Oxygen is an essential element for life on Earth, and can be found in many forms. It is a colorless, odorless GAS that makes up about 21% of the AIR we breathe. It is also found in OZONE, a form of oxygen with three atoms instead of two, which is found in the upper atmosphere and helps protect us from the sun's ultraviolet rays. Oxygen is also found in tents, where it is used to provide breathable AIR for campers.