Vishnupurana 6.1.5

6.1.5

kṛtaṃ tretā dvāparaṃ ca kaliśceti caturyugam /
divyair varṣasahasrais tu taddvādaśabhir ucyate //

PARÁŚARA.--Hear from me, Maitreya, exactly the circumstances of the end of all things, and the dissolution that occurs either at the expiration of a Kalpa, or that which takes place at the close of the life of Brahmá. A month of mortals is a day and night of the progenitors: a year of mortals is a day and night of the gods. Twice a thousand aggregates of the four ages is a day and night of Brahmá. The four ages are the Krita, Treta, Dwápara, and Kali; comprehending together twelve thousand years of the gods. There are infinite successions of these four ages, of a similar description, the first of which is always called the Krita, and the last the Kali. In the first, the Krita, is that age which is created by Brahmá; in the last, which is the Kali age, a dissolution of the world occurs.