Extended Data Fig. 7: Expected fossil assemblages of different hypothetical ecosystem scenarios.

a, Scenario with eukaryotes restricted to oxic habitats. If eukaryotes were planktonic, we would expect eukaryote fossils in sedimentary rock samples deposited in environments with oxic or anoxic bottom waters, as planktonic aerobes could have lived in the oxygenated surface waters. However, if all eukaryotes were benthic, then only rare, transported eukaryote fossils would be present in anoxic samples. b, Scenario with eukaryotes restricted to anoxic habitats. Regardless of whether eukaryotes were planktonic or benthic, we would expect to near-exclusively find eukaryote fossils in anoxic samples. c, Scenario with eukaryotes in oxic and anoxic habitats. In this scenario, we would expect to find eukaryote fossils in comparable abundances in oxic and anoxic samples, though the diversity and taxa may vary.