1. What’s it good for, anyway?
Soil
Where does it come from?
What kinds are there?
What’s it good for, anyway?
What’s happening to it?

2. TAKE HOME POINT
Soil comes from the physical and chemical breakdown of parent materials, which include bedrock and organic materials such as leaves and animals.

3. Earth’s surface processes
First a definition:
Weathering – Physical breakdown and chemical alteration of rock at Earth’s surface

4. Source: Tom Bean/DRK Photo

5. Mechanical Weathering
Mechanical weathering – breaking of rocks into smaller pieces
Four types of mechanical weathering
1. Frost wedging – freezing and thawing of water in cracks disintegrates rocks

6. Frost Wedging

7. Evidence of Frost Wedging in Wheeler Park, Nevada
Source: Tom Bean/DRK Photo

8. Rockfall caused by frost wedging

9. Source: Runk/Schoenberger/Grant Heilman
Tree roots growing in rock fractures, plus animal burrows, expose deep rocks to water
Source: Runk/Schoenberger/Grant Heilman

10. Increase in surface area by mechanical weathering

11. Differential weathering controlled by jointing patterns
Definitions:
Joints and Faults
Deep rock exposed to water

12. Joint-controlled weathering in igneous rocks

13. Chemical Weathering Breaks down rock and minerals
Important agent in chemical weathering is water
Water dissolves and transports ions and molecules
The dissolved ions later bond & form the cements in sedimentary rocks

14. Source: Ramesh Venkatakrishnan

15. Dissolution Weathered and Unweathered Limestone Boulders
Source: Ramesh Venkatakrishnan

16. Weathering Rates of weathering Others factors affecting weathering
Mechanical weathering aids chemical weathering by increasing surface area
Others factors affecting weathering
Rock characteristics e.g. minerals
Marble and limestone easily dissolve in weak acidic solutions -Dissolution

17. Soils
Our food grows in soils. Also very important in recognizing past climates

18. Soil Soil - combination of mineral and organic matter, water, and air
It is that portion of the regolith (weathered rock and mineral) that supports the growth of plants
Biotic AND abiotic parts

19. Components in soil that support plant growth

20. Soil Factors controlling soil formation Parent material
parent material is the underlying bedrock - composition affects soil types

21. Soil Factors controlling soil formation Time Climate
Soils get better developed (Thicker, with greater differences between layers)
with more time
Climate
Biggest control on soil formation
Key factors are temperature and precipitation

22. Soil Factors controlling soil formation Plants and animals Slope
Organisms influence soil properties
Also furnish organic matter to the soil (especially plants)
Slope
Steep slopes have poorly developed soils (due to faster erosion and downslope transport
Flatter terrain accumulates soil faster

23. Variations in soil development due to topography
Note location of agriculture

24. Soil Profile The soil profile
Soil forming processes operate from the surface downward
Vertical differences are called horizons – zones or layers of soil

25. An idealized soil profile with horizons

26. Mnemonic: Only Active Educators Become Champions
Soil
The soil profile
O horizon – organic matter
A horizon – organic and mineral matter
High biological activity (animals live here)
Together the O and A horizons make up topsoil
E horizon – little organic matter
Zone of leaching
B horizon – zone of accumulation
C horizon – partly altered parent material
Mnemonic: Only Active Educators Become Champions

27. Animal Activities in “A” horizon
Source: Runk/Schoenberger/Grant Heilman

28. Eluviation & Illuviation

29. Remember the different horizonsA E B C
Organic
Animal Activity
Exited
Back
Crushed Rock
Soluble Minerals
Soluble Minerals

30. pedalfer
pedocal
laterite
Evergreen forests
Shortgrass
tropics

31. New Jersey State soil
ftp://ftp-fc.sc.egov.usda.gov/NSSC/StateSoil_Profiles/nj_soil.pdf

33. Pedocal with Caliche in the B horizon
Organic
Activity
Leached
Accumulation
Crushed Rock

34. Caliche
Source: Teaching Collection/University of Washington, Department of Geological Science

35. Laterite in Sarawak, Borneo
Source: Fletcher & Baylis/Photo Researchers, Inc.

36. Earth’s surface processes
Erosion – the physical removal of material by mobile agents like water, wind, ice, or gravity

37. Soil Erosion Soil erosion Soil characteristics Climate Slope
Recycling of Earth materials
Natural rates of soil erosion depend on
Soil characteristics
Climate
Slope
Type of vegetation

38. Source: Ramesh Venkatakrishnan
Erosion
Headed for the Sea
Source: Ramesh Venkatakrishnan

39. Soil
Soil erosion
In many regions the rate of soil erosion is significantly greater than the rate of soil formation
Farmers now level fields with lasers to slow loss of topsoil
Terraces

40. Hydrolysis Cleopatra’s Needle, (Egypt)
Granite in a
Dry Climate
Source: New York Public Library, Locan
History and Genealogy Division

41. Hydrolysis Cleopatra’s Needle, (Central Park, NYC)
Granite in a
Wet Climate
Source: Runk/Schoenberger/Grant Heilman