CHNO compound characteristics differentiating CHNOS precursors (1st row, orange) and non-CHNOS precursors (2nd row, gray). From left to right: H/C-O/C, H/C-N/C, #H-#C, #N-#O, H/C-m/z plots. Two groups of CHNO compounds (CHNOS precursors (direct and indirect ones), orange, and non-CHNOS precursors, gray) have been identified via molecular network analysis (see details in main text "CHNO-CHNOS molecular network" and Methods section "Molecular network analysis"). Dashed lines represent mean values.