The Ethereum network today implemented the Muir Glacier hard fork following the mining of block number 9,200,000. The Ethereum Foundation announced the fork on December 23 as an emergency precaution to prevent the so-called “Ice Age,” which would have caused the network to clog up and slow down. 

The “Ice Age” refers to an unfortunate consequence of two overlapping features of the Ethereum network, according to the Ethereum Cat Herders, an independent group of Ethereum contributors who help coordinate hard forks.

Ethereum’s proof-of-work network uses two mechanisms to keep the average block-validation time between 10 and 20 seconds. First, it manipulates the time by retargeting the mining difficulty. Second, it has a “difficulty bomb,” which increases the mining difficulty every 100,000 blocks. 

Every so often, Ethereum delays the difficulty bomb with a hard fork to prevent it from making the network too slow—previous delays were implemented in 2017’s Byzantium Hard Fork and 2019’s Constantinople Hard Fork.

But, this time, Ethereum researchers got their math wrong; they predicted that the network would begin to clog up in the middle of the new year, giving them plenty of time to implement a solution.

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In reality, the network was slowing down far sooner than expected—block confirmation times would have reached 30 seconds by February, 10 seconds above the upper limit. “This will start making the chain bloated and more costly to use,” wrote Ethereum researchers on the proposal for the hard fork. 

The previous Ethereum hard fork, “Istanbul”, came out on December 7, giving developers less than a month to prepare for the update. Ethereum’s new hard fork delays the difficulty bomb approximately 611 days, giving developers nearly two years to prepare for the next difficulty bomb.