The process that maintains this trustless public ledger is known as mining. Undergirding the network of Bitcoin users who trade the cryptocurrency among themselves is a network of miners who record these transactions on the blockchain.
Recording a string of transactions is trivial for a modern computer, but mining is difficult because Bitcoin’s software makes the process artificially time-consuming. Without the added difficulty, people could spoof transactions to enrich themselves or bankrupt other people. They could log a fraudulent transaction in the blockchain and pile so many trivial transactions on top of it that untangling the fraud would become impossible.
By the same token, it would be easy to insert fraudulent transactions into past blocks. The network would become a sprawling, spammy mess of competing ledgers, and Bitcoin would be worthless.
Combining “proof of work” with other cryptographic techniques was Nakamoto’s breakthrough. Bitcoin’s software adjusts the difficulty miners face in order to limit the network to a new 1-megabyte block of transactions every 10 minutes. That way, the volume of transactions is digestible. The network has time to vet the new block and the ledger that precedes it, and everyone can reach a consensus about the status quo. Miners do not work to verify transactions by adding blocks to the distributed ledger purely out of a desire to see the Bitcoin network run smoothly; they are compensated for their work as well. We’ll take a closer look at mining compensation below.