Morton K. Blaustein Potdoctoral Fellow
Johns Hopkins University
Baltimore, MD
Microbes — bacteria, archaea, and simple eukaryotes — have been a major component of the biosphere throughout geologic history. These organisms and microbial ecosystems both shape and are shaped by their environments, driving the evolution of our planet as a biological and chemical system. However, we still do not fully understand how microbes and their environments have coevolved throughout Earth History. My research asks questions aimed at understanding the mechanisms by which microbial ecosystems and surface environments have influenced each other and the evolution of our plant.
How have microbial ecosystems influenced geochemical cycles (e.g., the silica and carbon cycles) and sedimentary processes throughout Earth history, from the Proterozoic into the Phanerozoic?
How did microbial ecosystems change through time and what were the chemical and physical 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 like the Snowball Earth Events, or mass extinctions and radiations?
To address these questions, I tap into two records of the evolution of life: the sedimentary and biosignature records and modern microbial ecosystems. I am particularly interested in the coevolution of life and the silica and carbon cycles and the records preserved in chert and carbonate.
The evolution of the biosphere across the Neoproterozoic
The Neoproterozoic was an important interval in the evolution of the biosphere and the environment. 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, causal relationships among environmental and biological changes remain poorly constrained. How did changes in the biosphere, climate, and geochemical cycles influence one another? I am particularly interested in understanding how the biosphere evolved across the Neoproterozoic and what drove major evolutionary and ecological changes during 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 the environments that hosted them. 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., 2025a) and Tonian deposits in Kazakhstan (Moore et al., in prep; Mohammed et al., in revision) 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 taphonomic window resulted in exceptionally detailed cellular preservation, 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 and the microbial contribution to the silica cycle.
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 and biogeochemistry). In the lab, I use modern organisms analogous to microfossils and simulated paleoenvironmental conditions to test how microbes interact with the chemical environment. With this approach, I attempt to constrain the mechanisms that allow for silica precipitation and organic 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 interpret the chert-hosted fossil record across the Proterozoic and Phanerozoic. This work is the key to using the chert and carbonate records as archives of past environmental conditions (physical and chemical), the ecosystems that inhabited past environments, surface processes, and geochemical cycles of silica and carbon.
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 these compounds. Under what conditions are certain compounds produced? What is their ecological context within a complex community? What is the evolutionary history of specific types of EPS that relate to stress responses? And what is the role of EPS and specific compounds in geochemical cycles and mineral forming mechanisms? I am interested in answering these questions to understand the evolution of key microbial stress responses 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 and the sulfur cycle.
Insights into paleoenvironments and paleoecology 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 with 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., 2025a). 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., 2025b). 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.
