Era

Era, term used in physical science and history. In geology an era is a major division of time. Eons, the longest division of time, are subdivided into eras and eras are subdivided into periods. The present, or Cenozoic Era, the shortest of all eras, has already covered a period of about 65 million years. In a historical sense, an era is a period of time computed from a specific moment or event. The present chronological era, the Christian Era, began on January 1 in the year 1 ad, conventionally fixed as the date of the birth of Christ.