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Geobiology of the Precambrian-Cambrian Boundary.


Currently, my research is focused on a succession of mixed carbonate and siliciclastic sedimentary rocks outcropping in Mongolia and Kazakhstan which capture the transition between a microbial world and a world with complex, multicellular life. These rocks originally formed between the Ediacaran Period and the lower Cambrian Period in a transitional foreland basin system. In these basins were preserved many trace and body fossils of some of the earliest complex multicellular life in Earth history, alongside sedimentary structures mediated by communities of single-celled organisms. My work is to try to further reconstruct the sedimentary and chemical settings which hosted these fossil multi- and single-celled organisms, in an effort to understand how and why they became fossilized, and what the style and extent of their fossilization can tell us about the relationship between organisms and the environment at a pivotal moment in the history of life. Why these rocks in particular, though? Because the sediments, cements, and fossils within them are often highly rich in phosphorus, making them one of many uniquely phosphate-rich sedimentary deposits which formed during the major climate and ecological upheaval which characterized the Precambrian-Cambrian Boundary! This connects the rocks of Central Asia to the rocks of Eastern Brazil...





My doctoral dissertation centered on Ediacaran-age mostly-carbonate rocks in Eastern Brazil. Why then and there? Because during the Ediacaran Period (between about 650 million and 550 million years ago), the São Francisco Craton that forms much of what is now Eastern Brazil was host to a large seaway where carbonate minerals freely precipitated from the water column and at the seafloor. Microorganisms in this ancient sea influenced and were influenced by aqueous chemistry and sedimentation. The record they left behind of those influences includes a range of sedimentary structures and mineral deposits (specifically phosphate mineral deposits). My work is reading and interpreting that record, in an effort to understand both the environment that these microorganisms lived in and their lifestyle and metabolic strategies therein. I am particularly interested in the role they may or may not have played in the accumulation and mineralization of phosphate, which is — in sedimentary deposits of similar age elsewhere in the world — capable of preserving microbial fossils in exquisite detail. In the course of this work, I visit Bahia and Minas Gerais states in Brazil to collect sedimentological and stratigraphic data, as well as structural data, of the Ediacaran-age rocks there. I also collect samples, which I bring back to my institution Caltech and subject to a range of analytical methods to examine their chemical and isotopic compositions and microstructures. The tools I use include: scanning electron microscopy, energy dispersive X-Ray spectroscopy, Raman spectroscopy, and optical microscopy, secondary-ion mass spectrometry, ICP-MS, IRMS, elemental analyzers, and more!

In addition to my research in Central Asia and Brazil, I have also assisted my colleagues in their work on Cryogenian-age carbonate rocks in the Namib-Naukluft National Park in Namibia. These rocks are more extensively recrystallized than the rocks I study in Brazil, in a way that has destroyed much of their primary microtexture and record of primary, depositional chemistry. However, they do contain microbially-influenced sedimentary structures that are visible on meso- and macro-scales, and they are an excellent case study in Neoproterozoic sequence stratigraphy and paleoclimate.

I have also worked with petrographic thin sections of the Gunflint Chert (~1.88 billion years old), located in Ontario, Canada: identifying microfossils of putative bacteria preserved in microcrystalline quartz, and measuring their carbon isotopic composition via secondary ion mass spectrometry. This is part of a larger effort to determine what information of ancient microbial metabolic strategy and ecology can be extracted from microbial fossils. 

In-Situ detection of life at planetary surfaces.


The study of life in the universe requires the ability distinguish the signs of extant or extinct life from those of abotic processes. This in turn requires understanding of how different organisms impact their specific environments, even before the ravages of diagenesis over millions or billions of years. To this end, I incubated communities of microorganisms extracted from a ~1-km-deep aquifer (on Earth) with rocks analogous to those found in the surface (and presumably subsurface) of Mars, and observed the physical and chemical influences they produced on different lithologies. This project involved the preparation of biological samples for scanning electron microscopy and UV-fluorescence microscopy, as well as the characterization of mineral substrates with IR and Raman spectroscopy. Samples with and without biological material were also subjected to secondary ion mass spectrometry for sulfur isotope analysis. This is a secondary area of research for me, but closely related to my current interests in the study of how geology preserves and destroys evidence of past life.



As an undergraduate, I worked on several projects related to the characterization of Mars' surface mineralogy and atmospheric composition via visible and IR spectroscopy. I also completed a senior thesis project in which I generated models of the input of greenhouse gases to Mars' Noachian atmosphere due to impact-induced hydrothermal processes (namely, serpentinization). This is no longer an area of active research for me, but I am still fascinated by the potential of Mars for the study of rocks closer to the age of the solar system, and the insights it may give us into prebiotic chemistry and the origins and evolution of life in extreme environments.

Other worlds.


In the course of my undergraduate and graduate studies, I have conducted theoretical research related to the atmospheres and interiors of other worlds: specifically, Saturn's ice-bound moon Enceladus and hypothetical Earth-like exoplanets orbiting M-dwarf stars. I have also worked with observational astronomers on the interpretation of Cassini CIRS data from the surfaces of Saturn's icy moons Dione, Rhea, Mimas, Iapetus, and Enceladus; and with theorists on mechanisms of formation of planetary systems, specifically the dynamics of ices in solar nebulae. These are no longer areas of active research for me, but I remain greatly interested in the formation and evolution of different worlds, and the possible origins and detection of life there.

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