The Earths atmosphere is 21% Oxygen. The rest is composed of Nitrogen (78%) Carbon Dioxide (.03%), plus other miscellaneous gases.
An atmosphere (New Latin atmosphaera, created in the 17th century from Greek ἀτμός [atmos] "vapor" and σφαῖρα [sphaira] "sphere") is a layer of gases surrounding a material body of sufficient mass that is held in place by the gravity of the body. An atmosphere is more likely to be retained if the gravity is high and the atmosphere's temperature is low.
Earth's atmosphere, which contains oxygen used by most organisms for respiration and carbon dioxide used by plants, algae and cyanobacteria for photosynthesis, also protects living organisms from genetic damage by solar ultraviolet radiation. Its current composition is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms.
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Elements are divided into metals, metalloids, and non-metals. Familiar examples of elements include carbon, oxygen (non-metals), silicon, arsenic (metalloids), aluminium, iron, copper, gold, mercury, and lead (metals).
The lightest chemical elements, including hydrogen, helium (and smaller amounts of lithium, beryllium and boron), are thought to have been produced by various cosmic processes during the Big Bang and cosmic-ray spallation. Production of heavier elements, from carbon to the very heaviest elements, proceeded by stellar nucleosynthesis, and these were made available for later solar system and planetary formation by planetary nebulae and supernovae, which blast these elements into space. The high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars, after the lighter gaseous elements and their compounds have been subtracted. While most elements are generally viewed as stable, a small amount of natural transformation of one element to another also occurs at the present time through decay of radioactive elements as well as other natural nuclear processes.
A Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. The essential component for any breathing gas is a partial pressure of oxygen of between roughly 0.16 and 1.60 bar at the ambient pressure. The oxygen is usually the only metabolically active component unless the gas is an anaesthetic mixture. Some of the oxygen in the breathing gas is consumed by the metabolic processes, and the inert components are unchanged, and serve mainly to dilute the oxygen to an appropriate concentration, and are therefore also known as diluent gases.
Air is the most common and only natural breathing gas. Other gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as SCUBA equipment, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft, medical life support and first aid equipment, high-altitude mountaineering and anaesthetic machines.
Carbonic acid gas
Dry ice (solid phase)
Breathing is the process that moves air in and out of the lungs or oxygen through other breathing organs such as gills. Breathing is one part of physiological respiration. Aerobic organisms of these types—such as birds, mammals, and reptiles—require oxygen to release energy via cellular respiration, in the form of the metabolism of energy-rich molecules such as glucose. Breathing is only one process that delivers oxygen to where it is needed in the body and removes carbon dioxide. Another important process involves the movement of blood by the circulatory system. Gas exchange occurs in the pulmonary alveoli by passive diffusion of gases between the alveolar gas and the blood in lung capillaries. Once these dissolved gases are in the blood, the heart powers their flow around the body (via the circulatory system). The medical term for normal relaxed breathing is eupnea.
In addition to removing carbon dioxide, breathing results in loss of water from the body. Exhaled air has a relative humidity of 100% because of water diffusing across the moist surface of breathing passages and alveoli. When a person exhales into very cold outdoor air, the moisture-laden atmosphere from the lungs becomes chilled to the point where the water condenses into a fog ("seeing the breath").