Glaciation events
Events in which there was large scale, global cooling
This is the modern ice ages that our ancestors experienced
The severe climatic changes during the ice age had major impacts on the fauna and flora.
With each advance of the ice, large areas of the continents became totally depopulated, and plants and animals retreating southward in front of the advancing glacier faced tremendous stress.
There has not been and ice-free period in the Arctic Ocean for 2.6 million years (although that may be quickly changing)
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.
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 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 env't
Both an increase in root depth and penetration as well as the ability of seed plants to conoloize drier, upland env'ts 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".
End of Ordovician ice age
Several glaciation events over 5-10 Ma
Each glaciation 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
Appearance of early land plants may have triggered the 2nd largest glaciation event (Lenton et al. 2012)
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 beginning of Cambrian.
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 equator
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 at 50 °C temporarily
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 until Rhyacian (2.1 Ga)
