Air

The atmosphere surrounding the Earth is full of air. The air in our atmosphere is made of molecules of different gases. The most common gases are nitrogen (77%) and oxygen (about 22%). There are other types of air molecules as well, but in very small quantities and much less important. Air is important for almost all life on Earth including plants and animals. Plants need air gas to do their photosynthesis. Animals need to breath air to get the oxygen they need to survive. As you move up in altitude through the atmosphere, the concentration of air molecules decreases. Some people call this "thin air". The air is thinner higher in the atmosphere because there is lower pressure the higher you go up. 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.