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Cited by 93Space Science and Extraterrestrial LifePaleontology and Stratigraphy of FossilsEarth Systems and Cosmic Evolution

False Negatives for Remote Life Detection on Ocean-Bearing Planets: Lessons from the Early Earth

Open access
Reinhard, Christopher T., Olson, Stephanie L., Schwieterman, Edward W., Lyons, Timothy W.·2017·Astrobiology
DOI 10.1089/ast.2016.1598PMC PMC5399744
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Abstract

Ocean-atmosphere chemistry on Earth has undergone dramatic evolutionary changes throughout its long history, with potentially significant ramifications for the emergence and long-term stability of atmospheric biosignatures. Though a great deal of work has centered on refining our understanding of false positives for remote life detection, much less attention has been paid to the possibility of false negatives, that is, cryptic biospheres that are widespread and active on a planet's surface but are ultimately undetectable or difficult to detect in the composition of a planet's atmosphere. Here, we summarize recent developments from geochemical proxy records and Earth system models that provide insight into the long-term evolution of the most readily detectable potential biosignature gases on Earth—oxygen (O2), ozone (O3), and methane (CH4). We suggest that the canonical O2-CH4 disequilibrium biosignature would perhaps have been challenging to detect remotely during Earth's ∼4.5-billion-year history and that in general atmospheric O2/O3 levels have been a poor proxy for the presence of Earth's biosphere for all but the last ∼500 million years. We further suggest that detecting atmospheric CH4 would have been problematic for most of the last ∼2.5 billion years of Earth's history. More broadly, we stress that internal oceanic recycling of biosignature gases will often render surface biospheres on ocean-bearing silicate worlds cryptic, with the implication that the planets most conducive to the development and maintenance of a pervasive biosphere will often be challenging to characterize via conventional atmospheric biosignatures. Key Words: Biosignatures—Oxygen—Methane—Ozone—Exoplanets—Planetary habitability. Astrobiology 17, 287–297.

AI snapshot

Written from the paper’s full text.

TL;DR

This paper argues that Earth’s biosphere would often have been a false negative for remote life detection, especially via the canonical O2-CH4 disequilibrium biosignature. It combines geochemical proxies, Earth-system models, and synthetic spectra to show that atmospheric O2/O3 was a poor biosignature proxy for all but the last ∼500 million years, while CH4 detection was problematic for most of the last ∼2.5 billion years.

Key findings

  • The O2-CH4 disequilibrium biosignature would likely have failed for most of Earth’s ∼4.5-billion-year history, particularly at low to moderate spectral resolving power (R ≤ 10,000).
  • Archean atmospheric pO2 was below 10−5 PAL and more likely below ∼10−7 PAL, while pCH4 may have been ∼102–103 ppmv, potentially making CH4 detectable at 1.65 μm.
  • Mid-Proterozoic pO2 was ∼10−3.3–10−2 PAL and pCH4 ∼1–20 ppmv; both O2 and CH4 would have been undetectable, and O3 would have been challenging to detect.
  • During the Phanerozoic, pO2 was ∼0.25–1.4 PAL and pCH4 ∼0.7–6 ppmv; O2/O3 would likely have been detectable for most of the last ∼500 million years, but CH4 detection would have been problematic with low- to moderate-resolution spectroscopy.

Methods

  • The authors synthesize geochemical proxy records and Earth-system model results to estimate atmospheric pO2 and pCH4 across geological epochs, using values summarized in Table 1.
  • They generate synthetic direct-imaging reflectance spectra with the SMART radiative transfer model, scaling a modern midlatitude Earth atmosphere profile to the evolving gas abundances.
  • They focus on the O3 UV Hartley-Huggins bands (∼0.25 μm), the O2 Fraunhofer A band (0.76 μm), and the 1.65 μm CH4 band, using 1 cm−1 resolution and a solar zenith angle of 60°.

Limitations

  • The paper states that there is no available geochemical proxy for ancient atmospheric CH4 levels, that atmospheric O2 levels for most of the ∼2.5 billion years after the Great Oxidation Event are poorly constrained, and that the sulfur isotope system is insensitive above ∼1–2 ppmv O2.
  • The spectral assessment is qualitative: reflectances are arbitrarily scaled, and actual detectability depends on observing parameters and instrumentation not fully modeled here.
  • The authors note that results are broadly applicable to Earth-analog planets orbiting Sun-like stars, but stellar environment differences require further work; they also state that the feasibility of high-resolution CH4 detection has not been conclusively demonstrated.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1089/ast.2016.1598

Cites

102 of 102 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 79 cited sources checked · 0 supported · 0 flagged

  • Findingreasoning

    During the mid-Proterozoic, O3 would have been challenging to detect.

    “and are consistent with the possibility that O3 would have been challenging to detect.”
    Quote in the paperSubstantial claim
  • Findingreasoning

    During the mid-Proterozoic, both O2 and CH4 would have been undetectable.

    “Combined proxy and model results indicate that, during the mid-Proterozoic, both O2 and CH4 would have been undetectable”
    Quote in the paperSubstantial claim
  • Findingreasoning

    The 1.65 μm CH4 band would likely have been visible during Archean time.

    “The 1.65 μm CH4 band would likely have been visible during Archean time (Fig. 4)”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Methane has the stated spectral features: five weak features between 0.6 and 1.0 μm, two at 1.65 and 2.4 μm, and a significant feature at ∼7.7–8.2 μm.
  • Findingreasoning

    During the Archean (∼3.8-2.5 Ga), atmospheric CH4 levels may have been generally within or above the range that would be remotely detectable.

    “Currently available proxy and model constraints indicate that, during the Archean (∼3.8–2.5 Ga), atmospheric CH4 levels may have been generally within or above the range that would be remotely detectable.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Methane has the stated spectral features: five weak features between 0.6 and 1.0 μm, two at 1.65 and 2.4 μm, and a significant feature at ∼7.7–8.2 μm.
  • Findingcitation

    During the Archean, atmospheric O2 levels were many orders of magnitude below detection of either O2 or O3, with the possible exception of pulsed pO2 increases during the late Archean.

    “In contrast, atmospheric O2 levels were many orders of magnitude below detection of either O2 or O3, with the possible exception of pulsed pO2 increases during the late Archean (e.g., Anbar et al., 2007; Kendall et al., 2015).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Anbar et al., 2007

      Not checked in the free run.

    • cites Kendall et al., 2015

      Not checked in the free run.

  • May combine two claims. 24
  • The quote only partly states this claim. 1
  • Classified as probably not a substantial claim. 8

  • May combine two claims.

    Findingcitation

    Peak mid-Proterozoic atmospheric O3 would have been ∼0.1-1 ppmv based on the ground-level pO2 values estimated for this time interval (e.g., pO2 ∼ 0.1-1% PAL) and many orders of magnitude below this during the Archean.

    “The results of this exercise suggest that peak mid-Proterozoic atmospheric O3 would have been ∼0.1–1 ppmv based on the ground-level pO2 values estimated for this time interval (e.g., pO2 ∼ 0.1–1% PAL) and many orders of magnitude below this during the Archean.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Kasting and Donahue, 1980

      Not checked in the free run.

  • The quote only partly states this claim.

    Findingown data

    Results from Earth system models indicate that detection of atmospheric CH4 would have been problematic with low- to moderate-resolution spectroscopy during the last ∼500 million years.

    “However, results from Earth system models indicate that detection of atmospheric CH4 would have been problematic with low- to moderate-resolution spectroscopy during this same period.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Methane has the stated spectral features: five weak features between 0.6 and 1.0 μm, two at 1.65 and 2.4 μm, and a significant feature at ∼7.7–8.2 μm.

  • May combine two claims.

    Interpretationreasoning

    Atmospheric O2/O3 levels have been a poor proxy for the presence of Earth's biosphere, and O2/O3 may only have been applicable as a potential biosignature, during the last ∼500 million years (∼10% of Earth's lifetime).

    “atmospheric O2/O3 levels have been a poor proxy for the presence of Earth's biosphere for all but the last ∼500 million years”
    • Also stated in: § 1. Introduction · hedged
      “it is possible that O2/O3 may only have been applicable as a potential biosignature during the last ∼10% of Earth's lifetime”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Cryptic biospheres may be a particularly acute problem on ocean-bearing planets, with the implication that many of the most favorable planetary hosts for surface biospheres will also have high potential for attenuation of atmospheric biosignatures.

    “Finally, we argue that cryptic biospheres may be a particularly acute problem on ocean-bearing planets, with the implication that many of the most favorable planetary hosts for surface biospheres will also have high potential for attenuation of atmospheric biosignatures.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Despite vigorous biological O2 production in the shallowest oceanic environments, a planetary atmosphere can remain pervasively reducing as a result of either low globally integrated surface fluxes or elevated atmospheric sinks (or some combination).

    “Thus, despite vigorous biological O2 production in the shallowest oceanic environments, a planetary atmosphere can remain pervasively reducing as a result of either low globally integrated surface fluxes or elevated atmospheric sinks (or some combination).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Oceanic filtering of atmospheric biosignatures could occur on a wide range of ocean-bearing silicate planets and in many cases will be an important process even on reducing planetary surfaces.

    “Such oceanic filtering of atmospheric biosignatures could in principle occur on a wide range of ocean-bearing silicate planets and in many cases will be an important process even on reducing planetary surfaces.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Most of Earth's history may have been characterized by either high abundances of a single biogenic gas that can also have significant abiotic sources (e.g., CH4) or by a cryptic biosphere that was widespread and active at the surface but remained ultimately unrepresented in the detectable composition of Earth's atmosphere.

    “As a result, most of our planet's history may have been characterized by either high abundances of a single biogenic gas that can also have significant abiotic sources (e.g., CH4) or by a cryptic biosphere that was widespread and active at the surface but remained ultimately unrepresented in the detectable composition of Earth's atmosphere.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    The apparent loss of Fe (and in some cases Mn) as dissolved reduced species from paleosols during some periods of the Proterozoic and the general lack of significant chromium (Cr) isotope fractionation in marine sediments are both consistent with very low atmospheric pO2 between ∼1.8 and 0.8 Ga.

    “For example, the apparent loss of Fe (and in some cases Mn) as dissolved reduced species from paleosols (ancient weathering profiles) during some periods of the Proterozoic (Holland, 1984) and the general lack of significant chromium (Cr) isotope fractionation in marine sediments (Planavsky et al., 2014b; Cole et al., 2016) are both consistent with very low atmospheric pO2 between ∼1.8 and 0.8 Ga”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Holland, 1984 source

      Not checked in the free run.

    • cites Planavsky et al., 2014b

      Not checked in the free run.

    • cites Cole et al., 2016

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The sulfur isotope anomalies fingerprinting extremely low atmospheric O2 disappear relatively rapidly during the Great Oxidation Event (GOE) of the early Paleoproterozoic and are not seen again in typical marine sedimentary rocks for the remainder of Earth's history.

    “The sulfur isotope anomalies fingerprinting extremely low atmospheric O2 disappear relatively rapidly during the Great Oxidation Event (GOE) of the early Paleoproterozoic (Holland, 2002; Luo et al., 2016) and are not seen again in typical marine sedimentary rocks for the remainder of Earth's history (Fig. 1).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Holland, 2002

      Not checked in the free run.

    • cites Luo et al., 2016

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    There is some evidence for transient periods of elevated pO2 during the Archean.

    “Though there is some evidence for transient periods of elevated pO2 during the Archean (Anbar et al., 2007; Reinhard et al., 2009; Kendall et al., 2015), these deviations are poorly understood from a quantitative standpoint, and the overall background state during Archean time appears to have been one of exceptionally low atmospheric O2.”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Anbar et al., 2007

      Not checked in the free run.

    • cites Reinhard et al., 2009

      Not checked in the free run.

    • cites Kendall et al., 2015

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Most microbial CH4 cycling in the ocean occurs through anaerobic processes and can occur through common electron acceptors that will not necessarily be in equilibrium with corresponding atmospheric gases.

    “Indeed, most of this cycling occurs through anaerobic processes in the ocean (Valentine, 2011) and can occur through a number of common electron acceptors that will not necessarily be in equilibrium with corresponding atmospheric gases (Martens and Berner, 1977; Hoehler et al., 1994; Regnier et al., 2011; Sivan et al., 2011; Deutzmann et al., 2014; Riedinger et al., 2014).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Valentine, 2011

      Not checked in the free run.

    • cites Martens and Berner, 1977

      Not checked in the free run.

    • cites Hoehler et al., 1994

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Planets with cryptic oxygenic biospheres may be capable of accumulating significant quantities of reduced biosignature gases but will be false negatives for the presence of oxygenic photosynthesis and will have limited capacity for preservation and detection of associated oxidized biosignature gases (e.g., O3, N2O).

    “Such planets may be capable of accumulating significant quantities of reduced biosignature gases but will be false negatives for the presence of oxygenic photosynthesis and will have limited capacity for preservation and detection of associated oxidized biosignatures gases (e.g., O3, N2O).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    When interpreted in the context of photochemical models, the presence of non-mass-dependent sulfur isotope anomalies implies a ground-level atmospheric pO2 value below 10−5 times the present atmospheric level (PAL) and more likely below ∼10−7 PAL.

    “When interpreted in the context of photochemical models (Pavlov and Kasting, 2002; Ono et al., 2003; Zahnle et al., 2006; Ueno et al., 2009), the presence of these isotopic anomalies implies a ground-level atmospheric pO2 value that was below 10−5 times the present atmospheric level (PAL) and more likely below ∼10−7 PAL (e.g., Claire et al., 2006; Zahnle et al., 2006).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Pavlov and Kasting, 2002

      Not checked in the free run.

    • cites Ono et al., 2003

      Not checked in the free run.

    • cites Zahnle et al., 2006

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductown data

    The spectral limits shown are representative of both uncertainties in atmospheric abundance and variability of those abundances over the course of each epoch.

    “Limits are representative of both uncertainties in atmospheric abundance and variability of those abundances over the course of each epoch (Table 1).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Ozone has a number of spectral features in the IR, visible, and UV range, including a strong feature at 9.7 μm, the Chappuis bands between 0.5 and 0.7 μm, and the Hartley-Huggins bands at ∼0.35-0.2 μm.

    “Ozone has a number of spectral features in the IR, visible, and UV range, including a strong feature at 9.7 μm, the so-called “Chappuis” bands between 0.5 and 0.7 μm, and the “Hartley-Huggins” bands at ∼0.35–0.2 μm (Des Marais et al., 2002; Domagal-Goldman et al., 2014).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Des Marais et al., 2002

      Not checked in the free run.

    • cites Domagal-Goldman et al., 2014

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The Fraunhofer A band is the most prominent O2 feature but is likely to have appreciable depth only at atmospheric pO2 levels of ∼1% or higher.

    “Of these, the Fraunhofer A band is the most prominent but is likely to have appreciable depth only at atmospheric pO2 levels of ∼1% or higher (Fig. 4; Des Marais et al., 2002).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Des Marais et al., 2002

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Peak O3 abundances near the upper range of Proterozoic estimates would potentially have been a promising candidate for detection via the UV-Hartley band, but even this feature may have been challenging to observe at the lower end of pO2 estimates.

    “Peak O3 abundances near the upper range of Proterozoic estimates would potentially have been a promising candidate for detection via the UV-Hartley band, but even this feature may have been challenging to observe at the lower end of pO2 estimates.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    The O3 UV Hartley-Huggins, O2 Fraunhofer A, and 1.65 μm CH4 bands were chosen in part because they will likely be included in the instrumentation suite of future direct-imaging telescopes and because mid-IR direct imaging of exoplanets is unlikely for the intermediate future.

    “These bands were chosen in part because they will likely be included in the instrumentation suite of future direct-imaging telescopes (e.g., Dalcanton et al., 2015) and because mid-IR direct imaging of exoplanets is unlikely for the intermediate future.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Dalcanton et al., 2015

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Atmospheric pO2 during the earliest Paleozoic (∼543-400 Ma) was likely higher than that of the late Proterozoic but well below modern.

    “Atmospheric pO2 during the earliest Paleozoic (∼543–400 Ma), though not particularly well constrained at present, was likely higher than that of the late Proterozoic but well below modern (Bergman et al., 2004; Dahl et al., 2010; Lyons et al., 2014).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Bergman et al., 2004

      Not checked in the free run.

    • cites Dahl et al., 2010

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    • cites Lyons et al., 2014

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The combined Hartley-Huggins band in the near-UV centered at ∼0.25 μm is the most promising O3 feature from a detection standpoint, is the most sensitive to small O2 abundance, and saturates at O3 fractions of <1 ppmv.

    “The most promising of these from a detection standpoint is the combined Hartley-Huggins band in the near-UV centered at ∼0.25 μm (Fig. 4), which is the most sensitive to small O2 abundance and saturates at O3 fractions of <1 ppmv.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Des Marais et al., 2002

      Not checked in the free run.

    • cites Domagal-Goldman et al., 2014

      Not checked in the free run.

  • May combine two claims.

    Premisereasoning

    The biospheric production and consumption fluxes of CH4 are directly or indirectly linked to atmospheric O2 levels via the availability of oxidants at a planet's surface (e.g., O2, Fe3+, SO42−), and the quantitative relationship between atmospheric O2 and CH4 will be extremely complex on ocean-bearing silicate planets.

    “Because the biospheric production and consumption fluxes of CH4 are also directly or indirectly linked to atmospheric O2 levels via the availability of oxidants at a planet's surface (e.g., O2, Fe3+, SO42−), the quantitative relationship between atmospheric O2 and CH4 will be extremely complex on ocean-bearing silicate planets.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Molecular oxygen (O2) has no significant spectral features at mid-IR wavelengths, but it has three significant features in the optical range: the Fraunhofer A and B bands (at 0.76 and 0.69 μm, respectively) and an additional feature at 1.26 μm.

    “Molecular oxygen (O2) has no significant spectral features at mid-IR wavelengths, but it has three significant features in the optical range (Des Marais et al., 2002). These are the so-called “Fraunhofer” A and B bands (at 0.76 and 0.69 μm, respectively), along with an additional feature at 1.26 μm.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Des Marais et al., 2002

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Geochemical records during the Neoproterozoic (∼1000-541 Ma) suggest significant ocean-atmosphere redox shifts just prior to the Sturtian glacial epoch at ca. 720 Ma followed by a potentially highly dynamic interval leading up to the Precambrian-Cambrian boundary at 541 Ma.

    “Geochemical records during the Neoproterozoic (∼1000–541 Ma) suggest significant ocean-atmosphere redox shifts just prior to the Sturtian glacial epoch at ca. 720 Ma (Planavsky et al., 2014b; Thomson et al., 2015) followed by a potentially highly dynamic interval leading up to the Precambrian-Cambrian boundary at 541 Ma (Sahoo et al., 2016).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Planavsky et al., 2014b

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    • cites Thomson et al., 2015

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    • cites Sahoo et al., 2016

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  • Probably not a substantial claim: may not pass S4 (based).

    Premisenone given

    There is at present no available geochemical proxy for ancient atmospheric CH4 levels.

    “Though there is at present no available geochemical proxy for ancient atmospheric CH4 levels”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    Both the altitude and overall abundance of peak O3 increase with ground-level atmospheric pO2.

    “In addition, both the altitude and overall abundance of peak O3 increase with ground-level atmospheric pO2 (Fig. 2A).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Kasting and Donahue, 1980

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisenone given

    On the modern Earth, stratospheric O3 is ultimately derived from the photolysis of atmospheric O2, which generates oxygen atoms that subsequently combine with O2 molecules to yield O3.

    “On the modern Earth, stratospheric O3 is ultimately derived from the photolysis of atmospheric O2, which generates oxygen atoms that subsequently combine with O2 molecules to yield O3 (the first two of the so-called “Chapman reactions”)”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The reflectances in the synthetic spectra are arbitrarily scaled to provide a qualitative assessment of potential detectability.

    “Note that reflectances are arbitrarily scaled to provide a qualitative assessment of potential detectability.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    The charcoal record strongly suggests that pO2 values during most of the last ∼400 million years have been above ∼50% PAL, making O2 a dominant constituent of Earth's atmosphere for most of the last half-billion years.

    “Thereafter, the charcoal record strongly suggests that pO2 values during most of the last ∼400 million years have been above ∼50% PAL (e.g., Cope and Chaloner, 1980; Chaloner, 1989), making O2 a dominant constituent of Earth's atmosphere for most of the last half-billion years (Fig. 1; Table 1).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Cope and Chaloner, 1980

      Not checked in the free run.

    • cites Chaloner, 1989

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The calculations of peak O3 as a function of ground-level pO2 are not particularly sensitive to assumed atmospheric scale height (7 km) or temperature range (200-240 K).

    “The calculations assume an atmospheric scale height of 7 km and a range of temperatures between 200 and 240 K but are not particularly sensitive to either of these values.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductcitation

    The SMART radiative transfer model is well validated by remote observations of the whole Earth, Venus, and Mars and has been previously used in spectral studies of the Archean Earth.

    “We use the Spectral Mapping Atmosphere Radiative Transfer Model (SMART; Meadows and Crisp, 1996; Crisp 1997), which is well validated by remote observations of the whole Earth (Robinson et al., 2011, 2014), Venus (Arney et al., 2014), and Mars (Tinetti et al., 2005) and has been previously used in spectral studies of the Archean Earth (Arney et al., 2016).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Meadows and Crisp, 1996

      Not checked in the free run.

    • cites Crisp 1997

      Not checked in the free run.

    • cites Robinson et al., 2011, 2014

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    A planet with a biosphere largely (or entirely) confined to the marine realm will in many cases remain invisible to remote detection as a result of biosignature filtering by ocean biogeochemistry, a difficulty that may apply to both presence/absence and thermodynamic techniques.

    “Our analysis suggests that a planet with a biosphere largely (or entirely) confined to the marine realm will in many cases remain invisible to remote detection as a result of biosignature filtering by ocean biogeochemistry—a difficulty that may apply to both presence/absence and thermodynamic techniques.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Earth's early history can serve as an analogue for terrestrial exoplanets.

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given

    There may be plausible abiotic routes to high CH4 in a reducing planetary atmosphere.

    “although there may be plausible abiotic routes to high CH4 in a reducing planetary atmosphere”
    Quote in the paperNot a substantial claim
32 of 32

  • The paper relies on this without support.

    Much less attention has been paid to false negatives than to false positives in remote life detection.

    “Though a great deal of work has centered on refining our understanding of false positives for remote life detection, much less attention has been paid to the possibility of false negatives, that is, cryptic biospheres that are widespread and active on a planet's surface but are ultimately undetectable or difficult to detect in the composition of a planet's atmosphere.”

  • The paper relies on this without support.

    The early Earth is a useful analog for exoplanetary ocean-bearing planets.

    “False Negatives for Remote Life Detection on Ocean-Bearing Planets: Lessons from the Early Earth”
    “As a proof on concept, we briefly summarize the remote detectability of O2/O3, CH4, and the O2-CH4 disequilibrium throughout Earth's history.”
    “we stress that internal oceanic recycling of biosignature gases will often render surface biospheres on ocean-bearing silicate worlds cryptic”

  • The paper relies on this without support.

    Methane has the stated spectral features: five weak features between 0.6 and 1.0 μm, two at 1.65 and 2.4 μm, and a significant feature at ∼7.7–8.2 μm.

    “Methane has a number of features in the mid-IR and visible to near-IR ranges, including five weak features between 0.6 and 1.0 μm, two at 1.65 and 2.4 μm, and a significant feature at ∼7.7–8.2 μm.”

  • The paper relies on this without support.

    Earth's early history can serve as an analogue for terrestrial exoplanets.

    “we can place the O2-O3-CH4 disequilibrium biosignature on Earth in a broader temporal context as a possible analogue for terrestrial exoplanets.”
4 of 4

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Cites

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Research works printed but not linked: 2

  1. Anbar A.D., 2007, Nature, 317, 1903
  2. Meadows V.S., 2010, Exoplanets, 441

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Authors
Reinhard, C. T., Olson, S. L., Schwieterman, E. W., & Lyons, T. W.
Affiliations
  • Georgia Institute of Technology (US)
  • University of California, Riverside (US)
Corresponding author
Reinhard, Christopher T.
ORCID
Lyons, Timothy W.
Venue
Astrobiology
Publisher
SAGE Publications
Published
2017-04
Volume
17
Issue
4
Pages
287-297
ISSN
  • 1531-1074 (ISSN-L)
  • 1557-8070
DOI
10.1089/ast.2016.1598
PMC
PMC5399744
OpenAlex
W2608145888
Semantic Scholar
cc4bba77502b4619b99915d149c1a362ecbeef5f
Cited by
93
References
100
Citations by year
2026: 1 · 2025: 5 · 2024: 6 · 2023: 8 · 2022: 9 · 2021: 11 · 2020: 13 · 2019: 12 · 2018: 23 · 2017: 5
FWCI
7.93
Type
journal article
Language
en
Open access
Locations
  • Astrobiology (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by-nc)
  • PubMed Central (publishedVersion, cc-by-nc)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • eScholarship (California Digital Library) (submittedVersion, cc-by-nc)
  • arXiv (Cornell University)
Funders
  • National Aeronautics and Space Administration
  • Alfred P. Sloan Foundation
  • University of Washington
  • Universities Space Research Association
  • NASA Astrobiology Institute
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Space Science and Extraterrestrial Life
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
  • Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Earth Systems and Cosmic Evolution
Keywords
false-negative results, atmospheric biosignatures, early Earth, oxygen, ozone, methane, Earth system models, exoplanets, habitability
MeSH terms
Atmosphere, Extraterrestrial Environment, Methane, Oceans and Seas, Oxygen, Ozone, Spectrum Analysis, Planets, Earth, Planet, Exobiology

About these checks

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.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-10.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-10.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

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