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The Theory of Plate Tectonics What are tectonic plates? What are tectonic plates? lithosphere- the crust and rigid upper layer of the mantle, broken up into blocks called tectonic plates 3 types of tectonic plates (a.k.a. crust) 1) Continental crust = low-density silicate rock (granite) 2) Oceanic crust = dense, Iron/Mg rich rock (basalt) 3) A combination of continental and oceanic Where are tectonic plates found? The plates are Earth’s shell; but unlike an eggshell, these pieces are always being created, destroyed, or moved How is plate movement explained? The theory of plate tectonics- How tectonic plates move around on a plastic layer of the mantle called the asthenosphere “Plastic”- like nacho cheese, pudding, or syrup Where is plate movement happening? Where is plate movement happening? Where one plate ends and another plate begins; cracks in the lithosphere mark plate boundaries What are the 3 plate boundaries? There are 3 kinds of boundaries: Divergent = spreading boundaries Convergent = colliding boundaries Transform = sliding boundaries What are mid-ocean ridges? What are mid-ocean ridges? Divergent = spreading boundaries Mid-ocean ridge- An undersea mountain range with a rift valley running through the center of it Hot magma rises to the surface, cools as rock, and the new crust spreads out 60 foot-wide boundary of the N. American and Eurasian plates Mid-ocean ridges = rift zones Rift- cracks in the center of a ridge where magma, which is less dense than rock, flows upward Mid-ocean ridges = rift zones Rifting causes new crust to push the older crust aside; they are divergent, or spreading, boundaries What is paleomagnetism? Iron inside the Earth makes Earth a giant magnet When hot magma cools off, the bits of iron in the crust will point to the poles like a compass needle Paleomagnetism = Earth’s magnetic memory Iron in new crust pushes the older crust aside; they record their polar-charge for thousands of years The magnetic poles have reversed in the past, and the rocks on the sea-floor show this change Proof for the Theory of Plate Tectonics: Recording movement at plate boundaries (earthquakes) Studying how magma forms new crust at rift valleys and mid-ocean ridges (rifting) Observing that many volcanoes are occurring near plate boundaries, such as, the Ring of Fire What is the Ring of Fire? What is the Ring of Fire? A zone of active volcanoes and earthquakes that marks the Pacific Plate boundary Deep- point that goes very far down into the crust Trench- steep, narrow valley where a plate ends For your summary answer… What are tectonic plates made of? What are the 3 types of boundaries? What is paleomagnetism? Resources Wikipedia http://images.google.com/imgres?imgurl=http://mens abarbie.com/bloggerimages/MB_Leif_luck_bridge_tect on%2520copy.JPG&imgrefurl=http://mensabarbie.blogspot.com/2007_03_01_archive.html&usg=_ _AjtDMB4aNJNetWXCb0hnRWFnrM=&h=272&w=425&sz=33&hl=en&star t=3&um=1&itbs=1&tbnid=Gm8U8eb0aJOBM:&tbnh=81&tbnw=126&prev=/images%3Fq%3DBr idge%2Bacross%2Bthe%2B%25C3%2581lfagj%25C3 %25A1%2Brift%2Bvalley%26um%3D1%26hl%3Den %26sa%3DN%26rlz%3D1R2GWYE_en%26tbs%3Di sch:1 What is the Ring of Fire? A zone of active volcanoes and earthquakes that marks the Pacific Plate boundary Deep- point that goes very far down into the crust Trench- steep, narrow valley where a plate ends Warm up 1) Describe one part of this figure or, describe a part that you do not understand. 2) What do you think is a good title for this figure? 3) How many plate boundaries do you see?