2 Aim: How does weathering change Earth’s surface?
3 WeatheringIs surface processes that work to breakdown rocks into smaller piecesSmaller loose pieces are sedimentsGravel, Sand, silt and clay describe sizes of sedimentsSize order: gravel, sand, silt, clay (largest to smallest)Wears mountains down to hillsProduces strange rock formations2 Types of weathering:Mechanical WeatheringChemical Weathering
4 Aim: How do mechanical weathering and chemical weathering differ?
5 Mechanical Weathering Occurs when rocks are broken apart by physical processesChemical makeup of the rock stays the same2 ways this can happen:Plants and AnimalsWater and nutrients that collect in the cracks or rocks enable plants to growAs the roots grow they enlarge the cracksEx: tripped on crack in the sidewalk near a tree
6 Burrowing animals loosen sediments and push them to the surface Sediments reach the surface and other weathering processes occurIce WedgingOccurs in temperate and cold climatesWater enters cracks in rocks and freezesPressure builds up in the cracks causing them to expand and break apart the rockThe ice melts and this happens all over againThe process of freezing and thawing occurs over and over, especially in mountains
7 Ice wedging wears mountain peaks It can also break up roads and highwaysMechanical weathering reduces rocks to smaller pieces giving the rock more surface areaAs the surface area increases more rock is exposed to water and oxygen which aids in chemical weathering
8 Chemical WeatheringChemical reactions dissolve the minerals in rocks or change them to different mineralsChanges the chemical composition of the rockNaturally occurring acids, such as carbonic acid, react with calcite in limestoneThe acid weathers away the limestone to form cavesKaolinite clay is created when acids react with feldspar in graniteClay is an end product in weathering
9 Plant acids can dissolve minerals in rocks and breaks the rocks into smaller pieces This weathering also enables nutrients to be available for plantsOxygen also causes weatheringOxidation occurs when some materials are exposed to oxygen and waterEx: rust
10 Effects of Climate on Weathering Chemical weathering is more rapid in warm, moist climatesMechanical weathering is important in dry climates and in cold climates
12 Formation of SoilIs a mixture of weathered rock, decayed organic matter, mineral fragments, water and airCan take thousands of years to formClimate, slope, types of rock, types of vegetation and length of time of weathering affect rock formationThere are different kinds of soil all over the world based on these factors4 steps
13 Weathering of rocksNatural acids in rainwater weather the surface of exposed bedrockWater can freeze in cracks to break them apartPlant GrowthPlants begin growing in cracks of rocksAs they grow they continue the process of breaking down rocksThen a thin layer of soil begins to form
14 Living OrgansimsInsects & worms live underground with the plant rootsTheir wastes and dead material add organic matter to the soilOrganic Matteras organic matter increases, the bedrock continues to breakdownThis causes the soil layer to thickenRich topsoil supports trees and plants with large root systems
16 Composition of Soil Most organic matter in soil comes from plants Animals and microorganisms remains also add organic matter to the soilDecayed organic matter over time turns into a dark-colored material called humusHumus is a source of nutrients for plantsAnimals burrowing in the ground mix the humus with fragments of rocksGood quality soil have equal amounts of humus and weathered rock material
17 Layers of Soil Layers of soil are called horizons All soil horizons form a soil profileMost soils have 3 horizonsA Horizontop layer-AKA topsoilIn a forest it is covered with litterLitter helps prevent erosion and evaporation of water from the soilTopsoil has more humus and fewer rock and mineral fragments than the other horizons
18 Is dark and fertileB Horizonis below the A horizonLighter in color (less organic matter)Less fertileLeaching moves minerals that have been dissolved in water from A horizon down into the B horizon
19 C HorizonBottom layerContains partially weathered rockThickest horizonNot affected by leaching and doesn’t have much organic materialCoarser sedimentsMost like the parent material, which is rock
20 Aim: What determines the different types of soil?
21 Types of Soil Many different types of soil exist Climate affects soil Desert soil has a small amount of organic matter and is thinPrairies have thick, dark A horizon soil due to the organic matter from the large amount of grasses presentForest soil has a thinner A horizon than prairies because trees and leaves don’t supply as much organic matter as grasses do
22 The type of rocks soil comes from affects the type of soil Sandstone turns into a sandy soilClay soil comes from basaltType of vegetation that grows in an affects soil formationSlope of the land affects soil developmentThe soil on the slope is poorly developedSoil in a valley is rich in organic matter
23 Aim: How has human activity affected Earth’s soil?
24 Soil ErosionSoil erodes when it is moved from the place where it formedWater and wind move sediments and cause erosionMore severe on steep slopesHumans cause erosion to form faster by removing vegetation (ground cover) which helps increase soil erosionSerious problem for agricultureSoil loses nutrients, which plants need to grow
25 When soil erodes farmers compensate for the nutrient lose by buying fertilizer Forest harvesting also causes soil erosionRemoving forests creates severe problems for the environment, especially rain forestsForests are cleared for lumber, farming and grazingOvergrazing also increases soil erosionSheep and cattle are grazed on land until no ground cover remainsWithout protection from plants that soil is carried away by wind and water
26 Too much soil erosion, sediments can damage the environment This can cause streams to be covered, eggs from organisms die, or reduce downstream water quality
28 Preventing Soil Erosion Plant shelter belts of trees-this blocks the strength of the windNo-till farming-farmers do not plow the fieldsThis practice provides cover for the soil all year round and reduces water runoff and soil erosionContour farming used on slopes-this slows the flow of water down the slope and reduces soil erosionTerracing-leveled areas are built on slopes (looks like steps)
29 This practice reduces runoff by creating flat areas and shorter sections of slope