Oxygen is a chemical element (atomic number 8) that is a colorless, odorless gas at room temperature. Roughly 23% of the atmosphere is molecular oxygen (O2). Oxygen is also the second most abundant element in the earth's crust after silicon, although it is often found bound in other molecules such as water (H2O).
Oxygen was discovered as an independent element by Joseph Priestly in the late 18th century. He also discovered that oxygen is essential to all animal life and that an animal deprived of oxygen will suffocate in a matter of minutes. He also discovered that oxygen is produced from carbon dioxide (CO2) as a by-product of photosynthesis by plants.
- "You know how they say that you can't live without love? Well oxygen is even more important."
- ―House, on the importance of oxygen in Acceptance
Modern science now understands that oxygen is required by all tissues of the body in order to extract energy at the molecular level in the cell. The brain is by far the organ that has the highest requirement for oxygen, using approximately 20% of the body's total oxygen and nutrient requirements despite making up less than 2% of its mass. Depriving the brain of oxygen for as little as three minutes results in irreversible damage.
Hospitals have a ready supply of pure oxygen, which is routinely given to patients suffering from lung or heart problems.
However, pure oxygen at high pressures, such as those that exist in a hyperbaric chamber, can be toxic as the oxygen degrades organic tissues because of its highly reactive nature.