Heavy metal, sex and granites: Crustal differentiation and bioavailability in the mid-Proterozoic

Biogeochemical and genomic studies have suggested that the availability of trace metals has been essential to the progressive evolution of life on Earth. In particular, the evolution of eukaryotes to diverse complex multicellular life has been related to the availability of trace metals. The radiation of eukaryotes, and the evolution of sex, is timed at Mesoproterozoic, but at this time the metals may have been preferentially sequestered in a sulfidic deep ocean. However, the addition of a huge volume of new crust to form a supercontinent at c. 1.9 Ga, including an unprecedented episode of within-plate anorogenic magmatism, led to an extraordinary new flux of metals to the upper crust in the mid-Proterozoic. The appearance of sulfate evaporites from ~1.7–1.6 Ga indicates extensive weathering of metallic sulfides. Erosion of the supercontinent into Mesoproterozoic sediments thence introduced key metals to near surface reservoirs, providing an enhanced biogeochemical environment conducive to the expansion of an evolving biota.