Ethereum is one of many [[Blockchains]]. Beyond being a ledger, it also has the capability to couple the execution of a small program to the transfer of Ethereum, called "Smart Contracts". Like Bitcoin, it used a Proof of Work consensus mechanism until [[#The Merge]]. The first [[Decentralized Autonomous Organization]] organized itself around Ethereum, named "The DAO", it was hacked and led to the Ethereum Fork. See [[Decentralized Autonomous Organization#The DAO]]. ## Smart Contracts Smart contracts are written in a language called [Solidity](https://soliditylang.org/) and then compiled into a stack-machine based intermediate representation.  Any smart contract is run for only a limited number of instructions until it either completes or is terminated. The measure of the amount of compute is called “[Gas](https://docs.soliditylang.org/en/latest/introduction-to-smart-contracts.html#gas)”, with various instructions and operations costing a different amount of gas to process. Once a smart contract is created, each transaction is charged with a certain amount of gas that has to be paid for by the originator of the transaction. The total cost of a transaction is the amount of gas consumed times the gas price. Any given block of the Ethereum blockchain represents a maximum amount of execution, currently 30 million gas. And the system adds a new block every 15 seconds, which means the total compute of the Ethereum network is 2 million gas / second, since that is the amount of computation that gets recorded into the Ethereum ledger. A 256 bit integer addition would cost 3 gas each, meaning that on a worldwide basis this system rates at 600,000 adds per second, which is absurdly low. At the current price of roughly $4000 per Ether this means a **second** of Ethereum’s compute costs $250. See [The Web3 Fraud | USENIX](https://www.usenix.org/publications/loginonline/web3-fraud) ## The Merge From inception in 2015 to September 2022 Ethereum was a proof of work Blockchain. The footprint was horrendous, as expected. Even worse, Ethereum chose an “ASIC-resistant” proof-of-work algorithm, meaning that it was mostly mined on GPU's, which makes the energy usage per miner even higher. See [Ethereum Energy Consumption Index - Digiconomist](https://digiconomist.net/ethereum-energy-consumption) Ethereum had promised a switch to Proof of Stake since 2016, however it was "only 6 months away" until it finally happened in 2022. Since then the energy consumption went towards zero, however the mining activity further centralized.