 The process by which natural forces break down rocks.  There are two types Mechanical Weathering (Broken Apart) Chemical Weathering (Chemical Reaction )

 There are 4 types of mechanical weathering: Ice Wedging: Water freezes and expands, causing rocks to split apart. Pressure Release: Earth’s forces can push rock that is formed underground to the surface. The release of pressure can cause the rock to expand and crack. Plant Root Growth: Plants can grow in cracks of rock and wedge open the cracks. Abrasion: Water can wear rocks down in riverbeds due to friction.

 A change in the composition of the rock due to chemical reactions from water and air. There are two types: Dissolving: Water dissolves minerals or causes reactions where acids are formed. Air pollution can make rainwater acidic and cause acid rain. Rusting: Oxygen reacts with iron to form iron oxide, or rust.

 The rate of weathering is not the same for all rocks. The rate is affected by: Surface Area: The more of a rocks surface that is exposed, the faster it will break down. Rock Composition: Different kinds of rocks break down at different rates. Climate: Chemical weathering occurs faster in hot, wet regions than cold and dry regions. Mechanical weathering occurs more in cold regions than in hot regions.

 Soil is a mixture of four materials: Weathered rock particles Organic Matter (once living organisms) (5%) Water (20% to 30%) Air (20% to 30%) Decayed organic matter is known as HUMUS. THREE TYPES OF SOIL ARE CLAY, SILT AND SAND. DIRT IS NOT SOIL!!!!!

 Soil develops in a series of horizontal layers called soil horizons. Each horizon is a layer of soil with different properties than the last. A Horizon: Commonly called topsoil. Upper layer. Has the most organic matter. Dark in color. B Horizon: Brownish to reddish color. Little organic matter. C Horizon: Consists of the largest and least weathered rock particles. Light yellowish brown. Bedrock: Earth’s crust, underneath all other soil layers. SOIL PROFILE: Soil horizons in a particular location.

TROPICAL SOILS: Warm, rainy regions. Heavy rains wash away minerals leaving a thin layer of humus. Tropical soils are not suitable for growing crops. DESERT SOILS: Form in dry regions. Little organic matter. Low rainfall so chemical weathering and soil formation occur at slow rates. TEMPERATE SOILS: Regions with moderate rainfall and temperatures. Dark colored and rich in organic matter. Good for crops. ARCTIC SOIL: Cold, dry regions where chemical weathering is slow. They do not contain well developed horizons. Contain a lot of rock fragments. (Due to ice wedging)

 Texture (size of weathered particles)  Color (amount humus)  Pore Space (space between soil particles)  Chemistry (how well nutrients dissolve in water)

 Humus  Chemical Weathering  Mechanical Weathering  Soil Horizon Abrasion Exfoliation Soil Profile Microorganism (page 126)

 Mining: Digging of mines removes plants and soil from ground.  Farming: Some fertilizers make it difficult for microorganisms in soil to produce nutrients. Trees are cleared to make room to grow crops. Overgrazing leads to desertification.  Construction: To make roads and houses people dig up the soil. The soil is washed away and ends up in rivers, lakes or reservoirs.

 Crop Rotation: Planting different crops on the same field in different growing seasons.  Conservation Tillage: Reducing the number of times fields are tilled in a year.  Terraces: Flat, step-like areas built on a hillside to keep rainwater from running downhill.  Contour Plowing: Plowing along the curves of a slope. Keeps rainwater from running downhill.  Windbreaks: Rows of trees planted between fields to break the force of the wind that blows soil away.