> Would love for you to point me in the direction of the supporting evidence.

There is scholarly work arguing for this. George Selgin comes to mind as someone who I believe has written about this. There's probably also scholarly work arguing the other side. I can't take the time to dig this up for you right now.

> But it's absurd to think that money supply should be fixed to the arbitrary quantity of a random element that we can dig out of the ground.

It certainly isn't absurd. There are lots of people who think this is a good idea, with good reason. Plus, it is historically precedented, and for good reason.