Plate Tectonics
Theory of why and how plates
move
Pangaea
• http://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 MidAtlantic 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.