Cited by 333Space Science and Extraterrestrial LifeAstro and Planetary SciencePlanetary Science and Exploration

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The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

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Arney, Giada, Domagal-Goldman, Shawn D., Meadows, Victoria S., Wolf, Eric T., Schwieterman, Edward, Charnay, Benjamin, Claire, Mark, Hébrard, Eric, Trainer, Melissa G.·2016·Astrobiology

DOI 10.1089/ast.2015.1422PMC PMC5148108

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Abstract

Recognizing 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 CO 2 . 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. Key Words: Haze—Archean Earth—Exoplanets—Spectra—Biosignatures—Planetary habitability. Astrobiology 16, 873–899.

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Written from the paper’s full text.

TL;DR

Coupled climate-photochemical-microphysical simulations of hazy Archean Earth show that organic haze can cool the surface by about 20 K but still permit habitable temperatures with liquid surface water, because thick hazes self-limit via UV self-shielding. The haze also strongly shields surface UV and produces distinctive spectral features, suggesting hydrocarbon haze may be a biologically mediated spectral biosignature on anoxic, CO₂-rich exoplanets.

Key findings

Hazy Archean climates were cold but likely habitable: for Cases A–D, stabilized surface temperatures with haze were 263, 274, 262, and 251 K, and with ice-albedo feedback 257, 271, 257, and 241 K, all above the adopted 248 K habitability threshold; haze cooling reached up to ∼20 K, with maximum haze optical thickness leveling off at τ ∼ 5 at 200 nm.
Haze is self-limiting: optically thicker hazes shield CH₄ from photolysis, shutting down haze formation and preventing catastrophic cooling; the CH₄/CO₂ ratios needed to initiate haze formation were 0.18, 0.15, 0.19, and 0.28 for Cases A–D.
UV shielding was substantial: for Case B with CH₄/CO₂ = 0.21, surface UVC flux was about 0.03 W/m² at SZA = 60° and 0.22 W/m² at SZA = 0°, compared with 0.93 and 2.62 W/m² for the haze-free case, a reduction of about 97%; this may have allowed survival of land-based organisms 2.7–2.6 billion years ago.
Hazy Archean Earth would be a “pale orange dot,” with a broad UV absorption signature, a 6 μm transit-transmission haze feature, and a weaker 3 μm feature; the CH₄ flux needed to initiate haze was about 1 × 10¹¹ to 3 × 10¹¹ molecules/cm²/s, far above estimated maximum abiotic serpentinization fluxes of 6.8 × 10⁸ and 1.3 × 10⁹ molecules/cm²/s for 1 and 5 Earth-mass rocky planets.

Methods

Used the coupled 1-D photochemical-climate model Atmos and the 1-D radiative transfer model SMART; the photochemical model has 200 plane-parallel layers from the surface to 100 km, 76 chemical species, and fractal hydrocarbon haze microphysics, while the climate model uses correlated-k absorption and a δ-2-stream radiative transfer scheme, iterating between models to convergence.
Simulated four Archean cases spanning pCO₂ = 0.0036–0.018 bar and surface pressure = 0.5–1 bar, with solar constant at 2.7 Ga = 0.81 S/S₀, surface O₂ = 1.0 × 10⁻⁸, and varied CH₄/CO₂; about 60 coupled Atmos runs were required.
Generated synthetic reflectance, thermal emission, and transit transmission spectra with SMART, including binned haze particle modes and, for Case B, tests with water clouds.

Limitations

Stated in paper: the climate model could only be run to about 80 km while the photochemical model extends to 100 km, with isoprofiles above the climate grid; sensitivity tests showed <5% difference in largest haze particles and <0.5 K surface temperature effect. Older CH₄ coefficients may overestimate surface temperature by ≲5 K, while the model underpredicts Archean temperature by about 2–5 K compared with 3-D models, so these may cancel.
Stated in paper: the 1-D model lacks atmospheric circulation, precipitation, cloud formation, cloud scattering and absorption, and long-wave cloud radiative forcing; comparison with GCMs suggests the presented temperatures may be underestimates by about 3–5 K, and ice-albedo feedback, haze deposition, haze circulation, and cloud feedbacks are left to future GCM studies.
Stated in paper and evident from text: haze formation chemistry is not well understood, and the model assumes C₄H₂ and C₅H₄ condense directly to haze particles, possibly overestimating aerosol formation; only one Archean haze refractive index measurement exists, at 532 nm, and the study uses Titan-like Khare optical constants; NH₃ was not included in the photochemical scheme; nominal haze spectra exclude water clouds.

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Registry

Crossref · 10.1089/ast.2015.1422

Cites

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Claims the paper makes

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In the paper
“The haze can produce a stronger UV shield compared to the low O2 atmosphere (0.1% PAL) proposed recently by Planavsky et al. (2014) for our atmospheric assumptions.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.2. UV shielding
What the sources say
- Not checked yetcites Planavsky et al., 2014
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“By using the updated habitability threshold of Tsurf > 248 K, all our cases even with thick hazes are habitable.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
- Rests on an assumption: A planet with any nonzero fraction of open ocean is habitable.
In the paper
“However, the CH4 levels in the Domagal-Goldman et al. solar simulations were an order of magnitude lower than the ones shown here.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
What the sources say
- Not checked yetcites Domagal-Goldman et al.
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“At the range of pCO2 allowed by Driese et al. (2011), we find that the CH4 flux needed to initiate haze formation ranges between about 1 × 1011 and 3 × 1011 molecules/cm2/s”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.1. Haze and biology
What the sources say
- Not checked yetcites Driese et al. (2011)
Load-bearingStrength:plain· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
The paper states this without a source or data behind it here, so there is nothing to check it against. The quote shows it is in the paper.
In the paper
“Thus, at longer wavelengths, cloudy worlds are brighter than their haze-only counterparts.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
Strength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
- Rests on an assumption: Water vapor clouds have an approximately gray opacity from the visible into the NIR.
In the paper
“The haze-free surface temperatures we generate are broadly consistent with the Haqq-Misra et al. nonhazy results with C2H6.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Haqq-Misra et al.
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“We have shown that a hazy Archean Earth consistent with geochemical constraints on CO2 concentration and geological constraints on surface pressure could have had habitable surface temperatures.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 5. Conclusions
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
- Rests on an assumption: The geochemical constraints on Archean CO2 concentration and geological constraints on surface pressure used in the study are valid.
In the paper
“photolysis of sulfur gases in an anoxic atmosphere is the only known mechanism that produces large-magnitude Δ33S and Δ36S seen in the rock record (Farquhar et al., 2001, 2007)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Farquhar et al., 2001, 2007
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“the Archean (3.8–2.5 billion years ago) haze was likely biologically mediated via CH4 produced from methanogenesis, one of the earliest metabolisms (Woese and Fox, 1977; Ueno et al., 2006)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction
What the sources say
- Not checked yetcites Woese and Fox, 1977
- Not checked yetcites Ueno et al., 2006
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Those spectral studies that consider Archean Earth and anoxic planets have not examined hazes (Meadows, 2006; Kaltenegger et al., 2007; Domagal-Goldman et al., 2011).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction
What the sources say
- Not checked yetcites Meadows, 2006
- Not checked yetcites Kaltenegger et al., 2007
- Not checked yetcites Domagal-Goldman et al., 2011
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“This hydrocarbon haze, generated by methane (CH4) photolysis, would have formed when the ratio of CH4 to carbon dioxide (CO2) in the atmosphere exceeded about 0.1 (Trainer et al., 2006).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction
What the sources say
- Not checked yetcites Trainer et al., 2006
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“existing spectral studies are largely focused on the observables of modern-day Earth (e.g., Sagan et al., 1993; Woolf et al., 2002; Robinson et al., 2011, 2014a)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction
What the sources say
- Not checked yetcites Sagan et al., 1993
- Not checked yetcites Woolf et al., 2002
- Not checked yetcites Robinson et al., 2011, 2014a
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“Its recurrence at both ends of the Archean eon implies that, within 0.8 billion years of Earth's formation, a common mechanism for S-MIF production was already established in the atmosphere (Thomassot et al., 2015).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Thomassot et al., 2015
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“After the GOE, all the sulfur in the atmosphere would have been oxidized into a single exit channel, eliminating any fractionation created in the atmosphere (Pavlov and Kasting, 2002).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Pavlov and Kasting, 2002
Load-bearingStrength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Geochemical data suggest 3–5 distinct intervals of organic haze during the later Archean (Zerkle et al., 2012; Izon et al., 2015)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zerkle et al., 2012
- Not checked yetcites Izon et al., 2015
Load-bearingStrength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“but the biotic flux of methane to the Archean atmosphere was likely much higher than the abiotic flux (Kharecha et al., 2005), as it is on Earth today”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction
What the sources say
- Not checked yetcites Kharecha et al., 2005
Load-bearingStrength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“The geochemical evidence, described below, implies Neoarchean hazy intervals (Zerkle et al., 2012; Izon et al., 2015) lasting for less than 1 million years.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zerkle et al., 2012
- Not checked yetcites Izon et al., 2015
Strength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“The authors analyzed sediments aged 2.65–2.5 Ga collected from the Ghaap Group in South Africa and showed that variations of Δ36S/Δ33S associated with changes in atmospheric chemistry were contemporaneous with highly negative excursions of δ13Corg values.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zerkle et al., 2012
Load-bearingStrength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“Hörst and Tolbert (2013) measured a similar effective particle density, 0.65 g/cm3, for a 0.1% CH4 haze experiment using a UV lamp.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Hörst and Tolbert, 2013
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Negative values of δ13Corg below −37‰ are typically interpreted as evidence for methanogenesis (biological methane production) followed by subsequent incorporation into sediments by methanotrophy (methane consumption)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Urey and Greiff, 1935
- Not checked yetcites Schopf, 1983
- Not checked yetcites Schidlowski, 2001
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“At ∼2.9 Ga, there is geological evidence suggesting a glaciation event (Young et al., 1998) may have occurred during the same period when the S-MIF Δ33S signal dips to lower values.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Young et al., 1998
Load-bearingStrength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Earth's record of sedimentary sulfates does show a significant change in their minor sulfate isotope behavior between 2.73 and 2.71 Ga (Kurzweil et al., 2013; Izon et al., 2015)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Kurzweil et al., 2013
- Not checked yetcites Izon et al., 2015
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“The links between S-MIF signals and biogenic methane production have been recently expanded over multiple cores and locations, suggesting multiple changes in atmospheric chemistry during the Neoarchean (Izon et al., 2015).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Izon et al., 2015
Strength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“Our older CH4 coefficients may overestimate the surface temperature by ≲5 K at the CH4 mixing ratios used here (Byrne and Goldblatt, 2015).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.1. Coupled photochemical-climate model
What the sources say
- Not checked yetcites Byrne and Goldblatt, 2015
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Changes observed in the slope of Δ36S/Δ33S vary between −1.5 and −0.9 and are interpreted to reflect changes in the S-MIF source reactions driven by varying atmospheric haze thicknesses.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zerkle et al., 2012
- Not checked yetcites Kurzweil et al., 2013
- Not checked yetcites Izon et al., 2015
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“Their weakened visible extinction and enhanced forward scattering compared to spherical particles means they produce less cooling since they scatter less incident sunlight back to space (see Fig. 3 in Wolf and Toon, 2010).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.1. Coupled photochemical-climate model
What the sources say
- Not checked yetcites Wolf and Toon, 2010
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“The contemporaneous excursions of the sulfur and Corg isotopes suggest a close linkage between S-MIF signals and biogenic methane.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zerkle et al., 2012
Load-bearingStrength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“Our Archean simulations use the solar constant at 2.7 Ga (0.81 = S/S0, where S0 is the modern solar constant and S is the solar constant at 2.7 Ga) modified by a wavelength-dependent solar evolution correction (Claire et al., 2012).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Claire et al., 2012
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“The mean field approximation we use for fractal scattering has been validated against scattering by silica fractal aggregates (Botet et al., 1997) and Titan's hazes (Rannou et al., 1997; Larson et al., 2015).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.1. Coupled photochemical-climate model
What the sources say
- Not checked yetcites Botet et al., 1997
- Not checked yetcites Rannou et al., 1997
- Not checked yetcites Larson et al., 2015
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“SMART has been validated against observations of multiple solar system planets (Robinson et al., 2011; Arney et al., 2014).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.2. The SMART model
What the sources say
- Not checked yetcites Robinson et al., 2011
- Not checked yetcites Arney et al., 2014
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“In the photochemical model, we set a haze monomer density of 0.64 g/cm3, which is consistent with the laboratory results of Trainer et al. (2006) for early Earth.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Trainer et al., 2006
Strength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“These conditions reflect the time period after the evolution of oxygenic photosynthesis but prior to Earth's GOE in which substantial biogenic fluxes of both oxygen and methane would have vented into a predominantly reducing atmosphere (Claire et al., 2014).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Claire et al., 2014
Load-bearingStrength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“Recent paleosol measurements have constrained the CO2 partial pressure (pCO2) in the Archean at 2.7 Ga to be between 0.0036 and 0.018 bar [10–50 × the present atmospheric level (PAL)] (Driese et al., 2011)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results
What the sources say
- Not checked yetcites Driese et al., 2011
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Although the cold climates we have simulated are “habitable” in the sense that they have open ocean, a cold climate with extended ice caps (Tsurf < 273 K) from a thick haze may be consistent with a reported glaciation event at 2.9 Ga (Young et al., 1998) as a previous study has suggested (Domagal-Goldman et al., 2008).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
What the sources say
- Not checked yetcites Young et al., 1998
- Not checked yetcites Domagal-Goldman et al., 2008
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“while recent estimates of Archean surface pressure (Psurf) are consistent with values as low as 0.5 bar (Som et al., 2012; Marty et al., 2013).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results
What the sources say
- Not checked yetcites Som et al., 2012
- Not checked yetcites Marty et al., 2013
Load-bearingStrength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“Both of these values are sufficient for sterilization (Pierson et al., 1992).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.2. UV shielding
What the sources say
- Not checked yetcites Pierson et al., 1992
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Our SZA = 60° flux, 0.03 W/m2, is low enough to allow growth of Chloroflexus aurantiacus over the length of a day in the late Archean [about 18–19 h for a day-night cycle; Denis et al. (2002)].”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.2. UV shielding
What the sources say
- Not checked yetcites Pierson et al., 1992
- Not checked yetcites Denis et al., 2002
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“On the other hand, hazes can also act as cloud condensation nuclei, enhancing cloud formation (Hasenkopf et al., 2011).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
What the sources say
- Not checked yetcites Hasenkopf et al., 2011
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“The maximum abiotic methane production rate from serpentinization, its primary nonbiological source, has been estimated as 6.8 × 108 and 1.3 × 109 molecules/cm2/s for rocky planets of 1 and 5 Earth masses, respectively (Guzmán-Marmolejo et al., 2013)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.1. Haze and biology
What the sources say
- Not checked yetcites Guzmán-Marmolejo et al., 2013
Load-bearingStrength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“For an ocean-covered planet with no haze, the LMD model produces a mean surface temperature of 287 K (Charnay et al., 2013).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Charnay et al., 2013
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“broadly consistent with estimates for the biological Archean methane flux after the origin of oxygenic photosynthesis (Kharecha et al., 2005; Claire et al., 2014).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.1. Haze and biology
What the sources say
- Not checked yetcites Kharecha et al., 2005
- Not checked yetcites Claire et al., 2014
Load-bearingStrength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“but this would not be possible on planets with hydrocarbon hazes due to these strong short-wavelength absorption effects.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion
What the sources say
- Not checked yetcites Benneke and Seager, 2012
Load-bearingStrength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“However, since clouds have a major impact on the planet's spectral appearance and albedo (e.g., Kitzmann et al., 2011b), we show spectra with water clouds included in Section 3.3.1.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
What the sources say
- Not checked yetcites Kitzmann et al., 2011b
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“In Earth-like clear-sky atmospheres, the minimum atmospheric altitude transit observations are able to probe will typically be limited by refraction (García Muñoz et al., 2012; Bétrémieux and Kaltenegger, 2014; Misra et al., 2014b)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
What the sources say
- Not checked yetcites García Muñoz et al., 2012
- Not checked yetcites Bétrémieux and Kaltenegger, 2014
- Not checked yetcites Misra et al., 2014b
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“Haqq-Misra et al. show that a planet with pCO2 = 0.01 and CH4/CO2 = 0.1 has a surface temperature of about 282 K, which is close to our 283.4 K for a comparable atmosphere.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Haqq-Misra et al.
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“every model of hydrocarbon haze formation in early Earth's atmosphere—including ours—has assumed that aerosol formation will occur through the formation of acetylene (C2H2) and its further polymerization to higher polyacetylene chains (Pavlov et al., 2001b; Domagal-Goldman et al., 2008; Haqq-Misra et al., 2008; Zerkle et al., 2012; Kurzweil et al., 2013; Claire et al., 2014)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Pavlov et al., 2001b
- Not checked yetcites Domagal-Goldman et al., 2008
- Not checked yetcites Haqq-Misra et al., 2008
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“as we have argued, a mean surface temperature of the freezing point of water is not a useful threshold for global habitability (Charnay et al., 2013; Shields et al., 2013; Wolf and Toon, 2013; Kunze et al., 2014)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Charnay et al., 2013
- Not checked yetcites Shields et al., 2013
- Not checked yetcites Wolf and Toon, 2013
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“Similar to our study, the Haqq-Misra et al. study found it was difficult to maintain surface temperatures above the freezing point of water with spherical haze particles.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Haqq-Misra et al.
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“By using far-UV radiation (115–400 nm), organic aerosol production from a CH4/CO2/N2 mixture was shown to exceed that from a pure CH4/N2 mixture (Trainer et al., 2006)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Trainer et al., 2006
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Studies have shown the formation of HCN, CH3CN, and other nitrile gas species are formed using the same type of UV source in a CH4/N2 gas mixture, thus corroborating the indirect nitrogen photochemistry (Trainer et al., 2012; Yoon et al., 2014).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Trainer et al., 2012
- Not checked yetcites Yoon et al., 2014
Strength:boosted· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“However, since our nonhazy comparison atmosphere was about 1.4 K warmer than the comparable Haqq-Misra atmosphere, a small component of the warmer temperatures we see here may also result in part from updates to our climate model made by Kopparapu et al. (2013).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Kopparapu et al. (2013)
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“and organic aerosol formation was experimentally observed to occur down to C/O ratios as low as 0.1 (Trainer et al., 2006; DeWitt et al., 2009).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Trainer et al., 2006
- Not checked yetcites DeWitt et al., 2009
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
None of the sources cited for this claim have been checked yet.
In the paper
“Nitrogen incorporation was recently observed in the aerosols generated by far-UV photolysis of CH4/CO2/N2 gas mixtures (Trainer, 2013) and in CH4/N2 mixtures (Sebree et al., 2015).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Trainer, 2013
- Not checked yetcites Sebree et al., 2015
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“For example, for a planet with 1 bar of pressure and 2% CO2, the Haqq-Misra et al. spherical haze drops the planet's temperature to below 260 K.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Haqq-Misra et al.
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
In the paper
“so some of the Haqq-Misra et al. spherical haze results may actually be “habitable.””
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Haqq-Misra et al.
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“For instance, organic molecules with oxygen-containing functional groups (alcohols, carbonyls) tend to have stronger absorbances at longer UV wavelengths as compared to similar hydrocarbon molecules (Workman, 2000).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Workman, 2000
Strength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
In the paper
“These compositional differences should change the properties of the aerosol material sufficiently to be able to distinguish a hazy early Earth from a modern-day Titan (Hasenkopf et al., 2010).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Hasenkopf et al., 2010
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
A conclusion the paper draws from its own results — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Haze can cut down the surface-incident UVC radiation on Archean Earth from ∼0.9 W/m2 to ∼0.03 W/m2 for a SZA of 60°, and may have allowed survival of otherwise unshielded life at the surface of our Archean planet.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 5. Conclusions
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
- Rests on an assumption: UVC radiation is harmful to unshielded life.

Probably not a substantial claim. 40
It may state two separate claims as one. 58

The paper states this without a source or data behind it here, so there is nothing to check it against. The quote shows it is in the paper.
In the paper
“We find that hazy Archean climates were cold but most likely habitable (Fig. 4).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
Load-bearingStrength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
- Rests on an assumption: A planet with any nonzero fraction of open ocean is habitable.
In the paper
“its buildup in our spectra is not inconsistent with the results of Domagal-Goldman et al. (2011)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
What the sources say
- Not checked yetcites Domagal-Goldman et al. (2011)
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“We achieve the closest match to the Charnay et al. results for a modern continental land mass arrangement: in the GCM, this yields an average albedo of 0.34 and a temperature of 283.7 K, close to our result of 281.1 K for this configuration.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Charnay et al.
Strength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
It may state two separate claims as one.
In the paper
“This difference in temperature is smaller than the difference of using spherical versus fractal particles: our comparison to the Haqq-Misra et al. (2008) study in Section 4.2 shows that particle shape can result in temperature differences >10 K.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.5. Optical constants
What the sources say
- Not checked yetcites Haqq-Misra et al. (2008)
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
It may state two separate claims as one.
In the paper
“the modeling work of Domagal-Goldman et al. (2008) suggests a longer Mesoarchean to Neoarchean hazy period between 3.2 and 2.7 Ga.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Domagal-Goldman et al., 2008
Strength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“S8 is the most important species to rain out S-MIF from the atmosphere; because a more reducing atmosphere enhances the ability of S8 to polymerize, S-MIF is more easily preserved under reducing conditions (Zahnle et al., 2006).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zahnle et al., 2006
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“Several studies have proposed links between haze and the mass-independent sulfur isotope fractionation signal (S-MIF) (Farquhar et al., 2000) preserved in the geological record before the Great Oxygenation Event (GOE) at about 2.5 Ga”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Farquhar et al., 2000
- Not checked yetcites Domagal-Goldman et al., 2008
- Not checked yetcites Zerkle et al., 2012
Load-bearingStrength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
None of the sources cited for this claim have been checked yet.
In the paper
“Early in Earth's history, an anoxic atmosphere could have supported the formation of an organic haze (Pavlov et al., 2001a; Trainer et al., 2004, 2006; DeWitt et al., 2009; Hasenkopf et al., 2010; Zerkle et al., 2012; Kurzweil et al., 2013; Claire et al., 2014; Izon et al., 2015) that strongly interacted with visible and UV radiation, cooling the planet's climate (Pavlov et al., 2001b; Domagal-Gol”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction
What the sources say
- Not checked yetcites Pavlov et al., 2001a
- Not checked yetcites Trainer et al., 2004, 2006
- Not checked yetcites DeWitt et al., 2009
Load-bearingStrength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“Δ36S/Δ33S in Archean sedimentary rocks is generally around −1, but stratigraphic variations in this slope have been observed in the geological record and interpreted as evidence of changes to the S-MIF production mechanism resulting from changes in atmospheric composition (Zerkle et al., 2012; Kurzweil et al., 2013; Izon et al., 2015), suggesting the influence of haze.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zerkle et al., 2012
- Not checked yetcites Kurzweil et al., 2013
- Not checked yetcites Izon et al., 2015
Load-bearingStrength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
In the paper
“In general, compared to spherical particles, fractal particles produce more extinction in the ultraviolet (UV) but less in the visible and near infrared (NIR).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.1. Coupled photochemical-climate model
What the sources say
- Not checked yetcites Wolf and Toon, 2010
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
In the paper
“they discuss a change in the slope of Δ36S/Δ33S from −1.5 to −0.9 at 2.71 Ga and interpret this to be caused by a decrease in the CH4/CO2 ratio at 2.71 Ga, possibly indicating an organic haze was present for some period of time prior to 2.71 Ga and cleared afterward.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Kurzweil et al., 2013
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim. It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“An upper atmosphere haze that decreased tropospheric SO2 photolysis by blocking UV photons and cooled the planet could explain both the glaciation and the decrease in S-MIF.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Domagal-Goldman et al., 2008
- Not checked yetcites Haqq-Misra et al., 2008
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
None of the sources cited for this claim have been checked yet.
In the paper
“In this interpretation, haze-free and reducing atmospheric conditions dominated after 2.71 Ga, with haze reappearing in brief intervals of time as suggested by the Zerkle et al. (2012) and Izon et al. (2015) measurements.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Zerkle et al., 2012
- Not checked yetcites Izon et al., 2015
Load-bearingStrength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“In a real atmosphere, the molecules would be larger before aerosols condense, and back-reactions should occur, so this model may overestimate the rate of aerosol formation.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.1. Coupled photochemical-climate model
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
- The authors state this as an assumption: C4H2 and C5H4 condense directly to haze particles.
In the paper
“Spherical particles in SMART are binned according to log-normal size distributions using the radii mentioned previously and a mode standard deviation of 1.5, which is realistic for an aerosol distribution (Tolfo, 1977).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.2. The SMART model
What the sources say
- Not checked yetcites Tolfo, 1977
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“Note that the version of the model used here can simulate atmospheres ranging from extremely anoxic (pO2 = 10−14) to modern-day O2 levels (Zahnle et al., 2006).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.1. Coupled photochemical-climate model
What the sources say
- Not checked yetcites Zahnle et al., 2006
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“In addition, fractals tend to be more forward scattering in the visible and NIR and more isotropically scattering in the UV compared to equal-mass spherical particles.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.1. Coupled photochemical-climate model
What the sources say
- Not checked yetcites Wolf and Toon, 2010
Load-bearingStrength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
In the paper
“Δ33S typically correlates with enrichments in δ34S and with depletions in δ36S”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Claire et al., 2014
Strength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
It may state two separate claims as one.
In the paper
“In this conceptual model, the end of the cold period typified by low Δ33S may be due to a decrease in the atmospheric CH4/CO2 ratio, which would have cleared any haze present in the atmosphere.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Claire et al., 2014
Load-bearingStrength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
In the paper
“Unlike previous studies of the Archean climate under a haze, we use realistic fractal (rather than spherical) particles, which have different spectral properties and climatic effects.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Wolf and Toon, 2010
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“Kurzweil et al. (2013) noted that an increase in magnitude of S-MIF signals after 2.73 Ga (Thomazo et al., 2009) occurred during a prolonged negative shift in δ13Corg, suggesting enhanced biological methane activity at this time.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 1. Introduction > 1.1. Evidence for an Archean haze
What the sources say
- Not checked yetcites Kurzweil et al., 2013
- Not checked yetcites Thomazo et al., 2009
Strength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
None of the sources cited for this claim have been checked yet.
In the paper
“However, more recent 3-D studies have shown that Archean Earth can maintain an open ocean fraction of >50% for TGAT ≥ 260 K and an equatorial open ocean belt for TGAT ≥ 248 K (Wolf and Toon, 2013; Charnay et al., 2013).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
What the sources say
- Not checked yetcites Wolf and Toon, 2013
- Not checked yetcites Charnay et al., 2013
Load-bearingStrength:plain· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
In the paper
“This might lead to cooling of the planet or even warming depending on cloud particle size and the altitude—and therefore temperature—of the cloud layer (Goldblatt and Zahnle, 2011).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
What the sources say
- Not checked yetcites Goldblatt and Zahnle, 2011
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
It may state two separate claims as one.
In the paper
“but a recent study of chromium isotopes suggests that the Proterozoic O2 mixing ratio was, at most, 0.1% PAL (Planavsky et al., 2014).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.2. UV shielding
What the sources say
- Not checked yetcites Planavsky et al., 2014
Load-bearingStrength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
None of the sources cited for this claim have been checked yet.
In the paper
“Later purported hazy periods around 2.7 Ga (Kurzweil et al., 2013; Izon et al., 2015) and between 2.65 and 2.5 Ga (Zerkle et al., 2012) are not associated with glaciations and may be consistent with the thinner-haze solution space of Cases A and C or even the thickest haze solution space of the warmer Case B.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
What the sources say
- Not checked yetcites Kurzweil et al., 2013
- Not checked yetcites Izon et al., 2015
- Not checked yetcites Zerkle et al., 2012
Load-bearingStrength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“DNA damage is most acute in the UVC (λ < 0.28 μm) wavelength range (Pierson et al., 1992; Dillon and Castenholz, 1999), but in the modern atmosphere, UVC is fully blocked by O2 and ozone.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.2. UV shielding
What the sources say
- Not checked yetcites Pierson et al., 1992
- Not checked yetcites Dillon and Castenholz, 1999
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
In the paper
“Unless otherwise specified, the surface albedo used by the climate model is 0.32. This includes the effect of clouds, which is standard in this 1-D treatment (Kopparapu et al., 2013) and is the albedo that reproduces the average temperature of present-day Earth (288 K) with modern atmospheric conditions.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Kopparapu et al., 2013
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
In the paper
“We set the mixing ratio of O2 at the surface to 1.0 × 10−8, consistent with the Zerkle et al. (2012) study.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Zerkle et al., 2012
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
In the paper
“Furthermore, Abbot et al. (2011) argued that ocean open belts can remain climatologically stable, even if the ice latitude is reduced to 5–15°.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.1. Hazy climates
What the sources say
- Not checked yetcites Abbot et al., 2011
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
A conclusion the paper draws from its own results — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Because methane-producing metabolisms evolved early and Earth's atmosphere was anoxic for about a billion years after the origin of life, pale orange dots may proliferate in the Galaxy if other habitable worlds evolve on similar paths to Earth.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
Strength:hedged· not yet calibratedCausal:conditional· not yet calibratedSingle case
Tests✓ Asserted: passes✗ Checkable: fails✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. It may be too vague to check against evidence. The paper’s conclusions may not depend on it. It may state two separate claims as one.
- Rests on an assumption: Methane-producing metabolisms evolved early.
- Rests on an assumption: Earth's atmosphere was anoxic for about a billion years after the origin of life.
In the paper
“Of course, the true cloud distribution on Archean Earth is unknown, and clouds may have had important climatic effects on our early planet (Goldblatt and Zahnle, 2011).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Goldblatt and Zahnle, 2011
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
In the paper
“The solar zenith angles (SZAs) used in the climate and photochemical models were chosen to best represent globally averaged behavior of the physics in each specific model, which Segura et al. (2003) found as SZA = 45° in the photochemical model and SZA = 60° in the climate model. These zenith angles are both tuned to reproduce modern-day Earth's average chemical profiles and climate, respectively.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 2. Models and Methods > 2.3. Model inputs
What the sources say
- Not checked yetcites Segura et al., 2003
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“The impact of these hazes on the biosphere goes beyond temperature reduction: their fractal nature makes them strong absorbers at short wavelengths and therefore a potential shield against damaging UV radiation for the anoxic Archean (Wolf and Toon, 2010), which would have received significantly more UV at the surface than the planet today (Rugheimer et al., 2015).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.2. UV shielding
What the sources say
- Not checked yetcites Wolf and Toon, 2010
- Not checked yetcites Rugheimer et al., 2015
Load-bearingStrength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
In the paper
“which showed much greater C2H6 accumulation on planets orbiting low-mass stars compared to worlds orbiting the Sun.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
What the sources say
- Not checked yetcites Domagal-Goldman et al. (2011)
Strength:plain· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“Based on their calculations, Guzmán-Marmolejo et al. (2013) suggested that an atmospheric CH4 concentration greater than 10 ppmv is suggestive of life.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.1. Haze and biology
What the sources say
- Not checked yetcites Guzmán-Marmolejo et al. (2013)
Load-bearingStrength:hedged· not yet calibratedCausal:correlational· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
In the paper
“The Charnay et al. results for the same atmospheric properties but with an equatorial supercontinent result in the same overall planetary albedo (0.33) but a lower mean temperature of 285 K”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Charnay et al.
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“Laboratory experiments on organic haze formation have shown that haze-formation chemistry can involve the formation of important prebiotic molecules such as amino acids and nucleotide bases (Khare et al., 1986; McDonald et al., 1994; DeWitt et al., 2009; Hörst et al., 2012; Trainer, 2013)”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.1. Haze and biology
What the sources say
- Not checked yetcites Khare et al., 1986
- Not checked yetcites McDonald et al., 1994
- Not checked yetcites DeWitt et al., 2009
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“We also tested our model results against the Community Atmosphere Model (CAM) GCM nominal Archean atmosphere reported by Wolf and Toon (2013).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.2. Comparison with other climate studies
What the sources say
- Not checked yetcites Wolf and Toon (2013)
Load-bearingStrength:plain· not yet calibratedSingle case
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
In the paper
“C2H6 is a greenhouse gas, and its ability to warm in a CH4- and haze-rich atmosphere has been discussed previously (Haqq-Misra et al., 2008).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 3. Results > 3.3. Spectra
What the sources say
- Not checked yetcites Haqq-Misra et al., 2008
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
In the paper
“The Mahjoub study tested the impact of methane concentration in the gas phase on the resultant hydrocarbon optical properties with gas mixtures containing 1%, 2%, 5%, and 10% CH4 in CH4-N2 mixtures.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.5. Optical constants
What the sources say
- Not checked yetcites Mahjoub et al.
Strength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
None of the sources cited for this claim have been checked yet.
In the paper
“Following Sagan and Chyba (1997), Wolf and Toon calculated a NH3 atmospheric lifetime of 7 × 107 years for a solar incident flux at a 45° angle assuming τ ∼ 11 at 200 nm.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.3. Potential for NH3 greenhouse gas shielding
What the sources say
- Not checked yetcites Sagan and Chyba (1997)
- Not checked yetcites Wolf and Toon
Load-bearingStrength:plain· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
Probably not a substantial claim.
In the paper
“As an example and test of the impact different refractive indices have on our spectra, we examined the sensitivity of our nominal spectra to varied refractive indices measured by Mahjoub et al. (2012).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.5. Optical constants
What the sources say
- Not checked yetcites Mahjoub et al. (2012)
Strength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“Mass spectrometry of aerosol analogues formed with C/O = 0.1 indicates the formation of carbonyl and carboxyl groups rather than aromatic cycles and long-aliphatic chains, and even suggests the formation of organic acids such as succinic acid (C4H6O4) (DeWitt et al., 2009).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites DeWitt et al., 2009
Load-bearingStrength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
In the paper
“Unfortunately, only one study, that of Hasenkopf et al. (2010), has measured an Archean Earth haze refractive index (as opposed to a titanian haze), and this was only done at a single wavelength (532 nm).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.5. Optical constants
What the sources say
- Not checked yetcites Hasenkopf et al. (2010)
Load-bearingStrength:plain· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“Early Earth's atmosphere would have contained negligible O2 but significant amounts of CO2 (e.g., Kasting, 1993; Driese et al., 2011), whereas Titan's atmosphere is extremely reducing (de Kok et al., 2007).”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Kasting, 1993
- Not checked yetcites Driese et al., 2011
- Not checked yetcites de Kok et al., 2007
Load-bearingStrength:hedged· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✓ Load-bearing: passes✓ Based: passes
It may state two separate claims as one.
None of the sources cited for this claim have been checked yet.
In the paper
“In situ measurements by several instruments on board Cassini have found direct evidence for long hydrocarbons and nitriles chains, benzene (C6H6) and toluene (C6H5CH3), and indirect evidence for polycyclic aromatic hydrocarbons (PAHs) and nitrogen-containing polycyclic aromatic hydrocarbons (PANHs), indicating that these compounds might play a role in the formation of Titan's hazes (Waite et al.,”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.4. Haze formation pathways
What the sources say
- Not checked yetcites Waite et al., 2007
- Not checked yetcites López-Puertas et al., 2013
Strength:hedged· not yet calibratedCausal:conditional· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
In the paper
“Wolf and Toon (2010) commented on the possibility of a fractal hydrocarbon haze shielding ammonia (NH3) from photolysis, allowing this greenhouse gas to build up in the Archean atmosphere.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.3. Potential for NH3 greenhouse gas shielding
What the sources say
- Not checked yetcites Wolf and Toon (2010)
Strength:hedged· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes✗ Load-bearing: fails✓ Based: passes
Probably not a substantial claim. The paper’s conclusions may not depend on it.
In the paper
“Mahjoub et al. found that refractive indices have a strong dependency on the CH4 concentration over 0.37–1 μm: results indicate that the imaginary index of refraction (k) decreases with increasing CH4 concentration, and the real index of refraction (n) increases with CH4 for the compositions tested.”
§ The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth > 4. Discussion > 4.5. Optical constants
What the sources say
- Not checked yetcites Mahjoub et al.
Strength:boosted· not yet calibratedCausal:direct· not yet calibrated
Tests✓ Asserted: passes✓ Checkable: passes? Load-bearing: unclear✓ Based: passes
It may state two separate claims as one.

89 of 89

The authors state this as an assumption.
Fixed isoprofiles are assumed for CO2 and N2 in the atmospheres considered here.
“Fixed isoprofiles are assumed for CO2 and N2 in the atmospheres considered here.”
The authors state this as an assumption.
C4H2 and C5H4 condense directly to haze particles.
“it is assumed that C4H2 and C5H4 condense directly to haze particles (called HCAER and HCAER2 in Supplementary Table S1).”
The paper relies on this without support.
A planet with any nonzero fraction of open ocean is habitable.
“Since a planet with any nonzero fraction of open ocean is habitable, we regard these updated globally averaged temperatures—all of which are significantly below freezing—to be more realistic habitability thresholds than 273 K.”
The paper relies on this without support.
Methane-producing metabolisms evolved early.
“Because methane-producing metabolisms evolved early and Earth's atmosphere was anoxic for about a billion years after the origin of life, pale orange dots may proliferate in the Galaxy if other habitable worlds evolve on similar paths to Earth.”
The paper relies on this without support.
Earth's atmosphere was anoxic for about a billion years after the origin of life.
“Because methane-producing metabolisms evolved early and Earth's atmosphere was anoxic for about a billion years after the origin of life, pale orange dots may proliferate in the Galaxy if other habitable worlds evolve on similar paths to Earth.”
The paper relies on this without support.
Water vapor clouds have an approximately gray opacity from the visible into the NIR.
“water vapor clouds have an approximately gray opacity from the visible into the NIR.”
The paper relies on this without support.
The tropopause on Earth is at roughly 10 km.
“The tropopause on Earth is at roughly 10 km”
The paper relies on this without support.
Geochemical evidence suggests hazy conditions were not present throughout the entire Archean.
“geochemical evidence suggests hazy conditions were not present throughout the entire Archean”
The paper relies on this without support.
The geochemical constraints on Archean CO2 concentration and geological constraints on surface pressure used in the study are valid.
“consistent with geochemical constraints on CO2 concentration and geological constraints on surface pressure”
The paper relies on this without support.
UVC radiation is harmful to unshielded life.
“may have allowed survival of otherwise unshielded life at the surface of our Archean planet”

10 of 10

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

Conflicting criteria for haze-particle growth
Minor
The methods say particles can grow when the coagulation lifetime is longer than the removal lifetime, but the results say growth occurs when the coagulation timescale is shorter than the removal timescale.
Sulfur isotope relationship uses the wrong isotope on its right-hand side
Minor
The text says δ36S is roughly twice δ34S, but the stated mass-dependent relationship makes δ36S proportional to itself instead.
Example does not give equal log-space bin distances
Minor
The stated binning rule uses distance in log space, but 0.33 μm is not halfway in log space between 0.3 and 0.4 μm. Those bins therefore would not each receive 50% of the mass under the stated rule.

3 of 3

Phylogenetic structure of the prokaryotic domain: The primary kingdoms
Woese, C. R., & Fox, G. E. (1977) · Proceedings of the National Academy of Sciences · doi:10.1073/pnas.74.11.5088 · Cited by 4,131 · cited 2×
“5 billion years ago) haze was likely biologically mediated via CH4 produced from methanogenesis, one of the earliest metabolisms (Woese and Fox, 1977; Ueno et al., 2006).”
Influential
The formation, properties and impact of secondary organic aerosol: current and emerging issues
Hallquist, M., Wenger, J., Baltensperger, U., Rudich, Y., Simpson, D. M., Claeys, M., Dommen, J., Donahue, N. M., George, C., Goldstein, A. H., et al. (2009) · Atmospheric chemistry and physics · doi:10.5194/acp-9-5155-2009 · Cited by 4,039 · cited 1×
“Since the full chemical scheme that leads to aerosol formation is not well understood despite both laboratory and theoretical studies ( e.g. , Hallquist et al. , 2009; Hicks et al. , 2015), it is assumed that C 4 H 2 and C 5 H 4 condense directly to haze particles (called HCAER and HCAER2 in…”
The HITRAN2012 molecular spectroscopic database
Rothman, L. S., Gordon, I. E., Babikov, Y., Barbe, A., Chris Benner, D., Bernath, P. F., Birk, M., Bizzocchi, L., Boudon, V., Brown, L. R., et al. (2013) · Journal of Quantitative Spectroscopy and Radiative Transfer · doi:10.1016/j.jqsrt.2013.07.002 · Cited by 3,255 · cited 1×
“The Line-by-Line Absorption Coefﬁcients (LBLABC) code, a companion to SMART, creates line-by-line absorption ﬁles for input gas mixing ratios and temperature-pressure proﬁles using HITRAN 2012 line lists (Rothman et al. , 2013).”
Diffuse radiation in the Galaxy
Henyey, L. C., & Greenstein, J. L. (1941) · The Astrophysical Journal · doi:10.1086/144246 · Cited by 2,971 · cited 1×
“Spherical particles use a full Mie phase function, while fractal particles employ a Henyey-Greenstein phase function (Henyey and Greenstein, 1941).”
Atmospheric Influence of Earth's Earliest Sulfur Cycle
Farquhar, J., Bao, H., & Thiemens, M. (2000) · Science · doi:10.1126/science.289.5480.756 · Cited by 1,805 · cited 16×
“Thus, S-MIF is generally regarded as robust evidence for an anoxic Archean atmosphere.”
Influential
HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES
Kopparapu, R. K., Ramirez, R., Kasting, J. F., Eymet, V., Robinson, T. D., Mahadevan, S., Terrien, R. C., Domagal-Goldman, S., Meadows, V., & Deshpande, R. (2013) · The Astrophysical Journal · doi:10.1088/0004-637x/765/2/131 · Cited by 1,615 · cited 7×
“The version we use here is based directly on that used by Kopparapu et al. (2013).”
InfluentialSelf-citation
Earth's Early Atmosphere
Kasting, J. F. (1993) · Science · doi:10.1126/science.11536547 · Cited by 1,374
A Serpentinite-Hosted Ecosystem: The Lost City Hydrothermal Field
Kelley, D. S., Karson, J. A., Früh-Green, G. L., Yoerger, D. R., Shank, T. M., Butterfield, D. A., Hayes, J. M., Schrenk, M. O., Olson, E. J., Proskurowski, G., et al. (2005) · Science · doi:10.1126/science.1102556 · Cited by 1,288 · cited 1×
“In addition, several abiotic processes including serpentinization (the hydration of ultramaﬁc rocks, mainly olivine and pyroxenes) can form methane (Kelley et al. , 2005; Etiope and Sherwood Lollar, 2013; Guzma´n-Marmolejo et al. , 2013), but the biotic ﬂux of methane to the Archean atmosphere was…”
Photochemistry of the atmosphere of Titan - Comparison between model and observations
Yung, Y. L., Allen, M., & Pinto, J. P. (1984) · The Astrophysical Journal Supplement Series · doi:10.1086/190963 · Cited by 1,081 · cited 2×
“Following the mechanism proposed for the formation of Titan’s hydrocarbon haze (Allen et al. , 1980; Yung et al. , 1984), every model of hydrocarbon haze formation in early Earth’s atmosphere—including ours—has assumed that aerosol formation will occur through the formation of acetylene (C 2 H 2 )…”
Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b
Kreidberg, L., Bean, J. L., Désert, J.-M., Benneke, B., Deming, D., Stevenson, K. B., Seager, S., Berta-Thompson, Z. K., Seifahrt, A., & Homeier, D. (2013) · Nature · doi:10.1038/nature12888 · Cited by 938 · cited 2×
“Unlike the hazes that may exist around exoplanets with thick hydrogen-dominated atmospheres (Sing et al., 2011; Knutson et al., 2014; Kreidberg et al., 2014), the Archean (3.”
Influential

Flagged first, then by citations

Show all 136 references

Research works printed but not linked: 5

10.1051/0004-6361/201014343 · DOI
Schopf J.W., editor. (1983) Earth's Earliest Biosphere: Its Origin and Evolution, Princeton University Press, Princeton, NJ.
Sciamma-O'Brien E., , Dahoo P.-R., , Hadamcik E., , Carrasco N., , Quirico E., , Szopa C., , and Cernogora G. (2012) Optical constants from 370nm to 900nm of Titan tholins produced in a low pressure RF plasma discharge. Icarus, 218:353–363.
Traub W.A. (2003) Extrasolar planet characteristics in the visible wavelength range. In Proceedings of the Conference on Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets, Heidelberg, Germany, pp 231–239.
Workman J., editor. (2000) The Handbook of Organic Compounds, Three-Volume Set: NIR, IR, R, and UV-Vis Spectra Featuring Polymers and Surfactants, Academic Press, San Diego, CA.

Sorted by citations

Living at the Extremes: Extremophiles and the Limits of Life in a Planetary Context
Merino, N., Aronson, H. S., Bojanova, D. P., Feyhl‐Buska, J., Wong, M. L., Zhang, S. J., & Giovannelli, D. (2019) · Frontiers in Microbiology · doi:10.3389/fmicb.2019.00780 · Cited by 707
The Archean atmosphere
Catling, D. C., & Zahnle, K. J. (2020) · Science Advances · doi:10.1126/sciadv.aax1420 · Cited by 568
“Thus, attenuation of sunlight saturates (1, 163).”
Background
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life
Schwieterman, E. W., Kiang, N. Y., Parenteau, M. N., Harman, C. E., DasSarma, S., Fisher, T. M., Arney, G. N., Hartnett, H. E., Reinhard, C. T., Olson, S. L., et al. (2018) · Astrobiology · doi:10.1089/ast.2017.1729 · Cited by 630
“…al., 2013), a purple Archean ocean due to photosynthetic purple bacteria (Sanromá et al., 2014); an orange Archean Earth due to an organic-rich atmospheric haze (Arney et al., 2016); and trajectories of O2 fluxes over geologic time given estimated atmospheric concentrations (Gebauer et al., 2017).”
BackgroundMethodInfluentialSelf-citation
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life
Schwieterman, E. W., Kiang, N. Y.-L., Parenteau, M. N., Harman, C. E., DasSarma, S., Fisher, T. M., Arney, G., Hartnett, H. E., Reinhard, C. T., Olson, S. L., et al. (2017) · eScholarship (California Digital Library) · Cited by 452
Self-citation
Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment
Meadows, V., Reinhard, C. T., Arney, G., Parenteau, M. N., Schwieterman, E. W., Domagal-Goldman, S. D., Lincowski, A., Stapelfeldt, K. R., Rauer, H., DasSarma, S., et al. (2018) · Astrobiology · doi:10.1089/ast.2017.1727 · Cited by 341
“Such hazes may have been present during early periods of Earth’s history when the atmosphere was more reducing (Arney et al., 2016).”
BackgroundMethodSelf-citation

See all 333

Authors: Arney, G., Domagal-Goldman, S. D., Meadows, V. S., Wolf, E. T., Schwieterman, E., Charnay, B., Claire, M., Hébrard, E., & Trainer, M. G.
Affiliations: Goddard Space Flight Center (US)
University of Washington (US)
University of Colorado Boulder (US)
University of California, Riverside (US)
University of St Andrews (GB)
NASA Goddard Space Flight Center
Corresponding author: Arney, Giada
ORCID: Charnay, Benjamin
Venue: Astrobiology
Publisher: SAGE Publications
Published: 2016-11
Volume: 16
Issue: 11
Pages: 873-899
ISSN: 1531-1074 (ISSN-L)
1557-8070
DOI: 10.1089/ast.2015.1422
PMC: PMC5148108
OpenAlex: W2534050968
Semantic Scholar: 62da501fd3e70b940830188582e2e383e75193d3
Cited by: 327
References: 136
Citations by year: 2026: 22 · 2025: 59 · 2024: 28 · 2023: 33 · 2022: 33 · 2021: 30 · 2020: 33 · 2019: 25 · 2018: 45 · 2017: 18 · 2016: 1
FWCI: 14.17
Type: journal article
Language: en
Open access: hybrid
doi.org
Licence: cc-by-nc
creativecommons.org/licenses/by-nc/4.0/ (vor)
journals.sagepub.com/page/policies/text-and-data-mining-license (tdm)
Locations: Astrobiology (publishedVersion, cc-by-nc)
PubMed Central (publishedVersion, cc-by-nc)
PubMed (publishedVersion)
Open Research Exeter (University of Exeter) (acceptedVersion)
arXiv (Cornell University) (submittedVersion)
HAL (submittedVersion)
eScholarship (California Digital Library) (submittedVersion, cc-by-nc)
St Andrews Research Repository (St Andrews Research Repository) (submittedVersion, cc-by-nc)
arXiv (Cornell University)
Funders: Natural Environment Research Council (NE/J022802/2)
Topics: Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Space Science and Extraterrestrial Life
Physical Sciences › Earth and Planetary Sciences › Space and Planetary Science › Astro and Planetary Science
Physical Sciences › Earth and Planetary Sciences › Space and Planetary Science › Planetary Science and Exploration
Keywords: Archean, atmospheric haze, habitability, faint young Sun, UV protection, biosignatures, methane, self-shielding, exoplanet atmospheres, surface cooling
MeSH terms: Atmosphere, Climate, Extraterrestrial Environment, Gases, Models, Theoretical, Particle Size, Spectrophotometry, Ultraviolet, Temperature, Ultraviolet Rays, Water, Earth, Planet, Exobiology

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

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The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

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