Beacon Chain

The Beacon Chain went live on 1 December 2020 as a separate proof-of-stake chain running alongside proof-of-work Ethereum. At first it only coordinated validators and their deposits; it carried no user transactions. In September 2022 the Merge joined the two: the original chain became the execution layer, and the Beacon Chain became the consensus layer that decides which blocks are added and when they are final.

It organises time into 12-second slots grouped in epochs of 32 slots. In each slot one validator is chosen to propose a block and committees of others attest to it; once enough stake has voted across two epochs, blocks are finalised and practically irreversible. Staking deposits, rewards, penalties, slashing and withdrawals are all tracked here, so staking dashboards and explorers such as beaconcha.in read Beacon Chain data.

After the Merge the term is used less, since there is only one Ethereum, but it still names the consensus side. Early stakers locked ETH on it with no way to withdraw until the Shapella upgrade in 2023.