Oxygen is the element commonly referred to as the "breath of life," due to its critical role in supporting animal and human life. It is essential for the process of cellular respiration, a metabolic process where organisms convert glucose and other nutrients into energy. This process produces carbon dioxide as a byproduct, which must be expelled from the body. Oxygen makes up about 21% of Earth's atmosphere and is crucial for sustaining aerobic life forms. Without oxygen, most life on Earth would be unsustainable, making it a vital component of our biosphere.