Chapter F4
Chapter F4 Plate Tectonics
Table of Contents
Section 3 The Theory of Plate Tectonics
Section 4 Deforming the Earth’s Crust
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Chapter F4
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.
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Chapter F4
Section 1 Inside the Earth
The Composition of the Earth
• The Earth is divided into three layers —the crust, the mantle, and the core —based on the compounds that make up each layer.
• The Crust is the outermost layer of the Earth. The crust is 5 to 100 km thick, and is the thinnest layer of the Earth.
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Chapter F4
Section 1 Inside the Earth
The Composition of the Earth, continued
• There are two types of crust —continental and oceanic. Oceanic crust is thinner and denser than continental crust.
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Chapter F4
Section 1 Inside the Earth
The Composition of the Earth, continued
• The Mantle is the layer of the Earth between the crust and the core. The mantle is much thicker than the crust and contains most of the Earth’s mass.
• The crust is too thick to drill through, so scientists must draw conclusions about the composition and other properties of the mantle from observations made on the Earth’s surface.
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Chapter F4
Section 1 Inside the Earth
The Composition of the Earth, continued
• The Core is the central part of the Earth that lies below the mantle. The core makes up about onethird of Earth’s mass.
• Scientists think that the Earth’s core is made mostly of iron and contains smaller amounts of nickel but almost no oxygen, silicon, aluminum, or magnesium.
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Chapter F4
Section 1 Inside the Earth
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Chapter F4
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.
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Chapter F4
Section 1 Inside the Earth
Physical Structure of the Earth, continued
• The outermost, rigid layer of the Earth is called the lithosphere.
• The lithosphere is made of two parts —the crust and the rigid upper part of the mantle.
• The lithosphere is divided into pieces that are called tectonic plates .
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Chapter F4
Section 1 Inside the Earth
Physical Structure of the Earth,
continued
• The asthenosphere is a plastic layer of the mantle on which the tectonic plates move.
• The asthenosphere is made of solid rock that flows very slowly.
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Chapter F4
Section 1 Inside the Earth
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Chapter F4
Section 1 Inside the Earth
Physical Structure of the Earth, continued
• The mesosphere is the strong, lower part of the mantle between the asthenosphere and the outer core.
• The prefix mesomeans “middle.”
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Chapter F4
Section 1 Inside the Earth
Physical Structure of the Earth, continued
• The Earth’s core is divided into two parts.
• The outer core is the liquid layer of the Earth’s core that lies beneath the mantle.
• The inner core is the solid, dense center of our planet that extends from the bottom of the outer core to the center of the Earth, about 6,380 km beneath the surface.
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Chapter F4
Section 1 Inside the Earth
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Chapter F4
Section 1 Inside the Earth
Tectonic Plates
• Pieces of the lithosphere that move around on top of the asthenosphere are called tectonic plates.
• Tectonic plates consist of the crust and the rigid, outermost part of the mantle.
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Chapter F4
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.
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Chapter F4
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.
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Chapter F4
Section 1 Inside the Earth
Tectonic Plates
Click below to watch the Visual Concept.
Visual Concept
You may stop the video at any time by pressing the Esc key.
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Chapter F4
Section 1 Inside the Earth
Tectonic Plates, continued
• Tectonic plates “float” on the asthenosphere. The plates cover the surface of the asthenosphere, and they touch one another and move around.
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Chapter F4
Section 2 Restless Continents
Bellringer
What is meant by the 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.
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Section 2 Restless Continents
Chapter F4
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 midocean ridges.
• Explain how magnetic reversals provide evidence for sea-floor spreading.
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Chapter F4
Section 2 Restless Continents
Wegener’s Continental Drift Hypothesis
• Continental drift is the hypothesis that states that continents once formed a single landmass, broke up, and drifted to their present locations.
• Scientist Alfred Wegener developed the hypothesis in the early 1900s.
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Chapter F4
Section 2 Restless Continents
The Breakup of Pangaea
• Wegener 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.
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Chapter F4
Section 2 Restless Continents
Continental Drift
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Visual Concept
You may stop the video at any time by pressing the Esc key.
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Chapter F4
Section 2 Restless Continents
Sea-Floor Spreading
• Evidence to support the continental drift hypothesis comes from sea-floor spreading.
• Sea-floor spreading is the process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies.
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Chapter F4
Section 2 Restless Continents
Sea-Floor Spreading, continued
• Mid-Ocean Ridges and Sea-Floor Spreading
Mid-ocean ridges are underwater mountain chains that run through Earth’s ocean basins.
• These mid-ocean ridges are the places where sea-floor spreading takes place.
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Chapter F4
Section 2 Restless Continents
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Chapter F4
Section 3 The Theory of Plate Tectonics
Bellringer
If the sea floor is spreading an average of 4 cm a year, how many years did it take New York and the northwest coast of Africa to reach their current locations, 676,000,000 cm apart?
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Chapter F4
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.
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Chapter F4
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.
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Chapter F4
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 how the tectonic plates move relative to one another.
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Chapter F4
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
There are three types of tectonic plate boundaries:
• Convergent Boundaries
• Divergent Boundaries
• Transform Boundaries
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Chapter F4
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
• When two tectonic plates collide, the boundary between them is a convergent boundary.
• What happens at convergent boundaries depends on the kind of crust at the leading edge of each tectonic plate.
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Chapter F4
Section 3 The Theory of Plate Tectonics
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Chapter F4
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries
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Visual Concept
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Chapter F4
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
• When two tectonic plates separate, the boundary between them is called a divergent boundary.
• New sea floor forms at divergent boundaries.
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Chapter F4
Section 3 The Theory of Plate Tectonics
Tectonic Plate Boundaries, continued
• When two tectonic plates slide past each other horizontally, the boundary between is called a transform boundary.
• The San Andreas Fault in California is an example of a transform boundary.
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Chapter F4
Section 3 The Theory of Plate Tectonics
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Chapter F4
Section 3 The Theory of Plate Tectonics
Causes of Tectonic Plate Motion
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Visual Concept
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Chapter F4
Section 3 The Theory of Plate Tectonics
Possible Causes of Tectonic Plate Motion
• What causes the motion of tectonic plates? This movement occurs because of changes in the density within the asthenosphere.
• The following Visual Concept presentation examines three possible driving forces of tectonic plate motion.
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Chapter F4
Section 3 The Theory of Plate Tectonics
Tracking Tectonic Plate Motion
• Tectonic plate movements are so slow and gradual that you can’t see or feel them. The 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.
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Chapter F4
Section 3 The Theory of Plate Tectonics
Newton’s Second Law of Motion, continued
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Visual Concept
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Chapter F4
Section 4
Deforming the Earth’s Crust
Bellringer
Compare the mountains in the photographs. Write a description of each mountain, and suggest how it might have formed.
Do you know where these various types of mountains are found in the world? Have you ever visited any of them? Would it ever be dangerous to study them?
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Chapter F4
Section 4
Deforming the Earth’s Crust
Objectives
• Describe two types of stress that deform rocks.
• Describe three major types of folds.
• Explain the differences between the three major types of faults.
• Identify the most common types of mountains.
• Explain the difference between uplift and subsidence.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Deformation
• Whether a material bends or breaks depends on the how much stress is applied to the material.
• Stress is the amount of force per unit area on a given material.
• Different things happen to rock when different types of stress are applied.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Deformation, continued
• The process by which the shape of a rock changes because of stress is called deformation .
• Rock layers bend when stress is placed on them.
• When enough stress is placed on rocks, they can reach their elastic limit and break.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Deformation, continued
• The type of stress that occurs when an object is squeezed, such as when two tectonic plates collide, is called compression.
• When compression occurs at a convergent boundary, large mountain ranges can form.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Deformation, continued
• Tension is stress that occurs when forces act to stretch an object.
• Tension occurs at divergent plate boundaries, such as mid-ocean ridges, when two tectonic plates pull away from each other.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Folding
• The bending of rock layers because of stress in the
Earth’s crust is called folding.
• Types of Folds Depending on how rock layers deform, different types of folds are made.
• The major types of folds are anticlines, synclines, and monoclines.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Faulting
• Some rock layers break when stress is applied. The surface along which rocks break and slide past each other is called a fault.
• The blocks of crust on each side of the fault are called fault blocks .
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Chapter F4
Section 4
Deforming the Earth’s Crust
Faulting, continued
• When a fault is not vertical, its two sides are either a hanging wall or a footwall.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Faulting, continued
• The type of fault depends on how the hanging wall and footwall move in relationship to each other.
• When a normal fault moves, it causes the hanging wall to move down relative to the footwall.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Faulting, continued
• When a reverse fault moves, it causes the hanging wall to move up relative to the footwall.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Faulting, continued
• A third major type of fault is a strike-slip fault . These faults form when opposing forces cause rock to break and move horizontally.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Plate Tectonics and Mountain Building
• When tectonic plates collide, land features that start as folds and faults can eventually become large mountain ranges.
• When tectonic plates undergo compressions or tension, they can form mountains in several ways.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Mountain Building, continued
• Folded Mountains form when rock layers are squeezed together and pushed upward.
• Fault-Block Mountains form when large blocks of the Earth’s crust drop down relative to other blocks.
• Volcanic Mountains form when magma rises to the Earth’s surface and erupts.
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Chapter F4
Section 4
Deforming the Earth’s Crust
Uplift and Subsidence
• Vertical movements in the crust are divided into two types —uplift and subsidence.
• Uplift is the rising of regions of the Earth’s crust to higher elevations.
• Subsidence is the sinking of regions of the Earth’s crust to lower elevations.
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Chapter F4
Plate Tectonics
Concept Map
Use the terms below to complete the concept map on the next slide.
transform boundaries tectonic plates divergent boundaries converge diverge
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Chapter F4
Plate Tectonics
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Chapter F4
Plate Tectonics
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Chapter F4
End of Chapter F4 Show
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Chapter F4
Standardized Test Preparation
Reading
Read each of the passages. Then, answer the questions that follow each passage.
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Chapter F4
Standardized Test Preparation
Passage 1 The Deep Sea Drilling Project was a program to retrieve and research rocks below the ocean to test the hypothesis of sea-floor spreading.
For 15 years, scientists studying sea-floor spreading conducted research aboard the ship
Glomar Challenger . Holes were drilled in the sea floor from the ship.
Continued on the next slide
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Chapter F4
Standardized Test Preparation
Passage 1, continued Long, cylindrical lengths of rock, called cores, were obtained from the drill holes. By examining fossils in the cores, scientists discovered that rock closest to mid-ocean ridges was the youngest.
The farther from the ridge the holes were drilled, the older the rock in the cores was. This evidence supported the idea that sea-floor spreading creates new lithosphere at mid-ocean ridges.
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Chapter F4
Standardized Test Preparation
1. In the passage, what does conducted mean?
A directed
B led
C carried on
D guided
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Chapter F4
Standardized Test Preparation
1. In the passage, what does conducted mean?
A directed
B led
C carried on
D guided
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Chapter F4
Standardized Test Preparation
2. Why were cores drilled in the sea floor from the
Glomar Challenger ?
F to determine the depth of the crust
G to find minerals in the sea-floor rock
H to examine fossils in the sea-floor rock
I to find oil and gas in the sea-floor rock
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Chapter F4
Standardized Test Preparation
2. Why were cores drilled in the sea floor from the
Glomar Challenger ?
F to determine the depth of the crust
G to find minerals in the sea-floor rock
H to examine fossils in the sea-floor rock
I to find oil and gas in the sea-floor rock
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Chapter F4
Standardized Test Preparation
3. Which of the following statements is a fact according to the passage?
A Rock closest to mid-ocean ridges is older than rock at a distance from mid-ocean ridges.
B One purpose of scientific research on the Glomar
Challenger was to gather evidence for sea-floor spreading.
C Fossils examined by scientists came directly from the sea floor.
D Evidence gathered by scientists did not support sea-floor spreading.
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Chapter F4
Standardized Test Preparation
3. Which of the following statements is a fact according to the passage?
A Rock closest to mid-ocean ridges is older than rock at a distance from mid-ocean ridges.
B One purpose of scientific research on the Glomar
Challenger was to gather evidence for sea-floor spreading.
C Fossils examined by scientists came directly from the sea floor.
D Evidence gathered by scientists did not support seafloor spreading.
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Chapter F4
Standardized Test Preparation
Passage 2 The Himalayas are a range of mountains that is 2,400 km long and that arcs across Pakistan,
India, Tibet, Nepal, Sikkim, and Bhutan. The Himalayas are the highest mountains on Earth. Nine mountains, including Mount Everest, the highest mountain on
Earth, are more than 8,000 m tall.
Continued on the next slide
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Chapter F4
Standardized Test Preparation
Passage 2, continued The formation of the Himalaya
Mountains began about 80 million years ago. A tectonic plate carrying the Indian subcontinent collided with the
Eurasian plate. The Indian plate was driven beneath the Eurasian plate. This collision caused the uplift of the Eurasian plate and the formation of the Himalayas.
This process is continuing today.
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Chapter F4
Standardized Test Preparation
1. In the passage, what does the word arcs mean?
A forms a circle
B forms a plane
C forms a curve
D forms a straight line
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Chapter F4
Standardized Test Preparation
1. In the passage, what does the word arcs mean?
A forms a circle
B forms a plane
C forms a curve
D forms a straight line
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Chapter F4
Standardized Test Preparation
2. According to the passage, which geologic process formed the Himalaya Mountains?
F divergence
G subsidence
H strike-slip faulting
I convergence
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Chapter F4
Standardized Test Preparation
2. According to the passage, which geologic process formed the Himalaya Mountains?
F divergence
G subsidence
H strike-slip faulting
I convergence
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Chapter F4
Standardized Test Preparation
3. Which of the following statements is a fact according to the passage?
A The nine tallest mountains on Earth are located in the Himalaya Mountains.
B The Himalaya Mountains are located within six countries.
C The Himalaya Mountains are the longest mountain range on Earth.
D The Himalaya Mountains formed more than 80 million years ago.
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Chapter F4
Standardized Test Preparation
3. Which of the following statements is a fact according to the passage?
A The nine tallest mountains on Earth are located in the Himalaya Mountains.
B The Himalaya Mountains are located within six countries.
C The Himalaya Mountains are the longest mountain range on Earth.
D The Himalaya Mountains formed more than 80 million years ago.
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Chapter F4
Standardized Test Preparation
Interpreting Graphics
This illustration shows the relative velocities (in centimeters per year) and directions in which tectonic plates are separating and colliding. Arrows that point away from one another indicate plate separation. Arrows that point toward one another indicate plate collision.
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Chapter F4
Standardized Test Preparation
1. Between which two tectonic plates does spreading appear to be the fastest?
A the Australian and the Pacific
B the Antarctic and the Pacific
C the Nazca and the Pacific
D the Cocos and the Pacific
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Chapter F4
Standardized Test Preparation
1. Between which two tectonic plates does spreading appear to be the fastest?
A the Australian and the
Pacific
B the Antarctic and the Pacific
C the Nazca and the Pacific
D the Cocos and the Pacific
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Chapter F4
Standardized Test Preparation
2. Where do you think mountain building is taking place?
F between the African and South
American plates
G between the Nazca and South
American plates
H between the North American and Eurasian plates
I between the African and North
American plates
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Chapter F4
Standardized Test Preparation
2. Where do you think mountain building is taking place?
F between the African and South
American plates
G between the Nazca and South
American plates
H between the North American and Eurasian plates
I between the African and North
American plates
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Chapter F4
Standardized Test Preparation
Math
Read each question, and choose the best answer.
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Chapter F4
Standardized Test Preparation
1. The mesosphere is 2,550 km thick, and the asthenosphere is 250 km thick. If you assume that the lithosphere is 150 km thick and that the crust is 50 km thick, how thick is the mantle?
A 2,950 km
B 2,900 km
C 2,800 km
D 2,550 km
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Chapter F4
Standardized Test Preparation
1. The mesosphere is 2,550 km thick, and the asthenosphere is 250 km thick. If you assume that the lithosphere is 150 km thick and that the crust is 50 km thick, how thick is the mantle?
A 2,950 km
B 2,900 km
C 2,800 km
D 2,550 km
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Chapter F4
Standardized Test Preparation
2. If a seismic wave travels through the mantle at an average velocity of 8 km/s, how many seconds will the wave take to travel through the mantle?
F 318.75 s
G 350.0 s
H 362.5 s
I 368.75 s
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Chapter F4
Standardized Test Preparation
2. If a seismic wave travels through the mantle at an average velocity of 8 km/s, how many seconds will the wave take to travel through the mantle?
F 318.75 s
G 350.0 s
H 362.5 s
I 368.75 s
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Chapter F4
Standardized Test Preparation
3. If the crust in a certain area is subsiding at the rate of
2 cm per year and has an elevation of 1,000 m, what elevation will the crust have in 10,000 years?
A 500 m
B 800 m
C 1,200 m
D 2,000 m
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Chapter F4
Standardized Test Preparation
3. If the crust in a certain area is subsiding at the rate of
2 cm per year and has an elevation of 1,000 m, what elevation will the crust have in 10,000 years?
A 500 m
B 800 m
C 1,200 m
D 2,000 m
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Chapter F4
Standardized Test Preparation
4. A very small oceanic plate is located between a midocean ridge and a subduction zone. At the ridge, the plate is growing at a rate of 5 km every 1 million years. At the subduction zone, the plate is being destroyed at a rate of 10 km every 1 million years. If the oceanic plate is
100 km across, how long will it take the plate to disappear?
F 100 million years
G 50 million years
H 20 million years
I 5 million years
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Chapter F4
Standardized Test Preparation
4. A very small oceanic plate is located between a midocean ridge and a subduction zone. At the ridge, the plate is growing at a rate of 5 km every 1 million years. At the subduction zone, the plate is being destroyed at a rate of 10 km every 1 million years. If the oceanic plate is
100 km across, how long will it take the plate to disappear?
F 100 million years
G 50 million years
H 20 million years
I 5 million years
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Chapter F4
Section 1 Inside the Earth
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Chapter F4
Section 4
Deforming the Earth’s Crust
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Chapter F4
Section 4
Deforming the Earth’s Crust
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Chapter F4
Section 4
Deforming the Earth’s Crust
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Chapter F4
Section 4
Deforming the Earth’s Crust
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Chapter F4
Section 4
Deforming the Earth’s Crust
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Chapter F4
Section 4
Deforming the Earth’s Crust
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Chapter F4
Standardized Test Preparation
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter F4
Section 1 Inside the Earth
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Chapter F4
Section 1 Inside the Earth
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Chapter F4
Section 2 Restless Continents
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Chapter F4
Section 3 The Theory of Plate Tectonics
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