The element with the atomic number 8 is oxygen (O). Oxygen is a diatomic molecule that is essential for most forms of life on Earth. It plays a critical role in respiration for animals and is a vital component of water (H2O), which sustains nearly all life forms. Oxygen is also involved in various chemical reactions, including combustion. In the Earth's atmosphere, oxygen makes up about 21% of the volume, providing the essential element for aerobic metabolism, which is the process by which living organisms convert nutrients into energy. Its discovery and understanding have been pivotal in the fields of chemistry and biology.