Plate Tectonic Theory Evidence

TEK 8.9A

Main Concept

• TEK 8.9A - Describe the historical development of evidence that supports plate tectonic theory.

•Why are there so many Earthquakes near us?

Brain Break

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

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

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

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.

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

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

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.

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.