> So the base of this [100 years] trash pyramid would be about 4.5 miles by 4.5 miles, and the pyramid would rise almost 3 miles high.

> That's a big landfill but its just not true that its unsustainable.

That is NOT a big landfill. That volume could be easily hidden in all but a couple of US states.

Moreover, it is a concentrated supply of many useful materials. It might not be profitable to mine it today, but if the "earth is running out of resources" people are correct, it will be. (And, if they're not, generating trash isn't a problem.)