The atmosphere is composed of layers of air surrounding Earth. It contains gases like water vapor ranging from 0-7% and ozone, a form of oxygen that absorbs harmful UV radiation from the sun. Ozone in the atmosphere protects life at Earth's surface from UV radiation's harmful effects. Greenhouse gases like nitrous oxide, methane, and carbon dioxide trap heat from the sun, keeping Earth warm. Increasing levels of these gases from sources such as car exhaust, factories, and deforestation cause global warming by trapping more heat in the atmosphere.