activities 1&2 Weathering (Sessions I and II) BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade 4 Quarter 1 Activities 1 & 2 SC.D.1.2.1 The student knows that larger rocks can be broken down into smaller rocks, which in turn can be broken down to combine with organic material to form soil. SC.D.1.2.5 The student knows that some changes in the Earth s surface are due to slow processes and some changes are due to rapid processes. SC.H.1.2.2 The student knows that a successful method to explore the natural world is to observe and record, and then analyze and communicate the results. SC.H.1.2.3 The student knows that to work collaboratively, all team members should be free to reach, explain, and justify their own individual conclusions. SC.H.1.2.4 The student knows that to compare and contrast observations and results is an essential skill in science. SC.H.1.2.5 The student knows that a model of something is different from the real thing, but can be used to learn something about the real thing. SC.H.3.2.4 The student knows that through the use of science processes and knowledge, people can solve problems, make decisions, and form new ideas. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 40 hands-on activities at this grade level. 1. Session I Activity 1: Weathering of Earth material is all around us. Scientists always search for evidence. Have students look at the outside walls, sidewalks, and steps of your school building for signs of physical weathering. Tell them to make a list of this evidence. (Answers will vary based on the age of the school, but signs such as cracks, smoothed or rounded surfaces and edges, should be easily noticed, similar to what students saw in the broward county hands-on science Quarter 1 31
32 activity.) Have students check to see if there is a difference from one side of the building s walls to another. (Students might notice more physical weathering on the side of the school facing west and north, where most of the windy and rainy weather hits the walls, but exposure to sun on the south side might also account for additional physical weathering.) 2. Session II Activity 2: As with physical weathering, the outside school surfaces might show the effect of chemical weathering. Have students go back outside and look for this evidence. (A hand lens might be helpful.) Look at places where bricks are held together with mortar. The brick and the mortar that holds it together react differently to acid rain. (Bricks are less affected.) Ask, Do you notice any evidence of chemical weathering? (The older a building made of brick and mortar, the greater the differences will be, so students may or may not be able to find these subtle examples. Have students look for other places where water can collect, such as sidewalks or on steps.) 3. Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. activities 1 & 2 Weathering
activities 1&2 Weathering OBJECTIVES Students are introduced to a process that must take place before erosion can occur: weathering. They examine the ways in which weathering causes the disintegration of rocks and minerals on Earth s surface. For the class 1 roll paper towels* 1 btl vinegar DSR Erosion *provided by the teacher The students discuss physical and chemical weathering observe and record signs of physical weathering on their way to and from school simulate the chemical weathering of a mineral sample SCHEDULE Session I Activity 1 About 20 minutes Session II Activity 2 About 40 minutes VOCABULARY acid rain chemical weathering oxidation physical weathering weathering MATERIALS For each student 1 Activity Sheet 1 1 pair safety goggles* For each team of four 1 bottle, dropper 1 calcite chip 1 magnifier PREPARATION Session I Activity 1 Make a copy of Activity Sheet 1 for each student. 1 Session II Activity 2 Fill each dropper bottle half-full with vinegar, attach the tip, and screw on the cap. 1 2 Each team of four will need a dropper bottle with vinegar, a calcite chip, a magnifier, and some paper towels. BACKGROUND INFORMATION Earth s surface is constantly being worn away by a process called weathering. There are two types of weathering: physical and chemical. Physical weathering is the mechanical breaking down of rocks. For example, the constant buffeting by wind, windblown particles, and rain can cause rocks to disintegrate. In areas subject to extreme daytime and nighttime temperatures, rocks expand (get larger) in the hot sun, then contract (get smaller) in the night s cold. This constant expansion and contraction can cause the rocks to crack. Water then seeps into these cracks, freezes, and expands, causing further cracking. Plant seeds or spores may also lodge in these cracks. As they grow, they expand the cracks even more, causing the rocks to break into smaller pieces. broward county hands-on science Quarter 1 33
1 Mechanical weathering also happens when the pressure on a mass of rock changes. For example, as rock covering granite is removed, granite expands, and thin curved sheets of granite break off at the surface. The rock mass left behind is a round dome. Stone Mountain, Georgia, is a granite dome. Chemical weathering is the process of breaking down Earth s surface by changing the chemical composition of rocks and minerals. For example, acid rain a weak acid solution formed when rain mixes with sulfur dioxide and nitrogen oxides in the air dissolves some of the minerals that are constituent parts of certain kinds of rocks, breaking the rocks into smaller pieces. Oxidation, the chemical reaction of rusting, occurs when certain substances are exposed to oxygen in the air and can also cause rocks to weather. In these two activities, the students will discuss both types of weathering. In Session II, they will simulate the destructive action of acid rain on a marble monument by putting drops of vinegar (a mild acid) on a piece of calcite (a constituent mineral of marble). Guiding the Activity Session I Activity 1 Write the word weathering on the board. Ask, What do you think this word means? Explain that weathering is the very slow process of breaking down rocks and minerals on the earth s surface into smaller pieces. There are two types of weathering: physical and chemical. Tell students that they will investigate physical weathering today and chemical weathering next time (Session II). 34 activities 1 & 2 Weathering Activity Sheet 1 Weathering Session I Activity 1 1. What are some examples of physical weathering that you observe on your way to and from school? Examples Caused by Examples will vary but may include the following: cracked sidewalks tree roots split boulders ice gully or ditch flowing water washed away lawn rain from roof gutter potholes freezing and thawing of roadway smoothed stones running water Session II Activity 2 2. What causes acid rain? 3. What did you observe when you put vinegar on the mineral sample? 4. How does acid rain affect a statue carved from marble? Additional Information (The chemical used in this activity is vinegar.) Rain mixes with pollution or chemicals in the air and forms a weak acid solution. Small bubbles appeared in the vinegar and some of the mineral dissolved. Marble contains the mineral calcite. Acid rain dissolves calcite. If the marble statue is exposed to acid rain for any length of time, it will become brittle and may crumble. Write the word at the top of the board so that additional information can be written beneath it. This class chart will be used during Session II as well, so write it where it can be left overnight. The term weathering refers only to the breaking down of rocks into smaller pieces not the carrying away of those pieces, which is called erosion and will be explored in subsequent activities. y
2 3 4 5 Guiding the Activity Write the words physical and chemical as column headings under weathering (see Figure 1-1). Tell students that physical weathering is the mechanical breaking down of rock. Ask, What can you think of that could cause physical weathering? Write the word temperature under the column heading physical. Tell students that extreme changes in daytime and nighttime temperatures can cause rocks to crack. Explain that as a rock heats up, it expands (gets larger). As it cools down, it contracts (gets smaller). Furthermore, the outside of the rock will get hotter than the inside during the day and will cool off faster at night. A rock will crack when constantly subjected to uneven rates of temperature change. Write the word water under the word temperature on the class chart. Ask, How do you think water might help break rocks apart? Explain that when water (from rain, snow, fog, or dew) seeps into the cracks in rocks and freezes, it expands, making the cracks larger and eventually breaking the rocks into smaller pieces. Write the word vegetation under the word water. Ask, How do you think plants contribute to weathering? Tell students that the roots of plants can grow in the cracks of rocks, further breaking down the rocks. Explain that lichens and tiny plants, such as moss, are usually the first to grow in small cracks. Then, after they widen the cracks, larger plants may join them and crack the rocks even more. Write the word wind under the word vegetation. Ask, How can wind weather rocks? Additional Information Encourage answers that relate to temperature, water, plant roots, and wind. Some students may know that ice can help crack rocks. Water is one of the few substances that expands when it freezes. Some students may have seen the damage that tree roots can do to a sidewalk. 6 Encourage answers that involve the breaking down of rock (weathering), not the carrying away of the rock particles (erosion). broward county hands-on science Quarter 1 35
Guiding the Activity Explain that wind is an effective weathering agent. Not only does the force of the wind push against rock, but it can also carry particles of sand or soil that will wear away the rock. This constant buffeting by the wind and by windblown particles weathers rock. Additional Information Weathering Physical Chemical temperature water vegetation wind 7 8 9 10 Distribute a copy of Activity Sheet 1 to each student. Tell students that they are to look for signs of weathering on their way home and on their way back to school. Have them record their observations on the activity sheet. Save the class chart for use in Session II. Session II Activity 2 Have students retrieve their activity sheets. Discuss the evidence of physical weathering that they observed. Refer to the class chart to support the observations they have made. Point to the chemical column heading on the class chart. Tell students that chemical weathering is the breaking down of rock caused by changes in the chemical composition of the rock. Write the word oxidation on the board under the column heading chemical. Tell students that oxygen in the air can react with certain deposits in rocks, such as iron, weakening the rocks and causing them to crumble. This process is known as oxidation. Ask students to raise their hands if they have ever seen rust. Ask, Did the rust you observed weaken the metal? 36 activities 1 & 2 Weathering Figure 1-1. The class chart, listing four physical weathering agents. Cracks in sidewalks caused by tree roots, potholes caused by freezing and thawing of streets, and stones under rain gutters, worn by falling water, are all evidence of weathering. A rusty piece of metal is weaker than a piece that is not rusty.
11 12 Guiding the Activity Tell students to imagine an iron ore deposit in a huge rock. If the iron ore is exposed to the air, oxygen in the air will react chemically with the iron ore, weakening it and causing the rock around it to crumble. This is an example of chemical weathering by oxidation. Tell students that they will experiment with another type of chemical weathering. Ask, What do you think acid rain is? Have students answer question 2 on their activity sheets. Write the term acid rain under the term oxidation. Tell students that they will simulate acid rain to determine how it affects certain minerals in rocks. Figure 1-2 shows the completed chart. Distribute paper towels, a calcite chip, a dropper bottle of vinegar, safety goggles, and a magnifier to each team of four. Tell teams to put several drops of vinegar on their calcite chip and to observe what happens. Students should record their observations on the activity sheet. Ask, What is the vinegar doing to the mineral? Tell students that vinegar is a mild acid. In this experiment, the vinegar represents acid rain. The mineral sample is calcite. Calcite is found in marble, limestone, and chalk. In this experiment, the calcite represents a marble statue, a limestone building, or a chalk deposit. Additional Information Acid rain is rain that comes in contact with contaminants, such as industrial exhausts, and becomes acidic. Weathering Physical Chemical temperature water vegetation wind oxidation acid rain Figure 1-2. The completed class chart, including two chemical weathering agents. You may need to remind students that rocks are made primarily of minerals. Students will see very small bubbles in the vinegar and should notice that some of the calcite chip has dissolved. broward county hands-on science Quarter 1 37
Guiding the Activity Ask, What do you think will happen to a statue made of marble or a building made of limestone if acid rain falls on it? Additional Information Acid rain will slowly dissolve the calcite in the rock (the marble or limestone), causing the structure to become brittle and eventually crumble. Have students complete the activity sheet. Explain that acids reacting with certain minerals in rocks, causing the rocks to break and crumble, is another form of chemical weathering. As appropriate, read or review pages 5 6 from the Delta Science Reader Erosion. R EINFORCEMENT Ask students to explain what would happen to a monument carved from rock if exposed to hot, windy conditions during the day, followed by cold, moist conditions at night. SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. 38 activities 1 & 2 Weathering C LEANUP The calcite chips can be thrown away. The magnifiers and dropper bottles of vinegar should be returned to the kit. SCIENCE AT HOME Have students investigate human-caused weathering in their homes. For example, are the floors or carpets worn from foot traffic?
Connections Science Extension To demonstrate that water expands and exerts pressure when it freezes, have each team fill a small plastic (not glass) bottle with a snap-on lid to the top with water, put on the lid, and place it in a freezer overnight. Ask students to predict what they think will happen. The next day, have students examine their bottles and explain what happened. If possible, arrange a class field trip to a cemetery. The dates carved on the headstones will give students an idea of how long the stones have been exposed to weathering. Ask students to compare headstones of different ages and to look for evidence of physical and chemical weathering of the older stones. Examples of physical weathering may include cracks or broken pieces resulting from the growth of plants or freezing and thawing. Examples of chemical weathering may include indistinct lettering or carving as the result of acid rain or the chemical action of the roots of mosses or lichens. Science and Math Ask volunteers to research the names and percentages of the elements that make up Earth s crust: oxygen 45%, silicon 25%, aluminum 7%, iron 5%, sodium 5%, calcium 4%, nickel 3%, magnesium 3%, potassium 2%, all other elements 1%. (Different sources may give slightly different percentages.) Have students make a pie chart showing the elements and their proportions. Science and the Arts Suggest that students research the names, comparative thicknesses, and composition of the Earth s layers. Using pictures in science textbooks, library books, or encyclopedias, students can make cutaway drawings or models showing the layers. Emphasize that only the outermost layer, the crust, is affected by weathering. Science and Health In addition to weathering rocks and damaging stone buildings, statues, and headstones, acid rain causes health and environmental problems. Encourage students to research the causes and sources of acid rain and its effects on plants, wildlife, and people. Science and Language Arts If students have encountered the terms physical changes and chemical changes in their previous science studies, review these terms and concepts now. Ask students to identify examples of physical and chemical changes and discuss the differences between the two types of changes. Then relate these terms to the terms physical weathering and chemical weathering. Make sure students understand that physical and chemical weathering are types of physical and chemical changes. Science and Social Studies Encourage interested students to research and report on the recent restoration of the Statue of Liberty to repair damage caused by physical and chemical weathering. What types of damage had weathering caused? How was that damage repaired? What was the total cost of the restoration, and what was the source of those funds? Did the restoration include any special techniques or materials to help prevent future weathering? As appropriate, encourage supervised use of the Internet for research projects related to weathering and erosion. A list of related websites is provided in the References and Resources section. broward county hands-on science Quarter 1 39
40 activities 1 & 2 Weathering 40