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9.3: Lesson 9.2: Soils

Difficulty Level: At Grade Created by: CK-12
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Key Concepts

  • Characteristics and importance of soil
  • Soil formation
  • Soil texture
  • Soil horizons and profile
  • Types of soils
  • Soil conservation

Lesson Objectives

  • Discuss why soil is an important resource.
  • Describe how soil forms from existing rocks.
  • Describe the different textures and components of soil.
  • Draw and describe a soil profile.
  • Define the three climate-related soils: pedalfer, pedocal, and laterite soil.

Lesson Vocabulary

  • deciduous forest: forest that consists mainly of trees that lose their leaves once a year
  • humus: organic portion of soil that consists of partially decayed remains of plants and animals
  • inorganic: not related to life or living organisms; not organic
  • laterite: nutrient-poor, red soil that forms in tropical rainforests
  • loam: type of soil that contains about equal proportions of sand, silt, and clay
  • organic: related to life or living organisms
  • pedalfer: very fertile, dark soil that forms in mid-latitude deciduous forests
  • pedocal: moderately fertile soil that forms in grasslands
  • residual soil: soil that forms from the bedrock upon which it is found
  • soil horizon: individual layer of a soil profile; A, B, or C horizon
  • soil profile: entire set of soil layers, or horizons, for a particular soil
  • subsoil: B-horizon of a soil profile, which lies beneath the topsoil
  • topsoil: A horizon of a soil profile, which is the uppermost and most fertile layer of soil
  • transported soil: soil that forms from weathered components that have been transported from a different area

Teaching Strategies

Introducing the Lesson

Introduce soil by letting students examine a soil sample. The sample should contain a good mix of sizes of rock particles and plenty of organic matter. Give any students who wish a chance to look at the soil with a hand lens. Ask them to name anything they can identify in the soil. Tell students they will learn what soil is made of and how it forms when they read this lesson.


Have students do the activity “What’s in My Soil?” at the following URL. They will separate, examine, and identify the major components of soil to better understand how these components give soil its unique physical characteristics.



One of the easiest to overlook, yet one of the most important, components of soil is air. Air in soil is needed by soil organisms and it keeps open soil pores for water to pass through. Do the simple demonstration described at the URL below to show students that soil contains air. By doing the demonstration with different soil samples, you can show the class that soils vary in the amount of air they contain.


Differentiated Instruction

Pair any English language learners or less proficient readers with other students, and ask partners to make a flow chart showing how soil forms (in situ), starting with unweathered bedrock. Suggest that they add the flow chart to their science notebook.


Ask one or more interested students to investigate careers in soil science. The following URL is an excellent place to start their investigation. They should report back to the class on at least one or two of the careers.


Science Inquiry

Have groups of students do the activity “Who Did It?” at the URL below. In this soil forensics activity, students will identify physical characteristics of soil, determine the density of soil samples, and conclude who committed a crime based on the evidence and laboratory investigations. The Web site includes a lesson plan, lecture notes, lab handouts, and homework.


Real-World Connection

The acidity, or pH, of soil is an important factor in plant growth. Most plants do best in soil with a small range of pH values. Give students a chance to test the pH of garden soil. Soil testing kits are available at garden centers. After they determine the pH of the soil, have them go online to find garden plants that would do well in soil with that pH. If the pH is very low or very high, then students should investigate how to correct the pH of the soil.

Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Earth Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 9.2 Quiz in CK-12 Earth Science for Middle School Quizzes and Tests.

Points to Consider

Why is soil such an important resource?

Do you think a mature soil would form faster from unaltered bedrock or from transported materials?

If soil erosion is happening at a greater rate than new soil can form, what will eventually happen to the soil in that region?

Do you think there are pollutants that could not easily be removed from soil?

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