Chapter 3
Land as a Natural Resource
We live on it. We use it to grow crops. We mine minerals from it. We use it to build things. What is it? It's Land! How is the Land changing?
People Using Science
Resources Management Specialist
Jordon C. Pope Works for the Bureau of Land Management in Washington, D.C. This bureau manages 264 million acres of public lands. Public lands are owned by all Americans.
Jordon Pope's job is to analyze people's ideas on how to best use the public lands. Some public lands are national parks and forests. Other public lands may be used for mining fossil fuels and minerals. Still other public lands are set aside for dinosaur digs, as wildlife refuges, and as historical and cultural sites.
Jordo n Pope said the most rewarding part of his job is knowing that he has helped protect and preserve public lands and other resources for future Americans. What are land resources? To find out, read this chapter.
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Coming Up
INVESTIGATION 1: HOW DO THE Forces of nature Change Earth’s Surface? D48
INVESTIGATION: WHY ARE ROCKS AND SOIL IMPORTANT? D54
---Jordon Pope studies how to best use public Lands.
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Investigation 1
How Do the Forces of Nature Change Earth’s Surface?
How can a mountain be changed if it's hard as rock? In this investigation you'll find out how forces- of nature can change mountains.
Activity
Hard Rock
How hard are rocks? Find out!
Materials
· goggles
· small rocks
· white paper
· Science Notebook
Safety
Wear goggles during this activity.
Procedure
With your group, predict what will happen if you rub two rocks against each other. Record your prediction in your Science Notebook. Hold two small rocks over a clean sheet of white paper. Press them together and rub hard. Record your observations.
Analyze and Conclude
1. What happened to the rocks when they were rubbed together?
2. Infer what might happen to large rocks that are struck over and over again by wind-blown sand.
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Activity
A Force of Nature
Can we change Earth's surface? Find out!
Materials
· goggles
· small rocks or gravel, sand, water
· small plastic container
· freezer
· ruler soil
· rectangular aluminum pan
· paper towel
· Science Notebook
Safety
Wear goggles during this activity. Clean up spills immediately.
Procedure
1. Make a model of a glacier (gla'shar). A glacier is a large mass of slow-moving ice. Place a handful of small rocks in the bottom of a small container. Sprinkle some sand among the rocks. Then fill the container with water and place it in a freezer.
2. With your group predict what will happen to the surface of the soil if the glacier is dragged over it. Record your predictions in your Science Notebook.
3. The next day, put about ,5 cm of soil in an aluminum baking pan. Take the model glacier out of the container. Use a paper towel to move the glacier in one direction over the soil in the pan. Record your observations.
4. Predict what the soil will look like if the glacier melts. Leave the ice in the pan until it melts. Record your observations.
Analyze and Conclude
1. What happened to the soil when you moved the glacier over it? What happened to the soil after the glacier melted?
2. Infer what would happen if a glacier the size of a football field slid slowly down a mountain. How would the mountain be affected? How is your model different from a real glacier? How is it like a real glacier?
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Resources
Wearing Down and building Up
Reading Focus: What are two fast changes and two slow changes that can occur on Earth's surface?
Earth's surface is always changing. What causes it to change? The answer lies deep within Earth. Pretend that you could bore a tunnel into Earth. If you could travel safely through the tunnel, what might you see?
It's a Bore
In most places you would pass a layer of soil at the surface of Earth. This soil layer could be anywhere from a few centimeters to about 30 m (100 ft) thick.
As you went farther into Earth, you would begin to see layers of different kinds and colors of rock. These rock layers lie beneath the land. Similar layers of different kinds of rock lie beneath the oceans. As you continued down the tunnel, you'd pass thick layers of solid rock. Farther down, the rock layers change. The great mass of rock in the upper layers weighs heavily on the deeper rock layer. As a result, heat and pressure are very great. The heat causes some of the rock to flow like liquid. This liquid rock inside Earth is called magma (mag'ma).
Quick Change
On your return to Earth's surface, you are happy to once again be on solid ground. And yet, Earth's surface is really a lot less solid and unchanging than it might look! Several different forces in nature cause changes to Earth's surface.
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Hot Rock
Sometimes the changes that occur to Earth's surface are sudden. In some parts of the world, magma is close to Earth's surface. Sometimes this hot liquid shoots out of an opening in the ground called a volcano (val ka'no). Once on the surface of Earth, the liquid rock is called lava (la'va).
Hot liquid rock cools and hardens when it reaches the surface. When the lava cools around the opening, it may form a cone-shaped volcano. Lava flowing away from the volcano can burn everything in its path before it cools. When the lava cools, it adds a layer of rock to Earth's surface. So volcanoes are one of the forces of nature that change Earth's surface.
Trembling Earth
Other sudden changes to Earth's surface can result from an earthquake. The solid layers of rock beneath the surface are actually broken up into large sections. Sometimes these sections move suddenly. This sudden movement of large sections of rock beneath Earth's surface causes an earthquake.
The energy of an earthquake can cause landscapes to change in a dramatic way. During an earthquake, hills and boulders can appear where none were in sight just moments before. Other times, rocks and hills disappear in an instant. You can see that Earth's surface can change quickly during an earthquake.
---Lava can flow far from the volcano as shown in this photo from Hawaii. How is Earth's surface changing? •
---An earthquake in Idaho caused ' sudden change to Earth's surface. Here, a section of the ground dropped.
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Slow Motion
The changes to Earth's surface caused by volcanoes and earthquakes happen very quickly. But slow changes to the surface are taking place all the time. Sometimes the results of these changes can only be seen after many years. The Grand Canyon is one example.
About 6 million years ago, there was no Grand Canyon. Over time the Colorado River slowly wore away the rock along its banks and carried away the rock materials. Even today the river continues to carve the Grand Canyon deeper and deeper.
The breaking up or wearing away of rocks is called weathering (we t11'ar ii)). The breaking up and moving of weathered rocks from one place to another is erosion (e ro'zhan). Rain weathers the cliff walls of the Grand Canyon by wearing away pieces of rock on either side. Then erosion washes the weathered rock material into the Colorado River, which carries it away.
Where does all this weathered rock go? Some is left along the sides of the river, as shown in the photo. The rest is carried to the end, or mouth, of the river. Over time, weathered materials build up Earth's land surface.
Blowing in the Wind
Wind is another force of nature that can cause weathering. Wind can pick up sand and blow it against large rocks. In the activity on page D48, two rocks are rubbed together. This is like the action of sand blowing against large rocks. Windblown sand can act like sandpaper, wearing away the large rocks. Strong winds can carry pieces of weathered rock from one place and deposit them in other places. So wind causes erosion, too.
Using Math: The Colorado River carries enough soil out of the Grand Canyon every day to fill 2 million pickup trucks! How much soil is moved by the river in a week?
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A Frozen Force
Moving ice can also cause weathering and erosion. A glacier (gla'shar) is a large mass of slowmoving ice. As it moves and melts, a glacier changes the surface beneath it as shown in the activity on page D49. A glacier can pick up and move soil and huge rocks great distances.
The changes that are caused by earthquakes and volcanoes occur quickly. Those caused by moving water, wind, and glaciers occur more slowly. But all these forces of nature change Earth's surface through weathering and erosion. •
---This glacier in Alaska is melting. The rocks in the water were pushed there by the glacier.
Technology Link CD-ROM
Investigate Further
Use the Best of the Net CD-ROM, Earth Sciences, Blackcomb Glaciers site to find out how glaciers form and move You'll also find out how fast a glacier can move and you'll learn about ice worms.
INVESTIGATION 1 WRAP-UP
REVIEW
1. Identify four forces of nature that change Earth's surface. Describe how each can cause change.
2. How do erosion and weathering differ?
CRITICALTHINKING
3. Explain how gravity and temperature help glacier change Earth's surface.
4. Describe two ways that Earth's surface can be built up by forces of nature.
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Investigation 2
Why are Rocks and Soil Important?
Have you ever heard the phrase "It's dirt cheap"? It seems as though dirt should be cheap. But soil is a very valuable resource. What other valuable resources come from the land? How can ' these resources be protected?
Activity
Soak It Up
How are soils different? Does water pass through different soils at the same rate?
Materials
· goggles
· newspaper
· plastic soda bottle, cut in half
· cheesecloth
· rubber band
· gravel, sand, topsoil
· metric measuring cup
· water
· container
· timer
· plastic dish
· Science Notebook
Safety
Wear goggles during this activity. Clean up spills immediately.
Procedure
1. Cover your work area with newspaper. Use the top part of a plastic soda bottle as a funnel. Place a piece of cheesecloth over the opening in the neck of the funnel, as shown. Hold the cheesecloth tightly in place with a rubber band.
2. Place the funnel, neck down, in the bottom part of the bottle. Fill the funnel halfway with gravel.
3. Pour 250 mL of water into a measuring cup. Now pour the water into the funnel. Wait one minute.
See Science and Math Toolbox page H7 if you need to review Measuring Volume.
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4. After one minute, move the funnel to an empty container. Pour the water from the bottom part of the bottle into the empty measuring cup. Measure the amount of water that passed through the gravel.
5. In your Science Notebook, make a chart like the one shown below.
Kind of Soil / Water That Passed Through in One Minute (in mL)Gravel
Sand
Topsoil
6. In the chart record the amount of water that passed through the gravel. Empty the measuring cup and the funnel, and rinse off the cheesecloth.
7. Talk with your group and predict what will happen if you repeat the activity, first using sand and then using topsoil. Record your predictions. Repeat the steps, using sand and then topsoil.
Analyze and Conclude
1. Through which kind of soil did the water pass the fastest? the slowest? Compare your predictions with the results.
2. Describe the different properties of the three soils. Of the soils tested, which absorbed water the best? How do you know?
3. Infer what can happen to rainwater when it falls on different kinds of soil.
Unit Project Link
Continue your plans for an Environmental Fair. With your class, plan and carry out a way that you can help care for Earth's land. Then, with your group, make a poster to show what you did to protect Earth's land.
Technology Link For more help with your Unit Project, go to www.eduplace.com .
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On Rocky Ground
Reading Focus Why are rocks and soil called natural resources?
What are some uses of rocks? The photos show two buildings that were built from rock. What other ways do people use rocks where you live?
Rock as a Resource
Rock was the first strong, lasting material that people used for building. Houses, roads, and bridges are made of rock. But what is rock made of?
You learned earlier that a mineral is a solid, found in nature, that has a definite chemical makeup. Rocks are made up of minerals. Some rocks contain just one or two kinds of minerals. Other rocks contain several kinds of minerals. Rocks differ from each other in the kinds of minerals they are made from.
Some rocks are soft and weather easily. But other rocks are very hard and do not weather easily. Rocks of all kinds have been used for building.
The Soil of Life
Which is more valuable, gold or soil? Soil is the loose material that covers much of Earth's surface. As attractive as gold is, it can't be used to grow food. If it weren't for soil, gold couldn't even be used to buy food. Without soil, there would be no food to buy.