The four eras of man kind :
According Hinduism there are 4 eras of man kind.
These eras are called Yugas.
Rita (satya) Yuga :
This is an era with a perfect world. There are no gods and demons and men
live without disease.
This Yuga will last for 1,7 million human years.
Treta Yuga :
This is the era of offering and the virtue decreased with one quarter.
This yuga will last for 1,3 million human years.
Dwapara Yuga :
This is an era of decline.
The Virtue decreased with a half. desire, diseases and misfortune came into the world. This yuga will last for 0,9 million human years.
This is an era of corruption.
Only one quarter is left of the virtue.
This Yuga will last for 0,4 million human years.
We live in the last yuga (kali yuga).
The four yugas together will last for 4,320,000 human years.
A 1000 of these periods are equal to one day of Brahma.
So 1 day of Brahma is equal to 4320 million human years.
One day in the live of Brahma is called Kalpa.
When Brahma wakes up and his eyes open the universe is created.
When he goes to sleep the universe will be destroyed.