1. Weathering and Soil Formation
Chapter 4
Weathering and Soil Formation

2. Weathering breaks down rocks into smaller pieces 1
Weathering breaks down rocks into smaller pieces 1. Mechanical weathering 2. Chemical weathering

3. Mechanical weathering produces physical changes in rocks:
Ice wedging
Pressure release-causes rock to expand, cracking and leading to exfoliation
Exfoliation-process in which layers of exfoliation
rock gradually break off.
Plant root growth
Abrasion-wearing down by friction, the rubbing of one object or surface against another

4. Chemical weathering
Breakdown of rocks by chemical reactions that change the rocks composition (what it is made of)
Water (dissolving)
Rusting

5. Weathering occurs at different rates
Surface area-the more exposed area, the faster the break down of rock (chemical)
Rock composition ex: Granite compared to limestone
Climate:
chemical weathering occurs in wet, hot areas faster than cold, dry regions
Mechanical weathering caused by freezing and thawing

6. Weathering and organic processes form soil
Soil- a mixture of weathered rock particles and other materials
Humus-decayed organic (living things) in the soil

7. Soil formation is affected by:
Rock in an area
Climate: tropical, desert, temperate, artic
Landforms: mountains and valleys
Plant cover: provide organic matter
Living organisms: microorganisms and animals
Time

8. Soil composition
Soil horizon-a layer of soil with properties that are different than the layers above and below it
Soil profile- soil horizons in a specific area

9. Soil Properties
Texture-determined by size of weathered rock particles it contains
Color-most comes from iron and humus
Pore space-the spaces between the particles
Chemistry-minerals and organic nutrients

10. Human activities Soil is a valuable resource for humans
1. Farming-soil loss and overgrazing results in desertification- expansion of desert in areas where natural plant cover has been destroyed
2. Construction and development
3. Mining
Strip mining
Open pit

11. Soil conservation Crop rotation Conservation tillage Terraces
Contour plowing
Windbreaks

12. Info for Soil lab
Climate in Missouri- Temperate soils form in region with moderate rainfall and temperatures. Some temperate soils are dark-colored, rich in organic matter and minerals, and good for growing crops.

13. Soil Horizons
The A horizon- is the upper layer of soil and is commonly called topsoil.
It contains the most organic matter out of all the horizons due to the humus that it contains gives it the dark color.

14. The B Horizon
This layer lies just below the A horizon. It has a little organic matter and is usually brownish or reddish color and contains clay and minerals.

15. The C horizon
This is the deepest layer of soil. This layer contains the largest and least-weathered rock particles. It is usually light yellowish brown.