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Transcript
Weathering 1 Weathering and Its Effects • Together, surface processes that work to break down rock are called weathering. • Weathering breaks rock into smaller and smaller pieces. • These smaller, loose pieces are called sediment. Weathering 1 Mechanical Weathering • Mechanical weathering occurs when rocks are broken apart by physical processes. This means that the overall chemical makeup of the rock stays the same. Click image to view movie. Water that’s found in the cracks of rocks can freeze. Once it freezes it expands breaking the surrounding rock; ICE WEDGING Animals or insects that dig in the ground break up rocks Weathering 1 Chemical Weathering • Chemical weathering occurs when chemical reactions dissolve the minerals in rocks or change them into different minerals. • This type of weathering changes the chemical composition of the rock, which can weaken the rock. Oxidation is a process that changes from one type to another when the mineral, oxygen and water reacts. alteration of the iron-bearing mineral magnetite to a rustlike material called limonite. Weathering 1 Weathering and Its Effects • Weathering wears mountains down to hills. • Rocks at the top of mountains are broken down by weathering, and the sediment is moved downhill by gravity, water, and ice. • Two different types of weathering—mechanical weathering and chemical weathering—work together to shape Earth’s surface. Murphy Marble Belt Valley and Ridge Blue Ridge Talc, Slate, Shale, Limestone Fall Line Piedmont Granite Kaolin, Sand Coastal Plain Mineral map of GA Think About it…. • In what type of climate would the rate of mechanical weathering happen the fastest? • In what type of climate would the rate of chemical weathering happen the fastest? Weathering 1 Effects of Climate • Climate is the pattern of weather that occurs in a particular area over many years. • In cold climates, where freezing and thawing are frequent, mechanical weathering rapidly breaks down rock through the process of ice wedging. Weathering 1 Effects of Climate • Chemical weathering is more rapid in warm, wet climates. • Lack of moisture in deserts and low temperatures in polar regions slow down chemical weathering. Quick Check 1 Question 1 Explain the difference between mechanical and chemical weathering. Section Check 1 Answer Mechanical weathering occurs by physical processes. Growing plants, burrowing animals and expanding ice are processes that can mechanically weather rock. Chemical weathering occurs when chemical reactions dissolve minerals in rocks or change them into different minerals. What is soil? • Soil is a mixture of weathered rock, decayed organic matters, mineral fragments, water, and air. How is soil formed? 1. weathering breaks down rocks or minerals on our surface, it creates a layer of rock sediments. 2. Over time, the sediments break down even more creating very fine (small) particles. 3. Plants and animals add organic matter, the wastes and dead plant material, to the rock fragments. • Soil can take thousands of years to form and ranges from 60 m thick in some areas to just a few centimeters thick in others. Soil Ecosystem Sediment sizes • Soils are classified according to their particle size as follows: Another look at the types of soils Composition of Soil 2 • Rock and mineral fragments, organic matter, air and water. • Animals and microorganisms provide additional organic matter when they die. • The decayed organic matter turns into a dark-colored material called humus (HYEW mus). Humus serves as a source of nutrients for plants. Soil profile • The top layer of soil typically is darker than the soil layers below it. These different layers of soil are called horizons • Most soils have three horizons—labeled A, B, and C. The Nature of Soil 2 A Horizon • The A horizon is the top layer of soil. • In a forest, the A horizon might be covered with litter. Litter consists of leaves, twigs, and other organic material that eventually can be changed to humus by decomposing organisms. • The A horizon also is known as topsoil. Horizon A: Wrap up • Top layer of soil that’s covered with litter. • The organic material can be changed into humus which provides nutrients • This layer is the very fertile and has few rocks and mineral fragments The Nature of Soil 2 B Horizon • The layer below the A horizon is the B horizon. • Because less organic matter is added to this horizon, it is lighter in color than the A horizon and contains less humus. • As a result, the B horizon is less fertile. The Nature of Soil 2 B Horizon • Leaching is the removal of minerals that have been dissolved in water. In soil, water seeps through the A horizon where it reacts with humus and carbon dioxide to form acid. • The acid dissolves some of the minerals in the A horizon and carries the material into the B horizon. The Nature of Soil 2 C Horizon • The C horizon consists of partially weathered rock and is the bottom horizon in a soil profile. • This horizon does not contain much organic matter and is not strongly affected by leaching. • It is the thickest layer of soil • What would you find if you dug to the bottom of the C horizon? • You would find rock—the rock that gave rise to the soil horizons above it. This layer of rock is called bedrock • What are the climate types for the each soil profile below? • Why do you think the profiles are different? The Nature of Soil 2 Soil Types Reflect Climate • Soils in deserts contain little organic material and also are thinner than soils in wetter climates. • Prairie soils have thick, dark A horizons because the grasses that grow there contribute lots of organic matter. The Nature of Soil 2 Other Factors • Parent material has an effect on the soils that develop from it. • Rock type also affects the type of vegetation that grows in a region, because different rocks provide different amounts of nutrients for plant growth. • Type of vegetation then affects soil formation. The Nature of Soil 2 Other Factors • Time also affects soil development. • If weathering has been occurring for only a short time, the parent rock determines the soil characteristics. The Nature of Soil 2 Other Factors • The slope of the land affects soil development. Thin, poorly developed soils form on steep slopes, but valleys often have thick, welldeveloped soils. As gravity, a type of force of erosion, moves soil and sediments downhill deposition occurs at the bottom of the hill (slope). This is why the soil formation is different in the two locations Possible Sentences for Soil ______________ Name of Topic Word Box soil horizons sand bedrock humus leaching silt topsoil litter soil profile clay parent rock Write 6 sentences by using two of the above words in each sentence. Do not use a word more than once. _____ 1. ____________________________________________________ ____________________________________________________ ____________________________________________________ _____ 2. ____________________________________________________ ____________________________________________________ ____________________________________________________ _____ 3. ____________________________________________________ ____________________________________________________ ____________________________________________________ _____ 4. ____________________________________________________ ____________________________________________________ ____________________________________________________ _____ 5. ____________________________________________________ ____________________________________________________ ____________________________________________________ _____ 6. ____________________________________________________ ____________________________________________________ ____________________________________________________ Warm UP • On a piece of paper you can hand in for a grade--• Write a paragraph to compare and contrast the two soils from yesterday’s observations. Explain why the soils looked differently and how minerals/organic material got into the soil. Give specific details and justify your answers with details. • You will have 15 minutes to • complete this task. INB Page 76 Complete the following Using your Textbook • List the 5 factors that affect soil formation (pg. 188). • Next to each factor, use pg. 193-194 to explain how that factor affects the formation of soil. (for example, type of rock affects soil formation because the minerals that make up the rock weather to form the soil) • On pg. 188, list the 5 components of soil (what the soil is made of) and draw a picture of each component. • Draw the soil profile on pg. 191 with the labels. Next to each layer, list 3 important facts about the soil. • Answer this question using pg. 193: Why do different areas of the United States have different types of soil? • http://www.epa.gov/acidrain/education/site_ students/acid_anim.html