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A blockchain is a growing list of records, called blocks, that are linked together using cryptography. It's also described as a "trustless and fully decentralized peer-to-peer immutable data storage" that is spread over a network of participants often referred to as nodes. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree). The timestamp proves that the transaction data existed when the block was published in order to get into its hash