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I've seen a lot of articles and even questions here which talk about how long modern human artifacts will last. Mostly it seems to boil down to modern materials not having great longevity, though stone has lasted thousands of years. I gather metal doesn't tend to last because it tends to react and corrode. What I'm wondering is this.

Without invoking handwavium super materials, it is plausible within known chemistry to engineer materials that could last for many millions of years? Could some synthetic form of stone resist weathering for extreme periods of time? Could some metal alloy? Would being buried under ground held or hinder this? Space and vacuum probably make this easy, no? Obviously we don't yet know of such things, so there is no specific material to be pointed to, but is the possibility plausible?

I don't mind leaving the material vague, but I'd feel better about it if I knew it wasn't completely nonsensical. I'm working on really old alien artifacts and ruins and am trying to gauge what could still be around and where, 60+ million years later.

Edit: Noticing a couple calls for clarification.

In the setting I'm working on, a bunch of aliens got wiped out over 60 millions ago. There might be some intact stuff here and there capable of maintaining itself, but mostly I'm wondering how feasible it is for them to have built tools, buildings, vehicles, etc out of materials that could survive to the present day. Buried, underwater, or out in the open, without having to invoke unobtanium/handwavium materials.

Is it plausible that a material based on chemical matter can be that durable?

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  • $\begingroup$ Maybe create half organic half elemental stuff with complicated biology that insures the it is constantly interacting with the environment and stabilizing the core structure. This seems pushing it as even suns die out. But if you have a sort of engineered biology that functions like a living thing with a strong "immunity system" and "intelligent" preservation mechanism then maybe. I mean atoms are always around doing something so maybe engineer stuff from there? $\endgroup$ – Seallussus Sep 22 '20 at 4:23
  • $\begingroup$ Aliens, just like us, would build artifacts for specific purposes, none of which would include "last undamaged for 60+ million years". And it's vanishingly improbable that they accidentally chose specific materials to use that happened to have extreme longevity. $\endgroup$ – GrumpyYoungMan Sep 22 '20 at 18:39
  • $\begingroup$ @GrumpyYoungMan Are you familiar with those aliens? How do you know that they are not followers of some religion that demands building structures that will last for several billion years? I can easily imagine an alien cult that builts sacrifices for the star gods to consume when they explode/turn into red giants. $\endgroup$ – Otkin Sep 22 '20 at 18:55
  • $\begingroup$ I can see aliens and even future humans making things to last for no other reason than to not do so is wasteful. $\endgroup$ – Sam D. Jones Sep 22 '20 at 19:27
  • $\begingroup$ Does this answer your question? Could written documents last for 3 million years? $\endgroup$ – JBH Sep 23 '20 at 23:06
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TL:DR Absolutely, not even an issue. There will undoubtedly be artifacts that are discernible from this alien civilization, after just a short period of time of only 60 million years. However, it depends on whether you want them to functionally survive, or just survive so that they are discernible.

In pure cosmological terms, 60 million years is just a drop in the bucket.

The oldest dated rocks formed on Earth, as an aggregate of minerals that have not been subsequently broken down by erosion or melted, are more than 4 billion years old, formed during the Hadean Eon of Earth's geological history. Meteorites that were formed in other solar systems can pre-date the Earth. Particles from the Murchison meteorite were dated in January 2020 to be 7 billion years old.2

As another poster in another answer has stated, the fossil record on Earth goes back at least that far. See this, for instance.

Sixty-six million years ago, the asteroid that wiped out the dinosaurs also ushered in the age of the mammals – an age that continues to this day.

Scientists have known little about the mammals that survived and flourished in the years after the asteroid impact. Until now.

A study on a recent discovery of thousands of mammal fossils at a nature preserve near Colorado Springs, Colorado, has shed light on the little-understood era.

So if archeologists on Earth can deduce what happened on Earth 60 million years ago, it is well within conjecture that remnants of a 60 million year old civilization could remain somewhere in the galaxy.

Based on the success of our archeologists today, here on Earth, we can say with some confidence:

If their function were purely decorative, they could still be discernible and their decorative nature appreciated.

If they were unmechanically functional (like a hammer, with no moving parts) their use would certainly still be discernible, and maybe even functional.

If they were mechanically functional (like a wheel and axle, a simple machine, or even gears and cogs) their function could be discernible, but they would probably not be functional.

If they depended on conducted energy, such as electricity, they would probably be a complete mess, undiscernible. Our electronics have a life much less than even 100 years, before the circuitry degenerates due to molecular and atomic drift. Passing electricity through a material causes all kinds of changes at the atomic level. However, advances in carbon nanotube technology suggests that with continued development, 'electronic' devices could be made from carbon nanotubes that might be discernible, but probably not functional, after that long. We simply do not know yet how stable we can make carbon nanotubes. After all, diamonds, that will last billions of years, are also made from carbon, in a matrix/lattice structure. If carbon nanotubes can be made even close to this stability, 60 million years is but a blink of the eye. It might depend on whether they are used, or dormant, for that length of time. Dormant devices may not degrade, as there is no conducted energy going through them. The problem with our electronics today, is that there is so much use of chemicals and substances that eventually dry out (insulation, heat transfer goo, and dielectrics in capacitors and transformers for instance). Our electronics will probably be discernible in a hundred years (if they are not recycled) but I doubt if they will be functional. Even electrical motors will be iffy after two hundred years of use.

Materials such as glass and diamonds will be around for billions of years. So if a diamond were engineered, for instance it was cut or engraved, it would be essentially intact. Decorative and functional objects and artifacts made from glass would also be intact and functional, after only such a short time.

A mathematical model shows it would take longer than the universe has existed for room temperature cathedral glass to rearrange itself to appear melted.

So yes, even after the demise of human civilization, after 60 million years there will still be evidence of our former existence from our artifacts that have survived. It will be much like archeologists sifting through the fossil record of Earth, going back some 60 million years ago, trying to decipher what we were all about, but our existence would certainly be evident.

However, functionality will be a completely different issue. But the question does not seem to require functionality, only discernibility.

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Fossils

We have many, many artifacts that are millions of years old. We have examples of teeth, bones, amber, and shells that are tens or hundreds of millions of years old. If you're just looking for evidence they existed, we have fossil impressions of dinosaur footprints where they happened to walk through mud that was subsequently buried.

As far as constructed artifacts go, the oldest stone tools we've found are about 3.3 million years old, about a million years older than the earliest Homo species.

Make something out of dense, water-resistant materials like stone and bury it in compacted clays or silt, and it can last millions of years if left undisturbed.

As a specific example, if they hadn't largely been excavated in the 18-20th centuries (and assuming they survived any further volcanic eruptions), I'd expect that the burial of Pompeii and Herculaneum by the eruption of Mt. Vesuvius could have resulted in a wealth of Roman-era fossils preserved under all the ash.

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  • $\begingroup$ This is a good answer, but fossils are not exposed to the elements for millions of years. I could use the OP clarifying his/her question, but it implies the materials were exposed to the elements. Mountains have eroded in less time when exposed to rain and wind. Fossils only exist because they're protected. $\endgroup$ – JBH Sep 23 '20 at 23:12
  • $\begingroup$ Perhaps a clarification is in order. Fossils are a given as we have ones hundreds of millions of years old. Fossilized imprints of artifacts are therefore easy to imagine. I'm more wondering if an artifact itself could last for tens of millions of years. Something made of artificial stone or a super-alloy of metal resistant to corrosion, etc. Buried is my primary concern, but I'm also curious if something exposed to the elements could conceivably be made durable enough to last in those conditions too. Artifact being anything artificial; tools, buildings, etc. $\endgroup$ – Sam D. Jones Sep 24 '20 at 2:15
  • $\begingroup$ Dunno about exposed to the elements, but the stone tools I mentioned are exactly what you're describing. Manually fashioned out of hard stone, used, lost, and then buried for millions of years. $\endgroup$ – Salda007 Sep 24 '20 at 6:13
  • $\begingroup$ As a side note: even their technology things could fossilize; so, if a car were to be buried in a landslide, the metal, plastics, etc could all break down and disappear and an impression of the vehicle in the the sedimentary rock that formed around it could retain the whole vehical's shape. $\endgroup$ – Nosajimiki Sep 24 '20 at 19:04
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    $\begingroup$ It's important to keep in mind that the vast majority of bones, amber, shells, etc. never become fossils, and of those that do, the vast majority of fossils do not last for millions of years. If you are intentionally leaving bones, amber, etc. or even artificially creating fossils, and want them to last for millions of years, you'll need huge quantities of them in various locations and conditions to maximize the chance that one of them will actually survive that long. $\endgroup$ – cowlinator Sep 28 '20 at 21:33
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This would give a different spin, but you could go for a machine that repairs itself. Say it only needs a handful of basic materials that are available in its vincinity. The machine would not have general intelligence, just enough to maintain itself and the messages it holds in some form.

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  • $\begingroup$ Atomic computing and molecular machines. I love it. $\endgroup$ – JBH Sep 23 '20 at 23:13
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This is currently being developed by the University of Southampton. The technology is called 5D optical data storage. I am no expert in this technology but the researchers claim that it can store information for billions of years:

The memory crystal is capable of storing up to 360 terabytes worth of data for billions of years. The concept was experimentally demonstrated in 2013.

The technology is being developed by Hitachi and Microsoft.

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    $\begingroup$ Wait, memory storage crystals are actually possible?? Looks like the Stargate franchise got something right. Saving this link for future writing. $\endgroup$ – Sam D. Jones Sep 29 '20 at 17:54
  • $\begingroup$ Of course, we have no actual evidence that they will last for billions of yeas. I guess we will just have to wait and see. But exactly what would we want to store for that long? Favorite recipies? The Caramilk secret? $\endgroup$ – Justin Thyme the Second Sep 29 '20 at 23:39
  • $\begingroup$ @JustinThymetheSecond you had me at favorite recipes. There is some precedent for extremely long message storage. The golden record on the Voyager satellite, and warning signs for nuclear waste disposal sites. However (as noted in proposals for the latter) the message runs the risk of out lasting the language (ever hear someone speak old English? Gibberish.) or even the civilization. So the question is much trickier than simply the material the message is stored in. $\endgroup$ – onb Sep 30 '20 at 3:36
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It depends the material. At time spans of millions of years, half lives of common elements can become important and this is a nuclear reaction, not a chemical or mechanical one and so progresses even if the material is otherwise chemically protected or non-reactive and mechanically protected.

This is part of the reason you can't just freeze a person in cryostasis indefinitely even if it somehow stops aging 100% because without biological functions and nutrients to cycle through and repair the body, the elements that constitute the body decay into other elements over a long enough period of time. The more something relies on things being exactly the element it is supposed to be, the more sensitive it will be to these changes.

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    $\begingroup$ Most (almost all, in fact) elements in common use are stable, or at least the proportion of unstable isotopes is $\scriptscriptstyle tiny$. Yes, our bodies includes some radioactive carbon-14 and potassium-40; but we are speaking of tiny fractions $\endgroup$ – AlexP Sep 22 '20 at 7:02

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