The habitability of a stagnant-lid Earth

Abstract

Context. Plate tectonics is considered a fundamental component for the habitability of the Earth. Yet whether it is a recurrent feature of terrestrial bodies orbiting other stars or unique to the Earth is unknown. The stagnant lid may rather be the most common tectonic expression on such bodies. Aims. To understand whether a stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we model the thermal evolution of the mantle, volcanic outgassing of H 2 O and CO 2 , and resulting climate of an Earth-like planet lacking plate tectonics. Methods. We used a 1D model of parameterized convection to simulate the evolution of melt generation and the build-up of an atmosphere of H 2 O and CO 2 over 4.5 Gyr. We then employed a 1D radiative-convective atmosphere model to calculate the global mean atmospheric temperature and the boundaries of the habitable zone (HZ).Results. The evolution of the interior is characterized by the initial production of a large amount of partial melt accompanied by a rapid outgassing of H 2 O and CO 2 . The maximal partial pressure of H 2 O is limited to a few tens of bars by the high solubility of water in basaltic melts. The low solubility of CO 2 instead causes most of the carbon to be outgassed, with partial pressures that vary from 1 bar or less if reducing conditions are assumed for the mantle to 100-200 bar for oxidizing conditions. At 1 au, the obtained temperatures generally allow for liquid water on the surface nearly over the entire evolution. While the outer edge of the HZ is mostly influenced by the amount of outgassed CO 2 , the inner edge presents a more complex behaviour that is dependent on the partial pressures of both gases. Conclusions. At 1 au, the stagnant-lid planet considered would be regarded as habitable. The width of the HZ at the end of the evolution, albeit influenced by the amount of outgassed CO 2 , can vary in a non-monotonic way depending on the extent of the outgassed H 2 O reservoir. Our results suggest that stagnant-lid planets can be habitable over geological timescales and that joint modelling of interior evolution, volcanic outgassing, and accompanying climate is necessary to robustly characterize planetary habitability.

Venusian Habitable Climate Scenarios: Modeling Venus through time and applications to slowly rotating Venus-Like Exoplanets

“…This scenario fits in very nicely with the recent work of (Weller & Kiefer, 2019) who give a timescale of order 1Gyr for the transition from a mobile to a stagnant lid mode on Venus in their simplified model. Without a mechanism to efficiently cycle volatiles in a stagnant lid mode (e.g., Tosi et al, 2017;Höning et al, 2019), outgassing would have continued without the major weathering and subduction surface sinks that operate on Earth, hence CO 2 and N 2 would build up over time to reach the levels we see on Venus today. Some studies have also shown that even in a stagnant lid mode it is possible to cycle volatiles, possibly up to gigayears in time (e.g., Foley & Smye, 2018;Godolt et al, 2019), but these mechanisms depend on the initial CO 2 budget and the retention of at least some water after cooldown.…”

Uncertainty Quantification in Planetary Thermal History Models: Implications for Hypotheses Discrimination and Habitability Modeling

“…The question above relates to the extension of thermal history studies from Earth to planetary application, habitability in particular [Kite et al, 2009, Schaefer and Sasselov, 2015, Komacek and Abbot, 2016, Foley, 2015, Foley and Driscoll, 2016, Tosi et al, 2017, Foley and Smye, 2018, Barnes et al, 2019. Thermal history models applied to the Earth are postdictive: they set out to match historical data.…”

Geoscience for Understanding Habitability in the Solar System and Beyond

“…The contrasting mantle fO2 conditions between both planetary bodies is certainly linked to planetary size (Wade and Wood, 2005). Nevertheless, the H2O/CO2 ratio of volcanic gases during that era was controlled by the atmospheric pressure, with dense atmospheres favoring dry volcanic emissions while tenuous atmospheres favored H2O-rich volcanic gases (Gaillard and Scaillet, 2014;Tosi et al, 2017). This is linked to the fact that H2O is orders of magnitude more soluble than CO2 in basalts and that solubility laws imply that, with decreasing pressure, the faction of water partitioning into the fluid must increase (see Iacono-Marziano et al, 2012).…”

“…Noteworthy, though this has never been specifically reviewed in the literature, this filtering process by volcanic degassing also applies to sulfur degassing (sulfur-rich magma may not degas sulfurrich gas). All this complicates the planetary degassing picture and introduces feedbacks that seem promising to address and to relate to the concept of formation of the oceans, climate and habitability (Gaillard and Scaillet, 2014;Tosi et al, 2017).…”

“…The paper has a different focus than most other habitability discussions in Earth-System sciences, planetary sciences and astronomy by encompassing the entire planet from the upper atmosphere to the deep interior and by including the exogenic influence within the framework of the study of its habitability. In this aspect, it is broader in scope than e.g., Lammer et al (2009), Javaux and Dehant (2010), Spohn (2014), Fritz et al (2014), Southam et al (2015), Cockell et al (2016), and Tosi et al (2017). The paper addresses questions within six main sections: (1) Formation of habitable planets, (2) role of cometary, meteorite and asteroid impacts on planetary evolution, (3) planetary interiors, mantle convection and their evolutions, (4) atmospheric evolution, (5) interaction of life with the atmosphere, geosphere and interior of planets, (6) identification of preserved life tracers in the context of the interaction of life with planetary evolution, (7) conclusion and implications for planet formation and habitability conditions and detection in exoplanetary systems.…”