Atoms of the elements carbon, oxygen, and nitrogen play critical roles in living systems. These elements are constantly recycled between the atmosphere and living systems as illustrated in the following video. (There are many technical terms in this video that can be ignored.) Have kids focus on how carbon atoms (particles) move from the atmosphere, to plants, to animals, and back to the atmosphere. This is known as the carbon cycle. Please post questions that kids ask. Sustainability of life on Earth is dependent on this recycling.