GRADE: Seventh

CONTENT STANDARD: Earth and Space Science

CONTENT TOPIC: Earth's History

CONCEPT: The earth's weather is an interaction of many parts of the environment

CONTENT OBJECTIVE: 7J2.00 To understand how weather conditions contribute to weathering and erosion

INSTRUCTIONAL OBJECTIVES: The learner will:

2.01 define these terms: weather, weathering, chemical weathering, physical weathering, erosion, dune, glacier, sheet erosion, flood
2.02 identify weather conditions that contribute to weathering.
2.03 recognize the causes and effects of physical and chemical weathering
2.04 explain the process of weathering of rocks caused by changes in temperature.
2.05 compare and contrast erosion which results from the action of wind, ice, and water.

I. Introduction to weathering
II. Chemical and physical weathering
III. Weathering of rocks due to changes in temperature
IV. Weathering of rocks and land due to wind, ice, and water

TN COMPONENT OF SCIENCE: Unifying Concepts of Science

TN GOAL:

To enable students to acquire scientific knowledge by applying concepts, theories, principles and laws from life/environmental, physical, and earth/space science.

2.5 CHANGE - Interactions within and among systems may result in changes in the properties, position, movement, form, or function of systems.

2.5b Cycles of change can be extended in scales of time, space, and material.

BENCHMARK: Some changes in the earth's surface are abrupt while other changes happen very slowly.

TIME REQUIRED:

3 to 5 instructional periods

Plain white paper, pencils, magnifying glasses, gas burner, piece of glass tubing, piece of cloth, container filled with ice water, small pieces of limestone, pliers, glass jar with lid, access to a freezer, fairly large shallow box filled with dry sand, twigs or small sticks, electric fan, coffee can with lid, various kinds of sizes of rocks, three ice trays, three boards (1 ft x 4 ft), soil, sod, aluminum foil, sprinkling can, paper towels.

Chemical weathering, dune, erosion, flood, glacier, physical weathering, sheet erosion, weather, weathering

Think of all the changes that are constantly occurring on the surface of the earth. Rocks are slowly crumbling. Winds grind down rocks. Fields are losing their soil. Water carries away sediment and deposits it somewhere else. Gullies are being formed. The earth's surface is changing all the time. Water, wind, and ice are constantly at work, wearing away and building up the land. Some changes take place in a very short time. Floods can change the course of a river in a few days. Dust storms can carry huge amounts of soil away very rapidly. However, most of the big changes in the earth's surface take thousands of years. At various times, the earth is exposed to along periods of extreme cold followed by periods of intense heat. Parts of the land we see now were once under water and land forms that were once above water are now deep under the water. In most cases the changes are so gradual we cannot detect them in the span of a lifetime. Today we want to learn how our weather has built up or worn down the earth's surface to form mountains, valleys, deserts, plains, soil, lakes, and rivers. (Have students do Activity One under Active Participation.)

We usually think of rocks as being hard, solid, and unchanging. But various forces are always at work on the earth's surface, breaking up rocks and wearing them away. Rocks are formed deep in the earth or under water. As soon as the rocks are exposed, the weather begins to destroy them. Weather is the term used to describe the changing state of the atmosphere. Weather conditions such as sunshine, rain, snow, sleet, or hail cause changes in land forms and rocks. Weathering is a process by which rocks are changed due to exposure to the weather.

Some of these changes are chemical changes while others are physical changes. Chemical weathering causes chemical changes in the minerals of a rock. It usually proceeds more rapidly in warm, moist climates. Physical weathering occurs when rocks are reduced to smaller fragments without being changed chemically and it is more likely to occur in cooler, more arid climates. Among the physical processes of weathering are ice, water, wind, and changes in temperature.

The plants that grow upon the earth could not exist without the thin, loose surface layer we call soil. Weathered rock particles make up a large part of the soil; the rest is formed of the decayed products of organic matter. The weathering that results in the formation of this soil is due in large part to changes in temperature. When the sun shines on rocks, they get hot. But only the outside is hot. The inside is cooler. So the outside expands more than the inside and cracks appear in the rock. At night, the outside is cooler than the inside so it contracts more and again cracks are formed. As the cracks get bigger and bigger, pieces of rock break off. (Have students do Activity Two under Active Participation.)

Cracks in the rocks let air and water in. Weathering then goes on inside the rocks as well as on the outside. Water begins its eroding and dissolving action. If freezing occurs, the expansion of the water exerts tremendous pressure this causes the rock mass to break into smaller pieces. (Have students do Activity Three under Active Participation.)

Erosion is the wearing away and removal of soil and rock fragments by wind, ice, and water. Winds rank high among the important forces of weather that shape the surface of the earth. Winds erode rock and soil, transport the eroded material over vast areas and deposit them upon the earth. In this way, they level land here, build it up there, and scoop out hollows elsewhere. You would probably think the stronger the wind, the more effective it would be as an agent of erosion, transportation and deposition. This is not the case. Violent winds, such as tornadoes and hurricanes, are not particularly important as agents or geologic change. They do not come often enough, or stay long enough, to cover a wide enough path to be effective.

The more moderate winds that blow for hours at a stretch, time and again through centuries, are far more important in altering the surface of the earth. As winds erode the land they work with two types of material sand and dust. Usually wind does not have enough force to move pebbles and stones. When sand is carried by the wind, it drifts along close to the ground until it accumulates in hills and ridges known as dunes. The sand blows along until a plant or other object slows the moving air. Then some of the sand is dropped and forms a small drift. As more and more sand is blown against the drift, it rolls up the front and settles behind. After this has gone on for some time, a dune is formed. The wind keeps on blowing sand up the front of the dune and dropping it behind. So a dune itself may move along, covering up trees and buildings and uncovering them later on. (Have students do Activity Four under Active Participation.)

The grains of blown sand can act like tiny chisels, scratching and scraping whatever surface they strike. In a sandstorm, cars can have their paint worn off and their windows frosted in a fraction of an hour. The effect of sandblasting on rocks is much greater. The softer parts of the rocks are worn away first. This gives the rocks different shapes. The rocks are slowly worn away. Grains of sand are often swept up into the air, carried far away, and finally settle to the earth in layers. Dust storms are prevalent in the Great Plains of the United States. Dust is spread much thinner than sand and covers a much larger area. While dust storms rage, the air is filled with choking dust. After the storm passes, dust is left everywhere. Sometimes a thin layer of dust can be deposited thousands of miles away from the point of origin. Dust storms usually occur in areas where the soil is dry, powdery and bare. As strong winds blow over this bare, loose earth, the finer material is carried away and the coarser material is blown along the ground, scraping loose more dust for the wind to pick up. (Have students do Activity Five under Active Participation.)

Over much of the northern part of our country is a layer of soil and rock that was not formed there. In some places this layer is 500 feet deep. This soil came from somewhere else. Huge glaciers, moved down from the north and then melted. They brought with them many cubic miles of rock, sand, and clay. As these glaciers moved along, they picked up rocks and ground them into fragments against one another. Rock particles embedded in the lower levels and sides of the glaciers scoured rock powder from the bedrock of the glacier's path. When the ice melts, the rock fragments and powder are either immediately deposited or carried away many miles by water flowing from the glacier. As the glaciers moved they also smoothed off hilltops and filled in valleys. Niagara Falls has its present form because of them. They also formed the Great Lakes and countless smaller lakes. It takes a long time for a glacier to form.

In areas where snow is common in winter, a snowdrift may last until early spring. Toward the end, the drift does not seem like snow. It is more like ice. The snow has slowly changed into bits of ice and then has frozen into almost solid ice. This is the way a glacier forms. Each year more and more snow is added and changed to ice. A very thick layer of ice gradually forms. Then, because of gravity, this ice moves down from the mountains. The whole glacier moves along by melting and freezing again a little at a time. Some glaciers move as much as 60 to 70 feet a day. A moving glacier picks up and carries with it all the loose materials in its path. Stones held by the ice leave scratches in solid rock. The scratches show that a glacier moved over the land and also the direction in which it moved. (Have students do Activity Six under Active Participation.)

Rain plays a very important part in molding the face of the earth. Its action is partly chemical and partly physical. In considering the chemical action of rain, you must keep in mind that it is not pure water. In the atmosphere it absorbs atmospheric gases oxygen, nitrogen, carbon dioxide. It also absorbs a certain amount of nitric acid, sulfuric acid and salts. Rain, than, has a varied chemical action on the rocks and soil on which it falls. Owing to its oxygen, it oxidizes or rusts various minerals, such as iron, which it passes over. Owing to the carbonic acid or sulfuric acid it contains, it dissolves limestone and marble. (Have students do Activity Seven under Active Participation.)

The physical action of rain is quite obvious. Running water is one of the most important agents eroding the surface of the earth. During and after rainstorms and the melting of ice and snow, water may run downhill in a sheet over the land, forming what is known as sheet erosion. Sheet erosion may wash immense quantities of soil and rock fragments down slopes. The erosive effects of sheet erosion are determined by the amount of water flowing down a slope, the steepness of the slope, and the resistance of the materials over which the water travels. Sheet erosion is not nearly so erosive if plant cover is reasonably dense. The impact of the falling rain is received chiefly by the plants and the roots bind the soil particles together and make them resistant to the on rush of the water. Sheet erosion reshapes the land by washing large quantities of soil and loose rock fragments down slopes and eventually into streams. Even greater damage occurs during floods.

Flooding is brought about when rain falls in such large amounts and so fast that it cannot be absorbed by the ground. When this happens, immense quantities of water pour down along the ground. Floods also occur when sudden rises in temperature during the spring quickly melt ice and snow. There have been cases when torrential rain produces floods of mud. This occurs especially in arid lands here vegetation is scanty or entirely absent. Many people have actually drowned in the awful torrent of mud. There have also been cases where rain has produced landslides in which large masses of earth and rock slide bodily downhill. It does this by causing the disintegration of soil and adding to its eight. It penetrates into crevices and cracks in rocks causing the rock to be broken up and begin sliding downward. (Have students do Activity Eight under Active Participation.)

1. Observations:
A. (Have students go outside and walk around the campus. Observe different land forms, types of soil, and changes in the earth's surface. Ask these questions before hand:) Do you think the land near here has always been about the same as it is now? (response) What changes might have taken place? (response) Are any changes still going on? (response) What may have caused these changes? (response) Did these changes take place slowly or quickly? (response)

B. (While outside, have students take several samples of soil from different places. Have them put a little dry soil on a piece of white paper. Examine the soil with a magnifying glass. Look for bits of sand, clay, humus, rocks with sharp corners, and rocks with rounded corners. Record what you observe and answer these questions:) Is the soil sticky and crumbly or loose and porous or closely packed and hard? (pause) Does it have any plant roots in it? (pause)

2. (Have students working in fairly large groups. Have one student hold one end of a piece of glass tubing over the flame of a gas burner until it is quite hot "be sure he holds it with piece of cloth". Then plunge the hot end into a pan of ice water.) What happens to the glass? (It cracks or breaks) Have a student heat a small piece of limestone over the flame of a gas burner. The limestone should be held with pliers or in a wire basket. Then drop the limestone quickly into a pan of ice water. What happens to the limestone? (It cracks or breaks) Why did the glass and the limestone crack? (The heat makes the molecules in the glass and limestone expand. The ice water forces the molecules to contract suddenly. The sudden changes cause the glass and limestone to crack.) Have students lay a stone on heavy piece of metal or wood. Cover it with a cloth to keep pieces of rock from flying out and break the stone with a hammer. Observe the inside. Is the inside like the outside? (No) Why? (The inside should be harder and less stained because it has not been exposed to weathering.)

3. (The entire class can observe the results of this investigation. Have a student pour water into a glass jar until it is completely full. Screw the lid on tightly. Wrap the jar in a cloth and put it in a paper bag. Put it in the freezer. Leave it there overnight. The next day have students examine the jar.) What happened? (The jar cracked and broke.) Why? (The volume of water increased because water expands when it freezes.) (If no freezer is available in your school you could set the jar in a small pail and pack a mixture of chipped ice and salt around it.) (This activity can be done with the entire class observing or in fairly large groups. It is best done outside. Have a shallow box filled with dry sand. Set twigs or sticks upright in the sand to slow down the moving air. Turn on an electric fan and direct the air movement on the sand. "Have students stand where the sand cannot blow into their eyes." They should carefully observe the formation of a dune.)

5. (Have students working in groups. Place rocks of various kinds and sizes in a coffee can with a lid. Cover the can with the lid. Have five or six students shake the can very hard about 100 times each.) Take the lid off and observe what has formed in the bottom of the can. (Small pieces of rock and sand) How might weather do the same thing in nature? (Wind blows sand and small rocks against other rocks, wearing away the surface.)

6. (Have students fill three ice trays "remove the centers" with water and put in rocks of various kinds and shapes and sizes. Freeze overnight. Take the glaciers outside. Create your own inclines by raising one end of a long board on which you have put a layer of wet soil its entire length; raise another board on which you dump dry soil; raise one end of the third board on which is a layer of sod. Loosen the ice from the trays and place one glacier at the top of each board. Observe the progress as the ice and rocks begin to melt and move downward.)

7. (Visit an old cemetery. The effects of chemical weathering shows up on old tombstones made of marble. Sandstone tombstones often show scaling and flaking. Granite tombstones may show only slight discoloration. Observe and record dates so students can see ho much time weathering takes. "Be sure to warn students never to touch, pull or lean on the stones")

8. Observing the effects of flooding:

A. (If it should rain during this unit have students collect samples of stream water after the rain. Allow the water to settle at least 24 hours. Observe the settling of fine silt and clay.)

B. (Have students make a pile of soil about a foot high in a large container. You could use a shallow cardboard box covered with aluminum foil. Use a sprinkling can to produce an imitation of heavy rain. Tilt the container and place paper towels at the lower end. Now pour the water from the sprinkler over the soil.) Observe, what happened? (The soil is carried away.) Is it all deposited in one place? (No) What shape do the deposits on the paper towels have? (Probably fan shaped) Now pile the soil back up and put a layer of sod on top of the soil. Repeat the experiment. What happened this time? (Very little soil washes down onto the paper towels - grass helps control erosion.)

You have learned many ways that rocks are constantly being broken up, worn away, and carried away all due to the weather. Rocks exposed to the atmosphere are changed by a process called weathering. Water, oxygen, and carbon dioxide may change them chemically into softer materials. Expansion and contraction during changes of temperature and the freezing of water in cracks breaks even the hardest rocks into pieces. Moving water, wind, and ice all grind rocks together and wear them down and even transport them to other areas.

chemical weathering - process that causes a chemical change in the minerals of rocks

dune - mound, or ridge, of loose sand heaped up by the wind

erosion - the wearing away and removal of soil and rock fragmented by wind, ice, and water

flood - immense flow of water over what is usually dry land caused by so much rainfall that it cannot be absorbed by the ground

glacier - a large mass of ice formed from snow wherever winter snowfall exceeds summer melting

physical weathering - process whereby rocks are reduced to smaller fragments without being changed chemically

sheet erosion - the process of erosion hereby water during and after a heavy melting runs downhill in a sheet

weather - term used to describe the changing state of the atmosphere with respect to sunshine, rain, snow, sleet or hail

weathering - process by which rocks are changed by exposure to the weather

This is the time this file has been accessed since 04/02/98.

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