Hydrogen is named from the Greek hydro, water and genes, forming, and was prepared many years before it was recognized as a distinct substance in 1766. Hydrogen is the most abundant of all elements in the universe, and it is thought that the heavier elements were, and still are, being built from hydrogen and helium. It has been estimated that hydrogen makes up more than 90% of all the atoms or three quarters of the mass of the universe. On earth, hydrogen occurs chiefly in combination with oxygen in water, but it is also present in organic matter such as living plants, petroleum, coal, etc. Great quantities of hydrogen are required commercially for the fixation of nitrogen from the air in the Haber ammonia process and for hydrogenation of fats and oils. It is also used in large quantities in methanol production, in hydroalkenation, hydrocracking and hydrodesulfurization. And it also used as a rocket fuel, for welding, for production of hydrochloric acid, for the reduction of metallic ores and for filling balloons. Production of hydrogen in the U.S is well over 3 billion cubic feet per year.