The end-Guadalupian and end-Triassic mass extinctions:
Many mass extinctions are contemporaneous with emplacement of large igneous provinces (LIPs), suggesting that the environmental effects of LIP volcanism were important kill mechanisms. Of major interest is whether rapid injection of volcanic CO2 into the ocean and atmosphere resulted in seawater acidification and eutrophication. The end-Guadalupian (ca. 260 Ma) and end-Triassic (ca. 201 Ma) extinctions were both associated with LIPs and saw preferential extinction of marine animals sensitive to changes in seawater pH or oxygen content. Carbon isotope fluctuations are consistent with some type of carbon cycle perturbation, and local proxies of acidification and anoxia are widespread. However, we have not yet been able to quantify the severity of acidification or anoxia during these events at a global scale. Calcium and uranium isotopes can be combined with carbon isotope data to constrain these phenomena. This is because the carbon cycle is linked to the calcium cycle via burial of CaCO3 and chemical weathering of Ca-minerals, and to the uranium cycle via organic carbon production and precipitation of uranium under reducing conditions. I use these non-traditional isotope systems, along with numerical models of their mass and isotopic fluxes, to constrain the cause of carbon cycle perturbations and the seawater geochemistry during each extinction.
Transitions from the Paleozoic to the Mesozoic Era:
The largest mass extinction of the Phanerozoic took place at the end of the Permian. The latest Permian and Early Triassic has been the focus of a tremendous amount of research in the last two decades. However, by comparison, almost nothing is known about ocean conditions in the few million years prior to the end-Permian extinction. Was the end-Permian extinction so damaging to life because conditions were already poor in the millions of years prior, or was the extinction solely a result of the events that took place in the very latest Permian? The Permo-Carboniferous was a very dynamic interval, characterized by a shift from calcite to aragonite seas, the growth and demise of the late Paleozoic ice sheets, anomalously high atmospheric O2 concentrations, and the assembly of Pangea. How did these major events contribute to the end-Permian extinction and the transition from Paleozoic to Modern fauna?
Neoproterozoic seawater chemistry during the rise of early eukaryotes:
The cause of the emergence and diversification of early eukaryotes remains one of the great unanswered questions in geobiology. In particular, it is unclear if and how the environmental conditions of the Earth’s early oceans facilitated or inhibited diversification. Fossil and molecular clock data place the origin of Eukarya between 1850 and 1650 Ma, though diversity and complexity remained low for nearly one billion years. Starting in the mid-Neoproterozoic (ca. 800 Ma), eukaryotic diversification began a slow acceleration towards the Cambrian Explosion and Ordovician Radiation, along the way developing fundamental aspects of complex life such as cell differentiation, multicellularity, and biomineralization.
This rise in eukaryotic diversity occurred during an extremely dynamic period in Earth’s climatic history. At least two global glaciations (the so-called Sturtian and Marinoan “Snowball Earth” events) occurred beginning in ca. 715 Ma and 635 Ma. The carbon isotope (δ13C) record of marine carbonates was relatively invariant across the Mesoproterozoic (1600–1000 Ma), but began showing massive (>10‰) positive and negative fluctuations ca. 811 Ma, consistent with frequent large-scale instabilities in the carbon cycle. Oxygen concentrations appear to have risen above 0.1% of present atmospheric levels for the first time at some point in the Early Neoproterozoic, though the spatial distribution and trajectory of O2 concentrations throughout the latter part of the Neoproterozoic is far from clear. Yet, the causes and consequences of these environmental events are not understood, and their relationship to the diversification of eukaryotes is only tentative. As an Agouron Postdoctoral Fellow, I will be working in collaboration with Prof. Kristin Bergmann of MIT to investigate these events using carbonate clumped isotope thermometry to constrain the climatic changes of the Neoproterozoic. Untangling these records will allow us to further constrain the relationship between environmental change and the diversification of early eukaryotes.
My personal research has brought me across southern and central China, as well as south-central Turkey and southern New York State. Outside of my research, I have also participated in geologic field trips to India, Italy, California, Nevada, Texas, and Newfoundland.
Teaching must be designed to engage students and prepare them for the rigors of scientific thought and discovery. I construct my courses to meet these goals by bringing research into the classroom, developing students' quantitative skills through numerical modeling and computer programming, and having students write early and often.
Current and past courses:
- Paleontology and the Fossil Record (Fall 2015, Vassar College ESCI/BIOL 275)
- Stable Isotopes in the Earth and Environmental Sciences (Fall 2015, Vassar College ESCI 385)