How will asphalt and concrete appear in the geological record? Would it not be identifiable? If we can recognize fossilized bones, a future civilization should civilisation able to recognize concrete with steel rebar inside, no?
Abandoned asphalt roads quickly return to nature. I remember some disused highways near me that were flaking and crumbling away after only 30 years. So bad that you'd have to walk your bike on them.
As for rebar, if any water were to get in there repeatedly it would all just rust away.
The specifics of the environment play huge here. Anything in a freeze-thaw cycle would get obliterated. Dry and cool areas would do better, but then only for so long. Maybe if things were intentionally buried in anoxic environments, like many fossils, you'd have a chance at retrieval.
About the rebar, yes it would oxidise and rust but would it not then react with the surrounding concrete and leave traces, "patterns" behind? Become a special type of mineral, just like so many other minerals that have categorization and names, etc.
It's called hematite and its very widespread. Also, rust reacts with concrete as is, though not as much as with water. Hence why you'll see rebar in those plastic sheaths sometimes. My SO does a lot of work with concrete and these effects are well studied. Turns out that concrete isn't super stable over kiloyear times, let along megayear times. I think you'd have a really hard time trying to conclusively say that some bit of rock was fabricated 10k+ years ago, as compared to all the other types of rocks out there.
Returning to nature is relative. The presence of long-chain petrochemicals in layers where they don't belong, would last for millions of years. And is evidence of that asphalt road.
Yeah, but you'd only see that in sedimenting areas there were uplifted and then weathered; like orogenized river deltas. After that, you'd need to have a lot of samples in the sediment so that there'd be enough exposed rock to care to look at all. Then you'd need enough sample in the rock to detect above background noise. Then you'd need to conclusively explain away any natural causes for the presence of the asphalt, which is naturally occurring anyway.
I'm not saying it's impossible, but it would take a lot of luck.
Yes but considering the total length of paved roads in the world, often using asphalt, how they stretch terrain from coast to coast, on all inhabited continents, that some of it will pass areas that will be uplifted and brought to daylight - I see it as inevitable. It might need a trained eye to see, but it would be there.
Maybe. The surface area of all the roads in the US is ~25k mi2. Which is ~0.6% of the surface area of the whole US. And the US is a pretty advanced country in terms of road density and variety. I think we can say that the total global road density is likely less than even that. Now sure, road density isn't randomly distributed across the surface of the Earth. But future people will still need to get lucky just to see roads at all.
