I didn’t see this before I posted the satellite thing.
Most stuff in low earth orbit will decay in a relatively short time - if we stop launching stuff into space, almost all of it will have come back to earth within a few hundred to a few thousand years. I’m not sure how long some of the geostationary satellites will last - maybe a long time. The LAGEOS ones I mentioned are intentionally places in an ultra-stable orbit, so I would guess that they will be the longevity champs. The OP already disallowed artifacts on the moon.
Someone earlier mentioned that geosynchronous satellites drift out of orbit… That’s partly true. After a while, they’re not in the exact orbit we want them to be in (that is to say, they’re not staying over the place we want them to stay over), but they’re still in orbit, and a very high one. At worst, a meteorite might smack right into one, but I suspect that the expected number of such events in the next 5 billion years is less than 1: Both meteors and satellites are very small targets. I don’t know of any natural phenomenon which could bring geosynch satellites down in bulk, short of the death of the Sun in several billion years. And even then, there’s at least five space probes which would survive, though it’s unlikely any aliens would ever find them.
Geez – is this still goin on? A lot of these points are ridiculous –
On filling buildings with mud: the entire city of Herculaneum was filled with mud. A river of it swept through the town, just as it did down the side of Mt. St. Helens. Preserved the buildings perfectly without collapsing them, and they were built of stone. (Pompeii was buried by ash, and its buildings, for the most part, didn’t collapse, either).
Much flimsier buildings can be preserved in mud, too. When I lived in Utah there was town you could see the remains of. It had been buried in mud during a flood, and the tops of the houses were still visible above the dirst – it was as if the flood had come through and the water had miraculously turned to solid earth in the houses (which isn’t too far off the mark of what happened).
As for towns being buried, see my much earlier statements about Ostia and Glanum. Ostia silted up (but the walls and even the wall paintings were prweserved). Ostia, too, was buried. I don’t know the precise process, but it wasn’t anything catastrophic like an eruption.
The LAGEOS satellites orbit about 5800 km above the surface. Geosynchronous orbit is considerably higer (about 36000 km about the surface). Geosynchronous orbits aren’t going to decay anytime in the next few million years, but they might be far enough out that satellites would eventually be perturbed into an orbit sufficiently elliptical to allow escape or eventual burnup.
How about road cuts through mountains and hills in areas outside of glaciation? Grading from Interstate highway rights-of-way in the US Southwest? The sudden beginning of high water marks in canyons upstream of the former location of a dam?
I know this thread is old, but I think this bump is justified to let all the participants know that the History Channel is doing a show on this very topic.
Life After People will first air tonight at 9:00pm Eastern, and then will be rebroadcast several times throughout the week. (Air times listed in the link.)
I think in the original OP it was said that only things you could see laying about (i.e. that some alien species coming to earth would stumble over without having to dig). It’s been a while since this thread was up and I don’t feel like going back through it.
It occurs to me that the destruction would be a somewhat stochastic process. For example, suppose that there is a structure that one can expect to last 500,000 years before it gets subducted or whatever. Well, there is a small chance that the same structure will last 600,000 years, 700,000 years or even 2 million years.
Given that there are millions of man made structures in the world, it seems likely that a few will stay recognizable long after their shelf life has expired.
Given the number of signals we have sent (by Frank Drake in '74 for example), it seems likely that an advanced civilization could easily detect the previous location of Earth even if it was destroyed by some irreversible process. WAG. IANAP.
Well, that was depressing. Life after Humans gave the vast majority of our civilization less than 500 years…and pretty much (according to them) nearly every trace of humans would be gone after 1000.
They rate Mt Rushmore as the most probable structure to survive for any real length of time (the one guy said something like 100k-300k).
I notice they didn’t really talk about what cities like Las Vegas or Phoenix would look like either…they concentrated mostly on New York with a couple of bones thrown in about Chicago (there would be a fire), Seattle (the Space Needle would fall over), Rome (it would burn again) and Paris (the Eiffel Tower would fall over)…with a lot of the rest of the show talking about the Hoover Dam (it would be one of the longest lasting structures in North America…according to the show).
As for discovering evidence a million or more years on, I think the erosion argument is compelling: A great deal of the trillions of tons of human artifacts will be buried. The processes that bury also reveal. It passes all probability that this sort of geological “churning” would not regularly reveal durable objects like arrowheads, ceramics, gravestones, etc.
If tectonic activity eventually recycles the whole of the Earth’s crust, that would do a fairly good job of erasing our traces, although it probably wouldn’t ever be complete, as some objects will be moved about and deposited/eroded out/redeposited in sedimentary formations, away from the subduction zone.
So, barring some anomalous event such as collision with a rogue planet large enough to melt the whole Earth, I think we’ll have to wait until the sun expands and wipes the slate clean.
One of the talking heads said that those signals would decay so much that they couldn’t be detected as something other than “noise” after only a light year or two. :dubious:
