The Neoproterozoic (= "new" Proterozoic), also called the Late Proterozoic, lasted from about 1.0 by to 0.542 by (542 my).
Glacial deposits formed roughly 600 to 700 million years ago.
Evidence for glaciation:
Glacial deposits are so widespread at this time that geologists refer to it
as "snowball Earth."
The formal name for this glaciation is the Varangian glaciation (named after an area in Norway).
The late Proterozoic ice age lasted about 240 my.
Plate tectonics may have had a role in cooling the planet. The continents were located at low and middle latitudes (around the equator) about 600 to 700 my ago. There was no tropical ocean. Heat lost by reflection from the rocks on the surface of the continents may have caused global cooling. (Note that land plants had not yet appeared.)
As continental glaciers and ice caps formed, the reflectivity of snow and ice caused further temperature decrease.
Glaciation was associated with a decrease in atmospheric CO2 and increase in O2.
Recall that CO2 increases the greenhouse effect and causes global warming. The decline in atmospheric CO2 may have led to cooling.
Decrease in CO2 was probably caused by the increase in the number of photosynthetic organisms (such as the cyanobacteria which formed stromatolites).
Limestones are associated with the glacial deposits, which is unusual. Limestones generally form in warm seas, not cold ones. The association of limestones with glacial deposits suggests that times of photosynthesis and CO2 removal alternated with times of glaciation.
Limestones (made of CaCO3) are a storehouse of CO2, which was removed from the atmosphere.
Glacial conditions may have inhibited photosynthesis by stromatolites. As a result, CO2 may have accumulated periodically and triggered short episodes of global warming. This produces the paradox of glaciers causing their own destruction.
October 30, 2005