Notable books in the design pattern genre include: 1  Gamma, Erich; Helm, Richard; Johnson, Ralph; Vlissides, John (1995). 2  Brinch Hansen, Per (1995). 3  Buschmann, Frank; Meunier, Regine; Rohnert, Hans; Sommerlad, Peter (1996). 4  Schmidt, Douglas C.; Stal, Michael; Rohnert, Hans; Buschmann, Frank (2000). 5  Fowler, Martin (2002).
Answer 1: The oxygen that we currently find in the air has two main sources. The first, and major, source is that oxygen is liberated as a by-product of photosynthetic chemical reactions. The second source occurs in the atmosphere itself when water molecules are split apart after being struck with ultraviolet radiation. This process is called photolysis. The molecule is broken down into one diatomic hydrogen molecule and one free oxygen. The hydrogen molecule is light, and has a quick thermal velocity,so it can escape Earth's atmosphere leaving behind the free oxygen to form a diatomic oxygen molecule. The main source of this atmospheric water was volcanic eruptions and outgassing. Basically before photosynthesis began on large scales, free oxygen molecules in the atmosphere were drawn down in oxidation reactions with free metal ions on the Earth's surface, mainly iron.
The oxygen passes into the atmosphere and the hydrogen joins with carbon dioxide to produce biomass. When living things need energy they take in oxygen for respiration. The oxygen returns to the atmosphere in the form of carbon dioxide. Oxygen gas is fairly soluble in water, which makes aerobic life in rivers, lakes and oceans possible. Natural abundance. Oxygen makes up 21% of the atmosphere by volume. This is halfway between 17% (below which breathing for unacclimatised people becomes difficult) and 25% (above which many organic compounds are highly flammable).