[ethbr0]

In order for a civilization to be undetectable, you'd essentially bound terms in a terrestrial version of the Drake Equation [0]

You'd need a civilization that did not produce long-lived technological signatures (e.g. glass panes), that did not have a large number of individuals (i.e. produce remains), that did not substantially alter their environment (i.e. leave geographic markers), AND that did not consume easily available resources (e.g. oil/gas or metal ore).

Which is to say... possible, but not very likely.

[0] https://en.m.wikipedia.org/wiki/Drake_equation#Equation

[safety1st]

After 100 million years, would any of those signatures be detectable? Glass decomposes, only takes a million years or so. The continents themselves have rearranged so any bets about structures that still remain are off. Depletion of easily available resources perhaps, but if a bunch of iron deposits were mined out that long ago, how would we know now?

This is the topic of the paper, I think the authors settled on climate markers and radiation from elements like plutonium-239 as among the very few pieces of evidence that might still be around on that time scale. They also observe that there has likely been enough exploitable energy in the form of oil, natural gas etc. to support an industrial civilization since about 250 million years ago.

[ethbr0]

Some glass decomposes.

It's chemically inert like aluminum (after oxidizing, e.g. foil), so the processes acting on it are mechanical and subject to probability.

Some amount is going to be abraded, buried, etc, but you only need a few pieces to remain. Given their ubiquity in our culture, there'd be some somewhere.

[carlmr]

>Given their ubiquity in our culture, there'd be some somewhere.

Yet we can barely imagine a society without wheels, but some human cultures in South America didn't get that idea.

Assuming that every civilization invented glass is very tenuous.

[mbostleman]

To me the most important component is not having a large number of individuals. Which is to say there was not a large amount of physical artifacts of the tech left behind. That seems to me like there would not be enough demand to scale much tech. So it's kind of a circular problem.