241-2 Modern Venus Could Have Been Earth-like Several Hundred Million Years Ago

Session: Petrology, Volcanology, and Mantle Plumes across the Solar System, Part I

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Abstract:

The average model age for the Venus surface is ~700 Myr. One might then ask: could Venus have plausibly undergone a transition from an Earth-like state to its present climate within that time frame?

The volume of modern Earth’s ocean basins of 1.34×10⁹ km³. There are numerous estimates for Earth’s present eruptive flux, ranging from a low of 3.4 km³/yr to 22.5 km³/yr. These eruptive values bracket the time needed to entirely fill Earth’s ocean basins with volcanic products from as long as 390 Myr to as rapidly as 60 Myr. Modern Venus has a surface occupied by about 72% volcanic plains. Were such plains occupying former ocean basins of an average depth comparable to that of Earth of 4 km, and under the assumption that Venus has a comparable eruptive flux to Earth, the fill times are virtually identical: 59–390 Myr.

An important constraint on any scenario under which modern Venus transitioned from an Earth-like state is the fate of O₂. With the onset of a runaway greenhouse, any oceans present would have evaporated and eventually be photodissociated by solar UV radiation. H was likely subject to thermal or non-thermal escape mechanisms, but O₂ would have been too massive to be lost to space. A likely repository of photodissociated O₂, then, would have been the planet’s crustal rocks.

The oxidation state of Venus’ crust is poorly known, as is the ability of the crust to serve as an oxygen sink. Nevertheless, should a clement Venus have had a comparable water ocean volume to Earth, the photodissociated O₂ could have been sequestered in an oxidized layer of basalt 50 km thick. Again, given the effusive flux of modern Earth, a layer of this thickness would be emplaced in 740 Myr. And if hydration reactions were possible (akin to water–rock reactions on Earth), an oxidized layer as thin as 10 km is required, emplaced in as little as 147 Myr.

These calculations demonstrate that Venus could have been Earth-like within the Phanerozoic. Earth’s climate may enter a runaway greenhouse under increasing solar luminosity within the next billion years. If its eruptive flux remains relatively constant, then Earth, too, could acquire the major planetary properties of Venus within only a few hundred million years.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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