Theory of Continental Drift

Cornell NotesPg. 93

The Theory of Continental Drift

• Alfred WegenerAlfred Wegener (1910)

• Formed a hypothesis that all the continents were once joined together and have drifted apart

What was Wegener’s evidence?

• Evidence from:1.1.LandformsLandforms—the continents fit together2.2.FossilsFossils—ancient plants and animals found in

many different continents3.3. ClimateClimate—Antarctica has plant fossils. Tropics have

rocks with ice scratches from glaciers- “glacial scarring”

4.4. Rock TypesRock Types- similar rocks found where continents may have once been joined together.

Wegener’s DATA

Pangaea• Continents were

joined together in one land mass• “The super

continent” 245 mya

Which way are the continents moving today?

The Theory of Sea Floor Spreading

Page 95

Sea Floor Spreading

• Harry Hess (1960)

• as the ocean floor spreads apart, new crust material rises from the mantle and creates new sea floor to fill the “hole.”

HESS (1960)

• Sea floor spreading • Continents were moving (as Wegener had proposed)• Evidence1.2.3.

1. The discovery of the Mid-ocean Ridge

• Scientists mapped 47,000 miles of underwater volcanic ridges by using sonar

Map of Mid-ocean Ridges

2. Ocean floor shows Magnetic Poles reversing

3. Ocean floor samples—older crust is further away from ridges