1. Earth Science Notes
Weathering and Soil

2. Weathering
Weathering : surface processes that work to breakdown rock into sediment
Types of sediment – sand, silt, clay

3. Types of Weathering

4. Types of Weathering
Mechanical Weathering - the physical break down of rocks
The chemical make up of the rock remains unchanged.
Ex: burrowing animals, growing plants, expanding ice
Ice wedging – water will enter cracks in rock and then freeze pushing the rock apart.
This increases surface area of rocks and allows them to be exposed more to chemical agents.

5. Mechanical Weathering increases Chemical Weathering

6. Mechanical Weathering

7. Types of Weathering
Chemical Weathering – chemical reactions dissolve rocks
Agents of chemical weathering
Carbonic acid (H2CO3) – acid produced from carbon dioxide in air and soil. Dissolves limestone.
Oxygen – reacts with iron containing minerals to form rust. Gives rocks and soil its reddish color.
Sulfuric acid (H2SO4) – acid produced by sulfates from factories. ACID RAIN.

8. Chemical Weathering

9. BIG IDEA: Weathering creates SOIL!!!

10. SOIL
Soil is a mixture of weathered rock, decayed organic matter, mineral fragments, water, and air.

11. Weathering and Soil Formation
Recall from the last Unit: weathering produces sediments.
Below are the classifications of sediments
Clay  silt  sand  pebble  Cobble  Boulder
Sand, silt, and clay are the main sediments that make up soil.
These sediments give soil its TEXTURE.

12. Weathering and Soil Formation
The relative proportions of sand, silt, and clay allow us to classify soils.
The USDA has a model it uses for classifying soil types based on the sediment composition (the triangle chart – next slide).
These soil classifications allow tell us how a soil will accept and retain moisture.
Sandy – doesn’t retain water
Clay – doesn’t accept water

13. Weathering and Soil Formation

14. Soil Formation
The weathering of Rock into soil occurs in stages (seen below)

15. Soil Profiles and Soil Horizons
Over time (and much weathering) distinct layers form in the soil. These layers are called soil horizons.

16. Soil Profiles and Soil Horizons
The first soil horizon to form is the C horizon. Again, weathering process convert the exposed bedrock to smaller sediments.

17. Soil Profiles and Soil Horizons
After the C horizon, the A horizon is the next to form. Weathering continues.
Plants begin to colonize the sediments and die. Their remains contribute to a growing layer rich in organic matter. This is the A horizon.

18. Soil Formation
Plants and Animals play a part in soil formation

19. Soil Profiles and Soil Horizons
The last layer to form is actually the B horizon. It forms as a result of minerals leaching downward from the A horizon to the C horizon.

20. Leaching
Removal of minerals by water

21. Soil Profiles and Soil Horizons
A soil profile is a cross-section of earth that shows the different soil horizons.

22. Soil Formation
Soils vary greatly in composition. In addition to sediment size (i.e. sand, silt, clay), the parent materials from which these soils come are very diverse.

23. Soil Formation is influenced by vegetation and climate.

24. Topography and Soil Formation
Soil Formation is influenced by Topography
Steeper land  influenced by force of gravity
Flatter land  water is more apt to settle

25. Ways to Reduce Soil Erosion
Terracing / No-till / Contour farming

26. Factors Affecting Soil Erosion
Exposure to elements (weathering)
Wind, rain, freezing, frost, etc.
Type of Parent material
Weight of material, Density, etc.
Farming
Overgrazing / tilling
Foresting and mining
Climate
Topography

27. Factors Affecting Soil Erosion

28. Factors Affecting Soil Erosion

29. Weathering and Soil Summary What is weathering? Types of Weathering
Mechanical and Chemical
Weathering Creates Soil
Soil Formation
Factors Affecting Soil Formation
Soil Profiles
Factors Affecting Soil Erosion