Sci. 4-3

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Sci. 4-3 The Theory of Plate Tectonics Pages
99-102
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A. Plate Tectonics- a theory that the Earths
lithosphere is divided into tectonic plates that
move around on top of the asthenosphere.
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B. 3 Possible Causes of Plate Tectonics 1) Ridge
Push- the process by which an oceanic plate
slides down the lithosphere-asthenosphere boundary
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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.
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3) slab pull- because oceanic lithosphere is
denser than the asthenosphere, the edge of the
oceanic plate sinks and pulls the plate with it.
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C. Plate Boundaries- 1) Convergent Boundary- 2
plates collide into each other
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a) mountains usually occur b) oceanic crust is
denser than continental crust so it goes under
when the 2 collide
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c) subduction zone- the area where oceanic crust
sinks down into the asthenosphere
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2) Divergent Boundaries- 2 plates pull apart from
each other a) Mid Ocean Ridges are at divergent
boundaries.
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3) Transform Boundaries- 2 plates slide past each
other a) often produces Earthquakes
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D. Global Positioning System (GPS)- a network of
satellites used to measure the rate of tectonic
plates movements