Role of hydrogen and proton transportation in Earth’s deep mantle

Hydrogen(H)is the most abundant element in the known universe,and on the Earth’s surface it bonds with oxygen to form water,which is a distinguishing feature of this planet.In the Earth’s deep mantle,His stored hydroxyl(OH−)in hydrous or nominally anhydrous minerals.Despite its ubiquity on the surface,the abundance ofHin the Earth’s deep interior is uncertain.Estimates of the totalHbudget in the Earth’s interior have ranged from less than one hydrosphere,which assumes an H-depleted interior,to hundreds of hydrospheres,which assumes thatHis siderophile(iron-loving)in the core.This discrepancy raises the questions of how H is stored and transported in the Earth’s deep interior,the answers to which will constrain its behavior in the deep lower mantle,which is defined as the layer between 1700 km depth and the core–mantle boundary.