The atmosphere surrounding the Earth consists of a mixture of gases commonly called air. The most common gases are nitrogen (77%) and oxygen (about 22%). There are other gases as well, but in very small quantities. The air is important for almost all life on Earth including plants and animals. Plants need carbon dioxide for photosynthesis. Animals need to breathe air to get the oxygen they need to survive. As altitude increases, the concentration of air molecules in the atmosphere decreases. The air is thinner higher in the atmosphere because there is lower pressure higher up in the atmosphere.
There is a special layer of air molecules high in the stratosphere layer of Earth’s atmosphere, called the ozone layer. The composition of the atmosphere is different in the ozone layer. There are more ozone molecules than anywhere else. Ozone molecules help block some of the Sun’s strongest rays. Currently, scientists are monitoring this layer. It has recently become so thin at the South Pole where the molecules are being destroyed that we call it a hole. The hole in the ozone layer has led to the widespread ban on chemicals called CFCs.