Iron Formations: A Record of Neoarchean to Paleoproterozoic Environmental History

Iron formations are chemical archives of Precambrian seawater chemistry. Given that they accumulated onto the seafloor for over two billion years of Earth’s history, temporal changes in their composition offer a unique glimpse into the environmental changes that took place during that time interval. Perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere. Linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes, the supply of nutrients to the oceans, and, ultimately, diversification of the biosphere to produce complex life forms, such as ourselves. This chapter reviews what iron formations are, and how they have been used to gain insights into the processes underpinning the global rise in oxygen.