R2–R3 diagram showing our two JADES sub-samples at z ∼ 6 (purple points) and z ∼ 8 (maroon points). Comparison samples from SDSS and MOSDEF are shown as in Fig. 3. We additionally show comparison with two populations of z ∼ 0 extreme starbursts: green peas (Yang et al. 2017a; orange plusses) and blueberries (Yang et al. 2017b; blue crosses). The three well-studied z > 7.5 galaxies from the SMACS 0723 ERO observations are shown as lime green pentagons, adopting the ratio values presented by Nakajima et al. (2023). Unlike the BPT and VO87 diagrams, the majority of our sample have > 3σ detections of all lines in individual spectra, revealing a large diversity within the sample. Ratios measured from stacked JADES spectra are shown as the open magenta and red diamonds (see Sect. 2.5).