Fast forward to 2140, when all 21 million bitcoins are in circulation, what will happen to the network? Will miners continue to secure the network when the reward goes away?
The Bitcoin network was created around the principle of controlled supply —only a specific number of Bitcoins are minted each year until the total number of coins reaches 21 million.
The Bitcoin network consists of nodes run by individuals, miners, businesses, and developers.
Miners run nodes on the Bitcoin network that broadcast new blocks, verify and add them to the blockchain. Without miners, transactions would not get added to the blockchain.
Every ten minutes, the Bitcoin miner that solves the cryptographic puzzle receives a reward —a fixed number of Bitcoins for their work called the "block reward." Currently, the “winning” miner receives 6.25 BTC. The block reward decreases every four years and it will take another 120 years before the last Bitcoin is mined because of the halving process.
Miners also receive a transaction fee, but transaction fees pale in comparison to block rewards. Transaction fees make up as little as 6.5% of a miner’s revenue.
Miners currently receive around 900 BTC (~$18 million) a day in block rewards, so securing the network is a big business.