Phosphorus availability on the early Earth and the impacts of life

A review of aqueous phosphorus availability on the Earth's early surface suggests a range of phosphorus sources supplied the prebiotic Earth, but that phosphorus availability declined as life evolved and altered geochemical cycling. Phosphorus (P) is critical to modern biochemical functions and can control ecosystem growth. It was presumably important as a reagent in prebiotic chemistry. However, on the early Earth, P sources may have consisted primarily of poorly soluble calcium phosphates, which may have rendered phosphate as a minimally available nutrient or reagent if these minerals were the sole source. Here, we review aqueous P availability on the early Earth (>2.5 Gyr ago), considering both mineral sources and geochemical sinks relevant to its solvation, and activation by abiotic and biological pathways. Phosphorus on Earth's early surface would have been present as a mixture of phosphate minerals, as a minor element in silicate minerals, and in reactive, reduced phases from accreted dust, meteorites and asteroids. These P sources would have weathered and plausibly furnished the prebiotic Earth with abundant and potentially reactive P. After the origin of a biosphere, life evolved to draw on not just reactive available P sources, but also insoluble and unreactive sources. The rise of an ecosystem dependent on this element at some point forged a P-limited biosphere, with evolutionary stress forcing the efficient extraction and recycling of P from both abiotic and biotic sources and sinks.