Expert: John Shea - 3/6/2005

Question
* What are Iceages
* When was the last Iceage
* Does an iceagen kill many people
* Will there be another iceage
* How many Iceages have there been

Answer
Hi Taryn
Ice ages are periods when there are extensive glaciers stretching away from the North and South pole towards the equator.  Because there are more continents closer to the North Pole, the glaciers tend to be more extensive in the north.  There are also glaciers that form on mountains in tropical latitudes.
For about the last 900,000 years, Ice Ages have occurred about every 110,000 years.  They are separated by warm periods, called interglacials, which are of shorter duration.  The last Ice age lasted between about 70,000-13,000 years ago.
Ice Ages probably moved people around (away from the pole, towards the equator, and to lower elevations) but our species actually underwent a dramatic expansion of our geographic range during the last Ice Age.  At 70,000 BP humans lived only in Africa, the Near East and possibly some parts of Southern Asia.  By 13,000 years ago, we were present all over Europe, Asia, Australia, and the Americas.
The ice ages are caused largely by predictable eccentricities in the Earth's orbit. We're due for the onset of another Ice Age in 3000-5000 years, unless it is delayed by global warming.
Over the course of the last 900,000 years, there have been about eleven major Ice Ages.  We know this by analysis of oxygen-isotopes in sediment cores drilled in the ocean bottom and ice cores drilled in Greenland and Antarctica.  For more on this, consult any basic geology textbook.
A good reference
Imbrie, J. &  Imbrie, K. P. (1979). Ice Ages: Solving the Mystery. Cambridge, MA: Harvard University Press.

Cheers
John Shea