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Cornell Notes Lecture, reading/chapter/novel/article during class, power point, movies (if need to collect info.) “Inside Earth” _________________________ __________________ Topic:__ Name: _______First & Last____________________________ Class: _____Science____________ Period: ___All_____ Date: ____________October 2016________________ Chapter 1, Section 4: Sea-Floor Spreading Essential Question: How does the theory of plate tectonics explain the cycling of Earth’s materials and the flow of energy that drives the process? Notes: Questions/Main Ideas: Chapter 1, Section 4: Sea-Floor Spreading Evidence for Sea-Floor Spreading * Mid-Ocean Ridges are chains of volcanoes that wind around Earth; the system is more than 50,000 km long. Most of the mountains are deep underwater, but the island of Iceland is a part of a mid-ocean ridge. What is Sea-Floor Spreading? * Harry Hess connected mid-ocean ridges to Wegener’s hypothesis of Continental Drift. * “In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carry the continents along with them. Evidence for Sea-Floor Spreading * “Several types of evidence supported Hess’s theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves. * Evidence from Drilling Samples: rock farther from the ridge is older; rock closer to the ridge is younger. Subduction at Trenches * In a process called subduction, which takes tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches. Summary: * The sea floor spreads apart along both sides of a mid-ocean ridge; new crust is added. The ocean floors move like conveyor belts, carrying the continents along with them. * Evidence for Hess’s theory sea-floor spreading: eruptions of molten material at mid-ocean ridges, magnetic patterns in the rock, and the ages of the rocks. * Subduction happens at deep-ocean trenches (and elsewhere), where oceanic crust sinks down into the mantle.