Where did the idea of blockchain come from? Git was already using it since 2005 With bitcoin's blockchain, each block's hash is computed with the previous block's hash. That makes all blocks an immutable chain.

This is not the first time people used a hash-chain. As far as I know, Git was already used it since 2005 for the commit-hash computing.

So, what is the earliest use of hash chains? Where did the idea of blockchain come from?
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)