A Late Archean Sulfidic Sea Stimulated by Early Oxidative Weathering of the Continents

Abstract

Of Ancient Iron and Oxygen Finding clues to understand the early evolution of ocean and atmospheric chemistry and its links to the evolution of life remains a daunting task. Often just a few rock samples provide our only evidence of what conditions on Earth were like long ago. Reinhard et al. (p. 713 ) combined iron speciation data from a 2.5-billion-year-old shale from Australia with sulfur isotope data from this and nearby formations to conclude that oxygen chemistry predominanty consisted of an anoxic sulfide–rich water column, instead of iron-rich oceans, as previously speculated. Thus, brief pulses of reduced iron from hydrothermal vents may have been responsible for the formation of nearby banded iron formations and may have provided enough buffering to prolong the appearance of atmospheric oxygen generated by the expansion of newly evolved cyanobacteria.