Overberg Geoscientists Group
720 Mya
Snowball Earth - 5 stages
The Earth has endured many changes in its 4.6 billion-year history, with some tumultuous twists and turns along the way. One especially dramatic episode appears to have come between 700 million and 600 million years ago (Cryogenian Period), when scientists have determined that ice smothered the entire planet, from the poles to the equator — twice in quick succession (Figure 1).
Figure 1: An artist’s impression of the extent of ice cover during a “Snowball Earth” period.
Drawing on evidence across many continents, scientists have determined that these Snowball Earth events may have paved the way for the Cambrian explosion of life that followed — the period when complex, multicellular organisms began to diversify and spread across the planet (Poppick, 2019)
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In southern Africa we have an extraordinary well exposed example of this event in Namibia. The Damara Belt of rocks extends along the entire west coast of Namibia and trends northeast, inland to the border of Botswana and beyond. As well as the Gariep Belt in Namaqualand. These rocks encompass this period of Earth’s history and the remarkable desert scenery enables relatively easy investigation of the many features related to Snowball Earth (Figure 2).
Figure 2: Schematic Geological Map of Namibia, showing the extent of the Damara Belt and the location of some Snowball Earth investigation sites (Bechstadt,T., et. al. 2018).
Figure 2: Schematic Geological Map of Namibia, showing the extent of the Damara Belt and the location of some Snowball Earth investigation sites (Bechstadt,T., et. al. 2018).
Some unique features of these rocks include the association with both banded ironstones as well as thick carbonate sequences. Scientific studies relate the development of both rock types to changes in ocean water chemistry initiated by the glacial periods.
Explosions of life in the oceans followed shortly (geologic time!) after these events.
Further reading:
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Bechstadt, T., et.al. 2018. The Cryogenian Ghaub Formation of Namibia – New insights into Neoproterozoic glaciations. Earth Science Reviews, Vol. 177, p 678 – 714.
Hoffman, P., 2021. Paul Hoffman on the Snowball Earth Hypothesis. Podcast. https://www.geologybites.com/paul-hoffman
McCarthy, T.S. and Rubidge, B. 2005. The Story of Earth and Life. Struik, Cape Town, p.119.
Poppick, L., 2019. Astronomy Magazine. https://www.astronomy.com/science/snowball-earth-the-times-our-planet-was-covered-in-ice/
Historical Geology: Snowball Earth. https://opengeology.org/historicalgeology/case-studies/snowball-earth/
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John Blaine July 2023