Working in groups, learners model the continuous destruction and creation of ozone (O3) molecules, which occur in the ozone layer. Some learners act as ultraviolet (UV) light and break apart gumdrop and toothpick models of ozone molecules into oxygen molecules and atoms. Meanwhile, other learners assemble ozone molecules from the oxygen molecules and atoms. In a second round, learners model the situation when pollutants such as chlorofluorocarbons (CFCs) are present. In subsequent rounds, the amount of CFCs changes according to historical data, and learners can see what happens to the proportion of ozone and oxygen in the ozone layer over time. Resource contains vocabulary definitions and suggestions for assessment, extensions, and scaling for different levels of learners.