Oxygen is one of the basic chemical elements. In its most common form, oxygen is a colorless gas found in air. It is one of the life-sustaining elements on Earth and is needed by all animals.Oxygen is also used in many industrial, commercial, medical, and scientific applications.hen oxygen is cooled below -297° F (-183° C), it becomes a pale blue liquid that is used as a rocket fuel. Oxygen is one of the most abundant chemical elements on Earth. About one-half of the earth's crust is made up of chemical compounds containing oxygen, and a fifth of our atmosphere is oxygen gas.