Ice age

The earth is currently in the Late Cenozoic Ice Age, an ice age that began 33.9 million years ago with the Antarctic Ice Cap.

The cause of ice ages, Köppen decided, is to be found in cool summers, not brutal winters.

[…] and the sloping collection of fractured rocks—known as talus—that tumbled down from the quartzite bluffs during the repeated freezings and unfreezings of the last Ice Age.