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Earth Today PBS: Sea-Floor Spreading Word: Continental Drift Hypothesis Word: Continent Word: Sea-floor Spreading Word: Tectonic Plate Word: Magma Word: Magnetic anomaly Word: magnetic reversal Word: paleomagnetism Word: Mid-ocean ridges Word: Rift (valley) Word: Subduction Word: Trench Magnetic Reversals in Oceanic Crust: Draw & Label Seafloor Spreading • supports the continental drift hypothesis process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies. Subduction supports the continental drift hypothesis Two major processes of plate tectonics •Seafloor spreading •Subduction Seafloor Spreading Mid-Ocean Ridges Mid-ocean ridges are underwater mountain chains that run through Earth’s ocean basins. • ● location where seafloor spreading takes place. Subduction • Moving seafloor collides into continental crust • Subduction occurs when a denser (oceanic) crust moves under a less dense (continental) crust ● occurs only at “convergent” boundaries Seafloor Spreading • Subduction forms “trenches” • Trench? hemispheric-long, narrow depressions of the sea floor. deepest parts of the ocean floor! Some not measurable most important natural boundaries formed between two lithospheric plates. • • • • Subduction form “trenches” ● A trench marks the position at which the denser slab begins to descend beneath another lithospheric slab (less dense). ● 3 to 4 km (1.9 to 2.5 mi) below the level of the surrounding oceanic floor. ● The deepest ocean depth to be sounded is Mariana Trench at a depth of 10,911 m (35,798 ft) below sea level. Seafloor Spreading • Who • How • Where • When study the Earth's ancient magnetic field Has magnetic field always pointed North? Magnetic Anomaly Fluctuations or variations in the intensity of the magnetic field Magnetic Reversals On seafloors: at the boundaries between New & Older sections seafloor Magnetic Field is Reversed in Direction On Continental Crust: Lots of magnetic anomalies, no set pattern or prediction Direction of N-S Polarity changes ~ +100 000 y MAGNETIC FIELDS A field of attraction or repulsion to another substance based on its composition MAGNETIC FIELDS ● Outer core of the Earth The molten iron flows creates an electric current (flow of electrons) & a magnetic field that surrounds Earth ● The magnetic field created in the center of the planet makes your compass point north Protects the Earth from solar winds. MAGNETIC FIELDS MAGNETIC FIELDS Who • How • Where • When • The older crust moves outward. Dates are confirmed by the Magnetic Reversal of the crust. Magnetic Strips along the Mid-Ocean Ridge Why does “Seafloor Spreading” support CD hypothesis? How does “Subduction” fit with “Seafloor Spreading” ? Earth’s Lithospheric Plates In the Future? RESOURCES • http://images.yourdictionary.com/pangaea • http://www.sciencebuddies.org/science-fairprojects/project_scientific_method.shtml • http://www.sciencedaily.com/articles/o/oceani c_trench.htm • www.appstate.edu/~marshallst/GLY1101/.../3Continental_Drift.pptx RESOURCES ● ● http://www.sciencebuddies.org/science-fairprojects/project_scientific_method.shtml http://www.sciencedaily.com/articles/o/oceanic_t rench.htm ● www.appstate.edu/~marshallst/GLY1101/.../3Continental_Drift.pptx