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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.

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Presentation on theme: "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."— Presentation transcript:

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

4 The Mid-Atlantic Ridge is splitting Iceland. The East African Rift Zone may be the next major ocean.

5  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  strange rocks shaped like tooth paste squeezed from a tube  form only when magma erupts underwater and quickly hardens  Magma = molten rock, minerals, gases  er/concepts/pillow_lava.html er/concepts/pillow_lava.html

7  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  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. Khan Academy_Magnetic Reversals animation with magnetic reversals

9  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  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

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14  Khan Academy." Khan Academy. N.p., n.d. Web. 24 Mar  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  Thinkfilm Inc. (Producer). (2005). Greatest Discoveries with Bill Nye: Earth Science. [Full Video]. Available from


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