Been thinking along the lines of Planet of the Apes -but without any man made catastrophe, meteorite impact and climate stabilization- what sort of structures or evidence of our civilization would remain in five or six million years if we all just vanish? Would an intelligent species of evolved insects -or something else- find buried artifacts in the ground like we did the dinosaurs? Would ancient structures like the pyramids or Great Wall remain for that long, and would any modern things like the Eiffel tower, Burj Khalifa, or even some present day Doomsday Vaults survive that amount of time? In our digitized age, I assume that not much would remain, other than satellites maybe or I suppose any modern species that just happens to get preserved like a dinosaur did.
AFAIK metals don’t really go away over time so I would think they would be easy to harvest from the metals that are here today, no?
I read a SIFI story were a future civilization was mining rebar out of collapsed cement structures and wondering how the ancients managed to get iron into rocks.
Any worked iron product rusts. If we’re talking about evolutionary time scales, any exposed metal - which is most of it - is going to be unusable within thousands of years, and even rebar embedded in concrete will be gone in millions. Heck, our concrete isn’t even as good as the Romans’, and even that’s going to break down in thousands of years.
We’ve stripped the raw, surface, easily accessible stuff and worked it into things that will degrade. There may be some scavenge, but nothing that can be gathered in any quantity to build an industrial society on. At best, future societies will be like medieval Japan, where iron is rare and steel precious and hoarded, only unlike Japan, there won’t be a future where they can import huge quantities of the stuff from China or Australia, because getting to the deposits now requires an industry and advanced mining equipment… which is all made out of iron they won’t have.
Gold will be interesting. Again, it’s not just laying around everywhere just under the surface. Instead, there will be isolated pockets of huge piles of the stuff. Gold doesn’t degrade, but it’s all hoarded. There’s a bunch in electronics, but in tiny, tiny amounts in each device; trying to salvage that is really hard, and yields trace amounts. No more nuggets the size of your thumb, or your fist. If a future civilization could build a global economy, then gold wouldn’t be an issue. Uranium will be hard, as will platinum, and platinum is a useful, but consumable, catalyst, and rare even today it’ll be almost unheard of in a perpetually pre-industrial post-apocalypse.
Fossil fuels are going to be the big issue, though. What’s left will simply be inaccessible, and without fossil fuels you don’t have plastics, industry, fertilizers at scale, global transportation, or the ability to work whatever metal you can find, at any scale.
But even rusted iron can be re-smelted, no?
Rust needs to be reduced back to ore, using a reactive, usually coke. Coke is purified coal. Coal is a fossil fuel. You can do it with charcoal, which can be made by burning wood, so it’s possible without coal, just not as efficient. This assumes you can gather the rust - it tends to break down and disperse into the environment, but if you broke up concrete to get at rusted rebar and could collect the rust, you could reduce it with charcoal.
Again, it’s a matter of scale. We mine iron and deposits because we can get large amounts in seams. If you’re trying to harvest rust and reduced it with charcoal, you’re producing iron on the scale of making knives and swords, not cars, or combine harvesters, or more rebar.
It’s a chicken-egg problem. We have been able to come as far as a have because oil, coal, and iron were just laying around on the surface, in huge quantities. Those are gone, and now you need the big tools first to get at the reserves that are left.