Where did the Water in Earth’s Oceans Come from?

Abstract:

How did Earth get the water to fill its oceans? Upper mantle minerals, in particular olivine, pyroxenes and others, retrieved at the Earth’s surface, have consistently been found to contain low hydroxyl concentrations, indicative of a low to very low solute H₂O contents. This has been interpreted for decades to mean that the upper mantle of the early Earth may not have had enough water to fill the oceans through volcanic and other degassing. To overcome this dilemma, large-scale cometary impacts are thought to have been necessary to supply the missing water. This interpretation is based on a misinterpretation of laboratory data obtained primarily by infrared absorption but also SIMS and related techniques. This interpretation disregards a pervasive redox conversion that takes place in the solid state, during cooling, changing pairs of solute hydroxyls into peroxy plus H₂. This redox conversion simply rearranges electrons within hydroxyl pairs. It takes place under thermodynamic non-equilibrium conditions, at temperatures so low that diffusional processes in the mineral matrix are already frozen. As a result every mineral and rock brought to the surface of the Earth and retrievable for analysis has undergone this redox conversion. Its importance is that it produces molecular H₂, interstitial in the matrix of minerals, difficult to assess analytically. It produces peroxy defects, which have been overlooked for a long time. H₂ molecules may diffuse out of mineral grains, leaving behind the peroxy as a memory of the former solute water content. In order to fully assess the true solute H₂O content in the Earth’s upper mantle it is necessary to take the peroxy contents into consideration.