The influence of oxygen and electronegativity on iron mineral chemistry throughout Earth’s history

Abstract

The mineral record contains chemical signatures that reflect the evolving redox conditions of Earth’s crust, and reveal trends in the bioavailability of life's critical elements. In particular, shifting redox states of transition metal elements that are used as co-factors by enzymes across all domains of life can be tracked in preserved mineral chemistry. The transition metal iron (Fe) is one of the most abundant elements in Earth’s core, mantle, and crust, and is commonly a major constituent of rock-forming minerals. Additionally, Fe is the most widely used metal in biology, and Earth’s redox history has profoundly impacted the chemical speciation and availability of Fe in aqueous systems. The diverse mineral chemistry of Fe can therefore reveal new insights into the redox evolution of Earth’s crust and subsequent biological impacts. Here, we apply a new mineral chemistry network analysis platform, dragon, to investigate the mineral chemistry of iron (Fe) over geologic-time. We present bipartite network graphs of iron minerals linked to their constituent elements or ions for several geological time intervals. These graphs illustrate the increasing importance of oxygen (O) abundance in the atmosphere from the Paleoarchean to the Mesoproterozoic in regard to the the emergence of new Fe minerals, as well as the influence of free O on trends in element electronegativity in mineral formation and electron transfer processes. The proportion of oxygen containing Fe minerals had the sharpest increase during the time periods of the Kenorland and Columbia supercontinent assembly events. Indeed, the rise of O is associated with O becoming more centralized in the network as well as with an increase through time in the number of Fe minerals containing combinations of high and low electronegativity elements. The importance of oxygen in the expansion of Fe mineral chemical diversity, and its influence on the bioavailability of Fe in the environment, is illustrated clearly in the Fe mineral chemistry network.