carboniferous glaciation
Figure modified after Scotese, C.R., 2001, Atlas of Earth History, Volume 1.

Several times in its history parts of the Earth have been covered by ice. The latest Ice Age started with a global cooling about 1.6 to 1.8 million years ago. Since then the Earth’s climate has been punctuated by an intermixing of warm and cold stages, with at least six major periods of ice advance and retreat. The periods when ice was either extensive or advancing are known as glaciations, while those times when ice was in sustained retreat are known as de-glaciations. In both instances, ice-affected areas were the subject of significant landscape changes as a result of the processes of 'glacial erosion' and 'glacial deposition'.

The 'Ice Age' is more formally referred to as the Pleistocene period, which is in turn the main period in the Quaternary era, the other being the Holocene period which covers the most recent 10,000 years. Two major glaciations have affected Ireland during the last half million years:

(1) the 'Munsterian' (300,000 to 132,000 years before present).

(2) the Midlandian (79,000 to about 13,000 years before present, including a long 'mild' stage).