Vishnupurana 6.1.p2

6.1.p2

Parāçara said:—Hear from me exactly, O Maitreya, the circumstances attending the dissolution of the world either at the expiration of a Kalpa or that which occurs at the close of the life of Brahmā. A month of men constitutes a day and night of the progenitors; a year of men is a day and night of the celestials. Twice a thousand aggregates of the four ages is a day and night of Brahmhā. The four ages are the Krita, Treta, Dwāpara and Kali, comprehending altogether twelve thousand years of the celestials. There are infinite successions of those four ages of a similar description, the first of which is always called Krita and the last the Kali. In the first, the Krita is that age which is created by Brahmā; in the last, which is the Kali age, a dissolution of the universe takes place.