Oxygen, an element found everywhere on Earth, plays a fundamental role in natural processes and human activities. It is the third most abundant chemical element in the universe, after hydrogen and helium. On our planet, oxygen is the most abundant element by mass in the Earth’s crust, making up approximately 47% to 49% of its composition, and about 89% of the world’s oceans. This element is a major component of our physical environment and underpins the existence and functioning of life itself.
The Breath of Life
Oxygen is directly involved in cellular respiration, the process by which most living organisms convert nutrients into energy. This process takes place within the mitochondria of cells, where oxygen acts as the final electron acceptor in the electron transport chain. The acceptance of electrons by oxygen facilitates the production of adenosine triphosphate (ATP), which is the primary energy currency used by cells to power various functions. Without oxygen, cells would rely on less efficient energy-producing methods, such as fermentation, yielding significantly less ATP.
Humans and animals depend on oxygen for breathing and survival, a process driven by pressure changes within the respiratory system. When we inhale, the diaphragm contracts and moves downward, along with the external intercostal muscles, increasing the chest cavity’s volume. This expansion creates a lower pressure inside the lungs compared to the outside atmosphere, causing air to rush in. Oxygen then diffuses from the tiny air sacs, called alveoli, into the bloodstream, where it binds to hemoglobin in red blood cells for transport throughout the body.
Oxygen enables the high metabolic rates necessary for complex life forms, particularly warm-blooded animals. Efficient oxygen delivery to cells is important for sustaining these elevated metabolic demands. Organisms with higher metabolic rates often have advanced circulatory systems that prevent the mixing of oxygenated and deoxygenated blood, ensuring a continuous supply of oxygen to respiring tissues. This supply supports the energy production required for maintaining body temperature, movement, and complex biological processes.
Shaping Our Planet
Oxygen’s influence extends far beyond biological processes, shaping the physical and chemical composition of Earth. It is a fundamental component of water, with each water molecule (H2O) consisting of two hydrogen atoms and one oxygen atom. Water, in its liquid, solid, and gaseous forms, is essential for all known life and geological processes, covering about 75% of the Earth’s surface. The presence of dissolved oxygen in water bodies also supports aquatic life.
Oxygen is a major constituent of the Earth’s atmosphere, making up approximately 21% of its volume, second only to nitrogen. This atmospheric oxygen is primarily a product of photosynthesis carried out by cyanobacteria, algae, and green plants over billions of years. Within the stratosphere, oxygen plays a unique role in forming the ozone layer (O3).
The ozone layer is formed when ultraviolet (UV) radiation from the sun splits oxygen molecules (O2) into individual oxygen atoms. These single oxygen atoms then combine with other oxygen molecules to form ozone (O3). This cycle absorbs most of the sun’s harmful UV radiation, shielding life on Earth from its damaging effects.
Fueling Industry and Everyday Processes
Oxygen is a participant in chemical reactions, driving many technological applications and everyday phenomena. It acts as an oxidizer in combustion, a process where a substance reacts with oxygen to release heat and light. For instance, when fossil fuels are burned, oxygen combines with hydrogen and carbon in the fuel to form water and carbon dioxide, releasing energy that powers engines and generates electricity. Industrial applications often use pure oxygen or oxygen-enriched air to boost combustion rates, leading to more efficient burning, which can reduce fuel consumption and emissions.
Oxygen is also involved in oxidation processes, such as rusting. Rusting is the oxidation of iron by atmospheric oxygen in the presence of moisture. In this electrochemical reaction, iron loses electrons while oxygen gains electrons, forming rust. The presence of electrolytes like salt can accelerate this process.
Industrially, oxygen sees widespread use. The steel industry is a major consumer, injecting high-purity oxygen into furnaces to remove impurities, enhancing steel quality and reducing smelting time. Oxygen is also combined with fuel gases for welding, cutting, and brazing, producing high flame temperatures for metal fabrication. In medicine, oxygen therapy provides supplemental oxygen to individuals with respiratory conditions, helping to increase blood oxygen levels and improve cellular function.