These complementary studies are relevant to photogeochemistry in that they illustrate reactions that may have a natural counterpart. For example, it has been shown that soils, when irradiated, can generate reactive oxygen species[26] and that clay minerals present in soils can accelerate the degradation of synthetic chemicals;[27] it may therefore be postulated that naturally occurring compounds are similarly affected by sunlight acting on soil. The conversion of N2 to NH3 has been observed upon irradiation in the presence of the iron titanate Fe2Ti2O7.[28][29] While such a compound is not known to occur naturally, it is related to ilmenite (FeTiO3) and pseudobrookite (Fe2TiO5), and can form upon heating of ilmenite;[28][30] this may imply a similar reaction with N2 for the naturally occurring minerals.