The Habitability of Venus and a Comparison to Early Earth
• +6
• Frances Westall,
• Dennis Höning,
• Guillaume Avice,
• Diana Gentry,
• Taras Gerya,
• Cedric Gillmann,
• Noam Izenberg,
• Michael Way,
• Colin Wilson
Frances Westall
CNRS-Centre de Biophysique Moleculaire, Orleans, France
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Dennis Höning
Potsdam-Institute for Climate Impact Research

Corresponding Author:dennis.hoening@pik-potsdam.de

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Guillaume Avice
Centre National de la Recherche Scientifique
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Diana Gentry
NASA Ames Research Center
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Taras Gerya
ETH Zürich
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Cedric Gillmann
Rice University
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Noam Izenberg
Johns Hopkins University
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Michael Way
NASA Goddard Institute for Space Studies
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Colin Wilson
University of Oxford
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## Abstract

Venus today is inhospitable at the surface, its average temperature of 750 K being incompatible to the existence of life as we know it. However, the potential for past surface habitability and upper atmosphere (cloud) habitability at the present day is hotly debated, as the ongoing discussion regarding a possible phosphine signature coming from the clouds shows. We review current understanding about the evolution of Venus with special attention to scenarios where the planet may have been capable of hosting microbial life. We compare the possibility of past habitability on Venus to the case of Earth by reviewing the various hypotheses put forth concerning the origin of habitable conditions and the emergence and evolution of plate tectonics on both planets. Life emerged on Earth during the Hadean when the planet was dominated by higher mantle temperatures (by about 200$^\circ$C), an uncertain tectonic regime that likely included squishy lid/plume-lid and plate tectonics, and proto continents. Despite the lack of well-preserved crust dating from the Hadean-Paleoarchean eons, we attempt to resume current understanding of the environmental conditions during this critical period based on zircon crystals and geochemical signatures from this period, as well as studies of younger, relatively well-preserved rocks from the Paleoarchean. For these early, primitive life forms, the tectonic regime was not critical but it became an important means of nutrient recycling, with possible consequences to the global environment on the long-term, that was essential to the continuation of habitability and the evolution of life. For early Venus, the question of stable surface water is closely related to tectonics. We discuss potential transitions between stagnant lid and (episodic) tectonics with crustal recycling, as well as consequences for volatile cycling between Venus’ interior and atmosphere. In particular, we review insights into Venus’ early climate and examine critical questions about early rotation speed, reflective clouds, and silicate weathering, and summarize implications for Venus’ long-term habitability. Finally, the state of knowledge of the venusian clouds and the proposed detection of phosphine is covered.