The gas that makes up almost ¼ of the air’s surrounding of the earth is the oxygen. Earth atmosphere’s contains around 20.95%. Oxygen is a chemical substance with a symbol of O and atomic number of 8. Oxygen is the gas that we inhale and goes to our respiratory system. According to the latest research, it is one of the most abundant gas in earth, it is on the third place. Most organic molecule contains oxygen like proteins, carbohydrates, fats and nucleic acid. Trees also produce oxygen and intake the carbon dioxide.