1. Earth’s Layered Structure (Ch. 8.4 in the Text)

2. Earth’s internal structure
Layers based on composition
Crust
Thin, rocky outer layer
Varies in thickness
Oceanic crust: Roughly 7 km (5 miles) thick
Continental crust: Averages 35–40 km (25 miles) thick

3. Earth’s layered structure
Discovering Earth’s major layers
Mohorovicic discontinuity (Moho)
Separates crust from underlying mantle

4. Earth’s internal structure
Layers based on composition
Mantle
Below crust to a depth of 2,890 kilometers (1,800 miles)
Over 82% of Earth’s volume
Common rock type in the upper mantle is Peridotite

5. Earth’s internal structure
Layers based on composition
Core
Composed of an iron–nickel alloy
Average density of nearly 13 g/cm3
Radius of 3,480 kilometers

6. Earth’s internal structure
Layers based on physical properties
Lithosphere
Crust and uppermost mantle
km thick
Cool, rigid, solid
Asthenosphere
Beneath the lithosphere
Part of the Upper mantle
To a depth of about 660 km
Soft, weak layer that is easily deformed

7. Earth’s internal structure
Layers based on physical properties
Lower Mantle
2230 km thick
More rigid layer than the Asthenosphere
Rocks are very hot and capable of gradual flow
Outer Core
Liquid layer
2,260 km (1,410 miles) thick
Convective flow of metallic iron within generates Earth’s magnetic field

8. Earth’s internal structure
Layers based on physical properties
Inner Core
1220 km thick
Compressed into a solid state by immense pressure

9. Plate Tectonics Ch. 9 (p. 246 - 277)

10. Continental drift: an idea before its time
Alfred Wegener
First proposed hypothesis of Continental Drift in 1915
Continental drift hypothesis
Supercontinent called Pangaea began breaking apart about 200 million years ago
Continents “drifted” to present positions

11. Pangaea approximately 200 million years ago

12. Continental drift: an idea before its time
Wegener’s continental drift hypothesis
Evidence used by Wegener
Fit of South America and Africa
Fossils match across the seas
Rock types and structures match
Ancient climates
Problem with Wegener’s Hypothesis: What force was moving the continents?

13. Similar mountain ranges on different continents

14. Paleoclimatic evidence for continental drift

15. Plate Tectonics: the new paradigm
The Theory of Plate Tectonics
We are now able to measure the movement of the continents due to technological advancements
Associated with Earth’s rigid outer shell
Called the lithosphere
Consists of several plates
Largest plate is the Pacific plate

16. Plate tectonics: the new paradigm
Asthenosphere
Exists beneath the lithosphere
Hotter and weaker (fluid like) than lithosphere
Allows for motion of lithosphere
Plate boundaries
All major interactions among plates occur along their boundaries

17. Plate tectonics: the new paradigm
Plate boundaries
Types of plate boundaries
Divergent plate boundaries (Constructive margins)
Two plates move apart
Mid Ocean ridges and seafloor spreading
Oceanic ridges develop along well-developed boundaries
Along ridges, seafloor spreading creates new seafloor

18. Divergent boundaries are located along oceanic ridges

19. The East African rift – a divergent boundary on land

20. Plate tectonics: the new paradigm
Plate boundaries
Convergent plate boundaries (destructive margins)
Plates collide, an ocean trench forms, and lithosphere is subducted into the mantle

21. Plate tectonics: the new paradigm
Plate boundaries
Types of plate boundaries
Convergent plate boundaries (destructive margins)
Oceanic–continental convergence
Denser oceanic slab sinks into the asthenosphere
Pockets of magma develop and rise
Continental volcanic arc forms
Examples include the Andes, Cascades, and the Sierra Nevadan system

22. An oceanic–continental convergent plate boundary

23. Plate tectonics: the new paradigm
Plate boundaries
Types of plate boundaries
Convergent plate boundaries (destructive margins)
Oceanic–oceanic convergence
Two oceanic slabs converge and one descends beneath the other
Often forms volcanoes on the ocean floor
Volcanic island arc forms as volcanoes emerge from the sea
Examples include the Aleutian, and Mariana.

24. An oceanic–oceanic convergent plate boundary

25. Plate tectonics: the new paradigm
Plate boundaries
Types of plate boundaries
Convergent plate boundaries (destructive margins)
Continental–continental convergence
When subducting plates contain continental material, two continents collide
Can produce new mountain ranges such as the Himalayas

26. A continental–continental convergent plate boundary

27. The collision of India and Asia produced the Himalayas

28. The collision of India and Asia produced the Himalayas

29. Plate tectonics: the new paradigm
Plate boundaries
Types of plate boundaries
Transform fault boundaries
Plates slide past one another
No new crust is created or destroyed

30. Testing the plate tectonics model
Evidence from ocean drilling
Some of the most convincing evidence confirming seafloor spreading has come from drilling directly into ocean-floor sediment
Age of sediments
Thickness of ocean-floor sediments verifies seafloor spreading

31. Testing the plate tectonics model
Hot spots and Mantle Plumes
Caused by rising plumes of mantle material
Volcanoes can form over them (Hawaiian Island chain)

32. The Hawaiian Islands have formed over a hot spot

33. Testing the plate tectonics model
Evidence for the plate tectonics model
Paleomagnetism
Probably the most persuasive evidence
Ancient magnetism preserved in rocks
Paleomagnetic records show
Polar wandering (evidence that continents moved)

34. Measuring plate motion
By using hot spot “tracks” like those of the Hawaiian Island chain
Using space-age technology to directly measure the relative motion of plates
Global Positioning System (GPS)

35. Directions and rates of plate motions

36. What drives plate motion
Driving mechanism of plate tectonics
Earth’s heat is the driving force
Convective Currents

37. Mantle Convection

38. Layering at 660 km

39. Plate Motion at the Surface

40. A possible view of the world 50 million years from now