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

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.

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.

I've thought about the idea of some future civilization thinking they're the first and then finding subway tunnels and the flags planted on the moon

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.

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?

More than they're going to get otherwise. Also this is a series of questions, not a shower thought.

It is pure conjecture to say any other "intelligent" and industrious species would arise, but many modern constructions would have little to no sign of existence. Any metal, even most stainless steels, would be rusted away or buried many feet deep after millions of years. Even plastics and cement would be deteriorated enough that there would mostly just be the greatly disturbed strata that would give big clues that something either catastrophic or massively industrious happened. Only very rare areas that are geologically stable and have low corrosion would have much of a chance to retain anything recognizable, like how only some cave paintings are still around today.

So, maybe a couple military bases might retain enough structure to piece some things together, but it'll still be a mess by the time another equivalently ~~self-centered~~ intelligent species comes about.

Very little, if anything, would remain of our civilization in five or six million years. At least I wouldn't think so, aside from what we have floating in outer space. Six million years is an awfully long time, and it's not like our consumer-based society builds things to last...

The Earth would finally be safe.

I vaguely remember there being a doco on what would happen to the earth if people disappeared. I remember it showed the cities getting all grown over, but it stopped and talked about each stage and what would happen.