weathering and erosion (and “how did the picture get...

Unit Plan: Weathering, Erosion, petroglyphs

Content Areas: Earth Science and Social StudiesAuthor: Carolyn FlahartyGrade Level: 4th – 8th Time Required: 4 to 6 class periods (60 minute)

Standards:Science Standard 1: Students apply the processes of scientific investigation and design, conduct, communicate about, and evaluate such investigations

Science Standard 4: Earth and Space Science: Students know and understand the processes and interactions of Earth's systems and the structure and dynamics of Earth and other objects in space.

Science Standard 5: Students understand that the nature of science involves a particular way of building knowledge and making meaning of the natural world.

Geography Standard 3: Students understand how physical processes shape Earth's surface patterns and systems.

Objectives: The student will… Know that mechanical weathering and chemical weathering are the two main

types of weathering. Know what a petroglyph is and how it is created. Understand the difference between weathering and erosion. Simulate types of weathering and erosion in a lab setting. Identify weathering and erosion processes depicted in photos. Use an index to assess the type and amount of weathering impact on petroglyphs

depicted in photos.

Materials:1. Photos of weathered rocks, some containing petroglyphs POWERPOINT2. Lab sheets and materials for each lab. (Lab sheets are attached and can be

photocopied. Materials for each lab are listed in the lab descriptions.)3. Science Notebooks, one per student4. Weathering assessment index (attached—will need one copy per student)

Vocabulary:WeatheringChemical weatheringMechanical weatheringAbrasion SedimentOxidationErosion Petroglyph

Background: Students should have some understanding of the rock cycle and the characteristics of different types of rocks.

Lesson 1: Rock Weathering (2 - 3 Class Periods)

Preparation:Arrange students into groups of 4.Set up and review power pointSet up lab stations, or plan teacher demonstrations, for weathering simulations

Part 1—Engage (POWERPOINT Presentation) Do rocks last forever? Provide students with 3-5 photos of weathered rocks, some containing

petroglyphs. POWERPOINT Ask the students to observe the photos carefully and write down in detail what

they see. (Allow at least 5 minutes) Have students share their observations, and create a class list. In the photos with

petroglyphs, if students only described the glyphs, ask them to look again at the photos and describe the rock that contains the artwork.

Ask students what is happening to these rocks. Is there evidence that the rocks are changing?

What are some forces that might cause a rock to change size, shape, texture, color, or location? (Create a list of student answers.)

Post and discuss the definitions of weathering and erosion (leave up throughout the unit):

Weathering refers to the destructive forces that change the physical or chemical character of a rock at or near the earth’s surface. There are two main types of weathering: mechanical and chemical.

Mechanical weathering is the breaking apart of the rock into smaller pieces by physical force without changing its chemical composition. Chemical weathering is the breakdown of rock from exposure to water and atmospheric gases (mainly carbon dioxide, oxygen, and water vapor), resulting in the creation of new chemical compounds.

Erosion is the movement or carrying away of weathered rock by water, wind, or other agents.

Part 2 -- Explore Students work in groups at lab stations. BE SURE TO USE SAFETY

PRECAUTIONS, INCLUDING GOGGLES. Students record each lab in science notebooks: Date, Question/Problem/Lab

Name, Prediction, Materials, Procedure, Observations, (Drawings/Diagrams), Claims and Evidence, Conclusion, Reflection

Students will follow directions on lab sheet for each lab.

Lab #1 Mechanical Weathering (Freeze-Thaw)

Lab #2 Mechanical Weathering (Abrasion)

Lab #3 Chemical Weathering (Acid)

Lab #4 Chemical Weathering (Oxidation)

Part 3 Explain:

Students will record observations, drawings, data, and conclusions in science notebooks. Each lab sheet will also have questions for students to answer about that lab that will extend their thinking.

When all labs have been completed, bring the students together for a discussion. Allow them to share their findings and answer any questions they may have.

Summarize/ Review weathering: (POWERPOINT) Weathering is nature’s way of breaking rocks down into smaller pieces. Weathering

is a long and slow process. That is why we think that rocks last forever. There are two major types of weathering: mechanical and chemical. Mechanical

weathering causes rock to break into smaller fragments without changing the chemical make-up of the rock. Chemical weathering is the process of changing the make-up of rock through chemical reactions.

In nature, mechanical and chemical weathering usually occur together. Fractures (or cracks) in rocks are expanded slowly by frost action or plant growth (roots pry into fractures). This exposes more surface area of the rock to chemical weathering.

Mechanical weathering continues until the rock slowly falls apart. Most chemical weathering is caused by water. Water can dissolve most minerals that

hold rocks together. Oxidation is the process in which oxygen chemically combines with another

substance. The result of oxidation is the formation of an entirely different substance (such as rust in the demonstration we did)

Acids can also cause chemical weathering. When carbon dioxide from the atmosphere dissolves in water, a weak carbonic acid is formed. This acid can dissolve some types of minerals. Another acid that causes chemical weathering in rocks and minerals is sulfuric acid from acid rain. Plants can also produce weak acids that dissolve minerals.

Examples of mechanical weathering include temperature, freeze/thaw, plant and animal (including human) activity, and abrasion.

Weathering breaks down rock into loose particles that can be easily eroded. Erosion is the movement or carrying away of weathered rock by water, wind, or other agents.

(Note: Photos or examples of rocks that show the different types of weathering, if available, should

be included as visuals–SEE POWERPOINT)

Lab #1: Freeze/Thaw

Materials: (For each group)Plastic zip-lock baggiesBall of potter’s clay (fist-size)Water Masking tapeMagnifying glass

Prediction:What will happen to the clay as it freezes and thaws?

Procedure:1. Moisten the ball of clay with a small amount of water,2. Observe and record its appearance (in your science notebook, make a table like the

one below).3. Divide the clay into two equal pieces and roll each piece into a ball or form it into a

square.4. Place each piece in a separate plastic baggie and seal the baggie; label both pieces

with your group members’ names on a piece of masking tape. 5. Place one piece of clay in the freezer and leave the other piece on the counter. Let the

clay remain in the freezer overnight. 6. The next day, take the clay out of the freezer and remove both pieces from the plastic

bags.7. Observe. (Use a hand magnifying glass) Do the clay pieces look different? If so,

how? Record your observations in the table.8. Put the clay pieces back in the plastic baggies and return the one piece to the freezer;

the other will remain sitting on the counter. 9. The next day, observe and record the appearance of both pieces of clay. 10. Repeat steps 8 and 9.

Original Appearance

Appearance after day 1



Clay on counter

Clay in freezer

Questions:

1. What happened to the clay as it was frozen and thawed several times? Was this what you had predicted would happen?

2. Is this an example of mechanical or chemical weathering?3. How did the frozen clay differ from the other clay?4. Draw a picture or diagram showing the difference between the frozen clay and the

unfrozen clay after three days.5. How does this demonstration simulate what happens to a rock in a natural setting?6. In what type of climate would freeze/thaw weathering be common?7. What other forces, other than freeze/thaw, can cause cracks to form and/or expand in

a rock?

Lab #2: Abrasion

Materials:2 sandstone rocks (approx. 8 cm in length and width)2 granite, feldspar or quartz rocks (approx. 8 cm in length and width)a twig or small tree branch2 sheets of white copy paperSet of measuring spoons

Predictions:What will happen when two of the stones are rubbed together? What will happen when the twig is rubbed back and forth across the surface of a stone?Will the results be different for different stones?

Procedure:1. Copy this table into your science notebook and fill in your results2. Rub the two pieces of sandstone together over a sheet of white paper.3. Observe the results and measure (or describe) the amount of dust produced; record it

in the table.4. Repeat steps 1 & 2, this time using sandstone and one of the other rocks. 5. Repeat steps 1 & 2, this time using the two non-sandstone rocks.6. Rub the twig back and forth across the surface of a sandstone rock; record your

results.7. Rub the twig back and forth across the surface of each of the non-sandstone rocks;

record your results.

Type of abrasion Result (appearance of rocks and amount of dust produced)

Sandstone – sandstone

Sandstone – non-sandstone

Non-sandstone – non-sandstone

Sandstone – twig

Non-sandstone – twig

Questions:

1. What did your results show? Was it what you had predicted?2. This type of weathering is called abrasion. Is it an example of mechanical weathering

or chemical weathering?3. Draw a picture or diagram of your results.4. How does this demonstration simulate what happens to a rock in a natural setting?5. What other forces (including human ones) could cause abrasion on rock surfaces?

Lab #3: Acid Effect on Rock

Materials:1 small piece of limestone per group 2 glass jars or beakers per groupdropper vinegarwatersafety goggles

Prediction:What will happen to the limestone (calcium carbonate) in vinegar water?

Procedure:1. In your science notebook, create table like the one below.2. Put on safety goggles. 3. Place a piece of limestone in one of the jars. Fill to about 2/3 full with water. 4. Place a piece of limestone in the other jar. Fill to about 2/3 full with water. Add 5-8 droppers of vinegar. 5. Observe what happens and record your results in the chart. 6. After 10 minutes, observe and record again. 7. Remove the limestone from both jars. Is there sediment (material that settled at the bottom) in one or both jars?

Solution Immediate Reaction

After 10 minutes Sediment?

Water

Vinegar

Questions:

1. What happened to the limestone in the vinegar water? Was it what you had predicted?2. The limestone (calcium carbonate) reacted with the vinegar (acetic acid) to form sediment made of small particles of calcium acetate. Was this an example of mechanical weathering or chemical weathering?3. Draw a picture or diagram of your results.4. What might be some other sources of acids that cause chemical weathering in rock? (Hint: carbonic acid and sulfuric acid are common chemical weathering agents. Both are made from something in the air.)

Lab #4: Oxidation

Materials:3 pieces of steel wool per group 3 shallow dishes per groupwatersaltgloves Sharpie pen for labeling

Prediction:What will happen to the steel wool when it is exposed to water? To water and salt?

Procedure:1. In your science notebook, make a table like the one below. 1. Place each piece of steel wool in a shallow dish (wear gloves because steel wool can

give splinters). Label each dish with its contents and group members names. 2. Pour equal amounts of water over two of the pieces of steel wool. Leave the third

piece dry.3. Sprinkle one of the wet pieces with plenty of salt. 4. Observe and compare the pieces every day for 3 days. Record your observations. 5. Remove the steel wool on the third day and try to pull apart each of the pieces. What

happens? Record your observation. Draw a picture of diagram of your results.

Contents of dish

Observation Day 1

Observation Day 2

Observation Day 3

Observation of pieces when pulled apart

Steel wool

Steel wool and water

Steel wool,

water and salt

Questions:1. What happened to the steel wool? Was it what you predicted? Which piece changed the most?2. Which piece of steel wool acted as a control?3. The steel wool contains iron. Many rocks also contain iron. What would you expect to happen to an iron-containing rock when it is exposed to water.4. This type of weathering is called oxidation. In this demonstration, oxygen in the water combined with iron in the steel wool to form an iron oxide, or rust. Is this an example of mechanical weathering or chemical weathering?5. How do you think the salt affected the oxidation process?Lesson 2: Erosion (1 - 2 Class Periods)

(Note: If they have not already done so, students should continue to observe and record day 2 and 3 results from labs #1 and #4).

Purpose: To demonstrate the process of erosion by water. To demonstrate that weathering and erosion are connected processes.

Preparation: Outdoors in an appropriate place, or indoors in a large tray or pan, create a small

mound of dirt with rocks of varying sizes and shapes embedded within it. Fill a watering can with water. For extension, gather sand, soil, rocks, ice cubes, and pebbles.

Procedure: (This will be done as a teacher demonstration.) (Note: Begin with a quick review of the definitions of weathering and erosion, and brief summary

of the learning from the weathering labs.)1. Show the mound to the students and have them describe how and of what it is

built.2. Ask students to predict what will happen to the mountain when the watering can

is emptied over it. 3. Hold the watering can above the mound and slowly pour all of the water out.4. Students should note what happens (in words and/or pictures) in their science

notebooks. (The dirt/sand should wash away, leaving the rocks exposed. Some rocks might shift or move.) Ask them to explain in their notebooks why the result occurred.

5. As they finish, discuss erosion processes that may have occurred (such as undercutting, rocks tumbling or shifting, channels forming, etc.)

Extension: Students will be asked to build a “mountain” that they believe will have the least amount of erosion when water is poured over it.

Students will work in small groups Make available sand, small rocks, soil, pebbles, ice cubes, etc. Group members will work together to plan a design for their mountain and record

the plan in their science notebooks. They should also write their reasons for why they believe it will best hold up against erosion from the water.

Students observe all group “mountains” and make predictions. When mountains are complete, the teacher will pour water from the watering can

over each. In science notebooks, students record what happened and explain why they think

each mountain had the result that it did. They will also write suggestions for improving their own mountain.

When students have completed writing in their notebooks, gather them together to discuss, share findings, and answer questions.

Summarize/Review erosion: (POWERPOINT) Weathering and erosion are different processes, but they work together.

Weathering is when rocks are broken into pieces due to wind, weather, temperature, abrasion, and other forces. Erosion occurs when the rock pieces are moved.

Water is a powerful erosion force (e.g. streams, oceans, rivers, as well as rain and ice); wind is another erosion force (e.g. the moving of sand to create sand dunes).

Erosion can be slowed by things such as vegetation and boulders that help to anchor soil.

Lesson three: Weather, Erosion and Petroglyphs (1 Class Period)

Preparation: Obtain photos of petroglyphs; create a slide show or use document camera and

projector to display them to the class. (SEE POWER POINT) Make copies of Index—one sheet per student (4 indices per sheet)

Procedure:1. Show the photos of petroglyphs2. Discuss with students Ask:

What are the pictures on these rocks? (petroglyphs) How do you think they were made? (by pecking or chiseling with a

harder rock or metal tool) How old do you think these pictures are? (depending on the source,

most are hundreds of years old) Do you think that these rocks have changed since the pictures were

made? (Yes, weathering and erosion have been at work on them for a long time)

What types of weathering and/or erosion are evident? (point out any fractures, splintering, flaking, scaling, discoloration/oxidation, plant growth, abrasion, etc.)

Do you think the creators of the petroglyphs thought about weathering? Do you think they were expecting the pictures and/or the rock to last forever? Or did it matter to them? Does it matter to us today whether they last a long time?

3. Choose four photos of petroglyphs that show weathering or erosion. SEE POWER POINT 4. Tell students that they will be using a checklist to determine how much weathering and/or erosion is evident on the petroglyph and the rock on which it was made. This will help to determine how much longer the petroglyph might last. 5. Hand out checklist and go over it with students. 6. Looking at one of the photos, fill out the checklist together as a class as an example of what students will be expected to do. Answer any questions students might have. 7. Show the other 3 photos one at a time. Ask students to fill out a checklist for each one. 8. Collect the checklists to use as an assessment.9. Introduce the RASI project:

RASI stands for rock art stability index. A checklist, similar to the one you just used, is filled out for each panel of rock

art that is being assessed. The purpose of assessing the amount of weathering affecting the petroglyph is to

determine how much it is in danger of disappearing. The results of the assessment will be used by National Parks and others to make

decisions about protecting and preserving the art. Some people want the art preserved so that future generations can see and appreciate it..

The RASI project is an example of scientists working with the government, with Indians whose ancestors created the petroglyphs, and with the public. The scientists are using their research skills and knowledge of science (particularly geology) to provide useful information to people who have an interest in the future of these cultural treasures.

Optional Art Extension: (Requires 1-3 additional class periods) Have students create their own rock art. Several possibilities:

Use terra cotta potter’s clay, create a slab or tablet, draw into the clay, fire it, rub with charcoal and seal with lacquer spray (to simulate desert varnish)

Use salt clay, draw into the clay, and allow to harden at room temperature.

Use flat pieces of sandstone, chisel or peck a design into the rock with metal tools or a harder rock (this is the closest simulation to a real petroglyph).

Students can use designs from the petroglyphs they have been viewing, or can create their own designs/symbols to tell a story.

Name: _________________________________________ Date: _____________-

Directions: (Modified RASI checklist) For each petroglyph, fill out a checklist. You will be looking for evidence of

weathering and erosion that are affecting the art and the rock on which it was created.

For each item on the checklist: Circle 0 if you do not see the evidence Circle 1 if you see the evidence but it is not a big problem Circle 2 if you see the evidence and it is a big problem to the

survival of the petroglyph Add up the circled numbers for each petroglyph. The larger

the score, the more likely the petroglyph is in danger.

Sample Petroglyph:Type of

weathering/erosioNot

presenPresent but

Present and a

Type of weathering/erosio

Not presen

Present but

Present and a

n t not a big

problem

danger to petroglyp

h

n t not a big

problem

danger to petroglyp

h

Fissures (cracks) 0 1 2 Abrasion 0 1 2Roots/plant growth 0 1 2 Piles of crumbs or

grains of rock0 1 2

Scaling or flaking (small or large pieces broken or peeled off)

0 1 2 Lithobiont growth(algae, fungus, lichen, moss)

0 1 2

Undercutting 0 1 2 Oxidation (red rust film)

0 1 2

Total Score: ______________ (0 -8 = little or no danger; 9-16=moderate to great danger);

Petroglyph 1:Type of

weathering/erosion

Not presen

t

Present but not a big

problem

Present and a

danger to petroglyp

h


n

Not presen

t


problem

Present and a

danger to petroglyp

h


grains of rock0 1 2



0 1 2


0 1 2



weathering/erosion

Not presen

t


problem

Present and a

danger to petroglyp

h


n

Not presen

t


problem

Present and a

danger to petroglyp

h

Fissures (cracks) 0 1 2 Abrasion 0 1 2Roots/plant growth 0 1 2 Piles of crumbs or 0 1 2

grains of rockScaling or flaking (small or large pieces broken or peeled off)


0 1 2


0 1 2



weathering/erosion

Not presen

t


problem

Present and a

danger to petroglyp

h


n

Not presen

t


problem

Present and a

danger to petroglyp

h


grains of rock0 1 2



0 1 2


0 1 2


Assessments:

Lesson 1: Weathering & Lesson 2 : Erosion

Use the following rubric to assess student performance in labs/project and quality of notebook entries:

Response Criteria Points

Exemplary Completes all steps for labs and project. Shows leadership in group. Entries in notebook are complete, thorough, and in-depth. Extends learning by asking additional questions or performing related investigations.

4

Competent Completes all steps for labs and project. Participates actively in group.Entries in notebook are complete but may be brief or lack depth.

3

Satisfactory Completes nearly all steps for labs and project. Participates only as directed to by other members of group. Notebook is nearly complete, or is not well organized, or entries are not thoughtful.

2

Nearly Satisfactory

Completes some steps for labs and project. Some participation in group.Notebook entries are sketchy, or disorganized, or not thoughtful.

1

No Attempt Made

Did not participate in lab or project.No entries in notebook

0

Lesson 3: and what they have to do with petroglyphs

Use the modified RASI checklists from each student to assess whether he/she can identify examples of weathering and erosion.

weathering and erosion (and “how did the picture get...

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