The first blockchain was developed by Satoshi Nakamoto, the inventor of bitcoin. It uses what's known as the Nakamoto Consensus which relies on: 1) 'proof of work' to decide who gets to add the next block, and 2) 'longest chain' to decide which block it gets added to. You guessed it - the longest one!In proof of work, all nodes act as validators. They race to solve complex cryptographic problems. This is called mining. The winner of the race - that is, the first validator to solve the problem - selects the transaction data to include in the block, add it to the longest chain, and receive the block reward.

The rest of the validators or miners then check to ensure the solution was correct and that the block was added to the longest chain.Although proof of work is a trusted and robust method, it is also very time and energy-consuming because all nodes are racing to solve the problem even though only one wins. The carbon footprint of bitcoin has been compared to that of a small country. Over time, other methods of arriving at a consensus have been developed. Notably, proof of stake.