Reevaluating the nutrient timeline: Francevillian basin geochemistry reveals early permissive conditions for eukaryotic life

• Geochemical data reveal nutrient- and oxygen-rich seawater in the 2.1 Ga Francevillian Basin. • Paleoproterozoic phosphate and zinc levels rivaled or exceeded those of Cambrian oceans. • Key chemical conditions for complex life existed over a billion years earlier than thought. • Nutrient-rich window coincides with Francevillian macrobiota, challenging evolutionary and environmental timelines. Environmental thresholds of oxygen and nutrients have played a pivotal role in shaping the timing and nature of major biological transitions throughout Earth’s history. Limited marine phosphate availability is thought to have constrained the tempo and trajectory of early eukaryotic evolution. A sustained global rise in marine P and trace metal nutrient availability, reaching near-modern levels, coincided with the Neoproterozoic Oxidation Event (NOE) and the emergence and radiation of Ediacaran and Cambrian animal lineages. Here, we present new geochemical evidence from the 2.1-billion-year-old (Ga) Francevillian Basin that reveals a striking exception to this timeline. Our data indicate that Paleoproterozoic seawater in the Francevillian Basin episodically reached nutrient and oxygen levels comparable to, and in the case of phosphate and zinc, potentially exceeded concentrations associated with the seawater in which the Cambrian biota of Burgess Shale emerged. The data suggest that permissible key chemical conditions for complex life existed in the Francevillian sea long before the Ediacaran–Cambrian nutrient surge. The coincidence of this anomalous Paleoproterozoic nutrient-rich window with the earliest known marine experimentation at macrobiological complexity, represented by the much-debated 2.1 Ga Francevillian macrobiota, challenges established timelines of biological innovation and environmental prerequisites.