Molecular and Isotopic Geobiology

How exactly do single-celled organisms interact with their environment, and what evidence of these activities do they leave in the geologic record? Geobiologists approach such questions both from the standpoint of experimental biochemistry, and from observational geochemistry. What specific molecules allow bacteria to breathe arsenate, or respire methane? What biomarker or isotopic signals do they leave behind that might identify them? What exactly do these molecular fossils tell us about how ancient organisms lived? Recent examples of some projects in this area include:

  • Identifying the distribution and cellular function of 2-methylhopanoids, a class of sterol-like molecules that can be found in rocks more than a billion years old. What do these molecules tell us about ancient life? (Newman, Sessions)
  • Showing that magnetic biominerals – tiny magnets precipitated inside of bacteria – can be preserved in sediments and rocks, and give us clues about ancient life. (Kirschvink)
  • Identification of hydrogen isotope signals that allow us to distinguish between heterotrophic and autotrophic microbes (Sessions, Leadbetter)