Simon Poulton, Leeds University: these projects involve examining the chemical conditions in the oceans that prevailed around 600 million years ago, as the atmospheric oxygen concentrations began to rise level that allowed the evolution of animal life in the Cambrian Explosion. We have used selenium isotopes, and are using molybdenum and stage uranium isotopes to examine the ocean redox conditions at this time. In particular the selenium showed that animal evolution was preceded by over 100 million years of gradually increasing oxygen.
Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere
Neoproterozoic (1,000–542 Myr ago) Earth experienced profound environmental change, including ‘snowball’ glaciations, oxygenation and the appearance of animals. However, an integrated understanding of these events remains elusive, partly because proxies that track subtle oceanic or atmospheric redox trends are lacking. Here we utilize selenium (Se) isotopes as a tracer of Earth redox conditions. We find temporal trends towards lower δ82/76Se values in shales before and after all Neoproterozoic glaciations, which we interpret as incomplete reduction of Se oxyanions.