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Beyond Earthly Skies

Snowball Earth: Thawing a Snowball

4 Sep 2013, 22:00 UTC
Snowball Earth: Thawing a Snowball
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During the Neoproterozoic era (~1000 to ~540 Mya), the Earth experienced at least two global-scale glaciations at ~740 and ~635 Mya, where glaciers covered most of the Earth’s surface down to the deep tropics (Trindade and Macouin, 2007). Each global-scale glaciation or Snowball Earth event lasted for several million years. Over those millions of years, atmospheric CO2, a greenhouse gas, is expected to accumulate to immense levels due to continuous emission by volcanic activity and greatly reduced weathering on a frozen planet.Figure 1: CO2 emitted by volcanos accumulates in the atmosphere of a Snowball Earth. The removal of CO2 from the atmosphere is limited by the absence of rainfall. Furthermore, the drawdown of atmospheric CO2 is almost nonexistent because silicate weathering is greatly reduced due to the overlying ice cover and very cold ground temperatures.It is believed that the Earth thawed from a snowball state when the amount of atmospheric CO2 reached a level high enough to generate a sufficiently strong greenhouse effect. Evidence show that the amount of atmospheric CO2 towards the end of a Snowball Earth event accumulated to ~10 percent concentration; equivalent to ∼0.1 bar partial pressure (Bao et al., 2008). However, most climate models show that ...

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