Weathering and Soil Formation

1
Chapter 10
Weathering and Soil Formation
Preview
Section 1 Weathering Section 2 Rates of
Weathering Section 3 From Bedrock to
Soil Section 4 Soil Conservation
Concept Mapping
2
Section 1 Weathering
Chapter 10
Bellringer
Think about how potholes form in paved roads.
Write a few sentences that describe how water
contributes to the formation of potholes.
Illustrate how cycles of freezing and thawing
help cause potholes to grow. Record your
response in your science journal.
3
Section 1 Weathering
Chapter 10
Objectives

• Describe how ice, water, wind, gravity, plants,
  and animals cause mechanical weathering.
• Describe how water, acids, and air cause chemical
  weathering of rocks.

4
Section 1 Weathering
Chapter 10
Mechanical Weathering

• Ice The alternate freezing and thawing of soil
  and rock, called frost action, is a form of
  mechanical weathering.
• Abrasion Abrasion is the grinding and wearing
  away of rock surfaces through the mechanical
  action of other rock or sand particles.
• Wind, Water, and Gravity Wind, water, and gravity
  carry rocks, causing them to abrade against one
  another.

5
Section 1 Weathering
Chapter 10
Ice Wedging
Click below to watch the Visual Concept.
Visual Concept
6
Section 1 Weathering
Chapter 10
Mechanical Weathering, continued

• Plants As a plant grows, the force of the
  expanding root becomes so strong that it can
  break a rock apart.
• Animals Almost any animal that burrows causes
  mechanical weathering by mixing and digging
  through soil and rock particles.

7
Section 1 Weathering
Chapter 10
Animals and Mechanical Weathering

• Animals that burrow in the ground break up soil
  and loosen rocks to be exposed to further
  weathering.

8
Section 1 Weathering
Chapter 10
Chemical Weathering

• Water Even hard rock, such as granite, can be
  broken down by water. The next slide shows how
  this can happen.
• Acid Precipitation The high level of acidity in
  acid precipitation can cause very rapid
  weathering of rock.
• Acids in Groundwater When acidic groundwater
  comes into contact with limestone, the limestone
  is dissolved and forms karst features.

9
Section 1 Weathering
Chapter 10
10
Section 1 Weathering
Chapter 10
Chemical Weathering, continued

• Acids in Living Things Some living things, such
  as lichens, produce acids that can slowly break
  down rocks.
• Air Oxygen in the air causes oxidation. Oxidation
  is the chemical reaction in which an element,
  such as iron, combines with oxygen to form an
  oxide.

11
Section 1 Weathering
Chapter 10
Oxidation
Click below to watch the Visual Concept.
Visual Concept
12
Section 2 Rates of Weathering
Chapter 10
Bellringer
Imagine that you are in a sand castle-building
competition at the beach. Come up with ways to
protect your castle against the weathering
effects of the wind and waves. Record your
response in your science journal.
13
Section 2 Rates of Weathering
Chapter 10
Objectives

• Explain how the composition of rock affects the
  rate of weathering.
• Describe how a rocks total surface area affects
  the rate at which the rock weathers.
• Describe how differences in elevation and climate
  affect the rate of weathering.

14
Section 2 Rates of Weathering
Chapter 10
Differential Weathering

• What Is Differential Weathering? Differential
  weathering is a process by which softer, less
  weather resistant rock wear away and leave
  harder, more weather resistant rock. The image
  below is an example of differential weathering.

15
Section 2 Rates of Weathering
Chapter 10
The Shape of Rocks

• Surface Area The more surface area of a rock that
  is exposed to weathering, the faster the rock
  will be worn down.
• Increasing the Rate of Weathering If a large rock
  is broken down into smaller fragments, weathering
  of the rock happens much more quickly.

16
Section 2 Rates of Weathering
Chapter 10
17
Section 2 Rates of Weathering
Chapter 10
Weathering and Climate

• What Is Climate? Climate is the average weather
  condition in an area over a long period of time.
• Temperature and Water The rate of chemical
  weathering happens faster in warm, humid
  climates. Water also increases the rate of
  mechanical weathering.

18
Section 2 Rates of Weathering
Chapter 10
Weathering and Elevation

• High Elevations Rocks at higher elevations, as on
  a mountain, are exposed to more wind, rain, and
  ice than rocks at lower elevations.
• Steep Slopes The steepness of mountain slopes
  increases the effects of mechanical and chemical
  weathering. Steep slopes cause water and
  sediments to quickly run down the side of the
  mountain.

19
Section 3 From Bedrock to Soil
Chapter 10
Bellringer

• Answer the following questions
• Has there always been soil on Earth?
• What makes soil valuable to humans?
• Write your answers in your science journal.

20
Section 3 From Bedrock to Soil
Chapter 10
Objectives

• Describe the source of soil.
• Explain how the different properties of soil
  affect plant growth.
• Describe how various climates affect soil.

21
Section 3 From Bedrock to Soil
Chapter 10
The Source of Soil

• What Is Soil? Soil is a loose mixture of small
  mineral fragments, organic material, water, and
  air that can support the growth of vegetation.
• Residual and Transported Soil Soil that remains
  above its parent rock is called residual soil.
  Soil that is blown or washed away from its parent
  rock is called transported soil.

22
Section 3 From Bedrock to Soil
Chapter 10
Residual and Transported Soil
Click below to watch the Visual Concept.
Visual Concept
23
Section 3 From Bedrock to Soil
Chapter 10
Soil Properties

• Soil Texture and Soil Structure Soil texture is
  the soil quality that is based on the proportions
  of soil particles. Soil structure is the
  arrangement of soil particles.

24
Chapter 10
Section 3 From Bedrock to Soil
25
Section 3 From Bedrock to Soil
Chapter 10
Soil Properties, continued

• Soil Fertility A soils ability to hold nutrients
  and to supply nutrients to a plant is described
  as soil fertility.
• Soil Horizons Because of the way soil forms, soil
  often ends up in a series of layers called
  horizons.
• Soil pH Soils can be acidic or basic. The pH
  scale is used to measure how acidic or basic a
  soil is.

26
Section 3 From Bedrock to Soil
Chapter 10
Leaching
Click below to watch the Visual Concept.
Visual Concept
27
Section 3 From Bedrock to Soil
Chapter 10
Soil and Climate

• Tropical Rain Forest Climates The warm soil in
  tropical rain forest climates allows dead plants
  and animals to decay easily. This provides rich
  humus to the soil.
• Desert Climates The lack of rain in desert
  climates leads to low rates of chemical and
  mechanical weathering.

28
Section 3 From Bedrock to Soil
Chapter 10
Soil and Climate, continued

• Temperate Forest and Grassland Climates Temperate
  forest and grassland climates get enough rain to
  cause a high level of chemical weathering, but
  not too much that nutrients are leached out.
• Arctic Climates In arctic climates, as in desert
  climates, chemical weathering occurs very slowly.
  Low temperatures slow the formation of humus.

29
Section 4 Soil Conservation
Chapter 10
Bellringer
Franklin D. Roosevelt once said The nation that
destroys its soil destroys itself. What do you
think this quote means? Record your response in
your science journal.
30
Section 4 Soil Conservation
Chapter 10
Objectives

• Describe three important benefits that soil
  provides.
• Describe four methods of preventing soil damage
  and loss.

31
Section 4 Soil Conservation
Chapter 10
The Importance of Soil

• Nutrients Soil provides minerals and other
  nutrients for plants. All animals get their
  energy from plants.
• Housing Soil provides a place for animals to
  live.
• Water Storage Without soil to hold water, plants
  would not get the moisture or the nutrients they
  need.

32
Section 4 Soil Conservation
Chapter 10
Soil Damage and Loss

• Overuse Overused soil can lose its nutrients and
  become infertile.
• Soil Erosion When soil is left unprotected, it
  can be exposed to erosion. Erosion is the process
  by which wind, water, or gravity transport soil
  and sediment from one location to another.

33
Section 4 Soil Conservation
Chapter 10
Contour Plowing and Terracing

• Contour Plowing In contour plowing, the rows of
  soil act as a series of dams to prevent water
  from eroding topsoil away.
• Terracing If hills are steep, farmers can using
  terracing. Terracing changes one steep field into
  a series of smaller, flatter fields.

34
Section 4 Soil Conservation
Chapter 10
Cover Crop and Crop Rotation

• Cover Crops Cover crops are crops that are
  planted between harvests to replace certain
  nutrients and prevent erosion. Cover crops
  prevent erosion by providing cover from wind and
  rain.
• Crop Rotation Farmers can rotate crops that use
  different nutrients so that nutrients in the soil
  have time to become replenished.

35
Weathering and Soil Formation
Chapter 10
Concept Mapping
Use the terms below to complete the concept map
on the next slide.
36
Weathering and Soil Formation
Chapter 10
37
Weathering and Soil Formation
Chapter 10