Morton K. Blaustein Potdoctoral Fellow
Johns Hopkins University
Baltimore, MD
Microbes have been a dominant component of the biosphere throughout geologic history. 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 microbial ecosystems change through time and what were the conditions of the environments that hosted these ecosystems?
What ecological and environmental factors drove the evolution of life, particularly during key intervals of environment, biological, and ecological shifts (e.g., the Neoproterozoic)?
How did microbes adapt to and help to shape their environments (e.g., mineral formation, sedimentary processes, and geochemical cycles)?
How did microbial ecosystems and geochemical cycles (e.g., the silica and carbon cycles) coevolve throughout Earth history, from the Proterozoic into the Phanerozoic?
To fully address these questions, I tap into two records of the evolution of life: the sedimentary and microfossil record and modern microbial communities.
The evolution of the biosphere across the Neoproterozoic
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. I have studied post-Sturtian cap carbonates from Zambia, Namibia, and Mongolia (Moore et al., 2017a), the Cryogenian Ikiakpuk Group of Arctic Alaska (Moore et al., 2017b; Moore et al., in prep), and am currently investigating microfossil assemblages from a Neoproterozoic deposits in Kyrgysztan (Moore et al., in review) and Tonian deposits in Kazakhstan (Moore et al., in prep; Mohammed et al., accepted) 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 microfossils and simulated paleoenvironmental conditions to observe how microbes interact with the chemical environment and constrain the mechanisms that allow for preservation in different environments through time.
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 past environments and constrain the chemical conditions in these environments and the role of microbes in the formation of chemical sediments and geochemical cycles (Moore et al., 2023).
Future work will continue to study the mechanisms and the abiotic and biological factors that drive silica precipitation in marine and terrestrial environments. By considering a range of environmental conditions and microbial-environmental interactions through time, we can apply these findings to better understand the chert-hosted fossil record across the Proterozoic and Phanerozoic.
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 and microbial-environmental interactions through time. 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. Importantly, EPS is also often a contributing factor to mineral nucleation and may therefore play a key role in shaping sedimentary processes and geochemical cycles across different environments through time.
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.
Insights into ancient microbes, paleoenvironments, the silica cycle, and microbial-environmental interactions from the chert-hosted biosignature record
If we can constrain the mechanisms that underpin silica precipitation and biosignature preservation, we can combine insights from experimental studies with the record of life preserved in chert to better characterize early microbial communities, paleoenvironmental conditions, and microbial-environmental interactions. By studying chert-hosted biosignatures from different environments through time, we can gain insight into how the biosphere, the environment, and the silica cycle have evolved together through time.
An example of this is Proterozoic peritidal deposits. With the discovery of a mechanism of silicification of cyanobacteria analogous to Proterozoic peritidal 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.
This concept of cation-bridging can also be applied to fossils preserved in Neoproterozoic deposits. Tube-shaped microfossils preserved in Neoproterozoic limestones from Kyrgysztan are composed of silica with minor amounts of organic matter and iron (Moore et al., in review). In this case, Fe rather than Ca or Mg may have acted as a cation bridge. Further studies will investigate the role of these different cations in silica precipitation across different environments and what cation-enrichment can tell us about paleoenvironmental conditions and microbial-environmental interactions in the past.
Although this mechanism of cation-bridging 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 expanded this work to investigations of silicified fossil assemblages from the Cretaceous presalt deposits in the Santos Basin (Moore et al., 2024; Moore et al., 2025). Ongoing and future work will investigate silicification and the silica cycle at key moments in Earth and life history including the Neoproterozoic and the Permian and Triassic.
