Sure, compost is made from kitchen scraps ranging from broccoli stems to coffee grounds, but the term is usually applied to plant material once microbes have heated, then transformed it into a rich, earthy mixture. Eighth grade student Aaron Didich had another idea.
"Our homes have locks on the door, latches on the window, and insurance policies in the dresser drawer.... Meanwhile, outside our windows, every rainstorm carries away thousands of tons of valuable topsoil upon which we depend for our very survival." -- Malcolm Margolin, Naturalist
"My third graders had been exploring trees as part of a history unit when several began to wonder what happens to the leaves that fall in the autumn," reports Merion, PA, teacher Judith Linker. "They wondered why we aren't buried in old leaves!" Although some students had thoughts about what factors might contribute to decomposition, the class as a whole was unsure, says Judith.
Students sometimes believe that plants get their "food" from the soil. Scientists, meanwhile, understand that plants manufacture their own food -- simple sugars -- using energy from sunlight, water, and carbon dioxide from the air.
Soil and water have a dynamic and important relationship. Different-sized soil particles create air spaces that can hold air or water. When rain falls, water and dissolved nutrients fill the soil spaces and become available to plant roots.
Before beginning a soil unit, ask students to draw or predict what they would find in a sample of soil. Then bring in or have students collect samples of soils from different settings: a building site, a garden, woods, and schoolyard, for instance. Invite each small group of students to examine a sample with hand lenses, toothpicks, and other tools, then describe the soil's color, texture, moisture, and smell. Ask students to identify, describe, and record the different materials they find. What evidence of plant and animal life do they see?
"When I asked my second through fifth graders what soil was, they concurred that it was just made of dirt," reports St. Louis, MO, teacher Brenda Kukay. "But after dissecting and inspecting soils from different contexts, then trying to create some from scratch, they were surprised at its life and complexity, and began to appreciate it as something valuable," she adds.
Challenge students to guess the length of an earthworm, then try using a ruler or tape measure to determine the actual size. Ask, What problems do you encounter? After watching how earthworms move, why do you think it's difficult to measure their true length? What is it about their bodies that might cause them to seem to shrink and grow? How do you think this helps them move through soil? Draw bar graphs comparing an estimate of a worm's length with its true length, both when stretched out and when shortened.