"What mammalian species would be most suited to live on a teraformed Mars. Primarily as a source of protein for humans"
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Assessing Ni Isotope Fractionation During Abiotic Processes
PI: Laura Wasylenki
A new biosignature for methanogenic activity in the Late Archean based on Ni isotopes may soon shed light on an important turning point in the history of life on Earth. Cameron et al. (2009; PNAS 106:10944) reported preferential assimilation of lighter Ni isotopes in culturing experiments with methanogens. In contrast, they observed little variation among a small set of carbonaceous chondrites, basalts, loess, and riverine sediments. This result raises the tantalizing possibility that Ni consumption by methanogens may be the only process that significantly fractionates Ni isotopes. In that case Ni isotope variations recorded in ancient marine sediments may reflect the rise, predominance, and decline of methanogenesis, a trend that profoundly influenced the chemical evolution of the atmosphere and oceans and biological evolution of life on our planet.
Measurement of Ni isotope compositions in Archean rocks will thus likely be undertaken very soon. Interpretation of the data, however, must be made with caution until it is first demonstrated that observed variations do, in fact, represent biological processes. Many metals, including Li, Mg, Ca, Cu, Zn, Sr, Mo, Cd, and U, are known to fractionate abiotically, often without changes in oxidation state. Therefore while it is important to move forward with analysis of natural samples, it is also critical to pursue careful, fundamental investigations of abiotic processes that may fractionate Ni isotopes as well.
Our objective is to design, conduct, and analyze experiments to determine whether abiotic processes fractionate Ni isotopes. Guided by our recent work on metal isotope fractionation during adsorption of metals to mineral surfaces, leaching of metals from minerals, and exchange reactions between metal-ligand complexes, we will investigate which of these processes drive isotope effects for Ni. If any of these reactions are found to fractionate Ni, we will quantify fractionation factors, seek to constrain the mechanisms that cause fractionation, and assess the potential for complication of biological isotope signatures recorded in ancient samples. If we find no fractionation, then we shall have provided the grounds for more robust interpretation of the Ni isotope record left by methanogens in Archean sediments.
May 16, 2012
