Will It Decompose?
The United States generates almost 200 million tons of solid waste a year, so where does all of the garbage go? In this investigation, we are going to spend a month finding out if different materials will or will not decompose. We will be predicting how many weeks we think it will take for different material to decompose and discuss whether or not each material is healthy for the earth if it remains in the soil. We will observe and collect data on the materials in our tubs of soil at the end of 2 weeks and at the end of 4 weeks to verify our predictions and results.
Approximately 60 minutes.
Instructional Support Downloads
Task Write Up
For their predictions, you can ask the children to bring in a variety of materials that have been discussed during the recycling unit. They may also bring in materials that we have not discussed.
I provided the students with the following materials for their tubs of soil: paper clips, red plastic margarine lids cut up, pieces of very thin wood, eggshells, apple peels, Styrofoam peanuts, bread, ripe banana slices, shavings, foil, paper-towel pieces, a dishcloth and uncooked macaroni. Next time I would include glass marbles for prediction and discussion. I would also extend prediction times for a possible response "between four weeks and never," in case students bring in materials such as orange peels, which take quite long to decompose.
Decomposition involves a whole system of large and small organisms (living things) that become food for each other or that clean up each other’s debris. Decomposition happens in landfills, compost piles and other places, like forest floors. My first graders are enthusiastically involved in our environmental unit of study, which began with a focus on the importance of soil and worms. Soil is integral to our survival, yet we take it for granted. The students started with observing and collecting data on different types of soil, growing plants with different soil nutrients, learning about the importance of worms in breaking down plant matter and creating fertile soil, and examining several stages of decomposition in forests while on their field trips. All of these activities led to our focus on recycling and the problems created by too much toxic trash that does not decompose in the earth.
This particular environmental task is a culmination of a lot of scientific reasoning, organizing and recording, which is why I chose this for the end of the year for my first graders. This task provided a lot of information for extension in reasoning and for making connections in their environment.
This investigation demonstrates how children apply their skills in observing and predicting physical materials that naturally decompose and those that do not. (All organic materials will eventually decompose, but some take longer than others.) They will classify and compare a variety of materials that are healthy and not healthy for the soil. This task encourages use of scientific organizational strategies, reasoning, making ecological decisions related to human impact, and communicating by sharing and recording observable results at two weeks and at four-weeks in order to complete the inquiry task. Within this unit, the children are also observing the life cycle from seed back to seed and the change from germination to decay. They are applying many concepts learned in our “cycles and changes” studies this year. This task doesn’t require scientific tools, although hand lenses or a dissecting microscope could be used to further examine the “fuzzy stuff” (fungi, molds, etc.) that seems to appear and change colors when things are rotting. Students could also measure soil temperatures during the composting process.
We began our investigation with classroom predictions about which materials the students thought would decompose and which would not, and a discussion of the information they based their ideas on (evidence of use of prior knowledge and experience). Students predicted that the following would decompose: eggshell, apple skin, bread, banana, macaroni, wood shavings, paper and a sea shell. They predicted that the following would not decompose: Styrofoam, paper clip, cloth, plastic, and foil. They put the thin piece of wood in the middle with a “maybe.” My first graders selected their materials one at a time to examine and bury in their tub of soil. They had to predict and record whether each material would decompose with a “yes” or “no.” Then, they had to record how long they thought it would take to decompose by indicating 1, 2, 3 or 4 weeks, or never. The students removed all of the contents with a plastic fork at the end of two weeks and recorded their results, including a description of what they observed for changes. The tubs of soil were examined again at the end of four weeks, and the students recorded any changes that they observed in the decomposing cycle.
Extended investigations integrated with this activity might include testing the water-holding and draining capacity of soils, creating a healthy soil, growing plants under different conditions, making a compost pile, making a worm farm for observations, creating and observing soil erosion, and visiting a recycling center, sewage disposal plant or local landfill. Students could also build “decomposition columns” from plastic soda bottles to study the effects of worms on decomposition or to have a “rot race.” (Directions for these can be found in a wonderful book, Bottle Biology, by Mrill Ingram.) Students could also record changes in odor and temperature during decomposition.
Have teams of children graph the amounts of recycled materials collected during the week. Weigh food waste from lunches for several days, and make a prediction about how much would be wasted in a month or a year. Students could investigate the length of time for decomposition based on the part size – for example, tiny pieces of the same amount apple peel have more surface area and will therefore decompose faster. (Students should weigh the larger and smaller parts to be sure that they have kept that variable – the amount of apple peel – the same and are only testing for the size of the pieces.) Take a field trip to a health food store and a local grocery store to compare the layers and amount of packaging on certain kinds of food products. Students can also time the movement of water through different soil samples. If your classroom does a worm study to determine the health of the soil, then data can be collected on quantity of worms in certain size samples. Try to create a visual representation of what 200 million tons of solid waste looks like, by starting with a unit of solid waste they can understand.
Language Arts/Social Studies
There are many books that support this scientific inquiry task, such as Where Does The Garbage Go? by Isaac Asimov; Recycle, by Gail Gibbons; and Don’t Throw It Away! (a predictable Social Studies Big Book), by JoAnne Nelson. Poetry might include, “Sara Sylvia Cynthia Stout Would Not Take the Garbage Out,” by Shel Silverstein. We also used a big book titled Earthworms, by Keith Pigdon and Marilyn Woolley, to learn about the important role worms play in nature’s cycle of decomposing. Writing activities can be integrated with science and math investigations. The class can write a factual big book about worms, write recycle poems from their experiences, or keep a journal about many of their inquiry activities and their testable questions. Paper bags can be recycled for worms in their underground habitat and journal covers for environmental data recording. To allow them to feel they have a voice and are making a difference, children could write to different environmental groups and/or local government representatives about their environmental concerns.
Have the children choose environmental songs from CDs like “Evergreen, Everblue,” by Raffi; “Piggyback Planet,” by Sally Rogers; and “Vermont Songs For Kids of All Ages,” by Tracy Wolters.
Children can design murals with partners to represent food chains that include decomposing. (Students should include earthworms, snails, slugs, flies and beetles, which feed on bacteria and fungi and become food for birds and larger insects.) Students can make banners to support recycling that could also show the negative effects of not recycling on the Earth. Students could create sculptures from recycled materials. (I’ve even heard of one school where the students made globes from old basketballs!)
Science, Technology, and the Environment:
Influence of science, engineering, and technology on society and the natural world.
I asked the children to bring in a variety of materials that they use in their daily routines and that they thought would decompose and would not decompose. We spent several days sorting and classifying these materials while asking:
- Will this material decompose? How can you tell?
- How is this material healthy or unhealthy for the soil?
- How long do you think it will take to decompose? What do you think will help it to decompose? (water/moisture, air, heat/warmth, microorganisms, insects, etc.)
- Are there other factors that affect the soil that would help the material decompose but are not in our tubs of soil? Could we add something to the tubs?
- Which materials might change in color? Smell? Why?
- Which materials might change in texture? How?
- Why is composting good for soil? What do we need?
- Were there some materials that surprised you by what they did? How?
- What do think is actually happening when something decomposes? (breaks down, gets eaten, gets slimy, etc.)
- What happens to its energy? (becomes food for another animal, nutrients go into soil to support plants)
(Unifying concepts/big ideas and science concepts to be assessed using the Science Exemplars Rubric under the criterion: Science Concepts and Related Concepts)
Life Science – Populations and Ecosystems: Students classify materials according to whether they will decompose or not decompose.
Physical Science – Properties of Matter: Students observe and compare reactions and physical properties of solids over time (change and constancy) when conditions are created for studying decomposition (cause and effect). Students describe and show an example of food chains/webs in the environment and how decomposition is part of the process for sustaining its members (interdependence).
Science in Personal and Societal Perspetives – Population, Resources and Environments: Students identify materials which can be recycled or disposed of in landfills or that naturally decompose. Students understand that a model of a landfill, the soil tub, can teach us about how a landfill actually works (models) and about properties of soil.
Mathematics: Students use precise measurements and compare attributes or effects. Students collect, organize and analyze data and use graphs, tables and representations appropriately.
In this task, the students should accurately predict the materials that will decompose in their tubs of soil: wood shavings, eggshells, bread, cloth, apple peel, macaroni and paper towel. Some of the materials might decompose within the two weeks, but other materials may take the full four weeks or longer. The students should be able to identify those materials that will not decompose such as a metal paper clip, a plastic lid and foil. The thin wood might not fully decompose after four weeks. The student should be able to describe and record some observations about the condition of each material after two weeks and at four weeks.
Note: Some students might raise the question about the metal paper clip rusting, over a longer period of time. Oxidation does break down the metal; but this is different from decomposition, which is the effect of microbes acting on plant or animal matter and part of the food chain’s life cycles.
This student does not use scientific reasoning, draw from prior knowledge or make enough observations using the materials so that accurate conclusions can be made. The student recorded “yes” for the plastic, yet predicted "never" for the timeframe. The student was also confused with the eggshell and paper clip, which indicates that s/he does not understand the concept of decomposition. This student does not label all materials in the chart or complete the task. There are not enough scientific notations for the fourth week so that comparisons of decomposing can be made.
This student uses some understanding, prior knowledge and organizational strategies moving through the different columns and attempts to carry out most of the testing. The recordings demonstrate incomplete explanations and some inaccurate observations at two weeks. (The apple peel and cloth do not decompose in two weeks but do decompose at four weeks.) This student labels all materials in the chart, but some items are mislabeled. The student does not record the specific kind of changes at four weeks for wood.
This student shows a clear understanding of the science concepts involved with materials that will and will not decompose. The scientific recordings are organized and demonstrate a strategy that leads to completion of the investigation. This student makes accurate time predictions except for the cloth. This student accurately records observable characteristics of the different materials that are tested.
This sample is only subtly different from the Practitioner sample. This student shows a deep understanding, prior knowledge, steps used and data gathered in this investigation. All the predictions about decomposing and timing are reasonably accurate. There is an appropriate, specific recording for each two-week and four-week observation. This student is accurate about all the materials, which demonstrates clear scientific reasoning and conceptual understanding of the properties of organic and inorganic matter.