Table of Contents Rocks and Weathering How Soil Forms Soil Conservation

1. Weathering and Soil Table of Contents Rocks and Weathering How Soil Forms Soil Conservation

2. The minerals that make up a rock determine some of the rocks properties. • http://ed101.bu.edu/StudentDoc/Archives/ED101sp07/rjayneb/propertiesrocks.htm • Rock properties are • color- is the rock red, blue, green, brown, black • Luster- how shiny is the rock? • Pattern –look at the layers of the rock. Is it striped or no stripes (not all rocks will have a pattern) • Texture- rough, smooth • Shape- rectangular, round, oval or square • The properties of rock can change in 2 ways • Physical change- does not alter the chemical composition • Chemical change- produces one or more new substances

3. Let’s discover…… • What Breaks Down Rocks? • Uniformitarianism- This principle states that geologists can use present day forces and processes to explain geological event’s in Earth’s past. • Erosion- process of wearing down and carrying away rocks. Rock is removed using wind, water, ice and gravity. • Weathering- process of breaking down rocks and other substances. Heat, cold, water, ice and gases all play a part in weathering. • Compare and Contrast erosion and weathering in your groups.

4. What Causes Weathering? • There are 2 ways that weathering takes place • Mechanical weathering- rock is physically broken into smaller pieces. • -mechanical weathering usually works slowly • -mechanical weathering, as part of erosion, can wear away a whole mountain. • How does Mechanical weathering take place?

5. Rocks and Weathering Forces of Mechanical Weathering

6. Agents of Mechanical Weathering • Are you up for the challenge? • In your groups look at the pictures listed. • Determine which types of weathering made the rock change. • Your choices are • Abrasion • Freezing and thawing • Animal actions • Plant growth • Release of pressure

7. Chemical weathering-is the process that breaks down rocks through chemical changes. • can produce new minerals as it breaks down rocks • Agents of chemical weathering are • Water-dissolves some rocks since it carries oxygen and carbon dioxide that break down rock. • Oxygen-iron combines with oxygen in the presence of water in a process called oxidation • Carbon dioxide- this gas that is in our air causes chemical weathering when it dissolves in water. It produces an acid called carbonic acid. Carbonic acid or (carbon dioxide weathering) easily weathers marble and limestone • Living organisms-when a plant’s roots grow, they produce weak acids that dissolve rocks and the roots. Lichens are plantlike organisms that grow on rocks and make acid. • Acid rain-rainwater is acidic. Burning coal, oil and gas for energy pollutes the air with sulfur, carbon and nitrogen compounds. These compounds reacts with water vapor in clouds making the acid even stronger than normal rain. Acid rain causes very rapid chemical weathering.

8. Rocks and Weathering Weathering and Surface Area Weathering breaks rock into smaller pieces. While the pieces are usually irregularly shaped, you can model the process with cubes. The diagram shows what would happen if a rock cube broke into smaller cubes.

9. How Fast Does Weathering Occur? • The most important factors that determine the rate at which weathering occurs are the type of rock and climate. • Rocks that are made of minerals that do not dissolve easily will weather slowly. • Some rocks weather more easily because they are permeable. • Permeable-means the material is full of tiny connected air spaces that allow water to seep through it. The spaces increase a rocks surface area. As water goes into those spaces it carries chemicals that dissolve the rock.

10. Rocks and Weathering Which Weathered Faster? The data table shows how much stone was lost due to weathering for two identical pieces of limestone from different locations. Use the data to make a double-line graph and provide the axes, a key and a title.

11. Climate- refers to the average weather conditions in an area. Both chemical and mechanical weathering occur faster in wet climates. Chemicals reactions occur at higher temperatures. Chemical weathering occurs quickly where the climate is hot and wet.

12. What Is Soil?? Soil-is the loose weathered material on Earth in which plants can grow. Soil is a mixture of rock particles, minerals, decayed organic material, water and air. Bedrock- is the solid layer of rock beneath the soil. Once bedrock is exposed to water, air and living things it gradually weathers into smaller particles that are the most common components of soil. Humus- is the decayed organic material. Humus is dark in color that forms as plant and animal remains decay. Humus contains nutrients that plants need and help create spaces in soil for air and water.

13. How Soil Forms Soil Particle Size The particles shown here have been enlarged. Discuss where a 1.5-mm particle would fall on the graph.

14. Soil Fertility Fertile soil is rich in nutrients that plants need to grow. Soil that has high humus has good fertility. Soil texture- depends on the size of the soil particles. Soil texture is important for plant growth. Soil that is made up of equal parts of clay, sand and silt is called loam. Loam is the best soil for growing most kind of plants. Soil pH- soil can be acidic or basic. A pH scale measures acidity.

15. How Soil Forms Soil Texture Triangle The soil texture triangle is used to determine the type of soil based on the percentages of silt, sand, and clay in a soil sample.

16. The Process of Soil Formation Soil forms as rock is broken down by weathering and mixes with other materials on the surface. Soil forms constantly as bedrock weathers. Soil formation continues over long periods of time. Gradually soil develops layers called horizons. A soil horizon is a layer of soil that differs in color, texture and composition from the layers above and below it.

17. A Horizon- is made up of topsoil. It is a crumbly, dark brown soil that is made up of humus, clay and other minerals. Topsoil forms as plants add organic material to the soil, and plant roots weather pieces of rock. B Horizon-is also called subsoil. It consists of clay and other particles of rock but little humus. It forms as rainwater washes away the materials from the A horizon. C Horizon-forms as bedrock begins to weather. Bedrock is on the bottom

18. How Soil Forms Soil Layers Gradually, soil develops layers, called horizons. Horizons differ in color, texture, and composition.

19. How do living things affect soil? Many organisms live in soil. Some soil organisms make humus, the material that makes soil fertile. Other soil organisms mix the soil and make spaces for air and water. Forming Humus- dead leaves, roots and other plant materials help to form humus. Humus forms in a process called decomposition. Decomposers- organisms that break down the dead organisms into smaller pieces and digest them with chemicals. This material then mixes with the soil as humus.

20. Types of soil decomposers- fungi (mushrooms) bacteria and worms. Earthworms and burrowing animals mix humus with air and other materials in the soil. As earthworms eat their way through the soil, they carry humus down to the subsoil and subsoil up to the surface. Mice, moles and prairie dogs break up hard compacted soil and mix humus with it.

21. How Soil Forms Life in Soil What are the three soil horizons? Are the organisms pictured decomposers, burrowers, or humus sources?

22. How Soil Forms From Rock to Soil The illustrations show a rock and rich, fertile soil. What are the three processes that could change rock into soil?

23. Soil Conservation Prairie Grasses Soils on the Great Plains are among the most fertile in the world. How do you think prairie grasses protect soil?

24. Soil Conservation Farming Method Contour plowing is one way to conserve soil.