The Driftless zone was relatively unaffected the last time one of these occurred.
The Huronian one may have been triggered by the oxygen castrastrophe. The Driftless zone was relatively unaffected the last time one of these occurred. Variation within one of these can be caused by Milankovitch cycles. An event called the Wisconsinan occurred during the most recent one which is named for the Pleistocene epoch. During these time periods, relatively drumlins and moraines were formed. For 10 points, name these periods of low global temperatures and increased glacial extent.
The Huronian one may have been triggered by the oxygen castrastrophe.
{ice age} [accept {glacial age} or {glacial period} before mentioned]