Apologies for the delay in rebooting the Whatlington and Vinehall Street Archive,this posting describes a period when the planet's surface was covered in snow and ice is written at the same time the village has entered a period when the snow and ice has covered much of the Whatlington and Vinehall Street.
The Cryogenian period combines the two Greek words for both "ice" and "birth" and it suggests that this period that ran from 850 to 630 million years ago. Within these 220 million years, the Earth had to deal with two glacial periods - the Sturtian and the Marinoan - where the glacial work extended to the the equator.
It is possible to record the work of erosion by ice (glacial erosion) by studying the palaeo-landscape and the debris left by the glacial retreat (the warmer climate melts the ice). These deposits have been found in Australia, China, Congo, Ireland, North America, Norway, the Sahara desert and Scotland.
The Sturtian glacial period is estimated to have run from 750 to 700 million years ago, whereas the Marinoan (also known as the Varanger - named after the Norwegian fjord where tillite (glacial deposit) was found by Reusch in 1891) ended in ??
There are several mdoels or hypotheses that suggest the potential process or cause for the initial conditions for the model of Snowball Earth (they can be found here of which I have summarised below):
Williams (1975) proposed that the angle of the Earth's orbit was greater than the present angle; if the angle were greater than 54 degrees, the energy from the sun would heat the polar regions more than the equator and potentially allow glaciers to form around the equator. The Milankovitch cycle, named after a Serbian civil engineer and mathematician, suggests that a global wobble of a few degrees over a period of tens of thousands, but not tens of degrees. A study of stromatolites (remember those?) in the 1980's suggest that the angle of the Earth to the sun was within its present limits.
Another model suggested that the sun's heat was less than today due to the maturation of the sun, this may have led to the planet more susceptible to global freezing and despite an early glacial period, the Huronian glaciation in the Siderian Period, it does not suggest why more glacial periods did not occur previously.
There are more three more theories that range from a change in the sea levels that affected the global energy budget; the global location of the continents around the equatorial region that led to a change in the carbon dioxide levels in the atmosphere; even the break up of the supercontinent Rodinia may have led to Snowball Earth.
Equally, there are a similar number of theories that led to the melting of the two glacial periods and these can be found here.
