I read a book by Alan Weisman titled The World Without Us, which covers this very specific topic. According to it, among the very last man-made structures left after hundreds of thousands – if not millions – of years would be the Channel Tunnel between England and France. Another notable example would be the stone faces on Mount Rushmore, as well as some old steel bridges built in an era when engineers couldn’t yet calculate structural load precisely, so they simply overbuilt everything.

The biggest challenge for future intelligent species, and the reason why I know we're the first technological ones, is that we've mined all of the easily accessible metals and all of the easily accessible fossil fuels. Any intelligence arriving after us is going to have to make a civilization without iron, precious metals, oil, or coal. Unless you get into some sci-fi bio-engineering scenario where they're growing high tech, they're doomed to being stuck in the stone age. It's going to be hard for them to escape the planet, defend it from asteroids, deal with super-volcanoes, build advanced calculating devices... all of the stuff we would already find challenging even with all the resources we have.

Millions of years are not enough to replenish the fossil fuels, and the sun is going to start expanding before enough life lives and dies to produce any useful amount of biomass. Before then, more metals will become accessible, in places, but good luck working it at industrial levels without fossil fuels.

I'm not saying it's impossible, but we've given a severe handicap to advancing beyond a rudimentary agrarian society for any successor species; even if it's our own descendants re-arrising from a post-apocalyptic environmental catastrophe.

According to What If, a layer of processed hydrocarbons in the geological record.

A totally not serious answer. Today, I was sitting across from a Starbucks and staring at the logo. It is really weird. I started thinking that if something were to happen to civilization, all these cups, sleeves, merchandise and plastic stir sticks emblazoned with the Starbucks logo may cause future archaeologists to think that we worshipped some half fish woman thing (or whatever the logo is supposed to be).

Alternatively, this xkcd could be fun to do.

You should check out the "documentary" (for lack of a better word) called ~~"After Us"~~ "Life After People." It is specifically about what Earth might look like if humans just suddenly vanished from the face of the Earth.

This is material for No Stupid Questions or Ask Lemmy communities, not a Showerthought

See the Silurian hypothesis:

The Silurian hypothesis is a thought experiment, which assesses modern science's ability to detect evidence of a prior advanced civilization, perhaps several million years ago.

In theory eventually any earth we lived on would be lost to tectonic plate movements and it would be like we were never here. And then the sun explodes so...

Depends on the time period honestly. Biggest signs are gonna be massive buildings or infrastructure projects. I wonder how long voyager will last just drifting?

The Earth would finally be safe.