Discover how human-driven activities have led to changes in animal populations and ecosystems, an increase in air pollution, a depletion of the ozone layer and global climate change. We learn about the effects of deforestation, the size of earth's population, extinct animals, fossil fuels, smog, acid rain, makeup and value of the ozone layer, plankton in the ocean food chain, carbon dioxide, methane, protecting wildlife, and the Montreal Protocol. Learn what we can do to reduce the impact on Earth's systems.  Reviews at the end of each segment reinforce important concepts.