Pongola glaciation explained
The Pongola glaciation is a glacial episode that occurred in the Mesoarchean, 2.9 Ga ago for about 150 Ma. It is the oldest known glaciation on the planet.
Geology
The oldest known traces of glaciation date from the Mesoarchean. They correspond to the diamictite of the Pongola supergroup (more precisely to the Mozaan formation,) in KwaZulu-Natal and in Eswatini.
Climate
Even if the climate of the Archean is not well known, the study of the oxygen isotopes in the cherts of the time seem to show that the climate of the Archean was warm or, at least, temperate, in particular due to high levels of methane and carbon dioxide in the atmosphere; a glaciation around 2.9 Ga is therefore likely to have been caused by a drop in the rate of these greenhouse gases. The Pongola glaciation is also associated with changes in sulfur isotopes (δ34S), suggesting that this may also involve early and short-lived oxygenation of the Earth's atmosphere.
Extension
The extension of the glaciation is not determined with certainty. Some authors argue that the glacial deposits were formed at low latitudes, below 30° N, therefore close to the tropics, which would imply extensive glaciation, while others argue that the area was located at mid-latitude or even high latitude, closer to the pole, where a polar glacier could have formed, like the current situation.
Regarding its duration, the corresponding glacial deposits fall within the interval 2985 ± 1 and 2837 ± 5 Ma.
Notes & references
References
See also
Bibliography
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- Web site: Pongola supergroup. The first record of ancient life . University of KwaZulu-Natal . en . .
- Young . Grant M. . von Brunn . Victor . Gold . Digby J. C. . Minter . W. E. L. . 1998 . Earth's Oldest Reported Glaciation: Physical and Chemical Evidence from the Archean Mozaan Group (~2.9 Ga) of South Africa . The Journal of Geology . en . 106 . 5 . 523-538 . 10.1086/516039. 129717765 .
- Robert E. . Kopp . Joseph L. . Kirschvink . Isaac A. . Hilburn . Cody Z. . Nash . 9 August 2005 . The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis . PNAS . en . 102 . 32 . 11131–11136 . 10.1073/pnas.0504878102 . 16061801 . 1183582 . free .
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- Kasting . James F. . Howard . M. Tazewell . 29 October 2006 . Atmospheric composition and climate on the early Earth . Philosophical Transactions B . en . 361 . 1474 . 1733–1742 . 10.1098/rstb.2006.1902. 17008214 . 1664689 .
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