The Merge, which took place around September 2022 (depending on the source you consult), was a pivotal moment in Ethereum's history. It marked the successful transition of the Ethereum network from a Proof-of-Work (PoW) consensus mechanism to a Proof-of-Stake (PoS) one. Here's a breakdown of what happened during The Merge:

Before The Merge:

Proof-of-Work (PoW): Ethereum previously relied on a PoW system, similar to Bitcoin. In PoW, miners used powerful computers to solve complex puzzles, validating transactions and securing the network. This process, however, was energy-intensive and expensive.

The Merge:

Two Chains Merge: The Merge wasn't simply a switch. It involved merging the existing Ethereum mainnet (responsible for processing transactions) with the Beacon Chain, which had been operating in parallel since December 2020.
Beacon Chain Takes Over: The Beacon Chain, which already used PoS, became the central engine for block validation. Validators, who staked their ETH (Ethereum tokens), replaced miners as the network's security force.

After The Merge:

Increased Efficiency: PoS consumes significantly less energy compared to PoW. Estimates suggest a reduction of over 99% in energy consumption for Ethereum transactions.
Enhanced Scalability: While not the sole solution, PoS paves the way for future scalability improvements for the Ethereum network.
Environmental Impact: The shift to PoS makes Ethereum a more environmentally friendly platform.
Staked ETH: Staking ETH became a way to participate in network security and earn rewards.

What Didn't Change:

Existing Transactions: The Merge did not affect the history of transactions already processed on the Ethereum blockchain. Everything remained intact.
Ether (ETH): The native currency of Ethereum, ETH, remained the same.

The Merge marked a significant step towards a more sustainable and scalable Ethereum network. While it wasn't a complete overhaul, it laid the groundwork for future advancements in the Ethereum ecosystem.