Matsyapurana 142.19

142.19

catvāryāhuḥ sahasrāṇi varṣāṇāṃ tatkṛtaṃ yugam
tasya tāv acchatī saṃdhyā saṃdhyāṃśaśca tathāvidhaḥ //

The duration of the ages have been laid down on the Divine units The Bhâratakhaṇḍa notices four yugas or ages, viz., Kṛitayuga, Tretâ, Dvâpara, and Kaliyuga Of these Kṛita or Satyayuga is the first, Tretâ is the second after which come Dvâpara and Kaliyuga Satyayuga consists of 4000 Divine years Its Sandhyâ consists of 400 Divine years and the Sandhyâṁśa of the same number of years Tretâ consists of 3 000 Divine years This is what has been said about it by those well up in calculations Its Sandhyâ is made up of 300 Divine years and the Sandhyâṁśa is also of similar duration Dvâpara consists of 2,000 Divine years and its Sandhyâ and Sandhyâṁśa of 200 years each Kaliyuga is of 1,000 Divine years and its morning and twilight are each of 100 years—18-24