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Comment by CalRobert | Hacker News Reader

A few months ago it was speculated that if Earth had seen industrial civilizations before, we would be none the wiser. While this isn't saying that would be the cause, it does give one pause.

https://www.theatlantic.com/science/archive/2018/04/are-we-e...

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> When it comes to direct evidence of an industrial civilization—things like cities, factories, and roads—the geologic record doesn’t go back past what’s called the Quaternary period 2.6 million years ago.

What a nonsense argument, unless they managed to build an industrial civilization without iron (https://en.wikipedia.org/wiki/Banded_iron_formation). It would be glaringly obvious if these ores had already been mined.

Maybe, but stuff tends to erode and shift a lot over millions of years, possibly smoothing over evidence to a degree where we wouldn't be able to recognize it today... on Earth. However, AFAIK the moon is fairly stable, so if there were prior civilizations, they would have to have been far less advanced than we are. Otherwise they would have surely left evidence of their existence on the moon.

... Do you know about the iron catastrophe (https://en.wikipedia.org/wiki/Iron_catastrophe), banded iron formations (https://en.wikipedia.org/wiki/Banded_iron_formation), and the oxygen catastrophe (https://en.wikipedia.org/wiki/Great_Oxygenation_Event) and how they are related? Would it really be possible for us to not notice prior large-scale industrial mining of iron? Your point about lunar exploration is great, but it's also very likely there has never been industrialized life like us in Earth's history.

Being that animals did not even appear until about 600 million years ago, It's quite unlikely industrial beings evolved before that. And any industrial civilization after 600m would leave sufficient fossils/evidence. If there were civilization before 600m, it would likely have to be aliens.

What evidence of us will exist in 600 million years? Some of the combusion products of engines are distinct as I understand it, perhaps some materials are stable that long (and if so, they could pose large pollution problems)?

I'm sure there's plenty of junk in landfills that will make for interesting fossils. The material doesn't have to be "stable", it just has to make an imprint. Most existing fossils don't comprise the original material, but are rather "mineral shadows" of what was there before.

Never mind iron; we'd probably find evidence of the mining of oil, coal, lignite, peat. More likely, we wouldn't find oil.

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