The
geologic clock below depicts to scale the major
units of geological time along with pivotal milestones
of the history of Earth and life. The Hadean eon is now officially
by the International Commission on Stratigraphy taken to begin
at 4.0 Ga (billion years ago). Other geological period major
events in the evolution of
life on Earth; the Archean and Proterozoic are both eons,
the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic
eon. The two million year Quaternary period, the time of recognizable
humans, is too small to be visible at this scale. |