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Comment by vfc1 | Hacker News Reader

Not an expert here, but after a billion years, what would be the detectable residues of such civilization could realistically be detected?

I mean everything made of organic material would be gone, and all constructions would have been turned to dust.

Not saying that there was anything ever in Mars or Venus in terms of intelligent life, but non-intelligent life what traces would it leave?

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>all constructions would have been turned to dust

I don't think that's true. There are detailed structured fossils and strata on Earth that are billions of years old, and our planet is geologically active with much more weather erosion.

> There are detailed structured fossils and strata on Earth that are billions of years old

Yes but that is not detectable from space, right? Also in Mars for example, without excavating specifically for fossils which I think hasn't been done yet, is there a way like certain geological structures that would remain intact after a billion years that would indicate life?

Likely radioactive substances that were once in large amounts with long half-lives

For example, we are now moving away from nuclear due to the dangers associated, so we only have it for less than 100 hundred years.

The half-life of uranium is 4.5 billion years. Let's say civilization of earth is wiped out and someone visits the planet a billion years from now.

Could they tell that there was something here just by the levels of uranium, assuming that say we only used it for 200 years before moving fully to clean energy?

A billion years is a long time. But if they came in a million, they probably could - if not from radioisotopes, then just from observing that the surface layer composition of metals doesn't fit any reasonable geological model. We dug up a lot of stuff, and while this initially concentrates them, as our works decay, they get dispersed into the environment, and I doubt a million years is enough for them to reintegrate back into the crust.

But wouldn't those substances be buried deep in the soil 1 billion years later? Or in the case of Earth with all the plate tectonics, entire plates could be already inside Earth's mantle.

steroids

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