Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Theory of Plate Tectonics Chapter 4 Section 5 Key Terms Plate Plate Tectonics Fault Spreading Boundary Rift Valley Colliding Boundary Sliding Boundary What are Tectonic Plates? The cracks in the continents are similar to the cracks in a broken eggshell. In the 1960’s, scientists proposed that these cracks break the lithosphere into separate sections called plates. The plates are responsible for carrying the continents and ocean floor. How Plates Move Plate Tectonics: the theory that states that pieces of Earth’s lithosphere are in slow, constant motion driven by the convection currents in the mantle. The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates. The plates are carried along like ice is carried on water. Plate Boundaries The edges of Earth’s plates meet at plate boundaries. Faults: breaks in the Earth’s crust where rocks have slipped past each other. There are three kinds of plate boundaries. The plates move about 1 to 24 centimeters per year. http://www.youtube.com/watch?v=ifke1GsjNN0 Type 1: Spreading Boundaries Spreading boundary: where two plates move apart. These are found along the edge of midocean ridges. Some can occur on land. A deep valley called a rift valley forms along the spreading boundary. Type 2: Colliding Boundaries Colliding boundary: the place where two plates come together (aka convergent boundary). Collision 1: two plates of oceanic crust collide, and the more dense plate sinks underneath. Collision 2: a oceanic plate collides with a continental plate, and subduction occurs. Collision 3: two plates of continental crust collide, but neither sinks. Instead, they push up mountain ranges. Sliding Boundaries Sliding boundary: a place where two plates slip past each other, moving in opposite directions (aka transform boundaries). Crust is neither created nor destroyed. Plate Motions Over Time Scientists have seen evidence showing that there were other super continents before Pangaea. Pangaea formed when Earth’s land masses came together about 260 million years ago. About 225 million years ago, Pangaea began spreading apart. http://www.youtube.com/watch?v=cQVoSyV u9rk