![Modern Earth clear-atmosphere transmission spectrum at R ∼ 105 with molecule-by-molecule attribution over 0.4-1.8 µm. In all panels, species are color-coded as in the legend. (A) Continuum-subtracted transit-depth excess (Rp/Rs) 2 (black), measured relative to the 5th-percentile continuum floor (gray fill), with muted “only-molecule” traces of the active absorbers. (B) Molecular contributions ∆ = (full − leave-one-out) in ppm for the same wavelength; O2 and H2O dominate selected optical-NIR intervals, while CO2, CH4, CO, HCN, C2H6, and O3 provide weaker secondary features. (C) Offset contribution zooms over 0.68-1.30 µm isolating the O2 B/A and 1.27 µm bands (upper) against overlapping H2O (lower). (D) Offset contribution zooms over 1.35-1.75 µm through the near-infrared H2O/CO2/CH4 forest (top to bottom). O3 contributions appear only where the O3 line list is available (λ ≳ 1.4 µm). Aerosols are not considered in the radiative transfer.-- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/11/From-Anoxic.png?fit=1200%2C672&ssl=1)
[astro-ph.EP]. Earth’s atmosphere evolved from an anoxic, methane-bearing Archean state through Proterozoic oxygenation to the O2-rich modern atmosphere. However, most biosignature detectability studies focus on modern Earth, leaving earlier atmospheric states comparatively unexplored.
We investigate how atmospheric evolution and stellar environments influence the detectability of O2, CH4, H2O, and CO2, and their potential to distinguish anoxic from oxygenated atmospheres. We construct two complementary photochemical grids: representative Archean, Proterozoic, and modern-Earth scenarios around the Sun, and four geological epochs (3.9, 2.0, 0.8 Ga, and modern Earth) across FGKM hosts.
Combining one-dimensional photochemical modeling, high-resolution transmission spectral simulations, and instrument-noise modeling, we assess molecular detectability with ELT/ANDES under optimistic photon-noise-limited conditions. For solar-host Archean and Proterozoic models, CH4 requires approximately 33 and 42 transits, respectively, to reach the adopted 5σ criterion, whereas O2 remains below 3σ within the observing limits. Modern-Earth O2 reaches 3σ after approximately 38 transits.
Across the FGKM grid, O2 does not reach 5σ for the 3.9 Ga models. However, For the M3V, K2V, and M8V proxies, modern-Earth O2 reaches 5σ in 9, 15, and 20 transits, respectively, whereas CH4 requires 11, 12, and 28 transits at 3.9 Ga and only 2–4 transits across the oxygenated epochs.
These results reveal a strong O2 detectability contrast around M and K-dwarfs, but not Sun-like hosts in the YJH bands. Robust biosignature interpretation requires complementary molecular constraints, including informative non-detections, within the context of atmospheric evolution and stellar environment.
Dwaipayan Dubey, Spandan Dash, Liton Majumdar
Comments: Submitted to AAS (31 pages, 20 figures). Comments are most welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2610.41621 [astro-ph.EP] (or arXiv:2610.41621v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2610.41621
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Submission history
From: Dwaipayan Dubey
[v1] Fri, 30 Oct 2026 11:58:18 UTC (14,436 KB)
https://arxiv.org/abs/2610.41621
Astrobiology,
