DILIP RAJEEV
Whenever there is a decline of righteousness, O Arjuna, and rise of unrighteousness, then I manifest Myself! ( Verse 7, Chapter 4, The Gita, translated by Sivananda ) For the protection of the good, for the destruction of the wicked, and for the establishment of righteousness, I am born in every age. ( Verse 8, Chapter 4, The Gita, translated by Sivananda) In Indian cosmology, there have been four yugas on this earth, the first one having been 1.44 million years long, in human years, the last one 360 thousand, the four yugas being in 4:3:2:1 proportion in length, according to a few ancient sources. Sources vary in their opinions on the length of Yugas.
The Bhagavat Gita, Verse 6, Chapter 4, says, अजोऽनप सन्नव्ययात्मा भूतािामीश्वरोऽनप सि ।् प्रकृ नतं स्वामनधष्ठाय संभवाम्यात्ममायया ॥४-६॥ 242