Where the hydrides of the inner Earth meet the oxides of the upper mantle and crust, tectonism originates and the division between the two outer geospheres of the planet is defined.
The core is recognizably different from the mantle based on density, perhaps being ultimately-compressed intermetals or a new material, an "ultimetal." The essential dichotomy of the two outer geospheres devolves from the gross chemical and physical incompatibility of hydrides and oxides.
Hydride reactions at the transition between inner and outer geospheres are primarily molecular hydride reactions with water.
The proposed triple geospheres theory of the Earth is a dichotomy, a core of unknown "ultimetal," a middle geosphere (underworld) of intermetals, energy-rich hydrides, and an outer geosphere or carapace of energy-poor oxides.
The only known contrast between thee two inner geospheres is simple density, whereas the contrast between the outer two geospheres clearly involves latent energy content as well as density.
Thusly, hydride dissociation and oxidation above a steadily degassing inner geosphere originated the lithosphere and continue to maintain it.
The low silicon density would give it a differential buoyancy among metals; and the ability to form both hydrides and oxides would make it a chemical arbiter between the reduced interior geosphere dominated by the Earth's most abundant element, hydrogen, and the exterior geosphere dominated by the second most abundant element, oxygen.
Within the micro-fractures, hydrides react with water and rock minerals, thus transferring mass and energy from inner to outer geosphere. Silanes in particular deliver the silicon for rock formation as well as the energy for endogeny.
A key to when the outer geosphere developed is given in the evolution of living cells.