an era is a very long span of geologic time
No, a geologic era is a longer unit of time than a geologic period. Geologic eras are divided into periods, which are further subdivided into epochs. The hierarchy from largest to smallest is era, period, epoch.
Era
After an era, the next smallest division of time would be an epoch. An epoch is equal to around 10,000,000 years, where as an era is 100,000,000 years.
A period is smaller than an era in the geologic time scale. It is further subdivided into epochs and ages.
The 3 eras of geologic time is Palezozoic era, Mesozoic era, and Cecozoic era
Precambrian Era.
precambrian times
Eon.
The order of units of geologic time from longest to shortest is: eon, era, period, epoch.
Era
Era
This period is called holocene.