UNIT-2 WEATHERING WITH YOU

Weathering and Soil Formation

• Weathering: The process that disintegrates and decomposes rocks and minerals to form soil.

Processes of Weathering

1. Physical Weathering

• Disintegration of rocks and minerals into smaller fragments without changing chemical composition.

• Causes:

  • Mechanical disintegration

  • External agents: Water, ice, wind, and biological influences.

2. Mechanical Weathering

• Frost Wedging: Expansion of ice in rock cracks leads to further cracking.

• Exfoliation: Peeling away of surface layers from parent rock.

• Thermal Expansion: Extreme temperature changes can shatter rocks, particularly in deserts.

Chemical Weathering

• Decomposition that changes chemical composition, releases soluble materials, and forms new minerals.

Involves:

• Hydration: Water reacts but doesn't destroy the original chemical structure.

• Hydrolysis: Water reacts and destroys the original structure, producing acids and bases.

• Solution: Soluble substances removed by water, causing decomposing.

• Carbonation: Reaction of carbonic acid with minerals to form soluble products.

• Oxidation: Addition of oxygen to minerals, often affecting iron-bearing rocks.

Resistance to Weathering

• Order: Quartz > Muscovite > K feldspar > Na/Ca feldspar > Biotite > Hornblende > Augite > Olivine > Dolomite > Calcite > Gypsum.

Dating Rocks

Relative Dating

• Determines the sequential order of events without knowing specific ages.

Absolute Dating

• Determines the actual age of rocks or fossils using radioactive decay.

Rules of Relative Dating

1. Sedimentary rocks form in bodies of water.

2. Weathering and erosion occur on the surface.

3. Bottom layers are the oldest (Law of Superposition).

4. Layers deposited horizontally (Law of Original Horizontality).

5. Intrusions are younger than the rocks they affect.

6. Faults are younger than the rocks they cut through.

7. Unconformities represent a break in the rock record.

Types of Unconformities

1. Angular Unconformity: Horizontal layer over tilted layers.

2. Disconformity: Eroded layers appear continuous but have a time gap.

3. Nonconformity: New sediments deposited on eroded igneous/metamorphic rock.

Post-Test Questions

1. Define weathering.

2. What are the two types of weathering processes?

3. Describe exfoliation.

4. Which substances are soluble in water?