No, all of Earth's carbon dioxide supply is not constantly being used by organisms. While many organisms and ecosystems play a role in exchanging carbon dioxide with the environment through processes such as photosynthesis and respiration, there are also other natural processes that contribute to the global carbon cycle, including volcanic activity and abiotic processes like weathering. Additionally, human activities, primarily the burning of fossil fuels, have caused an increase in atmospheric carbon dioxide levels above what would naturally occur, leading to more carbon dioxide being present in the atmosphere.
