Vladimir, C.W. Hunt et al, hypothized that the Earth expands over time (or has expanded) because it has a hydridic (Hydrogen-rich) core. It seems to me that this hypothesis has some real strengths which are worth considering for a number of reasons.

Hydrogen was super-abundant when the solar-system formed, and it may have been similarly abundant in the original materials from which comets formed. If the Earth accreted from that same reservoir of materials at a rate sufficiently fast to have trapped alot of hydrogen in the zone which became the core, then the Hydrogen may have been absorbed into the abundant metals at pressures and temperatures that would have allowed the diffusion of the Hydrogen as a naked proton. (Remember that Hydrogen IS a metal, and unlike any other element, becomes an entity of Nuclear rather than Atomic dimensions with the loss of only one electron...) Russian theory and experiments suggest that the protons could fill the interstices between atoms and perhaps even some volumes inside the outermost valences of Iron and Nickel atoms.

The salient point as far as Earth expansion is concerned, is that the density of the core may have risen much higher, due to the protons filling the interstices, than it would have otherwise - perhaps 18 or more grams/cc. Then, as the Hydrogen diffuses outwards, the protons would at some point recover their electrons, become atoms/molecules (probably as Silanes) and, obviously, recover the volume appropriate to atomic size scales. This would decrease the density of the core, and bloat the volume of Earth. The bloating would happen at the rate at which the Hydrogen diffuses, and the oceans may originate from this process.

If the diffusion of the Hydrogen does occur as a Silane (like Methane only with a Silicon atom instead of a Carbon atom) then the Silane would oxidize to quartz and water as soon as it encountered enough oxygen in the mineral matter encountered along the way. The oxidation of Silanes is exothermic and this heat source may be part of what melts reservoirs of magmas.

I suspect that the physics of Hydrogen's absorption into metallic matrices with the loss of a single electron, and eventual diffusion of the Hydrogen and reaquisition of it's lost electron, might provide a mechanism of expansion (without hypothesizing Ex Nihilo creation of new mass) as well as the generation of Earth's magnetic field. I also suspect that the rate at which the newly accreted planet could cool might be orders of magnitude faster assuming alot of Hydrogen in the initial mixture, than would be possible otherwise.