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Comment by timoth3y | Hacker News Reader

It more convincing to look at it the other way.

It's not what such civilizations would have left, but what they would have taken.

Our early civilizations found easily accessible deposits or tin, copper, gold, etc that would have been depleted if another advanced civilization had existed in the past 10 million years or so.

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Tin was actually very hard to find. Which is a huge problem for civilizations that wanted to be a part of the Bronze age. Most of the tin used in Europe and western Asia was mined from just a few places in England, France, and Spain. if you find an Assyrian weapon from the 12th century BC in northern Iraq, it shouldn't surprise you if you find it was forged with tin mined in Cornwall.

IIRC tin was one of main motivating factors for the Roman invasion of Britain

Oil, especially, would probably be less common if there was an ancient industrial civilization.

If there was one involving humans, sure. Involving dinosaurs (or earlier)? No. Oil is constantly reforming and the oil we drill today wouldn't have formed back then. Sure, we suck it up a LOT faster than the replenish rate or the rate of natural reintroduction of fossilized carbohydrates into the circulation, but over geological timespans oil has a best-before date. Eventually there will be fissures (due to land movement or erosion) and it would end up being released onto the surface in one way or another.

"Depleted" in this case would just mean mined, transported, and made into something. It doesn't seem farfetched to imagine that, say, an electronics factory would be reduced to an easily accessible deposit of copper or gold in a few million years.

It depends how long the civilization is around. A lot of metal could end up impractical to mine. You can recycle metals, but little chips are being lost to wear and corrosion over time. We're slowly spreading small amounts everywhere.

Some of that would be theoretically be recoverable with a lot of effort and energy, but some of it will basically be gone. No one is going to get back small bits of metal fallen off ships into the deep ocean.

> Our early civilizations found easily accessible deposits or tin, copper, gold, etc that would have been depleted if another advanced civilization had existed in the past 10 million years or so.

Perhaps they also found remains of other advanced civilizations and axploited those?

10 million years is nothing in geological terms.

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