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Aim: How does the Theory of Plate
Tectonics influence the way the Earth is
today?
I. Plate Tectonics
A. Theory of Plate Tectonics
1. The surface of the Earth is composed of
about a dozen major rigid, moving crustal
plates and several smaller plates
2. Plates
a. Slabs of Earth’s lithosphere (crust and
upper mantle)
b. Average thickness is 100 km (62 miles)
c. Most plates support both continent and
ocean
B. Continental Drift – states that the
continents have drifted and still are drifting
apart.
C. Why do the plates move?
1. Due to tremendous heat, rock in the
asthenosphere is like hot taffy
2. This allows plates to ride on top of hot,
flowing rock.
3. Plates move because heat is being
released from deep inside the earth.
4. Convection currents causes hot material
to rise and expand (plates diverge) and
cooler material to sink and contract
(plates converge).
Alfred Wegener
D. Alfred Wegener – proposed that in the
distant past, the Earth’s continents were all
joined as a single landmass.
1. Evidence for his theory
a. South America and Africa would fit
remarkably well, shoreline to shoreline.
b. If the Americas were moved next to Africa
and Europe, there would be a match of
ancient continental rocks and tectonic (fold
and fault) structures.
c. Pangaea – when Wegener placed all the
continents together like a puzzle, it formed
a large landmass which he called Pangaea.
Fossil Evidence
GIF image 240x180 pixels
http://www.hartrao.ac.za/geodesy/tectonics.html
Animated Plate Tectonic Reconstruction
http://pubs.usgs.gov/publications/text/dynamic.html
http://www.geocities.com/jac6610805
http://wrgis.wr.usgs.gov/docs/parks/animate/A14.gif
http://wrgis.wr.usgs.gov/docs/parks/animate/A08.gif
http://www.ucmp.berkeley.edu/geology/anim1.html
http://www.eram.k12.ny.us/education/sctemp/7dc4527a0
49452e89e289cec62ecb878/tectonics.swf
http://www.ucmp.berkeley.edu/geology/anim11.html
http://wrgis.wr.usgs.gov/docs/parks/animate/PLATES_3.MPG