Equifinality Of Venus-like CO2 Atmospheres

While Earth locks much of its carbon in its crust as carbonates, Venus retains a comparable carbon inventory almost entirely in its atmosphere as CO₂.

On Earth, the geological carbon cycle that has produced this vast crustal carbonate inventory is regulated by biology, liquid water, and plate tectonics, which together have stabilised climate over geological timescales. Venus presently lacks all these processes.

We test whether Venus’s massive CO₂ atmosphere is diagnostic of a specific evolutionary pathway by quantifying three routes: primary magma-ocean outgassing, secondary volcanic degassing in a stagnant-lid regime, and remobilisation of crustal carbonates after climate destabilisation. Using a coupled climate–weathering framework, we find that a past habitable Venus could have stored ∼20 bar of CO₂ as crustal carbonates. Following transition to runaway conditions, crustal heating releases this reservoir over tens of Myr.

In stagnant-lid secondary-degassing models with a MORB-like mantle, outgassing reaches only ∼25 bar CO₂, limited by progressive mantle volatile depletion. However, Venus-like inventories can be achieved through: (i) magmatic carbon enrichment, (ii) increased magmatic delivery to the surface (high extrusion or melt production), and (iii) the recycling of undegassed carbon back into the planet’s interior.

Primary magma-ocean outgassing can generate >10² bar CO₂, but the retained fraction after early escape remains uncertain. Ultimately, a Venus-like massive CO₂ atmosphere is an equifinal outcome and does not uniquely diagnose a temperate past.

Tereza Constantinou, Oliver Shorttle, Harrison Nicholls

Comments: Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2604.25810 [astro-ph.EP] (or arXiv:2604.25810v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2604.25810
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Submission history
From: Tereza Constantinou
[v1] Tue, 28 Apr 2026 16:20:19 UTC (12,947 KB)
https://arxiv.org/abs/2604.25810

Astrobiology, exoplanet,