Evidence for life on Earth before 3,800 million years ago

Mojzsis, S. J.; Arrhenius, Gustaf; McKeegan, Kevin D.; Harrison, T. Mark; Nutman, Allen P.; Friend, C. R. L.

doi:10.1038/384055a0

Cited by 1,169 publications

(637 citation statements)

References 23 publications

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“…Thus, cyanobacterial calcification is plausible at that time and was probably the most important rockforming process of biomineralization (Altermann, 2002. As life probably existed on Earth already at 3.8 Ga (Mojzsis et al, 1996;Rosing, 1999;McKeegan et al, 2007;Schopf et al, 2007), it would not be surprising to find evidence for cyanobacteria even in the 3.5 Ga Streely Pool stromatolitic reefs of Western Australia (Allwood et al, 2006). Thus, cyanobacteria may not only have shaped the face of the Earth by their influence on the composition of the atmosphere, but primarily by introducing a new rock type to the sedimentary inventory of our planet Earth.…”

Section: Discussionmentioning

confidence: 99%

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

Kaźmierczak

Altermann

Kremer

et al. 2009

Precambrian Research

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a b s t r a c tThe sparse Archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post-mortem silicification. Hitherto as an exception, sedimentary carbonate rocks from the Neoarchean Nauga Formation of South Africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria (Chroococcales and Pleurocapsales). Their remains, visible under the scanning electron microscope (SEM) after etching of polished rock samples, comprise capsular envelopes, mucilage sheaths, and groups of cells mineralized by calcium carbonate with an admixture of Al-K-Mg-Fe silicates. The capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the Neoarchean microbiota described and their modern analogues. The new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the Neoarchean, and offer a solution to the problem of the origin of Archean carbonate platforms, stromatolites and microbial reefs.

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Section: Discussionmentioning

confidence: 99%

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

Kaźmierczak

Altermann

Kremer

et al. 2009

Precambrian Research

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“…Following life's origin, which probably occurred prior to 3.9 Ga [Mojzsis et al, 1996], methanogenic bacteria quickly evolved and converted most of this H2 into CH4. The increased greenhouse effect of CH4, combined with continued growth of the continents, led to CO2 drawdown.…”

Section: A Possible Evolutionary Scenario For the Archean Atmospherementioning

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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“…The oldest recorded accretions around uraninite are in the Swaziland Supergroup in southern Africa (Saager et al, 1982) at 3.3 Ga or older (Figure 1). Carbonaceous coatings are also recorded around uranium-bearing apatite grains in the early Archean of the >3.85 Ga Akilia Island metasediments, Greenland (Mojzsis et al, 1996), although an origin for these coatings by irradiation has not been assessed and there is debate about whether this carbon is of biogenic origin (Manning et al, 2001;Fedo and Whitehouse, 2002;Ueno et al, 2002) and its time of formation (van Zuilen et al, 2002). The record clearly extends back through most of Earth's history, comparable to the time frame which yields evidence for life ( Figure 1).…”

Section: Precipitation Around Radioactive Grains In the Geological Rementioning

confidence: 99%

“…This type of irradiation should be more locally effective, as energetic particles in solids Figure 1. Early Precambrian record of crustal evolution, radioactive minerals, and organic evolution (data from Wilde et al, 2001;Peck et al, 2001;Maas et al, 1992;Saager et al, 1982;Mojzsis et al, 1996;Ozima and Tatsumoto, 1997;Rasmussen and Buick, 2000). Radioactive minerals predate oldest evidence for life.…”

Section: Introductionmentioning

confidence: 99%

Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth

Parnell

2004

Orig Life Evol Biosph

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Abstract. Irradiation of organic molecules by mineral radioactivity is a feasible alternative to cosmic irradiation to precipitate solid organic carbon-rich matter on the early Earth. Radioactive (uranium-and thorium-rich) minerals have been concentrated at the Earth's surface, and accumulated accretionary coatings of carbon due to irradiation, since early Archean times. The organic accretion process could have occurred at the surface or in the sub-surface, and is independent of a terrestrial or extraterrestrial source for the carbon.

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Evidence for life on Earth before 3,800 million years ago

Abstract: IT is unknown when life first appeared on Earth. https://ntrs.nasa.gov/search

Cited by 1,169 publications

References 23 publications

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere

Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth

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Evidence for life on Earth before 3,800 million years ago

Abstract: IT is unknown when life first appeared on Earth. https://ntrs.nasa.gov/search

Cited by 1,169 publications

References 23 publications

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

UV shielding of NH3and O2by organic hazes in the Archean atmosphere

Mineral Radioactivity in Sands as a Mechanism for Fixation of Organic Carbon on the Early Earth

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UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere