Oxygen is named from the Greek oxys, acid, and genes, forming. Oxygen was prepared by several workers, including Bayen and Borch, but they did not know how to collect it, did not study its properties, and did not recognize it as an elementary substance. Priestley is generally credited with its discovery. Oxygen is the third most abundant element found in the sun and it plays a part in the carbon-nitrogen cycle. Oxygen as a gaseous element forms 21% of the atmosphere by volume from which it can be obtained by liquefaction and fractional distillation. The element and its compounds make up 49.2%, by weight, of the earth's crust. About two thirds of the human body and nine tenths of water is oxygen. Oxygen is very reactive and capable of combining with most elements. It is a component of hundreds of thousands of organic compounds and is essential for respiration of all plants and animals and for practically all combustion. Oxygen enrichment of steel blast furnaces accounts for the greatest use of the gas.