1. Preview Section 1 Inside the Earth Section 2 Restless Continents
Plate Tectonics
Preview
Section 1 Inside the Earth
Section 2 Restless Continents
Section 3 The Theory of Plate Tectonics
Section 4 Deforming the Earth’s Crust
Concept Mapping

2. Section 1 Inside the Earth
Question of the Day
If you journeyed to the center of the Earth, what do
you think you would see along the way?
Draw an illustration of the journey for your QOD.

3. Section 1 Inside the Earth
Objectives
Identify the layers of the Earth by their chemical composition.
Identify the layers of the Earth by their physical properties.
Describe a tectonic plate.
Explain how scientists know about the structure of Earth’s interior.

4. The Composition of the Earth
Section 1 Inside the Earth
The Composition of the Earth
The Earth is divided into three layers.
Crust
Mantle
Core
Crust - the thin and solid outermost layer of the Earth above the mantle.
Crust is 5 to 100 km thick, and is the thinnest layer of the Earth.

5. The Composition of the Earth, continued
Section 1 Inside the Earth
The Composition of the Earth, continued
Two types of crust—continental (land) and oceanic (ocean).
Oceanic crust is thinner and denser than continental crust.

6. The Composition of the Earth, continued
Section 1 Inside the Earth
The Composition of the Earth, continued
Mantle - the layer of rock between the Earth’s crust and core.
The mantle is much thicker than the crust, it makes up about 2/3 of Earth.
We have never dug down that deep, so scientists must draw conclusions about what the mantle is made of and other physical properties from the Earth’s surface.

7. The Composition of the Earth, continued
Section 1 Inside the Earth
The Composition of the Earth, continued
Core - the central part of the Earth below the mantle.
The core makes up about one-third of Earth’s mass.
Scientists think that the Earth’s core is made mostly of iron.

8. Section 1 Inside the Earth

9. The Physical Structure of the Earth
Section 1 Inside the Earth
The Physical Structure of the Earth
The Earth is divided into five physical layers:
The lithosphere
The asthenosphere
The mesosphere
The outer core
The inner core
Each layer has its own set of physical properties.

10. Physical Structure of the Earth, continued
Section 1 Inside the Earth
Physical Structure of the Earth, continued
Lithosphere – the solid, outer layer of the Earth that consists of the crust and the rigid upper part of the mantle.
The lithosphere is divided into pieces that are called tectonic plates.

11. Physical Structure of the Earth, continued
Section 1 Inside the Earth
Physical Structure of the Earth, continued
Asthenosphere - the soft layer of the mantle on which the tectonic plates move.
The asthenosphere is made of solid rock that flows very slowly.

12. Section 1 Inside the Earth

13. Physical Structure of the Earth, continued
Section 1 Inside the Earth
Physical Structure of the Earth, continued
Mesosphere - is the strong, lower part of the mantle between the asthenosphere and the outer core.
The prefix meso- means “middle.”

14. Physical Structure of the Earth, continued
Section 1 Inside the Earth
Physical Structure of the Earth, continued
Earth’s core is divided into two parts.
The outer core is liquid and is right under the mantle.
The inner core is solid iron and is the center of the Earth.

15. Section 1 Inside the Earth

16. Section 1 Inside the Earth
Tectonic Plates
Tectonic Plate – a block of lithosphere that consists of the crust and the rigid, outermost part of the mantle.
These plates make the Earth look covered in puzzle pieces.

17. Tectonic Plates, continued
Section 1 Inside the Earth
Tectonic Plates, continued
A Giant Jigsaw Puzzle Each tectonic plate fits together with the tectonic plates that surround it.
The lithosphere is like a jigsaw puzzle. The tectonic plates are like the pieces of the puzzle.

18. Tectonic Plates, continued
Section 1 Inside the Earth
Tectonic Plates, continued
A Tectonic Plate Close-Up The following Visual Concept presentation shows the Earth’s major tectonic plates and how they fit together.
The presentation also illustrates what a tectonic plate might look like if you could lift it out of its place.

19. Tectonic Plates, continued
Section 1 Inside the Earth
Tectonic Plates, continued
Tectonic plates “float” on the asthenosphere.
The plates bump into one another when they move.

20. Mapping the Earth’s Interior
Section 1 Inside the Earth
Mapping the Earth’s Interior
Since we can’t dig in the Earth how do we know what is there?
Scientists measure speeds of seismic waves that travel through the Earth’s interior during earthquakes.
By using seismographs, scientists have learned that the Earth is made of different layers.

21. Question of the Day What is meant by the following statement:
Section 2 Restless Continents
Question of the Day
What is meant by the following statement:
“The United States is moving westward.”
From what you know about geology and plate tectonics explain if you believe this statement to be true or false.

22. Objectives Describe Wegener’s hypothesis of continental drift.
Section 2 Restless Continents
Objectives
Describe Wegener’s hypothesis of continental drift.
Explain how sea-floor spreading provides a way for continents to move.
Describe how new oceanic lithosphere forms at mid-ocean ridges.
Explain how magnetic reversals provide evidence for sea-floor spreading.

23. Continental Drift Hypothesis
Section 2 Restless Continents
Continental Drift Hypothesis
Continental drift - the hypothesis that states that continents once formed a single landmass, broke up, and drifted to their present locations.

24. Section 2 Restless Continents
The Breakup of Pangaea
It was theorized that all of the present continents were once joined in a single, huge continent he called Pangaea.
Pangaea is Greek for “all earth.”
Pangaea existed about 245 million years ago.

25. Section 2 Restless Continents
Sea-Floor Spreading
Evidence supporting continental drift hypothesis comes from sea-floor spreading.
Sea-floor spreading - the process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies.

26. Sea-Floor Spreading, continued
Section 2 Restless Continents
Sea-Floor Spreading, continued
Mid-ocean ridges are underwater mountain chains that run through Earth’s ocean basins where sea-floor spreading takes place.

27. Section 2 Restless Continents

28. Sea-Floor Spreading, continued
Section 2 Restless Continents
Sea-Floor Spreading, continued
Some of the most important evidence of sea-floor spreading comes from magnetic reversals recorded in the ocean floor.
Molten rock at the mid-ocean ridge contains tiny grains of magnetic minerals that act like compasses.

29. Sea-Floor Spreading, continued
Section 2 Restless Continents
Sea-Floor Spreading, continued
When the Earth’s magnetic field reverses, the magnetic mineral grains align in the opposite direction. The new rock records the direction of the Earth’s magnetic field.

30. Question of the Day If the sea floor is spreading an average of 4 cm a
Section 3 The Theory of Plate Tectonics
Question of the Day
If the sea floor is spreading an average of 4 cm a
year, how many years did it take New York and the west coast of Africa to reach their current locations, 6,760 km apart?
Calculate your answer in your science journal.

31. Objectives Describe the three types of tectonic plate boundaries.
Section 3 The Theory of Plate Tectonics
Objectives
Describe the three types of tectonic plate boundaries.
Describe the three forces thought to move tectonic plates.
Explain how scientists measure the rate at which tectonic plates move.

32. Tectonic Plate Boundaries
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries
As scientists’ understanding of mid-ocean ridges and magnetic reversals grew, a theory was formed to explain how tectonic plates move.
Plate tectonics is the theory that explains how large pieces of the Earth’s outermost layer, called tectonic plates, move and change shape.

33. Tectonic Plate Boundaries, continued
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
A boundary is a place where tectonic plates touch.
All tectonic plates share boundaries with other tectonic plates.
The type of boundary depends on which direction the tectonic plates move.

34. Tectonic Plate Boundaries, continued
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
Three types of boundaries:
Convergent Boundaries
Divergent Boundaries
Transform Boundaries

35. Tectonic Plate Boundaries, continued
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
Convergent boundary – the boundary formed by the collision of two lithospheric plates.
What happens at convergent boundaries depends on the kind of crust at the leading edge of each tectonic plate.

36. Section 3 The Theory of Plate Tectonics

37. Tectonic Plate Boundaries, continued
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
Divergent boundary – the boundary between two tectonic plates that are moving away from each other.
New sea floor forms at divergent boundaries. Sea-Floor Spreading.

38. Tectonic Plate Boundaries, continued
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
Transform boundary – the boundary between tectonic plates that are sliding past each other horizontally.
The San Andreas Fault in California is an example of a transform boundary.

39. Section 3 The Theory of Plate Tectonics

40. Causes of Plate Movement
Section 3 The Theory of Plate Tectonics
Causes of Plate Movement
What causes the motion of tectonic plates?
Tectonic plates move because of changes in the density in the asthenosphere.
The following Visual Concept presentation examines three possible driving forces of tectonic plate motion.

41. Tracking Plate Movement
Section 3 The Theory of Plate Tectonics
Tracking Plate Movement
Tectonic plate movements are so slow and gradual that you can’t see or feel them.
Tectonic plate movement is measured in centimeters per year.
Scientists use a system of satellites called the global positioning system (GPS) to measure the rate of tectonic plate movement.