Phosphogenesis in the 2460 and 2728 million‐year‐old banded iron formations as evidence for biological cycling of phosphate in the early biosphere

• Published in: Ecology and evolution 2013-01, Vol.3 (1), p.115-125
• Main Authors: Li, Yi‐Liang, Sun, Si, Chan, Lung S.
• Format: Article
• Language: English
• Subjects: Anaerobic microorganisms; Apatite; Banded iron formation; Biogeochemical cycles; Biomarkers; Biosphere; Cambrian; Cycles; Ecosystems; Ferric hydroxide; Flowers; Geology; Geosphere; great oxidation event; Iron; iron oxide; Lithology; Micrometers; Microorganisms; Mineralization; Minerals; Nutrient cycles; Oceans; Original Research; Oxidation; phosphate; Phosphorite; Phosphorus; Phytoplankton; Precambrian; Precipitation; primary productivity; Productivity; Ultrafines
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.443

The banded iron formation deposited during the first 2 billion years of Earth's history holds the key to understanding the interplay between the geosphere and the early biosphere at large geological timescales. The earliest ore‐scale phosphorite depositions formed almost at ~2.0–2.2 billion years ago bear evidence for the earliest bloom of aerobic life. The cycling of nutrient phosphorus and how it constrained primary productivity in the anaerobic world of Archean–Palaeoproterozoic eons are still open questions. The controversy centers about whether the precipitation of ultrafine ferric oxyhydroxide due to the microbial Fe(II) oxidation in oceans earlier than 1.9 billion years substantially sequestrated phosphate, and whether this process significantly limited the primary productivity of the early biosphere. In this study, we report apatite radial flowers of a few micrometers in the 2728 million‐year‐old Abitibi banded iron formation and the 2460 million‐year‐old Kuruman banded iron formation and their similarities to those in the 535 million‐year‐old Lower Cambrian phosphorite. The lithology of the 535 Million‐year‐old phosphorite as a biosignature bears abundant biomarkers that reveal the possible similar biogeochemical cycling of phosphorus in the Later Archean and Palaeoproterozoic oceans. These apatite radial flowers represent the primary precipitation of phosphate derived from the phytoplankton blooms in the euphotic zones of Neoarchean and Palaoeproterozoic oceans. The unbiased distributions of the apatite radial flowers within sub‐millimeter bands do not support the idea of an Archean Crisis of Phosphate. This is the first report of the microbial mediated mineralization of phosphorus before the Great Oxidation Event when the whole biosphere was still dominated by anaerobic microorganisms. The Archean Phosphorus Crisis hypothesizes that the precipitation of ferric oxihydroxide might have significantly removed phosphorus from the pre‐1.9 billion‐year‐old oceans that resulted in a primary productivity of the early marine ecosystem only equals to 25% or less of the modern marine ecosystem. We observed the primary precipitation of phosphate in banded iron formations may represent the mineralization of phosphorus from the localized phytoplankton blooms and suggest a biologically controlled, rather than geochemically controlled cycling of phosphorus.