Glaciation events

At the end of the Mesoarchean, the Earth experiences the first known glaciation: Pongola glaciation

For the first time in Earth’s history, organisms have impacted the global cycling of water, oxygen, and carbon dioxide on a massive scale

Ice may have encroached as far as the subtropical regions (El Albani et al., 2016). 

Oxygen increases in the atmosphere creating the Oxygen Catastrophe or Great Oxidation Event

• Many anaerobic bacteria to go extinct 

Huronian glaciation begins during this period (2.4 bya)

• Lasts 300,000 years until Rhyacian (2.1 Ga)

• Glaciers covered continents and crept close to the equator; sea levels dropped

• It is also correlated with a sharp spike in oxygen levels, which interacted with the atmosphere's methane, creating water and carbon dioxide. Methane is an effective greenhouse gas that traps more heat than carbon dioxide or water. causing global cooling

Large-scale glaciation events

• Two possible glaciation events

  • Marinoan glaciation (650 - 635 Ma)

  • Sturtian glaciation (750 - 700 Ma)

Snowball Earth hypothesis

• Glaciation extended to about 30° North and South latitudes

• Snow and ice reflect most incoming sunlight back into space

• Causes further glaciation, with ice covering the entire Earth, even the equator

• The water cycle severely restricted by ice over oceans which inhibited the normal flow of sediments into the sea

• Volcanism underneath the sea changed the ocean chemistry: gases could not escape

• The carbon cycle was affected, such that rain washes carbon dioxide out of the atmosphere into the ground, where carbonic acid reacts with rocks to form carbonates/bicarbonates, which are washed into the sea and eventually deposited on the sea floor

• Carbon dioxide levels increase due to volcanism, which triggers a greenhouse effect; ice sheets melt rapidly, and temperatures rise, perhaps reaching as high as 50 °C temporarily

Glaciations during the early part of the Ediacaran (Varanger-Marinoan ice ages: 585-605 Ma). 

Cooling with glaciation at high latitudes occurred towards the very end of the Ediacaran and the beginning of the Cambrian.

End of Ordovician Ice Age

• Several glaciation events over 5-10 Ma

  • Each glaciation is thought to last for a short (~500,000 years) period

  • Sea levels frequently rise and fall

• 2nd largest extinction on Earth

60% of marine life goes extinct

The appearance of early land plants may have triggered the 2nd largest glaciation event (Lenton et al. 2012)

Toward the end of the land plant radiation, the Earth experienced an ice age.

Possible cause: 

• Increase in plant biomass, and coincident photosynthesis, caused a draw-down of atmospheric carbon dioxide

• Loss of carbon dioxide in the atmosphere results in global cooling and glaciation.

"Biotic crisis" decimates tropical marine environments (Algeo and Sheckler 1998)

• Land plants may have increased weathering of rocks and soils, producing an influx of minerals to the marine environment

• Both an increase in root depth and penetration as well as the ability of seed plants to colonize drier, upland environments may have contributed to increased soil formation (pedogenesis)

• Increased nutrient input on rivers creates eutrophic conditions in epicontinental seaways, "resulting in algal blooms, widespread bottom water anoxia, and high sedimentary organic carbon fluxes."

The warm, moist climate continues to become dry

This resurgence of the Coal Forests seems to have coincided with a lowering of global temperatures, coinciding with a return of extensive polar ice in southern Gondwana. 

This lessening of the greenhouse effect maybe due to massive coal deposition extracting much carbon dioxide from the atmosphere.

This was a time of glaciation, with the poles extremely cold (particularly in the south). 

The equatorial regions remained wet and warm. 

This period of glaciation persisted into the Permian.