- Krita (done/made/created) had 100% dharma. Its Yuga dharma was that if one becomes adharmic, entire world suffers for his/her misdeeds. So, there were multiple incarnations, gods to relieve people from adharma. Every thing was made either by someone
- Treta (Tre = Three + ta = left) had 75% dharm. Its yuga dharma was that if one becomes adharmic, only people of his kingdon will suffer. Vaali, Ravana became adharmic.
- Dwapara (Dwa = Two, Para = Gone/Passed/Done) had 50% Dharma. Its yuga dharma was that if one does mistake, his family suffers. Yudhishtir gambled and his brothers+wife suffered. Duryodhana became adharmic and he along with his brothers died (along with those who supported him).
Brahma time related to Human time
From the same source, 12000 years make a Yuga ( = Krita + Treta + DwApara + Kali). Thousand such Yuga-s duration make Brahman’s day (i.e. morning, to be specific) and Thousand such Yuga-s duration makes Brahman’s night.
The learned say that these twelve thousand years constitute what is called a yuga. A thousand such yugas compose a single day of Brahman. The same is the duration of Brahman’s night.
That means Brahman’s full cycle constitutes 24 million years.
What happens during Brahma day and night
The manifestation occurs only during the 1st half of 12 million years. Remaining part is completely void or Moskha.
With the commencement of Brahman’s day the universe begins to start into life. During the period of universal dissolution the Creator sleeps, having recourse to yoga-meditation. When the period of slumber expires, He awakes. That then which is Brahman’s day extends for a thousand such yugas. His nights also extends for a thousand similar yugas. They who know this are said to know the day and the night. On the expiry of His night, Brahman, waking up, modifies the indestructible chit by causing it to be overlaid with Avidya. He then causes Consciousness to spring up, whence proceeds Mind which is identical with the Manifest.
This has a striking similarity with what Krishna said in Gita:
BG 8.17, 8.18, 8.19 – Knowing that thousand eras constitute a day of Brahman, [and] thousand eras complete a night, are the people who know day, [and] night. On arrival of day, all manifestations originate from “Unmanifest”; On arrival of night they annihilate into [what is] known as “Unmanifest” only. This [same] elementary world only happens again & again; Annihilates upon arrival of night, [and] originates upon arrival of day.
Maha Vishnu 