Postcard from a Fellow: Junyao Kang in the lab with ancient rocks
July 10, 2020
BY JUNYAO KANG
Hey folks! I hope everyone is staying safe and healthy. I’m Junyao Kang, a second year Ph.D. student from Department of Geosciences, and one of the newest IGC fellows. This summer, I’m working to analyze some 720-1000-million-years-old carbonate and shale samples, which I gathered in North China last summer. My research focuses on the oceanic environmental changes in deep time and their relationships with the evolution of life. To reconstruct the paleoenvironment and its related change, we rely on the sedimentary rocks forming at that time. The chemical and isotopic compositions of these rocks will tell us what has happened in the seawaters and sediments.
This time interval (about 539-1000 million years ago) is a critical one because it witnessed various eukaryotic innovations and even the origin of animals. Knowing the environmental context will help us better understand what has caused these major evolutionary events and also how the life co-evolved with the environment.
As I analyze samples this summer, I’m most interested in different iron species incorporated into rocks, because iron is really sensitive to the redox (reduction-oxidation) conditions of the water column. When the water is oxic, iron is mostly incorporated as Fe silicates. However, as it becomes increasingly anoxic, the relative proportion of Fe oxides and Fe carbonates would increase in ferruginous conditions (anoxic and containing free ferrous iron), whereas the relative proportion of Fe sulfides would increase in sulfidic conditions (anoxic and containing free hydrogen sulfide, as is happening deep in the Black Sea right now). Hence, I’m using an iron sequential extraction method to analyze different species of iron preserved in the rocks, which will reflect contemporaneous oceanic redox conditions.
As for isotopic compositions in the samples, I mainly focus on the carbon and sulfur isotopes. Isotopic fractionation will happen during photosynthesis (carbon isotopes) and bacteria using organic matters to reduce sulfate (sulfur isotopes). So isotopic analysis will help us better understand the biogeochemical cycle of carbon and sulfur in ancient oceans. Furthermore, of these two processes, photosynthesis and sulfate reduction, one is directly related to oxygen production while another one actually prevents oxygen being consumed by organic matter oxidation. Therefore, isotopic composition can offer us some information about net oxygen production during that time.
Fortunately for me, the COVID pandemic didn’t change my plans too much. But it’s impossible that this pandemic has no effect on my research plan… and quarantined life sometimes drives me crazy :). Because I need to use facilities in different labs within or outside of our department and some of them are still closed, I have needed to modify my research timelines. Also, as a second year student, I’m still learning a lot of lab skills, but the current situation makes it difficult to have some in-situ learning. I hope others are doing well, despite these challenges!