The genesis block is the first block of a blockchain. Every later block hashes back to it. It has no predecessor. Its hash comes from its own contents and a set nonce. Bitcoin's genesis block was mined by Satoshi Nakamoto on January 3, 2009. It included the text The Times 03/Jan/2009 Chancellor on brink of second bailout for banks, a newspaper headline used as a timestamp and a political note.
Immutability starts here. Every later entry traces to this block. Rewriting history means recomputing every later hash, which gets harder as the chain grows. The genesis block is hard-coded in the client so anyone can check the same root. It is the starting point that all subsequent blocks reference.
Because each block contains the hash of the block before it, the Genesis Block has no predecessor, its hash is calculated from its own contents and a predetermined nonce. The Genesis Block is hard-coded into the software, serving as a public anchor that anyone can verify.
Genesis Block Visualizer
Explore how the first block in a blockchain is created without a predecessor