2. Chapter Menu Lesson 1: Continental Drift Lesson 2: Seafloor Spreading
Lesson 3: Theory of Plate Tectonics
Click on a hyperlink to view the corresponding lesson.

3. 4.1 Continental Drift
continental drift
Pangaea

4. 4.1 Continental Drift
Drifting Continents
Continental drift is the idea that continents are moving very slowly, parallel to Earth’s surface.
Alfred Wegener proposed that the continents slowly drifted to their present-day locations over millions of years.

5. 4.1 Continental Drift
Pangaea
Approximately 255 million years ago, the continents were one big landmass named Pangaea.
Around 152 million years ago, the Atlantic Ocean began opening between Africa and North America.

6. 4.1 Continental Drift
Pangaea (cont.)
About 66 million years ago, the oceans widened and southern Pangaea began to break apart.

7. 4.1 Continental Drift
Pangaea (cont.)

8. Evidence for Continental Drift
Four major pieces of evidence:
the geographic fit of the continents
fossils
rock types/ mountain ranges
ancient climate evidence

9. 4.1 Continental Drift
Fossil Evidence
Wegener used fossil evidence from a fossil of a fern called Glossopteris.
Fern seed was too heavy to be carried by the wind.
Oceans were too wide to allow the seed to float across the waters.
Conclusion: When Glossopteris was alive, the continents must have been connected.

10. 4.1 Continental Drift
Fossils (cont.)

11. Rock Types and Mountain Ranges
4.1 Continental Drift
Rock Types and Mountain Ranges
Ancient rocks on the continents match up when you assemble the continents as Pangaea.

12. Rock Types and Mountain Ranges (cont.)
4.1 Continental Drift
Rock Types and Mountain Ranges (cont.)
Some mountain ranges appear as if they were once connected.

13. Climate Evidence Sedimentary rocks record clues about climate.
4.1 Continental Drift
Climate Evidence
Sedimentary rocks record clues about climate.
The ancient climate of certain locations was very different from the present-day climate.

14. 4.1 Continental Drift
Hypothesis Rejected
Wegener proposed that the same forces of gravity that produced tides moved the continents.
Scientists rejected this hypothesis because they did not accept Wegener’s explanation of how the continents moved.
New technology gathered additional evidence that supported the continental drift theory.

15. Approximately 152 million years ago, ____.
4.1 Continental Drift A B C D
Approximately 152 million years ago, ____.
A Pangaea was starting to form
B the Atlantic Ocean began to open between North America and Africa
C Southern Pangaea began breaking apart
D the continents were in the same locations as they are today
Lesson 1 Review

16. Clues about climate are preserved when ____ rocks form. A igneous
4.1 Continental Drift A B C D
Clues about climate are preserved when ____ rocks form.
A igneous
B metamorphic
C sedimentary
D foliated
Lesson 1 Review

17. Why was Wegener’s hypothesis rejected by scientists?
4.1 Continental Drift A B C D
Why was Wegener’s hypothesis rejected by scientists?
A He had no evidence of mountain ranges matching across the continents.
B He could not explain why Earth’s surface contains mostly water.
C He could not fully explain how the continents drifted.
D He had no fossil evidence to support his hypothesis.
Lesson 1 Review

18. End of Lesson 1

19. 4.2 Seafloor Spreading
mid-ocean ridge
seafloor spreading

20. Mid-Ocean Ridge Longest mountain ranges found on Earth
4.2 Seafloor Spreading
Mid-Ocean Ridge
Longest mountain ranges found on Earth
Located in the middle of the seafloor
Mapped by sonar

21. Mid-Ocean Ridge (cont.)

22. 4.2 Seafloor Spreading
Seafloor Movement
New seafloor is constantly being made at mid-ocean ridges.

23. Seafloor Movement (cont.)
4.2 Seafloor Spreading
Seafloor Movement (cont.)
Hot material in the mantle moves toward Earth’s surface by convection.
Lava flows through the cracks along the mid-ocean ridge, cools, and forms new seafloor.

24. Seafloor Spreading Explains continental drift hypothesis
Seafloor age increases as distance from the mid-ocean ridge increases.

25. Evidence for Spreading
4.2 Seafloor Spreading
Evidence for Spreading
Earth’s magnetic poles have reversed several times.
As oceanic crust forms from lava and cools, tiny crystals record the magnetic field orientation.

26. Magnetic Stripes on the Seafloor
4.2 Seafloor Spreading
Magnetic Stripes on the Seafloor
A magnetometer is used to measure Earth’s magnetic field.
When graphed, oceanic crust makes striped patterns due to the alternating stripes of rock with normal and reversed polarity.
By measuring the distance of a stripe of rock from the mid-ocean ridges and determining its age, the speed of the seafloor movement can be calculated

27. 4.2 Seafloor Spreading
Seafloor Drilling
Confirmed that the oldest rocks are located furthest from the mid-ocean ridge
Supported seafloor spreading hypothesis

28. What evidence supported the continental drift hypothesis?
4.2 Seafloor Spreading A B C D
What evidence supported the continental drift hypothesis?
A seafloor spreading
B magnetic pole reversal and caves
C mid-ocean ridges and volcanoes
D volcanoes and caves
Lesson 2 Review

29. What force moves hot material in the mantle toward Earth’s surface?
4.2 Seafloor Spreading A B C D
What force moves hot material in the mantle toward Earth’s surface?
A gravity
B convection
C buoyancy
D pressure
Lesson 2 Review

30. Seafloor age ____ as the distance from the mid-ocean ridge ____.
4.2 Seafloor Spreading A B C D
Seafloor age ____ as the distance from the mid-ocean ridge ____.
A increases, decreases
B remains the same, increases
C increases, increases
D remains the same, decreases
Lesson 2 Review

31. End of Lesson 2

32. 4.3 Theory of Plate Tectonics
lithospheric plate
plate tectonics
ocean trench
slab
Global Positioning System (GPS)

33. 4.3 Theory of Plate Tectonics
Earth’s Plates
Lithospheric plates are large brittle pieces of Earth’s outer shell.
The theory of plate tectonics explains the movement of lithospheric plates.
What are some characteristics of the ocean and the ocean floor?

34. Boundaries of Lithospheric Plates
4.3 Theory of Plate Tectonics
Boundaries of Lithospheric Plates
Mid-ocean ridges show boundaries of some lithospheric plates.
Earthquakes and volcanoes occur where the edges of plates are pushed together, pulled apart, or slide horizontally.
Ocean trenches are the deep parts of the seafloor where numerous earthquakes and volcanoes occur.
Seafloor is formed at ridges and destroyed at ocean trenches.

35. Boundaries of Lithospheric Plates (cont.)
4.3 Theory of Plate Tectonics
Boundaries of Lithospheric Plates (cont.)
Scientists’ current mapping of Earth’s lithospheric plates.

36. Boundaries of Lithospheric Plates (cont.)
4.3 Theory of Plate Tectonics
Boundaries of Lithospheric Plates (cont.)
Types of Lithosphere

37. What controls plate movement?
4.3 Theory of Plate Tectonics
What controls plate movement?
Some scientists believe that convection controls the movement of plates.

38. What controls plate movement? (cont.)
4.3 Theory of Plate Tectonics
What controls plate movement? (cont.)
Temperature increases with increasing depth.
Radioactive decay is one important source of internal heat.
Heat increases the temperature of rock which decreases the density.

39. Plate Movement and Convection
4.3 Theory of Plate Tectonics
Plate Movement and Convection
Slabs are cooler, denser lithospheric plates that sink down into the mantle.
They bend and break as they sink down into the mantle, causing earthquakes.

40. Ridge Push and Slab Pull
4.3 Theory of Plate Tectonics
Ridge Push and Slab Pull

41. Ridge Push and Slab Pull (cont.)
4.3 Theory of Plate Tectonics
Ridge Push and Slab Pull (cont.)

42. 4.3 Theory of Plate Tectonics
Plate Movement
Global Positioning System (GPS) is a network of satellites used to determine locations on Earth.
Measures the movement of plates
Using GPS and satellite laser ranging (SLR), plate movement has been estimated at a few centimeters per year.

43. Plate Tectonics and the Rock Cycle
4.3 Theory of Plate Tectonics
Plate Tectonics and the Rock Cycle

44. Where is the seafloor destroyed? A mid-ocean ridges
4.3 Theory of Plate Tectonics A B C D
Where is the seafloor destroyed?
A mid-ocean ridges
B continental shelf
C ocean trenches
D beaches
Lesson 3 Review

45. What controls the movement of lithospheric plates?
4.3 Theory of Plate Tectonics A B C D
What controls the movement of lithospheric plates?
A weather at Earth’s surface
B ancient climate data
C convection
D satellites
Lesson 3 Review

46. Lithospheric plates are estimated to move at a rate of ____.
4.3 Theory of Plate Tectonics A B C D
Lithospheric plates are estimated to move at a rate of ____.
A miles per hour
B centimeters per year
C kilometers per year
D inches per year
Lesson 3 Review

47. End of Lesson 3

48. Chapter Resources Menu
Chapter Assessment
California Standards Practice
Concepts in Motion
Image Bank
Science Online
Interactive Table
Virtual Lab
Click on a hyperlink to view the corresponding feature.

49. A its discovery made scientists finally accept Wegener’s hypothesisB C D
Glossopteris is important to the continental drift hypothesis because ____.
A its discovery made scientists finally accept Wegener’s hypothesis
B it was found on several different continents—4 continents and India
C it proved that Earth has undergone a change in polarity several times
D it allowed Wegener to prove the existence of mid-ocean ridges
Chapter Assessment 1

50. Scientists use sonar to ____. B C D
Scientists use sonar to ____.
A determine the topography of the seafloor using light waves
B determine the topography of the seafloor using sound waves
C determine magnetic polarity
D drill into landmasses and retrieve data
Chapter Assessment 2

51. Scientists can determine Earth’s magnetic field using ____. A drills B C D
Scientists can determine Earth’s magnetic field using ____.
A drills
B sonar
C magnetometers
D topographic maps
Chapter Assessment 3

52. The oldest rocks on the seafloor are ____. B C D
The oldest rocks on the seafloor are ____.
A closet to mid-ocean ridges
B parallel and close to mid-ocean ridges
C found deep in the lithosphere
D furthest from the mid-ocean ridge
Chapter Assessment 4

53. Oceanic lithosphere is ____ than continental lithosphere. B C D
Oceanic lithosphere is ____ than continental lithosphere.
A thicker and denser
B thick and less dense
C thinner and less dense
D thinner and denser
Chapter Assessment 5

54. Which accurately describes Earth’s layers?
SCI 1.b A B C D
Which accurately describes Earth’s layers?
A large brittle lithosphere, hot convecting mantle, dense metallic core
B hot convecting lithosphere, cold brittle mantle, dense metallic core
C dense metallic core, hot convecting layer, cold brittle lithosphere
D cold brittle mantle, hot convecting lithosphere, dense metallic core
CA Standards Practice 1

55. Heat from Earth’s interior primarily reaches the surface by ____.
SCI 4.c A B C D
Heat from Earth’s interior primarily reaches the surface by ____.
A conduction
B ocean currents
C convection
D drilling
CA Standards Practice 2

56. Plate movement, on average, is ____ per year. A a few meters
SCI 1.c A B C D
Plate movement, on average, is ____ per year.
A a few meters
B a few centimeters
C 1 mile
D 1 kilometer
CA Standards Practice 3

57. What ancient climate evidence is used to explain continental drift?
SCI 7.e A B C D
What ancient climate evidence is used to explain continental drift?
A glacial ancient formations
B plants
C rivers
D beaches
CA Standards Practice 4

58. B forming igneous rock at mid-ocean ridges, that move away as it cools
SCI 7.g A B C D
One way plate tectonics move Earth’s mantle through the rock cycle is by ____.
A forming metamorphic rocks at mid-ocean ridges, that move away as it cools
B forming igneous rock at mid-ocean ridges, that move away as it cools
C metamorphic rocks sinking into the mantle, as they move toward the mid-ocean ridge
D igneous rocks sinking into the mantle, as they move toward the mid-ocean ridge
CA Standards Practice 5

59. Concepts in Motion 1

60. Concepts in Motion 2

61. Concepts in Motion 3

62. Image Bank

63. Image Bank

64. Interactive Table

65. End of Resources