The element most commonly connected with water and life on Earth is oxygen. Water is composed of two hydrogen atoms bonded to one oxygen atom (H2O). Oxygen is essential for the survival of most living organisms, as it plays a critical role in cellular respiration, the process through which cells generate energy. Additionally, oxygen is vital for decomposing organic matter and cycling nutrients in ecosystems. The presence of oxygen in aquatic environments, alongside water, supports a diverse range of life forms, making it fundamental to biological processes.