On geological timescales, phosphorus is considered to be the ultimate limiting nutrient to primary productivity (Tyrrell, 1999), which is intrinsically linked to organic carbon production and burial, and therefore atmospheric oxygen content (Canfield et al., 2020). Knowing the sources, abundances, and transformations of phosphorus on the early Earth is critical to our understanding of the coevolution of life and its environment.Our knowledge of ancient marine phosphate concentrations (dissolved inorganic phosphate; DIP) principally relies on indirect measurements (e.g., total rock phosphorus abundance, or biomineralization). Marine DIP levels through time are qualitatively recorded by: (a) phosphorites, marine sediments that contain up to 20 wt % P 2 O 5 that require specific redox conditions to form (Kipp et al., 2020;Stüeken et al., 2021), occur infrequently with a record that only extends to ∼2.1 Ga (Planavsky, 2014); (b) biomineralizing organisms that produced their shells from apatite with the first appearance in the rock record at ∼810 Ma (Cohen et al., 2017); (c) P/Fe ratios and phosphate nanoparticles in banded iron formations which punctuate the rock record from ∼3.2 to 1.8 Ga (Bjerrum & Canfield, 2002;Rasmussen et al., 2021) and (d) rare traces of phosphite recorded in Eoarchean carbonate rocks (Pasek et al., 2013). To overcome the temporal limitations of these records, recent research has focused on the bulk phosphorus content of ancient marine mudstones, which are generally ubiquitous in the geologic record. Bulk phosphorus is measured in mudstone as homogenized fluorapatite, iron oxide-sorbed phosphorus