Have students bring in a small bag of soil from their yard. Place the samples beneath a microscope or use magnifying glasses to compare the soil composition. Chart the soil particle size, shape, hardness and color. Hypothesize why different yards contain different soils. Compare the yard samples with a sample from the school.
Dig a dirt sample roughly 6 to 7 inches deep. Fill half of a large mason jar or 2-liter bottle with this dirt. Try to keep grass and leaves out of the dirt sample. Fill the remainder of the jar or bottle with water. Tightly secure the lid and shake for a minute. Allow the experiment to sit overnight so the dirt can settle into layers. Have the students draw a diagram of the different soil layers. Discuss the different particle sizes and the composition of the layers, such as clay, sand and silt. Repeat this experiment with soil samples from other locations, such as the children's yards.
Fill two erosion trays with soil. Add small rocks, sticks and leaves on top of one tray. Have the students make predictions regarding both trays. Which tray will have more erosion? Why? Place a pan beneath both trays to catch the water runoff. Sprinkle one quart of water over both trays. Compare and chart how much soil ran off from both trays. Review the student's hypotheses. Tilt the trays and repeat the experiment. Chart any differences in soil loss from the first experiment to the second.
Explain the different levels of soil with a fun and edible activity. Place a full package of Oreo cookies in a gallon plastic bag. Seal well, then smash the cookies. In a second gallon plastic bag, add two boxes of chocolate pudding and 4 cups of milk. Seal the bag and shake until the pudding is mixed. (If the student's age or length of activity time is a concern, the previous steps can be completed prior to the activity.) Explain the differences in the soil layers as the children build their own soil sample. Give each child a small, clear plastic cup. Sprinkle chocolate chips as the first layer in the cup. The chips symbolize the rocks found in the bedrock layer. Next pour some chocolate pudding over the top of the chocolate chips. The pudding represents the minerals and humus found in the subsoil layer. The final layer, consisting of decaying matter, bacteria and fungus, is topsoil. Sprinkle a 1/4 cup of crushed Oreos on the top of the pudding for the topsoil layer. Poke a gummy worm in the topsoil for fun.