Abstract
Nitrogen is the major component of Earth's atmosphere and plays important roles in biochemistry. Biological systems have evolved a variety of mechanisms for fixing and recycling environmental nitrogen sources, which links them tightly with terrestrial nitrogen reservoirs. However, prior to the emergence of biology, all nitrogen cycling was abiological, and this cycling may have set the stage for the origin of life. It is of interest to understand how nitrogen cycling would proceed on terrestrial planets with comparable geodynamic activity to Earth, but on which life does not arise. We constructed a kinetic mass-flux model of nitrogen cycling in its various major chemical forms (e.g., N2, reduced (NHx) and oxidized (NOx) species) between major planetary reservoirs (the atmosphere, oceans, crust, and mantle) and included inputs from space. The total amount of nitrogen species that can be accommodated in each reservoir, and the ways in which fluxes and reservoir sizes may have changed over time in the absence of biology, are explored. Given a partition of volcanism between arc and hotspot types similar to the modern ones, our global nitrogen cycling model predicts a significant increase in oceanic nitrogen content over time, mostly as NHx, while atmospheric N2 content could be lower than today. The transport timescales between reservoirs are fast compared to the evolution of the environment; thus atmospheric composition is tightly linked to surface and interior processes.
Highlights
Atmospheres are the key observables that can be obtained remotely of planetary bodies within our solar system, as well as those orbiting other stars
Given a partition of volcanism between arc and hotspot types similar to the modern ones, our global nitrogen cycling model predicts a significant increase in oceanic nitrogen content over time, mostly as NHx, while atmospheric N2 content could be lower than today
We show the influence of those rates, initial conditions, and mantle redox state on the nitrogen content of the atmosphere and volcanic degassing fluxes
Summary
Atmospheres are the key observables that can be obtained remotely of planetary bodies within our solar system, as well as those orbiting other stars. For instance, Venus, Earth, and Mars have very different atmospheric nitrogen content, which may inform us about their history. In this contribution, we construct a planetary evolution model to track nitrogen distribution among major planetary reservoirs as mediated by abiotic processes known to occur on Earth. One goal of this study is to help understand what nitrogen content in planetary atmospheres can tell us about its evolution. Nitrogen ( referred to as N for the sake of accounting for the mass of nitrogen atoms), in the form of N2 (or molecular nitrogen), is the major component of the present atmosphere and plays important roles in biochemistry (Thomazo and Papineau, 2013). Bioavailable nitrogen (i.e., all molecular forms except N2), together with iron and phosphorous, is often a growth-limiting nutrient in the environment (Smith, 1984; Vitousek and Howarth, 1991)
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