Apollo will endure.
Yup, and those are just rocks. Do you think concrete and asphalt, electronics and cars will endure for 25,000 years?
Considering just how much we have found from the people who lived 25000 years ago, I think it’s extremely likely that plenty of traces of our civilization could remain.
Maybe not intact bits of technology, but relatively inert or huge things like aluminum, glass, tunnels, trenches, etc… could easily remain in a detectable state that long.
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Some of it would. Basically, we have footprints that were in mud that have lasted for 10’s or even 100’s of millions of years, so it’s not beyond the scope of possibility that some concrete or asphalt would or could last that long as well. Even if only 1 in a million or even 1 in a billion human artifacts are in a position with just the right environment to last you are talking about millions or more potential artifacts. Electronics are much the same…if we have soft tissue from dead animals lasting then it’s not that much of a stretch that some electronics would also last (and this leaves aside the metals and just the shape of them in mud or whatever). It’s one of the issues I have with that show…I could see whole human cities, or at least the outline of them being preserved in the same sorts of processes that preserve organic fossils. This isn’t to say that you’d have just the ruins on the Earth for 1000’s of years, but humans have built settlements and left artifacts across the globe, so it would be incredible if literally nothing was left. And, wrt the OP, a lot more would and could potentially be around for a lot longer, though how the alien space bats would keep the atmosphere away for ever is unclear.
Human beings have created billions of glass objects. Those glass objects can potentially last for billions of years, because glass is just a rock.
Oh, and while we’re quoting poetry…
This changes the previous calculations (Earth after humans) because Erosion would Change.
Again this changes the usual question: Earth is big. If onyl a few select regions are searched, the pyramids or the defaced mountains can be missed.
I think it’s very difficult to remove bias on what Aliens would consider artifical. We know that a lot of things are evidence of “human-made” because we know how natural Looks like, and what Erosion can and can’t do.
But Aliens who come to a changed planet - Earth with Erosion and bio-mass but suddenly neither - who might have a different Body and thus different tool use, would have to start studying at the very beginning to figure out how things looked like on earth before the Change.
If they were determined to be thorough, they might still Piece the puzzle together, but doing one fly-by and noticing “hey this is interesting and artifical” - I have my doubts.
Glass can also occur naturally - lighting strikes in the desert.
Which will eventually become sand
Would that be in the shape of animals, shot glasses, chess pieces, or any other figurines that would not be some random shape?
Speaking of quotes, this song is directly relevant:
None of those are among the more durable things humans have made - though I think it’s very naive to think that, for example, all remains of all cars (currently numbering over a billion) would be undetectable in 25,000 years. (Especially if the climate is Martian-like.)
But how about the truly durable evidence (much of which has been mentioned): glass objects, rock quarries, carved rock (gravestones?), etc. Mt Rushmore will cease to be evidence of human activity only when it’s somehow buried so deeply as to be unreachable.
How long before that happens to all places where humans have cut durable rock? It’s hard to say, but probably well into the hundreds of millions of years.
Things still expand and contract under heat/cold cycles
freeze maybe wrong world, but if you ultra heat and ultra cool concrete a bunch, seems it would begin to crumble fast? Its only small rocks, a bunch of sand, and cement
Other than as spots of high iron and aluminum content in the soil? Iron and aluminum rust and decay.
Here’s a thread on bwca.com about the remains of a vehicle I saw in the BWCA back circa 1990, with more recent pictures. Not much left of it.
How about the window glass? The ceramaic insulator in each spark plug?
I think that we have a winner here. Not only gold jewelry containing gemstones but any piece of gold that is recognizable as being deliberately shaped. If it is buried in a deposition environment (such as river deltas, landslides, graveyards and landfills in the right locations) there is no reason that they can’t be incorporated into rock and last until the land that they are on are subducted back into the mantle. Which can mean billions of years.
Under the right anoxic conditions, even organic materials can be preserved in fossils (most famously the Burgess Shale.) So I can imagine plastic objects being preserved in a similar way to Burgess-type fossils, as a flattened but distinctively shaped film of carbon. Future explorers might not be able to tell the fossilized film of a Barbie from a Skipper, but they would know that it wasn’t natural. And any base metal parts (and even glass, given long enough) may crumble to dust, but they would leave a distinctive chemical trace (and possibly even their original shape.) Under the right conditions objects can also quickly become the nucleation points of mineral nodules (such as the London hammer, if it is not a fraud–and even if it were a fraud, things like that could really happen.) And some landfills may be anoxic enough to preserve the overall shape at least of metal and glass objects more than you would expect from “normal” burial. I can imagine stacks of paper crushed into coal, but still splitable into planes, with the right instruments being able to detect traces of ink.
With the large number of places on Earth that garbage is being either intentionally or accidentally buried, some of them at least must be likely to be integrated into rock, and could be found by sufficiently lucky or meticulous aliens for a very, very long time.
Again, aren’t we assuming that Aliens - from a planet with likely a different weather and composotion - are familiar enough with Earth to know about natural processes pre-Event to distinguish natural from not-natural occuring things?
Our human scientists can distinguish natural stuff from not-natural stuff because thousands of People have studied natural Erosion and composition for hundreds of years. Aliens however will have studied the circumstances for their own planet; and Earth past-Event will look very differently and have different Patterns and mechanisms for natural occurring things.
But the OP speculated a fly-by. The probes humans have sent out so far have done very cursory fly-bys of our own planets. We got a ton of Information, sure, - but we also missed a hundred times more.
So if the Aliens have limited resources, and don’t have a library on Earth’s pre-Event geology etc., I doubt that one flyby, or probes of 10 random places, would indicate anything worthwhile digging deeper.
OTOH, one can posit that Aliens space-traveling must be so technologically advanced that the Computer takes one Picture, one soil sample and one sonar reading, calculates for one hour and spits out full Details on Earth’s pre-Event geology, and what exactly to look for as un-natural, and pin-points that Rushmore defacement or the Pyramids are not-natural and worth looking closer. It’s hard for me to predict how much advanced Alien Technology could possibly do and how much is still unrealistic.
But even alien planets are subject to the same laws of physics as Earth. I believe that they would conciser "natural generation of inflated, bilaterally symmetrical carbon-based but non-biological objects " is an improbable situation.