Abiotic ammonium formation in the presence of Ni-Fe metals and alloys and its implications for the Hadean nitrogen cycle

Abstract

Experiments with dinitrogen-, nitrite-, nitrate-containing solutions were conducted without headspace in Ti reactors (200°C), borosilicate septum bottles (70°C) and HDPE tubes (22°C) in the presence of Fe and Ni metal, awaruite (Ni 80 Fe 20 ) and tetrataenite (Ni 50 Fe 50 ). In general, metals used in this investigation were more reactive than alloys toward all investigated nitrogen species. Nitrite and nitrate were converted to ammonium more rapidly than dinitrogen, and the reduction process had a strong temperature dependence. We concluded from our experimental observations that Hadean submarine hydrothermal systems could have supplied significant quantities of ammonium for reactions that are generally associated with prebiotic synthesis, especially in localized environments. Several natural meteorites (octahedrites) were found to contain up to 22 ppm N tot . While the oxidation state of N in the octahedrites was not determined, XPS analysis of metals and alloys used in the study shows that N is likely present as nitride (N 3-). This observation may have implications toward the Hadean environment, since, terrestrial (e.g., oceanic) ammonium production may have been supplemented by reduced nitrogen delivered by metal-rich meteorites. This notion is based on the fact that nitrogen dissolves into metallic melts.

Beating the acetyl coenzyme A-pathway to the origin of life

“…Oxidation of methane and ammonia, another volatile likely present in alkaline hydrothermal fluids [65], resembling extant bioenergetic pathways, is therefore a possibility which needs to be taken seriously when inferring the ancestral types of metabolism.…”

The inevitable journey to being

“…at 1508C) by the brittle-to-ductile transition through serpentinization, whereas their pH is buffered to around 11 by the precipitation of magnesium hydroxide (the mineral brucite), and some cations (mainly calcium) are released to solution to balance charge [84,85]. At the same time, ferrous iron in olivine reduces some of the water to hydrogen as shown in this highly simplified reaction [85 [102][103][104][105][106][107]. A point to note here is that it is largely in the process of serpentinization that the cascade of dissipation engines relieving the Earth of its heat burden makes the fateful transition from largely physical to largely chemical FEC engines.…”

The evolution of Earth's biogeochemical nitrogen cycle

“…In the absence of this TiO 2 catalysis mechanism, N 2 oxidation to NO x species in post-impact plumes becomes the major source (~10 12 mol/yr) (Kasting, 1990), which, however, could have been insignificant over stretches of many millions of years when no impacts occurred and it would have declined rapidly after ~3.8 Gyr (Kasting, 1990). Hydrothermal reduction of N 2 to NH 4 + could have generated 10 9 -10 12 mol/yr of fixed nitrogen, according to some scaled laboratory estimates (Smirnov et al, 2008); however, those calculations assume an arbitrary reaction yield and an unlimited supply of the FeNi alloy that acts as a reductant or catalyst. Furthermore, modern hydrothermal fluids that do not assimilate nitrogen from organic-rich sediments are noticeably NH 4 + -poor (< 0.01mM, Lilley et al, 1993;von Damm, 1990).…”

“…Rates of up to 10 12 mol N/yr may have been achieved under high pCH 4 (1000ppmv) and <1% pCO 2 favoring the production of HCN later in the Archean (Tian et al, 2011;Zahnle, 1986), but pCH 4 would probably have been low in the Hadean under prebiotic conditions prior to the origin of methanogenic microbes, lowering this flux to 10 9 mol N/yr. Lightning and volcanism both generate NO x species which could have been reduced abiotically into the more bioavailable NH 4 + in hydrothermal vents, catalyzed by sulfide minerals or native metals (Brandes et al, 1998;Singireddy et al, 2012;Smirnov et al, 2008;Summers and Chang, 1993), provided that the reduction did not stop at N 2 (Section 2.3). Reduction of NO x to N 2 may have greatly diminished the abiotic supply of fixed nitrogen to prebiotic reactions and the earliest biosphere.…”