1. Plate Tectonics

2. In This Chapter: Composition of the Earth Continental Drift Theory
Layers of the Earth: crust, outer core, inner core, mantle
Continental Drift Theory
Evidence: fossil clues, climate clues, rock clues
Pangaea
Theory of Seafloor Spreading
Evidence: rock and magnetic clues
Plate Tectonics
Plate movements
Plate boundaries
Convection currents

3. Fossil Rock Anthem

4. Continental Drift Theory
Proposed by Alfred Wegner
Continents were at one time all joined together (“Pangaea”)

5. Pangaea

6. Clues to Pangaea Fossil Clues Reptile Mesosaurus Fern Glossopteris
Reptile Mesosaurus found in South America and Africa
Did this reptile swim?
Fern Glossopteris found in Africa, Australia, India, South America, AND Antarctica!

7. Clues to Pangaea Climate Clues
Fossils of warm water plants found on Arctic Ocean island (Glossopteris)
Glacial deposits & grooved bedrock in South America, Africa, India, and Australia
These areas were once connected

8. Clues to Pangaea Rock Clues
Similar rock structures are found on different continents
Ex. Appalachian Mountains:
Eastern U.S.
Greenland
Western Europe

9. How Do The Continents Drift?
Theory of Seafloor Spreading supports Wegener’s theory

10. Theory of Seafloor Spreading
Proposed by Harry Hess in 1960s
Hot, less dense material in mantle is forced upward to surface at Mid Ocean Ridge
It cools, contracts, turns, and flows sideways, carrying the seafloor away from the ridge in both directions
MAGMA!
Moves upward, flows into cracks, solidifies to form new seafloor

11. Evidence of Seafloor Spreading
Age difference in rocks
Glomar Challenger (research ship) found youngest rocks are near center of ridges
Magnetic clues
Magnetic field has reversed itself
Iron minerals being formed reflect direction of magnetic reversal

12. Plate Tectonics Plate movements
The Earth’s crust and upper mantle are broken into sections called “plates”
These sections move around on top of the mantle

13. Earth’s Composition Lithosphere Asthenosphere Upper mantle and crust
Rigid, less dense than material below it; divided into plates
“Floats” on asthenosphere
Asthenosphere
Located below lithosphere
More dense, plastic-like
Lithosphere
Upper mantle and crust
Rigid, less dense than material below it; divided into plates
“Floats” on asthenosphere

15. Plate Boundaries Divergent Boundary (divide)
Plates move away from each other
Plates of Earth move apart; one fault surface goes up, one goes down
Located on ocean floor
Volcanoes and earthquakes at these boundaries

16. Plate Boundaries Convergent Boundary
One fault surface is forced up and over the other fault surface
Forms mountains & subduction zones
Subduction zones
Movement of one tectonic plate descending under another
Ocean crust is subducted because it is more dense and thinner than continental crust

17. Plate Boundaries Transform Boundary Plates slide past each other
Not much upward/downward movement

18. Causes of Plate Tectonics
Convection Currents
Heating, rising, cooling, sinking of material or gas
Hot plastic-like material from mantle rises to lithosphere, moves horizontally, cools, and sinks back to mantle

19. Effects of Plate Tectonics
Volcanoes
Earthquakes
Mountain building
Ocean rift formation
Tsunamis
Ocean basins

20. Review What are the 3 types of clues for Pangaea?
Who proposed the Continental Drift Theory?
What theory did Harry Hess propose?
What is the difference between the lithosphere and asthenosphere?

21. References Glencoe McGraw-Hill, . Earth Science. 2007. Print.