It was designed to have a hard cap of 21 million Bitcoins, a limited coin supply that in some ways mimics the finite supply of other valuable goods like gold.

Over the course of a decade, the mainstream criptocurrency is nearing its next threshold: 19 million mined Bitcoins.

The obvious question is what happens when the world runs out of supply.

Half Life

The mining process is slowed down a lot when the number of Bitcoins mined for each block is halved.

The miners won't get any reward once the last one is mined. The final 21 millionth Bitcoins won't be mined for over 100 years.

We don't know if there are even 19 million Bitcoins circulating. Chainalysis found that around 3.7 million coins hadn't been touched for at least five years. Around three million will never be found, according to other firms.

More than 90 percent of the Bitcoins that will ever exist are already out there, a striking figure, because nobody really seems to know the significance of hitting the 19 million mark.

Proof of Work

The news hasn't had much of an effect on the value of a single Bitcoin, which is still worth over $45,000 at the time of writing.

But will it always be worth that much? The process of mining the token is an energy intensive and harmful one, meaning that once its value falls enough, miners may no longer be incentivized to continue.

Governments and the banking industry have begun to accept the virtual currency as a legitimate currency. The miners made record revenue from mining.

Governments around the globe have banned proof-of-work mining due to its huge carbon footprint and links to shady practices.

Where does that leave the future? The answer to the billion dollar question is as vague as ever.

There is a 19 million coin milestone.

Exxon Mobil is starting to burn excess gas to mine.

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