The original proof-of-stake blockchain, launched in 2020, was known as the Beacon Chain. Before enabling proof-of-stake consensus logic on Ethereum Mainnet, it was created to ensure its soundness and sustainability. As a result, it coexisted with the original proof-of-work Ethereum. On Ethereum, turning off proof-of-work and turning on proof-of-stake required instructing the Beacon Chain to accept transactions from the original Ethereum chain, bundle them into blocks, and then organize them into a blockchain using a proof-of-stake-based consensus mechanism.
At the same time, the original Ethereum clients disabled their mining, block propagation, and consensus logic, handing over control to the Beacon Chain. The Merge was the name given to this occurrence. There were no longer two blockchains after The Merge; there was only one proof-of-stake Ethereum chain.

The Beacon Chain is a foundational component of Ethereum 2.0, the upgrade transitioning Ethereum from a Proof-of-Work (PoW) to a Proof-of-Stake (PoS) consensus mechanism. Launched in December 2020, it introduced staking, allowing validators to secure the network by locking up ETH instead of relying on energy-intensive mining. The Beacon Chain coordinated validators, managed consensus, and enabled shard chains (scalability solutions) in Ethereum’s multi-phase upgrade. Though it initially ran parallel to the original Ethereum chain, it later merged with the Ethereum Mainnet in September 2022 (the "Merge"), fully transitioning Ethereum to PoS. This shift improved scalability, energy efficiency, and security, paving the way for future upgrades like sharding and layer-2 solutions. The Beacon Chain remains critical in Ethereum’s evolution toward a faster, more sustainable blockchain.