1. HOW SOIL FORMS
6.E.2.3 Explain how the formation of soil is related to the parent rock type and the environment in which it develops.

2. Thin soil overlaying bedrock
Soil is the loose, weathered material on Earth’s surface in which plants can grow. Bedrock is the solid layer of rock beneath the soil.
Thin soil overlaying bedrock

3. Soil Composition
Soil is the mixture of rock particles, minerals, decayed organic material, air, and water.
Together, sand, silt, and clay make up the portion of soil that comes from weathered rock.

4. Soil Composition
Loam, a type of soil, is made up of air, water, and organic matter as well as materials from weathered rock.

5. Humus
The decayed organic material in soil is humus, a dark colored substance that forms as plant & animal remains decay.
Humus helps create spaces in soil for air and water that plants must have.
The fertility of soil is a measure of how well the soil supports plant growth.

6. Soil Texture
Gravel
Silt
Soil texture depends on the size of individual particles, followed by silt particles.
The largest soil particles are gravel.
Next in size are sand particles, followed by silt particles.
Clay particles are the smallest.
Clay

7. Soil Texture (Cont.) Texture is important for plant growth.
Plants can drown for lack of air in clay soil, and they may die from lack of water in sandy soil.
The best soil for growing most plants is loam, which is soil that is made up of equal parts of clay, sand & silt.
Loam

8. Soil
Soil particles range in size from gravel to clay particles too small to be seen by the unaided eye. The sand, silt, and clay shown here have been enlarged.

9. Soil Formation
Soil forms as rock is broken down by weathering and mixes with other materials on the surface. It is constantly formed wherever bedrock is exposed.
Soil formation continues over a long period of time.
A soil horizon is a layer of soil that differs in color and texture from layers above or below it.

10. Soil Formation (Cont.)
A horizon- made of topsoil, crumbly, dark brown soil. (humus, clay, & other minerals)
B horizon- subsoil, consists of clay & other particles washed down from A horizon, but little humus.
C horizon- contains only partly weathered rock.

11. The Process of Soil Formation
Soil forms as rock is broken down by weathering and mixes with other materials on the surface. Soil is constantly being formed wherever bedrock is exposed.

13. Soil Formation (Cont.)
The rate at which soil forms depends on the climate and type of rock. Remember that weathering occurs most rapidly in areas with a warm, rainy climate. As a result, soil develops more quickly in these areas. In contrast, weathering and soil formation take place slowly in areas where the climate is cold and dry.

14. Soil Formation (Cont.)
Some types of rock weather and form soil faster than others. For example, limestone, a type of rock formed from the shells and skeletons of once-living things, weathers faster than granite. Thus, soil forms more quickly from limestone than from granite.

15. Soils are very different, depending on how they form

16. Soil Types
Scientist classify different types of soil into major groups based on climate, plants, and soil composition.
The most common plants found in a region are also used to help classify the soil.
Major soil types in North America include forest, prairie, desert, mountain, tundra, & tropical soils.

17. Soil Types (Cont.)
Scientists classify the different types of soil into major groups based on climate, plants, and soil composition.
An area’s climate and plant life help to determine what type of soil forms from bedrock.

18. Living Organisms in Soil
Some soil organisms make humus, the material that makes soil fertile. Other soil organisms mix the soil and make spaces in it for air and water.

19. Oak tree litter makes the soil soft ...
Humus
Plants contribute most of the organic remains that form humus. The leaves that plants shed form a loose layer on the ground called litter.
Oak tree litter makes the soil soft ...

20. Decomposers
Humus forms in a process called decomposition, in which organisms that live in the soil turn dead organic material into humus.
The organism that break the remains of dead organisms into smaller pieces and digest them with chemicals are called decomposers.

21. Decomposers
Fungi, bacteria, worms, and other organisms are the main soil decomposers.
Earthworms do most of the work of mixing humus with other materials in the soil.
Earthworms & burrowing animals also help aerate or mix air into, the soil.

22. Questions
What is the decayed organic material in soil? A. Rotten dirt B. Dark matter C. Humorous D. Humus

23. What are the smallest particles of soil. A. Gravel B. Sand C. Silt D
What are the smallest particles of soil? A. Gravel B. Sand C. Silt D. Clay

24. What is a layer of soil that differs in color and texture from layers above or below it? A. Soil Layers B. Soil Horizon C. Soil Horizontal D. Soil Verical

25. The End