// Mikey, The young earth theory emanated from James Ussher, Archbishop of Armagh, in the 17th century. The rest have jumped on that bandwagon. //
further on it says
Ussher's proposed date of 4004 BC differed little from other Biblically-based estimates, such as those of Jose ben Halafta (3761 BC), Bede (3952 BC), Ussher's near-contemporary Scaliger (3949 BC), Johannes Kepler (3992 BC) or Sir Isaac Newton (c. 4000 BC).
Numerology in the seventeenth century was a big thing
Dimensions of the temple had mystical meaning
I think Bishop Ussher himself would be surprised to be told he led the pack