Manvantara

Manvantara or Manuantara is a Sanskrit term which literally means "between Manus." H. P. Blavatsky defines it as "a period of manifestation, as opposed to Pralaya (dissolution or rest); the term is applied to various cycles, especially to a Day of Brahma--4,320,000,000 Solar years--and to the reign of one Manu--308,448,000--.

This concept is based on a cyclic model of the universe of alternating phases of creation and dissolution:

As the sun arises every morning on our objective horizon out of its (to us) subjective and antipodal space, so does the Universe emerge periodically on the plane of objectivity, issuing from that of subjectivity—the antipodes of the former. This is the "Cycle of Life." And as the sun disappears from our horizon, so does the Universe disappear at regular periods, when the "Universal night" sets in. The Hindoos call such alternations the "Days and Nights of Brahma," or the time of Manvantara and that of Pralaya (dissolution). The Westerns may call them Universal Days and Nights if they prefer.

There are different manvantaras according to the cycle of evolution in course:

There were several "Great Ages" mentioned by the ancients. In India it embraced the whole Maha-Manvantara, the "Age of Brahma," each "Day" of which represents the Life Cycle of a chain, i. e., it embraces a period of Seven Rounds (vide "Esoteric Buddhism," by A. P. Sinnett). Thus while a "Day" and a "Night" represent, as Manvantara and Pralaya, 8,640,000,000 years, an "age" lasts through a period of 311,040,000,000,000; after which the Pralaya or dissolution of the universe becomes universal. With the Egyptian and Greeks the "Great Age" referred only to the Tropical, or Sidereal year, the duration of which is 25,868 solar years. Of the complete age--that of the Gods--they said nothing, as it was a matter to be discussed and divulged only at the Mysteries, and during the Initiation Ceremonies. The "Great Age" of the Chaldees was the same in figures as that of the Hindus.