Earth
All around the Earth is the of air (the atmosphere). The mass of the Earth holds the gasses in the air down and does not let them go into outer space. The air is mostly made of nitrogen (about 78%) and oxygen (about 21%) and there are a few other gasses as well. Most living things need the air (or, more precisely,  the oxygen) to breathe and live. They use the gasses – especially oxygen and carbon dioxide – to make and use sugar and to give themselves power.