How long could an alien structure on earth survive?

[TithonusSyndrome]

I was relating the old Scientology story about the reprogramming of the Thetans to my cousin when it occurred to me that I don't recall ever hearing whether or not the Galactic Federation ever packed it up and took it with them when they left. If it was big enough to house the billions of murdered thetans for reprogramming purposes, I'm going to guess it wasn't built with any design features of a card table. So of course I got to thinking; what are the odds that an FTL-capable civilization who left a fueling station or an observatory or resort for their soldiers to relax and gawk at dinos at could've survived 65-75 million years of winds and weather and continental drift? Would anything remain as of the dawn of man, assuming that:

A) It's made of materials comparable to what we have available
B) It's made of materials which at the best available speculation, one would expect to find in use within such a civilization.

I doubt it would remain intact, but would it be possible to find even a receptionist's desk or sonic screwdriver or anything like that after so long? Or would time do away with literally anything any aliens left behind just on the far side of the K-T extinction?

[cosmicalstorm]

Even if they left something immortal like the Monoliths they would probably be dragged down into the mantle by the continental drift.
And if it was made out of "normal" materials the odds are even worse, currently i think that Mt Rushmore and the pyramids of Giza will last for two or three million years barred any major earthquakes/asteroid impacts.

[Lord of the Abyss]

I could see it surviving if it was made of something like a materiel coated/impregnated with solar powered repair nanotech, to make it impervious to normal wear. Or some kind of diamondlike composite that normal weather can't damage. For an interstellar culture something like that could be as standard as painting wood to make it last longer is to us. Once it gets buried, of course, the nanotech won't have any power and will stop working eventually, and geological forces can of course crush any realistic material, but at that point the simple fact that it's buried could preserve it somewhat. It would still more likely or not get destroyed in some fashion or another after millions of years, of course; but it might not. IIRC, there are even still a few rocks surviving from a billion years ago - just very, very few. So if it's as tough as rock, some of it might have lasted this long.

In fact, if it lasts long enough to get buried, it might even fossilize. And, in fact, fossils show that it's possible, with enough luck for at least the form of something that old to survive.

[Junghalli]

If humans were to disappear most of our construction would probably be gone within 50,000 years. If it was built out of conventional materials the odds of any traces surviving to today are pretty low.

Even if it was built out of unconventional materials, self repairing, or managed to get fossilized over 65 million years the odds are good that would have been buried under a mountain of sedimentary or volcanic rock, or ended up under the ocean, or been ground up in the middle of an upthrusting mountain range.

From what I know of Scientology (correct me if I'm wrong) this thing would probably have been a temporary structure built for a one-time operation, so there would have been no reason for it to be built to last over historical, let alone geologic timescales.

In short, Scientology is ridiculous in a number of ways, but this isn't one of them.

Orbiting facilities are the more interesting question. Assuming they're in a stable orbit (most sattelites orbiting today would quickly burn up if humanity disappeared) they could last much longer, because they're not subject to wind, rain, and other erosive effects you get on the surface of an Earthlike planet. How long they'd last, though, I'm not sure. I remember in one of the stories in Stephen Baxter's Evolution he mentioned a space probe that landed on Eros, and mentioned that in 30 million years bombardment by micrometeorites and radiation would have rendered it so fragile that it would "crumble at the touch of an astronaut's gloved hand". So I'm guessing things in space will disappear after a while, though it'll take a long time.

[Guardsman Bass]

What about if you put it somewhere where the climate changes usually result in a dry environment? Are there any areas that have been deserts for essentially the entire progression of time since 65 million years ago?

I'm thinking of some kind of desert highland away from anything resembling mountain building or the barrier between continental plates. That way, your relic doesn't end up worn away by rain, drowned by shifting seas, or buried in either sand or sediment.

As for the orbiting facility - couldn't you put it inside something like a decent sized asteroid? That way, short of a serious impact, the rock would take most of the damage and radiation.

[Shroom Man 777]

Put the facility in Antarctica.

[CaptainChewbacca]

Fifty to 100,000 years of neglect will take care of just about any structure that isn't a massive pile of solid stone. Deserts or arid areas are transitory on that timescale.

[Junghalli]

What about if you put it somewhere where the climate changes usually result in a dry environment?

You still have to worry about wind erosion, thermal expansion and contraction, the occassional storm, and drifting sand and dirt. That's light compared to what you'd get in, say, a rainforest but over the course of tens of millions of years I imagine even that would probably take care of all but the hardiest structures.

As for the orbiting facility - couldn't you put it inside something like a decent sized asteroid? That way, short of a serious impact, the rock would take most of the damage and radiation.

I think if protected from radiation, thermal stress, and meteoroid damage a structure in vacuum could last practically forever, yeah.

[Junghalli]

Put the facility in Antarctica.

Big glaciers really tear up the landscape as they move; it's going to get ground to scattered bits of junk and carried into the ocean in no time flat on a geologic timescale.

[Gomu Niwatari]

Put the facility in Antarctica.

Big glaciers really tear up the landscape as they move; it's going to get ground to scattered bits of junk and carried into the ocean in no time flat on a geologic timescale.

I think he was referencing Stargate...

[Crayz9000]

What would be amusing is if, 50,000 years from now an alien civilization (or a new Earth-borne civilization such as amphibious dolphins) comes and rediscovers the only remaining sites such as the Pyramids and a few modern sites such as the remains of Chernobyl's containment dome.

Assuming they studied both sites with barely a modern-day understanding, they might even come to the conclusion that Chernobyl served the same purpose as the Pyramids, that is, when they discover the bodies interred at Chernobyl they might assume that it functioned as a burial place for important people, with the radiation intended to prevent grave robbings.

Who knows... Either way it would be pretty amusing to watch the archaeologists scratch their heads.

[Illuminatus Primus]

Dude? 50,000 years? First of all, the Chernobyl construction is obviously not quarried rock (industrial-level sophistication, complex metallurgy, etc.) for simplistic burial ritual (not to mention pyramids et al are adorned with script we CAN READ telling us that it is). Second of all, Chernobyl will still be filled with some long-lived isotopes which will speak of its former role even if it is no longer dangerous.

[PeZook]

Furthermore, even if large-scale construction all crumbles and falls apart, they'd still be able to excavate tons of evidence for an industrial civilization, like titanium tools, processed metals, landfills, skeletons, polyester, plastic bottles, steel beams, Alpha-class submarine hulks...

The very amount of things we made would serve as a lasting memorial to our civilization, even if we all died tomorrow.

[Sikon]

I think that story involves the billions of thetans being killed by nuclear bombs. Some of the evidence for the asteroid impact wiping out the dinosaurs 65 million years ago is a layer in which there is a slight amount of iridium, and, analogously, if the imaginary galactic ruler used nukes heavily like that, it could mean at least some deposit of unusual isotopes from the thermonuclear devices.

Any substantial amounts of radiation come from short-lived isotopes that decay quickly, but there are others. Sometimes astronomically tiny amounts of unusual isotopes and isotope ratios can conceivably be detected, although the topic is hard to quantity to give a concrete answer about this timeframe.

As a very slight analogy, the following is about if an extraterrestrial civilization disposed of nuclear waste in their star,* something which has no real effect on the star considering the astronomical mass difference yet which might still leave detectable residue:

[A paper by] Whitmire and Wright gave another example of how inadvertent beacons can be transmitted by electromagnetic radiation. [...] If an ETC used its star as a dumping ground for radioactive waste, then the spectrum of the star could exhibit characteristics that would not easily be interpreted as natural. [...] Furthermore, the [very tiny yet detectable] alteration in the spectrum would not be a brief flicker; the spectral evidence of their nuclear waste disposal policy would be visible for billions of years

From here, referencing this.

* (Really, disposing of nuclear waste in a star would tend to be a waste of time when space elsewhere is more than vast enough to store the limited quantity, with lesser delta-v requirements too, but that's irrelevant to the analogy).

As for anything left by the civilization in space or on some extraterrestrial bodies, it might last an astronomically long time, excluding some cases like low orbit subject to degradation from atmospheric drag. Indeed, an approximate illustration is as follows, for the writing on the nameplate of the Apollo 11 Lunar Excursion Module:

If the engraving on the Apollo 11 plaque is a reasonable 1/10th of a millimeter deep, it will take a million years to wear away Richard Nixon's name.

To put that in perspective, I think the oldest people whose names we know are the Egyptian Pharohs, a comparatively recent 6000 years ago.

As strange as this may seem, even though the Moon is covered in craters largely from bombardment long ago, an object a few centimeters thick on the Moon could have a significant chance of having remains lasting even a billion years (see page 8 in PDF reader).

[TithonusSyndrome]

I'm not really interested in the forensics of Xenu's genocide, but the feasibility of ancient alien structures on earth has popped into my head before, at least as long ago as Halo 3 came out and the Forerunner relic was pretty much in the same spot in Africa that it always was.