The four yugas is a unique concept associated with Hinduism. This calculation of time in Hinduism is cyclical, not linear. A cycle of manifestation and dissolution is divided into four Yugas – Satya (Krta), Treta, Dwapara and Kali.
The four yugas is like a downward graph when it is studied on the basis of human activity. There is a gradual deterioration in the condition of human life and activity with the passing of each yuga.
The duration of the different yuga is as follows:
Satya – 1,728,000 human years
Treta – 1, 296, 000 human years
Dwapara – 864,000 human years
Kali – 432,000 human years
We are living the Kali Yuga, which began in 3102 BC.
The symbolic color associated with each yuga is as follows
Satya – White
Treta – Yellow
Dwapara – Red
Kali – Black
The four yugas are taken to be a Maha Yuga.
A Maha Yuga is one day and night of Brahma.
As per Hinduism, universe is Anadi – Ananta – without beginning and without end. Thus it goes through recurrent phases of manifestation and dissolution.