Plate Tectonics

Plates The lithosphere (crust and upper mantle) is broken into separate sections called plates.

Floating Plates These plates float on top of the asthenosphere through convection currents.

The Theory of Plate Tectonics States that pieces of the Earth’s lithosphere are in constant, slow motion This theory explains the movement and subduction of plates on Earth.

The Movement of the Plates The convection currents in the asthenosphere causes the plates to move No plate can budge without affecting the other plates surrounding it

Review The lithosphere is broken in different sections. What are these sections called? What do the plates float on top of? What causes the plates to move? T/F: When the plates move, they do not affect the other plates in the Lithosphere.

Which Way Are They Going? The plates move in different directions. Pg. 133 (figure 23)

Where The Plates Meet The plates meet at boundaries. There are 3 kinds of plate boundaries: Transform boundaries Divergent boundaries Convergent boundaries

Transform Boundaries At a transform boundary, plates slip past each other moving in opposite directions Earthquakes are frequent here

San Andreas Fault Creek offset by the San Andreas Fault

Divergent Boundaries At a divergent boundary, two plates move apart Most occur at the Mid-Ocean Ridge

Divergent Boundaries When a divergent boundary occurs on land, a rift valley forms. A rift valley is a deep valley formed where the plates are separating

The Great Rift Valley in Africa

Convergent Boundaries At a convergent boundary, two plates come together, or converge. There are 3 types of convergent boundaries: Oceanic crust collides with oceanic crust Oceanic crust collides with continental crust Continental crust collides with continental crust

And the winner is… When two plates collide, the density of the plates determines which one comes out on top Remember: oceanic crust is more dense than continental crust

Oceanic VS Oceanic Two oceanic plates meet at a trench And the winner is: The less dense plate comes out on top The plate which is more dense dives under the other one and returns to the mantle (called subduction)

Oceanic VS Continental And the winner is: Continental comes out on top The oceanic plate is more dense so it sinks and plunges under the continental plate (subduction)  Continental Oceanic 

Continental VS Continental Subduction does not occur (neither is dense enough to sink into the mantle) This makes mountains And the winner is: IT’S A DRAW!

Slow Motion The plates move from 1 to 10 centimeters per year!!! North America and Eurasia move apart 2.5 centimeters per year This is how fast your fingernails grow

Review What are the 3 different boundaries? Which boundary occurs when two plates slip past each other? Which boundary occurs when two plates move apart from each other? Which boundary occurs when two plates collide together? What two plates collide to form mountains?