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Unveiling the Hidden Mountains: Secrets of Sea-Floor Spreading

Explore the mysterious world of undersea mountains at the Mid-Ocean Ridge, Earth's largest mountain chain stretching across oceans. Uncover the process of sea-floor spreading, as molten material pushes older rocks aside. From Harry Hess's groundbreaking theories to magnetic stripes and subduction zones, learn how the ocean floor is continually changing. Discover how sonar technology helps map the ocean floor, revealing the dynamic forces shaping our planet. Are the oceans shrinking or expanding? Join the exploration to find out more!

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Unveiling the Hidden Mountains: Secrets of Sea-Floor Spreading

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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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