Oxygen is a colorless, odorless, tasteless gaseous chemical element which appears in great abundance on Earth, trapped by the atmosphere. Many people are familiar with oxygen, because it is a vital component of the respiration process; without oxygen, most organisms will die within minutes. A number of forms of oxygen and oxygen compounds can be found in nature. Oxygen can also be isolated and sold in pure form for an assortment of uses, and was first isolated and identified in 1774.

The atomic number of oxygen is eight, and it is identified by an O symbol on the periodic table of elements. In addition to being very widely distributed on Earth, oxygen is also the third most abundant element in the universe, and it is a key catalyst in many chemical reactions. Oxidation is one such reaction, and it occurs when oxygen mixes with other elements and compounds. Oxygen also plays a role in combustion.

There are several ways to extract pure oxygen. Water can be ionized, forcing the oxygen and hydrogen atoms to separate. More commonly, however, samples of air are cooled into a liquid form and then slowly heated. As the air heats, elements precipitate out in a process called fractional distillation, because different gaseous elements convert to a gas form at different temperatures. Once extracted, the oxygen can be bottled for use.

In medicine, oxygen has a number of uses. It is sometimes offered therapeutically, to patients who are having difficulty breathing. It is also used in anesthesia mixtures, ensuring that the patient gets a consistent supply of oxygen while unconscious. The element also plays a role in welding and industry, being combined with substances like acetylene, for example, to make welding torches.

Although pure oxygen is used medicinally and recreationally, as it brings about a state of mild euphoria, it is potentially dangerous. In high pressure environments, oxygen toxicity can damage the lungs, often quite severely. Depending on the pressure, symptoms may emerge right away, or they may take several hours to manifest, at which point it can be too late. Oxygen also represents a serious combustion hazard, and some oxygen compounds such as ozone and hydrogen peroxide are extremely toxic. These compounds can damage cells and DNA if they are left unchecked. Living organisms should consume a diet high in antioxidants to help avert one form of this damage, caused by free radicals in the body.