Molecular oxygen (\(\text{O}_2\)) makes up about 21% of the air and is necessary for the survival of nearly all complex life on Earth. While the sheer volume of atmospheric oxygen suggests an endless supply, its continued availability depends entirely on dynamic global processes. The balance between the production and consumption of this gas determines its classification as a resource.
Understanding What Makes a Resource Renewable
A renewable resource replenishes itself through natural processes at a rate comparable to or faster than its rate of consumption. This contrasts with nonrenewable resources, like fossil fuels, which are depleted much faster than they can be naturally reformed. For a resource to be truly renewable, the natural cycle must consistently maintain a positive or neutral balance between its source (production) and its sink (consumption). Judging oxygen requires evaluating whether its natural replenishment mechanism can keep pace with its continual use.
The Primary Source of Atmospheric Oxygen
The majority of free oxygen in the atmosphere is generated by oxygenic photosynthesis. This chemical reaction is performed by plants, algae, and certain bacteria, converting light energy into chemical energy. Photosynthesis uses carbon dioxide (\(\text{CO}_2\)), water (\(\text{H}_2\text{O}\)), and sunlight to produce glucose (sugar) and release molecular oxygen (\(\text{O}_2\)) as a byproduct.
The global supply of this oxygen is often mistakenly attributed mainly to terrestrial forests, but marine organisms contribute significantly to the total output. Microscopic organisms in the oceans, particularly phytoplankton and algae, are responsible for an estimated 50% or more of the planet’s total oxygen production. The oxygen released originates from the splitting of water molecules, a step known as photolysis, which occurs during the light-dependent reactions. A secondary, far smaller source comes from abiotic photolysis, where high-energy ultraviolet radiation breaks down water vapor in the upper atmosphere.
Maintaining Global Oxygen Levels Through the Cycle
The existence of the oxygen cycle confirms that oxygen is a renewable resource, as its production is directly linked to its consumption in a continuous, balanced system. The cycle involves a constant exchange between the atmosphere, biosphere, and other spheres. Consumption, which balances photosynthetic production, occurs primarily through respiration by animals, humans, and plants, where oxygen is used to break down glucose for energy and carbon dioxide is released.
Other consumption processes include the decomposition of dead organic matter by microbes and various forms of oxidation, such as burning (combustion) and the rusting of metals. Because the total biological production of oxygen (photosynthesis) is in equilibrium with the total consumption (respiration and decay) on a global scale, the concentration of atmospheric oxygen remains stable. This continuous, self-regulating balance driven by life processes classifies atmospheric oxygen as a renewable resource.