Chapter 7: Plate Tectonics
I. Earth’s Structure: The Earth’s interior has been mapped using the seismic waves from earthquakes.
A. Lithosphere
~This layer is made up of the crust and the upper most part of the mantle.
~The two types of crust are oceanic (thin and dense) and continental (thick but less dense)
~This layer is broken into large tectonic plates.
B. Asthenosphere
~This layer of the mantle is heated and flowing…The lithosphere floats on top of this layer.
C. Mesosphere
~This is the sturdy lower layer of the mantle.
D. Outer Core
~Molten liquid iron. This spinning and churning iron gives us our magnetic field.
E. Inner Core
~Solid iron under incredible pressure.
II. Continental Drift
A. Pangaea : This supercontinent started splitting and drifting apart 200 million years ago
~ Similar fossils are found on different continents that are now separated by ocean.
B. Sea floor spreading : new crust forms as lava seeps between the plates at mid ocean ridges
~ This movement averages about 5 centimeters a year.
III. Plate Tectonics :
A. Convergent Boundaries: occur where plates are colliding
1. Continental-continental collision causes uplift as the plates fold and buckle.
~ This is occurring with the Himalayan mountains as the Indian plate collides with Asia.
2. Continental-oceanic collisions cause ocean crust to subduct or sink beneath the continent.
B. Divergent Boundaries: occur where plates are separating.
C. Transform Boundaries: occur where plates are sliding past each other.
** The movement of the plates is driven by the convection currents that form inside the asthenosphere.**
IV. Faults
A. Normal faults occur when the hanging wall moves down the footwall
B. Reverse faults occur when the hanging wall moves up the footwall.
C. Strike-slip faults occur when the rocks slide horizontally against each other.
In a nutshell…
Convergent Boundaries  Colliding  Compression Reverse Faults
Divergent Boundaries Dividing  Tension  Normal Faults
Transform Boundaries  Sliding  Strike/Slip Faults  San Andreas in California
Figure 9-1