Natural hydrogen

Natural hydrogen is molecular hydrogen produced by geological and other natural processes and found in Earth’s crust. It can migrate through rock and accumulate in underground reservoirs.

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Serpentinization: A water–rock reaction in which water alters iron-rich minerals, often producing molecular hydrogen. This reaction can generate hydrogen when water encounters iron-bearing rocks underground.
Mantle degassing: The release of volatile substances from Earth’s mantle into the crust and atmosphere. Deep Earth degassing is one proposed source of hydrogen reaching the crust.
Hydrogen exploration: The search for naturally occurring hydrogen accumulations using geological, geochemical, and geophysical evidence. Exploration tests whether hydrogen sources, migration routes, and traps coincide.
Hydrogen resource assessment: The estimation of hydrogen quantities that may exist or be recoverable in geological formations. Resource estimates depend on uncertain generation rates, losses, and reservoir volumes.
Radiolysis: The decomposition of molecules by ionizing radiation, including radiation-driven splitting of water into hydrogen and oxidants. Radioactive minerals can produce hydrogen by splitting water in crustal rocks.
Water–rock interaction: Chemical reactions between water and rocks that alter minerals and change fluid composition. Serpentinization and related hydrogen-producing reactions belong to this broader process.
Hydrogen production: The processes used to obtain molecular hydrogen from feedstocks or natural deposits. Natural accumulations are one possible source within the broader hydrogen supply system.
Hydrogen geochemistry: The study of hydrogen’s chemical forms, reactions, and distribution in geological systems. Geochemical measurements help distinguish active production from stored or migrating hydrogen.
Fischer–Tropsch-type synthesis: A family of reactions that forms hydrocarbons from carbon monoxide or dioxide and hydrogen, often over mineral catalysts. These reactions can consume geological hydrogen and shape its underground abundance.
Oxidation of ferrous iron: A chemical reaction in which iron in the +2 oxidation state loses electrons and becomes iron in the +3 state. Iron oxidation can supply electrons that reduce water to molecular hydrogen.