The Cycling of Earth’s Rocks The three major types of rocks found in the earth’s crust—sedimentary, igneous, and metamorphic—are recycled very slowly by the process of erosion, melting, and metamorphism.

The crust is composed of rocks & minerals Minerals- elements or inorganic compounds that occur naturally in the earth’s crust as a solid with a regular internal crystalline structure Ex: gold, diamond, silver, salt, quartzite Rocks – a solid combination of one or more minerals found in the earth’s crust Example: Granite = mica + feldspar + quartz

Classifying Rocks There are three broad classes of rocks, based on formation Sedimentary (deposited) Igneous (volcanic) Metamorphic (heat & pressure) 3

There Are Three Major Types of Rocks (1) Sedimentary - piling of material over time (fossil record) Sandstone Shale Limestone Bituminous coal 4

There Are Three Major Types of Rocks (2) Igneous - cooling and crystallization of magma (form the bulk of the earth’s crust) Granite Lava rock Quartz

There Are Three Major Types of Rocks (3) Metamorphic (igneous or sed. subjected to heat and pressure) Anthracite Slate Marble 6

The Earth’s Rocks Are Recycled Very Slowly Rock cycle Slowest of the earth’s cyclic processes

Heat, pressure, stress Magma (molten rock) Erosion Transportation Weathering Deposition Igneous rock Granite, pumice, basalt Sedimentary rock Sandstone, limestone Heat, pressure Cooling Heat, pressure, stress Magma (molten rock) Figure 14.13 Natural capital: the rock cycle is the slowest of the earth’s cyclic processes. Rocks are recycled over millions of years by three processes: erosion, melting, and metamorphism, which produce sedimentary, igneous, and metamorphic rocks. Rock from any of these classes can be converted to rock of either of the other two classes, or can be recycled within its own class (Concept 14-2). Question: What are three ways in which the rock cycle benefits your lifestyle? Melting Metamorphic rock Slate, marble, gneiss, quartzite Fig. 14-13, p. 354

Soil Formation The Importance of Soil All life depends on the thin top layer of soil covering the earth’s surface. Created when rocks, dead animals or plants break down into tiny pieces Topsoil provides: Support Water Air Nutrients Filter/Buffer

Weathering: Biological, Chemical, and Physical Processes

Erosion – by wind

Erosion – by water

Glacier Receding

Weathering: Breakdown of Rock near the Surface Chemical Alteration Carbon dioxide, sulfur dioxide and various nitrogen compounds from the air form acids when dissolved in water. These acids may react with the rock and increase breakdown.

Chemical Weathering

Chemical Weathering

What Determines Soil Type Living Organisms Topography Climate Vegetation Time Parent Material Residual - Transported Least Important Factor for Mature Soils

Soil Composition

Soil Formation and Generalized Soil Profile 19

Soil Horizons and Profiles Soil Profile Suite of Layers at a Given Locality Soil Horizons Layers in Soil Not Deposited, they are Zones of Chemical Action Layers (horizons) of mature soils O horizon: leaf litter A horizon: topsoil B horizon: subsoil C horizon: parent material, often bedrock

Principal Soil Horizons O - Organic (Humus) Often Absent A – Leaching K, Mg, Na, Clay Removed B – Accumulation Absent in Young Soils Distinct in Old Soils Al, Fe, Clay (Moist) Si, Ca (Arid) C - Parent Material

Soil Characteristics Physical Texture Porosity Permeability Humus Color Chemical pH *You need to know how to fix pH problems Nitrogen Phosphorous Potassium

Permeability – the degree to which the pores in the rock or soil are connected together so that water can move freely Porosity - the percentage of interconnected space in rock and soil that can contain water

Main Soil Textures Soil Type Texture Permeability Porosity Sand Gritty High Low Silt Smooth & Slippery Med Clay Sticky

Soil Formation vs. Soil Erosion Takes hundreds of years to form 1 cm (0.4 inches) of soil Soil erosion Blown away in weeks or months from plowing and clearing forests – any time we leave the topsoil unprotected 26

Topsoil Erosion Is a Serious Problem in Parts of the World Two major harmful effects of soil erosion Loss of soil fertility through depletion of plant nutrients in topsoil Water pollution in nearby surface waters where eroded soil ends up as sediment Kills fish, shellfish Clogs irrigation ditches, reservoirs, lakes, and boat channels Eroded soil may also be polluted with pesticides and fertilizers

Dust Bowl of the 1930’s

China’s Dust Storms - 2006

Soil Textural Triangle Practice Exercises % Sand % Silt % Clay Texture Name 75 10 15 sandy loam 10 83 7 _______________

Reduce Soil Erosion Soil conservation, some methods Terracing Contour planting Strip cropping with cover crop Alley cropping, agroforestry Windbreaks or shelterbeds Conservation-tillage farming No-till Minimum tillage Identify erosion hotspots 31

Figure 12.24 Soil conservation methods include (a) terracing, (b) contour planting and strip cropping, (c) alley cropping, and (d) windbreaks (Concept 12-6A). Fig. 12-24a, p. 302

Figure 12.24 Soil conservation methods include (a) terracing, (b) contour planting and strip cropping, (c) alley cropping, and (d) windbreaks (Concept 12-6A). Fig. 12-24b, p. 302

Figure 12.24 Soil conservation methods include (a) terracing, (b) contour planting and strip cropping, (c) alley cropping, and (d) windbreaks (Concept 12-6A). Fig. 12-24c, p. 302

Figure 12.24 Soil conservation methods include (a) terracing, (b) contour planting and strip cropping, (c) alley cropping, and (d) windbreaks (Concept 12-6A). Fig. 12-24d, p. 302

Solutions: Mixture of Monoculture Crops Planted in Strips on a Farm 36

Conservation Tillage Conservation-tillage farming: method of soil cultivation that leaves the previous year's crop residue on fields before & after planting the next crop No-till: involve planting crops directly into residue that either hasn't been tilled at all Minimum tillage: some residue has been removed, but at least 30 to 70% remains

No Till & Minimum Tillage Planting into corn residue (no till) Soybeans grown in striped rows between corn residue (minimum tillage)

Benefits of Conservation Tillage Environmental benefits Reduces soil erosion by 60%-90% from rain & wind Improves soil and water quality by adding organic matter as crop residue decomposes Conserves water by reducing evaporation Conserves energy due to fewer tractor trips Reduces air pollution from dust and diesel Crop residue provides food and cover for wildlife

Benefits of Conservation Tillage Practical benefits Fewer trips across the fields saves time and money (lowers fuel, labor and machinery maintenance costs) and reduces soil compaction that can reduce yields Optimizes soil moisture, enhancing crop growth in dry periods or on droughty soils