Wikibooks: Historical Geology/Ice ages

• Format: Book
• Language: English
• Subjects: Greenland; Antarc*; Antarctica
• Online Access: https://en.wikibooks.org/wiki/Historical_Geology/Ice_ages

In this article we shall look at what an ice age is what causes ice ages and how we can identify the evidence for ice ages in the geological record. The reader will probably find it useful to look back at [[the main article on glaciers]] before reading further. =Definition of an ice age= An ice age or to use the more technical term a glaciation may be defined as a time when [[continental glaciers]] are present. This of course means that we are currently experiencing an ice age since there are continental [[glaciers]] on Antarctica and Greenland. To be more precise we are living in an interglacial a warmer interval within an ice age when the glaciers have retreated towards the poles. =Glaciations in the geological record= Geologists have identified and dated a number of ice ages in the geological record The Huronian glaciation (or Makganyene glaciation) extended from 2400 to 2100 million years ago The Cryogenian glaciation lasted from 850 to 635 million years ago. The Andean Saharan glaciation was from 460 to 430 million years ago. The Karoo Ice Age lasted from 360–260 million years ago. The Pliocene Quaternary ice age is the one now in progress and started about 2.6 million years ago. The methods of dating events have already been explained in other articles later in this article we shall discuss how we identify ice ages. =Causes of ice ages= We have quite a good idea of the causes of the present ice age which can be explained by continental drift affecting the oceanic circulation. The causes of previous ice ages are more obscure and debatable. This is because causality as such is not preserved in the geological record. We may be able to see that event A happened and was followed by event B but the fact (if it is a fact) that event A caused event B must be established on theoretical grounds by understanding the relationship between the events of the type in question. For example it is not hard to deduce a causal relationship between the feet of dinosaurs and dinosaur footprints because we have a good general ...