The chemical element represented by the symbol O is oxygen. Oxygen is a non-metal and a vital component of the Earth's atmosphere, making up about 21% by volume. It plays a critical role in supporting life, as it is necessary for respiration in most living organisms. Oxygen is also essential for combustion processes, enabling fire to sustain itself. In nature, it typically exists as a diatomic molecule, O2, and is involved in various chemical reactions, including oxidation and photosynthesis. Its abundance and reactivity make it one of the most important elements on our planet.