Award: OCE-1946137

The history of earth's life and climate is recorded in marine sedimentary rocks. A subset of this catalogue, evaporite minerals, provide a unique window into the salt carried by seawater through time. The source of one of these salts - seawater sulfate - carries information about the composiiton of the atmopshere and as such, has been used as a proxy for the ancient relationship between CO2 and O2. Through this award, our work has developed that proxy and applied it to portions of Earth history were it had not yet been explored. In series, we first investigated whether these evaporite minerals faithfully captured a seawater composition (Waldeck., Olson et al 2022 - a study of Messinian aged evaporites from the Mediteranean), which they do. We next built a 130 million year record of sulfate taken from marine sediment cores, where we learned that the isotope composition of that sulfate reflects microbial activity, and not an atmopsheric source (Waldeck et al., PNAS 2022). In contrast, a study of 3200 million year old sulfate recorded a purely atmopsheric signal reflective of an atmosphere without oxygen (Olson et al., EPSL 2022). In our final contribution from this award (Waldeck, Olson et al, Nature in review), we temporally pinpoint the transition between these two states - one where sulfate is an atmospheric proxy to one where sulfate is recording biogeochemistry. This transition is coincident with the colonization of the continents by land plants and the associated development of terrstrial soils. Last Modified: 04/23/2024 Submitted by: DavidTJohnston