Most of the living things on the earth absorb oxygen and exhale carbon dioxide in the process of breathing. People also consume a lot of oxygen and carbon dioxide when burning various fuels in production and life. However, the relative content of oxygen in the atmosphere did not decrease. This is because there are a wide range of green plants on the earth. The oxygen produced by green plants in photosynthesis consumes carbon dioxide in the atmosphere, which exceeds the oxygen demand of their own respiration. The oxygen produced is discharged into the atmosphere in the form of gas, so that the concentration of oxygen and carbon dioxide in the air of the biosphere is in a relatively balanced state.