1. Weathering, Erosion and Soils

2. Weathering
I. Weathering
Changes occur every day to Earth’s rocks and surface features.
Weathering is the chemical and physical processes by which rocks on or near Earth’s surface break down and change.
Erosion is the removal and transport of weathered material from one location to another.

3. A. Mechanical Weathering
Mechanical weathering, or physical weathering, is the process by which rocks and minerals break down into smaller pieces without changing their composition.
2. Mechanical weathering does not involve any change in a rock’s composition.

4. B. Mechanical Weathering Factors
1. Temperature
Frost wedging is the repeated thawing and freezing of water in the cracks of rocks.
2. Pressure
Weight of rocks and plant roots

5. Weathering
C. Chemical Weathering
1. Chemical weathering is the process by which rocks and minerals undergo changes in their composition as the result of chemical reactions.

6. D. Chemical Weathering Factors
1. Temperature influences the rate at which chemical reactions occur. Generally, chemical reaction rates increase with temperature.
2. Water is an important agent in chemical weathering because it can dissolve many kinds of minerals and rocks.

7. Chemical Weathering Factors
3. Oxygen because Iron in rocks and minerals readily combines with atmospheric oxygen to form minerals.

8. Chemical Weathering 4. Carbon Dioxide
Carbon dioxide, which is produced by living organisms during the process of respiration, contributes to the chemical weathering process.
When carbon dioxide combines with water in the atmosphere, it forms a weak carbonic acid that falls to Earth’s surface as precipitation. H2O + CO2 ® H2CO3

9. Chemical Weathering 5. Acid Precipitation
Acid precipitation negatively affects fish and aquatic plant populations in lakes.
When lake water becomes too acidic, the species diversity decreases.

10. Some aquatic species are more susceptible to acid precipitation.
Weathering
Chemical Weathering
Some aquatic species are more susceptible to acid precipitation.

11. II. What Affects the Rate of Weathering?
The natural weathering of Earth materials occurs very slowly.
Certain conditions and interactions can accelerate or slow the weathering process.

12. II. What Affects the Rate of Weathering?
A. Climate. More rain = more weathering.

13. What Affects the Rate of Weathering?
B. Rock Type and Composition
In general, sedimentary rocks are more easily weathered than harder igneous and metamorphic rocks.

14. What Affects the Rate of Weathering?
C. Surface Area
The greater the total surface area, the more weathering that occurs.

15. What Affects the Rate of Weathering?
D. Topography and Other Variables
Earth materials on level areas are likely to remain in place as they undergo changes.
Materials on slopes have a greater tendency to move as a result of gravity, thereby exposing underlying rock surfaces and thus providing more opportunities for weathering to occur.
Decaying organic matter and living plant roots release carbon dioxide, which combines with water to produce acid, which in turn increases the weathering rate.

16. III. Erosion and Deposition
Erosion is the process that transports Earth materials from one place to another.
4 methods of erosion: wind, water, glaciers, gravity.
Deposition is the process of dropping materials in another location when the movement of transported materials slows down.

17. A. Erosion by Running Water
Erosion and Deposition
A. Erosion by Running Water
1. With few exceptions, water has more power to move large particles of weathered material than wind does.
Stream erosion is greatest when a large volume of water is moving rapidly.
Swiftly flowing water can carry material over a greater distance.
Small streams at high elevations flow down to join larger streams at lower elevations draining an area called a watershed.

18. IV. Formation of Soil Soil is essential to life on Earth.
Humans and other organisms are dependent on plants, which grow in soil, for food and other basic needs.
Without rocks, there would be no soil, and no terrestrial life as we know it.

19. Formation of Soil
A. Development of Soil
1. Except for some steep mountain slopes and extremely cold regions, soil is found almost everywhere on Earth’s surface.
2. Soil is the loose covering of broken rock particles and decaying organic matter, called humus, overlying the bedrock of Earth’s surface.
3. Soil is the result of chemical and mechanical weathering and biological activity over long periods of time.
4. While all soils contain some organic matter, the amount varies widely among different types of soil.

20. Formation of Soil
B. Soil Composition
1. Soil forms in layers during the process of its development.
The parent rock is the solid bedrock from which weathered pieces of rock first break off.
The smallest pieces of weathered rock, along with living and dead organisms, remain in the very top layer.
Rainwater seeps through this top layer of materials, dissolves soluble minerals, and carries them into the lower layers of the soil.

21. Formation of Soil
C. Soil Profiles
1. A soil profile is the vertical sequence of soil layers.
2. A soil horizon is a distinct layer, or zone, within a soil profile.
3. There are 3 major soil horizons: A, B, and C.
Horizon A contains high concentrations of organic matter and humus.
Horizon B contains subsoils that are enriched with clay minerals.
Horizon C, below horizon B and directly above solid bedrock, contains weathered parent material.

22. Formation of Soil
D. Soil Types
Because climatic conditions are the main influence on soil development, soils are often classified based on the climates in which they form.
The 4 major types of soil are polar, temperate, desert, and tropical.

23. Formation of Soil
Soil Types

24. Soil Types 3. Desert Soils
Formation of Soil
Soil Types
3. Desert Soils
Deserts receive low levels of precipitation.
Desert soils often have a high level of accumulated salts and can support only a limited amount of vegetation.
Desert soils have little or no organic matter and a very thin A horizon, but they often have abundant nutrients.
Desert soils are also light-colored, coarse, and may contain salts and gypsum.

25. Formation of Soil
E. Soil Textures
Particles of soil are classified according to size as being clay, silt, or sand, with clay being the smallest and sand being the largest.
The relative proportions of these particle sizes determine a soil’s texture.
The texture of a soil affects its capacity to retain moisture and therefore its ability to support plant growth.

26. Formation of Soil
F. Soil Fertility
Soil fertility is the measure of how well a soil can support the growth of plants.
Factors that affect soil fertility include:
Availability of minerals and nutrients
Number of microorganisms present
Amount of precipitation available
Topography
Level of acidity

27. Soil Fertility 3. Soil Color
Formation of Soil
Soil Fertility
3. Soil Color
A soil’s composition and the climate in which it develops are the main factors that determine a soil’s color.
Topsoil is usually dark-colored because it is rich in humus.
Red and yellow soils may be the result of oxidation of iron minerals.
Yellow soils are usually poorly drained and are often associated with environmental problems.
Grayish or bluish soils are common in poorly drained regions where soils are constantly wet and lack oxygen.

28. Soil Classification chart. Also called a Ternary diagram.

29. How would we classify a soil with 75% sand, 10% silt, 15% clay
How would we classify a soil with 75% sand, 10% silt, 15% clay? How would we classify a soil with 10% sand, 83% silt, 7% clay? How would we classify a soil with 42% sand, 21% silt and 37% clay?
Sandy Loam

30. How would we classify a soil with 75% sand, 10% silt, 15% clay
How would we classify a soil with 75% sand, 10% silt, 15% clay? How would we classify a soil with 10% sand, 83% silt, 7% clay? How would we classify a soil with 42% sand, 21% silt and 37% clay?
Sandy Loam
Silt

31. Sandy Loam Silt Clay Loam
How would we classify a soil with 75% sand, 10% silt, 15% clay? How would we classify a soil with 10% sand, 83% silt, 7% clay? How would we classify a soil with 42% sand, 21% silt and 37% clay?
Sandy Loam
Silt
Clay Loam

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