Where did the idea of blockchain come from? Git was already using it since 2005
According to Bitcoin and Cryptocurrency Technologies (BaCT), the Princeton Bitcoin textbook, the block chain dates back to a "paper by Haber and Stornetta in 1991. Their proposal was a method for secure timestamping of digitaldocuments, rather than a digital money scheme." (BaCT p.15)

The chaining of Merkle trees instead of single documents was proposed in a later paper. (BaCT p.16)