Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. The “homemade” rock sample in the Prelab Activity should be prepared two to three days before starting Part 8 of the Procedure.
2. Obtain local soil samples for use in Parts 1 and 2 of the procedure. Gathering soil samples may be done by the students or by the instructor.
3. Each lab group will also need two local rock samples for Part 4 of the procedure. Gathering of rock samples may be done by the students or by the instructor.

Safety Precautions

Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Use extreme care when performing the demonstrations using heat and also those resulting in broken glass. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All materials may be thrown away in the trash or flushed down the drain according to Flinn Suggested Disposal Methods #26a and #26b.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs.
• Three to four class periods will be required to complete parts 1–9 of the procedure. Part 10 of the procedure will require roughly two weeks before final observations may be recorded.
• Soil with some “diversity of material” works best for Parts 1 and 2 of the procedure.
• The glass vial should be placed in a freezer by the instructor in Part 6 of the procedure. Contact cafeteria personnel and see if their freezer may be used if available. If the vial is placed in the cafeteria freezer, it should be placed within a larger container, such as a Styrofoam^® cup to avoid leaving glass pieces behind in the freezer.
• Part 7 of the procedure may be completed in the laboratory by students or it may be done as an instructor demonstration. A hot plate or Bunsen burner should be used in this part. Make sure gloves and safety glasses are worn.

Further Extensions

• Have students investigate different rock types and the types of soil they form when decomposed.
• Have students design a procedure or demonstration to show the effects of wind erosion.
• Have students investigate the drainage rate and porosity of different soil types. Flinn Scientific sells a Porosity and Drainage Rate of Soil Kit, Catalog No. AP5313, that introduces students to these topics.

Sample Data

Answers to Questions

Part 1. Soil Observation

1. How would you describe your soil sample (e.g., clay, sand, topsoil)?

   The soil sample was similar to rich topsoil.

2. Was any evidence of once living material found in the soil sample? Explain.

   There were pieces of plant roots in the soil sample.

Part 2. Rock Observation

1. Were any rock fragments found in the soil?

   There were a few rock fragments in the soil.

2. If so, how are the rocks different than the soil?

   The rocks were more jagged and lighter in color than the soil.

Part 3. Water Erosion

1. How did the “raindrops” simulation affect the soil sample?

   Each “raindrop” made a circle about 5 mm in diameter.

2. How did the “rill” simulation affect the soil sample?

   An oval-shaped ditch was formed. An excess of displaced sand surrounded the ditch.

3. How did the “gully” simulation affect the soil sample?

   A large area of sand was displaced in this sample. A bare spot on the surface of the pan was formed.

Part 4. Geological Changes

1. What happened to the two rocks as they were rubbed together?

   The rocks formed whitish/pink, fine, sand-like particles.

2. What could this possibly be simulating?

   Rubbing the rocks together simulates the geological erosion of rock.

Part 5. Glacial Changes

1. What happened to the surface of the ice cube?

   The surface of the ice cube became scraped by the sand.

2. Describe what happened to the surface of the Styrofoam block.

   The surface of the Styrofoam became rough.

3. Predict what would happen if a glacier moved across the surface of land.

   A glacier would erode the surface of the land, remove existing soil particles and create valleys.

Part 6. Ice Expansion

1. Explain what happened to the glass vial.

   The glass vial broke into two pieces. The water expanded when it froze—this increased the pressure on the surface of the glass and caused the vial to shatter.

2. Give an everyday example of ice expansion.

   Cracks in the pavement.

Part 7. Expansion and Contraction Effects

1. Judging from the heating and rapid cooling of the glass vial in this procedure, what do you think happens to rocks as they are heated and cooled?

   As rocks are heated and then cooled, they may fracture into smaller pieces.

Part 8. Chemical Processes

1. What happened when water was placed on the homemade rock?

   The water spread out and went into the small pores of the rock.

2. What happened when vinegar was placed on the homemade rock?

   When vinegar was placed on the rock, a gas was formed. Bubbles formed on the rock and cracks were created in the rock.

3. Vinegar is an acidic solution. Using what was learned in this procedure, what effect do you think acid rain has on rocks?

   Acid rain would cause erosion and breakdown of rock.

Part 9. Organic Processes

1. How did the growing bean seeds affect the simulated rock in this procedure?

   The growing bean seeds caused the simulated rock to crack. This cracking increased as the bean seedlings grew.

2. Name two everyday or common examples of “organic” soil disruption.

   Growing plant roots, animals digging tunnels, etc.

Introduction

Perform a series of hands-on reactions to understand the chemical and physical processes involved in rock and soil formation and decomposition.

Concepts

• Soil
• Erosion
• Rock
• Rock cycle

Background

Soil is the bridge between the living and non-living world. Most life on Earth depends on soil and it is ultimately where most of our food originates. Soil is composed of minerals, organic material (also known as humus), water and air. Although the composition of soil may vary from region to region, the major components do not. Most soil contains roughly a one-half mix of minerals and humus and a remaining half that consists of pore spaces where air and water can be circulated.

Under ideal circumstances, new soil accumulates at a rate of 4 tons per acre per year. This is enough soil to completely cover the surface of one acre with 1 mm of soil. Under poor conditions, it may take thousands of years to build that much soil. In some parts of the world, as much as 2.5-cm of topsoil is lost per year due to soil erosion. Soil erosion is a natural phenomenon that occurs at a much faster rate today than it did in the past. Extensive farming, logging and loss of shrubs and other vegetation have all dramatically increased soil erosion rates.

Soil erosion is part of the constant movement and recycling of Earth’s material called the rock cycle. The rock cycle illustrates the origin of the three basic rock types (igneous, sedimentary and metamorphic) and the role of geological processes that transform one type of rock into another (see Figure 1).

Three general processes contribute to the breakdown of rock—physical processes, chemical processes and organic processes. Examples of physical processes include glacial activity, water erosion, wind erosion and ice expansion.

Thousands of years ago, glaciers covered much of the Earth. Glaciers are thick ice masses that originate on land from the accumulation and compaction of snow. Most of the soil present in North America today was formed and deposited by glacier movements. As these large glaciers moved (or flowed), they exerted a great amount of force on the rocks and other surfaces below them. Glaciers erode land in two ways—plucking and abrasion. Plucking occurs when a glacier moves over a fractured rock surface and loosens and picks up large pieces of rock. Abrasion occurs when a glacier and its load of rock pieces moves along and grinds away at the surfaces of the Earth. Glaciers are responsible for formations such as the Alps and Yosemite Valley.

As each drop of rainwater hits the surface of the Earth, small amounts of soil particles are moved. As the rainwater moves over the surface of the Earth, it carries small bits and pieces of soil and rock fragments that eventually wear away or erode the Earth’s surface. In early stages, the water flowing across the Earth’s surface is originally in the form of thin sheets of water. This movement of thin sheets of water is known as sheet erosion. After flowing for relatively small distances sheet erosion generally develops into small channels known as rills. As the water moves through the rills, still larger depressions or cuts in the soil form and are called gullies. As water moves through gullies, a large amount of the dislodged soil particles are deposited in a new location. The newly deposited soil and rock fragments are called sediment. The most well known example of water erosion is the Grand Canyon.

Moving air, just like moving water, is capable of picking up particles and causing erosion. Wind erosion is most prevalent in arid regions where particles are not likely to bind to surrounding vegetation. A great example of wind erosion occurred during the 1930s in many parts of the Great Plains states. Extensive grazing and plowing over of vegetation followed by severe drought and high winds led to the right conditions for a major dust storm called the Dust Bowl. During the Dust Bowl the high winds and flying particles were so overwhelming that at times, no sunlight struck the surface of the Earth.

Ice expansion is another form of a physical change. Ice is less dense and takes up more room than the same amount of water. This explains why ice cubes float in a glass of water. When water freezes it expands. If water seeps down into small crevices or cracks of rock and then freezes, a great amount of pressure will be exerted on the rock. An example of this pressure is seen in the formation of potholes in roads. Rainwater and snow seep into small cracks in the road. As the water freezes pressure is exerted on the road and potholes and cracks will form.

Chemical processes break down soil and rock as well. Water plays the most important role in this breakdown. Although water itself is not generally chemically reactive to rock, a small amount of dissolved material can really cause an impact. For example, oxygen, O₂, dissolved in water will oxidize certain materials. Rocks containing iron-rich materials will actually develop a rust layer due to the dissolved oxygen. Carbon dioxide, CO₂, dissolved in water, H₂O, forms carbonic acid, H₂CO₃. Carbonic acid ionizes to form very reactive H⁺ ions and the bicarbonate ion, HCO₃^–. Hydrogen ions, H⁺, attack and disrupt the chemical makeup of various types of rock.

Erosion also occurs due to organic processes. Activities of organisms, such as plants, animals and humans, can cause stress on the Earth’s surface. Rapidly growing plant roots looking for minerals and water can break apart rocks. Animals that dig tunnels can disrupt soil and fragment rocks as they burrow. Decaying organisms can also be acidic and can further lead to the chemical decomposition of rock. Humans also destroy soil and rock formations in the search for minerals or during road construction.

Materials

Prelab Questions

Preparation of a “Homemade Rock”

1. Obtain an aluminum dish.
2. Using a marker, label the bottom of the aluminum dish with your group’s initials.
3. Place two spoonfuls of sand and two spoonfuls of sodium bicarbonate in the aluminum dish.
4. Mix the sand and sodium bicarbonate together with a spoon.
5. Add water one drop at a time until a thick paste forms.
6. Form the mixture into a mound and let it sit for 2–3 days. The homemade rock will be used in Parts 8 and 9.

Safety Precautions

Follow all normal classroom guidelines. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part 1. Soil Observation

1. Obtain a new aluminum dish.
2. Use a marker and label the dish with your group’s initials.
3. Place a locally collected soil sample into the dish.
4. Using a magnifying glass, examine the soil and record all observations in the data table. Record information such as shape, size, color and presence of any living or once living material.
5. Answer the questions for Part 1—Soil Observation.

Part 2. Rock Observation

1. Locate any rocks or rock fragments in the local soil sample from Part 1.
2. Using forceps or tweezers, remove the rock fragments from the soil.
3. Use a magnifying glass to examine the rock fragments. Record all observations in the data table.
4. Answer the questions for Part 2—Rock Observation.

Part 3. Water Erosion

1. Place a thin layer of sand in a shallow pan.
2. Obtain a Beral-type pipet filled with water. Place drops of water on top of the sand—one drop at a time. Each drop of water represents a drop of rainwater. Record observations in the data table.
3. Refill the pipet with water. This time, squeeze the water out of the pipet all at once on top of the sand. This will represent a rill. Record all observations in the data table.
4. Obtain a 250- or 500-mL beaker of water. Pour all of the water from this container on top of the sand at once. This will represent a gully. Record all observations in the data table.
5. Dispose of the sand/water mixture as directed by your instructor.
6. Answer the questions for Part 3—Water Erosion.

Part 4. Geological Changes

1. Obtain two local rock samples and a white sheet of paper.
2. Simulate geologic changes on a miniature scale by rubbing the two rocks together over the white sheet of paper. Record all observations in the data table.
3. Answer the questions for Part 4—Geological Changes.

Part 5. Glacial Changes

1. Obtain an ice cube, sand, a paper towel and a Styrofoam tray.
2. Sprinkle a small amount of sand onto the Styrofoam tray.
3. Using a paper towel, hold onto the ice cube.
4. Slowly move the ice cube over the sand while pushing the ice cube down on the Styrofoam tray. The weight being placed on the ice cube simulates the many feet of ice and snow in a glacier.
5. After the ice cube has been moved over the surface of the Styrofoam tray, lift it up and record all observations in the data table.
6. Gently wipe the sand off of the Styrofoam tray. Describe the surface of the Styrofoam tray in the data table.
7. Answer the questions for Part 5—Glacial Changes.

Part 6. Ice Expansion—(Teacher Demonstration)

1. Fill one vial to the top with tap water. Let this vial sit for a minute to allow the gas bubbles to escape. Leave the other vial empty.
2. Seal the water-filled vial tightly to be sure there is no air left in the container.
3. Wrap the water-filled vial with a paper towel.
4. Place both the water-filled vial and the empty vial in a freezer.
5. The following class period, observe what happened to each of the vials.
6. Have students record all observations in the data table.
7. Answer the questions for Part 6—Ice Expansion.

Part 7. Expansion and Contraction Effects—(Teacher Demonstration)

Note: Demonstrator should wear safety glasses.

1. Use the empty vial from Part 6, a heat source, 500-mL beaker filled with cold water and tongs.
2. Remove the top from the empty vial.
3. Grasp the vial with tongs and heat for one minute.
4. After one minute of heating has passed, drop the vial into a beaker of cold water.
5. Have students record observations in the data table.
6. Have students answer questions for Part 7—Expansion and Contraction Effects.

Part 8. Chemical Processes

1. Obtain the homemade rock created in the Prelab Activity.
2. Use a magnifying glass to observe the hardened homemade rock. Record all observations in the data table.
3. Break the rock into two pieces and leave one piece in the aluminum dish. Place the other half of the homemade rock in another aluminum dish.
4. Add five drops of water to one-half of the homemade rock. Observe what happens to the rock. Record all observations in the data table.
5. Add five drops of vinegar to the other half of the homemade rock. Observe what happens to the rock. Record all observations in the data table.
6. Answer the questions for Part 8—Chemical Processes.

Part 9. Organic Processes

1. Obtain a new aluminum dish.
2. Label the bottom of the dish with your group’s initials.
3. Place two spoonfuls of calcium sulfate in the dish.
4. Add water until the calcium sulfate forms a thin paste.
5. Add 10 bean seeds to the dish.
6. Observe the simulated rock for the next two weeks and record all observations in the data table.
7. After two weeks have elapsed, answer the questions for Part 9—Organic Processes.

Student Worksheet PDF

10540_Student.pdf