The Oxygen–Carbon Cycle: How Nature Keeps Earth’s Atmosphere in Balance

As we know, animals consume oxygen from the air and release carbon dioxide. The air we breathe contains about 20% oxygen and only 0.03% carbon dioxide.

At first glance, given that the amount of oxygen in Earth’s atmosphere is limited, it would be reasonable to assume that one day the oxygen would run out and all living creatures would perish. Indeed, some early scientists who believed the world operated purely by chance feared exactly that. Others, who believed in a higher order and design in nature, were confident that because life continues, there must be a system in place to keep the balance.

Plants: Nature’s Built-In Oxygen Factory

As scientific research advanced, the hidden mechanism was revealed. The plant world requires massive amounts of carbon to create and sustain its trunks, stems, branches, leaves, and fruits. Logically, one would think plants must rely on existing carbon materials.

Astonishingly, researchers discovered that plants are equipped with a remarkable natural mechanism. Plants absorb the carbon dioxide released by animals and, in turn, release oxygen back into the air, that animals (including humans) need to survive. This creates a mutual life-sustaining cycle between the plant and animal worlds.

Photosynthesis: The Perfect Green Laboratory

Studies have shown that within green plants exists an incredibly sophisticated "laboratory" that human technology cannot replicate. Using nothing more than air, sunlight, and carbon dioxide, green plants produce the sugars they need for survival. During this process, they release oxygen into the atmosphere and due to this continuous exchange, the supply of oxygen essential for life never runs out.

The Question of Balance

How is the balance maintained so precisely? Without constant regulation, the system should naturally shift out of balance. If plant life (through natural growth or artificial planting) increased far more than the animal population, oxygen levels in the atmosphere would rise dramatically. Conversely, if animal populations outnumbered plants, carbon dioxide levels would climb.

These shifts would be disastrous. Fire, for example, consumes oxygen. The higher the oxygen concentration, the faster and more intensely fire spreads. Today’s atmosphere contains about 20% oxygen, which is the exact level our bodies require for healthy and comfortable breathing.

If oxygen levels were much higher, every lightning strike or even a small burning match could trigger uncontrollable global fires, destroying nearly all life on Earth. On the other hand, if oxygen levels were much lower, breathing would become extremely difficult, turning life itself into a constant struggle.

For thousands of years, the oxygen levels in Earth’s atmosphere have remained remarkably stable, despite fluctuations in both plant and animal populations. What ensures that this exact balance is maintained so perfectly?