Physical properties of galaxies at z > 7 are of interest for understanding both the early phases of star formation and the process of cosmic reionization .
Chemical abundance measurements offer valuable information on the integrated star formation history , and hence ionizing photon production , as well as the rapid gas accretion expected at such high redshifts .
We use reported measurements of [ O iii ] 88 \mu m emission and star formation rate to estimate gas-phase oxygen abundances in five galaxies at z = 7.1 - 9.1 using the direct T _ { \mathrm { e } } method .
We find typical abundances 12 + \mathrm { \log { ( O / H ) } } = 7.9 ( \sim 0.2 times the solar value ) and an evolution of 0.9 \pm 0.5 dex in oxygen abundance at fixed stellar mass from z \simeq 8 to 0 .
These results are compatible with theoretical predictions , albeit with large ( conservative ) uncertainties in both mass and metallicity .
We assess both statistical and systematic uncertainties to identify promising means of improvement with the Atacama Large Millimeter Array ( ALMA ) and the James Webb Space Telescope ( JWST ) .
In particular we highlight [ O iii ] 52 \mu m as a valuable feature for robust metallicity measurements .
Precision of 0.1–0.2 dex in T _ { \mathrm { e } } -based O/H abundance can be reasonably achieved for galaxies at z \approx 5 –8 by combining [ O iii ] 52 \mu m with rest-frame optical strong lines .
It will also be possible to probe gas mixing and mergers via resolved T _ { \mathrm { e } } -based abundances on kpc scales .
With ALMA and JWST , direct metallicity measurements will thus be remarkably accessible in the reionization epoch .