Geologic Era

An era is the second largest geochronologic time unit and is equivalent to a chronostratigraphic erathem. The cited article, Geologic time scale, which also defines the other three ranks because their own titles redirect to it, says there are ten defined eras, with none in the Hadean eon: the Eoarchean, Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic and Cenozoic. It adds that many of the names of erathem or era rank in use on the modern International Chronostratigraphic Chart were determined during the early to mid nineteenth century. Time units of this rank in the atlas are grouped under this entry.