How does oxygen exit the atmosphere?

Oxygen exits the atmosphere primarily through two processes: photosynthesis and respiration. During photosynthesis, plants and certain microorganisms take in carbon dioxide and release oxygen as a byproduct. Additionally, some oxygen is consumed by animals and other organisms during respiration, where it is utilized to produce energy, releasing carbon dioxide back into the atmosphere. Over geological timescales, oxygen can also be removed from the atmosphere through chemical reactions, such as the oxidation of minerals and the formation of compounds like iron oxide.