4.32 billion years
Brahma is a metaphor for the creative impulse in the cosmos
A Kalpa or 4.32 billion years is one day for Brahma
Manu is the metaphor for the supervisory impulse in nature
Supervisory impulse changes 14 times in a Kalpa
Certain order prevails among created beings during a Manu period
This order can change at the end of a Manu period
Dominant species can vanish at the end of a Manu period
12,000 precession cycles fit in a Manu period
Precesssion is the slow drift of seasons over centuries
Surya Siddhanta Text
An ancient Sanskrit text documents ancient knowledge of precession!
I published a book "Ancient Skies & Astronomy Now" with amazing and accurate facts known to ancient Indian astronomers.