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dc.contributor.authorArney, Giada
dc.contributor.authorDomagal-Goldman, Shawn D.
dc.contributor.authorMeadows, Victoria S.
dc.contributor.authorWolf, Eric T.
dc.contributor.authorSchwieterman, Edward
dc.contributor.authorCharnay, Benjamin
dc.contributor.authorClaire, Mark
dc.contributor.authorHébrard, Eric
dc.contributor.authorTrainer, Melissa G.
dc.identifier.citationArney , G , Domagal-Goldman , S D , Meadows , V S , Wolf , E T , Schwieterman , E , Charnay , B , Claire , M , Hébrard , E & Trainer , M G 2016 , ' The pale orange dot : the spectrum and habitability of hazy Archean Earth ' , Astrobiology , vol. 16 , no. 11 , pp. 873-899 .
dc.identifier.otherPURE: 248193166
dc.identifier.otherPURE UUID: 188628a6-c1c6-4d08-849a-e1dd29a6b9d9
dc.identifier.otherRIS: urn:30CE516716E2A709061D6CBA27EBA5BE
dc.identifier.otherScopus: 85000434675
dc.identifier.otherORCID: /0000-0001-9518-089X/work/34103237
dc.identifier.otherWOS: 000388284100006
dc.description.abstractRecognizing whether a planet can support life is a primary goal of future exoplanet spectral characterization missions, but past research on habitability assessment has largely ignored the vastly different conditions that have existed in our planet's long habitable history. This study presents simulations of a habitable yet dramatically different phase of Earth's history, when the atmosphere contained a Titan-like, organic-rich haze. Prior work has claimed a haze-rich Archean Earth (3.8–2.5 billion years ago) would be frozen due to the haze's cooling effects. However, no previous studies have self-consistently taken into account climate, photochemistry, and fractal hazes. Here, we demonstrate using coupled climate-photochemical-microphysical simulations that hazes can cool the planet's surface by about 20 K, but habitable conditions with liquid surface water could be maintained with a relatively thick haze layer (τ ∼ 5 at 200 nm) even with the fainter young Sun. We find that optically thicker hazes are self-limiting due to their self-shielding properties, preventing catastrophic cooling of the planet. Hazes may even enhance planetary habitability through UV shielding, reducing surface UV flux by about 97% compared to a haze-free planet and potentially allowing survival of land-based organisms 2.7–2.6 billion years ago. The broad UV absorption signature produced by this haze may be visible across interstellar distances, allowing characterization of similar hazy exoplanets. The haze in Archean Earth's atmosphere was strongly dependent on biologically produced methane, and we propose that hydrocarbon haze may be a novel type of spectral biosignature on planets with substantial levels of CO2. Hazy Archean Earth is the most alien world for which we have geochemical constraints on environmental conditions, providing a useful analogue for similar habitable, anoxic exoplanets.
dc.rights© Giada Arney et al., 2016. Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License ( which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.en
dc.subjectArchean Earthen
dc.subjectPlanetary habitabilityen
dc.subjectGE Environmental Sciencesen
dc.subjectQB Astronomyen
dc.subjectQH301 Biologyen
dc.titleThe pale orange dot : the spectrum and habitability of hazy Archean Earthen
dc.typeJournal articleen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews.School of Earth & Environmental Sciencesen
dc.contributor.institutionUniversity of St Andrews.St Andrews Isotope Geochemistryen
dc.contributor.institutionUniversity of St Andrews.Earth and Environmental Sciencesen
dc.description.statusPeer revieweden

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