Photochemistry of methane in the Earth's early atmosphere

Kasting, James F.; Zahnle, Kevin; Walker, James C. G.

doi:10.1016/0301-9268(83)90069-4

Cited by 130 publications

(60 citation statements)

References 80 publications

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“…Photochemical models have found that an organic haze is produced by photolysis as CH 4 concentrations approach the CO 2 concentration in a low-O 2 atmosphere (Kasting et al, 1983;Zahnle, 1986). Organic haze has been predicted by photochemical modelling at CH 4 / CO 2 ratios larger than 1 (Zahnle, 1986), and laboratory experiments have found that organic haze could form at CH 4 / CO 2 ratios as low as 0.2-0.3 (Trainer et al, 2004(Trainer et al, , 2006.…”

Section: Organic Hazementioning

confidence: 99%

Diminished greenhouse warming from Archean methane due to solar absorption lines

Byrne

Goldblatt

2015

Clim. Past

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Abstract.Previous research has shown that methane may have been sustained at high concentrations in the Archean atmosphere, helping to offset lower insolation and solve the faint young sun problem. However, recent updates to the HI-TRAN (High-Resolution Transmission) line database have significantly increased the shortwave absorption by CH 4 in comparison to older versions of the database (e.g. HITRAN 2000). Here we investigate the climatological implications of strong shortwave CH 4 absorption in an Archean atmosphere rich in CH 4 . We show that the surface warming at CH 4 abundances > 10 −3 is diminished relative to the HITRAN 2000 line data. Strong shortwave absorption also results in a warm stratosphere and lower tropopause. We discuss these results in the context of contemporary research on the Archean climate and how these results could affect the formation of stratospheric clouds and an organic haze.

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Section: Organic Hazementioning

confidence: 99%

Diminished greenhouse warming from Archean methane due to solar absorption lines

Byrne

Goldblatt

2015

Clim. Past

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“…The questions we are addressing are still first-order ones, and we feel that our approach to the modeling is commensurate with this level of accuracy. The photochemical model used here is a one-dimensional (horizontally averaged) model that has been adapted from one used in previous studies of the primitive terrestrial atmosphere [e.g., Kasting, 1982;Kasting et al, 1983;Zahnle, 1986;Kasting, 1990]. The model includes 72 chemical species involved in 337 reactions.…”

Section: Model Descriptionmentioning

confidence: 99%

UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere

Pavlov¹,

Brown²,

Kasting³

2001

J. Geophys. Res.

255

258

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Abstract. The late Archean atmosphere was probably rich in biologically generated CH4 and may well have contained a hydrocarbon haze layer similar to that observed today on Satum's moon, Titan. Here we present a detailed model of the photochemistry of haze formation in the early atmosphere, and we examine the effects of such a haze layer on climate and ultraviolet radiation. We show that the thickness of the haze layer was limited by a negative feedback loop: A haze optical depth of more than •0.5 in the visible would have produced a strong "antigreenhouse effect," thereby cooling the surface and slowing the rate at which CH 4 was produced. Given this climatic constraint on its visible optical depth, the amount of UV shielding provided by the haze can be estimated from knowledge of the optical properties and size distribution of the haze particles. Contrary to previous studies [Sagan and Chyba, 1997], we find that when the finite size of the particles is taken into account, the amount of UV shielding provided by the haze is small. Thus NH3 should have been rapidly photolyzed and should not have been sufficiently abundant to augment the atmospheric greenhouse effect. We also examine the question of whether photosynthetically generated 02 could have accumulated beneath the haze layer. For the model parameters considered here, the answer is "no": The upper limit on ground level 02 concentrations is • 10 -6 atm, and a more realistic estimate for pO2 during the late Archean is 10 -8 atm. The stability of both 02 and NH3 is sensitive to the size distribution and optical properties of the haze particles, neither of which is well known. Further theoretical and laboratory work is needed to address these uncertainties.

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“…Although the exact history of the primitive atmosphere and its evolution to its present state is still under active debate, there are, fortunately, well-established geochemical data from the abiotic and biotic fossil record that constrain model scenarios. Earth's second atmosphere of the Archean (the first atmosphere was probably lost to space during the heavy asteroid bombardment of between 4.4 and 4.2 Ga with a late spike in bombardment at between 3.9 and 3.8 Ga; post-latelunar bombardment; Gomes et al, 2005) is thought to have been composed mainly of N 2 , CO 2 , H 2 O, CH 4 , and some NH 3 , with the ratio CH 4 / CO 2 1 (Kasting et al, 1983;Kharecha et al, 2005), and perhaps up to 0.1 bar of H 2 (Tian et al, 2005), but with very little oxygen and therefore essentially no ozone. For commonly assumed Archean atmospheric pressures of around 1 bar, these gases are all nearly perfectly transparent above approximately 220 nm (Sagan, 1973).…”

Section: Evolution Of the Transparency Of Earth's Atmospherementioning

confidence: 99%

Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum

Michaelian

Simeonov²

2015

Biogeosciences

112

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Abstract. The driving force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate. In the upper atmosphere of today, oxygen and ozone derived from life processes are performing the short-wavelength UV-C and UV-B dissipation. On Earth's surface, water and organic pigments in water facilitate the near-UV and visible photon dissipation. The first organic pigments probably formed, absorbed, and dissipated at those photochemically active wavelengths in the UV-C and UV-B that could have reached Earth's surface during the Archean. Proliferation of these pigments can be understood as an autocatalytic photochemical process obeying non-equilibrium thermodynamic directives related to increasing solar photon dissipation rate. Under these directives, organic pigments would have evolved over time to increase the global photon dissipation rate by (1) increasing the ratio of their effective photon cross sections to their physical size, (2) decreasing their electronic excited state lifetimes, (3) quenching radiative de-excitation channels (e.g., fluorescence), (4) covering ever more completely the prevailing solar spectrum, and (5) proliferating and dispersing to cover an ever greater surface area of Earth. From knowledge of the evolution of the spectrum of G-type stars, and considering the most probable history of the transparency of Earth's atmosphere, we construct the most probable Earth surface solar spectrum as a function of time and compare this with the history of molecular absorption maxima obtained from the available data in the literature. This comparison supports the conjecture that many fundamental molecules of life are pigments which arose, proliferated, and co-evolved as a response to dissipating the solar spectrum, supports the thermodynamic dissipation theory for the origin of life, constrains models for Earth's early atmosphere, and sheds some new light on the origin of photosynthesis.

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Photochemistry of methane in the Earth's early atmosphere

Cited by 130 publications

References 80 publications

Diminished greenhouse warming from Archean methane due to solar absorption lines

Diminished greenhouse warming from Archean methane due to solar absorption lines

UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere

Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum

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Photochemistry of methane in the Earth's early atmosphere

Cited by 130 publications

References 80 publications

Diminished greenhouse warming from Archean methane due to solar absorption lines

Diminished greenhouse warming from Archean methane due to solar absorption lines

UV shielding of NH3and O2by organic hazes in the Archean atmosphere

Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum

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UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere