The punctuated evolution of the Venusian atmosphere from a transition in mantle convective style and volcanic outgassing.

A key question in the planetary sciences centers on the divergence between the sibling planets, Venus and Earth. Venus currently does not operate with plate tectonics, and its thick atmosphere has led to extreme greenhouse conditions. It is unknown if this state was set primordially or if Venus was once more Earth-like. Here, we explore Venus as an example of a planet that recently transitioned between tectonic regimes. Our results show that transitions naturally lead to substantial resurfacing and melt-generated outgassing from lithosphere-breaking events and overturns, with 3 to 10 bars of atmosphere generated per overturn over ~60-million year timescales and ~10 to 100 bars outgassed over billion-year time frames. We find that the observation of Venus with a thick greenhouse atmosphere and the inferences of currently low volcanic rates and previous prodigious volcanic rates are consistent with a planet that has undergone a transition in tectonics, suggesting that Venus once hosted clement surface conditions and was more Earth-like.