Ariel D. Anbar

Abstract Archean ocean marine primary productivity may have been limited by biologically available nitrogen. Due to low molybdenum abundances, early biological nitrogen fixation is thought to have relied on alternative nitrogenases that incorporate vanadium or iron instead of molybdenum. Here, we examine nitrogen fixation in a Cyanobacteria-dominated, ferruginous, low-sulfate, low-molybdenum lake, which replicates biological and chemical conditions relevant to early marine primary productivity.

Abstract A growing body of evidence suggests that molecular oxygen (O2) accumulated in some shallow marine environments beneath the effectively anoxic Archaean atmosphere 4.0 to 2.5 billion years (Ga) ago. Yet, the temporal and spatial distribution of these oxygen oases is not well known.

Abstract The Ediacaran Period (~635–539 Ma) is marked by the emergence and diversification of complex metazoans linked to ocean redox changes, but the processes and mechanism of the redox evolution in the Ediacaran ocean are intensely debated. Here we use mercury isotope compositions from multiple black shale sections of the Doushantuo Formation in South China to reconstruct Ediacaran oceanic redox conditions.