Point source pollution comes from a known location, while nonpoint source pollution does not have a specific origin. Runoff is water that flows over land rather than seeping into the ground. Global warming is an increase in average temperatures due to increased carbon dioxide levels. Fresh water is a vital resource because people use it for drinking, cooking, bathing, and growing food. The chemical composition of the atmosphere helps maintain life on Earth. Earth's land provides important resources like soil, forests, minerals, and energy.