The genesis block is the very first block in a blockchain, block number 0 (or 1, depending on the chain). It is hardcoded into the node software, has no previous block to reference, and serves as the foundation on which the entire chain is built. Every blockchain has exactly one genesis block.
What Is a Genesis Block?
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The short version
The genesis block is page one of the ledger, the starting point everyone agrees on before the system starts running. It's baked into the software itself, so every node begins with identical history. Without agreement on the genesis block, nodes can't agree on anything that follows.
How It Works
Unlike all subsequent blocks, the genesis block is not mined or validated through normal consensus, it's defined in the node software's source code. It typically contains: a timestamp, a difficulty target, a nonce, and often symbolic data. Bitcoin's genesis block (January 3, 2009) famously contains the newspaper headline about bank bailouts. Ethereum's genesis block (July 30, 2015) includes the initial account state from the presale. The genesis block's hash serves as the ultimate root reference, the chain's identity. Forks that share a genesis block share history up to their divergence point.
Bitcoin's genesis block details
Block 0, mined January 3, 2009. Previous block hash: 0000...0000 (all zeros, there is no previous block). Merkle root: points to a single coinbase transaction creating 50 BTC to address 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa. Those 50 BTC are unspendable due to a quirk in the original code. The coinbase contains the hex-encoded text: "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks." This proves the block wasn't pre-mined before that date and makes a political statement about the financial system Bitcoin was designed to provide an alternative to.
What People Get Wrong
The genesis block was mined normally
It was hardcoded, not discovered through proof of work. The nonce and hash in it are predetermined. It's a convention, not a computation result.
You can spend the genesis block reward
On Bitcoin, the genesis block's 50 BTC are provably unspendable due to how the code was originally written. Satoshi may or may not have done this intentionally.
All blockchains have the same genesis block format
Each blockchain defines its own genesis structure. Ethereum's genesis includes initial account balances (from the token sale). Bitcoin's has only the coinbase transaction.
Keep Reading
Sources & Further Reading
- Bitcoin Genesis Block (Blockstream Explorer)
View the actual Bitcoin genesis block and its embedded newspaper headline
- Ethereum Genesis State
The Go Ethereum source code defining the Ethereum genesis block
Questions People Also Ask
- When was Bitcoin's genesis block created?
- January 3, 2009 at 18:15:05 UTC. The timestamp is embedded in the block and verified by the newspaper headline reference.
- What is the genesis block hash for Bitcoin?
- 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f, the hash of the very first block, referenced by block 1.
- Can the genesis block be changed?
- Only by creating a new, separate blockchain. Changing the genesis block would create a different chain identity that existing nodes wouldn't recognize.