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One clue to there not being a civilization like ours in the past, is all the oil that we found in the earth. Such a convenient energy resource would have likely

One clue to there not being a civilization like ours in the past, is all the oil that we found in the earth. Such a convenient energy resource would have likely been used up before we arrived, had there been an industrial civilization before. If a future intelligent species would dig around a hundred million years from now, they'd see traces of us in the form of a radioactive sediment layer.

JPLeRouzic 6y ago
> Such a convenient energy resource would have likely been used up before we arrived, had there been an industrial civilization before. Isn't the earth crust constantly moving, so new petroleum reservoirs are constantly formed and other destroyed as dispersed liquid hydrocarbons move and migrate in reservoirs? So even if a civilization depleted its reserves, then new reservoirs would be available once the crust has moved enough? https://en.wikipedia.org/wiki/Petroleum_reservoir#Formation https://en.wikipedia.org/wiki/Petroleum_reservoir#Formation
- paulryanrogers 6y ago
  Well the carbon in the atmosphere might build up to a point that it cooks most life on earth. So probably still wise to leave it in the ground as much as possible
zmkzrk 6y ago
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."

JPLeRouzic 6y ago

> Such a convenient energy resource would have likely been used up before we arrived, had there been an industrial civilization before. Isn't the earth crust constantly moving, so new petroleum reservoirs are constantly formed and other destroyed as dispersed liquid hydrocarbons move and migrate in reservoirs? So even if a civilization depleted its reserves, then new reservoirs would be available once the crust has moved enough? https://en.wikipedia.org/wiki/Petroleum_reservoir#Formation https://en.wikipedia.org/wiki/Petroleum_reservoir#Formation

paulryanrogers 6y ago
Well the carbon in the atmosphere might build up to a point that it cooks most life on earth. So probably still wise to leave it in the ground as much as possible

zmkzrk 6y ago

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."