Shilad requested Indra to shed light on the special characteristics of each of the four eras.
Indra replied—Lord Brahma created the four eras (yugas)–Satya, Treta, Dwapar and Kali. These eras keep on occuring in a cyclic order where the former is followed by the latter. Satva guna (Pure) prevails during Satya Yuga. Rajas guna is the dominant quality prevailing during Treta Yuga. During Dwapar Yuga both Rajas guna and tamas guna are present. Tamas guna (Dark) is the dominant quality prevailing during Kali Yuga. During Satya Yuga, meditation was the means by the help of which a man could achieve salvation while oblation, devotion and donation were said to be the means capable of giving salvation during Treta Yuga, Dwapar Yuga and Kali Yuga respectively.
The inhabitants of Satya Yuga were virtuous and free from sorrow. But the vice of desire started to raise its head during Treta Yuga and people started being troubled by it. Lord Brahma created the warrior caste Kshatriya for the protection of virtuosity. Brahma propogated the rituals of oblation during Treta Yuga. Everything was fine till Treta Yuga but there was a drastic change in the human behaviour during Dwapar Yuga. All the vices surfaced and people were troubled by them. Some extraordinary literary feats were accomplished during dwapar–Sage Vyasa categorized the veda into four sections, all the major Puranas were compiled and smritis were written. Kali Yuga saw the decline of virtuosity and religiousness. Ignorance and false knowledge prevailed everywhere during this era.