1. Plate Tectonic Theory Evidence
TEK 8.9A

2. Main Concept Why are there so many Earthquakes near us?
TEK 8.9A - Describe the historical development of evidence that supports plate tectonic theory.
Why are there so many Earthquakes near us?

3. Brain Break

4. Notes Two main people are responsible for the theory Alfred Wegner
Started working on his theory in the early 1900’s
German
Harry Hess
Started his theory in the 1960’s
Worked for the US Navy

5. Notes Continued Alfred Wegner’s Theory
Called the ‘continental drift hypothesis’
First proposed the idea of Pangaea
Stated that it about took 200 million years to get to the current location
Idea came from the fact that all of the continents fit together like puzzle pieces
Actually took the idea from Abraham Ortelius

6. Notes Continued Concepts supporting Wegener
Puzzle like fit of continents
Matching sedimentary rock layers
Layers of rock on the east of the US matches rock layers on the west coast of Africa
Matching ranges of fossils
Like the sedimentary layers, fossils matched on different continents

7. Notes Continued Glacial remains in tropical areas
Showed the either that continents moved or glaciers were able to exist in hot, moist areas
Tropical plants fossils found in arctic areas
Same as above, how did they survive if the continent did not move.

8. Notes Continued Harry Hess’ Theory Seafloor Spreading Hypothesis
New crust was added on the ocean floor pushing the older crust out
Pushes North/South America away from Europe/Africa but pushed North America closer Russia on the other side
Still supported Wegener but provided proof

9. Notes Continued Concepts supporting Hess
Scientist measured the age of rock layers and found that rocks in the middle of the Atlantic Ocean were much younger than on the coasts

10. Notes Continued Magnetic striping
When rock cools the magnetic crystals point north and south
North and south move occasionally and there are organized bands of crystals pointing different ways.

11. Plate Tectonics Theory
Merged the two theories into one.
The crust, lithosphere, is broken into nine major plates
There are many smaller plates
Different types of faults make new crust and can also return the crust to the asthenosphere, or molten core.
Next week we study the fault types.