from two million to 11 thousand years ago; extensive glaciation of the northern hemisphere; the time of human evolution
any period of time during which glaciers covered a large part of the earth's surface
highly significant or important especially bringing about or marking the beginning of a new development or era
a period marked by distinctive character or reckoned from a fixed point or event
a unit of geological time that is a subdivision of a period and is itself divided into ages
(astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded
