Insights into the coevolution of early life and planets from silica-hosted biosignatures

 Presented by Dr. Kelsey Moore | NSF Postdoctoral Fellow, Johns Hopkins University 

Abstract: 

Since the dawn of life on Earth, microbial organisms have played a central role in shaping our planet. If life ever arose on other planetary bodies like Mars, the same is likely true of those early ecosystems. As our only known example of early life, microbial ecosystems on Earth are our best analog as we attempt to identify and interpret biosignatures on Mars.

On Earth, these early microbial ecosystems set life on its evolutionary trajectory and have influenced key geochemical cycles and sedimentary processes throughout Earth history. Silica is one of these key geochemical cycles, controlling our climate along with the carbon cycle, and siliceous sedimentary deposits (chert) preserve one of the best records of early life on Earth. As such, silica and the chert-hosted fossil record are a critical component of our understanding of the early biosphere and the coevolution of life and the planet. However, there are major outstanding questions surrounding the evolution of the silica cycle, the mechanisms of silicification, and the role of early ecosystems in shaping the silica cycle. I combine experimental geobiology with spatially-resolved analyses of chert-hosted biosignatures to better characterize early life and its evolution, the evolution of the silica cycle, and the role of microbes in shaping the silica cycle and the planet. In this talk, I will described how cyanobacteria and organic-cation-silica associations drive silicification and suggest that cyanobacteria may have played a critical role in the Proterozoic silica cycle. I will uncover insights into Proterozoic primary producers, their physiology, and adaptations to environmental stresses that help us better characterize the Proterozoic biosphere. Finally, I will extend these findings to help search for potential silica-hosted biosignatures on Mars. Through these studies, we can better characterize the coevolution of early life and our planet and perhaps extend these insights to early life on Mars, if it ever existed.