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.

Rocks to SoilAP 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

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

3. Chemical weathering Breakdown by Acids

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)

Slate

18171837

Marble

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

25%

25%

45%

5%water

air

mineral

humus (organic)

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

• Minerals: – From Weathering– Lost by Leaching– Replaced by Fertilizer

•Organic•Inorganic

– Can you identify the three most important?

Soil and Plant Growth: Minerals, Water, Air

• Water:– 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

• 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!