•Big Idea:Big Idea: Natural forces break rocks apart Natural forces break rocks apart and form soil, which supports life.and form soil, which supports life.

• Weathering is the process by Weathering is the process by which natural forces break down which natural forces break down rocks.rocks.

• There are 2 types of weathering:There are 2 types of weathering:

1.1. Mechanical weatheringMechanical weathering

2.2. Chemical weatheringChemical weathering

• Mechanical weathering is the Mechanical weathering is the breaking up of rocks by physical breaking up of rocks by physical forces.forces.

• There are 4 main types:There are 4 main types:

1.1. Ice wedgingIce wedging

2.2. ExfoliationExfoliation

3.3. Plant root growthPlant root growth

4.4. AbrasionAbrasion

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

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

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

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

• The breakdown of rocks by The breakdown of rocks by chemical reactions that change chemical reactions that change the rocks’ makeup, or the rocks’ makeup, or composition.composition.

• There are 2 main types:There are 2 main types:

1.1. DissolvingDissolving

2.2. RustingRusting

• Water is the main cause Water is the main cause of chemical weathering.of chemical weathering.

• Many more minerals Many more minerals dissolve in water that is dissolve in water that is slightly acidic – like slightly acidic – like lemonade.lemonade.

• The oxygen in air is also The oxygen in air is also involved in chemical involved in chemical weathering.weathering.

• Many common minerals Many common minerals contain iron. When these contain iron. When these minerals dissolve in water, minerals dissolve in water, oxygen in the air and the water oxygen in the air and the water combines to produce rust.combines to produce rust.

• Most weathering occurs over long Most weathering occurs over long periods of time – hundreds, periods of time – hundreds, thousands, or even millions of thousands, or even millions of years.years.

• There are 3 Influential factors:There are 3 Influential factors:1.1. Surface areaSurface area2.2. Rock compositionRock composition3.3. ClimateClimate

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

• Different kinds of rock break down Different kinds of rock break down at different rates.at different rates.

• Chemical weathering occurs faster Chemical weathering occurs faster in hot, wet regions than it does in in hot, wet regions than it does in cold, dry regions.cold, dry regions.

• Mechanical weathering caused by Mechanical weathering caused by freezing and thawing occurs more freezing and thawing occurs more in cold regions than in hot regions.in cold regions than in hot regions.

Big Idea: Natural forces break rocks apart and form soil, which supports life.

•Soil is a surface mixture of Soil is a surface mixture of rocks, minerals, organic rocks, minerals, organic matter, water, and air.matter, water, and air.

• The rocks and minerals The rocks and minerals come from weathering.come from weathering.

• The organic matter is The organic matter is called humus, which called humus, which comes from the decay of comes from the decay of different life forms in or on different life forms in or on the soil.the soil.

• Water is from precipitationWater is from precipitation• Soil air is from the Soil air is from the

atmosphere.atmosphere.

• Rocks, minerals, and organic Rocks, minerals, and organic matter form soil particles matter form soil particles (~ 50% of a soil by (~ 50% of a soil by volume).volume).

• The spaces between soil The spaces between soil particles are called soil poresparticles are called soil pores

(~ 50% of a soil by volume).(~ 50% of a soil by volume).• Water and air fill the pores.Water and air fill the pores.

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

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

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

•A variety of living things live A variety of living things live in soil.in soil.•Used for food production.Used for food production.•Used for construction (adobe) Used for construction (adobe) and fuel (peat).and fuel (peat).•Used for types of waste Used for types of waste treatment.treatment.

• 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.

Big Idea: Natural forces break rocks apart and form soil, which supports life.

• Supports the growth of plants, which Supports the growth of plants, which in turn supply us with many things, in turn supply us with many things, such as food, clothing, medicines, such as food, clothing, medicines, lumber, and even oxygen.lumber, and even oxygen.

• Purifies water as it drains through Purifies water as it drains through the ground and keeps water systems the ground and keeps water systems clean.clean.

• Nutrient recycling by decomposers in Nutrient recycling by decomposers in soil that enable plants to grow.soil that enable plants to grow.

• Home to a variety of living things.Home to a variety of living things.

Farming: use of fertilizers & practicesFarming: use of fertilizers & practices

• microorganisms have difficulty microorganisms have difficulty producing nutrients naturally.producing nutrients naturally.

• pollutes water systems.pollutes water systems.

• reduce plant cover and increases soil reduce plant cover and increases soil loss due to wind and water.loss due to wind and water.

• overgrazing by livestock. overgrazing by livestock.

Construction & Development: removal Construction & Development: removal of vegetation to buildof vegetation to build

• soil is blown or washed away.soil is blown or washed away.

• makes water systems muddy and can makes water systems muddy and can harm the organisms living there.harm the organisms living there.

• causes flooding.causes flooding.

Mining: removal of soilMining: removal of soil

• speeds up rates of chemical speeds up rates of chemical weathering by exposing rocks & weathering by exposing rocks & minerals to rainwater and air.minerals to rainwater and air.

• contaminates soil (sulfuric acid).contaminates soil (sulfuric acid).

• Crop rotation:Crop rotation: The practice of planting The practice of planting different crops on the same field in different crops on the same field in different years or growing seasons.different years or growing seasons.

• Conservation tillage:Conservation tillage: Reduces the number of times that Reduces the number of times that fields are tilled in a year; therefore fields are tilled in a year; therefore reducing the amount of erosion.reducing the amount of erosion.

• Terraces:Terraces: Flat, step-like areas built on a Flat, step-like areas built on a hillside to hold rainwater and prevent hillside to hold rainwater and prevent it from running downhill.it from running downhill.

• Contour plowing: Contour plowing: Plowing along the curves of a slope Plowing along the curves of a slope which helps channel rainwater which helps channel rainwater resulting in less erosion.resulting in less erosion.

• Windbreaks: Windbreaks: Rows of trees planted Rows of trees planted between fields to reduce the force of between fields to reduce the force of winds that can carry off soil.winds that can carry off soil.