%0 Journal Article
%T Abiotic ammonium formation in the presence of Ni-Fe metals and alloys and its implications for the Hadean nitrogen cycle
%A Alexander Smirnov
%A Douglas Hausner
%A Richard Laffers
%A Daniel R Strongin
%A Martin AA Schoonen
%J Geochemical Transactions
%D 2008
%I BioMed Central
%R 10.1186/1467-4866-9-5
%X Ammonia (NH3) or ammonium (NH4+), henceforth NH3/NH4+, are necessary precursors for reactions associated with prebiotic syntheses, such as the Strecker synthesis. It has been experimentally shown that NH3/NH4+ environments are more efficient in organic synthesis than those dominated by dinitrogen (henceforth N2) in both aqueous and gaseous environments [e.g., [1]] [2,3]. This notion is not unexpected, considering that, the strong triple bond (948 kJ.mol-1) of the N2 would presumably result in large reaction activation barriers (i.e., low conversion rates), even if the overall reaction is thermodynamically favored.Several possible pathways to abiotic NH3/NH4+ on early the Earth have been proposed: reduction of NO2-/NO3- by Fe++/FeS in the ocean [e.g., [4]] [5,6]; atmospheric production from N2 and HCN [e.g., [7]] [8]; release from rocks and minerals [e.g., [9]]; photoreduction on mineral surfaces [e.g., [10]] [11,12]; and hydrothermal aqueous reduction from N2 in the presence of minerals under conditions typical of submarine hydrothermal systems [e.g., [13]] [14,15]. Each of the mechanisms relies on a different set of assumptions and none of the proposed mechanisms has, in our opinion, gained universal acceptance in the scientific community as the predominant source of abiotic NH3/NH4+.In this scientific contribution we focus on the catalytic properties of Ni and Fe metals and their alloys which can form in submarine hydrothermal systems (SHS), especially those driven by exothermic hydration reactions (e.g., serpentinization) in an off-axis tectonic setting. Upon dissolution of Ni-containing rock-forming minerals (e.g., olivine, pyroxene, amphibole), released Ni and Fe can react to form metals and alloys under extreme reducing conditions imposed on the system by the serpentinization processes [16-18]. The conditions are commonly reducing enough to stabilize Ni-Fe alloys (e.g., awaruite ¨C Ni3Fe), metallic nickel (Ni0) and even iron (Fe0). These minerals occur regularl
%U http://www.geochemicaltransactions.com/content/9/1/5