Modeling pN₂ through Geological Time: Implications for Planetary Climates and Atmospheric Biosignatures

Abstract

Nitrogen is a major nutrient for all life on Earth and could plausibly play a similar role in extraterrestrial biospheres. The major reservoir of nitrogen at Earth's surface is atmospheric N 2 , but recent studies have proposed that the size of this reservoir may have fluctuated significantly over the course of Earth's history with particularly low levels in the Neoarchean -presumably as a result of biological activity. We used a biogeochemical box model to test which conditions are necessary to cause large swings in atmospheric N 2 pressure. Parameters for our model are constrained by observations of the modern Earth and reconstructions of biomass burial and oxidative weathering in deep time. A 1-D climate model was used to model potential effects on atmospheric climate. In a second set of tests, we perturbed our box model to investigate which parameters have the greatest impact on the evolution of atmospheric pN 2 and consider possible implications for nitrogen cycling on other planets. Our results suggest that (a) a high rate of biomass burial would have been needed in the Archean to draw down atmospheric pN 2 to less than half modern levels, (b) the resulting effect on temperature could probably have been compensated by increasing solar luminosity and a mild increase in pCO 2 , and (c) atmospheric oxygenation could have initiated a stepwise pN 2 rebound through oxidative weathering. In general, life appears to be necessary for significant atmospheric pN 2 swings on Earth-like planets. Our results further support the idea that an exoplanetary atmosphere rich in both N 2 and O 2 is a signature of an oxygenproducing biosphere.

Morphological and isotopic changes of heterocystous cyanobacteria in response to N2 partial pressure

“…The chemical composition and physical structure of Earth's ancient atmosphere are active areas of research because these properties can leave perceptible imprints on rocks (Rasmussen & Buick, 1999;Som, Catling, Harnmeijer, Polivka, & Buick, 2012;Som et al, 2016). Independent methods, including paleobarometric measurements (Busigny, Cartigny, & Philippot, 2011;Som et al, 2012;Marty, Zimmerman, Pujol, Burgess, & Philippot, 2013;Som et al, 2016;Avice et al, 2018; summarized schematically in Figure 1) and modeling efforts (Barry & Hilton, 2016;Berner, 2006;Goldblatt et al, 2009;Johnson & Goldblatt, 2017Mallik, Li, & Wiedenbeck, 2018;Stüeken, Kipp, Koehler, Schwieterman et al, 2016), have attempted to constrain pN 2 throughout Earth's history. Several nitrogen sources and sinks control the atmospheric nitrogen concentration.…”

Eolianite Grain Size Distributions as a Proxy for Large Changes in Planetary Atmospheric Density

“…Studies have found a mantle nitrogen abundance of 7 ± 4 times the present atmospheric level (Johnson & Goldblatt, ) and coupled with modern subduction recycling rates (Mallik et al, ), these imply that the mantle is a long‐term sink of atmospheric nitrogen that has been monotonically sequestered over time. However, modern fluxes only apply if redox conditions were constant through time, yet models including nitrogen speciation change indicate that redox has a substantial effect on the atmospheric reservoir (Laneuville et al, ; Stüeken et al, ). The stable form of deep sea nitrogen for the Archean would have been NH 4 + (Holland, ), not oxidized species like NO 3 − as in modern oceans.…”

Exploring cycad foliage as an archive of the isotopic composition of atmospheric nitrogen

“…However, pN 2 may have fluctuated over the course of Earth's ~4.5 billion-year history. Modeling work has demonstrated that large (>0.1 bar) pN 2 fluctuations are plausible on >10 7 year timescales under reasonable estimates of biogeochemical fluxes (Busigny, Cartigny, & Philippot, 2011;Goldblatt et al, 2009;Johnson & Goldblatt, 2018;Mallik, Li, & Wiedenbeck, 2018;Stüeken, Kipp, Koehler, Schwieterman, et al, 2016). Such large changes in pN 2 would carry implications for global climate due to the effect of pressure broadening on the absorption of infrared radiation by greenhouse gases in the troposphere (Goldblatt et al, 2009;Stüeken, Kipp, Koehler, Schwieterman, et al, 2016).…”

“…Modeling work has demonstrated that large (>0.1 bar) pN 2 fluctuations are plausible on >10 7 year timescales under reasonable estimates of biogeochemical fluxes (Busigny, Cartigny, & Philippot, 2011;Goldblatt et al, 2009;Johnson & Goldblatt, 2018;Mallik, Li, & Wiedenbeck, 2018;Stüeken, Kipp, Koehler, Schwieterman, et al, 2016). Such large changes in pN 2 would carry implications for global climate due to the effect of pressure broadening on the absorption of infrared radiation by greenhouse gases in the troposphere (Goldblatt et al, 2009;Stüeken, Kipp, Koehler, Schwieterman, et al, 2016). For this reason, there has been considerable effort in recent years to constrain pN 2 using geological proxies that are sensitive to atmospheric pressure (e.g., Som, Catling, Harnmeijer, Polivka, & Buick, 2012;Som et al, 2016;Goosmann, Catling, Som, Altermann, & Buick, 2018).…”

“…For instance, if past changes in pN 2 have been driven by the burial of nitrogen in biomass-which some models suggest is a likely mechanism (Johnson & Goldblatt, 2018;Stüeken, Kipp, Koehler, Schwieterman, et al, 2016)-then the isotopic composition of atmospheric N 2 would have shifted proportionally to the amount and isotopic composition of buried nitrogen via mass balance (similar to what is observed during glacial-interglacial changes in pCO 2 ; Leuenberger, Siegenthaler, & Langway, 1992;Marino, McElroy, Salawitch, & Spaulding, 1992). This may have driven the δ 15 N of atmospheric N 2 toward lower values at times if isotopically heavy (δ 15 N ≫ 0) biomass was being buried.…”