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Harry Hess

Harry Hess. Naval Officer in World War II Sea Floor Spreading Theory -mid-ocean ridges -magnetic striping - recycling of the seafloor. http://pubs.usgs.gov/gip/dynamic/HHH.html Biography of Harry Hess. Seafloor Spreading. Harry Hess

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Harry Hess

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  1. Harry Hess Naval Officer in World War II Sea Floor Spreading Theory -mid-ocean ridges -magnetic striping - recycling of the seafloor http://pubs.usgs.gov/gip/dynamic/HHH.html Biography of Harry Hess

  2. Seafloor Spreading Harry Hess 1960s – the theory of seafloor spreading proposed to explain presence of mid-ocean ridge. • SONAR (sound, navigation, and range) used to map the ocean floor • A system of underwater mountain ranges discovered around the world

  3. Seafloor Spreading • Questions Hess wanted answers to: • Why is there so little sediment deposited on the ocean floor? If the oceans have existed for at least 4 billion years, as most geologists believed, shouldn’t there be more? • Why are fossils found on the seafloor no more than 180 million years old? Marine fossils in sedimentary rocks on land -- some of which are found high in the Himalayas, over 8,500 m above sea level – are much older. • How do the continents move?

  4. Seafloor Spreading • Hess’ reasoning: • Sediment has been accumulating for about 300 million years at most. • Matches time needed for the ocean floor to move from the ridge crest to the ocean trenches, where oceanic crust descends into the trench and is destroyed. • Magma is continually rising along the mid-oceanic ridges, "recycling" crustal material by creating new oceanic crust. • Recycling of the seafloor explains why the oldest fossils found on the seafloor are no more than about 180 million years old.

  5. Seafloor Spreading • Explains how continents moved • Wegener thought the continents must simply "plow" through the ocean floor, critics argued this was physically impossible. • With seafloor spreading, the continents did not have to push through the ocean floor but were carried along as the ocean floor spread from the ridges.

  6. Sonar - Echo Sounding

  7. Evidence for Seafloor Spreading • molten material - erupting along mid-ocean ridges • magnetic striping - reversals of Earth’s magnetic field is recorded in stripes parallel to the ridges (last was 780,000 years ago) • drilling samples • Glomar Challenger – drilling ship built in 1968, youngest rocks were always found at the mid-ocean ridges

  8. What’s goin’ on? • Hot, less dense material below Earth’s crust rises upward to the surface at the mid-ocean ridges. • It then flows sideways, carrying the seafloor away from the ridge. • As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor.

  9. Seafloor Spreading

  10. Magnetic Striping

  11. Seafloor Spreading & Magnetic Striping • Mid-ocean ridge topography with magma chamber below, • Magma rises and new ocean plate spreads away from ridge. • Magnetic stripes form in igneous rocks containing iron as they move away from ridge.

  12. Magnetic Reversals • What is the process? • reversals happen infrequently—on average every 250,000 years • it's been over 700,000 years since the last reversal, and the next one may be currently underway • NOVA Animation of Magnetic Pole Reversals click on “Launch Interactive”

  13. Age of Crust Glomar Challenger

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