1. Table of Contents Earth’s Interior Convection and the Mantle
Drifting Continents
Sea-Floor Spreading
The Theory of Plate Tectonics

2. Exploring Inside the Earth
- Earth’s Interior
Exploring Inside the Earth
Geologists have used two main types of evidence to learn about Earth’s interior: direct evidence from rock samples and indirect evidence from seismic waves.

3. The Crust - Earth’s Interior
The crust is a layer of solid rock that includes both dry land and the ocean floor.

5. The Mantle - Earth’s Interior
Earth’s mantle is made up of rock that is very hot, but solid. Scientists divide the mantle into layers based on the physical characteristics of those layers.

6. Temperature Inside the Earth
- Earth’s Interior
Temperature Inside the Earth
The graph shows how temperatures change between Earth’s surface and the bottom of the mantle. On this graph the temperature at the Earth’s surface is 0oC. Study the graph carefully and then answer the questions.

7. Temperature Inside the Earth
- Earth’s Interior
Temperature Inside the Earth
Reading Graphs:
As you move from left to right on the x-axis, how does depth inside the Earth change?
The depth increases.

8. Temperature Inside the Earth
- Earth’s Interior
Temperature Inside the Earth
Estimating:
What is the temperature at the boundary between the lithosphere and the asthenosphere?
About 1,600oC

9. Temperature Inside the Earth
- Earth’s Interior
Temperature Inside the Earth
Estimating:
What is the temperature at the boundary between the lower mantle and the core?
About 3,200oC

10. Temperature Inside the Earth
- Earth’s Interior
Temperature Inside the Earth
Interpreting Data:
How does temperature change with depth in Earth’s interior?
It generally increases with depth.

11. The Core - Earth’s Interior
The core is made mostly of the metals iron and nickel. It consists of two parts–a liquid outer core and a solid inner core.

12. Using Prior Knowledge - Earth’s Interior
Before you read, look at the section headings and visuals to see what this section is about. Then write what you know about Earth’s interior in a graphic organizer like the one below. As you read, write what you learn.
What You Know
Earth’s crust is made of rock.
Earth is very hot near the center.
Dry land is part of the crust.
The mantle is very hot.
The core contains iron.
What You Learned
Geologists use seismic waves to study Earth’s interior.
Radioactive substances heat the interior of Earth.
The crust is thickest under high mountains.
The mantle is solid.
Movements in the outer core create Earth’s magnetic field.

13. Links on the Structure of Earth
- Earth’s Interior
Links on the Structure of Earth
Click the SciLinks button for links on the structure of Earth.

14. End of Section: Earth’s Interior

15. Types of Heat Transfer - Convection and the Mantle
There are three types of heat transfer: radiation, conduction, and convection.

16. Convection Currents - Convection and the Mantle
Heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion.

17. Convection Currents in Earth
- Convection and the Mantle
Convection Currents in Earth
Heat from the core and the mantle itself causes convection currents in the mantle.

18. Convection and the Mantle
Outlining
Convection and the Mantle
An outline shows the relationship between major ideas and supporting ideas. As you read, make an outline about heat transfer. Use the red headings for the main topics and the blue headings for the subtopics.
Types of Heat Transfer
Radiation
Conduction
Convection
Convection Currents
Convection in Earth’s Mantle

19. More on Convection Currents in the Mantle
- Convection and the Mantle
More on Convection Currents in the Mantle
Click the PHSchool.com button for an activity about convection currents in the mantle.

20. Click the Video button to watch a movie about mantle convections.
- Convection and the Mantle
Mantle Convection
Click the Video button to watch a movie about mantle convections.

21. End of Section: Convection and the Mantle

22. Continental Drift - Drifting Continents
Wegener’s hypothesis was that all the continents were once joined together in a single landmass.

23. Evidence for Continental Drift
- Drifting Continents
Evidence for Continental Drift
Fossils and rocks found on different continents provide evidence that Earth’s landmasses once were joined together in the supercontinent Pangaea.

24. Evidence for Continental Drift
- Drifting Continents
Evidence for Continental Drift
Fossils and rocks found on different continents provide evidence that Earth’s landmasses once were joined together in the supercontinent Pangaea.

25. Identifying Supporting Evidence
- Drifting Continents
Identifying Supporting Evidence
As you read, identify the evidence that supports the hypothesis of continental drift. Write the evidence in a graphic organizer like the one below.
Evidence
Shape of continents
Hypothesis
Earth’s continents have moved.
Fossils
Climate change

26. Links on Continental Drift
- Drifting Continents
Links on Continental Drift
Click the SciLinks button for links on continental drift.

27. End of Section: Drifting Continents

28. Mid-Ocean Ridges - Sea-Floor Spreading
The East Pacific Rise is just one of the many mid-ocean ridges that wind beneath Earth’s oceans.

29. What Is Sea-Floor Spreading?
In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

30. Evidence for Sea-Floor Spreading
Several types of evidence supported Hess’s theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

31. Subduction at Trenches
- Sea-Floor Spreading
Subduction at Trenches
In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle through deep-ocean trenches.

32. Growing an Ocean - Sea-Floor Spreading
Because of sea-floor spreading, the distance between Europe and North America is increasing by a few centimeters per year.

33. Sequencing - Sea-Floor Spreading
Make a flowchart to show the process of sea-floor spreading.
Magma erupts along mid-ocean ridge.
Magma cools to form new sea floor.
Sea floor spreads away from ridge.

34. More on Sea-Floor Spreading
Click the PHSchool.com button for an activity about sea-floor spreading.

35. Click the Video button to watch a movie about sea-floor spreading.

36. End of Section: Sea-Floor Spreading

37. How Plates Move - The Theory of Plate Tectonics
The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates.

38. Plate Boundaries - The Theory of Plate Tectonics
There are three kinds of plate boundaries: divergent boundaries, convergent boundaries, and transform boundaries. A different type of plate movement occurs along each type of boundary.

39. - The Theory of Plate Tectonics
Calculating a Rate
To calculate the rate of plate motion, divide the distance the plate moves by the time it takes to move that distance.
Rate = distance/time
For example, a plate takes two million years to move 156 km. Calculate its rate of motion.
156 km/2,000,000 years = 7.8 cm per year
Practice Problem
The Pacific plate is sliding past the North American plate. It has take ten million years for the plate to move 600 km. What is the Pacific plate’s rate of motion?
60,000,000 cm ÷ 10,000,000 years = 6 cm/yr

40. Continental Drift - The Theory of Plate Tectonics
It has taken the continents about 225 million years since the breakup of Pangaea to move to their present locations.

41. Continental Drift Activity
- The Theory of Plate Tectonics
Continental Drift Activity
Click the Active Art button to open a browser window and access Active Art about continental drift.

42. Building Vocabulary - The Theory of Plate Tectonics
A definition states the meaning of a word or phrase by telling about its most important feature or function. After you read the section, reread the paragraphs that contain definitions of Key Terms. Use all the information you have learned to write a definition of each Key Term in your own words.
Key Terms:
Examples:
divergent boundary
rift valley
convergent boundary
transform boundary
Key Terms:
Examples:
plate
The place where two plates move apart, or diverge, is called a divergent boundary.
The lithosphere is broken into separate sections called plates.
scientific theory
A deep valley called a rift valley forms along the divergent boundary.
A scientific theory is a well-tested concept that explains a wide range of observations.
plate tectonics
The theory of plate tectonics states that pieces of Earth’s lithosphere are in slow, constant motion, driven by convection currents in the mantle.
The place where two plates come together, or converge, is called a convergent boundary.
A transform boundary is a place where two plates slip past each other, moving in opposite directions.
fault
Faults are breaks in Earth’s crust where rocks have slipped past each other.

43. End of Section: The Theory of Plate Tectonics

44. Graphic Organizer Type of Plate Boundary Type of Motion
Effect on Crust
Feature(s) Formed
Transform boundary
Plates slide past each other.
Crust is sheared.
Strike-slip fault
Convergent boundary
Plates move together.
Subduction or mountain building
Mountains, volcanoes
Divergent boundary
Plates move apart.
Crust pulled apart by tension forces.
Mid-ocean ridge, ocean floor

45. End of Section: Graphic Organizer