Speaking of bitcoin,
Krugman said "Bitcoin... is by design, a kind of virtual gold. And like gold, it can be mined: you can create new bitcoins, but only by solving very complex mathematical problems that require both a lot of computing power and a lot of electricity to run the computers. Hence the location in Iceland, which has cheap electricity from hydropower and an abundance of cold air to cool those furiously churning machines. Even so, a lot of real resources are being used to create virtual objects with no clear use."
In other words bitcoin mining is actually wasting electricity and adding to the carbon footprint, but not really adding value to anything. The object itself is entirely fictional and speculative. At least gold can be made into jewelry or used in electronics, what can you use bitcoin for, other than speculating on it's price?
And what I find ironic is that 200 years ago, there was no Federal Reserve, and any bank could print their own money. Yet somehow people opted to use the currency backed by the US govt. So in a sense we are mining our way back to the 17th century.