Early habitability and crustal decarbonation of a stagnant-lid Venus

TL;DR

This study models the early evolution of Venus with a stagnant lid, showing potential habitability lasting up to 900 million years through weathering, followed by water loss and carbonate depletion, influenced by CO2 cycling.

Contribution

It introduces a coupled interior-atmosphere model to assess early Venus habitability and predicts bimodal CO2 distributions related to runaway greenhouse scenarios.

Findings

Habitability could last up to 900 Myr with liquid water presence.

Water evaporation leads to rapid crustal carbonate depletion.

High CO2 planets may have experienced runaway greenhouse effects.

Abstract

Little is known about the early evolution of Venus and a potential habitable period during the first one 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 CO$_2$ supply to the atmosphere the surface temperature rises further, the depth below which decarbonation occurs decreases, causing the release of even more CO$_2$. We assess the habitable period of an early stagnant-lid Venus by employing a coupled interior-atmosphere evolution model accounting for CO$_2$ 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 CO$_2$ 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 CO$_2$ could be associated with crustal carbonate depletion as a consequence of a runaway greenhouse, whereas planets with low atmospheric CO$_2$ would indicate active silicate weathering and thereby a habitable climate.