Rocks to Soil AP Env Sci 2011-2012

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

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

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

Frost wedging of Diabase Boulders at Sourlands Michael Hambrey

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

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

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

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

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

Weathering rates of gravestones (Kingston) Marble Slate 1817 1837

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

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

Soil: Big to Small Sand: 2 to 0.2 mm Silt: 0.02 to 0.002 mm Clay: 0.002 mm and smaller

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

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

Soil Profile

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.

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

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

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

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!