What Is a Block Header?
A block header is the part of a blockchain block containing data about the block.
This data includes a timestamp, difficulty target, Merkle root (to verify transactions), the previous block hash, and a nonce which is used for randomized hashing in the block mining process.
How Block Headers Function: An Overview
When mining blocks, miners collect the chosen transactions and create a block header that includes several elements critical to the mining process:
- Previous block hash: New blocks are formed from old ones. More specifically, the hash from the previous block is used in the mining process in combination with the nonce (more on that below) to find the next hash.
- Merkle root: Miners need a way to verify that the transactions they put inside a block are valid. Transactions packaged into a block can be verified using the Merkle root of their hashes.
- Timestamp: The block header includes the exact time it was created based on the miner’s system time. This value is later verified by other network participants.
- Difficulty target: A difficulty target controls the rate of block production in the face of rapidly improving computational capability and network participation. The network dynamically adjusts this target through consensus.
- Nonce: This element is a value chosen at random on every block creation attempt. It randomizes the input during the hashing process and, in doing so, changes the output hash. Once a hash matching the network’s current requirements is found, the nonce is baked into the final block header appended to the blockchain.
Conclusion
The block header is an essential element of every block in every blockchain. It holds the metadata necessary to continue the chain and review the validity of previous transactions.
