Proof of stake is a method of maintaining the integrity of the blockchain, ensuring that users of a cryptocurrency cannot mint coins that they have not earned.
During this time, the difficulty level will increase to the point where proof-of-work cryptocurrency mining is eventually impossible.
When the TTD reaches 58,750,000,000,000,000,000,000, the network merges its execution layer with the new consensus layer and transitions to the new proof-of-stake consensus protocol.
The merger followed a series of rehearsals that tested the transition from proof-of-work to proof-of-stake on multiple testnet environments, including Ropsten, Sepolia, Goerli.