Chapter Introduction

Lesson 1 Weathering

Lesson 2 Soil

Chapter Wrap-Up

What natural processes break down rocks and begin soil formation?

What do you think?

Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.

1. Weathering is the same as erosion.

2. Humans are the main cause of weathering.

3. Plants can break rocks into smaller pieces.

Do you agree or disagree?

4. Air and water are present in soil.

5. Soil that is 1,000 years old is young soil.

6. Soil is the same in all locations.

Do you agree or disagree?

• How does weathering break down or change rock?

• How do mechanical processes break big rocks into smaller pieces?

• How do chemical processes change rocks?

Weathering

• weathering

• mechanical weathering

• chemical weathering

• oxidation

Weathering

• The mechanical and chemical processes that change objects on Earth’s surface over time are called weathering.

• Over thousands of years, weathering can break rock into smaller and smaller pieces, such as sand, silt, and clay.

Weathering and Its Effects

Weathering and Its Effects (cont.)

weather

Science Use to change from the action of the environment

Common Use the state of the atmosphere

Weathering and Its Effects (cont.)

How does weathering break down or change rock?

• When physical processes naturally break rocks into smaller pieces, mechanical weathering occurs.

• The chemical makeup of a rock stays the same during mechanical weathering.

• Mechanical weathering can be caused by ice wedging, abrasion, plants, and animals.

Mechanical Weathering

• An example of mechanical weathering is when the intense heat of a forest fire causes nearby rocks to expand and crack.

• When something is broken into smaller pieces, it has a greater surface area.

• Surface area is the amount of space on the outside of an object.

Mechanical Weathering (cont.)

Mechanical Weathering (cont.)

What are five ways mechanical weathering breaks large rocks into smaller pieces?

• Chemical weathering changes the materials that are part of a rock into new materials.

• These granite obelisks show how chemical weathering can affect some rock.

Chemical Weathering

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• Water is important in chemical weathering because most substances dissolve in water.

• The process of dissolving breaks up the minerals in the rock into small pieces. The small pieces mix with water to form a solution and are washed away from the rock.

• Acids are also agents of chemical weathering and cause more chemical weathering than pure water does.

Chemical Weathering (cont.)

• Oxidation combines the element oxygen with other elements or molecules.

• The product of oxidation is called an oxide.

• When rocks that contain iron oxidize, a layer of iron oxide forms on the outside surface.

Chemical Weathering (cont.)

Chemical Weathering (cont.)

How does chemical weathering change rock?

• The environment helps determine the rate of weathering.

• Mechanical weathering occurs fastest in locations that have a lot of temperature changes.

• Chemical weathering is fastest in warm, wet places.

• The type of rock being weathered also affects the rate of weathering and determines what kinds of products result.

What affects weathering rates?

• Weathering is the mechanical and chemical processes that change things over time.

• Mechanical weathering does not change the identity of the materials that make up rocks. It breaks up rocks into smaller pieces.

• Chemical weathering is the process that changes the minerals that are part of every rock into new materials. Oxidation and reaction with an acid are both examples of chemical weathering.

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A. mechanical weathering

B. chemical weathering

C. ice wedging

D. abrasion

The minerals that make up rock change during which of these?

A. water

B. acids

C. animals

D. A and B

Which of these are agents of chemical weathering?

A. oxidation

B. mechanical weathering

C. surface area

D. abrasion

Which term refers to the amount of space exposed on the outside of an object?

1. Weathering is the same as erosion.

2. Humans are the main cause of weathering.

3. Plants can break rocks into smaller pieces.

Do you agree or disagree?

• How is soil created?

• What are soil horizons?

• Which soil properties can be observed and measured?

• How are soils and soil conditions related to life?

Soil

• soil

• organic matter

• pore

• decomposition

• parent material

Soil

• climate

• topography

• biota

• horizon

• Soil is a mixture of weathered rock, decayed organic matter, mineral fragments, water, and air.

• Organic matter is the remains of something that was once alive.

• Decomposition is the process of changing once-living material into dark-colored organic matter.

What is soil?

Soil contains gases that fill the soil pores–the small holes and spaces in soil.

What is soil? (cont.)

pore

from Greek poros, means “passage, way”

The sizes of pores change with differences in particle size.

What is soil? (cont.)

• Inorganic matter in soil is formed by the mechanical and chemical weathering of rocks into fragments.

• The term inorganic describes materials that have never been alive.

Formation of Soil

• Parent material is the starting material of soil.

• Parent material is made of the rock or sediment that weathers to form the soil.

Formation of Soil (cont.)

Formation of Soil (cont.)

What is the role of parent material in creating soil?

• The average weather of an area is its climate.

• If the parent material is in a warm, wet climate, soil formation can be rapid.

• Topography is the shape and steepness of the landscape.

Formation of Soil (cont.)

• The topography of an area determines what happens to water that reaches the soil surface.

• Water running downhill can carry soil with it, leaving some slopes bare of soil.

Formation of Soil (cont.)

• Biota is all of the organisms that live in a region.

• Biota in the soil help speed up the process of soil formation in various ways.

• Organisms can be involved in decomposition of organic matter or form passages in soil for water to move through.

Formation of Soil (cont.)

Rock and soil are affected by organism activity.

Formation of Soil (cont.)

How does biota aid in soil formation?

Mature soils develop layers as new soil forms on top of older soil.

• As time passes, weathering is constantly acting on rock and sediment, making soil formation a constant, but slow, process.

• Horizons are layers of soil formed from the movement of the products of weathering.

Horizons

horizon

from Latin horizontem, means “bounding circle”

Horizons (cont.)

• Each horizon has characteristics based on the type of materials it contains.

• The three horizons common to most soils are identified as A-horizon, B-horizon, and C-horizon.

• The top, organic layer is called the O-horizon and the unweathered, bedrock layer is the R-horizon.

Horizons (cont.)

Horizons (cont.)

What are soil horizons?

Soil Properties and Uses

Soil Properties and Uses (cont.)

• Some properties of soil can be determined just by observation.

• The amount of sand, silt, and clay in a soil can be estimated by feeling the soil.

• Many soil properties can be measured more accurately in a laboratory.

Soil Properties and Uses (cont.)

Laboratory measurements can determine exactly what is in each sample of soil.

Soil Properties and Uses (cont.)

List soil properties that can be observed and measured.

Plant growers can observe how well plants grow in the soil to get information about soil nutrients.

Soil Properties and Uses (cont.)

How is soil related to life?

The type of soil formed depends partly on climate.

Soil Properties and Uses (cont.)

Are soils the same everywhere?

• The inorganic matter in soil is made up of weathered parent material. The organic matter in soil is made by the decomposition of things that once lived.

• The five factors of soil formation are parent material, topography, climate, biota, and time.

• Soil contains horizons, which are layers formed from the movement of the products of weathering. Most soil contains A-, B-, and C-horizons.

A. biota

B. topography

C. decomposition

D. mechanical weathering

Which term refers to the process of changing once-living material into dark-colored organic matter?

A. parent material

B. bed rock

C. biota

D. horizons

Which of these refers to the starting material of soil?

A. A-horizon

B. B-horizon

C. C-horizon

D. O-horizon

Which of these is the top, organic layer of soil?

4. Air and water are present in soil.

5. Soil that is 1,000 years old is a young soil.

6. Soil is the same in all locations.

Do you agree or disagree?

Key Concept Summary

Interactive Concept Map

Chapter Review

Standardized Test Practice

Physical and chemical weathering are destructive forces that break down rocks, which begins the formation of soil.

• Weathering acts mechanically and chemically to break down rocks.

• Through the action of Earth processes such as freezing and thawing, mechanical weathering breaks rocks into smaller pieces.

• Chemical weathering by agents such as water and acids change the materials in rocks into new materials.

Lesson 1: Weathering

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Lesson 2: Soil

• Five factors–parent material, climate, topography, biota, and time–affect the formation of soil.

• Horizons are soil layers formed from the movement of the various products of weathering.

• Soil can be characterized by properties such as the amount of organic matter and inorganic matter.

• Plants depend on certain characteristics of soil, such as organic matter and amount of weathering.

A. chemical weathering

B. mechanical weathering

C. oxidation

D. ice wedging

Which term refers to what happens when physical processes naturally break rocks into smaller pieces?

A. oxygen

B. an oxide

C. acid

D. iron

What is the product of oxidation?

A. cool, dry places

B. places with a lot of temperature changes

C. warm, wet places

D. none of these

Where does chemical weathering occur fastest?

A. biota

B. pores

C. horizons

D. topography

Which term refers to the shape and steepness of a landscape?

A. organic matter

B. soil

C. biota

D. horizons

Which of these refers to all of the organisms that live in a region?

A. mechanical weathering

B. abrasion

C. chemical weathering

D. ice wedging

Which term refers to changes in the materials that are part of a rock into new materials?

A. ice wedging

B. abrasion

C. plants

D. all of the above

Which of these can cause mechanical weathering?

A. mechanical weathering

B. oxidation

C. chemical weathering

D. none of these

Which of these occurs fastest in locations that have a lot of temperature changes?

A. biota

B. pores

C. horizons

D. silt

Which term refers to the small holes and spaces in soil?

A. The surface area of the broken pieces is larger.

B. The surface area of the broken pieces is smaller.

C. The total weight of the rock decreases when it is broken.

D. The total weight of the rock increases when it is broken.

Why will weathering occur more quickly to a rock that has been broken into several pieces?