Lesson 1 Forces That Shape Earth

Lesson 1 Forces That Shape Earth
Chapter Introduction Lesson 1 Forces That Shape Earth Lesson 2 Landforms at Plate Boundaries Lesson 3 Mountain Building Lesson 4 Continent Building Chapter Wrap-Up Chapter Menu

How is Earth’s surface shaped by plate motion?
Chapter Introduction

What do you think? Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements. Chapter Introduction

Do you agree or disagree?
1. Forces created by plate motion are small and do not deform or break rocks. 2. Plate motion causes only horizontal motion of continents. 3. New landforms are created only at plate boundaries. Chapter Introduction

4. The tallest and deepest landforms are created at plate boundaries. 5. Metamorphic rocks formed deep below Earth’s surface sometimes can be located near the tops of mountains. 6. Mountain ranges can form over long periods of time through repeated collisions between plates. Chapter Introduction

7. The centers of continents are flat and old. 8. Continents are continually shrinking because of erosion. Chapter Introduction

Lesson 1 Reading Guide - KC
Forces That Shape Earth How do continents move? What forces can change rocks? How does plate motion affect the rock cycle? Lesson 1 Reading Guide - KC

Lesson 1 Reading Guide - Vocab
Forces That Shape Earth isostasy subsidence uplift compression tension shear strain Lesson 1 Reading Guide - Vocab

Plate Motion Mountain ranges are produced by plate tectonics.
The theory of plate tectonics states that Earth’s surface is broken into rigid plates that move horizontally on Earth’s more fluid upper mantle. Mountains and valleys form where plates move away from each other or slide past each other. Lesson 1-1

Vertical Motion Isostasy is the equilibrium between continental crust and the denser mantle below it. isostasy from Greek iso, means “equal”; and Greek stasy, means “standing” Lesson 1-2

You need to understand forces that act on Earth’s plates to understand how they can rise to form mountains. A continent floats on top of the mantle because the mass of the continent is equal to the mass of the mantle it displaces. This is also why icebergs float on the surface water.

Vertical Motion (cont.)
Plates formed of continental crust are less dense than the fluid rock that forms the mantle, and part of the continental crust floats above the surface of the mantle. The continental crust displaces some of the mantle below it until an equilibrium is reached, which is called isostasy. Lesson 1-2

The crust will sink and rise as its mass changes, in order to reach equilibrium. If a part of the continental crust becomes thicker, it sinks deeper into the mantle. The crust can also rise higher if it becomes lighter. The mantle will push up on the thicker crust until a balance is reached.

Weathering and erosion remove the top part of a mountain
Weathering and erosion remove the top part of a mountain. After this happens, the crust rises to maintain isostasy. The mountain stops moving when the mass of the mountain equals the mass of the mantle it displaces.

Much of North America was covered by glaciers more than 1 km thick 20,000 years ago. The weight of the ice pushed the crust downward into the mantle in a process called subsidence. Lesson 1-2

The downward vertical motion of Earth’s surface is called subsidence.

When the ice melted and the water ran off, the isostatic balance was upset. In response, the crust moved upward in a process called uplift. The upward vertical motion of Earth’s surface is called uplift.

What can cause Earth’s surface to move up or down? Lesson 1-2

Horizontal Motion Horizontal motion at plate boundaries applies much greater forces to rocks than vertical motion does. Forces at plate boundaries are strong enough to break rocks or change the shape of rocks. Lesson 1-3

Horizontal Motion (cont.)
Stress is the force acting on a surface. Squeezing stress is compression. Stress that pulls something apart is tension. Parallel forces acting in opposite directions are shear. Lesson 1-3

Compression, tension, and shear can all cause rocks to change shape.
Lesson 1-3

A change in the shape of rock caused by stress is called strain. Elastic strain does not permanently change, or deform, rocks. It occurs when stresses are small or rocks are very strong. Plastic strain creates a permanent change in shape. Lesson 1-3

plastic Science Use capable of being molded Common Use a commonly used synthetic material Lesson 1-3

Compression thickens and folds layers of rock. Tension stretches and thins layers of rock. Lesson 1-3

In the upper crust, the rocks are cold, and forces cause the rocks here to break rather than to change shapte. When strain breaks rocks rather than just changing their shape, it is called failure. When rocks fail, fractures—or faults—form. Lesson 1-3

What causes rocks to thicken or fold? Lesson 1-3

Plate Tectonics and the Rock Cycle
Rocks are always moving through the rock cycle, both vertically and horizontally. The theory of plate tectonics combined with uplift and subsidence explain why there is a rock cycle on Earth. The forces that cause plate tectonics produce horizontal motion. Isostasy results in vertical motion within continents. Lesson 1-4

Uplift brings metamorphic and igneous rock from deep in the crust up to the surface, where erosion breaks down rocks into sediment. Buried sediment becomes sedimentary rocks, which with pressure and temperature eventually become metamorphic rocks. Subduction takes all types of rocks deep into Earth, where they can melt and become new igneous or metamorphic rocks.

Horizontal tectonic motion and vertical motion by uplift and subsidence help move rocks through the rock cycle. Lesson 1-4

Plate Tectonics and the Rock Cycle (cont.)
How does plate motion affect the rock cycle? Lesson 1-4

Different types of stress change rocks in different ways.
As a mountain is eroded away, the continent will rise until isostatic balance is restored. Different types of stress change rocks in different ways. Lesson 1 - VS

Horizontal and vertical motions are part of what keep rocks moving through the rock cycle.
Lesson 1 - VS

What term refers to the equilibrium between continental crust and the denser mantle below it?
A. uplift B. subsidence C. isostasy D. compression Lesson 1 – LR1

Which term refers to a change in the shape of rock caused by stress?
A. tension B. strain C. compression D. shear Lesson 1 – LR2

What is the downward vertical motion of Earth’s surface called?
A. subsidence B. uplift C. isostasy D. none of the above Lesson 1 – LR3

2. Plate motion causes only horizontal motion of continents.
Do you agree or disagree? 1. Forces created by plate motion are small and do not deform or break rocks. 2. Plate motion causes only horizontal motion of continents. Lesson 1 - Now

Landforms at Plate Boundaries What features form where two plates converge? What features form where two plates diverge? What features form where two plates slide past each other? Lesson 2 Reading Guide - KC

Landforms at Plate Boundaries ocean trench volcanic arc transform fault fault zone Lesson 2 Reading Guide - Vocab

Landforms Created by Plate Motion
Massive, slow-moving tectonic plates have so much force they can build tall mountains, form deep valleys, and rip Earth’s surface apart. Compression, tension, and shear stresses each produce a different type of landform. Lesson 2-1

Landforms Created by Compression
The largest landforms on Earth are produced by compression at convergent plate boundaries. A collision between two continental plates can produce tall mountains that form slowly and in stages over millions of years. Although plates move horizontally, the collision cause the crust to move vertically as well. Lesson 2-2

The plates beneath India and Asia started colliding almost 50 million years ago. Because the plates are still colliding, the Himalayas grow a few millimeters each year due to compression. Lesson 2-2

Landforms Created by Compression (cont.)
When two plates collide, one can go under the other and be forced into the mantle in a process called subduction. A deep trench forms where the two plates meet. Ocean trenches are deep, underwater troughs created by one plate subducting under another plate at a convergent plate boundary. Lesson 2-2

What two landforms can form where two plates converge? Lesson 2-2

Volcanic mountains can form in the ocean where plates converge and one plate subducts under another one. The volcanoes form islands about 100 km in distance from where the two plates meet. The curved line of volcanic islands that forms parallel to a plate boundary is called a volcanic arc. Lesson 2-2

Volcanic arcs can also form on continents.
Lesson 2-3

Landforms Created by Tension
A long, tall mountain range that forms where oceanic plates diverge is called a mid-ocean ridge. Lesson 2-3

Where plates move apart, tension stresses stretch Earth’s crust.
At divergent boundaries, oceanic plates, move apart, and there are tension stresses that cause crust to spread apart. As tension stresses cause oceanic crust to spread apart, hot rock from the mantle rises.

The hot mantle rise and pushes the seafloor upward, making a long, tall ridge on the bottom of the ocean, called a mid-ocean ridge.

Landforms Created by Tension (cont.)
When divergent boundaries occur within a continent, they can form continental rifts, or enormous splits in Earth’s crust. Lesson 2-3

Tension stresses in the cold upper part of the crust create faults.
At these faults, large block of crust move downward, creating a rift valley between two ridges.

Landforms Created by Tension (cont.)
What features form at divergent boundaries? Lesson 2-3

Landforms Created by Shear Stresses
Shear stresses at transform boundaries produce faults where plates slide past one another horizontally. Transform faults form where tectonic plates slide horizontally past each other. Segments of mid-ocean ridges are sometimes separated by transform faults. Lesson 2-4

Landforms Created by Shear Stresses (cont.)
The yellow line on the map shows the mid-ocean ridge. The red lines are transform faults. Lesson 2-4

The transform faults are perpendicular to the mid-ocean ridges, and they get longer as the plates move. As the older transform faults move farther away from the mid-ocean ridge, new transform faults form.

A transform fault that can be seen at Earth’s surface is the San Andreas Fault in California.
Many transform faults that are part of this fault system cannot be seen on the surface of Earth, but instead are underground.

Landforms Created by Shear Stresses (cont.)
What features form where plates slide past each other? Lesson 2-4

An area of many fractured pieces of crust along a large fault is called a fault zone.
Lesson 2-4

The deepest and tallest landforms on Earth are created at plate boundaries.
Lesson 2 - VS

Tension stresses within continents can produce enormous splits in Earth’s surface.
Lesson 2 - VS

Faults at Earth’s surface can be part of much larger fault zones that have many underground faults.
Lesson 2 - VS

Which refers to the process of one plate going under the mantle when two plates collide?
A. compression B. rift C. subduction D. none of these Lesson 2 – LR1

Which term describes the place where tectonic plates slide horizontally past each other?
A. fracture zone B. transform faults C. fault zone D. none of these Lesson 2 – LR2

What is the term for a long, tall mountain range that forms where oceanic plates diverge?
A. mid-ocean ridge B. continental rift C. transform fault D. fracture zone Lesson 2 – LR3

3. New landforms are created only at plate boundaries.
Do you agree or disagree? 3. New landforms are created only at plate boundaries. 4. The tallest and deepest landforms are created at plate boundaries. Lesson 2 - Now

Mountain Building How do mountains change over time? How do different types of mountains form? Lesson 3 Reading Guide - KC

Mountain Building folded mountain fault-block mountain uplifted mountain Lesson 3 Reading Guide - Vocab

The Mountain-Building Cycle
Mountain ranges are built slowly and change slowly over millions of years. Because many different collisions occur to form the mountains, mountains are made up of many different kinds of rocks. The process of weathering and erosion can carry away all or parts of mountains. Lesson 3-1

When plates collide at a plate boundary, a combination of folding, faulting, and uplift form mountains. After millions of years, the forces that originally caused plates to move together can become inactive.

When the forces that caused two plates to move become inactive at the plate boundary, a single new continent is formed from the two old ones. Lesson 3-1

With no compression at a convergent plate boundary, the mountains stop growing.
The movement of earth’s tectonic plates causes the continents to always be changing. A divergent plate boundary that forms on a continent often forms close to the place where two plate first collided. First a large split, or rift forms; as it grows, water flows into it, forming an ocean.

Weathering has rounded the peaks and lowered the elevations of the Appalachian Mountains.
As a mountain erodes, the root under it must rise to restore the balance between what is left of the mountain and how it floats on the mantle.

Rocks deep under continents rise slowly toward Earth’s surface.
In old mountain ranges, metamorphic rocks that formed deep below the surface are exposed on the top of mountains.

The cycle of repeated collisions and rifting can create old and complicated mountain ranges, such as the Appalachian Mountains. Lesson 3-1

The Mountain-Building Cycle (cont.)
Appalachian from the Apalachee abalahci, means “other side of the river” Lesson 3-1

The Mountain-Building Cycle (cont.)
How can mountains change over time? Lesson 3-1

Types of Mountains Plate movements can change the positions of rocks within a mountain range. Folded mountains are made of layers of rocks that are folded. When erosion removes the upper part of the crust, folds are exposed on the surface. Lesson 3-2

The folds are perpendicular to the direction of the force of compression that created them.
Fault-block mountains are parallel ridges that form where blocks of crust move up at faults. If the tension that caused the mountains to form pulled in an east-west direction, the mountains will form ridges oriented in the north-south direction.

Fault-block mountains have a high ridge next to a valley; between these two landforms is a fault where the movement that cause the landforms occurred.

Tension can pull crust apart in the middle of a continent
Tension can pull crust apart in the middle of a continent. Where the crust breaks, fault-block mountains and valleys can form as blocks of the crust rise or fall. Lesson 3-2

Types of Mountains (cont.)
How do folded and fault-block mountains form? Lesson 3-2

When large regions rise vertically with very little deformation, uplifted mountains form. Lesson 3-2

One idea of how uplifted mountains form involves sinking mantle pulling crust downward, which causes the crust near the surface to become compressed and thicker. As the crust thickens, the upper part of the crust rises to maintain isostasy; sometimes the crust rises high enough to create tall mountains.

Volcanoes are special kinds of mountains.
Volcanic mountains form when molten rock erupts onto Earth’s surface and hardens Volcanic mountains that are dormant have not erupted in a long time, but they might erupt again someday.

Some of the largest mountains on Earth are made by volcanic eruptions. How do uplifted and volcanic mountains form? Lesson 3-2

Mountain ranges can be the result of repeated continental collision and rifting.
Lesson 3 - VS

Tension stresses create mountain ranges that are a series of faults, ridges, and valleys.
Lesson 3 - VS

Uplifted mountains rise with little rock deformation.
Lesson 3 - VS

B. fault-block mountains C. uplifted mountains D. volcanoes
When large regions rise vertically with very little deformation, what type of mountains form? A. folded mountains B. fault-block mountains C. uplifted mountains D. volcanoes Lesson 3 – LR1

Which of these can affect mountain ranges?
A. erosion B. uplift C. weathering D. all of these Lesson 3 – LR2

B. fault-block mountains C. uplifted mountains D. none of the above
Which type of mountains are parallel ridges that form where blocks of crust move up at faults? A. folded mountains B. fault-block mountains C. uplifted mountains D. none of the above Lesson 3 – LR3

5. Metamorphic rocks formed deep below Earth’s surface sometimes can be located near the tops of mountains. 6. Mountain ranges can form over long periods of time through repeated collisions between plates. Lesson 3 - Now

Continent Building What are two ways continents grow? What are the differences between interior plains, basins, and plateaus? Lesson 4 Reading Guide - KC

Continent Building plains basin plateau Lesson 4 Reading Guide - Vocab

The Structure of Continents
Most of the highest elevations are located near the edges of continents. Lesson 4-1

The Structure of Continents (cont.)
from Latin terra continens, means “continuous land” Lesson 4-1

The interiors of most continents are flat and located close to the middle of the continent; in these regions, the rocks exposed at Earth’s surface are old igneous and metamorphic rocks. Lesson 4-1

There are few moutnains in the interior of continents.
The interior parts of continents are formed of old igneous and metamorphic rocks an are the oldest parts of the continents. The middle parts of the continents are flat because millions or billions of years of erosion have worn the rocks smooth and level.

How Continents Grow One way continents get bigger is through the addition of igneous rocks by erupting volcanoes. A second way is when tectonic plates carry island arcs, whole continents, or fragments of continents with them. Lesson 4-2

When a plate carrying fragments reaches a continent at a convergent boundary, the least dense fragments get pushed onto the edge of the continent, causing the continent to grow. The green areas show parts of North America that were attached in this way. Lesson 4-2

Continents can change size and shape due to rifting and become smaller due to weathering and erosion.

How Continents Grow (cont.)
What are two ways continents grow? Lesson 4-2

Continental Interiors
Rocks in continental interiors tend to be stable, flat, very old, and very strong. A plain is an extensive area of level or rolling land. The plains have been flattened by millions of years of weathering and erosion. Lesson 4-3

In North America, most of the central area is called the Interior Plains.
The rock that form the Interior Plains came from smaller plates that collided about 1 billion years ago. Shallow seas once covered these plains, and over millions of years, weathering and erosion have worn the plains so they are nearly flat. Plate motion and isostasy can cause places to sink, or subside.

Continental Interiors (cont.)
What is a plain? Lesson 4-3

Areas of subsidence and regions with low elevation are called basins. Sediments eroded from mountains accumulate in basins. Lesson 4-3

Animal and plant remains can also get buried in basins and converted by pressure and heat over millions of years into oil, natural gas, and coal. Therefore, basins are often important places, economically, because they contain valuable energy resources.

Flat regions with high elevations are called plateaus. The Colorado Plateau is an example of a plateau formed through uplift. Lesson 4-3

The eruption of lava also can create large plateaus. Some parts of the Columbia River Plateau consist of more than 3 km of basalt. Lesson 4-3

What are the differences between plains, basins, and plateaus? Lesson 4-3

Dynamic Landforms The Earth’s surface is constantly changing.
Mountains form only to be eroded away. Continents grow, shift, and shrink. Lesson 4-4

Rocks at the center of most continents are very old, very strong, and flat.
Lesson 4 - VS

Fragments of crust are added to continents at convergent boundaries.
Lesson 4 - VS

Large, elevated plateaus are created through uplift and lava flows.
Lesson 4 - VS

Which term refers to flat regions with high elevations?
A. basins B. plains C. plateaus D. none of the above Lesson 4 – LR1

How do continents get bigger?
A. addition of igneous rocks by erupting volcanoes B. tectonic plates carry fragments of continents with them C. A and B Lesson 4 – LR2

Where are most of the highest elevations located on continents?
A. near the edges of continents B. the continental interiors C. both of these D. neither of these Lesson 4 – LR3

7. The centers of continents are flat and old.
Do you agree or disagree? 7. The centers of continents are flat and old. 8. Continents are continually shrinking because of erosion. Lesson 4 - Now

Interactive Concept Map Chapter Review Standardized Test Practice
Key Concept Summary Interactive Concept Map Chapter Review Standardized Test Practice Chapter Review Menu

The constructive and destructive forces created by the movement of tectonic plates are responsible for the variety of Earth’s constantly changing landforms, including volcanoes, mountains, and ocean basins. The BIG Idea

Lesson 1: Forces That Shape Earth
As continents float in the mantle, they rise and fall to maintain the balance of isostasy. Forces called compression, tension, and shear can deform or break rocks. Uplift and plate motion move rocks through the rock cycle. Key Concepts 1

Lesson 2: Landforms at Plate Boundaries
When two continental plates collide, tall mountain ranges form. When an oceanic plate subducts below another one, an ocean trench and a volcanic arc form. At divergent boundaries, mid-ocean ridges and continental rifts form. Transform faults can create large areas of faulting and fracturing, not all of which can be seen at Earth’s surface. Key Concepts 2

Lesson 3: Mountain Building
Mountain ranges can grow from repeated plate collisions. Folded mountains form by compression of plastic rock. Tension in continental crust creates parallel fault-block mountains. Key Concepts 3

Lesson 4: Continent Building
Continents shrink because of erosion and rifting. Continents grow through volcanic activity and continental collisions. Large, flat regions at high elevation are called plateaus. Basins are regions at low elevation where sediments accumulate or once accumulated. Key Concepts 4

What term refers to the upward vertical motion of Earth’s surface?
A. subsidence B. isostasy C. uplift D. tension Chapter Review – MC1

What term refers to pressure that pulls something apart?
A. tension B. strain C. compression D. shear Chapter Review – MC2

Which term refers to deep, underwater troughs created by one plate subducting under another plate at a convergent plate boundary? A. mid-ocean ridge B. ocean trench C. volcanic arc D. none of these Chapter Review – MC3

Which word best describes the interiors of most continents?
A. elevated B. unstable C. flat D. none of the above Chapter Review – MC4

How do plateaus form? A. eruption of lava B. through uplift C. A and B
D. none of these Chapter Review – MC5

Which term describes squeezing stress?
A. shear B. tension C. compression D. none of the above Chapter Review – STP1

What kind of strain creates a permanent change in shape?
A. elastic strain B. plastic strain C. fractures D. none of the above Chapter Review – STP2

What term describes the curved line of volcanic islands that forms parallel to a plate boundary?
A. ocean trenches B. fracture zone C. fault zone D. volcanic arc Chapter Review – STP3

Which of these has been flattened by millions of years of weathering and erosion?
A. basins B. plains C. mountains D. plateaus Chapter Review – STP4

Sediments eroded from mountains accumulate in which of these?
A. plateaus B. plains C. basins D. none of the above Chapter Review – STP5

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