1. Unit 4: Structural Geology Why Study Change?

2. What is the Recipe for Soil?  Soil is a mixture of weathered down rock, organic matter, water, living things, and a few other assorted things.

3. Soil is Formed in Stages: I. Stage I: Weather rock down into small particles that are sand-sized or smaller. Weathering – the process of breaking down rock either chemically or physically. Physical Weathering: Breaking a rock down without changing what it is. You have smaller pieces of the same rock. Chemical Weathering: Breaking a rock down and changing it into a completely new substance in the process. For example: iron + water = iron oxide (rust)

4. What Forces Weather Rock?  The action of water on Earth’s surface, such as rain, waves, rivers, streams, etc. *Moving water is the greatest agent of weathering on Earth’s surface!  The action of tree roots  Animals burrowing underground  Frost Action  Chemical reaction with acid rainwater  Human actions

5. Factors Controlling Weathering Rate and Time: I. Climate:

6. Climate and Weathering:  The type of climate you live in will affect the type of weathering that breaks down the rocks.  PHYSICAL WEATHERING will prevail in cold, dry climates.  CHEMICAL WEATHERING will prevail in warm and humid climates. WHAT TYPE OF WEATHERING WILL DOMINATE IN OUR CLIMATE?????

7. II. Mineral Composition:  Rocks made of harder minerals will be more resistant to weathering and will not break down easily.  Rocks composed of softer minerals will be less resistant to weathering and will break down quickly. Granite Limestone

8. III. Exposed Surface Area  A rock that is broken into smaller pieces will weather faster than a rock that is whole because there is more surface area exposed to be weathered.

9. Soil Horizons: A typical soil profile will show three distinct layers, or horizons: I. A -Horizon – also called topsoil, it is the upper layer of soil that contains lots of organic matter (humus), living things, and plant roots. It is rich in nutrients and dark in color due to the large amount of organic matter present in the soil.

10. II. B-Horizon: The middle layer of soil. It is lighter in color because it has less organic matter (humus). It has fewer plant roots, insects and animals, and has minerals mainly leached out of the A-horizon by rainwater. III. C-Horizon: The bottom layer of soil. It contains broken rock in various stages of weathering. Little to no organic matter or nutrients are present here. ***Solid Bedrock is Found Below the C- Horizon!

11. A Typical Soil Profile: