Geology - Glacial age

Ice Age

Vulcanism

One theory is the large amount of Volcanic activity can cause an Ice age . This theory works based on recent evidence when Mt . Pinatubo in the Philippines erupted in 1991 the vast amounts Volcanic gas actually caused world wide temperatures to drop if only by a small degree However , this theory is countered by the fact that large number of volcanoes simply do not erupt in unison and there is little evidence of large numbers of volcanoes erupting simultaneously

Snowball Earth

There is also the Snowball Earth

hypothesis which maintains that the severe freezing in the late Proterozoic was ended by an increase in CO2 levels in the atmosphere . Conversely the drop in Greenhouse gasses in the atmosphere was what began the Ice age . This theory proposes that changes in the earth 's Atmosphere cause the ice age to occur . It can be seen in current times , rising CO2 and other greenhouse gas levels are in fact , causing the Earth 's temperature to rise . However it is hard to determine what caused the greenhouse gas levels to drop in the first place

Position of the Earth 's orbit

This theory is perhaps the most plausible . The Earth is not orbiting the Sun in a perfectly ly circle . The orbit can fluctuate . Given how sensitive the Earth 's biosphere is even just a small change in the earth 's orbit an cause global temperatures to drop dramatically . This theory is supported by evidence that the orbits of other planets are not consistent . The main con is that based on these orbital fluctuation cycles , the Earth should be in ice age right now...