The Silicate Bridge: Low-Pressure Percolation, Inherited Redox, and the Onset of the Anoxic Iron-Silicate Ocean

We present a self-contained physical-chemical foundation linking nebular silicate assembly to the onset of Earth’s anoxic iron-silica surface regime. High-temperature crystalline silicates (forsterite and enstatite) and low-gravity porous aggregates (45–70% pore volume) establish permeable grain-boundary networks. Sulfur-rich Fe–S liquids at the Fe–FeS eutectic (approximately 988°C) reduce solid–liquid dihedral angles. Experimental data show that percolative connectivity is favored at planetesimal-to-embryo pressures of ≤1.0–1.5 GPa, enabling embryonic core formation before global melting. Subsequent giant-impact magma oceans and high-pressure metal–silicate equilibration (roughly 30–50 GPa and 2500–3800 K), combined with bridgmanite-hosted Fe²⁺ disproportionation, raise mantle oxygen fugacity from early values of ΔIW ≈ –4 to –2.5 to late-stage values of ΔIW ≈ –2 to –1.5. A four-stage iterative accretion model with approximately 0.5 wt% late veneer recovers the primitive upper mantle (PUM) abundances of Ni, Co, W, Mo, and Ir within uncertainty. The critical and previously under-treated step is the continuous transfer of this inherited redox state into surface boundary conditions. Residual melts at ΔIW ≈ –2.0 to –1.5 degas a strictly anoxic secondary atmosphere. Detrital zircons dated to approximately 4.4 Ga with elevated δ¹⁸O values require liquid-water–crust interaction within about 150 million years of the Moon-forming event. Serpentinization of still-hot ultramafic crust then couples silicate hydration to continuous abiotic H₂ production, alkaline fluids, and planetary-scale silica mobilization. This paper maps secondary-atmosphere speciation under the inherited redox window, quantifies porosity and critical melt fraction for percolation, and compiles laboratory and thermodynamic constraints that fix the order of magnitude of each link. The result is a continuous silicate-governed path from multi-stage core formation to the Fe²⁺–silica ocean that later hosts the long anoxic iron–silicate eon, without requiring discontinuous jumps in physics or chemistry. This standalone technical contribution provides maximum quantitative rigor on Phase I and the Bridge Interval. It is complemented by the broader three-phase narrative developed in The Silicate Continuum (open Zenodo overview).