Nickel Isotope Gives Hints to Very Early Microbes

A biomarker based on the stable isotopes of nickel

1. Vyllinniskii Camerona (a,b)
2. Derek Vance (b)
3. Corey Archer (b)
4. Christopher H. House (a)


a Department of Geosciences and Penn State Astrobiology Research Center, The Pennsylvania State University, University Park, PA 16802; and

b Bristol Isotope Group, Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom


Abstract:

The new stable isotope systems of transition metals are increasingly used to understand and quantify the impact of primitive microbial metabolisms on the modern and ancient Earth. To date, little effort has been expended on nickel (Ni) isotopes but there are good reasons to believe that this system may be more straightforward, and useful in this respect, than some others. Here, we present Ni stable isotope data for abiotic terrestrial samples and pure cultures of methanogens. The dataset for rocks reveals little isotopic variability and provides a lithologic baseline for terrestrial Ni isotope studies. In contrast, methanogens assimilate the light isotopes, yielding residual media with a complementary heavy isotopic enrichment. Methanogenesis may have evolved during or before the Archean, when methane could have been key to Earth's early systems. Our data suggest significant potential in Ni stable isotopes for identifying and quantifying methanogenesis on the early planet. Additionally, Ni stable isotope fractionation may well prove to be the fundamental unambiguous trace metal biomarker for methanogens.