Lecture 2 (January 9):Plate Tectonics I
Brief outline of this lecture:
1. Theories about the Earth
2. Evidence for plate tectonics
a. Evidence for moving continents
b. Evidence of dynamic ocean basins
3. Characteristics of Plates
4. Plate Boundaries
5. Divergent plate boundaries
Main points of this lecture:
A "Static Earth" theory in which neither continents nor sea floor moved was the default view of geologists into the 1900s.
"Continental Drift" (in the strict sense) was a theory that explained more observations than Static Earth theory but was flawed because it assumed that continents plow through passive oceanic crust.
Plate Tectonic theory assumes that rigid pieces of oceanic, or oceanic plus continental, lithosphere ("plates") move across the earth surface over a more ductile asthenosphere.
Where plates move apart at divergent plate boundaries, new lithosphere must form.
Where plates come together at convergent plate boundaries, lithosphere must be destroyed.
Subduction, the process in which relative old and cool lithosphere sinks into the mantle, is the process by which lithosphere is destroyed.
"Lithosphere" and "Asthenosphere" are terms distinguishing zones of brittle and ductile behavior, whereas "Crust" and "Mantle" are terms distinguishing zones of different chemistry and mineralogy.
The crust and Lithosphere are very thin compared to the scale of the entire earth.
Figures used in this lecture:
Large-scale theories of the Earth
Evidence for plate tectonics
Diagram showing general features of plate tectonics
Diagram showing the three kinds of plate tectonic boundaries
Diagram showing the Crust, Mantle, Lithosphere, and Asthenosphere
Cross-Section of the Earth to Scale
New Divergent plate boundaries sketches
New Convergent plate boundaries sketches
A map showing ages of the Hawaiian Islands
Old Divergent plate boundaries sketches
Old Convergent plate boundaries sketches
NOAA's map of seafloor crustal age
NOAA's image of seafloor and land topography
Reading assignment: Chapter 3.
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