Plate Tectonics Theory of why and how plates move

Pangaea

eo/flash/2_1.swfhttp://www2.wwnorton.com/college/geo/eg eo/flash/2_1.swf

I.Layers of the Earth A.Lithosphere: A combination of the earth’s crust and upper mantle 1. ~ 55 miles thick 2. Contains oceanic and continental crust

a.Oceanic crust: portion of the crust that lies underneath the ocean, dense basaltic rock b. Continental crust: portion of the crust that makes up the continents, less dense granite

B. Asthenosphere: Layer of earth beneath the lithosphere. 1. semi solid rock that is like silly putty 2. More dense than the lithosphere

II.Types of plate boundaries A. Divergent boundary: two plates are moving away from each other

B. Convergent Boundary: plates are moving towards each other

1. 3 types of collisions at convergent boundary a. Oceanic crust vs. continental crust i. More dense crust goes underneath the less dense (subduction)

ii. Continental crust vs. continental crust same density so they go up (mountain ranges)

iii. Oceanic crust vs. oceanic crust Island arc forms

deep ocean trench

C. Transform Boundary: plates slip past each other

III. Causes of plate movement A.Convection: less dense things rise while more dense things sink 1. As the magma rises at the Mid- Atlantic ridge and creates new oceanic crust, dense crust is being forced under continents at convergent boundaries

B.Paleomagnetism on the Ocean Floor: Magnetic patterns on the ocean floor alternate as liquid rock solidifies and locks in the magnetic orientation of the earth.