A compost bin with four tiers is displayed. A black arrow points to the contents and is labeled, “Biomass, including food waste, yard waste, and animal and human waste.” The biomass gradually begins to darken and change as it composes. Another black arrow appears, pointing to the biomass visible between the middle two tiers. This arrow is labeled, “Gaps in box allow for air circulation, breaking down waste materials and creating warm air.” A red arrow labeled “Warm air rises” appears above this black arrow and label and moves upward to illustrate the rise of the warm air toward the top of the compost bin. The biomass continues to darken and change, illustrating further decomposition.