Abstract:
Life on Earth originated in the Archaean oceans nearly 4 billion years ago, characterized by an absence of oxygen and high concentrations of dissolved iron. The oxidation of iron during early Earth is globally represented by extensive banded iron formations, yet the processes and timing of these events remain subjects of debate. Few aquatic environments today reflect the key physicochemical conditions of the early Archaean Ocean. Previous studies of complete ecosystem analogues have been limited to scarce, low-sulphur, permanently stratified lakes. In contrast, millions of boreal lakes that naturally exhibit anoxia present a unique opportunity to explore the biogeochemical and microbiological dynamics of early Archaean life. These lakes allow us to investigate processes within their anoxic zones, marked by naturally low sulfur and abundant ferrous iron, features predicted for the Archaean Ocean. Our data indicate that methanogens, anaerobic methanotrophs, and anoxygenic photosynthesizers are prevalent in these environments, characterized by distinctive isotope patterns of carbon, nitrogen, and iron. The evidence of interrelated iron oxidation, iron reduction, and methane oxidation challenges existing paradigms about both early Earth and modern aquatic ecosystems.