Figure 4: Reconstruction of the Δ’¹⁷O of upper atmospheric oxygen.

Plot of Δ'¹⁷O versus linearized δ¹⁸O showing the result of the model calculations (including MonteCarlo error calculation (N=500) grey dots) for I-type spherules 32–01 (a), 32–02 (b), 37–02 (c) and 7 m-01 (d). The measured composition of the I-type spherules is displayed (yellow circle). The oxygen isotope composition is controlled by oxidation (red arrow) and evaporation (blue arrow). The resultant Δ'¹⁷O (at given δ¹⁸O=24‰; this study) is displayed (yellow square) along with the composition of modern tropospheric O₂ (filled upside–down triangle). Given are 1σ-error bars.