msi postdoctoral fellow 2007

david johnston

Placing Experimental and Geochemical Constraints on the Evolution of the Neoproterozoic Biosphere

 

As an isotope and experimental geobiologist, David Johnston's primary interest is in better understanding the relationship between microorganisms and Earth surface evolution.  This interest ranges from tracking the onset or environmental expression of different metabolic processes to following atmospheric and oceanic oxidation and evolution.  His work blends an understanding of stable isotope systems (primarily sulfur [³²S, ³³S, ³⁴S, ³⁶S] and oxygen [¹⁶O, ¹⁷O, ¹⁸O]) with modern microbial ecology and geologic terrains.

In collaboration with Peter Girguis and Andy Knoll, David is investigating new means of constraining the evolution of the Precambrian biosphere and changes in ocean chemistry.  In the lab, their goal is to quantitatively track the relationship between environmental conditions and microbial populations.  Specifically, David is interested in using a novel bioreactor design to better fingerprint the microbial response (using isotopic and quantitative molecular techniques) to changes in seawater sulfate concentrations.  Field based studies employing proven techniques will be conducted in conjunction with the development of new proxies for uncovering the character of Proterozoic marine sediments.  These include, but are not limited to whole rock isotopic and elemental investigations (C, S, O, Fe…), extraction of trace phases (such as carbonate associated sulfate), and the mineralogical and isotopic study of black chert.

Following his time as a MSI Fellow at Harvard, David will be joining the faculty at Harvard University in the Department of Earth and Planetary Sciences.

Find out more about Dr. Johnston and his research...