Sci. 4-3 The Theory of Plate Tectonics Pages 99-102

A. Plate Tectonics- a theory that the Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere.

B. 3 Possible Causes of Plate Tectonics 1) Ridge Push- the process by which an oceanic plate slides down the lithosphere-asthenosphere boundary

2) convection- hot magma rises while cooler magma sinks since it is more dense. As it sinks, it heats up. As it rises, it cools. This is a continuous cycle. The motion of convecting mantle drags the plates.

3) slab pull- because oceanic lithosphere is denser than the asthenosphere, the edge of the oceanic plate sinks and pulls the plate with it.

C. Plate Boundaries- 1) Convergent Boundary- 2 plates collide into each other

a) mountains usually occur b) oceanic crust is denser than continental crust so it goes under when the 2 collide

c) subduction zone- the area where oceanic crust sinks down into the asthenosphere

2) Divergent Boundaries- 2 plates pull apart from each other a) Mid Ocean Ridges are at divergent boundaries.

3) Transform Boundaries- 2 plates slide past each other a) often produces Earthquakes

D. Global Positioning System (GPS)- a network of satellites used to measure the rate of tectonic plates movements