Microorganisms have had (and continue to have) a profound influence on our planet, but only with recent advances in molecular tools has tracking the diversity and function of microbial communities become possible. Dr. Dick will highlight two projects which illustrate how we are applying community genomics to study the interplay between microbiology and geochemistry. First, he will describe their work in deep-sea hydrothermal vent plumes, which host dynamic interactions between microbial communities and geochemical processes. They are employing metagenomic and metatranscriptomic approaches to address the following key questions: (1) What is the origin of plume microorganisms? (2) How does plume community structure and activity change across geochemical gradients? (3) Which hydrothermal inputs serve as the major energy sources for chemolithoautotrophy in plumes, and what are the implications for feedbacks onto biogeochemical functions? Second, Dr. Dick will introduce novel cyanobacterial mat communities inhabiting Great Lakes sinkholes. These cyanobacteria operate under low-oxygen conditions and are capable of both oxygenic and anoxygenic forms of photosynthesis. By addressing questions concerning the regulation of oxygenic vs. anoxygenic photosynthesis, competition between cyanobacteria and anoxygenic bacteria, and the molecular evolution of anoxygenic photosynthesis in the cyanobacteria, we aim to elucidate microbial processes that underpinned Earth’s oxygenation from the Great Oxidation Event (~2.4 billion years ago) through the Proterozoic.