1. Table of Contents Rocks and Weathering How Soil Forms
Soil Conservation

2. Chemical Weathering - Rocks and Weathering
As weathering breaks apart rock, the surface area exposed to weathering increases.

3. Which Weathered Faster?
- Rocks and Weathering
Which Weathered Faster?
The graph shows the rate of weathering for two identical pieces of limestone that weathered in different locations.

4. Which Weathered Faster?
- Rocks and Weathering
Which Weathered Faster?
Reading Graphs:
What does the x-axis of the graph represent?
Time in years

5. Which Weathered Faster?
- Rocks and Weathering
Which Weathered Faster?
Reading Graphs:
What does the y-axis of the graph represent?
The thickness of stone lost to weathering

6. Which Weathered Faster?
- Rocks and Weathering
Which Weathered Faster?
Reading Graphs:
How much thickness did Stone A lose in 1,000 years? How much thickness did Stone B lose in the same period?
Stone A lost about 8.5 millimeters; Stone B lost slightly more than 4 millimeters.

7. Which Weathered Faster?
- Rocks and Weathering
Which Weathered Faster?
Drawing Conclusions:
Which stone weathered at a faster rate?
Stone A weathered at a faster rate.

8. Which Weathered Faster?
- Rocks and Weathering
Which Weathered Faster?
Inferring:
Since the two identical pieces of limestone weathered at different rates, what can you infer caused the difference in their rates of weathering?
They were exposed to different climate conditions.

9. Relating Cause and Effect
- Rocks and Weathering
Relating Cause and Effect
A cause makes something happen. An effect is what happens. As you read, identify the causes of chemical weathering. Write them in a graphic organizer like the one below.
Causes
Oxygen
Effect
Chemical weathering
Water
Acid rain

10. Click the PHSchool.com button for an activity about weathering.
- Rocks and Weathering
More on Weathering
Click the PHSchool.com button for an activity about weathering.

11. End of Section: Rocks and Weathering

12. What Is Soil? - How Soil Forms
Loam, a type of soil, is made up of air, water, and organic matter as well as materials from weathered rock.

13. What Is Soil? - How Soil Forms
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.

14. The Process of Soil Formation
- How Soil Forms
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.

15. Soil Layers Activity - How Soil Forms
Click the Active Art button to open a browser window and access Active Art about soil layers.

16. Soil Types - How Soil Forms
Scientists classify the different types of soil into major groups based on climate, plants, and soil composition.

17. Living Organisms in Soil
- How Soil Forms
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.

18. Building Vocabulary - How Soil Forms
A definition states the meaning of a word or phrase by telling about its most important feature or function. Carefully read the definition of each Key Term and also read the neighboring sentences. Then write a definition of each Key Term in your own words.
Key Terms:
Examples:
loam
soil horizon
topsoil
Key Terms:
Key Terms:
Examples:
subsoil
litter
decomposer
Examples:
soil
The B horizon, often called subsoil, usually consists of clay and other particles washed down from the A horizon, but little humus.
Soil is the loose, weathered material on Earth’s surface in which plants can grow.
Soil that is made up of about equal parts of clay, sand, and silt is called loam.
bedrock
A soil horizon is a layer of soil that differs in color and texture from the layers above or below it.
Bedrock is the solid layer of rock beneath the soil.
As plants shed leaves, they form a loose layer called litter.
humus
Humus is a dark-colored substance that forms as plant and animal remains decay.
The A horizon is made up of topsoil, a crumbly, dark brown soil that is a mixture of humus, clay, and other materials.
Decomposers are organisms that break the remains of dead organisms into smaller pieces and digest them with chemicals.
fertility
The fertility of soil is a measure of how well the soil supports plant growth.

19. Click the Video button to watch a movie about soil.
- How Soil Forms
Soil
Click the Video button to watch a movie about soil.

20. End of Section: How Soil Forms

21. Soil Damage and Loss - Soil Conservation
Wind erosion is one cause of soil loss. For example, wind erosion contributed to the Dust Bowl on the Great Plains. The Dust Bowl ruined farmland in western Oklahoma and parts of the surrounding states. Wind blew dry particles of soil into great clouds of dust that traveled thousands of kilometers.

22. Previewing Visuals - Soil Conservation
Before you read, preview Figure 13, “The Dust Bowl”. Then write two questions that you have about the photo and map in a graphic organizer like the one below. As you read, answer your questions.
The Dust Bowl
Q. Where was the Dust Bowl?
A. The Dust Bowl was in western Oklahoma and parts of the surrounding states.
Q. What caused the Dust Bowl?
A. Farming practices exposed the soil so that in times of drought the topsoil quickly dried out, turned to dust, and blew away.

23. Links on Soil Conservation
Click the SciLinks button for links on soil conservation.

24. Click the Video button to watch a movie about soil conservation.

25. End of Section: Soil Conservation

26. Graphic Organizer Soil Horizons Bedrock begins to weather
The C horizon forms as bedrock breaks apart.
The A horizon develops from the C horizon where plants grow in it.
The B horizon develops as clay and minerals wash down from the A horizon.

27. End of Section: Graphic Organizer