EAES 101: Global Environmental Change Spring 2018 Possible Short Answer Question
ID: 289022 • Letter: E
Question
EAES 101: Global Environmental Change Spring 2018 Possible Short Answer Question 4: (20 points total) Think about the regolith under our feet and the key players. A) Identify one physical process and one chemical process that converts bedrock into regolith. For each process, write one to two sentences describing how this process produces regolith. (hint: make sure that you identify which process is the physical and which process in the chemical) (4 points) B) Soil is a part of regolith, but not all regolith is soil! Identify the key processes and components (maybe call them ingredients) needed to produce soils. (2 points) C) Sketch a complete (and idealized) soil profile, making sure to label each horizon. Identify which horizon(s) is/are in the zone of leaching and which is/are in the zone of accumulation. For each horizon, identify one observation you could make about that horizon that would be helpful for differentiating it from the others. Additionally, for each horizon, identify the primary composition/materials making up that layer. (10 points) D) Identify and discuss two ways in which soil profiles in the desert differ from soil profiles in the tropics. For each difference, write one to two sentence discussing how the difference reflects the differences in climate. (4 points)Explanation / Answer
A) Regolith is largely a product of weathering. The process of weathering and erosion affect bedroc. Outcrops exposed to wind and water are often decomposed, or weathered, overtime into regolith and erosion affect bedrock. Bedrock can also become regolith as a result of mechanical weathering, a process that breaks the rock into smaller pieces through the application of a force, such as thermal expansion, freeze-thaw cycles, or scouring by particles carried by wind and water. Plant roots can also assist the weathering process by penetrating and widening cracks already present in the rock.
The chemicals can alter the rock’s mineral content over time, breaking down some material into smaller components and separating it from the bedrock layer.
B) Soil is the part of the regolith that supports growth of the plants. The soil formation is the formation of two consequetive stages.
1) The wearthering of rock into regolith
2) The formation of true soil from regolith
The factors need for these process are parent material, relief , time, climate, vegetation &organism.
C) A soil horizon makes up a distinct layer of soil. The horizon runs roughly parallel to the soil surface and has different properties and characteristics than the adjacent layers above and below. The soil profile is a vertical section of the soil that depicts all of its horizons. The soil profile extends from the soil surface to the parent rock material.
There are 5 master horizons in the soil profile. Not all soil profiles contain all 5 horizons; and so, soil profiles differ from one location to another. The 5 master horizons are represented by the letters: O, A, E, B, and C.
O: The O horizon is a surface horizon that is comprised of organic material at various stages of decomposition. It is most prominent in forested areas where there is the accumulation of debris fallen from trees.
A: The A horizon is a surface horizon that largely consists of minerals (sand, silt, and clay) and with appreciable amounts of organic matter. This horizon is predominantly the surface layer of many soils in grasslands and agricultural lands.
E: The E horizon is a subsurface horizon that has been heavily leached. Leaching is the process in which soluble nutrients are lost from the soil due to precipitation or irrigation. The horizon is typically light in color. It is generally found beneath the O horizon.
B: The B horizon is a subsurface horizon that has accumulated from the layer(s) above. It is a site of deposition of certain minerals that have leached from the layer(s) above.
C: The C horizon is a subsurface horizon. It is the least weathered horizon. Also known as the saprolite, it is unconsolidated, loose parent material.
D) The soil profiels in desert differ from soil profiles in the tropics. Because of
The rainfall varies from just a few millimetres in the desert areas of the world to several thousand millimetres in the tropics.
The rocks of the earth are also very variable from one country to another and these differences mean that soils will also be different.
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