|Earth and Space Science||Structure of the Earth System 8I3.00||Process of Science||Questioning 1.2 a|
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CONTENT STANDARD: Earth and Space Science
CONTENT TOPIC: Structure of the Earth System
CONCEPT: Water passes through the water cycle dissolving minerals and gases.
CONTENT OBJECTIVE: 8I3.00 To understand the water cycle
INSTRUCTIONAL OBJECTIVE: The learner will:
TN COMPONENT OF SCIENCE: Process of Science
BENCHMARK: Shared experiences may help to develop an inquisitive mind.
1.2c Not all questions can be answered.
BENCHMARK: If more than one variable changes in an experiment, the end result of the experiment may be not be clearly attributable to any one of the variables.
The water cycle is called the hydrologic cycle. This is the cycle water makes as it passes from sea to land and land to sea. Moisture in the form of rain, sleet, hail, or snow falls to earth from the clouds. Some of this moisture evaporates from the ground and goes back into the air. (Evaporate means to go from a liquid to a gas. Water is present in the air in the form of a gas.) Plants also take in some of the water from the ground. Some of the moisture that falls to the earth will also pass into the soil. This water will move deep below the earth's surface. It can then flow into the oceans, rivers, ponds or streams where it can eventually evaporate back into the air. Questions: 1) Do you think we will run out of water if this cycle can continue? 2) What kinds of things could affect this cycle?
Almost 40 percent of the water that falls on land flows back to the sea by way of surface or underground streams. This water which flows on the surface and in rivers and streams is called runoff. There are several factors which affect the runoff. The first factor is rainfall. Rainfall in itself is affected by several factors. Rainfall not only depends on the amount of moisture, but also the rate of precipitation and the temperature. If there is snow or gentle rains, there will be more evaporation and absorption of the moisture than runoff. Heavy rains can cause rapid runoff. Warm temperatures increase evaporation and cooler temperatures encourage runoff. Gradient is another important factor in determining the rate of runoff. Steep hills or slopes promotes runoff where as gentle slopes or flat areas allow the water to evaporate or pass into the ground water zone. The third factor affecting runoff is the type of rock on which the rainfalls. If the rock is porous, the water is able to sink into the ground. Vegetation is also important in determining whether runoff occurs or absorption of water occurs. Question: How important do you think vegetation is to the amount of runoff? Why?
Underground water comes from rainfall that sinks into the ground. Some underground water is used by plants, some of it evaporates, and some of it is stored in rocks. However, most of the water that sinks underground will eventually rejoin the river system.
The zone of aeration is the upper rock layer through which water can trickle easily. Rainwater does not usually remain in this zone but continues its path downward. Rock openings have air except when it rains; it is this presence of air that gives the zone its name aeration. At the bottom of this zone some of the water is held in rocks by capillary attraction. Capillary tubes are very small tubes. The capillary action is possible because of the attraction the water has for the rock and the rock for the water.
The ground water zone or zone of saturation is right below the zone of aeration. The top surface of the ground water is referred to as the water table. Question: If you have a well, see if you can find out how deep it is to the water table. The bottom of this zone is usually a layer of rock which has no openings. The depth of the water table varies because of the amount of rainfall. Therefore, the water table is usually higher during the dryer seasons or times of drought. Question: Could the height of the water table determine the amount of water usage we have.
Gravity is the force that causes the ground water to move from higher elevations to lower elevations. Ground water usually follows the flow of surface water but flows more slowly. The movement of ground water usually depends on the slope of the rock layers, the permeability of the rock, and the supply of water. The results of this movement of ground water can produce aquifers, artesian water, springs and seeps. An aquifer is a rock which stores water in pores that are connected. Aquifers are usually made of sandstone, gravel, or sand. Artesian water is a natural upward movement of water due to the fact that water is held under pressure between layers of impermeable rock. A spring may occur when water reaches the surface under pressure and flows through an opening. Question: Have any of you ever seen an aeration well or a natural spring? Describe what you saw. A seep is a place where water oozes out only enough to moisten the ground.
Ground water is composed of rainwater which is a weak acid because it contains carbon dioxide dissolved in water CO2 + H2O --> H2CO3 (carbon acid). If the rainwater flows over limestone, it may carry with it dissolved minerals. If ground water contains more than 8 grains of mineral per gallon it is referred to as "hard" water. "Soft" water contains very little dissolved minerals. Water is considered hard if it contains calcium sulfate, or calcium, magnesium and iron carbonates in solution. Calcium Carbonate (CaCO3) is the most common mineral in hard water. Hard water does not lather well when soap is added and it sometimes leaves a ring of deposits on tubs and sinks. Question: Do you have hard or soft water at your home? How so you know? If you do not know try to find out.
Ground water transports many deposits and may help to concentrate these deposits of valuable minerals such as gold, silver, lead, copper. Sometimes petrified wood results when the wood fibers are replaced by silica (SiO2). Complete petrifaction takes many years. Stalactites are deposits of CaCO3 suspended from the ceilings of caves. Stalagmites are deposits of CaCO3 built up from the floor of a cave. Sometimes the two will meet and a column forms. Question: Have you ever been to a cave and seen stalactites and stalagmites? Share your experience with the class.
Ground water has many important uses. First, it transports and concentrates minerals for use by man and industry. However, the most important use of ground water is to help supply water for drinking and other needs of man and animals. Many surface water supplies are not adequate or are polluted; therefore, ground water must help supply our needs.
2. If a stream table is available, have students simulate different heights, amount of rain, etc. to determine the effects of runoff.
3. Stand two open-ended tubes of sand upright in a shallow pan or plate. Pour water into one tube until the sand is saturated and some of the water runs down into the pan or plate. What happens in the other tube of dry sand as the water reaches it?
4. Place a stalk of celery or a white carnation into a glass jar. Add water and a few drops of food coloring to the glass jar. Observe over several days. What happens to the celery or white carnation?
5. Set up 4 paper cups as follows:
a. Fill one cup 1/2 full of sand
b. Fill one cup 1/2 full of clay
c. Fill one cup 1/2 full of gravel
d. Fill one cup 1/2 full of a mixture of sand, clay, and gravel.
e. Punch 3 or 4 holes in the bottom of each cup.
f. Pour the same amount of water through each cup.
g. Note the permeability of each substance and the appearance of water after it has run through the cup.
2. From which cup did the cleanest water flow? the dirtiest water?
3. How would you describe the residual water from the cup of clay, sand, gravel?
4. Which type of soil would you consider to be the most permeable or can you say? Explain your choice.
Solute-substance to be dissolved
Solvent-substance that does the dissolving
Hydrologic cycle-cycle of water as it passes from sea to land and land to sea.
Evaporate-a phase change from a liquid to a gas below the boiling point
Runoff-water which flows on the surface and in rivers and streams.
Underground water-comes from rainfall that sinks into the ground
Zone of aeration-upper rock layer through which water trickles easily
Aeration-presence of air or oxygen
Capillary-small tube-like container
Zone of saturation-the zone right below the zone of aeration.
Aquifer-a rock which stores water in pores that are connected.
Artesian water-natural upward movement of water due to pressure
Spring-water reaching the surface through an opening in the rock
Seep-gentle oozing of water which just moistens the ground
Hard water-contains 8 grams of mineral per gallon of water.
Soft water-contains few dissolved minerals.
Stalactite-deposit of calcium carbonate hanging from ceiling in a cave.
Stalagmite-deposit of calcium carbonate produced on the floor of the cave
This is the time this file has been accessed since 04/04/98.
The University of Tennessee at Martin is not responsible for the information or views expressed here.
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