The paper discusses the longevity of radioactive isotopes over large time scales - basically only a few isotopes have half-lives long enough to last for tens of

The paper discusses the longevity of radioactive isotopes over large time scales - basically only a few isotopes have half-lives long enough to last for tens of millions of years, and those can be created naturally as well as artificially. On the point about oil, the paper points out that oil deposits have been created cyclically over large time scales: "At least since the Carboniferous (300–350 Ma), there has been sufficient fossil carbon to fuel an industrial civilization comparable with our own" There were three anoxic events, where the ocean was completely depleted of oxygen, in the Cretaceous period 132, 120 and 93 million years ago. "these [carbon] releases often triggered episodes of ocean anoxia (via increased nutrient supply) causing a massive burial of organic matter, which eventually became source strata for further fossil fuels. Thus, the prior industrial activity would have actually given rise to the potential for future industry via their own demise. Large-scale anoxia, in effect, might provide a self-limiting but self-perpetuating feedback of industry on the planet." Although, as the paper notes: "Alternatively, it may be just be a part of a long-term episodic natural carbon cycle feedback on tectonically active planets."