1. Tectonic Plate Theory Understanding Basic Principles of Earth Science Related to Geology

2. Earth’s Crust  Earth’s crust is the outermost layer.  The rigid crust “floats” on the molten part of the mantle called the asthenosphere.

3. Pangea  Pangea was the supercontinent from which all continents have split.  In 1915 Wegener proposed Earth’s continents looked this way about 225 million years ago.  The theory of continental drift was used to explain the current positions of the continents.  Wegener could not come up with a mechanism for continental drift.

4. Evidence that Pangea Existed  Fit of the continents  Fossil similarities  Rock similarities  Mountain chains  *Paleoclimatic evidence  *Paleomagnetism  Theory of Plate Tectonics

5. Fit of the Continents  North and South America match almost perfectly with Africa and Europe

6. Fossil Similarities  *Mesosaurus, a reptile similar to an alligator once lived in the shallow waters of both South America and Africa.

7. Rock Similarities  Rocks of same age are found in locations of South America and Africa that were once joined in Pangea.

8. Termination of Mountain Chains  The map shows location of Pangean mountain chains (dark blue) that correspond with current mountain chains.

9. Paleoclimatic Evidence  Glacial deposits at the equator  Coral reefs in Antarctica  Therefore the landmasses must have been in different locations in the past.

10. Magnetism  Earth is a bar magnet  Magnetic north and south poles  These are not the same location as the geographic north and south poles  Exact location varies year-to-year

11. Paleomagnetism  This is magnetism “frozen” in the rock at the time it was formed.  Geologists can determine pole reversals by studying rock all over the globe.

12. Sea Floor Spreading  Surveys of the ocean basins showed a system of ridges and trenches.  This led geologists to come up with the idea of Sea Floor Spreading.  Symmetrical magnetic “stripes” were discovered on either side of the Atlantic Mid-ocean ridge.

13. Sea Floor Spreading

14. Magnetic Reversals along a Mid-Ocean Ridge (“stripes”) Oldest rock is farthest from ridge. Youngest, newest rock is along the ridge.

15. Theory of Plate Tectonics  A rigid piece of lithosphere (outer crust) is floating on a partially plastic (molten, soft) asthenosphere  Seven Major Plates  3 types of Plate Boundaries

16. Plate Boundaries  *Divergent-Spreading Center- Ocean ridges and seafloor spreading (Atlantic Ocean)  *Convergent-Creates trenches and island arcs (Pacific Ocean)  *Transform-Plates move past one another (San Andreas Fault in California)

17. Divergent Boundaries  Magma from deep within Earth forces its way between two plates, pushing them apart.  The magma cools and forms new seafloor.  More magma emerges and pushes apart the cooled rock.  Seafloor Spreading/mid-oceanic ridges

18. Rift Valley  A rift valley forms when a continent is slowing splitting apart along a divergent boundary.  The African Rift Valley is an example.

19. Locations of Seafloor Spreading

20. Convergent  Plates move together  Oceanic crust slides under continental crust.  Subducting crust slides under.  Andes Mountains Chain in South America is an example.  Mountains formed from volcanoes along the convergent boundary.

22. Convergent Boundaries  The Pacific Ocean by several continental plates.  The ocean basin is sliding under the continental plates along the plate boundaries.  As a result, the Pacific Ocean is growing smaller.

23. Why the Pacific is Shrinking and the Atlantic is Growing

24. Hawaiian Islands are an island arc.

25. More Examples of Convergent Boundaries  Japanese Islands (Pacific Ocean)  Cascade Mountains (Northwestern U.S.A.)  Himalaya Mountains (Nepal-Asia )

26. Transform Plate Boundary  Plates move past one another along strike-slip faults

27. What Drives the Tectonic Plates??  Convection Cells  Hot Spots