Fig. 2.

Model results showing how seawater δ⁹⁸Mo responds to Mo burial into its different sinks (model details in SI Appendix). Contours show range of solutions for a given seawater δ⁹⁸Mo that represents modern seawater (2.3‰), early Devonian seawater (2.0‰), early Paleozoic seawater (1.4‰), and Mesoproterozoic seawater (1.1‰). The black circle represents modern state (Table S3). The shaded area at bottom left represents states where the sulfidic sinks are dominant, so that the ocean becomes heterogeneous in dissolved molybdenum. The faded area at top lacks the intermediate redox sink, despite the extreme end-members (OX and EUX) being substantial (top). Both regions are considered unlikely.