Okay well we do know how much gold is in Earth's crust: On average, a ton of rock from the crust holds 0.005 grams of gold-compared to 58,000 grams of iron. https://www.amnh.org/exhibitions/gold/incomparable-gold/form...

Also, we can talk about this again in 30 years or so when we actually have mining products return from space, how much do you want to bet that Bitcoin is still relevant in 30 years?