The sages of ancient India; thousands of years back in time, had studied and written the Cosmic Time Cycles, when most of humanity were living in caves. They understood that all of Existence; visible and invisible was governed by Time Cycles. These Cycles were fixed and their life span was pre determined and unchangeable.
The Cycles marked a progressive decay in the level or standards of Existence, till there was destruction; destruction was followed by re generation and this went on and on. The World we live on, the Continents, the Nations are governed by Time Cycles. This is not all even humans are subject to this unchangeable law; none escapes the Cycle of life and death.
Just as there is the birth and death of man; so also are civilizations and nation born and destroyed. We live at present in the Kali Yuga; the shortest of the Cosmic Time Cycles. We are in a period of progressive decay, which finally ends in doom.
There are 4 Yugas or Cycles; the next one being shorter in length by a ¼, than the one before it. The shortest being the Kali Yuga, lasting 432,000 years; a period of darkness and strife where there is total annihilation and after which reconstruction commences. A thousand such Yugas make a day in the life of Brahma.
A day in the life of the Creator Brahma comprises of 4320 Million years and at the end of this day the Universe, dissolves into Brahma. The night of Brahma; equal in span to the day, is a period of no creation. Creation commences at the end of the night, when Brahma wakes up. A year in the life of Brahma comprises of 360 days and hid entire life span is of 100 years; a mind boggling 311,040 Billion years.
The end of the life span of Brahma marks total dissolution of everything and this includes Brahma himself and the dissolution lasts for a period equal to that of the life of Brahma. Then a new Brahma manifests and this unending cycle of Creation and Destruction goes on and on.