The Cryogenian Period
This was the second period of the Neoproterozoic era that lasted from 850 million years to about 635 million years ago and the name was derived from the Greek word meaning “cold”. During this season the earth saw two major glaciations called the Sturtian and Marinaon that covered the entire earth leading to the snowball earth scenario. This era is sometimes referred to as the Varangian due the glaciations called the Varanger that took place about 800 to 630 million years ago.
The concept of the snowball earth was derived from the theory that when the glaciations were too intense which was enough for the glaciers to reach about 30 degrees of the North and the South latitudes, the albedo of the earth rose sufficiently to reflect a large part of the sunlight back into the space causing a series of cascading event that resulted in further glaciation covering the entire earth down to the equator making it appear like a snowball from the space.
It has been assumed that the existence of the super continent of Rodinia in the southern ocean prevented the proper flow of the ocean currents required for transferring heat between the equator and the poles. The snowball earth resulted in the compartmentalization of the earth’s geographical zones and even the water cycle was hampered. The snow over the ocean prevented the evaporation of the sea water and hence in its due course coming down back to this earth as rain or snow. The ocean chemistry was changed due to the volcanism underneath the sea as the gases were unable to escape freely. The dry climate prevented the natural movements of the sediments to the sea along with rain water. The carbon cycle was affected too, the rain water washed off carbon dioxide from the atmosphere. and the rainwater mixes with the rocks to form carbonates and bicarbonates. These finally washed down to the sea beds which wasn’t possible during this era. The carbon excursions during this Neoproterozoic era proved that unusual things happened with the carbon cycle though the interpretations were not settled.
The scenarios which can we assume most commonly that ended the snowball era was the accumulation of the carbon dioxide due to volcanism where the gases could not escape the earth’s atmosphere. . Excessive rise of the carbon dioxide caused the greenhouse effect and helped the earth’s temperature to rise nearly to 50 degrees causing the ice to melt off before the carbon dioxide escaped into the atmosphere. The cap carbonates proves this excessive rise of the carbon dioxide in the earth’s atmosphere.
Life in the Cryogenian period was, as expected, affected by massive glaciations and snowball earth. Studies claim that there was a dip in the abundance of all kinds of life forms in this period but there are some contradictory theories too. Several species may have evolved during this time period and have undergone significant changes and developments. The Cryogenian period saw the influx of the red and blue algae, ciliates, dinoflagellates and testate and also amoeba that are very significant as they are the first fossils that were evident of the eukaryotic heterotrophs.