from 13 million to 2 million years ago; growth of mountains; cooling of climate; more and larger mammals
highly significant or important especially bringing about or marking the beginning of a new development or era
from 13 million to 2 million years ago; growth of mountains; cooling of climate; more and larger mammals
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
