There is no set duration for an era. Instead, it is a temporal frame distinguished by specific traits, like historical occurrences. Periods make up an era in geology.
The Encyclopedia Britannica claims that geological eras span millions of years. Geologists consider the Paleozoic, Mesozoic, and Cenozoic eras to be the three primary geological periods.
For instance, the Mesozoic Era lasted roughly 185.5 million years, whereas the Paleozoic Era lasted roughly 291 million years. When measured from the beginning of time to the present, the Cenozoic Era has lasted roughly 65.5 million years.
Historical eras can be characterised by particular historical occurrences or by distinct time periods. For instance, the reign of Queen Elizabeth the First, who ruled England from 1558 to 1603, is what is known as the Elizabethan era.