Materials List: safety contract generated in Unit 1; three small paper bags: one with rice, one with sand, one with top soil; chart paper; large roll of paper/plastic; Touch and Describe BLM; hand lens, plastic spoons, paper cups for each group of three to four students; safety goggles and disposable gloves for each child.
Teacher Note: Prior to this activity, the teacher should obtain soil samples from the schoolyard, from his/her own yard, or other various areas. The areas in which the soil is collected should be free of ants and poison ivy. The types of soil that might be used are topsoil (dug as a shallow slab with grass, leaves, and twigs on top), topsoil dug more deeply then the layer of soil that we most commonly water (the soil beneath the surface having the roots of the plants), and sandy soil. (This may need to be a mix of sand and topsoil purchased from the store if there is not access to such soil.) If evidence of biotic (living) substances is not visible, the teacher may choose to add twigs or dead insects to either the top soil or sandy soil for students to discover.
Safety Note: Have students discuss reasons for not putting their hands near their eyes or mouth during this experiment. Ask them to identify other safety considerations for this lesson.
Invite the students to discuss words that will be used in observing the soil samples. Write the words color, texture, and particles on chart paper and have it visible throughout the lesson. Invite the students take turns reaching into a paper bag of rice, a paper bag of sand, and a paper bag of top soil and describe how each one feels (texture). The students may offer words for texture such as soft, bumpy, smooth, and slimy. List the words that are generated on chart paper. Explain that texture is partly determined by the size of the particles. Explain that they will be observing some types of soil found on Earth’s surface.
Prepare an area for each group of three or four students to observe and examine the soil samples. Laying out butcher paper or waxed paper for each group might be helpful, so that each type of soil can be separated and labeled as “topsoil” and “sandy soil.” (If the school cafeteria has old plastic trays to donate, these work well, too.) Provide each group with a hand lens, plastic spoons, paper cups, gloves, safety goggles, Touch and Describe BLM for recording observations, and a pencil.
Model the use of a hand lens as a scientific tool. Make sure students understand how to move the lens closer or further away to get a sharp image.
Divide students into groups of three or four. Provide each with the samples of topsoil and sandy soil. Students will explore the texture and observe characteristics of each soil and record their observations. They may choose to use the plastic spoons to put samples in cups for observation or the hand lens for viewing. Students may conclude that sandy soil is rough and contains sand and topsoil is dark and not as rough as sandy soil. The chart paper with the list of describing words should be on display for students to use as a spelling aid.
Have students observe a soil sample from the schoolyard; determine what type of soil this sample is most like; identify leaves, grass, and twigs that occur in the top layer of topsoil. Guide students to an understanding that the best soil (topsoil with organic materials) is at the surface and under that come other layers with more sand or formed from clay that are not as fertile (healthy) for growing things.
Questions for inquiry:
How does soil feel?
How does soil smell?
How can we describe the layers of soil?
What can soil be used for?
Can you separate the soil into different substances?
Where are these kinds of soil found? (beaches, deserts, farms, gardens, yard at home)
Does soil contain anything that is living? Does soil contain anything that is not living?
A fun, culminating activity would be to make and eat a great Soil Cake. Be sure to check any dietary limitations or food allergies for all students. The recipe is available at http://soil.gsfc.nasa.gov/soilcake/soilcake.htm. Have students recall the layers in the samples that were shown (decaying material on top with the soil beneath that having the roots of the plants) in relation to this cake.