Block Anatomy Explorer

The block version number indicates which set of block validation rules to follow. Version 1 was used from the genesis block. Later versions (2, 3, 4) activated soft forks like BIP34 (height in coinbase), BIP66 (strict DER sigs), and BIP65 (CHECKLOCKTIMEVERIFY).

A 256-bit hash referencing the previous block. The genesis block has all zeros because there is no preceding block. This field creates the "chain" in blockchain - each block cryptographically commits to the entire history before it. Changing any prior block invalidates all subsequent hashes.

The root of a Merkle tree (binary hash tree) of all transactions in the block. Allows efficient verification that a transaction is included without downloading all transactions (SPV proofs). The genesis block's Merkle root is just the hash of the single coinbase transaction.

Unix timestamp of when the miner started hashing the block header. Nodes reject blocks with timestamps more than 2 hours in the future. The median of the last 11 blocks must be less than the new block's timestamp. This prevents timestamp manipulation for difficulty gaming.

Compact representation of the target threshold. The block hash must be below this target to be valid. Difficulty 1 (the genesis value) means the target is the maximum possible. Adjusts every 2,016 blocks (~2 weeks) to maintain ~10 minute block intervals regardless of total network hash power.

A 32-bit number miners increment to find a hash below the target. With modern difficulty, 2^32 nonces are insufficient - miners also vary the coinbase transaction's extra nonce, timestamp, and transaction ordering. The genesis nonce means Satoshi tried ~2 billion combinations before finding a valid hash.