The Pleistocene was been characterised by repeated cycles of glaciation alternating with warmer interglacials. The last ice age, sometimes known as the "Great Ice Age" is known to have begun by 3 million years ago, making it not an exclusively Pleistocene phenomenon, beginning as it did in the Pliocene. It is believed that the glacial phases alternated with warmer interglacials up to possibly about 30 times since the Middle Pliocene.

It was not the first ice age, they have been occurring intermittently since the formation of the Earth. They have been found to have occurred at the end of the Eocene, about 35 million years ago. About 15 million years ago and, as part of the Terminal Miocene Event, about 6 million years ago, then the final glaciation, the Great Ice Age, began in the Pliocene about 3 million years ago, when the North Polar ice cap formed. The final peak of glaciation before the start of the present warmer phase occurred between about 16,000 and 14,000 thousand years ago.  This latest ice age had a direct effect on the evolution and lifestyle of humans leading up to the beginnings of  agriculture and the earliest beginnings of civilisation.

Considering the history of the world since the formation of continents it seems the normal condition of the world as a whole is is to have no polar ice caps and climates that were less seasonal than now, where the difference between winter and summer temperatures was less than at present. Ice ages have occurred about every 250 million years, each lasting about 50 million years. Based on this timetable it would seem the present warm phase would eventually end and be followed by a number of cold and warm phases for about another 15 million years. It hasn't been possible, so far for scientists to suggest when the present warm phase might end, especially as humans are changing the atmospheric chemistry so much by burning fossil fuels.

The climatic cycles of the Earth would have been strongly influenced by the breakup of Gondwana and the establishment of the Antarctic Circum Polar Current.

Pleistocene Climate

Sources & Further reading

1. Death of the Megabeasts, DVD, Madman, SBS
2. Josephine Flood, Archaeology of the Dreamtime, J. B. Publishing, 2004
3. Chris Johnson, Australia's Mammal Extinctions, a 50,000 year history, Cambridge University Press, 2006

Links