Weathering and Soil Rocks and Weathering Uniformitarianism - The same geologic processes that work today worked in the past to change Earth’s surface What are these processes?  Erosion- breaking of rocks into smaller pieces and removal of those rocks and pieces by wind, water, ice or gravity.  Weathering-Chemical and physical processes that break down rock and other substances, heat, cold, water, ice and gases contribute

Weathering and Soil Two Types of Weathering 1.) Mechanical-rock is physically broken down into smaller pieces --usually works slowly --over long periods of time, can wear down mountains  Freeze thaw- important in cold climates, H2O seeps into cracks in rocks, freezes and expands which forces the rock apart this is called FROST WEDGING  Release of pressure-erosions removes material from surface of a mass of rock, pressure on rock is reduced which causes the outside of the rock to crack and flake off  Plant growth-roots enter cracks of rocks, as plant grows, so will roots causing cracks to get larger  Action of animals-burrowing by moles. Gophers, prairie dogs and insects loosens soil and breaks apart rocks  Abrasion-the grinding away of rock by other rock particles carried in water, ice or wind

Weathering and Soil 2.) Chemical- process that breaks down rock through chemical processes --process works with mechanical weather --creates holes or soft spots in rocks --rock breaks into pieces creating larger surface area for chemical weathering to work  Water-dissolves rock and carries other substances that break down rock, ie O, CO2 and other substances  Oxygen- combines with Iron to form rust, this is called oxidation --rust makes rocks soft and crumbly and causes red/brown color  Carbon dioxide- when dissolved in water forms carbonic acid which easily weathers some rocks like marble and limestone  Living organisms-plant roots produce weak acid that breaks down rock, ie. lichens  Acid rain-burning of fossil fuels puts S, C and N in the air. These compounds react with water vapor, rain produced is more acidic than normal = acid rain. --Acid rain rapidly causes chemical weathering White lichens cover a blue granite gravestone like snow near Lake Champlain, New York. Lichens, symbiotic organisms that combine fungi and algae, can be powerful weathering agents, secreting chemicals called chelates that work to break down rock. The effects of acid rain can be seen on this close up of this statues face. The acid rain has reacted with the mineral grain of the rock which has over time caused cavities to form as well wearing away the definition of the facial features.

Weathering and Soil Rate of weathering depends on two thing 1.) Type of rock-minerals determine how fast the rock weathers Minerals that dissolve easily = fast weathering Porosity- a measure of how much of a rock is open space Permeable- characteristic of material that contains connected air spaces or pores, that water can easily seep through -spaces increase surface area of rock allowing weathering to occur more quickly 2.) Climate Wet climate = increase physical and chemical weathering High Temperature = increase chemical weathering **chemical reactions occur more quickly at high temperatures Human activities also can increase the rate of chemical weathering -more people in an area = more pollution = more acid rain (chemical weathering) Weathering and Surface Area Weathering breaks rock into smaller pieces. While the pieces are usually irregularly shaped, you can model the process with cubes. The diagram shows what would happen if a rock cube broke into smaller cubes.

Weathering and Soil How Soil Forms Soil-the loos weathered material at Earth’s surface in which plants can grow -mixture of rock, minerals., decayed organic material, water and air -forms constantly wherever bedrock weathers, continues over a long period of time. Composition Bedrock-solid layer of rock beneath soil -exposed to air, H2O and living things it weathers Soil Particle Size-gravel, sand, silt, clay = portion of soil from weathered rock Humus-dark colored, organic material in soil -creates spaces in soil for air and water, contains nutrients plants need Fertility Fertitility- a measure of how well soil supports plant growth -rich in humus = high fertility -sandy soil = low fertility (low humus)

Weathering and Soil Soil Texture  depends on particle size  Sandy soil = course, grainy  Soil with lots of clay = smooth and silky  important for plant growth  Mostly clay holds a lot of water and little air = plant death  Sandy soil = loses water quickly = plant death  Loam- rich fertile soil that is made up of equal parts clay, sand and silt  Best for growing MOST plants Soil pH pH less than 4 = acidic, reacts with some metals, turns blue litmus paper red pH greater than 10 is strongly basic, feels slippery turn red litmus paper red pH of 7 = neither acidic or basic, ie. water Soil can be acidic (most acidic = 4) or basic, garden plants like pH 6-7.5

Weathering and Soil Soil Formation Rock is broken down by weathering and mixes with other materials on surface--- soil is formed Soil Horizon Horizon A- Topsoil- dark, crumbly, mixture of clay, humus, and minerals formed from plants adding organic material and plant roots weather rock Horizon B- Subsoil-clay, particles of rock, little humus  Rain water washes materials down from horizon A Horizon C- small particles of weathered bedrock

Weathering and Soil Soils of North America  Soil, fertility, and climate affect the types and numbers of plants that grow in a region.

Weathering and Soil How Do Living Things Affect Soil  Organisms make humus  Mix soil to make space for air and water Forming Humus  Organic remains = dead leaves, roots, and plant materials  Formed from decomposition Decomposers- Mixing Soil  Burrowing mixes humus with air and materials in soil  Animal waste contributes to nutrients in soil From Rock to Soil  The illustrations show a rock and rich, fertile soil. What are the three processes that could change rock into soil?

Weathering and Soil Soil Conservation Natural resource- anything naturally occurring in the environment that people use  Soil = one of Earth’s most valuable resources  everything that lives on land depends directly or indirectly on soil  1/8 of land on Earth’s land is farmable  Soil takes a long time to form, few cm in hundreds of years Soil damage and Loss Loss of Fertility  Loss of moisture and nutrients– can occur when only one crop is grown  Desertification- the advance of desert like conditions into areas that previously were fertile Loss of Topsoil  Exposure to wind and water causes erosion  Plant covering can protect  Break force of falling rain  Hold soil together  Sod- the thick mass of tough roots at the surface of the soil, holds soil in place

Weathering and Soil Soil Conservation Three ways people use land that might cause changes 1.) farming 2.) mining 3.) development- construction of homes, roads and other structures Soil Conservation-the management of soil to minimize its destruction  Crop rotation-the planting of different crops in a field each year; corn or cotton one year followed by oats, barley or rye  Corn, cotton take up large amounts of nutrients  Peanuts, alfalfa and beans restore nutrients  Legumes contain pods of nitrogen fixing bacteria  Contour plowing-fields plowed along curves of a slope instead of straight rows  Slows runoff, prevents soil from washing away  Conservation plowing-dead weeds and stalks are plowed into the ground  Returns nutrients to soil, retains moisture and hold soil in place

Weathering and Soil Dust Bowl Parts of Oklahoma and surrounding states that lost soil is the 1930’s were called the DUST BOWL Farmers plowed the land removing the sod and exposed soil, drought dried out the topsoil which turned to dust and blew away = Desertification Land Reclamation- the process of restoring an area of land to a more natural, productive state