Text Pages 148 155 STUDY GUIDE Use the words to fill in the blanks of the paragraphs. Weathering plants pieces moisture ice wedging acids carbonic acid freezing chemical oxidation temperatures minerals climate desert mechanical cracks reacting Weathering is the breaking of rocks into of weathering. their chemical composition. In expands, forcing the rocks apart. As their roots grow and put pressure on rocks, fragments may fall off.. There are two main types weathering involves breaking rocks without changing, water trapped in rocks freezes and can also cause mechanical weathering. widen and rock weathering involves water, air, and other substances exposed to water and oxygen, with the minerals in the rocks. When metal is occurs and rust forms. in plant roots and mosses can also react with the in rocks. Water and carbon dioxide combine to form, which reacts with minerals such as calcite in limestone. How rapidly weathering occurs in an area depends on the happens more slowly in areas due to a lack of. Chemical weathering. Low in polar regions keep chemical weathering to a minimum there. Whenever and thawing alternate, mechanical weathering becomes an important form of weathering. 26
Text Pages 148 155 REINFORCEMENT Weathering Weathering includes mechanical weathering and chemical weathering. Mechanical weathering is any process that breaks up rock without changing its chemical composition. Chemical weathering is any process in which water, air, or other substances react with the minerals in the rock and change the chemical composition of the rock. Decide if the following descriptions are examples of mechanical weathering or chemical weathering. Write the word mechanical or chemical in the blank at the left. 1. Mosses growing on the surface of rocks, producing pits in the rocks 2. The wedging of tree roots along natural joints in granite outcrops 3. Limestone dissolved by carbonic acid 4. The oxidation of minerals that contain iron 5. Animal burrows dug in rock that let in water and air 6. Repeated freezing and thawing of water that cracks rock 7. The action of water, salt, and air on car fenders and panels 8. Acids from plant roots which break up rocks 9. Formation of potholes in streets during severe winters 10. Lifted sections of sidewalk along tree-lined streets 11. A small rock falling from a cliff 12. Feldspar mixing with acidic groundwater and producing clay minerals 13. Halite in rocks dissolving in water 14. Decaying plants dissolving some of the minerals in rocks 15. Tree roots cracking the concrete foundation of a house 26
Text Pages 156 163 STUDY GUIDE Soil Use the terms in the box to complete the sentences. Use the information in your textbook. soil humus A horizon horizons composition below topsoil parent top evolve bottom leaching soil profile water 1. is a mixture of sediments of weathered rock and organic matter. 2. Decaying plant and animal matter is called. 3. Due to weathering, different layers, or, of soil form. 4. Soil generally has three layers, and these make up a. 5. The A horizon is the layer and is also known as. 6. The B horizon is the layer the A horizon. 7. The C horizon is the layer in a soil profile; it contains partly weathered rock but no humus. 8. Below the bottom horizon is rock. 9. You can tell that the is the most fully evolved soil layer because it has more humus and smaller rock fragments than the other layers. 10. moving downward through the horizons dissolves and carries minerals into lower horizons by the process of. 11. The thickness of the soil layers and their depend on the climate, slope of the land, and the type of rock in an area and how long the soil has been evolving. 12. Soil horizons more slowly in an area that has little rainfall because chemical weathering occurs slowly in a dry climate. 27
Text Pages 156 163 REINFORCEMENT Soil Use the diagram of a soil profile to answer Questions 1 5 on the lines provided. Then answer Questions 6 and 7. A horizon: organic matter, roots, worms, insects and other living organisms B horizon: some roots and other living organisms, materials leached by water from the A horizon C horizon: materials leached by water from the B horizon, partly weathered rock fragments Solid Rock 1. Which soil layer contains the most humus? 2. How far into the soil do plant roots extend? 3. Where in this soil profile are worms and insects breaking down organic matter in the soil? 4. Where in this soil profile is solid rock being weathered into soil? 5. What is the name of the process by which water carries materials from the upper horizons down to the lower levels? 6. What factors in an area help determine the type of soil the thickness of the layers and their composition? 7. Choose a factor from Question 6 and explain how it can affect the soil in an area. 27
Text Pages 164 169 STUDY GUIDE Land Use and Soil Loss Match the items in Column I with the terms in Column II. Write the letter of the correct term in the blank at the left. Column I 1. Practice of leaving plant stalks in the field 2. Mechanical turning and loosening of the soil 3. Trees and plants in tropical regions 4. Desert formation Column II a. plowing b. rain forest c. strip cropping d. desertification e. no-till farming 5. Practice of alternating crops that cover the ground with crops that leave the land exposed Decide whether each of the following statements is true or false. Write the word true or false in the blank. If the statement is false, rewrite it so that it is true. 6. Soil loss is particularly severe in the tropics. 7. Plants are important to soil, because without them, soil evolution stops and no new soil develops. 8. Desertification is a slow process that affects very little land each year. 9. In dry areas, farmers minimize soil erosion by plowing under the natural vegetation. 10. Soil can easily recover the nutrients that crops use up. 28
Text Pages 164 169 REINFORCEMENT In the following statements, words have been scrambled. Unscramble the words and write them on the lines provided. Answer the following questions on the lines provided. 1. Poor farming practices can lead to liso slos. 2. Soil erosion can be caused by gonpliw. 3. Soil blown away by wind created dust storms in the tuds wolb. 4. Sheep and cattle grazing in dry areas can cause fatisodertineic. 5. Different crops are grown in the same areas each year in prist cnogippr. 6. Soil is destroyed by the clearing of hundreds of square kilometers of ianr setrof. 7. Why is it important that soil development continue? Land Use and Soil Loss 8. What effect does overgrazing have on topsoil? 9. Why shouldn t more land be cleared for farming and grazing as old land is worn out? 10. Why do people need soil? 11. What can farmers do to reduce or stop soil erosion? 28
CHAPTER REVIEW Weathering and Soil Part A. Vocabulary Review In the spaces provided, write the term that matches the description. The letters in the boxes form words that answer the question below. 1. Layers of soil 2. A layer in a garden soil profile 3. Type of weathering that changes the composition of a rock 4. A mixture of weathered rock and organic matter 5. Ice breaking apart a rock 6. Chemical weathering caused by exposure to water and oxygen 7. The formation of a desert 8. Organic matter made of decaying plants and animals 9. The passing of minerals down through soil layers 10. Type of weathering that breaks down a rock without changing its composition 11. The breaking up of rocks into sediments, either mechanically or chemically 1. 2. 3. K 4. 5. 6. 7. 8. 9. 10. 11. S 12. What does weathering cause? 15
Chapter Review (continued) Part B: Concept Review Answer the questions on the lines provided. 1. How does the climate in a region affect the weathering of rocks? 2. List five factors that affect the characteristics of the soil in a particular area. 3. What would happen to the animals on Earth if there were no soil? 4. What farming activities have contributed to soil loss? 5. Describe each of the three soil layers in a soil profile. 16