Brahma lives hundred years, but they are years of Brahma, not human years.
One Kalpa coincides with one Day of Brahma's life, and when the night will come, this Universe will be reabsorbed (Pralaya) in his divine sleep.
One Kalpa (Day or Night of Brahma) corresponds to 4.320.000.000 earthly years.
Indeed earthly time is divided in Yuga or Ages, which are:

Krita (or Satya)-Yuga	4.800 years
Treta-Yuga	3.600 years
Dwapara-Yuga	2.400 years
Kali-Yuga	1.200 years
tot.	12.000 years

Each Yuga's lenght decrease progressively in relation to moral and physical decadence in each age. Troughtout the Satya Yuga virtue prevails and evil is unknown; in the Treta Yuga virtue falls by a fourth; in the Dwapara Yuga virtue has diminished by half; in the Kali Yuga, the current age, but a fourth of virtue remains.
The four Yuga make one Mahayuga or Caturyuga.The Mahayuga's 12.000 years must be multiply by 360, the days of the human year.

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