Soil and Weathering Lab Report on Planet Earth’s Geology
Order ID:89JHGSJE83839 Style:APA/MLA/Harvard/Chicago Pages:5-10 Instructions:
Soil and Weathering Laboratory 4
___________________________
(name)Background
Soils are universal features of the Earths surface. You run into them daily, but
probably give them little notice or think of them as the dirt that your family grows
vegetables or flowers in. However, with a little thought, you might reach the conclusion that without soils much if not all of the terrestrial animal life of our planet would not be able to survive!
The United States Department of Agriculture National Resources Conservation
Service (NRCS) defines a soil as follows:The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants.
The upper limit of soil is the boundary between soil and air, shallow water, live
plants, or plant materials that have not begun to decompose. Areas are not
considered to have soil if the surface is permanently covered by water too deep
(typically more than 2.5 meters) for the growth of rooted plants.The lower boundary separating soil from non-soil is difficult to define. Commonly, soil grades at its lower boundary to
hard rock or to earthy materials virtually devoid of animals, roots, or other marks of
biological activity. For purposes of classification, the lower boundary of soil is
arbitrarily set at 200 cm (2 m).Soil Formation
There are three main processes that take place at the Earths surface, or very near it, that contribute to soil formation. These processes are weathering, water, and organic activity
1. Weathering processes include chemical and physical processes. For example,
chemical reactions occur when minerals come in contact with air and water. Some reactions involve volume expansions which in turn produce internal stresses that can physically break the rock into smaller and smaller bits and pieces. In short, weathering contributes to the formation or production of new material as loose debris, mineral grains, and ions in solution.2. Water is a relatively ubiquitous solvent on planet Earth. As rain falls on the Earth some runs off into streams and gutters while some infiltrate the cracks and holes produced by weathering and biological activity. As water percolates downward it carries dissolved ions derived from chemical weathering and clay particles derived from physical weathering. The region within the soil where this activity takes place is referred to as the zone of leaching. To reiterate, the zone of leaching is where the removal or extraction of ions and small clay particles occurs. Further down the removed clay particles may be deposited and the ions can precipitate as new minerals. That part of the soil profile where deposition precipitation occurs is called the zone of accumulation.
3. Organisms within soils consume nutrients from it, mix and redistribute soil particles, and build burrows for shelters. For example, earthworms and microbes physically mix and break up the soil, and their waste adds organic matter to soils. When they die they rot adding more organic material to soils. Any gardener will tell you their compost bin would not be effective without the help of worms and bugs. The accumulation of rotten organic material is called humus.
Soil Horizons
As a result of the above three processes, rock and regolith are over time converted into soil. The composition and character of the soil evolve into something very different than its starting composition. Soil forming processes act differently at different depths to produce a soil that is commonly layered in appearance. Each layer is designated a soil horizon, and a vertical section cut through a soil reveals its profile (Figure 1). Not all of the horizons shown in Figure 1 are present in every soil profile: climate and vegetation determine which will form.
Figure 1. Soil horizons in an idealized soil profile (image from world wide web). Not all the horizons are present in every soil profile.
Horizon Description
O Organic layer, almost no mineral matter. Dark in color
A
Mixed mineral and an organic layer, darker in color than those layers beneath itE
Abundance of quartz due to removal of clays, known as the zone
of leaching. Light in colorB
Deposition of ions and clays occurs here, known as the zone of accumulation.C
Contains material close to the starting composition, but may be broken up into smaller pieces. No leaching or accumulation has occurred.
R
Rock. Unweathered starting composition material found here.Table 1: Brief descriptions of the character and processes the distinguish each of the key soil horizons.
The soil profile shown in figure 1 and adjacent to table 1 contains all the horizons, but as noted earlier not all the horizons are always present. Below are two soil profiles, the first is located in a grassland whereas the second is located in a tropical rainforest. Use the descriptions provided in the table adjacent to each profile to label the horizons as either O, A, E, B, C, or R.
1. Soil profile exposed in a grassland. Label each horizon based on the given descriptions. The scale in the image is in cm.Horizon Description
Organic rich layer, lacking in mineralsContains organic material and minerals
Zone of leaching
Zone of accumulation
2. Soil profile found in a tropical rainforest. Label each horizon based on the given descriptions. Note the boy for scale.
Horizon Description
Contains organic material and minerals.Deposition of ions and clays occurs here, known as the zone of accumulation.
Contains material close to the starting composition, but may be broken up into smaller pieces.
3. When comparing the profile found in a grassland to one found in a rainforest are they the same? If not, how are they different? Which horizons didnt form in each location? Hypothesize why a horizon may be missing or did not form? You should use words like water/rainfall, weathering, rainforest, and grassland in your response.
Soil Forming FactorsFarmers and farming may be the words you associate with soils; however, ranchers, foresters, and geologists are also interested in soils and how they form. All of these professions understand that soils are not the same from one location to the next and that they may differ in composition, thickness, and texture. Crops, trees, and grass may grow well in one soil and not grow well in another soil. This difference exists because of several soil-forming factors.
A. Climate (you can think of this as rainfall and temperature)
-Large amounts of rainfall and warm temperatures accelerate chemical weathering
and soil formation.
-Less rainfall and cooler temperatures result in slower soil formation.
B. Starting Composition (Rock horizon)
-Soils can form on just about any rock type, such as basalt, granite, volcanic ash,
and even quartz=rich sandstones, to name a few.
-The starting composition controls the composition of the soil
For example, a soil-forming on basalt would be higher in iron (Fe) than one form on a quartz-rich sandstone.
-Also, soils tend to form faster on unconsolidated material like ash than hard bedrock like granite.
C. Slope (steep like a cliff or flat like grasslands)
-The steeper the slope the less soil will form
-The flatter or more gradual a slope more soil can accumulate.
-All things being equal (all soil-forming factors) soil thickness decreases
as slope increases.D. Time (the time it takes to form soil depends on the region)
-In a protected warm, moist region soils can form in 1 to 10s of years.
-In exposed cold, dry regions soils can take thousands of years to form.
E. Vegetation (what plants are growing)
-All plants add and extract different amounts of organic matter and nutrients to and from soils.
-Some plants have shallow roots while others have deep roots
Deeper roots tend to help keep soils intact and prevent/limit erosion.4. Which soil-forming factor(s) played the biggest role in producing the soil profile from question 2 based on the information you were given (i.e., it formed in a tropical rainforest and is composed of the horizons portrayed in the given image)?
5. Your answer to question 4 may or may not include climate and vegetation but lets assume it did. Now explain in three or four sentences why you think climate and vegetation played such a big role in the production of the profile. If your answer to question 4 mentioned more factors than climate and vegetation include those in your answer as well.
Soil Classification
Soil scientists worldwide have struggled to develop a classification scheme that everyone agrees upon. Here in the United States, we use the U.S. Comprehensive Soil Classification System, this system distinguishes 12 orders of soil based on physical characteristics and the environment of soil formation (Table 2). For the purposes of this lab, its not your goal to learn and be able to recognize all 12 soil types, we are going to focus on the three bolded soils. They represent the end members (young and old soils) and the soil in which our food is grown.
Alfisol Has subsurface clay accumulation and abundant plant nutrients. Forms in humid forests.
Andisol Forms in volcanic ash
Aridisol Low in organic matter, has carbonate horizons. Forms in arid environments
Entisol Has no horizons. Formed very recently.
Gelisol Underlain with permanently frozen ground.
Histosol Very rich in organic debris. Forms in swamps and marshes.
Inceptisol Moist, has poorly developed horizons. Formed recently.
Mollisol Soft, black, and rich in nutrients. Forms in subhumid to subarid grasslands.
Oxisol Very weathered, rich in aluminum oxide and iron oxide, low in plant nutrients. Forms in tropical regions
Spool Acidic, low in plant nutrients, ashy, has accumulations of iron and aluminum. Forms in humid forests.
Ultisol Very mature, strongly weathered soils, low in plant nutrients.
Vertisol Clay-rich soils capable of swelling when wet, and shrinking and cracking when dry.
Table 2: Soil Orders of the U.S. Comprehensive Soil Classification System. Note the three bolded soils.Entisols are soils that have no distinguishable horizons. They are essentially unaltered from their starting composition, which can be loose sediment or hard rock. They are common in arid regions.
Ultisol is red clay-rich soil. They are the product of continuous weathering in a wet climate found in tropical regions, and are a common soil found in the SE United States
Mollisols are soils that represent the foundation of the agricultural midcontinental
part of the United States. This soil is characterized by a thick, dark surface horizon that represents the long-term addition of organic materials. Mollisols are the state soils for Illinois, Iowa, Kansas, Montana, Nebraska, North Dakota, Oklahoma, and South Dakota.
6. Based on the above descriptions of entisol, ultisol, and mollisol, which best fits the image in question 1 of the grassland profile?7. Which best fits the image in question 2 of the tropical rainforest profile?
Below in figure 2 is a Global Soil Regions map that shows the distribution of soil types using the U.S. Soil Classification System. Notice entisols are displayed in aqua blue, ultisols in yellow, and mollisols in green.
8. The locations of entisols in figure 2 are shown in an aqua blue color. What one or two other soil type(s) appear to be found along with entisols?
8.1. Look at table 2 for the descriptions of the soils from your answer to question 8 above. Does it make sense that they would all be found alongside entisols? Why or why not and what climate region are these soils typically found in?
8.2. Using the given latitudes in figure 2 circle the combination of latitudes below that best describes where the majority of entisols seem to occur.
A. 30°N and 60°N C. 15°N and 45°N
B. 15°N and 15°S D. 15°S and 45°S9. Ultisols are displayed in figure 2 in yellow. What are the one or two other soil type(s) that can be found along with ultisols?
9.1. Look at table 2 for the descriptions of the soils from your answer to question 9 above. Does it make sense that they would all be found alongside ultisols? Why or why not and what climate region are these soils typically found in?
9.2. Using the given latitudes in figure 2 circle the combination of latitudes below that best describes where the majority of ultisols seem to occur.
A. 30°N and 60°N C. 15°N and 45°N
B. 15°N and 15°S D. 15°S and 45°S10. Based on figure 2 mollisols and alfisols form together. The latter is the state soil of California. Does this make sense based on their descriptions in table 2? Why are these soils important to you as a human?
10.1 Describe where in North America these soils form (i.e., are they only in the US?). Where are the closest mollisols and alfisols to San Diego? What does that mean about where we most likely get our food?Use figure 3, below to answer questions 11 14.
Figure 3: World map displaying arid regions in brown and tan, wet regions in dark green, and ice in white. Labeled on the left side of the map are notable lines of latitude, the equator at 0°, 30°N, and S, and 60° N and S for reference. Note that each line of latitude equals 15°.
11. In figure 3 arid regions are shown in tan and light brown. Circle the latitudes below that best describes where the majority of arid regions occur on Earth.
A. 30°N and 60°N C. 15°N and 45°N
B. 15°N and 15°S D. 15°S and 45°S11.1 Does your answer to question 11 match your answer to question 8.2?
12. In general, when people refer to the tropics they mean the area around the equator. In figure 3 wet regions are shown in dark green. Circle the latitudes below that best describes where the majority of tropical (wet) regions occur on Earth.
A. 30°N and 60°N C. 15°N and 45°N
B. 15°N and 15°S D. 15°S and 45°S12.1 Does your answer to question 12 match your answer to question 9.2?
13. Notice that there are wet regions found on Earth other than those found at the equator. Take a moment to locate these in figure 3. With these locations in mind look at figure 2. What soil type (entisol, ultisol, or mollisol) is located here?
14. In three or four sentences summarize where on Earth entisols, ultisols, and mollisols occur. You should use words like, arid regions, tan, wet regions, green, and latitude.
15. Why should you care about mollisols?
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Soil and Weathering Lab Report on Planet Earth’s Geology