Air

Most of the Earth's atmosphere is contained within 30 kilometers of the planet’s surface. This atmosphere provides oxygen, nitrogen, carbon dioxide and other gases needed by living organisms. In the stratosphere at an altitude of 20 to 30 kilometers lies the ozone layer. Ozone present in stratosphere is of great benefit to life on the Earth as it absorbs ultraviolet radiation, which is harmful to living tissues in our body. The discovery of ozone hole with depletion of ozone over Antarctic continent demonstrates the potential threat to stratospheric ozone posed by chlorofluorocarbons (CFCs). In a number of ways, however, human activities are sources of air pollution resulting in smog, especially over urban areas. Earth absorbs the solar energy and radiates infrared waves. Green house gases (carbon dioxide, water vapor and other select gases) absorb and re–emit much of this infrared energy back to the ground. This process, called the greenhouse effect, helps keep the Earth warm. Human activities, such as the burning of fossil fuels and deforestation are responsible for increase in green house gases, which will result in global warming. Rise in temperatures and its potential effects may lead us for ice age or warm deserts. Developing alternative energy sources, searching for drought–resistant crop strains and negotiating international agreements offer widespread benefits.