Section 4.1 Notes: Mechanical & Chemical Forces Break Down Rocks Big Idea: Natural forces break rocks apart and form soil, which supports life.

Weathering breaks rocks into smaller pieces Weathering is the process by which natural forces break down rocks. There are 2 types of weathering: Mechanical weathering Chemical weathering

Mechanical weathering produces physical changes in rocks Mechanical weathering is the breaking up of rocks by physical forces. There are 4 main types: Ice wedging Exfoliation Plant root growth Abrasion

Ice Wedging When water freezes, it expands. When water freezes in the cracks and pores of rocks, the force of its expansion is strong enough to split the rocks apart.

Exfoliation The process in which layers or sheets of rock gradually break off due to the expansion of the rock caused by a decrease in pressure.

Plant Root Growth Trees, bushes, and other plants may take root in cracks of rocks. As the roots of these plants grow, they wedge open the cracks.

Abrasion The process of wearing down by friction, the rubbing of one object or surface against another.

Chemical weathering changes the mineral composition of rocks The breakdown of rocks by chemical reactions that change the rocks’ makeup, or composition. There are 2 main types: Dissolving Rusting

Dissolving Water is the main cause of chemical weathering. Many more minerals dissolve in water that is slightly acidic – like lemonade.

Rusting The oxygen in air is also involved in chemical weathering. Many common minerals contain iron. When these minerals dissolve in water, oxygen in the air and the water combines to produce rust.

Weathering occurs at different rates Most weathering occurs over long periods of time – hundreds, thousands, or even millions of years. There are 3 Influential factors: Surface area Rock composition Climate

Surface Area The more of a rock’s surface that is exposed to air and water, the faster the rock will break down.

Rock Composition Different kinds of rock break down at different rates.

Climate Chemical weathering occurs faster in hot, wet regions than it does in cold, dry regions. Mechanical weathering caused by freezing and thawing occurs more in cold regions than in hot regions.

Section 4.2 Notes: Weathering & Organic Processes Form Soil Big Idea: Natural forces break rocks apart and form soil, which supports life.

What is soil? Soil is a surface mixture of rocks, minerals, organic matter, water, and air.

Where do the ingredients come from? The rocks and minerals come from weathering. The organic matter is called humus, which comes from the decay of different life forms in or on the soil.

Where do the ingredients come from? Water is from precipitation Soil air is from the atmosphere.

What determines the soil in an area? Type of rock Climate and overall weather Landforms – mountains & valleys Plant cover Organisms Time

How are the soil parts arranged? Rocks, minerals, and organic matter form soil particles (~ 50% of a soil by volume). The spaces between soil particles are called soil pores (~ 50% of a soil by volume). Water and air fill the pores.

How does soil develop? Over time, soils develop horizons, distinct layers of soil identified by color, texture, and particle structure.

How does soil develop? O: Decaying organic matter on soil surface (fallen leafs). A: Loose dark surface soil good for food production (topsoil).

How does soil develop? B: Dense light-colored sub-surface soil not good for food production (contains rocks). C: Mostly partially weathered rocks and minerals (bedrock).

Properties of soil can be observed & measured Texture: determined by the size of the weathered rock particles. Color: indicates the content of the soil and how well it drains. Pore space: the spaces between soil particles. Chemistry: determines how well nutrients dissolve in water.

Section 4.3 Notes: Human Activities Affect Soil Big Idea: Natural forces break rocks apart and form soil, which supports life.

Soil is a necessary resource Supports the growth of plants, which in turn supply us with many things, such as food, clothing, medicines, lumber, and even oxygen. Purifies water as it drains through the ground and keeps water systems clean.

Soil is a necessary resource Nutrient recycling by decomposers in soil that enable plants to grow. Home to a variety of living things.

Land-use practices can harm soil Farming: use of fertilizers & practices farmers lose 5 metric tons of soil per 1 metric ton of grain microorganisms have difficulty producing nutrients naturally. pollutes water systems. reduce plant cover and increases soil loss due to wind and water. overgrazing by livestock. Desertification!

Land-use practices can harm soil Construction & Development: removal of vegetation to build soil is blown or washed away. makes water systems muddy and can harm the organisms living there. causes flooding.

Land-use practices can harm soil Mining: removal of soil speeds up rates of chemical weathering by exposing rocks & minerals to rainwater and air. contaminates soil (sulfuric acid).

Soil can be protected and conserved Crop rotation: The practice of planting different crops on the same field in different years or growing seasons. Conservation tillage: Reduces the number of times that fields are tilled in a year; therefore reducing the amount of erosion.

Soil can be protected and conserved Terraces: Flat, step-like areas built on a hillside to hold rainwater and prevent it from running downhill. Contour plowing: Plowing along the curves of a slope which helps channel rainwater resulting in less erosion.

Soil can be protected and conserved Windbreaks: Rows of trees planted between fields to reduce the force of winds that can carry off soil.