Climate during the Pleistocene epoch
to 10 kya) continued to become cooler, and the earth entered a period
of constantly fluctuating climate
known as the Great Ice Age
; the fluctuations were minor until about 800 kya
, when periods
of intense cold occurred about every 90 ky, with minor oscillations about 20 ky and 40 ky apart; about one third of the earth’s surface was covered during glacial maxima; sea levels fell at least 100 m (some report up to 250 m) as sea water
became permanently locked up in glacial ice sheets.