Topic-1:GE: Geological Cycle of Soil Origin

 

Geological Cycle of Soil Origin

The Geological Cycle of Soil Origin describes the processes that lead to the formation and transformation of soil from parent rocks. This cycle involves various physical and chemical processes that break down rocks into smaller particles, which eventually form soil. The cycle is influenced by multiple factors such as weathering, erosion, transportation, deposition, and soil formation.

Processes Involved in the Geological Cycle of Soil Origin

1. Weathering: The breakdown of rocks into smaller particles. Weathering is the initial step in soil formation and is caused by both physical and chemical agents.

   • Physical Weathering: Also known as mechanical weathering, this process involves the breakdown of rocks without any change in their chemical composition. The main agents responsible for physical weathering are:

     • Temperature Changes: Repeated heating and cooling cause rocks to expand and contract, leading to the formation of cracks and eventually breaking the rock apart.
     • Frost Action: Water enters cracks in rocks, freezes, and expands, causing the rock to break apart. This is also known as freeze-thaw weathering.
     • Abrasion: The mechanical scraping of rocks by friction with moving particles such as sand, water, ice, and wind.
     • Biological Activity: Roots of plants and burrowing animals can exert pressure on rocks, causing them to break apart.

   • Chemical Weathering: This involves the alteration of the chemical composition of rocks and minerals. The main agents responsible for chemical weathering are:

     • Water: Acts as a solvent, dissolving minerals and transporting ions.
     • Oxygen: Causes oxidation, which is the reaction of oxygen with minerals (e.g., rusting of iron-bearing minerals).
     • Carbon Dioxide: Combines with water to form carbonic acid, which reacts with minerals such as feldspar to form clay minerals.
     • Acids from Biological Sources: Organic acids produced by plants and microorganisms can dissolve minerals in rocks.

2. Erosion: The process by which weathered rock particles are removed and transported by natural agents such as wind, water, and ice.

3. Transportation: The movement of soil particles from their original location to new locations by natural agents like rivers, glaciers, winds, or gravity.

4. Deposition: The process by which transported soil particles settle in a new location, forming sediment layers. These layers accumulate over time and eventually form soil.

5. Soil Formation (Pedogenesis): The final stage of the geological cycle where the accumulated sediments undergo further weathering and mixing with organic materials to form soil. The soil formation process involves the development of distinct soil horizons (layers) due to various soil-forming factors such as climate, organisms, relief, parent material, and time.

Physical and Chemical Agents Responsible for Weathering

• Physical Agents:

  1. Temperature Fluctuations: Cause expansion and contraction of rocks.
  2. Frost Action: Causes freeze-thaw cycles in rocks.
  3. Wind Erosion: Carries away fine particles.
  4. Water Erosion: Rivers and streams transport rock particles.
  5. Glacial Erosion: Glaciers grind rocks into finer particles.
  6. Biological Activities: Roots, animals, and microbes physically break rocks.

• Chemical Agents:

  1. Water: Dissolves minerals and transports ions.
  2. Oxygen: Causes oxidation and rusting of minerals.
  3. Carbon Dioxide: Forms weak carbonic acid with water, leading to chemical reactions.
  4. Organic Acids: Produced by plants and microorganisms to chemically break down minerals.
  5. Acid Rain: Rainwater mixed with pollutants like sulfur dioxide forms sulfuric acid, leading to accelerated weathering.