1. HOW DOES EARTH PLATES HELP SHAPE LANDFORMS Chapter 8 Section 2

2. Continental Drift  In 1912, Alfred Wegener suggested a reason for why the coastlines of certain continents looked like they fit together at one time.  He felt that the continents were all joined about 225 million years ago.  He called this Super continent- Pangaea- meaning all Earth

3. Continental Drift  Wegener thought all the continents were joined at one time and slowly drifted apart.  Proof for the Continental Drift Theory  The coastlines fit together like puzzle pieces  Plant and animal fossils found on West Coast of Africa matched those found on the East Coast of South America  Rock layers on W coast of Africa matched rock layers on E. coast South America

4. Problems  Wegener could not explain what forces moved the continents apart.  It was not until much later that scientist figured out the forces pulling the continents apart. They had to look to the seafloor.

5. Seafloor Spreading  Harry Hess- 1960  He noticed that new seafloor forms at ocean ridges.  The magma rises and forms a ridge which pushes the old seafloor away  The magma rises when the plates pull apart

6. Convection current  Arthur Holmes- 1930’s  He noticed that when you heat liquids the particles move faster and the hot liquid rises.  The hot liquid will eventually cool and sink down  This process of heating and cooling is a convection current.  Convection currents move the plates because the molten rock in the mantle rises then cools.

7. Final Proof of Continental Drift  Scientists studied the magnetism of the rocks near the Mid ocean Ridge  They saw that in some places the magnetism faced north while in some places it faced south.  Every half-million years the pattern flips. This proves that old rock is pushed from the newly formed rock at the Mid- ocean ridge