Download Inside Restless Earth 4

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 lithosphereasthenosphere 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