Weathering and Soil Formation

• Weathering is the process of breaking down rocks and materials on Earth’s surface.
• The two main types of weathering are mechanical (physical) and chemical.

Mechanical (Physical) Weathering

• Mechanical weathering breaks rocks into smaller pieces without changing their chemical makeup.
• Ice wedging involves water freezing in cracks, expanding, and breaking the rock.
• Abrasion occurs when rock particles grind against each other due to wind, water, or ice.
• Plant roots can grow into cracks and break rocks apart.
• Animal actions, such as burrowing, loosen rock.

Chemical Weathering

• Chemical weathering breaks down rock through chemical changes.
• Oxidation occurs when oxygen reacts with iron in rocks, forming rust.
• Acid rain, caused by pollution, breaks down rock.
• Carbonation involves carbon dioxide in water forming weak acids that dissolve limestone.
• Living organisms like lichen and moss produce acids that break down rock.

Soil Formation

• Soil is a mixture of weathered rock, minerals, organic material, water, and air.

Layers of Soil (Soil Horizons)

• Topsoil (Horizon A) is dark and rich in organic material (humus), making it best for plant growth.
• Subsoil (Horizon B) contains clay and minerals washed down from topsoil.
• Bedrock (Horizon C/R) is the solid rock beneath the soil.

Types of Soil

• Loam, a balanced mix of sand, silt, and clay, is ideal for plant growth.
• Humus is decayed organic material that adds nutrients to the soil, improving soil fertility.

Factors Affecting Weathering and Soil Formation

• Warm, wet climates accelerate chemical weathering.
• Softer rocks weather more quickly.
• Soil formation takes hundreds to thousands of years.
• Biological activity from plants and animals aids in breaking down rock and forming soil.