GEOLOGY

Detailed explanation-1: -Eras are further divided into periods, and periods are divided into epochs. Each unit of time is defined by specific events and changes that took place on Earth, such as the formation of the planet, the evolution of life, and mass extinctions.

Detailed explanation-2: -Very significant events in Earth’s history are used to determine the boundaries of the eras. Eras are subdivided into periods. The events that bound the periods are wide-spread in their extent but are not as significant as those which bound the eras.

Detailed explanation-3: -Two or more periods compose on Era. One Era is hundreds of millions of years in duration.

Detailed explanation-4: -The eras are the four major divisions of the geological time scale: Precambrian, Paleozoic, Mesozoic, and Cenozoic.

Detailed explanation-5: -Another common way world history is divided is into three distinct ages or periods: Ancient History (3600 B.C.-500 A.D.), the Middle Ages (500-1500 A.D.), and the Modern Age (1500-present).