Mass Extinctions!
We study the past to understand how we arrived at the present, but also to predict the course into the future. Ancient mass extinctions (think: giant meteor impacts, farewell dinos) have shaped the course of Life on Earth. However, extinctions, and the causes behind them, are quite variable in scope and nature. While the loss of charismatic animals is a classic portrayal, extinction also effects the invisible microbial life that drives biogeochemical cycling and regulates the functioning of the planet. Learning how microbes responded to ancient mass extinction events can help define environmental tipping points in modern systems, clarify broader effects to Earth’s biogeochemical systems, and, critically, inform how (and how quickly) ecosystem recovery may take place.
The Devonian Period (419 - 359 million years ago) of the Earth came to it’s conclusion with a series of unusual mass extinction events. Records of these events are hidden within extensive black shales, which feature prominently in the Paleozoic strata of the Appalachian Basin, USA. The widespread deposition of these organic-rich rocks suggests that this ancient ocean environment (think modern day Gulf of Mexico) had little to no oxygen and was often full of sulfide - a substance toxic to most animal life. I (and many colleagues!) have worked to understand the spatial and temporal extent of oxygen and sulfide stress in this region and relate it to potential extinction magnitude. I use geochemical (organic and inorganic) and paleontological methods to better understand the depositional history of these black shales and the microbial communities that thrived throughout these deadly waters.
Hangenberg mass extinction microbial community dynamics: https://doi.org/10.1111/gbi.12314
Frasnian-Famennian extinction high vs low latitude microbial community response: https://doi.org/10.1016/j.orggeochem.2016.05.007
Effects of prolonged oxygen stress in the Appalachian Basin during Devonian Mass Extinctions: https://doi.org/10.1016/j.palaeo.2021.110226
After collecting rocks of interest in the field, I do a sequence of steps to isolate and extract the mobile (bitumen) and immobile (kerogen) organic matter (think: oil), which is made of the remnants of ancient organisms. The picture above shows preparative column chromatography to purify chemically distinct organic fractions for analysis - this allows us to determine what kind of organisms left behind their matter within these rocks!
