EESB05 - Chapter 2.docx

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Environmental Science
Marney Isaac

EESB05 Chapter 2: Formation of Soils from Parent Materials - Soils in every landscape differ from each other, and each influence ecological processes in their own way WEATHERING OF ROCKS AND MINERALS - The physical and chemical breakdown of particles occur everywhere - Weathering breaks up rocks and minerals, modifies or destroys their physical and chemical characteristics Characteristics of Rocks and Minerals - Rocks are classified as igneous, sedimentary, or metamorphic Igneous - Composed of primary minerals Ex. Light-coloured quartz, muscovite, feldspar, dark-coloured biotite, augite, hornblende - Randomly dispersed interlocking pattern of mineral grains give it a “salt and pepper” look - Easily weathered Sedimentary - Formed when weathering of other older rocks collect underwater as sediment and reconsolidated into new rock Ex. Weathered quartz sand from granite may become cemented by calcium or iron in water to form sandstone - Sedimentary rocks the most common type of rock, covering 75% of Earth’s surface Metamorphic - Rocks formed by metamorphism, a process where rocks undergo tremendous heat and pressure, and these forces may compress and partially remelt or distort the rocks Ex. Igneous rocks such as granite can be modified to form gneiss (a rock with light and dark mineral bands) Weathering: A General Case - Weathering is a biochemical process that involves destruction and synthesis - Rocks are physically broken down into smaller rocks, and into smaller particles - These smaller particles are made up of minerals that decompose chemically, and release soluble materials and synthesize new minerals - Particles continue to decrease in size and dissolve in aqueous weathering solution, and these dissolved substances may recombine into new minerals (secondary minerals) Physical Weathering (Disintegration) Temperature - Heating of rocks by sunlight or fires - Some minerals expand more than others, and rocks may crack under different heat or stresses - Outer layers of rocks tend to be hotter or colder than its interior, and may peel away (exfoliation) Ex. Water in the cracks of rocks can freeze, and ice expands to break away layers and dislodging mineral grains from smaller fragments Abrasion by Water, Ice, and Wind - Water with sediment has tremendous cutting power Ex. Ravines, valleys, rounding of rocks, beach sand grains, etc. - Windblown dust wears down rocks by abrasion - Ice masses embedded with soil and rock fragments grind down rocks and carry away material Plants and Animals - Plants and animals cause less significant effects on rocks - Plant roots may pry rocks apart by entering cracks - Animal burrowing may help disintegrate rocks to a certain extent Biochemical Weathering - Chemical reactions most intense in hot and wet climates - Chemical weathering is enhanced by geological agents such as water and oxygen, and biological agents such as acids produced by microbial and plant-root metabolism - This process is described as biochemical weathering in which primary minerals are converted into secondary minerals FACTORS INFLUENCING SOIL FORMATION - The soil is a collection of individual soils - V.V. Dukochaev and his team of Russian scientists discovered similar profile layering in distant soils 5 Major Factors that Control the Formation of Soils 1) Parent materials 2) Climate 3) Biota 4) Topography 5) Time - Soils are dynamic natural bodies having properties derived from climate and biotic activities, modified by topography, acting on parent materials over periods of time 1) PARENT MATERIALS - Parent material can influence the different developments in clay as soil evolves Classification of Parent Materials - Classification depends on the mode of placement in their current location - The properties of parent material is modified by climate, organisms, topography, and time, therefore it varies within each group of classification - Inorganic parent materials formed by material weathered from rock or transported - Organic parent materials accumulated from residues of many generations of vegetation Residual Parent Material - Develops from weathering of the underlying rock, and other soil-forming factors such as climate and vegetation - Climates that are warm and humid, residual parent material tend to be thoroughly leached and oxidized and show red and yellow colours - Climates that are cooler and drier, residual parent material tend to appear more
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