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There is a finite number of bitcoins that can be mined (21 million) which puts a timeline for when the last bitcoin will be mined to 2140. With the exhaustion of the Bitcoin reserves, miners will lose their block rewards and will need to resort to other ways of earning with bitcoin. The next bitcoin halving event set to occur in less than a year, block rewards will be cut by half (6.25 BTC) leading to a significant reduction in revenue from mining. Miners will have to rely on transaction fees to keep themselves financially afloat.