have reversed themselves. • If the poles suddenly reversed themselves today, your compass needle would point south. • Rock that makes up the ocean floor lies in a pattern of magnetized “stripes”.

  10. http://www.sciencechannel.com/tv-shows/greatest-discoveries/videos/100-greatest-discoveries-magnetic-field-reversal.htmhttp://www.sciencechannel.com/tv-shows/greatest-discoveries/videos/100-greatest-discoveries-magnetic-field-reversal.htm

  11. Evidence from Drilling Samples • The Glomar Challenger, a drilling ship built in 1968, gathered rock samples by drilling into the ocean floor. • Scientists determined the age of the rock. • The farther away from the ridge the samples were taken, the older the rocks were. • The youngest rocks were always in the center of the ridges.

  12. Subduction • Oceanic crust created along the mid-ocean ridge is destroyed at a deep-ocean trench. • In the process of subduction, oceanic crust sinks down beneath the trench into the mantle.

  13. Are the oceans shrinking? • Subduction and sea floor spreading can change the size and shape of the oceans. • The ocean floor is renewed about every 200 million years. • Pacific Ocean is shrinking while the Atlantic Ocean is expanding.

  14. Words Worth Knowing (ISN #44) • mid-ocean ridge • sonar • sea-floor spreading • deep-ocean trench • subduction

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