In the early 19th century, Agassiz was the first to suggest the 'Great Ice Period' theory, re-interpreting surficial deposits previously ascribed to marine inundation as glacial. Penck and Bruckner (1909) in probably the most influential early work on glacial cycles, linked four river terrace sequences in the northern Alps to four separate glacial episodes named in descending order of age - the Gunz, the Mindel, the Riss and the Wurm. Today, deep marine cores indicate the possibility of over 30 glacial-interglacial cycles since 2.6 million years ago. Marine records are complemented by much higher resolution ice core records for at least the last glacial cycle (120,000 years). A great deal of attention has been focused on the magnitude and duration of the last 5 stadial - interstadial events which comprise the last glacial cycle. In particular, termination 1, or the transition from the last glacial maximum to the
Holocene, has proven to be particularly well preserved, revealing the Younger Dryas - Bölling/Alleröd climatic transitions. Improved chronologies of these events suggest they may have been global in extent, extremely rapid and severe.
