Astrobiology Science and Technology for Exploring Planets (ASTEP)

PI: Knoll, Andrew

Sedimentary rocks deposited during the later Neoproterozoic Era (ca. 800-542 million years ago) record the first unambiguous signs of animal life, multiple glaciations of global dimensions, and the oxidation of the deep ocean. Despite recognition that Earth and life changed fundamentally during this interval, much remains to be understood about the interrelationships of and feedbacks between Neoproterozoic biological and physical events. Here we propose to couple detailed chemostratigraphic analyses of paleobiologically informative Neoproterozoic sedimentary successions with geobiological experiments designed to provide empirical calibration of temporal changes in seawater sulfate. The microbiological experiments will employ a novel, continuous flow bioreactor system that will provide quantitative constraints on the relationships among seawater sulfate concentration, microbial activity (and diversity), and sulfur isotope fractionation. Many biochemical reactions discriminate against minor isotopes, resulting in end products that are isotopically distinct relative to the substrate pool. Therefore, all isotopes of sulfur [ ³² S, ³³ S, ³⁴ S, ³⁶ S] will be measured in substrates and products. Complementary geochemical analyses will focus on fossiliferous Neoproterozoic successions that record physiologically distinct events in early animal (and algal)evolution; detailed profiles of carbon isotopes (to facilitate correlation with other localities) and iron-speciation chemistry (which provides a proxy for redox conditions in waters overlying the seafloor) will be joined with measurements of the total isotopic composition of sulfur. The proposed research will, thus, marry high resolution chemostratigraphic data and microbial experiments to test hypotheses about the relationship between evolution and environmental history on the one planet where life is known to exist. The sulfur isotopic data will also provide a baseline for interpreting total sulfur isotopic abundances in sedimentary surface minerals collected during sample return missions to Mars.