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Sea Floor Spreading

Sea Floor Spreading. Mid-Ocean ridge continuous chain of volcanoes on the ocean floor . Longest mountain system Encircles the Earth Peaks up to 12,000 feet high. New oceanic crust is made here by magma erupting from the mantle. Rift valley is 15–30 miles wide

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Sea Floor Spreading

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  1. Sea Floor Spreading

  2. Mid-Ocean ridgecontinuous chain of volcanoes on the ocean floor Longest mountain system Encircles the Earth Peaks up to 12,000 feet high New oceanic crust is made here by magma erupting from the mantle

  3. Rift valley is 15–30 miles wide This is where tectonic plates are moving apart and where magma erupts to form new oceanic crust Mid-Ocean Ridge Steep sided valley splits the top of the mid-ocean ridge ...called a rift valley Bill Nye_Seafloor Spreading Video Clip

  4. Parts of the Mid-Ocean Ridge are above sea level The Mid-Atlantic Ridge is splitting Iceland. The East African Rift Zone may be the next major ocean.

  5. Seafloor spreading begins at the mid-ocean ridge • Tectonic plates here are moving apart and new oceanic crust is created by magma erupting from the mantle • ...like two giant conveyor belts slowly moving in opposite directions and transporting newly formed oceanic crust away from the rift valley seafloor spreading animation

  6. Molten Material • strange rocks shaped like tooth paste squeezed from a tube • form only when magma erupts underwater and quickly hardens • Magma = molten rock, minerals, gases • http://www.pmel.noaa.gov/vents/nemo/explorer/concepts/pillow_lava.html

  7. Oceanic crust made of mostly BASALT • Basalt is volcanic rock • Rich in iron and magnetite • Grains of magnetite behave like little magnets, aligning with Earth’s magnetic field • Magma cools and “locks in” magnetite

  8. Magnetic Stripes Khan Academy_Magnetic Reversals • Earth’s magnetic poles have reversed themselves many times. • Stripes of rock parallel to mid-ocean ridge alternate in magnetic polarity. • The stripes match perfectly on both sides of the ridge. animation with magnetic reversals

  9. Drilling Samples • Rock samples further away from the mid ocean ridge are older than rocks closer to the mid ocean ridge. • Newly formed oceanic crust pushes older crust outward and away from the rift

  10. Subduction • Oceanic crust created along the mid-ocean ridge is destroyed and recycled at a deep ocean trench • This is where tectonic plates are colliding. • The plate carrying denser oceanic crust is forced under the other plate and back into the mantle • Seafloor spreading and subduction recycle ocean floor about every 200 million years and move continents around

  11. Magma Plumes hypothesis

  12. Ridge-push Hypothesis

  13. Slab-Pull hypothesis

  14. Works Cited • Khan Academy." Khan Academy. N.p., n.d. Web. 24 Mar. 2012. <http://www.khanacademy.org/>. • Kious, W. Jacquelyne, and Robert I. Tilling. "USGS Developing the Theory." This Dynamic Earth: The Story of Plate Tectonics. USGS Publications Warehouse, n.d. Web. 23 Mar. 2012. http://pubs.usgs.gov/gip/dynamic/dynamic • Thinkfilm Inc. (Producer).  (2005). Greatest Discoveries with Bill Nye: Earth Science. [Full Video].  Available from http://www.discoveryeducation.com/

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