Greenhouse warming by CH4 in the atmosphere of early Earth
TL;DR: It is found that a CH4 mixing ratio of 10(-4) (100 ppmv) or more in Earth's early atmosphere would provide agreement with the paleosol data from 2.3-2.4 Ga, which could have triggered the Earth's first widespread glaciation.
Abstract: Earth appears to have been warm during its early history despite the faintness of the young Sun. Greenhouse warming by gaseous CO 2 and H 2 O by itself is in conflict with constraints on atmospheric CO 2 levels derived from paleosols for early Earth. Here we explore whether greenhouse warming by methane could have been important. We find that a CH 4 mixing ratio of 10 -4 (100 ppmv) or more in Earth's early atmosphere would provide agreement with the paleosol data from 2.8 Ga. Such a CH 4 concentration could have been readily maintained by methanogenic bacteria, which are thought to have been an important component of the biota at that time. Elimination of the methane component of the greenhouse by oxidation of the atmosphere at about 2.3 - 2.4 Ga could have triggered the Earth's first widespread glaciation.
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TL;DR: The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth’s history.
Abstract: The rapid increase of carbon dioxide concentration in Earth’s modern atmosphere is a matter of major concern. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by early biological production. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth’s history.
1,821 citations
TL;DR: Evidence for a fourth pathway to produce oxygen is presented, possibly of considerable geochemical and evolutionary importance, and opens up the possibility that oxygen was available to microbial metabolism before the evolution of oxygenic photosynthesis.
Abstract: Only three biological pathways are known to produce oxygen: photosynthesis, chlorate respiration and the detoxification of reactive oxygen species. Here we present evidence for a fourth pathway, possibly of considerable geochemical and evolutionary importance. The pathway was discovered after metagenomic sequencing of an enrichment culture that couples anaerobic oxidation of methane with the reduction of nitrite to dinitrogen. The complete genome of the dominant bacterium, named ‘Candidatus Methylomirabilis oxyfera’, was assembled. This apparently anaerobic, denitrifying bacterium encoded, transcribed and expressed the well-established aerobic pathway for methane oxidation, whereas it lacked known genes for dinitrogen production. Subsequent isotopic labelling indicated that ‘M. oxyfera’ bypassed the denitrification intermediate nitrous oxide by the conversion of two nitric oxide molecules to dinitrogen and oxygen, which was used to oxidize methane. These results extend our understanding of hydrocarbon degradation under anoxic conditions and explain the biochemical mechanism of a poorly understood freshwater methane sink. Because nitrogen oxides were already present on early Earth, our finding opens up the possibility that oxygen was available to microbial metabolism before the evolution of oxygenic photosynthesis. A previously unknown pathway producing oxygen during anaerobic methane oxidation linked to nitrite and nitrate reduction has been found in microbes isolated from freshwater sediments in Dutch drainage ditches. The complete genome of the bacterium responsible for this reaction has been assembled, and found to contain genes for aerobic methane oxidation. The bacterium reduces nitrite via the recombination of two molecules of nitric oxide into nitrogen and oxygen, bypassing the familiar denitrification intermediate nitrous oxide. This discovery is relevant to nitrogen and methane cycling in the environment and, since nitrogen oxides arose early on Earth, raises the possibility that oxygen was available to microbes before the advent of oxygen-producing photosynthesis. In certain microbes, the anaerobic oxidation of methane can be linked to the reduction of nitrates and nitrites. Here it is shown that this occurs through the intermediate production of oxygen. This brings the number of known biological pathways for oxygen production to four, with implications for our understanding of life on the early Earth.
1,463 citations
TL;DR: The recent discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum as discussed by the authors, which does not account for major features such as abrupt onsets and terminations of discrete glacial events, their close association with large (> 10&) negative d 13 C shifts in seawater proxies, the deposition of strange carbonate layers (cap carbonates) globally during postglacial sea-level rise, and the return of large sedimentary iron formations.
Abstract: The gradual discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum. Was the Earth’s orbital obliquity > 60� (making the tropics colder than the poles) for 4.0 billion years following the lunar-forming impact, or did climate cool globally for some reason to the point at which runaway ice-albedo feedback created a ‘snowball’ Earth? The high-obliquity hypothesis does not account for major features of the Neoproterozoic glacial record such as the abrupt onsets and terminations of discrete glacial events, their close association with large (> 10&) negative d 13 C shifts in seawater proxies, the deposition of strange carbonate layers (‘cap carbonates’) globally during post-glacial sea-level rise, and the return of large sedimentary iron formations, after a 1.1 billion year hiatus, exclusively during glacial events. A snowball event, on the other hand, should begin and end abruptly, particularly at lower latitudes. It should last for millions of years, because outgassing must amass an intense greenhouse in order to overcome the ice albedo. A largely ice-covered ocean should become anoxic and reduced iron should be widely transported in solution and precipitated as iron formation wherever oxygenic photosynthesis occurred, or upon deglaciation. The intense greenhouse ensures a transient post-glacial regime of enhanced carbonate and silicate weathering, which should drive a flux of alkalinity that could quantitatively account for the world-wide occurrence of cap carbonates. The resulting high rates of carbonate sedimentation, coupled with the kinetic isotope effect of transferring the CO2 burden to the ocean, should drive down the d 13 C of seawater, as is observed. If cap carbonates are the ‘smoke’ of a snowball Earth, what was the ‘gun’? In proposing the original Neoproterozoic snowball Earth hypothesis, Joe Kirschvink postulated that an unusual preponderance of land masses in the middle and low latitudes, consistent with palaeomagnetic evidence, set the stage for snowball events by raising the planetary albedo. Others had pointed out that silicate weathering would most likely be enhanced if many continents were in the tropics, resulting in lower atmospheric CO2 and a colder climate. Negative d 13 C shifts of 10–20& precede glaciation in many regions, giving rise to speculation that the climate was destabilized by a growing dependency on greenhouse methane, stemming ultimately from the same unusual continental distribution. Given the existing palaeomagnetic, geochemical and geological evidence for late Neoproterozoic climatic shocks without parallel in the Phanerozoic, it seems inevitable that the history of life was impacted, perhaps profoundly so.
1,409 citations
Cites background from "Greenhouse warming by CH4 in the at..."
...Because atmospheric methane is not equilibrated with the ocean, as is CO2, any substantial dependence on methane greenhouse could counter-intuitively trigger a snowball event if the methane supply was interrupted for any reason (Pavlov et al., 2000; Schrag et al., 2002)....
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TL;DR: In this paper, a review of the Precambrian history of atmospheric oxygen is presented, starting with a brief discussion of the possible nature and magnitude of life before the evolution of oxygenic photosynthesis, followed by a summary of the various lines of evidence constraining oxygen levels through time.
Abstract: ▪ Abstract This paper reviews the Precambrian history of atmospheric oxygen, beginning with a brief discussion of the possible nature and magnitude of life before the evolution of oxygenic photosynthesis. This is followed by a summary of the various lines of evidence constraining oxygen levels through time, resulting in a suggested history of atmospheric oxygen concentrations. Also reviewed are the various processes regulating oxygen concentrations, and several models of Precambrian oxygen evolution are presented. A sparse geologic record, combined with uncertainties as to its interpretation, yields only a fragmentary and imprecise reading of atmospheric oxygen evolution. Nevertheless, oxygen levels have increased through time, but not monotonically, with major and fascinating swings to both lower and higher levels.
909 citations
Cites background from "Greenhouse warming by CH4 in the at..."
...…(2001) both take a reducing Archean atmosphere as a given and focus on the oxidation of the Earth’s surface around 2.3 Ga. Catling et al. (2001) considers the potential consequences of an Archean atmosphere rich in CH4, as some recent models of atmospheric evolution propose (Pavlov et al. 2000)....
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TL;DR: In this paper, the results of the Sun in Time multiwavelength program (X-rays to UV) of solar analogs with ages covering 0.1-7 Gyr were reported.
Abstract: We report on the results of the Sun in Time multiwavelength program (X-rays to UV) of solar analogs with ages covering ~0.1-7 Gyr. The chief science goals are to study the solar magnetic dynamo and to determine the radiative and magnetic properties of the Sun during its evolution across the main sequence. The present paper focuses on the latter goal, which has the ultimate purpose of providing the spectral irradiance evolution of solar-type stars to be used in the study and modeling of planetary atmospheres. The results from the Sun in Time program suggest that the coronal X-ray-EUV emissions of the young main-sequence Sun were ~100-1000 times stronger than those of the present Sun. Similarly, the transition region and chromospheric FUV-UV emissions of the young Sun are expected to be 20-60 and 10-20 times stronger, respectively, than at present. When we consider the integrated high-energy emission from 1 to 1200 A, the resulting relationship indicates that about 2.5 Gyr ago the solar high-energy flux was about 2.5 times the present value and about 3.5 Gyr ago was about 6 times the present value (when life supposedly arose on Earth). The strong radiation emissions inferred should have had major influences on the thermal structure, photochemistry, and photoionization of planetary atmospheres and have played an important role in the development of primitive life in the solar system. Some examples of the application of the Sun in Time results on exoplanets and on early solar system planets are discussed.
846 citations
Cites background from "Greenhouse warming by CH4 in the at..."
...The gases that have been suggested to account for this enhanced greenhouse effect are CO2, NH3 or CH4 (see, e.g., Rye et al. 1995; Sagan & Chyba 1997; Pavlov et al. 2000)....
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References
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TL;DR: A phylogenetic analysis based upon ribosomal RNA sequence characterization reveals that living systems represent one of three aboriginal lines of descent: the eubacteria, comprising all typical bacteria, the archaebacteria, and the urkaryotes, now represented in the cytoplasmic component of eukaryotic cells.
Abstract: A phylogenetic analysis based upon ribosomal RNA sequence characterization reveals that living systems represent one of three aboriginal lines of descent: (i) the eubacteria, comprising all typical bacteria; (ii) the archaebacteria, containing methanogenic bacteria; and (iii) the urkaryotes, now represented in the cytoplasmic component of eukaryotic cells.
3,522 citations
TL;DR: In this article, it is suggested that the partial pressure of carbon dioxide in the atmosphere is buffered, over geological time scales, by a negative feedback mechanism, in which the rate of weathering of silicate minerals (followed by deposition of carbonate minerals) depends on surface temperature, which in turn depends on the carbon dioxide partial pressure through the greenhouse effect.
Abstract: It is suggested that the partial pressure of carbon dioxide in the atmosphere is buffered, over geological time scales, by a negative feedback mechanism, in which the rate of weathering of silicate minerals (followed by deposition of carbonate minerals) depends on surface temperature, which in turn depends on the carbon dioxide partial pressure through the greenhouse effect. Although the quantitative details of this mechanism are speculative, it appears able to partially stabilize the earth's surface temperature against the steady increase of solar luminosity, believed to have occurred since the origin of the solar system.
1,837 citations
TL;DR: High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and iron sulfides.
Abstract: Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.
1,582 citations
Book•
01 Jan 1984
TL;DR: Holland et al. as mentioned in this paper reconstruct the chemical evolution of the Earth's atmosphere and oceans using data from a wide spectrum of fields to trace the history of the ocean-atmosphere system.
Abstract: In this first full-scale attempt to reconstruct the chemical evolution of the Earth's atmosphere and oceans, Heinrich Holland assembles data from a wide spectrum of fields to trace the history of the ocean-atmosphere system A pioneer in an increasingly important area of scholarship, he presents a comprehensive treatment of knowledge on this subject, provides an extensive bibliography, and outlines problems and approaches for further research The first four chapters deal with the turbulent first half billion years of Earth history The next four chapters, devoted largely to the Earth from 39 to 06 bybp, demonstrate that changes in the atmosphere and oceans during this period were not dramatic The last chapter of the book deals with the Phanerozoic Eon; although the isotopic composition of sulfur and strontium in seawater varied greatly during this period of Earth history, the chemical composition of seawater did not
1,536 citations
TL;DR: In this article, the authors show that the surface equilibrium temperature of the atmosphere with a given distribution of relative humidity is almost twice as sensitive to change of various factors such as solar constant, CO2 content, O3 content, and cloudiness than that of the one with a fixed relative humidity.
Abstract: Radiative convective equilibrium of the atmosphere with a given distribution of relative humidity is computed as the asymptotic state of an initial value problem. The results show that it takes almost twice as long to reach the state of radiative convective equilibrium for the atmosphere with a given distribution of relative humidity than for the atmosphere with a given distribution of absolute humidity. Also, the surface equilibrium temperature of the former is almost twice as sensitive to change of various factors such as solar constant, CO2 content, O3 content, and cloudiness, than that of the latter, due to the adjustment of water vapor content to the temperature variation of the atmosphere. According to our estimate, a doubling of the CO2 content in the atmosphere has the effect of raising the temperature of the atmosphere (whose relative humidity is fixed) by about 2C. Our model does not have the extreme sensitivity of atmospheric temperature to changes of CO2 content which was adduced by M...
1,485 citations