How long after man is gone...

[Butters]

Was thinking about this today, and what would happen to overpasses?

Nature would reclaim the roads and highways sure enough, and forests would take the road deck, but by the time the bridge would fail, would root structures have taken hold and ensure its rigidity, or would root growth and weight of the biomass collapse the structure?

 

[Finn]

The only ones I can think of are the ones that are found in the tropics, in wet regions. It wouldn't survive in Minnesota, so Bye-Bye-Bye to all bridges over the Mississippi up there.

 

[YellowSubmarine]

Nature would reclaim the roads and highways sure enough, and forests would take the road deck, but by the time the bridge would fail, would root structures have taken hold and ensure its rigidity, or would root growth and weight of the biomass collapse the structure?

I was wondering something similar. Would it be possible to create a structure that's very durable and would survive for a long time without maintenance, and incorporates vegetation in the design?

 

[Finn]

^One big block of granite chiseled into a bridge. It would last several million years.

 

[Squiggy]

Was thinking about this today, and what would happen to overpasses?

Nature would reclaim the roads and highways sure enough, and forests would take the road deck, but by the time the bridge would fail, would root structures have taken hold and ensure its rigidity, or would root growth and weight of the biomass collapse the structure?

I think the bridges would fail long before enough nature could grow to support it.

 

[Crazy Eddie]

I think you're going to have to wait for the end of the Earth itself. While we make a lot of stuff that breaks and crumbles in only a few years -- skyscrapers might last a few centuries -- a lot of the little things we make might last forever. Consider a tungsten carbide drill bit. It won't corrode. The workbench on which it sits might rot and the drill in which it's mounted might fall apart, but the drill bit itself and many of the components won't be appreciably affected by time.

I imagine a lot of jewelry will withstand eons, too. Buried in the ground by the passage of time, these things would have to be subducted under a continental plate before they'd be destroyed, but there are places on this planet that are billions of years old.

We'll leave, at the very least, a nice thick layer of abandoned technology strata behind for future archaeologists to find.

I think you're right...
The whole idea of a Saurian race evolving and leaving for the stars is unlikely as they too would left some sort of sign.

Not on Earth, not in the timescales we're talking. When you consider that the lifespan of a sentient and technological species might be something like 50,000 years from written language to extinction and decay (our civilization is about 10,000 years old), that's half a blink of an eye in geologic time, not even long enough to form a distinct stratum. We like to think of the various dinousaur fossils we've unearthed as belonging to generally the same era, or the same geologic epoch, but the actual case is that two different fossils discovered right next to each other--even belonging to the same species--could well have lived and died tens of millenia apart, and we could put both fossils on display in the same museum without having any idea that the ancestor of one and the descendent of the other briefly walked on the moon.

At best, a continent produces a handful of fossils every million years, and fossils are already difficult to find. As for technology, we wouldn't recognize it unless we knew EXACTLY what we were looking for (as we currently do with fossils). And even then, the true extent of it would be hard to determine; the more advanced the technology, the more sophisticated the material, the more quickly it decays into a more basic form.

Lots of things would certainly remain in space, of course. Spent rocket stages, satellites, space stations, probes, various installations and machinery on moons and asteroids that have no atmospheres and no active volcanic systems. Some of them would be discovered eventually, but after sixty million years they won't be in an obvious location, nor would they be easy to spot.