Strange messenger: A new history of hydrogen on Earth, as told by Xenon

Zahnle, Kevin; Gacesa, Marko; Catling, David C.

doi:10.1016/j.gca.2018.09.017

Cited by 148 publications

(155 citation statements)

References 109 publications

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“…The corollary is that the halogen/seawater ratio remained constant within ~20-30% from 3.5 Ga to present, implying that the potential escape of hydrogen from photodissociation of atmospheric H2O might have been limited. A ~30% water loss is consistent with modeling of the escape of atmospheric xenon which requires approximately this amount of oceanic water to be dissociated and resulting hydrogen to be lost into space in order to lift up Xe ions(Zahnle et al 2019).…”

supporting

confidence: 77%

“…If hydrogen originated from the photo-dissociation of H2O vapor, its escape could have resulted in change on the volume and composition of the hydrosphere. Zahnle et al (2019) suggested that a volume of water corresponding to about 30 % of the present oceans could have escaped although this amount would be overestimated if Xe escape happened in short and intense episodes. Alternatively, hydrogen could have originated from CH4 dissociation (Catling et al 2001).…”

Section: Escape Models and Research Avenuesmentioning

confidence: 99%

“…See alsoCatling & Zahnle (2020) for a review on the Archean atmosphere and on the potential meanings of the isotopic evolution of atmospheric xenon. The model ofZahnle et al (2019), through escape of Xe ions together with hydrogen ions, requires a source of hydrogen. For Xe…”

mentioning

confidence: 99%

“…The difference between these two values could be due to potential spallation excesses on light Xe isotopes for the latter, but the debate remains open(Avice et al 2018a; Conrad et al 2016). In any case, the extent of fractionation is comparable for Mars and Earth.Having a similar isotopic fractionation for atmospheric Xe on Mars and Earth is striking.Indeed, the escape process proposed byZahnle et al (2019) depends on parameters such as the gravity of the body, the ionization rate of Xe in the atmosphere and the Solar irradiation activity, and probably the strength and shape of the magnetic field since Xe escapes as ions.All these parameters have different values on Earth and Mars and some of them have also varied with time. It is thus surprising to end up with a similar isotopic fractionation and depletion factor for Mars and Earth atmospheric Xe.…”

mentioning

confidence: 99%

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Perspectives on Atmospheric Evolution from Noble Gas and Nitrogen Isotopes on Earth, Mars & Venus

Avice

Marty

2020

Space Sci Rev

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The composition of an atmosphere has integrated the geological history of the entire planetary body. However, the long-term evolutions of the atmospheres of the terrestrial planets are not well documented. For Earth, there were until recently only few direct records of atmosphere's composition in the distant past, and insights came mainly from geochemical or physical proxies and/or from atmospheric models pushed back in time. Here we review innovative approaches on new terrestrial samples that led to the determination of the elemental and isotopic compositions of key geochemical tracers, namely noble gases and nitrogen. Such approaches allowed one to investigate the atmosphere's evolution through geological period of time, and to set stringent constraints on the past atmospheric pressure and on the salinity of the Archean oceans. For Mars, we review the current state of knowledge obtained from analyses of Martian meteorites, and from the direct measurements of the composition of the present-day atmosphere by rovers and spacecrafts. Based on these measurements, we explore divergent models of the Martian and Terrestrial atmospheric evolutions. For Venus, only little is known, evidencing the critical need for dedicated missions.

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supporting

confidence: 77%

Section: Escape Models and Research Avenuesmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Perspectives on Atmospheric Evolution from Noble Gas and Nitrogen Isotopes on Earth, Mars & Venus

Avice

Marty

2020

Space Sci Rev

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“…Our calculations assumes all

{NO}_{X}^{-}

entering the ocean goes to

{NO}_{X}^{-}

and neglects reactions of

{NO}_{X}^{-}

with other reductants which may have been abundant on early Earth, such as H 2 , CH 4 , or Mn 2+ (Fischer et al, ; Tian et al, ; Zahnle et al, ). Consequently, our estimates should be considered upper bounds on prebiotic [

{NO}_{X}^{-}

].…”

Section: Discussionmentioning

confidence: 99%

Nitrogen Oxide Concentrations in Natural Waters on Early Earth

Ranjan

Todd

Rimmer

et al. 2019

Geochem Geophys Geosyst

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A key challenge in origins‐of‐life studies is estimating the abundances of species relevant to the chemical pathways proposed to have contributed to the emergence of life on early Earth. Dissolved nitrogen oxide anions ( NOX−), in particular nitrate ( NO3−) and nitrite ( NO2−), have been invoked in diverse origins‐of‐life chemistry, from the oligomerization of RNA to the emergence of protometabolism. Recent work has calculated the supply of NOX− from the prebiotic atmosphere to the ocean and reported steady state [ NOX−] to be high across all plausible parameter space. These findings rest on the assumption that NOX− is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NOX− is unstable in the reducing environment of early Earth. Sinks due to ultraviolet photolysis and reactions with reduced iron (Fe2+) suppress [ NOX−] by several orders of magnitude relative to past predictions. For pH = 6.5–8 and T = 0–50 °C, we find that it is most probable that [ NOX−] <1μM in the prebiotic ocean. On the other hand, prebiotic ponds with favorable drainage characteristics may have sustained [ NOX−] ≥1μM. As on modern Earth, most NOX− on prebiotic Earth should have been present as NO3−, due to its much greater stability. These findings inform the kind of prebiotic chemistries that would have been possible on early Earth. We discuss the implications for proposed prebiotic chemistries and highlight the need for further studies of NOX− kinetics to reduce the considerable uncertainties in predicting [ NOX−] on early Earth.

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Atmospheric Escape Processes and Planetary Atmospheric Evolution

Gronoff¹,

Arras

Baraka

et al. 2020

Preprint

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The habitability of the surface of any planet is determined by a complex evolution of its interior, surface, and atmosphere. The electromagnetic and particle radiation of stars drive thermal, chemical, and physical alteration of planetary atmospheres, including escape. Many known extrasolar planets experience vastly different stellar environments than those in our solar system: It is crucial to understand the broad range of processes that lead to atmospheric escape and evolution under a wide range of conditions if we are to assess the habitability of worlds around other stars. One problem encountered between the planetary and the astrophysics communities is a lack of common language for describing escape processes. Each community has customary approximations that may be questioned by the other, such as the hypothesis of H-dominated thermosphere for astrophysicists or the Sun-like nature of the stars for planetary scientists. Since exoplanets are becoming one of the main targets for the detection of life, a common set of definitions and hypotheses are required. We review the different escape mechanisms proposed for the evolution of planetary and exoplanetary atmospheres. We propose a common definition for the different escape mechanisms, and we show the important parameters to take into account when evaluating the escape at a planet in time. We show that the paradigm of the magnetic field as an atmospheric shield should be changed and that recent work on the history of Xenon in Earth's atmosphere gives an elegant explanation to its enrichment in heavier isotopes: the so-called Xenon paradox. Plain Language SummaryIn addition to having the right surface temperature, a planet needs an atmosphere to keep surface liquid water stable. Although many planets have been found that may lie in the right temperature range, the existence of an atmosphere is not guaranteed. In particular, for planets that are kept warm by being close to dim stars, there are a number of ways that the star may remove a planetary atmosphere. These atmospheric escape processes depend on the behavior of the star as well as the nature of the planet, including the presence of a planetary magnetic field. Under certain conditions, a magnetic field can protect a planet's atmosphere from the loss due to the direct impact of the stellar wind, but it may actually enhance total atmospheric loss by connecting to the highly variable magnetic field of the stellar wind. These enhancements happen especially for planets close to dim stars. We review the complete range of atmospheric loss processes driven by interaction between a planet and a star to aid in the identification of planets that are both the correct temperature for liquid water and that have a chance of maintaining an atmosphere over long periods of time.

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Strange messenger: A new history of hydrogen on Earth, as told by Xenon

Cited by 148 publications

References 109 publications

Perspectives on Atmospheric Evolution from Noble Gas and Nitrogen Isotopes on Earth, Mars & Venus

Perspectives on Atmospheric Evolution from Noble Gas and Nitrogen Isotopes on Earth, Mars & Venus

Nitrogen Oxide Concentrations in Natural Waters on Early Earth

Atmospheric Escape Processes and Planetary Atmospheric Evolution

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