5. Natural hydrogen

Hydrogen in its molecular state, H ₂ , has long been considered not to exist in nature except in trace amounts, as is the case at Mount Chimera in Turkey, where flames have been observed for millennia due to the continuous emanation of a mixture mainly made up of methane and dihydrogen (figure 7 ). To obtain it in large quantities, it had to be, and still has to be, produced by the chemical or electrochemical processes described above. With the development of suitable detection systems, however, emanations of natural hydrogen have since been discovered, first on the ocean floor and more recently on land