Iron and oxygen isotope fractionation during iron UV photo-oxidation: Implications for early Earth and Mars

The oxygen isotopic composition of lepidocrocite precipitated from the photo-oxidation experiment was measured and it is related to the composition of water by mass-dependent fractionation. The precipitate-fluid 18O/16O isotope fractionation of ∼+6‰ is consistent with previous determinations of oxygen equilibrium fraction factors between iron oxyhydroxides and water.