What is oxygen

Last updated: April 1, 2026

Quick Answer: Oxygen is a colorless, odorless gas comprising about 21% of Earth's atmosphere and is essential for cellular respiration and energy production in most living organisms.

Key Facts

Oxygen is the third most abundant element in the universe by mass, after hydrogen and helium
Animals require oxygen to convert glucose into usable energy (ATP) through aerobic respiration
Plants produce oxygen as a byproduct of photosynthesis, releasing it into the atmosphere
Oxygen was first isolated and identified by Swedish chemist Carl Wilhelm Scheele and British scientist Joseph Priestley in 1774
Liquid oxygen at -183°C is used in rocket fuel, medical applications, welding, and industrial processes

Oxygen: The Essential Element

Oxygen is a highly reactive, nonmetallic element with atomic number 8. It exists in nature as diatomic molecules (O₂) that form a substantial portion of Earth's atmosphere. Without atmospheric oxygen, complex life as we know it would be impossible, making it one of the most critical elements for survival on our planet.

The Role of Oxygen in Living Organisms

All aerobic organisms depend on oxygen for survival. When you breathe, oxygen enters your lungs and binds to hemoglobin in red blood cells, which transport it throughout your body. At the cellular level, mitochondria use oxygen to break down glucose in the process of aerobic respiration, generating energy in the form of ATP. This energy powers every function in your body—from movement to thought.

Oxygen Production and the Carbon Cycle

Oxygen production began millions of years ago when photosynthetic organisms evolved. Plants, algae, and cyanobacteria use sunlight to split water molecules during photosynthesis, releasing oxygen into the atmosphere. This process fundamentally transformed Earth's atmosphere and enabled the evolution of complex life. Today, roughly half of atmospheric oxygen comes from ocean phytoplankton.

Industrial and Medical Applications

Medical Use: Supplemental oxygen treats respiratory diseases, heart conditions, and helps patients in critical care
Rocket Fuel: Liquid oxygen serves as an oxidizer in rocket propulsion systems
Steel Production: Pure oxygen increases combustion efficiency in metal smelting
Water Treatment: Oxygen kills bacteria and removes contaminants from drinking water
Welding and Cutting: Oxygen-acetylene torches cut and weld metals at high temperatures

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