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 (Formula presented.) supply to the atmosphere the surface temperature rises further, the depth below which decarbonation occurs decreases, causing the release of even more (Formula presented.). We assess the habitable period of an early stagnant-lid Venus by employing a coupled interior-atmosphere evolution model accounting for (Formula presented.) 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 (Formula presented.) 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 (Formula presented.) could be associated with crustal carbonate depletion as a consequence of a runaway greenhouse, whereas planets with low atmospheric (Formula presented.) would indicate active silicate weathering and thereby a habitable climate.
Bibliographical noteFunding Information:
The authors thank two anonymous reviewers for helpful comments and suggestions. D. Höning was supported through the NWO StartImpuls. P. Baumeister, N. Tosi, and J. L. Grenfell acknowledge support from the DFG Priority Program SPP 1992 “Exploring the Diversity of Extrasolar Planets” (TO 704/3‐1 and GO 2610/2‐1). P. Baumeister and N. Tosi also acknowledge support from the DFG Research Unit FOR 2440 “Matter under planetary interior conditions.” M. J. Way was supported by NASA's Nexus for Exoplanet System Science (NExSS). Resources supporting this work were provided by the NASA High‐End Computing (HEC) Program through the NASA Center for Climate Simulation (NCCS) at Goddard Space Flight Center. M. J. Way acknowledges support from the GSFC Sellers Exoplanet Environments Collaboration (SEEC), which is funded by the NASA Planetary Science Division's Internal Scientist Funding Model.
© 2021. The Authors.
- carbon cycle
- planetary evolution