Nitrogen isotopic composition of microbial biomass grown in the laboratory under N2-fixing conditions. Also included are meta-data that describe the experimental conditions. The conditions were chosen to mimic specific parameters of the early Earth, in particular variable CO2 and O2 supplies, to test if d15N data recorded in ancient biomass in the rock record is affected. Also included are data from the wider literature for comparison, as well as the results of statistical tests.

The data include P speciation data (reduced and polymerized P) from Archean rocks in the Moodies Group in South Africa (3.2 Ga), spanning across basaltic intrusions into sedimentary strata, as well as experimental data from simulations of phosphate heating in the presence of organic matter and iron as would have occurred during magma intrusions. Also included are auxiliary geochemical data of bulk elemental abundances to characterize the rock samples.