NSF Postdoctoral Fellow
Johns Hopkins University
Baltimore, MD
Microbes have been a dominant component of the biosphere throughout geologic history and they interact on a fundamental level with the environment, shaping the evolutionary trajectory of the biosphere and our planet since the dawn of life. However, we still do not fully understand how microbes/microbial ecosystems and the environment coevolved throughout Earth History. How did microbes adapt to their environments? How did microbial ecosystems evolve over the course of the Proterozoic and what ecological and environmental factors drove the evolution of life? How diverse were early microbial ecosystems across different environments? And how did microbes and microbial ecosystems influence mineral formation, sedimentary processes, and geochemical cycles? To fully address these questions, I tap into two records of the evolution of life: the microfossil record and modern microbes.
The Neoproterozoic Microfossil Record:
The Neoproterozoic was an important interval in the evolution of the biosphere and the geosphere. This interval experienced two global glaciations (the Snowball Earth events) punctuated by a global warming interval (the Cryogenian non-glacial interlude) alongside perturbations to the carbon cycle, a potential Neoproterozoic rise in oxygen, and the diversification and proliferation of eukaryotes. However, questions remain surrounding how changes in the geosphere and biosphere influenced one another. I am particularly interested in understanding how the biosphere evolved over the Neoproterozoic and what drove major evolutionary and ecological changes through the Tonian and Cryogenian.
Past and ongoing work has included field and laboratory studies to characterize microfossil assemblages from Tonian and Cryogenian deposits. The goal of these studies is to better characterize Neoproterozoic ecosystems and their environments. In the past, I have studied post-Sturtian cap carbonates from Zambia, Namibia, and Mongolia (Moore et al., 2017a). More recently, I am reinvestigating the Cryogenian Ikiakpuk Group of Arctic Alaska (Moore et al., 2017b; Moore et al., in prep) and have begun investigating microfossil assemblages from a Neoproterozoic deposits in Kyrgysztan (Moore et al., in review) and Tonian deposits in Kazakhstan and Death Valley.
The Microbial Role in Silicification
Many of the best examples of Proterozoic microfossil assemblages are preserved in chert from peritidal environments. This mode of preservation resulted in cellular preservation with exception detail, but there are gaps in our understanding of the mechanism(s) that underpin silica precipitation and microfossil preservation in different environments through time. I am interested in the role of microbes in this process. In an effort to understand the chemical conditions, microbial communities, and microbial-environmental interactions that facilitated silicification in Proterozoic tidal environments, I use fossilization experiments (experimental geobiology). In the lab, I use modern organisms analogous to Proterozoic fossils and simulated Proterozoic marine tidal environments to observe how microbes interact with the chemical environment and constrain the mechanisms that allow for preservation. My previous work identified one mechanism of silicification mediated by marine cyanobacteria that involves cation bridging and organic-cation-silica interactions (Moore et al., 2020; 2021). Through this type of experimental work, we can identify microbial-environmental interactions that may have characterized Proterozoic environments and constrain the chemical conditions in these environments and the role of microbes in the formation of chemical sediments and geochemical cycles.
The Proterozoic Chert- and Carbonate-Hosted Microfossil Record:
With the discovery of a mechanism of silicification of cyanobacteria analogous to Proterozoic fossils, I began to search for evidence of this mechanism in Proterozoic chert-hosted fossil assemblages. The goal of this work was to determine whether or not this mechanism is relevant to Proterozoic tidal environments. If so, the combination of experimental geobiology and geochemical and micropaleontological studies of Proterozoic deposits may help us better constrain the chemical conditions and microbial communities that characterized Proterozoic tidal environments. Using a combination of spatially resolved analytical techniques (light microscopy, SEM/EDS, XRF, and Raman Spectroscopy), I uncovered cation enrichments and cation-rich phases associated with chert-hosted microfossils that point to organic-cation-silica interactions (Moore et al., 2022). This work provides evidence for a microbially influenced mechanism of silicification that involved cation bridging in Proterozoic tidal environments and suggest that microbes may have played a larger role in silica precipitation and silica cycling in Proterozoic oceans than previously thought. Although this mechanism can explain silicification in Proterozoic tidal environments, there are likely many mechanisms of silicification that characterize different environments and microbial ecosystems throughout Earth history. Understanding the variety of mechanisms, environments, and microbial ecosystems through time is something that I will continue to investigate in the future. I have also expanded this work to investigations of silicified fossil assemblages from the Cretaceous presalt deposits in the Santos Basin (Moore et al., 2024) and plan to investigate silicification in other Phanerozoic deposits in the future.
Microbial Stress Responses and Taphonomic Biases
In addition to the ways that microbes shape their environments by contributing to geochemical cycles and mineral forming processes, I am fascinated by how microbes and microbial ecosystems evolve and adapt in response to changes in their environments. These adaptations, both at an ecosystem and individual level, are a key component of microbial evolution. I am particularly interested in how microbes and microbial ecosystems respond to environmental stresses and the production of various types of exopolymeric substances (EPS). EPS broadly and specific types of EPS are often produced in response to environmental stresses like UV radiation, desiccation, and salinity stresses, among others. While the production of EPS in modern organisms has been widely studied, there are outstanding questions about the production of these compounds, their ecological context within a complex community, the evolutionary history of certain types of EPS, and the role of EPS and specific compounds in geochemical cycles and mineral forming mechanisms. I am interested in understanding microbial stress responses in the past and their role in ancient ecosystems, mineral forming processes, and potential taphonomic biases. Past and ongoing projects related to this overarching theme include experimental studies of the diversity and stress responses of microbial mats grown under UV stress (Moore et al., in review), the role of sulfated polysaccharides in silica precipitation (Moore et al., 2021), and the role of sulfated polysaccharides in pyritization.
