1. Rocks to Soil AP Env Sci 2011-2012

2. Earth’s Surface is Constantly Changing
Internal Processes: elevating parts of Earth’s surface
Mountain Building
Volcanic Activity
External Processes: breaking rock and moving it to lower elevation
Weathering
Mass Wasting
Erosion
Weathering Processes Make Soil

3. Soil Formation Soil – several ways to define:
Unconsolidated material overlying bedrock
* Material capable of supporting plant growth *
Soil is produced by weathering
Physical, Chemical, Biological Processes
Climate, topography, source material composition, and time are factors

4. Mechanical Weathering
Large pieces are broken up into smaller pieces
Frost Wedging
Biological Activity
Processes do not work alone!
Chemical processes attack exposed surface, so:
smaller pieces -> more surface area exposed
more exposure -> more chemical attack

5. Frost wedging of Diabase Boulders at Sourlands
Michael Hambrey

7. 2. Mech. weathering – Biological activity
Biological activity does mechanical work and introduces chemicals to rock

8. What does the Weathering?
Chemical Weathering
What does the Weathering?
Water, with small quantities of dissolved components
ex. CO2 (forms carbonic acid) -> H2CO3
ex. O2 (oxidizer)
Crust is made up primarily of silicate minerals
Fate of Most Abundant Elements:
Sodium, Calcium, Potassium, Magnesium – form ions
Iron – oxidizes to iron oxides (red/yellow)
Aluminum, Silicon, Oxygen – form clays

9. Example: Granite
Granite: mainly quartz & potassium feldspar (KAlSi3O8)
Potassium Feldspar reacts with Carbonic Acid:
2(KAlSi3O8) + 2(H2CO3) + H2O ->
Al2Si2O5(OH)4 + 2K+ + 2HCO3- +4SiO2
Product is clay mineral and ions in solution
Quartz is resistant to chemical weathering
Quartz (sand) is transported to sea or elsewhere

10. Breakdown by Acids 3. Chemical weathering Natural sources:
Decaying organic matter makes CO2.
CO2 + water  carbonic acid
Anthropogenic source (human impact):
SO2 and NOx create acids when combined with water  acid rain

12. Factors Affecting Rate of Weathering
Exposed Surface Area
Rock Characteristics
Mineral composition
Solubility
Cracks, etc
Climate
Temperature
Moisture
Warm temperature/high moisture favors chemical weathering

13. Weathering rates of gravestones (Kingston)
Marble
Slate
1817
1837

14. What is Soil?
Soil is a combination of mineral and organic matter, water, and air.
It is the part of the regolith (rock and mineral fragments produced by weathering) that supports the growth of plants

15. Characterizing Soil Texture: The Soil Triangle
Source: EID
Let’s Practice….

16. Soil: Big to Small
Sand: 2 to 0.2 mm
Silt: to mm
Clay: mm and smaller

17. You Need to Know the Soil Triangle: Why?
Texture impacts soil’s ability to retain and transmit air:
Larger particles have larger spaces between them
Packing -> loose = easily aerated (sand)
Texture impacts soil’s ability to retain and transmit water:
Surface area -> small particles have more SA/volume
Nutrients and water retained by surfaces
Sandy soils drain fast, dry out rapidly
Clay drains slowly
Texture affects “workability” (agriculture)
Loam soils supports plant life best

18. Control of Soil Formation
Parent Material: Source of weathered mineral matter
Parent = Bedrock – residual soils
Parent = Sediment – transported soils
Time: How Long?
Climate: Temperature and Precipitation
Plants and Animals: Source of organic matter
Topography:
Steep slopes often poor soil
Bottomlands often poor drainage, much organic
Best: flat to undulating uplands

19. Soil Profile

20. Soil Profile O Horizon: Loose and partly decayed organic matter
A Horizon: Mineral matter mixed with some humus
E Horizon: Light colored mineral particles. Zone of eluviation and leaching
B Horizon: Accumulation of clay transported from above
C Horizon: Partially altered parent material
Solum: O, A, E, and B layers. The “true soil” where soil formation processes are underway and plant and animal life exist.

22. Soil and Plant Growth: Minerals, Water, Air
From Weathering
Lost by Leaching
Replaced by Fertilizer
Organic
Inorganic
Can you identify the three most important?

23. Soil and Plant Growth: Minerals, Water, Air
Absorbed through roots
Lost through transpiration
Soil gains water through Infiltration
Soils retain water to varying degrees: Water-Holding Capacity

24. Soil and Plant Growth: Minerals, Water, Air
Roots need air
Aeration of soil creates space for air to enter
Compaction has opposite effect

25. Soil Gains and Losses Gain Organic Matter:
Ample organic matter (humus)
Nutrients, infiltration and water-holding capacity, aeration all increase
Lose Organic Matter:
Humus loss (how?)
Nutrients, infiltration and water-holding capacity, aeration all decrease
Mineralization: Near Complete Loss of Organic Component!