according to the indian way of the measurement of time there are four major eras of the world, i.e. -'Sat', 'Tretaa', 'Dvaapar' and 'Kali'. Each of the them having twice greater than the other.
the time measurement of the Kali-era is 432000 earth years, in which by addition of the same can give thew measure of the other three, i.e. -
432000 * 2 = dvaapar-era
432000 * 3 = Tretaa-era
432000 * 4 = Sat-era (or Satyug)
The assembling of the four eras is called a "Mahayuga' or the Great era.
there are total of 71 Great-eras which are combined to form a "Manvantar' or the age of a Manu or an aeon.
There are total of 14 aeons or the ages of manu. According to the Hindu philosophy after every aeon there is a short catastrophe in which the whole world is sink down in the disastrous hands of the nature and one of the surviving human titled as manu is give the task to lay the foudation of the human race on the earth. he is often called as the "Progenitor" and titled as the king.
