Hydrogen gas is gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its lightweight, which enables it to escape from Earth's gravity more easily than heavier gases. Still, hydrogen is the third most abundant element on the Earth's surface, mostly in the form of chemical compounds such as hydrocarbons, minerals, and water.

Sources of Hydrogen

Hydrogen gas is produced by some bacteria and algae and is a natural component of flatus, as is methane, itself a hydrogen source of increasing importance. Hydrogen is frequently produced from natural gas, which comprises the removal of hydrogen from hydrocarbons at very high temperatures.

Hydrogen occurs in several forms in minerals. The most common are hydroxyl (OH) groups and water (H2O). Chemically speaking the simplest minerals are found as hydroxides and oxyhydroxides, for example, brucite(Mg(OH)2) , gibbsite and bayerite (Al(OH)3), diaspore (AlOOH), goethite (FeOOH), manganite(MnOOH), and so¨hngeite (Ga(OH)3).

Hydrogen preparation

Hydrogen can be formed through the reaction of water or dilute acids on electropositive metals such as alkali metals, alkaline earth metals, the metals of Groups 3, and 4, and the lanthanoids. The reaction can be explosively violent. 

Suitable laboratory methods use sodium amalgam or calcium with water, or zinc with hydrochloric acid. The reaction of aluminum or ferrosilicon with aqueous sodium hydroxide has also been applied.

Effect on the human body

Hydrogen is the most abundant element in the human body in terms of the number of atoms of the element but the third most abundant element by mass. H2 occurs in the breath of humans due to the metabolic activity of hydrogenase-containing microorganisms in the large intestine and is a natural component of flatus. The concentration in the breath of fasting people at rest is typically less than 5 parts per million (ppm) but can be 50 ppm when people with intestinal disorders consume molecules they cannot absorb during diagnostic hydrogen breath tests.