Early Habitability and Crustal Decarbonation of a Stagnant‐Lid Venus

• Published in: Journal of geophysical research. Planets 2021-10, Vol.126 (10), p.n/a
• Main Authors: Höning, Dennis, Baumeister, Philipp, Grenfell, John Lee, Tosi, Nicola, Way, Michael J.
• Format: Article
• Language: English
• Subjects: Atmosphere; Atmospheric evolution; Carbon cycle; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbonate sediments; Carbonates; Decarbonation; Degassing; Depletion; Evaporation; Evolution; exoplanets; Extrasolar planets; Greenhouse effect; Habitability; Liquid surfaces; planetary evolution; Planets; Plate tectonics; Plates (tectonics); Sediments; stagnant-lid; Surface temperature; Surface water; Tectonics; Venus; Venus atmosphere; Venus surface; Volcanic activity; Weathering
• ISSN: 2169-9097; 2169-9100; 2169-9100
• DOI: 10.1029/2021JE006895

Little is known about the early evolution of Venus and a potential habitable period during the first 1 billion years. In particular, it remains unclear whether or not plate tectonics and an active carbonate‐silicate cycle were present. In the presence of liquid water but without plate tectonics, weathering would have been limited to freshly produced basaltic crust, with an early carbon cycle restricted to the crust and atmosphere. With the evaporation of surface water, weathering would cease. With ongoing volcanism, carbonate sediments would be buried and sink downwards. Thereby, carbonates would heat up until they become unstable and the crust would become depleted in carbonates. With CO2 supply to the atmosphere the surface temperature rises further, the depth below which decarbonation occurs decreases, causing the release of even more CO2. We assess the habitable period of an early stagnant‐lid Venus by employing a coupled interior‐atmosphere evolution model accounting for CO2 degassing, weathering, carbonate burial, and crustal decarbonation. We find that if initial surface conditions allow for liquid water, weathering can keep the planet habitable for up to 900 Myr, followed by evaporation of water and rapid crustal carbonate depletion. For the atmospheric CO2 of stagnant‐lid exoplanets, we predict a bimodal distribution, depending on whether or not these planets experienced a runaway greenhouse in their history. Planets with high atmospheric CO2 could be associated with crustal carbonate depletion as a consequence of a runaway greenhouse, whereas planets with low atmospheric CO2 would indicate active silicate weathering and thereby a habitable climate. Plain Language Summary Today, Venus has a thick atmosphere mainly composed of CO2 and a surface that is too hot for any liquid water to exist. However, 4 billion years ago, the Sun was much fainter, and if Venus' atmosphere contained much less CO2 than today, liquid water may have existed. Small amounts of atmospheric CO2 are commonly associated with plate tectonics because of its ability to recycle carbon into the interior. It is not clear, however, whether or not early Venus possessed plate tectonics. Here, we simulate the evolution of Venus as a planet without plate tectonics, and show that weathering processes can keep the atmospheric CO2 low enough to maintain liquid surface water for almost 1 billion years. During this time, weathering ensures that most of the CO2 degassed from the interior via v