Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 37

Sanskrit:

अयं तु कथित: कल्पो द्वितीयस्यापि भारत ।वाराह इति विख्यातो यत्रासीच्छूकरो हरि: ॥ ३७ ॥

ITRANS:

ayaṁ tu kathitaḥ kalpodvitīyasyāpi bhāratavārāha iti vikhyātoyatrāsīc chūkaro hariḥ

Translation:

O descendant of Bharata, the first millennium in the second half of the life of Brahmā is also known as the Vārāha millennium because the Personality of Godhead appeared in that millennium as the hog incarnation.

Purport:

The different millenniums known as the Brāhma, Pādma and Vārāha kalpas appear a little puzzling for the layman. There are some scholars who think these kalpas to be one and the same. According to Śrīla Viśvanātha Cakravartī, the Brāhma-kalpa in the beginning of the first half appears to be the Pādma-kalpa. We can, however, simply abide by the text and understand that the present millennium is in the second half of the duration of the life of Brahmā.