Early Habitability and Crustal Decarbonation of a Stagnant‐Lid Venus. Issue 10 (6th October 2021)

• Record Type: Journal Article
• Authors: Höning, Dennis; Baumeister, Philipp; Grenfell, John Lee; Tosi, Nicola; Way, Michael J.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 10(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-06
• Subjects: carbon cycle -- exoplanets -- habitability -- planetary evolution -- stagnant‐lid -- Venus; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2021JE006895
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: 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 C O 2 supply to the atmosphere the surface temperature rises further, the depth below which decarbonation occurs decreases, causing the release of even more C O 2 . We assess the habitable period of an early stagnant‐lid Venus by employing a coupled interior‐atmosphere evolution model accounting for C O 2 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 C O 2 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 C O 2 could be associated with crustal carbonate depletion as a consequence of a runaway greenhouse, whereas planets with low atmospheric C O 2 would indicate active silicate weathering and thereby a habitable climate. Plain Language Summary: Today, Venus has a thick atmosphere mainly composed of C O 2 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 C O 2 than today, liquid water may have existed. Small amounts of atmospheric C O 2 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 C O 2 low enough to maintain liquid surface water for almost 1 billion years. During this time, weathering ensures that most of the C O 2 degassed from the interior via volcanism gets stored in the crust in the form of carbonates. Yet, part of the degassed C O 2 keeps accumulating in the atmosphere causing the surface temperature to rise because of the greenhouse effect. Ultimately, the liquid water on the surface evaporates and weathering stops. As soon as this happens, the crust becomes rapidly depleted in carbonates, thereby building up Venus' C O 2 ‐thick atmosphere that is observed today. Key Points: Stagnant‐lid model scenarios of early Venus tuned to reproduce present‐day observations suggest an early habitable period of up to 900 Myr After runaway greenhouse, ongoing volcanism and crustal burial on stagnant‐lid planets cause rapid crustal decarbonation and raise of CO2 Stagnant‐lid planets have bimodal distribution of atmospheric CO2 : abundance is low on habitable worlds and high after runaway greenhouse