As per Hindu cosmology, the world was created only to get destructed completely and once that happens, this destruction will once again give way to Creation. As per the timeline of gods, especially Pravu Bramha, this takes just the duration of one day and night which in our timeline, would be 40K years. According to Hindu Vedas and scriptures, the universe is made up of four Yugas or epochs which also mean ages or the cycle of time −
The Yugas get repeated in a cyclical method that is similar to the rising of tides, the four seasons, or the waxing and waning of the moon. Based on the Manu laws the length of each Yuga they say is as follows −
4800 years + 3600 years + 2400 years + 1200 years = 12000 years. This is just half a cycle and so, the full cycle takes 24, 000 years to complete. Each Yuga denotes the decline and demolition of dharma and virtue.
Satya Yuga − Dharma was at its peak during this period while the human caliber was predicted at 21 cubits. The average human life during this time was 100, 000 years.
Treta Yuga − The virtue declined to one - fourth of the Satya Yuga during this time with the human caliber reduced to 14 cubits. The average life expectancy for a human was 10, 000 years at this time.
Dvapar Yuga − Virtue reduced to half during this period while sin took rest of the half. The human caliber at this point was reduced to 7 cubits while the human life expectancy declined to 1000 years.
Kali Yuga − This is the worst of the Yugas where virtue is reduced to only one quarter and the remaining is a sin. While the Human caliber reduced to as low as 3.5 cubits, the average human life expectancy is at 100 years. According to Vedas, the average human life expectancy is expected to go down to 20 years which is said to be the worst dark age.