Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

A 200-million-year delay in permanent atmospheric oxygenation

Abstract

The rise of atmospheric oxygen fundamentally changed the chemistry of surficial environments and the nature of Earth’s habitability1. Early atmospheric oxygenation occurred over a protracted period of extreme climatic instability marked by multiple global glaciations2,3, with the initial rise of oxygen concentration to above 10−5 of the present atmospheric level constrained to about 2.43 billion years ago4,5. Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago4, which represents the estimated timing of irreversible oxygenation of the atmosphere6,7. Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron–sulfur–carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10−5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Simplified Palaeoproterozoic stratigraphy of the Eastern Transvaal Basin, South Africa, showing the studied interval.
Fig. 2: Geochemical and isotopic profiles for drill cores EBA-1 and EBA-2.
Fig. 3: Multiple-sulfur isotope systematics and summary of atmospheric and oceanic redox conditions.
Fig. 4: Compilation of Δ33S data and simplified carbonate C isotope (δ13C) trends for the 2.5–2.0 Ga time interval.

Data availability

All data generated or analysed during this study are included in this published article and its Supplementary Information.

References

  1. 1.

    Canfield, D. E. The early history of atmospheric oxygen: homage to Robert M. Garrels. Annu. Rev. Earth Planet. Sci. 33, 1–36 (2005).

    ADS  CAS  Google Scholar 

  2. 2.

    Bekker, A. & Kaufman, A. J. Oxidative forcing of global climate change: a biogeochemical record across the oldest Paleoproterozoic ice age in North America. Earth Planet. Sci. Lett. 258, 486–499 (2007).

    ADS  CAS  Google Scholar 

  3. 3.

    Rasmussen, B., Bekker, A. & Fletcher, I. R. Correlation of Paleoproterozoic glaciations based on U–Pb zircon ages for tuff beds in the Transvaal and Huronian Supergroups. Earth Planet. Sci. Lett. 382, 173–180 (2013).

    ADS  CAS  Google Scholar 

  4. 4.

    Gumsley, A. P. et al. Timing and tempo of the Great Oxidation Event. Proc. Natl Acad. Sci. USA 114, 1811–1816 (2017).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  5. 5.

    Warke, M. R. et al. The Great Oxidation Event preceded a Paleoproterozoic “snowball Earth”. Proc. Natl Acad. Sci. USA 117, 13314–13320 (2020).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  6. 6.

    Bekker, A. et al. Dating the rise of atmospheric oxygen. Nature 427, 117–120 (2004).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  7. 7.

    Luo, G. et al. Rapid oxygenation of Earth’s atmosphere 2.33 billion years ago. Sci. Adv. 2, e1600134 (2016).

    ADS  PubMed  PubMed Central  Google Scholar 

  8. 8.

    Holland, H. D. Volcanic gases, black smokers, and the Great Oxidation Event. Geochim. Cosmochim. Acta 66, 3811–3826 (2002).

    ADS  CAS  Google Scholar 

  9. 9.

    Farquhar, J., Bao, H. M. & Thiemens, M. Atmospheric influence of Earth’s earliest sulfur cycle. Science 289, 756–758 (2000).

    ADS  CAS  PubMed  Google Scholar 

  10. 10.

    Farquhar, J. & Wing, B. A. Multiple sulfur isotopes and the evolution of the atmosphere. Earth Planet. Sci. Lett. 213, 1–13 (2003).

    ADS  CAS  Google Scholar 

  11. 11.

    Pavlov, A. A. & Kasting, J. F. Mass-independent fractionation of sulfur isotopes in Archean sediments: strong evidence for an anoxic Archean atmosphere. Astrobiology 2, 27–41 (2004).

    ADS  Google Scholar 

  12. 12.

    Catling, D., Zahnle, K. & McKay, C. Biogenic methane, hydrogen escape, and the irreversible oxidation of early Earth. Science 293, 839–843 (2001).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  13. 13.

    Goldblatt, C., Lenton, T. M. & Watson, A. J. Bistability of atmospheric oxygen and the Great Oxidation. Nature 443, 683–686 (2006).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  14. 14.

    Hoffman, P. F. The Great Oxidation and a Siderian snowball Earth: MIF-S based correlation of Paleoproterozoic glacial epochs. Chem. Geol. 362, 143–156 (2013).

    ADS  CAS  Google Scholar 

  15. 15.

    Kasting, J. F. Methane and climate during the Precambrian era. Precambr. Res. 137, 119–129 (2005).

    ADS  CAS  Google Scholar 

  16. 16.

    Claire, M. W., Catling, D. C. & Zahnle, K. J. Biogeochemical modelling of the rise in atmospheric oxygen. Geobiology 4, 239–269 (2006).

    CAS  Google Scholar 

  17. 17.

    Zahnle, K., Claire, M. W. & Catling, D. The loss of mass-independent fractionation in sulfur due to a Palaeoproterozoic collapse of atmospheric methane. Geobiology 4, 271–283 (2006).

    CAS  Google Scholar 

  18. 18.

    Daines, S. J. & Lenton, T. M. The effect of widespread early aerobic marine ecosystems on methane cycling and the Great Oxidation. Earth Planet. Sci. Lett. 434, 42–51 (2016).

    ADS  CAS  Google Scholar 

  19. 19.

    Guo, Q. et al. Reconstructing Earth’s surface oxidation across the Archean-Proterozoic transition. Geology 37, 399–402 (2009).

    ADS  Google Scholar 

  20. 20.

    Reinhard, C. T., Planavsky, N. J. & Lyons, T. W. Long-term sedimentary recycling of rare sulphur isotope anomalies. Nature 497, 100–103 (2013).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  21. 21.

    Philippot, P. et al. Globally asynchronous sulphur isotope signals require re-definition of the Great Oxidation Event. Nat. Commun. 9, 2245 (2018).

    ADS  PubMed  PubMed Central  Google Scholar 

  22. 22.

    Killingsworth, B. A. et al. Constraining the rise of oxygen with oxygen isotopes. Nat. Comm. 10, 4924 (2019); author correction 11, 4996 (2020).

    ADS  CAS  Google Scholar 

  23. 23.

    Ono, S. et al. New insights into Archean sulfur cycle from mass-independent sulfur isotope records from the Hammersley Basin, Australia. Earth Planet. Sci. Lett. 213, 15–30 (2003).

    ADS  CAS  Google Scholar 

  24. 24.

    Kaufman, A. J. et al. Late Archean biospheric oxygenation and atmospheric evolution. Science 317, 1900–1903 (2007).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  25. 25.

    Cameron, E. M. Evidence from early Proterozoic anhydrite for sulphur isotopic partitioning in Precambrian oceans. Nature 304, 54–56 (1983).

    ADS  CAS  Google Scholar 

  26. 26.

    Bekker, A., Karhu, J. A. & Kaufman, A. J. Carbon isotope record for the onset of the Lomagundi carbon isotope excursion in the Great Lakes area, North America. Precambr. Res. 148, 145–180 (2006).

    ADS  CAS  Google Scholar 

  27. 27.

    Crockford, P. W. et al. Claypool continued: extending the isotopic record of sedimentary sulfate. Chem. Geol. 513, 200–225 (2019).

    ADS  CAS  Google Scholar 

  28. 28.

    Coetzee, L. L., Beukes, N. J., Gutzmer, J. & Kakegawa, T. Links of organic carbon cycling and burial to depositional depth gradients and establishment of a snowball Earth at 2.3 Ga: evidence from the Timeball Hill Formation, Transvaal Supergroup, South Africa. S. Afr. J. Geol. 109, 109–122 (2006).

    CAS  Google Scholar 

  29. 29.

    Planavsky, N. J. et al. The evolution of the marine phosphate reservoir. Nature 467, 1088–1090 (2010).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  30. 30.

    Kendall, B. et al. Pervasive oxygenation along late Archaean ocean margins. Nat. Geosci. 3, 647–652 (2010).

    ADS  CAS  Google Scholar 

  31. 31.

    Olson, S. L., Kump, L. R. & Kasting, J. F. Quantifying the areal extent and dissolved oxygen concentrations of Archean oxygen oases. Chem. Geol. 362, 35–43 (2013).

    ADS  CAS  Google Scholar 

  32. 32.

    Koehler, M. C., Buick, R., Kipp, M. A., Stüeken, E. E. & Zaloumis, J. Transient surface ocean oxygenation recorded in the 2.66-Ga Jeerinah Formation, Australia. Proc. Natl Acad. Sci. USA 115, 7711–7716 (2018).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  33. 33.

    Hoffman, P. F., Kaufman, A. J., Halverson, G. P. & Schrag, D. P. A Neoproterozoic Snowball Earth. Science 281, 1342–1346 (1998).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  34. 34.

    Mills, B. et al. Timing of Neoproterozoic glaciations linked to transport-limited global weathering. Nat. Geosci. 4, 861–864 (2011).

    ADS  CAS  Google Scholar 

  35. 35.

    Bekker, A. & Holland, H. D. Oxygen overshoot and recovery during the early Paleoproterozoic. Earth Planet. Sci. Lett. 317–318, 295–304 (2012).

    ADS  Google Scholar 

  36. 36.

    Humbert, F. et al. Palaeomagnetism of the early Palaeoproterozoic, volcanic Hekpoort Formation (Transvaal Supergroup) of the Kaapvaal craton, South Africa. Geophys. J. Int. 209, 842–865 (2017).

    ADS  CAS  Google Scholar 

  37. 37.

    Clarkson, M. O., Poulton, S. W., Guilbaud, R. & Wood, R. A. Assessing the utility of Fe/Al and Fe-speciation to record water column redox conditions in carbonate-rich sediments. Chem. Geol. 382, 111–122 (2014).

    ADS  CAS  Google Scholar 

  38. 38.

    Poulton, S. W. & Canfield, D. E. Ferruginous conditions: a dominant feature of the ocean through Earth’s history. Elements 7, 107–112 (2011).

    CAS  Google Scholar 

  39. 39.

    Izon, G. et al. Multiple oscillations in Neoarchaean atmospheric chemistry. Earth Planet. Sci. Lett. 431, 264–273 (2015).

    ADS  CAS  Google Scholar 

  40. 40.

    Bekker, A. in Encyclopedia of Astrobiology (eds Gargaud, M. et al.) 1399–1404 (Springer, 2014).

  41. 41.

    Coetzee, L. L. Genetic Stratigraphy of the Paleoproterozoic Pretoria Group in the Western Transvaal. MSc thesis, Rand Afrikaans Univ. (2001).

  42. 42.

    Visser, J. N. J. The Timeball Hill Formation at Pretoria—a prograding shore-line deposit. Annals Geol. Surv. Pretoria 9, 115–118 (1972).

    Google Scholar 

  43. 43.

    Eriksson, K. A. The Timeball Hill Formation—a fossil delta. J. Sediment. Res. 43, 1046–1053 (1973).

    Google Scholar 

  44. 44.

    Eriksson, P. G. & Reczko, B. F. F. Contourites associated with pelagic mudrocks and distal delta-fed turbidites in the Lower Proterozoic Timeball Hill Formation epeiric basin (Transvaal Supergroup), South Africa. Sedim. Geol. 120, 319–335 (1998).

    ADS  Google Scholar 

  45. 45.

    Eriksson, P. G. et al. The Transvaal sequence: an overview. J. Afr. Earth Sci. 16, 25–51 (1993).

    ADS  Google Scholar 

  46. 46.

    Bekker, A., Krapež, B. & Karhu, J. A. Correlation of the stratigraphic cover of the Pilbara and Kaapvaal cratons recording the lead up to Paleoproterozoic Icehouse and the GOE. Earth Sci. Rev. 211, 103389 (2020).

    Google Scholar 

  47. 47.

    Hannah, J. L., Bekker, A., Stein, H. J., Markey, R. J. & Holland, H. D. Primitive Os and 2316 Ma age for marine shale: implications for Paleoproterozoic glacial events and the rise of atmospheric oxygen. Earth Planet. Sci. Lett. 225, 43–52 (2004).

    ADS  CAS  Google Scholar 

  48. 48.

    Bekker, A. et al. Chemostratigraphy of the Paleoproterozoic Duitschland Formation, South Africa: implications for coupled climate change and carbon cycling. Am. J. Sci. 301, 261–285 (2001).

    ADS  CAS  Google Scholar 

  49. 49.

    Schröder, S., Beukes, N. J. & Armstrong, R. A. Detrital zircon constraints on the tectono-stratigraphy of the Paleoproterozoic Pretoria Group, South Africa. Precambr. Res. 278, 362–393 (2016).

    ADS  Google Scholar 

  50. 50.

    Moore, J. M., Tsikos, H. & Polteau, S. Deconstructing the Transvaal Supergroup. South Africa: implications for Palaeoproterozoic palaeoclimate models. J. Afr. Earth Sci. 33, 437–444 (2001).

    ADS  Google Scholar 

  51. 51.

    Van Kranendonk, M. & Mazumder, R. Two Paleoproterozoic glacio-eustatic cycles in the Turee Creek Group, Western Australia. Geol. Soc. Am. Bull. 127, 596–607 (2015).

    Google Scholar 

  52. 52.

    Krapež, B., Müller, S. G., Fletcher, I. R. & Rasmussen, B. A tale of two basins? Stratigraphy and detrital zircon provenance of the Palaeoproterozoic Turee Creek and Horseshoe basins of Western Australia. Precambr. Res. 294, 67–90 (2017).

    ADS  Google Scholar 

  53. 53.

    Cui, H. et al. Searching for the Great Oxidation Event in North America: a reappraisal of the Huronian Supergroup by SIMS sulfur four-isotope analysis. Astrobiology 18, 519–538 (2018).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  54. 54.

    Poulton, S. W. & Canfield, D. E. Development of a sequential extraction procedure for iron: implications for iron partitioning in continentally derived particulates. Chem. Geol. 214, 209–221 (2005).

    ADS  CAS  Google Scholar 

  55. 55.

    Canfield, D. E., Raiswell, R., Westrich, J. T., Reaves, C. M. & Berner, R. A. The use of chromium reduction in the analysis of reduced inorganic sulfur in sediments and shales. Chem. Geol. 54, 149–155 (1986).

    ADS  CAS  Google Scholar 

  56. 56.

    Raiswell, R. & Canfield, D. E. Sources of iron for pyrite formation in marine sediments. Am. J. Sci. 298, 219–245 (1998).

    ADS  CAS  Google Scholar 

  57. 57.

    Poulton, S. W. The Iron Speciation Paleoredox Proxy (eds Lyons, T. et al.) (Cambridge Univ. Press, 2021).

  58. 58.

    Raiswell, R. & Canfield, D. E. Rates of reaction between silicate iron and dissolved sulfide in Peru Margin sediments. Geochim. Cosmochim. Acta 60, 2777–2787 (1996).

    ADS  CAS  Google Scholar 

  59. 59.

    Poulton, S. W., Fralick, P. W. & Canfield, D. E. Spatial variability in oceanic redox structure 1.8 billion years ago. Nat. Geosci. 3, 486–490 (2010).

    ADS  CAS  Google Scholar 

  60. 60.

    Doyle, K. A., Poulton, S. W., Newton, R. J., Podkovyrov, V. N. & Bekker, A. Shallow water anoxia in the Mesoproterozoic ocean: evidence from the Bashkir Meganticlinorium, Southern Urals. Precambr. Res. 317, 196–210 (2018).

    ADS  CAS  Google Scholar 

  61. 61.

    Alcott, L. J. et al. Development of iron speciation reference materials for paleoredox analysis. Geostand. Geoanal. Res. 44, 581–591 (2020).

    CAS  Google Scholar 

  62. 62.

    Johnston, D. T. et al. Placing an upper limit on cryptic marine sulphur cycling. Nature 513, 530–533 (2014).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  63. 63.

    Cheney, E. S. Sequence stratigraphy and plate tectonic significance of the Transvaal succession of Southern Africa and its equivalent in Western Australia. Precambr. Res. 79, 3–24 (1996).

    ADS  CAS  Google Scholar 

  64. 64.

    Beukes, N. J. & Gutzmer, J. Origin and paleoenvironmental significance of major iron formations at the Archean-Paleoproterozoic boundary. Soc. Econ. Geol. Rev. 15, 5–47 (2008).

    Google Scholar 

  65. 65.

    Zerkle, A. L., Claire, M. W., Domagal-Goldman, S. D., Farquhar, J. & Poulton, S. W. A bistable organic-rich atmosphere on the Neoarchaean Earth. Nat. Geosci. 5, 359–363 (2012).

    ADS  CAS  Google Scholar 

  66. 66.

    Izon, G. et al. Biological regulation of atmospheric chemistry en route to planetary oxygenation. Proc. Natl Acad. Sci. USA 114, 2571–2579 (2017).

    Google Scholar 

  67. 67.

    Mishima, K. et al. Multiple sulfur isotope geochemistry of Dharwar Supergroup, Southern India: late Archean record of changing atmospheric chemistry. Earth Planet. Sci. Lett. 464, 69–83 (2017).

    ADS  CAS  Google Scholar 

  68. 68.

    Raiswell, R. et al. Turbidite depositional influences on the diagenesis of Beecher’s Trilobite Bed and the Hunsrück Slate; sites of soft tissue pyritization. Am. J. Sci. 308, 105–129 (2008).

    ADS  Google Scholar 

  69. 69.

    Papineau, D., Mojzsis, S. J. & Schmitt, A. K. Multiple sulfur isotopes from Paleoproterozoic Huronian interglacial sediments and the rise of atmospheric oxygen. Earth Planet. Sci. Lett. 255, 188–212 (2007).

    ADS  CAS  Google Scholar 

  70. 70.

    Zerkle, A. L. et al. Onset of the aerobic nitrogen cycle during the Great Oxidation Event. Nature 542, 465–467 (2017).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

Download references

Acknowledgements

S.W.P. acknowledges support from a Leverhulme Research Fellowship and a Royal Society Wolfson Research Merit Award. A.B. acknowledges support from the University of Johannesburg in the form of a Distinguished Visiting Professorship. D.T.J. acknowledges support from a NASA Exobiology award (NNX15AP58G). We thank R. Walshaw for assistance with SEM analyses.

Author information

Affiliations

Authors

Contributions

S.W.P., A.B. and D.E.C. designed the research, S.W.P., A.B. and A.L.Z. collected samples, and S.W.P., V.M.C. and D.T.J. performed analyses. S.W.P. wrote the manuscript, with contributions from all co-authors.

Corresponding author

Correspondence to Simon W. Poulton.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Bryan Killingsworth, Lee Kump and Sune Nielsen for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Generalized stratigraphic correlation between the Transvaal/Griqualand (South Africa), Hamersley (Pilbara, Western Australia) and Huronian (Ontario, Canada) successions.

Figure adapted from ref. 46 with permission from Elsevier. The exact stratigraphic position of the loss of MIF-S in the Huronian Basin is uncertain53,69 and hence not shown.

Extended Data Fig. 2 Geochemical data for the lower part of the Pretoria Group.

Dashed lines on FeHR*/FeT plots represent the boundaries for distinguishing oxic and anoxic deposition, and on Fepy/FeHR* plots represent the boundaries for distinguishing ferruginous and euxinic water-column conditions38. Dashed lines on Δ33S plots are at −0.3‰ and +0.3‰.

Extended Data Fig. 3 Scanning electron microscope images of pyrite and Fe oxide morphologies.

A, EBA-2, Rooihoogte Formation, 1,346.2 m. Sample deposited under oxic conditions; Δ33S = +2.16‰. B, EBA-1, Rooihoogte Formation, 1,168 m. Sample deposited under oxic conditions; Δ33S = +1.77‰. C, EBA-1, Timeball Hill Formation, 1,137 m. Sample deposited under ferruginous conditions; Δ33S = +1.44‰. D, EBA-2, Rooihoogte Formation, 1,335.6 m. Sample deposited under ferruginous conditions; Δ33S = +0.25‰. E, EBA-2, Rooihoogte Formation, 1,338.3 m. Sample deposited under euxinic conditions; Δ33S = +0.17‰. F, EBA-1, Timeball Hill Formation, 706 m. Water-column redox state not analysed; Δ33S = +1.61‰.

Extended Data Fig. 4 Sulfur isotope trends for Rooihoogte–Timeball Hill Formation samples.

A, Orthogonal data regression for samples with MIF-S (Δ33S > 0.3‰), showing the calculated Δ36S/Δ33S slope (blue line) and 3σ confidence interval (shaded blue area). Samples from above the Rooihoogte Formation are denoted as open blue circles. B, Orthogonal data regression for MDF-S samples (Δ33S = –0.3‰ to +0.3‰, showing the calculated Δ36S/Δ33S slope (red line) and 3σ confidence interval (shaded red area).

Extended Data Fig. 5 Sulfur isotope data from Fennoscandia5 and Western Australia21,22.

Blue dashed lines represent the range for the ARA23,24 (−0.9 ± 0.1; 1σ). ‘Perturbed slope range’ represents the maximum deviation from the standard ARA due to temporal effects of either enhanced methane-derived organic haze39,65,66 or volcanic sulfur input67.

Extended Data Fig. 6 Simplified geological map of the Transvaal Supergroup outcrop area.

Figure adapted from ref. 70, Springer Nature.

Extended Data Fig. 7 Ocean redox data for EBA-1.

The dashed line on the Fe/Al plot represents the upper boundary for distinguishing anoxia37 and on the FePRS/Al plot the Phanerozoic average68. Dashed lines on the FeHR/FeT and FeHR*/FeT plots distinguish oxic and anoxic deposition38. Dashed lines on the FePRS plot represent the average Phanerozic range (1.80 ± 0.85 wt%; 1σ)68.

Extended Data Fig. 8 Ocean redox data for EBA-2.

The dashed line on the Fe/Al plot represents the upper boundary for distinguishing anoxia37 and on the FePRS/Al plot the Phanerozoic average68. Dashed lines on the FeHR/FeT and FeHR*/FeT plots distinguish oxic and anoxic deposition38. Dashed lines on the FePRS plot represent the average Phanerozic range (1.80 ± 0.85 wt%; 1σ)68.

Supplementary information

Supplementary Tables

This file contains Supplementary Tables 1-4.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Poulton, S.W., Bekker, A., Cumming, V.M. et al. A 200-million-year delay in permanent atmospheric oxygenation. Nature 592, 232–236 (2021). https://doi.org/10.1038/s41586-021-03393-7

Download citation

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links