The Ethereum network will be undergoing a scheduled upgrade 
soon called “Arrow Glacier,” a change that aims to mimic the “Muir 
Glacier” upgrade. Essentially, Ethereum’s Arrow Glacier changes the 
parameters of the network’s Difficulty Bomb delay to June 2022. This 
will give the Ethereum network another six months until it leads to the 
“Ice Age” proof-of-stake (PoS) transition.
Arrow Glacier Aims to Postpone Ethereum’s Ice Age
At Ethereum block height 13,773,000 the network will implement the Arrow Glacier upgrade
 which aims to postpone Ethereum’s Difficulty Bomb. The bomb mechanism 
has been around since 2015 and makes the network’s mining difficulty 
increase over time. The end result will lead to the Ice Age, a moment in
 time when the blockchain stops proof-of-work (PoW) block production and
 the chain is 100% reliant on proof-of-stake (PoS) consensus.
The Difficulty Bomb was supposed to happen 4,000,000 blocks or 611 days after the Muir Glacier
 network upgrade. However, Arrow Glacier will push the bomb back further
 to June 2022. This will give ethereum PoW miners another six months to 
continue mining the Ethereum blockchain until the June 2022 change. Once
 the Difficulty Bomb does happen the mining difficulty will make it so 
PoW miners get phased out because it will be too difficult.
Arrow Glacier is expected to happen between now and Wednesday, 
December 8, 2021. “The Arrow Glacier network upgrade, similarly to Muir 
Glacier, changes the parameters of the Ice Age/Difficulty Bomb, pushing 
it back several months,” Ethereum developers expain. “This has also been
 done in the Byzantium, Constantinople and London network upgrades. No 
other changes are introduced as part of Arrow Glacier.” The announcement
 adds:
The Difficulty Bomb only affects proof-of-work networks,
and hence only exists on the Ethereum mainnet and the Ropsten test
network. With the recent progress
towards Ethereum’s transition to proof-of-stake, it was decided to only
delay the bomb on mainnet for now and to try and run the proof-of-stake
transition on Ropsten before the bomb goes off on that network.
Ethereum Hashrate Taps All-Time High, Ether Is the Second-Most Profitable Coin to Mine in 2021
While Ethereum network participants have been waiting a long time for
 the Ice Age PoS transition, ethereum miners have been enjoying the PoW 
incentives. During the early morning hours of December 7, Ethereum’s hashrate
 reached 1 petahash per second (PH/s). The recorded metric is the 
highest the hashrate has ever been and currently Ethereum’s processing 
power is coasting along at 900 terahash per second (TH/s).
Additionally, besides kadena (KDA) mining, ethereum (ETH) mining is currently the second-most profitable cryptocurrency
 to mine today. At $0.12 per kilowatt-hour (kWh) and today’s ether 
exchange rates, a 1,500 megahash per second (MH/s) machine can get 
around $91 per day. Mining ethereum with the most profitable ether 
mining rig is 68.85% more profitable than mining bitcoin (BTC) with today’s best performing SHA256 bitcoin miner which gets a touch over $28 per day in profits.
source link :  https://news.bitcoin.com/delaying-the-ice-age-ethereum-network-participants-prep-for-upcoming-arrow-glacier-upgrade/