Ethereum has undergone many transformations over the years, and it can be difficult to keep the changes in order.
Ethereum, the second most significant blockchain, is perhaps also the most evolved network based on the series of critical hard forks it has undergone. These changes represent more than just technical revisions.
They represent growth and the continued efforts to take Ethereum mainstream.
From inception to the total transition of the consensus mechanism, these are the ten most significant Ethereum hard forks in order.
The Frontier Thawing, also known as the Ice Age, was one of the first unplanned forks on the Ethereum blockchain, which came into effect on September 7, 2015, at block number 200,000. Essentially, this fork lifted the 5,000 gas limit per block and established the default gas price at 51 GWEI.
This fork was crucial as it introduced the difficulty bomb, a mechanism designed to increase the difficulty level of the mining process as a way to disincentivize mining and encourage the transition from Proof-of-Work (PoW) to Proof-of-Stake (PoS), a more energy-efficient consensus mechanism.
In addition, it provided security and speed updates that made the network more robust and capable of handling transactions more efficiently, laying the groundwork for future updates.
The Homestead upgrade, which took place on March 14, 2016, was the first planned hard fork on the network. It introduced several protocol improvements to enhance the system's robustness, marking the departure from the beta phase of Ethereum.
These changes came from three Ethereum Improvement Proposals (EIPs), namely, EIP-2, EIP-7, and EIP-8, which aimed at refining the functionality of the Ethereum blockchain, more precisely, smart contract creation and development protocol forward compatibility.
The Homestead upgrade laid a foundation for Ethereum's continued development and paved the way for the blockchain's maturity and widespread adoption.
The DAO Fork is the most significant hard fork in the early years of Ethereum. It was executed on July 20, 2016, due to a DAO (Decentralized Autonomous Organization) attack, which led to the loss of 3.6 million ETH.
The Ethereum community voted to move the affected funds to a new contract to allow the original owners to withdraw their funds at a rate of 1 ETH for every 100 DAO tokens they had. This led to a rift within the Ethereum community, resulting in a blockchain split into Ethereum (ETH) and Ethereum Classic (ETC).
The fork was a technical response to a critical vulnerability and a test of the community's values, influencing Ethereum's governance and future direction.
The Byzantium fork, executed on October 16, 2017, at block 4,370,000, was part of Ethereum's two-stage network upgrade, Metropolis. It aimed to enhance the blockchain's privacy, scalability, and security.
It included several crucial EIPs, such as EIP-100, which changed the difficulty adjustment formula, contributing to a more consistent block time; EIP-197 and EIP 197, which enables ZK-Snarks, a form of zero-knowledge cryptography that helps increase privacy; and EIP-649, which delayed the difficulty bomb by one year and reduced mining rewards from 5 ETH to 3 ETH.
Byzantium's changes paved the way for future scaling solutions, diminished ETH inflation, and introduced new functionalities enabling more complex smart contracts and DApps to be built on Ethereum.
The Constantinople hard fork was executed on February 28, 2019, at block 7,280,000. It aimed to improve the overall efficiency and economics of the Ethereum network as it transitioned towards Ethereum 2.0.
The fork included several important EIPs, such as EIP-145, which introduced native bitwise shifting instructions to the Ethereum Virtual Machine (EVM), and the EIP-1234, which delayed difficulty bomb for approximately 12 months and reduced the block rewards from 3 ETH to 2 ETH.
Constantinople was a significant fork, for it introduced optimizations that laid the groundwork for the shift to a PoS consensus algorithm, which is part of Ethereum's long-term scaling strategy.
The Istanbul hard fork, activated on December 8, 2019, at block 9,069,000, aimed at increasing the network's compatibility with other protocols. It involved several EIPs, such as EIP-152, that added the ability for interoperability between Ethereum and Zcash blockchain.
Other significant EIPs included EIP-1108, which reduced the gas cost for privacy and scaling solutions like SNARKs and STARKs; EIP-1884, which increased gas cost for certain EVM operations to prevent spam attacks; and EIP-2028, which reduced the gas cost for zk-SNARKs and zk-STARKs, aiding in Layer 2 scaling solutions like Plasma.
Through this fork, Ethereum enhanced scalability, privacy, and resistance to denial-of-service attacks, all significant strides toward optimizing the platform for developers and users.
The Beacon Chain hard fork was launched on December 1, 2020, a fundamental step in Ethereum's planned transition to a PoS consensus mechanism. The chain ran parallel to the existing PoW chain, helping to test and secure the PoS mechanism before the shift.
By introducing the Beacon Chain, Ethereum showed commitment to the shift from energy-intensive mining to staking. In this system, validators lock up ETH to participate in block validation, enhancing security and decentralization.
The Beacon chain is still a significant element of Ethereum as it manages the PoS protocol while maintaining the network's state and transaction processing in a separate execution layer.
The London upgrade came as a recommendation of EIP-1559 and was aimed at changing the transaction fee model of the network. Executed in August 2021, the fork changed the old system of bidding for transaction fees and introduced a new model with a base fee for burned transactions, hence reducing supply and, in turn, boosting the ETH price.
Unlike Bitcoin, which has a maximum of 21,000,000 tokens, Ethereum doesn't have maximum mineable tokens. Hence, the London upgrade was made to improve the economic sustainability of the network.
While it reduced the earnings of validators, it was a necessary move and the last significant fork before the Merge.
Depending on how you look at it, The Merge is arguably the most transformational fork on the Ethereum blockchain. It was executed on September 15, 2022, marking the complete transition of Ethereum from a PoW to a PoS consensus mechanism.
Most notably, The Merge significantly impacted the environment since it reduced energy consumption by approximately 99.95%. This solved one of the main critiques of blockchain technology and allowed it to align with growing regulatory and societal concerns about energy use.
While the change didn't address transaction costs and speed issues, Ethereum made a significant leap toward network sustainability, security, and scalability.
Technically, these were two hard forks executed on the same day, April 12, 2023, at block 17,034,870. Shanghai introduced staking withdrawals on the execution layer, while Capella was an upgrade of the Beacon Chain, making it possible for blocks to accept withdrawal operations. Together, they enable staking withdrawals.
The Shapella hard fork alleviated concerns among investors and stakers about the liquidity of their staked assets, making staking more accessible and flexible. By encouraging more users to become validators, this fork increased the security and decentralization of the network.
It's clear that each update of Ethereum has been a stepping stone towards a more sophisticated and capable network. All these changes have collectively made it better. Yet, it seems there are more updates in line, such as Danksharding, which will impact scalability, and maybe another that deals with the high transaction fees of the network. As such, Ethereum blockchain evolution doesn't seem to be stopping anytime soon.
Elvis Gwaro is a technical writer specializing in crypto and Web3 content. He actively invests in and advocates for the adoption of crypto and Web3 projects.