Life Potential on Early Venus Connected to Climate and Geologic History

Introduction: A key observation and open question in the Earth and Planetary Sciences is that the Earth is seemingly unique in that it exhibits plate tectonics and a buffered climate allowing liquid water to exist at the surface over its geologic lifetime. While we know plate tectonics is currently in operation on the Earth, the timing of its onset, the length of its activity, and its prevalence outside the Earth are far from certain. Recent work suggests that the Earth has not always been within a plate-tectonic regime, and that it has evolved over time. Multiple lines of geochemical and geologic evidence, as well as geophysical models of planetary evolution, suggest the Earth initiated in a stagnant-lid (one plate-planet), followed by an "adolescent" episodic-lid (alternating between stagnant and mobile-lids), before settling into a "mature" modern style of plate-tectonics (mobile-lid) [e.g., 1 – 6]. This implies that life and habitable conditions have existed on the Earth during episodic behavior. Modeling of an episodic early Earth has further shown habitable climates to be viable [7]. Currently, Venus shows no clear evidence of Earthlike plate tectonic activity or surface conditions. Observations reveal a world that has both a thick 92 bar atmosphere, comprised of 96.5% CO2 and surface temperatures of ~740 K, and been resurfaced by vast volcanic plains that cover ~ 80% of the surface, which are thought to have been emplaced in the last 300 – 1000 Myr [8 – 10], perhaps ‘catastrophically’ [9, 10]. These observations, along with inferences of limited large scale shortening [11], are consistent with suggestions of an episodic-lid regime [12 – 14]. If an early episodic Earth could support a habitable climate [7], what of Earth's "twin", Venus? Could an episodic Venus have been habitable? Here we examine this possibility, and show links between atmospheric evolution, habitability, and the deep interior.