> The most radioactive substances decay in years or decades, not millennia. s/decay in/have half-lives of/ Some of the stuff made in a nuke is not made by any

> The most radioactive substances decay in years or decades, not millennia. s/decay in/have half-lives of/ Some of the stuff made in a nuke is not made by any other earthbound process, and even a tiny amount of it is dangerous. Plutonium has a half-life around 20,000 years. At a stretch, European civilization is 10,000 years old (and we generally struggle to read texts that old - when they exist at all).