Research Interests

I'm probably best described as a geobiologist. In earlier work, I studied the fates of organic carbon, Fe and sulfur in marine sediments. This turned out to be relevant for understanding the long-term evolution of biogeochemical cycles on Earth. Here, I have focused on the history of atmospheric oxygen as well as interactions between biological evolution and the history of Earth surface chemical change. This work requires a 2-prong approach. I work with modern microbes and modern microbial ecosystems to understand how they cycle elements and importantly what clues of their activity they might be left in the geologic record. This is interfaced with geological field work. Here, we collect and analyze ancient sediments from key periods in Earth history to deduce the chemical nature of the environment in which the sediments formed. If lucky, we can also deduce the ecology of the organisms that once lived in the environment. Some key recent findings include: the proposition and later demonstration of middle Precambrian sulfidic marine conditions, the demonstration of late Neoproterozoic marine deep water oxygenation in approximate concert with early evolution of large animals, and the discovery of a new microbial nitrogen metabolism, the ANAMMOX process, in oxygen-free zones of the marine water column.

Membership Type


Election Year


Primary Section

Section 15: Geology

Secondary Section

Section 63: Environmental Sciences and Ecology