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Warm-Up Weathering and Soil

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Lesson Goals

Identifyfactors thataffect the rateof weathering.

Explain howsoil is formed.

Classifydifferent typesof soil.

Distinguishbetweenmechanicaland

weathering.

Describe the

of soil.

Lesson Question

Words to Know

Fill in this table as you work through the lesson. You may also use the glossary to help you.

abrasionthe process of rocks and particles scraping against

one another, away their surfaces

bedrock a layer of solid rock found beneath

chemical weatheringthe of rocks that also changes

their mineral composition

erosion the process by which of rock are

loosened and carried away

fertility the ability of soil to agricultural plant growth

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Warm-Up Weathering and Soil

Words to Know

humus dark, highly organic matter in soil

mechanical weatheringthe physical breakdown of rocks without changing

their composition

oxidationchemical reaction in which a substance combines with

sedimentsmall, solid pieces of material from rocks or

soil an accumulation of loose, material

covering much of Earth’s surface

soil horizon a recognizable of soil with characteristic properties

soil profilea section of soil that ranges from the

surface to the bedrock

uniformitarianismthe idea that Earth’s features have formed gradually

by processes that are still occurring

weathering the breakdown of rocks into particles by natural processes

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Warm-Up Weathering and Soil

Famous Landmarks

A variety of landmarks are formed by being broken down.

The Canyon National Park, Utah

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Weathering and Soil

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Weathering

Weathering is the of rocks into smaller particles by natural processes.

• It can be caused by:

• .

• wind.

• cold and heat.

• gases.

• The small particles created by weathering are called .

Erosion

Erosion is the process by which fragments of rock are loosened and

away.

• Sediment is transported as solid material or components.

• The most common transporting agent is water.

• Other transporting agents include and ice.

Instruction

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Weathering and Soil

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Uniformitarianism

Uniformitarianism is a principle in geology that suggests Earth’s geologic

processes acted in the manner and intensity in the past as they do in the present.

• Accounts for all geologic change

• Shows how layers of collected on Earth’s surface

The present is the key to the past.

Mechanical Weathering

In mechanical weathering, rocks are broken down into smaller pieces

changing their composition.

Mechanical weathering is caused by:

• and thawing.

• release of .

• plant growth.

• action of .

• abrasion.

Instruction

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Instruction Weathering and Soil

Factors That A�ect Rates of Weathering

Two key factors a�ect the rate of weathering—rock type and .

• Rock type

• Minerals that easily weather faster.

• Softer minerals apart more easily.

• Porous minerals weather more easily.

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Chemical Weathering

In chemical weathering, rocks are broken down, and their composition

. Chemical weathering is caused by:

• .

• .

• carbon dioxide.

• organisms.

• rain.

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Factors That A�ect Rates of Weathering

Climate is the single most important factor that a�ects the rate of weathering.

• Chemical reactions occur faster at higher .

• Warm climates favor weathering.

• Cold climates favor mechanical weathering, principally

and thawing.

• The more moisture, or precipitation present, the more noticeable the weathering

Soil

Soil is an of loose, weathered material covering much of

Earth’s surface.

Bedrock is a solid layer of rock lying beneath Earth’s soil layer. Bedrock:

• is the source of rock and mineral that make up soil.

• is not weathered if it is not exposed to and water.

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Instruction Weathering and Soil

Soil Composition

• Soil is a mixture of:

• rock particles—sand, silt, and clay.

• .

• organic material—humus.

• water.

• air.

• Fertility refers to the ability of soil to plant growth.

Soil Texture

The texture of soil depends on its particle .

• – fine

grains, very little space for water

• – coarse

grains, loose, water drains quickly

• – medium

grains, retains water

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Instruction Weathering and Soil

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Soil Profile

A soil profile is a section

of soil that ranges from the surface to the

.

• Each layer of a soil profile is

referred to as a soil .

• Horizon O is the top layer,

where is

present.

• Horizon A is topsoil.

• Horizon B is subsoil.

• Horizon C contains weathered rock.

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Instruction Weathering and Soil

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Formation of Soil Horizons

Soil forms as rock is broken down by and mixes with other materials.

• Horizon O forms at the surface due to the accumulation of organic material.

• Horizon A is mineral rich and forms due to

organic material from above.

• Horizon B undergoes the most change and no longer resembles parent material.

• Horizon C features parent material and is barely

a�ected by the formation process.

Rate of Soil Formation

The rate of soil formation depends on climate and type of parent material.

• Climate

• : Warmer weather creates soil faster.

• : More precipitation creates soil faster.

• Type of parent material

• composition: Some minerals are more resistant

to weathering.

• : Rocks that have a larger grain size break down

more quickly.

• Layers: Rocks with clearly defined layers undergo weathering at a faster pace.

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Instruction Weathering and Soil

Soils of America

In the Plains, where many crops are grown, the soils are mostly

, which are fertile soils.

In the southeastern portion of the country, there is a lot of yellow-orange,

representing , which is weathered soil.

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Soil Classification

Soil scientists recognize major orders of soils.

• The groups are based on:

• .

• type.

• soil .

Gelisols: frozen Histosols: organic, wet

Spodosols: sandy

Andisols: volcanic

Oxisols: very weathered

Vertisols: shrink and swell

Aridisols: very dry

Ultisols: weathered

Mollisols: fertile Alfisols: lightly weathered

Inceptisols: young

Entisols: newly formed

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Instruction Weathering and Soil

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Organisms and Soil

Organisms have a great e�ect on soil.

• Formation of humus

• litter

•

• Mixing of soil by earthworms and burrowing animals

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Summary Weathering and Soil

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Review: Key Concepts

Weathering is the breakdown of rocks into smaller pieces of sediment. The rate of weathering is a�ected by the type of rock and the climate.

Weathering

• Physical breakdown of rock into smaller pieces without changing the rock’s minerals

Weathering

• Chemical breakdown of rock that includes changing the minerals present in the rock

Answer

Lesson Question How does weathering a�ect Earth’s surface?

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Summary Weathering and Soil

Review: Key Concepts

Weathered material eventually forms soil.

Soil Soil Soil

• Texture is determined by particle size.

• Loam is a combination of clay, silt, and sand.

• Humus is rich in nutrients.

• Weathering forms soil.

• The soil profile shows layers of soil as soil horizons.

• Soil is classified into twelve major groups based on climate and soil composition.

Use this space to write any questions or thoughts about this lesson.

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