Time-evolution of fO2

[nichollsh]

At the moment we keep fO2 fixed. Realistically, this would vary over time as the magma ocean becomes more oxidised. We know for measurements of zircons that Earth's mantle was oxidised early in its life, although it would have started as highly reducing from accretion.

We need some way to model/quantify this as it has important implications for atmospheric composition, chemistry, escape, cooling, and observations.

Somewhat connected to: #215, #93, #205, #168, #57.

Maybe this can be handled by https://github.com/FormingWorlds/ABASSI

[nichollsh]

A better option is to quantify this self-consistently with the atmospheric composition. This would inherently account for oxidation by escape, through the removal of hydrogen.

See:
https://iopscience.iop.org/article/10.3847/PSJ/ac67a9/pdf eq 10 (peridotite) and eq 11 (basalt)
https://www.science.org/doi/10.1126/sciadv.abd1387
https://www.sciencedirect.com/science/article/pii/S0016703722001715 eq 21