1. The Structure of the Earth
Learning Objectives:
Describe the layers of the structure of the Earth.
Describe the theory of continental drift.
Describe the theory of plate tectonics.
Explain how earthquakes and volcanoes form.

2. Structure of the Earth Crust = thin, rocky outer layer
Mantle = properties of solid but flows slowly
Outer core = liquid nickel and iron
Inner core = solid liquid and iron

3. Continental Drift
1912 Alfred Wegner came up with the theory of crustal movement or continental drift.
Theory of Continental Drift = continents were once joined together and gradually moved apart
Wegener’s ideas were not accepted at the time.

4. Evidence Supporting Continental Drift
Apparent fit of the continents = continents fit like puzzle pieces
Fossil Correlation = identical fossils have been found on either side of the ocean
Rock and Mountain correlation = identical rocks and mountain structures have been found on either side of the ocean
Paleoclimate Data – coal found in cold regions and glacial evidence found in warm regions

5. Plate Tectonics
Theory of Plate Tectonics = the Earth’s crust is broken up into pieces called tectonic plates which float on top of the mantle

6. Convection Currents Cause Plates to Move
Heat in the Earth causes convection currents in the mantle.
Convection currents push the tectonics plates which float on the slowly moving mantle.

7. Plate Boundaries = where plates meet

8. Plate Boundaries

9. Divergent Plate Boundary: New Crust Formation

10. Continental Collision Boundary: Mountain Ranges

11. Transform Boundaries: Earthquakes
Earthquakes can occur at all moving plate boundaries.
Plates do not move smoothly due to friction.
Pressure builds up and plates “slip” suddenly

12. Subduction Zone Boundaries: Volcanoes
When one plate is pushed under another, oceanic crust is pushed into the Earth.
Melting crust releases gases which can get pushed upwards creating a volcano.