Bitcoin

 ₿) is the first decentralized cryptocurrency. Nodes in the peer-to-peer bitcoin network verify transactions through cryptography and record them in a public distributed ledger, called a blockchain, without central oversight.
Consensus between nodes is achieved using a computationally intensive system based on proof-of-work called mining. Bitcoin mining requires increasing quantities of electricity and was responsible for 0.2% of world greenhouse gas emissions as of 2022.
Based on a free market ideology, bitcoin was invented in 2008 by Satoshi Nakamoto, an unknown person. Use of bitcoin as a currency began in 2009, with the release of its open-source implementation. In 2021, El Salvador adopted it as legal tender. Bitcoin is currently used more as a store of value and less as a medium of exchange or unit of account. It is mostly seen as an investment and has been described by many scholars as an economic bubble. As bitcoin is pseudonymous, its use by criminals has attracted the attention of regulators, leading to its ban by several countries as of 2021.
Mining

Bitcoin mining facility with large amounts of mining hardware
The mining process in Bitcoin involves maintaining the blockchain through computer processing power. Miners group and broadcast new transactions into blocks, which are then verified by the network. Each block must contain a proof-of-work (PoW) to be accepted, involving finding a nonce number that, combined with the block content, produces a hash numerically smaller than the network's difficulty target.: ch. 8 This PoW is simple to verify but hard to generate, requiring many attempts.: ch. 8 PoW forms the basis of Bitcoin's consensus mechanism
The difficulty of generating a block is deterministically adjusted based on the mining power on the network by changing the difficulty target, which is recalibrated every 2,016 blocks (approximately two weeks) to maintain an average time of ten minutes between new blocks. The process requires significant computational power and specialized hardware.8
Miners who successfully find a new block can collect transaction fees from the included transactions and a set reward in bitcoins. To claim this reward, a special transaction called a coinbase is included in the block, with the miner as the payee. All bitcoins in existence have been created through this type of transaction. 8 This reward is halved every 210,000 blocks until ₿21 million,[d] with new bitcoin issuance slated to end around 2140. Afterward, miners will only earn from transaction fees. These fees are determined by the transaction's size and the amount of data stored, measured in satoshis per byte.
The proof-of-work system and the chaining of blocks make blockchain modifications very difficult, as altering one block requires changing all subsequent blocks. As more blocks are added, modifying older blocks becomes increasingly challenging. In case of disagreement, nodes trust the longest chain, which required the greatest amount of effort to produce. To tamper or censor the ledger, one needs to control the majority of the global hashrate. The high cost required to reach this level of computational power guarantees the security of the bitcoin blockchain
Bitcoin mining's environmental impact is significant and has attracted the attention of regulators, leading to restrictions or bans in various jurisdictions. As of 2022, bitcoin mining is estimated to represent 0.4% of global electricity consumption and to be responsible for 0.2% of world greenhouse gas emissions, as about half of the electricity used is generated through fossil fuels. Moreover, mining hardware's short lifespan results in electronic waste. The amount of electrical energy and e-waste generated by bitcoin mining is often compared with countries like Greece or the Netherlands.