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Duplicating any part of this book is prohibited by law. © 2017 Triumph Learning, LLC 62 Unit 2 Changes in Earth Over Time Each photo shows natural features of Earth. With a partner, discuss the photos. What landscapes and formations do the photos show? How are they alike? How are they different? Record your observations about each photo. Imagine taking a trip to a beach with your family. You build a magnificent sand castle. Describe what will happen to the sand castle after you leave. Lesson 5 Earth’s Changing Surface
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Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

May 22, 2020

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Page 1: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

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62 Unit 2 • Changes in Earth Over Time

Each photo shows natural features of Earth. With a partner, discuss the photos. What landscapes and formations do the photos show? How are they alike? How are they different? Record your observations about each photo.

Imagine taking a trip to a beach with your family. You build a magnificent sand castle. Describe what will happen to the sand castle after you leave.

Lesson 5

Earth’s Changing Surface

Page 2: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

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Lesson 5 • Earth’s Changing Surface 63

Earth’s surface is always changing. Some processes wear down rock formations such as mountains and cliffs. Other processes build up new landforms such as beaches and islands. Sudden events such as earthquakes and volcanoes can fundamentally alter Earth’s surface in a matter of seconds, minutes, or hours. This lesson looks at processes that happen over much longer time periods—thousands or millions of years.

The photo below shows Lake Champlain. It is the eighth-largest natural lake in the United States. The lake is relatively new. For hundreds of thousands of years, a kilometer-thick layer of ice covered the region.

How could a lake form in a place that was once covered with ice? Record your ideas below.

Look AheadWater in its various forms is a key force in the transformation of Earth’s surface. How do rivers wear down—and build up—features on our planet’s surface? What role do oceans play in changing the landscape along coastlines? What are glaciers, and how do they shape the face of the planet? Continue reading to find answers to these and other questions.

Page 3: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

Explore!

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64 Unit 2 • Changes in Earth Over Time

Wearing It DownMaterials• Plastic container with lid • Water• Salt pellets • Ruler• Scale

Steps

Weigh the plastic container and record its weight in the table below (in the Container column). Put the salt pellets into the container, weigh the container with the salt pellets, and record the weight (in the Total column). Use subtraction to find the weight of the salt pellets.

Total Container Salt

Weight (g)

Measure and describe a salt pellet. Predict how a pellet will change in Step 3, when you will swirl all of them in water for one minute.

Pour enough water into the container to fill it halfway. Move the container in a circular motion for one minute, swirling the pellets and the water around.

Pour all of the water out of the container, making sure to retain the salt pellets. Was your prediction about how a pellet would change correct? Explain. Use the ruler to measure the length, width, and depth of a salt pellet. Then describe it.

1

2

3

4

Page 4: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

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Lesson 5 • Earth’s Changing Surface 65

Write your container’s empty weight from Step 1 in the table below. Weigh the container with the salt pellets and record the weight in the Total column. Use subtraction to find the weight of the salt left in the container.

Total Container Salt Left

Weight (g)

Calculate the amount of salt lost. Then calculate the percentage decrease in salt. Record your data in the table below.

Original Salt (g) Salt Left (g) Salt Loss (g) Percentage

Decrease (%)

Describe the results of the activity. What do you think would happen if you swirled the remaining salt pellets in water for another minute? Another two minutes?

Think About It

5

6

7

The activity models the process of rocks being worn away. A model can represent a natural process—often on a different scale. How do you think this model changes the scale of time? Explain your ideas.

Talk with your group about Step 6. What happened to the salt that was lost? How might this relate to the process of rocks wearing away?

Page 5: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

66 Unit 2 • Changes in Earth Over Time

Understand

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66 Unit 2 • Changes in Earth Over Time

Rock formations on Earth’s surface are constantly being worn away in a process called weathering. Weathering breaks rock down into smaller pieces of rock, sand, or particles. There are two types weathering—chemical and mechanical. Water plays an important role in both kinds of weathering.

In chemical weathering, water—especially water containing an acid—reacts with minerals in the rock. A chemical reaction breaks down the surface of the rock. New substances form. As a result, the surface of the rock slowly dissolves or crumbles.

In mechanical weathering, a rock’s surface is physically broken down. The rock’s chemical composition stays the same. Water hitting a rock can break off small pieces. When water seeps into a crack in a rock and freezes, the ice expands, forcing the crack to widen. As the crack widens, pieces of rock may chip off, allowing more water to seep in.

Think about your model of rocks wearing away in the Explore activity. Did you model chemical weathering, mechanical weathering, or both? Explain your ideas.

Page 6: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

Lesson 5 • Earth’s Changing Surface 67

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Lesson 5 • Earth’s Changing Surface 67

Mechanical weathering is increased by abrasion, the grinding away of a rock’s surface by other rocks or particles. Think of a river or an ocean wave. The water may contain small rocks, sand, or particles. When the water hits a rock, these small pieces act like sandpaper. They scrape at the surface of the rock, grinding it away.

Abrasion can also speed up chemical weathering. Imagine water hitting a rock that is being chemically weathered. If the water contains sand or rock particles, the sand and particles will grind away the new substances formed by the chemical reaction. This exposes more of the rock’s surface, opening new areas where the chemical reaction can take place. In this case, chemical weathering and mechanical weathering work together to wear away the rock.

Gravity also causes mechanical weathering. Recall that gravity is the force of attraction between two bodies. Earth’s gravitational force pulls rocks toward the planet’s center.

Cliff

RockCracks

Ice

Pieces of rock

Think back to your model in the Explore activity. How could you change the activity to model abrasion? Explain your ideas.

Look closely at the diagram. How does water work with gravity to weather the cliff?

Page 7: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

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68 Unit 2 • Changes in Earth Over Time

Weathering is not the only way that water changes Earth’s landscapes. Moving water causes erosion. Erosion is the process in which weathered rock is moved to new locations. The same water that weathers a rock may also erode the weathered pieces.

The photo below shows the Grand Canyon in Arizona. The Colorado River formed the canyon over millions of years.

Rivers are a key part of erosion processes around the globe. A river can carry many kilograms of weathered rock particles past any point in its course each day. Where the river slows, these particles settle to the bottom and form a layer of sediment. All rivers slow when they reach their mouths, where they empty into a lake or an ocean. Over time, the sediment in rivers’ mouths builds up, forming land called a delta.

Look closely at the photo. Describe how the Colorado River could have formed the Grand Canyon. What roles did abrasion and gravity play?

Describe how a mountain might become a river delta hundreds of miles away.

YellowRiver

Delta

Sediment

China’s Yellow River carries moresediment than any other river.

NASA's Earth Observatory

YellowRiver

Delta

Sediment

China’s Yellow River carries moresediment than any other river.

NASA's Earth Observatory

Page 8: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

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Lesson 5 • Earth’s Changing Surface 69

Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet of ice that moves slowly across the land. Today, most of the world’s glaciers are located near the polar regions. But in earlier, colder periods of Earth’s history, glaciers covered vast landscapes, including much of North America.

Some glaciers move just a few centimeters per year. Others move more than a meter per day. As glaciers move, they grind rocks in their pathway and carry away the debris. The photo below shows the Smith Glacier in Alaska.

Some glaciers form in valleys. Over thousands of years, these glaciers may scrape the valleys wider and deeper. If they move across soil or other soft material on Earth’s surface, the glaciers may scoop out vast holes. They erode all this weathered material, pushing it along their paths. When the climate warms and glaciers retreat, the rocks, sand, and other debris are left behind, sometimes forming dams. As the glaciers melt, the valleys and holes may fill with water.

Study the photo. Relate the glacier to the processes of weathering and erosion.

Look again at the photo of Lake Champlain at the beginning of this lesson. Think about what you have learned about glaciers. Have your ideas about the formation of Lake Champlain changed? Explain any changes.

Page 9: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

70 Unit 2 • Changes in Earth Over Time

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70 Unit 2 • Changes in Earth Over Time

Weathering also occurs along ocean shores. Waves pound against cliffs and rocks, breaking small pieces off. Earth’s gravitational force pulls the pieces downward. Depending on the slope underneath, the worn pieces may accumulate as a rocky beach. As waves continue to break against the shore, the pieces of rock are ground into smaller pieces, or sand.

Recall that rivers deposit sediment at their mouths. Ocean currents can then move the sediment up or down the coast. Ocean currents are like rivers within the ocean—streams of water that flow in certain directions. Currents tend to move sediment along the same paths and deposit it in the same locations.

How might a sandy beach accelerate the weathering of an ocean cliff?

How can ocean currents cause an island such as Chincoteague to form? Explain your ideas.

Chincoteague is a barrier island o� the coastof Virginia. Barrier islands are narrow, low,sandy islands that are parallel to coastlines.

Chincoteague is a barrier island o� the coastof Virginia. Barrier islands are narrow, low,sandy islands that are parallel to coastlines.

Page 10: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

Lesson 5 • Earth’s Changing Surface 71

Go FurtherD

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Lesson 5 • Earth’s Changing Surface 71

When rain falls and flows over ground into streams and rivers, not all of the water ends up in lakes or oceans. Some water seeps underground. This groundwater may pick up chemical compounds that allow it to dissolve certain kinds of rock. If groundwater then seeps through cracks in such a rock, it will dissolve the rock’s surface. As time passes, the cracks grow larger. Eventually, a cave may form. A cave is a natural underground chamber that can extend for miles.

When groundwater dissolves rock, it picks up minerals from the rock. The water may then drip from a cave ceiling, and it may drip from the same point for hundreds or thousands of years. With each drip, a tiny ring of the mineral forms on the ceiling. Below, where the drip lands, a thin layer of the mineral forms on the cave floor. Delicate formations called stalactites and stalagmites slowly grow. Stalactites—hanging from the ceiling—and stalagmites—building up from the floor—can be seen in the photo of Carlsbad Cavern.

Think about your model in the Explore activity. How does the model relate to the process of cave formation? Explain your ideas.

Discuss the Explore activity with a partner. How could you modify the activity to model the formation of stalactites and stalagmites? Explain your ideas.

Carlsbad Cavern is a cave inNew Mexico.Carlsbad Cavern is a cave inNew Mexico.

Page 11: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

72 Unit 2 • Changes in Earth Over Time

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72 Unit 2 • Changes in Earth Over Time

Not all weathering is caused by water. Wind, especially when it is strong enough to carry dust, can wear away rocks. In some places, wind is also an important force of erosion. Wind erodes sand, soil, and other particles by lifting them and blowing them away.

The photo shows dunes in an Arizona desert. A dune is a hill of sand deposited by wind. Use what you know about weathering and erosion to describe how the sand in the Arizona dunes might have gotten there. Where did the rock particles originate?

Page 12: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

Lesson 5 • Earth’s Changing Surface 73

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Check YourUnderstanding

Lesson 5 • Earth’s Changing Surface 73

1 Draw a diagram to show how ocean erosion can create a beach. Be sure to label the parts of your diagram.

2 Describe how mechanical weathering and chemical weathering are similar and how they are different.

3 Can a river cause weathering and erosion at the same time? Explain your ideas.

Page 13: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet

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74 Unit 2 • Changes in Earth Over Time

4 The photo shows rock pieces left behind by a glacier that melted.

Explain how the glacier acted on rock to form the landscape you see. Include two processes in your answer.

5 How does abrasion affect weathering and erosion? Explain your ideas.

Page 14: Lesson 5 Earth’s Changing Surface · Lesson 5 • Earth’s Changing Surface 69 Glaciers are another way that water changes the planet’s surface. A glacier is a huge, thick sheet