1. Plate Tectonics Section 1: Earth’s Interior
Section 2: Convection and the Mantle
Section 3: Drifting Continents
Section 4: Sea-Floor Spreading
Section 5: The Theory of Plate Tectonics

2. Earth’s Interior
How have geologists learned about Earth’s inner structure?
Geologists have used two main types of evidence to learn about Earth’s interior:
Direct evidence
from rock samples
Indirect evidence
from seismic waves

3. Earth’s Interior Geologists cannot look inside Earth
Use an indirect method.
Seismic Waves (Earthquake waves)
Study how they travel through Earth.
Data reveals several layers

4. Earth’s Interior

5. Earth’s Interior
Crust
Mantle
Outer Core
Inner Core

6. Earth’s Interior Crust
Solid layer of rock that includes both dry land and the ocean floor
Between 5 and 40 km thick
Dry land
Granite
light in color
less dense
Ocean floor
Basalt
dark in color
more dense

7. Earth’s Interior Mantle very hot, but solid rock about 3,000 km thick
Lithosphere
Crust and Upper Mantle region
“Lithos”, Greek for Stone
Asthenosphere
Remainder of Mantle
Very soft and hotter than Lithosphere
“Asthenes”, Greek for Weak
*Lower Mantle
Solid and extends to the Core region

8. Earth’s Interior

9. Earth’s Interior Core Mostly Iron and Nickel Outer Core Inner Core
molten metal (Fe and Ni) that surrounds the Inner Core.
Liquid
creates the magnetic field of the Earth
Bar-magnet with North and South Poles
Inner Core
dense ball of metal (Fe and Ni)
Intense pressure prevents it from changing from solid to liquid.

10. Earth’s Interior
Pressure and Temperature increase as you move towards the center of the Earth

11. Earth’s Interior
Core

12. Earth’s Interior Assessment Questions
Why is it difficult to determine Earth’s inner structure?
How are seismic waves used to provide evidence about Earth’s interior?
List Earth’s three main layers
What is the difference between the lithosphere and the asthenosphere?
In which layer is each located?

13. Section 1.2 Convection in the Mantle
How is heat transferred?
There are three types of heat transfer:
Radiation
Conduction
Convection

14. Radiation The transfer of energy through space.
No direct contact between a heat source and an object.
Sunlight warms the Earth

15. Conduction
Heat transfer within a material or between materials that are touching.
Holding a hot spoon.
Conduction is responsible for some of the heat transfer inside Earth.

16. Convection Heat transferred by the movements of liquids and gases.
Caused by:
Density differences
Gravity
Density
mass in a given volume
More heat = expansion = less dense
Less heat = contraction = more dense

17. Convection What causes convection currents? Gravity
Difference in Density of liquids or gases.
Gravity pulls denser materials downward
More heat = expansion = less dense = moves upward
Less heat = contraction = more dense = moves downward

18. Convection

19. Convection Currents What causes convection currents in Earth’s mantle?
Heat from the core and mantle causes convection currents in the mantle.

20. Visual Summary of the Three Types of Heat Transfer

21. 1.2 Assessment Questions 1. How is heat transferred?
2. What causes convection currents?
3. What causes convection currents in Earths mantle?
4. What is conduction?

22. 1.2 Assessment Questions
5. What is the role of gravity in creating convection currents?
6. What part of Earth’s interior is like the soup in the pot? What part is like the burner on the stove? (Fig 9)
7. How is heat transferred through space?
8. What is a convection current?

23. 1.2 Assessment Questions
9. In general, what happens to the density of a fluid as it becomes hotter?
10. Describe how convection currents form.
11. Name two layers of Earth in which convection currents take place.
12. What causes convection currents in the mantle?
13. What will happen to the convection currents in the mantle if Earth’s interior eventually cools down? Explain.

24. Section 1.3 Drifting Continents
What was Alfred Wegener’s hypothesis about the continents?
What evidence supported Wegener’s hypothesis?
Why was Wegener’s hypothesis rejected by most scientists of his day?

25. Continental Drift
Why do the coasts of several continents match so neatly?
West Africa and Eastern South America seem to fit together like puzzle pieces.

26. Continental Drift Alfred Wegener
Hypothesized that Earth’s continents has moved over time.
All part of one large, ancient landmass
Drifted apart over time
His idea was called “Continental Drift”

27. Pangaea Ancient landmass “All Lands” All continents connected together
300 million years ago

28. Pangaea Slowly broke apart to where continents are located today.
Supported by studying:
land features
fossils
evidence of climate change

29. Pangaea Supporting Evidence Land Features
mountain ranges on Africa and South America lined-up.
coal fields in Europe and North America match-up

30. Supporting Pangaea: Land Features

31. Pangaea Supporting Evidence Fossils Glossopteris
fernlike plant
Mesosaurus and Lystrosaurus
land-dwelling dinosaurs
Fossils of these organisms are found on many different continents separated by great oceans!!
How could that be possible?

32. Supporting Pangaea: Fossils

33. Pangaea Climate Spitsbergen South Africa
Present location: Arctic Ocean (Cold!!)
Tropical plant fossils are found there!
South Africa
Present climate: Mild/Warm
Deep scratches, caused by glaciers are found in the crust.
Glaciers exist in very cold environments!!
*Climates changed because landmasses moved.

34. Hypothesis Rejected!!
Wegener was not able to provide a satisfactory explanation for the force that pushes or pulls the continents.
More evidence would be needed.

35. Mountain Formation
Wegener hypothesized that when continents collide, their edges crumple and fold.
Huge mountains form.

36. 1.3 Assessment Questions
1. What was Alfred Wegener’s hypothesis about the continents?
2. What evidence supported Wegener’s hypothesis?
3. Why was Wegener’s hypothesis rejected by most scientists of his day?

37. 1.3 Assessment Questions
4. What do the matching mountain ranges in Africa and South America show, according to Wegener’s hypothesis?
5. How would continental drift affect the continent’s climate?
6. According to Wegener, how do mountains form?

38. 1.3 Assessment Questions
7. Who proposed the concept of continental drift?
8. According to the hypothesis of continental drift, how would a world map have changed over the last 250 million years?
9. What evidence supported the hypothesis of continental drift?
10. How did fossils provide evidence for continental drift?

39. 1.3 Assessment Questions
11. Deposits of coal have been found beneath the ice of Antarctica. But coal only forms in warm swamps. Use Wegener’s hypothesis to explain how coal could be found so near to the South Pole.
12. Why did most scientists reject Wegener’s hypothesis of continental drift?
13. Do you think the scientists of Wegener’s time should have accepted his hypothesis? Why or why not?

40. Chapter 1.4 Sea-Floor Spreading
Mid-Ocean Ridges
an undersea maintain chain where new ocean floor is produced.
divergent (moving apart) plate boundary

41. Chapter 1.4 Sea-Floor Spreading
What device is used to map the ocean floor?
Mapped in the mid-1900’s by using SONAR.
Underwater soundwaves
How long does the echo take to travel? = distance to the bottom.

42. Mid-Ocean Ridge

43. Chapter 1.4 Sea-Floor Spreading
What is the process of Sea-Floor Spreading?
Sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added from below.

44. Evidence of Sea-Floor Spreading
What is the evidence of Sea-Floor Spreading?
1. Molten Material
Bubble-shaped rocks found on the ocean floor.
caused only by cooling magma

45. Evidence of Sea-Floor Spreading
2. Magnetic Stripes
Iron in molten rock aligns to magnetic poles
Poles “Flip” over many thousands of years
Repeated pattern of north and south orientation.
pattern is the same on both sides of the Mid-Ocean Ridge.

46. Magnetic Reversal Stripes

47. Evidence of Sea-Floor Spreading
3. Drilling Samples
Oldest rocks
farther from Mid-Ocean Ridge
Youngest rocks
closer to Mid-Ocean Ridge

48. Subduction at Trenches
What happens at Deep-Ocean Trenches?
Trenches
Opposite of Sea-Floor Spreading
Oceanic rock is forced downward, or subducts, and eventually melts into magma.

49. Deep Ocean Trenches

50. Subduction at Trenches
Together, Subduction and Sea-Floor Spreading act as a conveyor belt
cooling magma into new rock (Mid-Ocean Ridges).
melting old rock into magma (Trenches)

51. 1.4 Assessment Questions
1.Along what feature of the ocean floor does sea-floor spreading begin?
2.What are the steps in the process of sea-floor spreading?
3.What three types of evidence provided support for the theory of sea-floor spreading?
4.How do rocks along the central valley of the mid-ocean ridge provide evidence of sea-floor spreading?

52. 1.4 Assessment Questions
5.Where would you expect to find the oldest rock on the ocean floor?
6.What is a deep-ocean trench?
7.What happens to oceanic crust at a deep–ocean trench?